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## Abstract

The disinfection of surfaces is perhaps the simplest and most predictable application of ultraviolet germicidal radiation. UV is highly effective at controlling microbial growth and at achieving sterilization of most types of surfaces. Early applications included equipment sterilization in the medical industry. Modern applications include pharmaceutical product disinfection, area disinfection, cooling coil and drain pan disinfection, and overhead UV systems for surgical suites. Such applications often involve using bare UV lamps and as such there may be UV hazards associated with them. Cooling coil disinfection with ultraviolet light has proven so effective that such installations often pay for themselves in short order. The use of UV is fairly common in the packaging industry and in the food processing industry where it is sometimes used for irradiating the surfaces of foodstuffs. Lower room UV systems are not common although they have been used in hospitals in the past. This chapter provides basic design information for each type of surface disinfection system based on theoretical analysis and field testing results. Good design practices are discussed and general guidelines are provided.

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... Ultraviolet from the sunlight is the main factor that destroys microbial control agents. The activity of microbial control agents, including Baculovirus, can be inactivated by the ultraviolet B (280-320 nm wavelength) of sunlight [6,7]. Thus, in order to improve the pathogenicity of Baculovirus, some ultraviolet protectant from natural ingredients have been used as additives. ...
... The wavelength used for the spectrophotometry analysis for this research ranges from 190 -420 nm because it shows the wavelength of ultraviolet spectrum. UV radiation consists of UVA (320-400 nm), UVB (280-320), and UVC (200-280) [6]. This research showed that all of the A. atlas cocoon extract concentration variations (0.5, 1, 2, and 2.5%) can be read in the wavelength (λ) of 190 -420 nm. ...
... death. The primary dimer formed in DNA due to UV exposure is thymine dimers [6,20]. UV-B radiation is one of the most important solar energy that can cause the formation of 3 types of DNA damages namely cyclobutane pyrimidine dimer (CPD), photoproduct pyrimidine 6-4 pyrimidine (6-4 PPs), and Dewar isomer [21]. ...
Conference Paper
Full-text available
Spodoptera exigua (Lepidoptera: Noctuidae) is the common pest known for attacking shallot crop. Baculovirus (Nucleopolyhedrovirus : NPV) is a biological agent that is widely used as the pest control agent. However, the activity of NPV is deteriorated when applied in the field due to the influence of ultraviolet from the sun. Attacus atlas silkworm cocoon has UV protectant ability due to the presence of sericin protein. Thus, the aim of this study is to determine the degree of UV protectant ability from A. atlas cocoon extract for NPV to prevent its deterioration and to increase its effectiveness against S. exigua pest. The stages of this study consist of UVB irradiation of A. atlas cocoon extract as NPV protectant and pathogenicity test of NPV activity against the first instar larvae of S. exigua. Experiments were carried out by exposing NPV to UVB irradiation for 0, 1, 2, 3, 4 weeks long with the addition of A. atlas cocoon extract in varied concentrations (0, 0.5, 1, 2, and 2.5%). The concentrations derived from 7.5 gram A. atlas cocoon was dilluted 1 gram TRO and 150 ml aquades. The results proved the UV protectant ability of A. atlas cocoon for NPV. After a week of UVB irradiation, the NPV applied in A. atlas cocoon extract (0-2.5%) caused larval mortality of 43.33%, 76.67%, 60%, 65%, 80%, respectively. After 2 weeks of UVB irradiation, the NPV applied in A. atlas cocoon extract (0-2.5%) caused larval mortality of 46.67%, 78.33%, 71.67%, 66.67%, 66.67%, respectively. Thus, for further applications, the findings of this research need to be tested in an actual field condition.
... In addition to medications, vaccinations and personal protective equipment, disinfection measures are an important element in the fight against all infections. Irradiation with ultraviolet radiation in the UVC spectral range of 200-280 nm is one of the oldest and most effective disinfection techniques [3], which can quickly reduce pathogens by several orders of magnitude, even at very low irradiation doses [4,5]. The effect is based on the destruction of DNA and RNA of bacteria, fungi and viruses [3][4][5] including coronaviruses like SARS-CoV-2 [4,[6][7][8]. ...
... Irradiation with ultraviolet radiation in the UVC spectral range of 200-280 nm is one of the oldest and most effective disinfection techniques [3], which can quickly reduce pathogens by several orders of magnitude, even at very low irradiation doses [4,5]. The effect is based on the destruction of DNA and RNA of bacteria, fungi and viruses [3][4][5] including coronaviruses like SARS-CoV-2 [4,[6][7][8]. Unfortunately, radiation of these wavelengths also cause harm to human DNA, which is why UVC radiation should not be applied in the presence of humans. ...
... In combination with the violet LEDs, the antimicrobial effect of the presented test illumination is about 10 times stronger than with pure white light (2,400 lux) alone, but 3.5 hours of irradiation are still required for a 90% bacterial reduction. This is still very long compared to typical UVC disinfection durations of minutes to seconds [5][6][7][8][30][31][32][33][34][35][36][37][38][39]. However, for less time-critical applications, such as the disinfection of work areas or rooms overnight, such irradiation with white-violet light is conceivable and in contrast to UVC emitters, without any relevant risk to humans. ...
Article
Full-text available
The spread of infections, as in the coronavirus pandemic, leads to the desire to perform disinfection measures even in the presence of humans. UVC radiation is known for its strong antimicrobial effect, but it is also harmful to humans. Visible light, on the other hand, does not affect humans and laboratory experiments have already demonstrated that intense visible violet and blue light has a reducing effect on bacteria and viruses. This raises the question of whether the development of pathogen-reducing illumination is feasible for everyday applications. For this purpose, a lighting device with white and violet LEDs is set up to illuminate a work surface with 2,400 lux of white light and additionally with up to 2.5 mW/cm² of violet light (405 nm). Staphylococci are evenly distributed on the work surface and the decrease in staphylococci concentration is observed over a period of 46 hours. In fact, the staphylococci concentration decreases, but with the white illumination, a 90% reduction occurs only after 34 hours; with the additional violet illumination the necessary irradiation time is shortened to approx. 3.5 hours. Increasing the violet component probably increases the disinfection effect, but the color impression moves further away from white and the low disinfection durations of UVC radiation can nevertheless not be achieved, even with very high violet emissions.
... While UVC is a fairly common technique for disinfection (inactivation of vegetative bacteria and viruses) of water (Masschelein and Rice 2016) and air (Kesavan and Sagripanti 2014), e.g., aerosols, and air ducts (Kowalski 2009), its use on surfaces for the inactivation of bacterial spores (e.g., those of B. anthracis) is not widely used commercially. Most commercial UV germicidal equipment for surface disinfection is used for building and ventilation system surfaces or for dental and medical equipment. ...
... Most commercial UV germicidal equipment for surface disinfection is used for building and ventilation system surfaces or for dental and medical equipment. UVC inactivation rates for microbes in air are typically much higher than for surfaces (Kowalski 2009). Spores of bacteria are generally 5-10 times more resistant to UVC than their corresponding vegetative cells (Coohill and Sagripanti 2008). ...
... Decontamination efficacy is strongly dependent on the material with which the microorganisms are associated with, and most if not all UVC studies reported in the literature typically use only laboratory substrates such as glass or filters, rather than relevant realistic materials. Our study also examined the effect of relative humidity (RH) on UVC inactivation efficacy, which is another data gap (Kowalski 2009). ...
Article
Aims: To obtain quantitative efficacy data of two ultraviolet light (UVC) technologies for surface inactivation of Bacillus anthracis Ames and Bacillus atrophaeus spores. Methods and results: Spores were deposited onto test coupons and controls of four different materials, via liquid suspension or aerosol deposition. The test coupons were then exposed to UVC light from either a low-pressure mercury vapor lamp or a system comprised of light emitting diodes, with a range of dosages. Positive controls were held at ambient conditions and not exposed to UVC light. Following exposure to UVC, spores were recovered from the coupons and efficacy was quantified in terms of log10 reduction (LR) in the number of viable spores compared to that from positive controls. Conclusions: Decontamination efficacy varied by material and UVC dosage (efficacy up to 5.7 LR was demonstrated). There was no statistical difference in efficacy between the two species or between inoculation methods. Efficacy improved for the LED lamp at lower relative humidity, but this effect was not observed with the mercury vapor lamp. Significance and impact of study: This study will be useful in determining whether UVC could be used for the inactivation of B. anthracis spores on different surface types.
... Here k is a microorganism susceptibility constant (m 2 /J; sometimes denoted Z) that is species dependent and experimentally derived. Typical values for a range of microroganisms are presented in a number of sources, with Kowalski (2009) presenting the most comprehensive compilation of published values from numerous experimental studies. Equation 1 represents a first-order decay assumption that is realistic for many microorganisms, including Mycobacterium tuberculosis and other Mycobacterium species in air (Kowalski 2009). ...
... Typical values for a range of microroganisms are presented in a number of sources, with Kowalski (2009) presenting the most comprehensive compilation of published values from numerous experimental studies. Equation 1 represents a first-order decay assumption that is realistic for many microorganisms, including Mycobacterium tuberculosis and other Mycobacterium species in air (Kowalski 2009). Other models incorporating a threshold dose or two-stage decay characteristics have been proposed for certain pathogens (Kowalski 2009). ...
... Equation 1 represents a first-order decay assumption that is realistic for many microorganisms, including Mycobacterium tuberculosis and other Mycobacterium species in air (Kowalski 2009). Other models incorporating a threshold dose or two-stage decay characteristics have been proposed for certain pathogens (Kowalski 2009). ...
Article
Full-text available
The effectiveness of ultraviolet irradiation at inactivating airborne pathogens is well proven, and the technology is also commonly promoted as an energy-efficient way of reducing infection risk in comparison to increasing ventilation. However, determining how and where to apply upper-room Ultraviolet Germicidal Irradiation devices for the greatest benefit is still poorly understood. This article links multi-zone infection risk models with energy calculations to assess the potential impact of a Ultraviolet Germicidal Irradiation installation across a series of inter-connected spaces, such as a hospital ward. A first-order decay model of ultraviolet inactivation is coupled with a room air model to simulate patient room and whole-ward level disinfection under different mixing and ultraviolet field conditions. Steady-state computation of quanta-concentrations is applied to the Wells-Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative influence of different design factors for susceptible patients co-located with an infectious source or in nearby rooms. In each case, energy requirements are calculated and compared to achieving the same level of infection risk through improved ventilation. Ultraviolet devices are seen to be most effective where they are located close to the infectious source; however, when the location of the infectious source is not known, locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones. Results show an ultraviolet system may be an energy-efficient solution to controlling airborne infection, particularly in semi-open hospital environments, and considering the whole ward rather than just a single room at the design stage is likely to lead to a more robust solution.
... In recent years, interest has grown in the potential for photochemical air filters, such as UV-C irradiation, to supplement or replace fine particle filtration for microbial control. These devices have the capacity of destroying or decomposing microorganisms and potentially volatile organic compounds (VOCs), and they may have energy performance benefits over conventional filters (Blatt 2006; Kowalski 2009 In-duct devices typically comprise one or more UV-C lamps mounted within the HVAC system to create a UV irradiation field inside an airflow duct. Microorganisms contained in the air passing through the UV field incur DNA damage proportional to the UV irradiance, time of exposure, and species of microorganism; with sufficient exposure, the damage may be lethal, rendering microorganisms inactive. ...
... Microorganisms contained in the air passing through the UV field incur DNA damage proportional to the UV irradiance, time of exposure, and species of microorganism; with sufficient exposure, the damage may be lethal, rendering microorganisms inactive. The technology has also shown reduction of bacteria concentration on surfaces after UV-C has been installed within a ventilation system (Taylor et al. 1995), leading to applications for reducing bio fouling of cooling coils and the potential for improving system energy efficiency (Blatt 2006; Kowalski 2009; Lee et al. 2009). With increasing application of in-duct UV-C systems, it is important to accurately quantify the technology's performance, and appropriate analysis and test mechanisms must be set in place. ...
... microorganisms in the UV field within a duct or device, microorganism susceptibility to UV irradiation, air velocity, air temperature, humidity, reflectivity of duct or device internal surfaces, velocity profile, air mixing, and lamp position. A number of studies have explored the influence of some of these parameters through mathematical modeling. Kowalski (2009) predicted UV device performance with average irradiation fields determined using a view factor approximation, and Lau (2009) explored the effects of airflow velocity and temperature on lamp output. However, these models assumed a fully mixed airflow and did not consider the 3D flow–UV field interaction that happens in a real case. Compu ...
Article
Full-text available
UV-C is becoming a mainstream air sterilization technology and is marketed in the form of energy-saving and infection-reduction devices. An accurate rating of device performance is essential to ensure appropriate microbial reduction yet avoid wastage of energy due to over performance. This article demonstrates the potential benefits from using computational fluid dynamics to assess performance. A computational fluid dynamics model was developed using discrete ordinate irradiation modeling and Lagrangian particle tracking to model airborne microorganisms. The study calculates the UV dose received by airborne particles in an in-duct UV system based on published EPA experimental tests for single-, four-, and eight-lamp devices. Whereas the EPA tests back calculated UV dose from measured microorganism inactivation data, the computational fluid dynamics model directly computes UV dose, then determines inactivation of microorganisms. Microorganism inactivation values compared well between the computational fluid dynamics model and the EPA tests, but differences between UV dosages were found due to uncertainty in microorganism UV susceptibility data. The study highlighted the need for careful consideration of test microorganisms and a reliable dataset of UV susceptibility values in air to assess performance. Evaluation of the dose distribution demonstrated the importance of creating an even UV field to minimize the risk of ineffective sterilization of some particles while not delivering excessive energy to others.
... Airborne microorganisms from the occupied zone can be transported to the upper-zone by ventilation flows and convention currents, passing the microorganisms through the UV field. Exposure of microorganisms to UV-C light at a wavelength close to 254 nm, damages the microorganism DNA; at a sufficient dose this can be lethal, effectively killing the microorganism [12]. Several experimental studies have verified the disinfection performance of UVGI for a range of microorganisms in various settings [13 16], and a recent study conducted in clinical setting demonstrated a 70% reduction in TB transmission risk following the installation of an upper-room UVGI system [17] One of the major difficulties of implementing upper-room UVGI systems is that the disinfection performance relies on the room airflow patterns which are responsible for transporting the microorganisms through the UV field. ...
... The parameter D is cumulative and depends on the 3D UV field present within the space as well as the path taken by a given microorganism. For a known pathogen, the dose received by a microorganism can be used, together with the microorganism susceptibility [12], to calculate the expected microorganism survival fraction, and hence the reduction in airborne concentrations. For many hospital environments the actual pathogens present are unknown, so the dose is a good parameter to represent the effectiveness of a UVGI system without requiring knowledge of microorganism species. ...
... Here Co represents the initial microorganism concentration and the term, k (m 2 /J), represents the microorganism susceptibility constant [12]. Microorganism susceptibilities are determined experimentally, and published values can vary substantially, which may be due to the experimental conditions or the particular strain of microorganism used. ...
Article
Full-text available
Ultraviolet germicidal irradiation (UVGI) has been shown to be an effective technology for reducing the airborne bioburden in indoor environments and is already advocated as a potential infection control measure for healthcare settings. However, much of the understanding of UVGI performance is based on experimental studies or numerical simulation in mechanically ventilated environments. This study considers the application of an upper-room UVGI system in a naturally ventilated multi-bed hospital ward. A computational fluid dynamics model is used to simulate a Nightingale-type hospital ward with wind-driven cross-ventilation and three wall-mounted UVGI fixtures. A parametric study considering 50 different fixture configurations and three ventilation rates was carried out using a design of experiments approach. Each configuration was assessed by calculating the UV dose distribution over the ward and at each bed. Results show that dose is influenced by the location of the fixtures and the ventilation regime. Thermal effects are likely to be important at low ventilation rates and may reduce UV effectiveness. A metamodel-based numerical optimisation was applied at a ventilation rate of 6 air changes per hour. In this case, the optimum result is achieved when UVGI fixtures are mounted on the leeward wall at their lowest mounting height.
... The device employed was an upperroom ultraviolet germicidal irradiation (UVGI) system. UVGI devices make use of light in ultraviolet wavelengths, specifically in the germicidal range of 200 – 320 nm, to disinfect air and surfaces [4]. UVGI disinfects by causing photochemical changes in the deoxyribonucleic acid (DNA) of a microorganism, thus destroying its ability to reproduce. ...
... The germicidal effects of UV irradiation have been recognized for many decades; in 1932, Ehrismann and Noethling [5] identified the germicidal effectiveness of UV to peak at 253.7 nm, today it is estimated to be at approximately 260 – 265 nm. This wavelength corresponds to the peak of UV absorption by bacterial DNA [4], although this varies between species. An upper-room UVGI system is one where UV fixtures are used to create a zone of UV irradiation in the upper portion of a room, well above head height. ...
... One major advantage of this system is that the disinfection device is continuously operational within the room, where the source of hazardous microbes typically exists. Furthermore, the system can be retrofitted to most existing rooms, is relatively inexpensive and has been proven to be an effective against a wide variety of airborne viruses and bacteria (e.g. [4], [6], [7], [8] and [9]). To specifically quantify the effectiveness of an upper-room UVGI system is difficult, due to the intricacy of the biological processes involved and the vast number of variables associated with its operation. ...
Conference Paper
Full-text available
An experimental investigation was carried out to determine the effectiveness of an UltraViolet Germicidal Irradiation (UVGI) system for eradicating airborne pathogens in an indoor environment. Experimental and environmental conditions were varied and the resultant inactivated percentage of Staphylococcus aureus was measured. Results indicate that it is paramount to keep experimental parameters constant to achieve reliable and comparable results. In particular; the sampling plates used in the Andersen sampler must have a consistent depth of nutrient agar, and sufficient time (~ 40 mins) must be given for steady state conditions to be achieved prior to the commencement of air sampling. Furthermore a change in environmental conditions such as ventilation regime and ventilation rate, were found to significantly influence the determination of the effectiveness of an upper-room UVGI system; with a ventilation regime of in low, out high resulting in an average of 16 % higher microorganism inactivation than a regime of in high, out low. The environmental conditions for which the device was deemed most effective, i.e. which resulted in the highest percentage of airborne microorganisms inactivated (96.0 ± 3.2 %) were: for a ventilation rate of 3 air changes per hour (ACH) and ventilation regime of in low, out high.
... In-duct UVGI systems can also be deployed to treat air streams as they pass through HVAC ductwork, and potentially reduce the respiratory diseases that are transmitted through the ductwork. Since air is being recirculated a number of times, an overall increase in removal rate is expected for in-duct air disinfection as compared to single pass system [9]. This paper will focus on the performance and economics of in-duct UVGI system in treating air streams by taking the dynamic environmental conditions as experienced in the AHU of the VAV system into consideration. ...
... Relative humidity might have an effect on UV susceptibility of microorganisms. However, some results indicate positive influence, others show negative influence [9]; effect of relative humidity is therefore not considered here. In this paper, the survival of a population of microorganisms exposed to UVC is approximated by a single stage exponential decay equation: ...
... The design of UVGI systems depends greatly on the target (group of) microorganisms to be treated. In fact, Kowalski [9], suggests that it is more convenient and definitive to use "dose" as a design parameter, in which D 90 (dose for 90% inactivation) for many infectious agents were published. For example, if a UVGI system is designed to deliver a certain dose, any infectious agent of lower D 90 will be inactivated 90% in a single pass. ...
... Conventionally it can be measured with spherical actinometry method [34,35]. In actual condition, the reflectivity of wall for 254-nm ultraviolet radiation mainly depends on the wall material surface [25,32,36]. For most of painted walls, the reflection for 254-nm ultraviolet radiation is on the order of 5% [32]. ...
... Likewise, the comparison of our model and the existing bare lamp model was also discussed. In reported bare lamp model, the spatial radiance is calculated as [30,36]: ...
... In practice, non-ideal situation is encountered . Generally, the reflectivity of polished aluminum reflector ranges from 0.79 to 0.91 [36,37]. In order to investigate the effect of possible reflectivity with our reflector, the additional results of f = 0.9 is studied in details. ...
Article
There has been an increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) system because of its proven disinfection effect for airborne microorganisms. To better design and explore further potential applications of UVGI systems, it is of critical importance to predict the spatial UV intensity in enclosures. In this paper, we developed a new mathematical model to predict spatial radiation intensity for upper-room ultraviolet germicidal irradiation systems. The detail geometries of the lamp and the reflector were removed and replaced by introducing a fictitious irradiation surface near louver slots. The view factor approach was applied to evaluate the UV irradiance in a three-dimensional space with different louver configurations. With this approach no detail meshing of the fixture is required and this leads to significant simplification of the entire systems from modeling perspectives. To validate the model, experiments were performed in a full-scale environmental controlled chamber in which one UVGI fixture was mounted on a sidewall. The UV irradiance was measured by a radiometer. The results predicted by the present model agree very well with the experimental measurements. Factors affect the accuracy of the model was also discussed.
... It has been extensively used in the disinfection of equipment, glassware and air by food and medical industries for many years. Low pressure mercury (Hg) lamps are often called " germicidal " because most of their total radiation energy is at a wavelength of 253.7 nm, which is near the maximum for germicidal effectiveness, hence its usefulness in the control of microorganisms (Kowalski, 2009). While the application of hormesis is used in the context of this chapter on the benefits to plant tissues, hormic responses have also been shown in bacteria, fungi, animals and humans (Shama, 2007). ...
... These oxidation stresses become severe with the physiological age of the tissue and it responds by generating an array of detoxifying mechanisms (antioxidants and enzymes) against free radical attack. It is documented that short wavelength radiation exerts two pronounced effects on plant metabolism viz: at low intensities, it may give rise to an enhancement of secondary stress metabolites which can protect the plant from free radical damage, while at high intensities, it can cause an inhibition of these substances often leading to detrimental effects on the plant (Kowalski, 2009). Certain plants have repair mechanisms which involve the production of secondary stress metabolites for example, antioxidant compounds such as carotenoids, phenols, flavonoids, and polyamines. ...
... The UVGI room used UV-C rays with 254 nm wavelength which was effective to disinfect air, water, and surface. 1 UVGI room has its advantages, which are short disinfection duration, huge capacity in one cycle, easy to use and relatively affordable to prepare and maintain. On the previous study, it was known that UVGI room of RSCM had the ability to disinfect SARS-CoV-2 viral using 1J/cm 2 dose. 2 The safe standard of N95 respirator mask according to NIOSH is, if the N95 mask had the ability to filter >95%. ...
Article
... Since the occurrence of the COVID-19 pandemic, a lot of effort has been dedicated to the development of photonic devices for fighting against SARS-CoV-2, both for virus diagnostic and inactivation purposes. The use of ultraviolet germicidal irradiation (UVGI, 200-280 nm) for sanification purposes dates back to the beginning of the XX century, and its efficacy against bacteria, viruses, and fungi is well known [1]. ...
Conference Paper
Ultraviolet C-band (UV-C) sources based on LED arrays, for near-field irradiation purposes, have been designed, realized, and thoroughly characterized both from an optical and a thermal point of view. Here we report the main theoretical and experimental results and discuss the preliminary applications of these sources.
... Ultra-violet (UV) germicidal activity was first reported in the nineteenth century [21,22]. UV light encompasses three wavelength ranges: 400 to 315 nm (UV-A), 315 to 280 nm (UV-B), and 280 to 200 nm (UV-C). ...
Article
Full-text available
Almost two years have passed since COVID-19 was officially declared a pandemic by the World Health Organization. However, it still holds a tight grasp on the entire human population. Several variants of concern, one after another, have spread throughout the world. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant may become the fastest spreading virus in history. Therefore, it is more than evident that the use of personal protective equipment (PPE) will continue to play a pivotal role during the current pandemic. This work depicts an integrative approach attesting to the effectiveness of ultra-violet-C (UV-C) energy density for the sterilization of personal protective equipment, in particular FFP2 respirators used by the health care staff in intensive care units. It is increasingly clear that this approach should not be limited to health care units. Due to the record-breaking spreading rates of SARS-CoV-2, it is apparent that the use of PPE, in particular masks and respirators, will remain a critical tool to mitigate future pandemics. Therefore, similar UV-C disinfecting rooms should be considered for use within institutions and companies and even incorporated within household devices to avoid PPE shortages and, most importantly, to reduce environmental burdens.
... [2,3] In particular, microbiological studies have shown that the exposure of microorganisms and nonliving organisms, such as viruses, to UV-C radiation results in photochemical changes to nucleic acids, which impairs their ability to reproduce and leads them to be inactive. [4][5][6] Furthermore, a precise UV-C radiation dose could effectively be used to decompose microplastics in wastewater treatment plants. [7,8] Accordingly, the study of UV-C radiation plays an important role in meeting the demands and desires in various applications. ...
Article
An ultraviolet (UV) light source is continuously required for applications of sterilization as well as industrial value. In particular, research on materials and devices emitting UV‐C radiation in the range from 210 to 280 nm is very meaningful and challenging work. Herein, UV‐C electroluminescence (EL) from an all‐solution processed CaSiO3:Pr3+ (CSO) thin film is reported for the first time. The CSO thin film is formed on a Si substrate (size of 13 × 13 mm2), and structurally, the UV‐C EL device has a metal‐oxide‐semiconductor (MOS) shape consisting of CSO and interlayered SiOx of 100 and 150 nm thickness, respectively, on Si. The emission and electrical properties of the UV‐C EL device are investigated under an alternating current system. The results reveal UV‐C emission peaking at 276 nm attributed to the 4f5d‐3H(F)j transition of Pr3+ ions within CSO, with a maximum output optical power of 8.37 µW cm−2 (power efficiency of 0.15%) at an operating voltage of 40 Vop (50 Hz). The work can provide a feasible method for realizing large‐area UV‐C‐emitting devices based on the MOS structure. The ultraviolet (UV)‐C emitting device is introduced based on metal‐oxide‐semiconductor structure consisting of CaSiO3:Pr3+ and interlayered SiOx on Si. The results reveal UV‐C emission peaking at 276 nm attributed to electronic transition of Pr3+ ions within CaSiO3, with a maximum output optical power of 8.37 µW cm−1 at an operation voltage of 40 V (50 Hz).
... The accuracy of the experimental data was verified again by the derived kinetic expression. As shown in Table 2, by comparing the linear relationship between inactivation rate and UV dose fitted by data points, it can be seen that the Z value of reaction rate coefficient of different kinds of microorganisms in the process of photocatalytic inactivation was different, and the Z value also reflected the difficulty of microbial inactivation to a certain extent, which was related to the microstructure of cells [22]. In our study, the Z value of E.coli was the highest (19.48 ×10 − 3 cm 2 /μJ), while the Z value of A. versicolor spore was the lowest (3.02 ×10 − 3 cm 2 /μJ). ...
Article
Bacteria, fungi and viruses are airborne microorganisms, which can survive and spread in the form of aerosols, posing a serious threat to human health. A dynamic continuous flow photocatalytic reactor containing TiO2/MXene filler was developed to study the inactivation characteristics of four different microorganisms treated by ultraviolet and photocatalysis. By establishing the kinetic fitting model (−lgNpcN0=εAbΦNE1IrtPC+A), it was known that there were differences in the inactivation efficiency of airborne microorganisms with different microstructures. The introduction of catalysis greatly reduced the energy consumption of disinfection. The electrical efficiency per log order (EE/O) of UV254 inactivated E. coli was reduced from 0.012-0.015 kW·h·m⁻³ to 0.0016-0.0040 kW·h·m⁻³. Furthermore, the self-repair phenomenon was not obvious in a very short time (40 h) under UV irradiation, but the microbial activity continued to decline after photocatalytic treatment. Short wave ultraviolet had stronger penetration than long wave ultraviolet. High radiation intensity can provide more photons and produce more reactive oxygen species (ROS) for photocatalysis, while too high humidity (RH=95%) will inhibit it. Appropriate residence time (4.3 s) can efficiently treat airborne microorganisms with higher concentration (10⁹ CFU·m⁻³). These external factors affected the photocatalytic disinfection process of different kinds of microorganisms.
... Since Pr 3+ ion is located at a highly symmetrical lattice site, it provides a suitable crystal field for efficient 4f 1 5d 1 →4f 2 interconfigurational transition of Pr 3+ with deep-UV emission. In response to 240-nm light excitation, the LCGO:Pr 3+ yields a broadband deep-UV emission (~240-330 nm), that is overlapping well with the germicidal effectiveness curve (~220-280 nm) [39] and phototherapy cure in broadband UVB emission (290−320 nm) [40]. ...
Article
Perusing multimode luminescent materials capable of being activated by diverse excitation sources and realizing multi-responsive emission in a single system remains a challenge. Herein, we utilize a heterovalent substituting strategy to realize multimode deep-ultraviolet (UV) emission in the defect-rich host Li2CaGeO4 (LCGO). Specifically, the Pr3+ substitution in LCGO is beneficial to activating defect site reconstruction including the generation of cation defects and the decrease of oxygen vacancies. Regulation of different traps in LCGO:Pr3+ presents persistent luminescence and photo-stimulated luminescence in a synergetic fashion. Moreover, the up-conversion luminescence appears with the aid of the 4f discrete energy levels of Pr3+ ions, wherein incident visible light is partially converted into germicidal deep-UV radiation. The multi-responsive character enables LCGO:Pr3+ to response to convenient light sources including X-ray tube, standard UV lamps, blue and near-infrared lasers. Thus, a dual-mode optical conversion strategy for inactivating bacteria is fabricated, and this multi-responsive deep-UV emitter offers new insights into developing UV light sources for sterilization applications. Heterovalent substituting in trap-mediated host lattice also provides a methodological basis for the construction of multi-mode luminescent materials.
... Se divide en 4 grupos principales, ver Fig.1 [5], cada uno con un efecto germicida diferente: UV-A (315-400nm), UV-B (280-315nm), UV-C (200-280nm), UV en vacío (100-200nm). El uso de radiación UV es conocido desde hace más de 60 años para la eliminación de bacterias y en particular la radiación UV-C de 200nm a 280nm para la eliminación de virus en general [6] [7]. Actualmente se emplea radiación UV-C para esterilización de: quirófanos, instrumental, de aire en Aire Acondicionadores y de agua en plantas de tratamiento [8][9] [10]. ...
Conference Paper
Full-text available
... UV irradiation is germicidal mainly because its wavelength corresponds to the peak UV absorption of protein, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). UV absorption into pathogen genomes triggers radiolytic cleavage or radical reactions, causing changes in the pathogen's nucleic acids that eventually lead to inactivation (2,3). UV rays that inactivate double-stranded DNA viruses are thought to also inactivate single-stranded RNA genomes such as coronaviruses (4,5). ...
Article
Full-text available
During the coronavirus disease 2019 (COVID-19) pandemic, the use of ultraviolet (UV) rays to disinfect skin areas, clothes and other objects at the entry/exit points of public spaces has been widely discussed by stakeholders. While ultraviolet germicidal irradiation (UVGI) has been shown to effectively inactivate coronaviruses, including severe acute respiratory syndrome coronavirus (SARS-CoV)-1 and Middle East respiratory syndrome coronavirus (MERS-CoV), no specific evidence proves that it effectively inactivates the new SARS-CoV-2 virus that causes COVID-19. Because UV rays damage human tissue, UVGI should be used with caution and not directly on human skin. Various guidelines recommend that UVGI should not be used as a sole agent for disinfecting surfaces or objects but as an adjunct to the latest standard disinfecting procedures.
... The genome of SARS-CoV-2 has a 79,5-82 % homology to SARS-CoV 8,9 . UVC susceptibility studies of SARS-CoV have been described in literature 10 . Therefore, we can infer the UVC susceptibility of SARS-CoV-2. ...
Preprint
Due to the SARS-CoV-2 pandemic a shortage of personal protective equipment, including surgical facemasks and Filtering Facepiece Particle Respirators has occurred. SARS-CoV-2 has a 79,5-82% homology to SARS-CoV-2. The SARS-CoV UVC sensitivity is described in literature. We have performed UVC transmission measurements of surgical facemasks and respirators. In addition, we performed UVC disinfection experiments of S. aureus with surgical facemasks and respirators. Results show that we can achieve an 8-log reduction of S. aureus in the inner layers of FFP1 respirators and the exterior of surgical facemasks. Furthermore, we showed a 7-log reduction of S. aureus in the inner layers of FFP2 respirators. We conclude that UVC disinfection is an effective, safe and scalable method for reuse of surgical facemask and respirators.
... This capacity to reflect is highly dependent on the material of the surfaces. For example, organic material will absorb the penetration and block reflection of UVC, which is why surfaces should be cleaned manually to remove organic substances before decontamination [6]. ...
Article
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... The second candidate was ultraviolet (UV) germicidal light. UV is highly effective at controlling microbial growth and at achieving disinfection at most types of surfaces (Kowalski 2009). UV radiation in the wavelength range of 250 ± 10 nm (UV-C) is lethal to most micro-organisms, i.e. bacteria, viruses, protozoa, mycelial fungi, yeasts and algae. ...
Article
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Ultraviolet germicidal (short wavelength UV-C) light was studied as surface disinfectant in an Emergency Sanitation Operation System® smart toilet to aid to the work of manual cleaning. The UV-C light was installed and regulated as a self-cleaning feature of the toilet, which automatically irradiate after each toilet use. Two experimental phases were conducted i.e. preparatory phase consists of tests under laboratory conditions and field testing phase. The laboratory UV test indicated that irradiation for 10 min with medium–low intensity of 0.15–0.4 W/m2 could achieve 6.5 log removal of Escherichia coli. Field testing of the toilet under real usage found that UV-C irradiation was capable to inactivate total coliform at toilet surfaces within 167-cm distance from the UV-C lamp (UV-C dose between 1.88 and 2.74 mW). UV-C irradiation is most effective with the support of effective manual cleaning. Application of UV-C for surface disinfection in emergency toilets could potentially reduce public health risks.
... Typical values for a range of microroganisms are presented in a number of sources including Kowalski (2009) and Noakes et al (2004). Equation (1) represents a first order decay assumption which is realistic for many microorganisms; other models incorporating a threshold dose or two-stage decay characteristics have been proposed for certain pathogens (Kowalski 2009). ...
Conference Paper
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The effectiveness of UV-C irradiation at inactivating airborne pathogens is well proven, and the technology is already advocated for control of some respiratory diseases such as Tuberculosis. UV-C air disinfection is also commonly promoted as an energy efficient way of reducing infection risk in comparison to increasing ventilation. However determining how and where to apply UVGI devices for the greatest benefit is still poorly understood. This paper focuses on upper-room UVGI systems, where microorganism inactivation is accomplished by passing contaminated room air through an open UV field above the heads of occupants. Multi-zone models are developed to assess the potential impact of a UVGI installation across a series of inter-connected spaces such as a hospital ward; this may comprise rooms for one or more patients that are all connected to a common zone that may be a corridor or may act as a communal space, housing fore xample the nurses station. Simulation of dose couples the ventilation, air mixing and upper-zone average field to explore factors influencing device coverage. A first-order decay model of UV inactivation is coupled with the room air model to simulate patient room and whole-ward level disinfection under different mixing and UV field conditions. Steady-state computation of quanta concentrations are applied to the Wells-Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative benefits of different system options for susceptible patients co-located with an infectious source or in nearby rooms. In each case energy requirements are also calculated and compared to achieving the same level of risk through improved ventilation. A design of experiment technique is applied to sample the design space and explore the most effective system design for a given scenario. Devices are seen to be most effective where they are located close to the infectious source. However, results show that when the location of the infectious source is not known,locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones.
... These systems produce an irradiance field which is limited to the upper air zone in the room of interest. Provided that the wavelength of the UV field is close to 254 nm, this has the potential to disinfect the air by killing bacteria, viruses and fungus spores which pass through the field [5]. Numerous experimental studies have verified the disinfection performance of UVGI for a range of microorganisms in various settings [6][7][8][9]. ...
Conference Paper
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The airborne transmission of pathogens including tuberculosis and influenza pose a significant threat to human health. This is especially the case in healthcare settings such as hospital wards which inevitably contain a high concentration of viruses and bacteria. These have the potential to infect both patients with weakened immune systems and healthcare workers. In order to reduce the infection risk, improvements in hospital ward design and the application of disinfection systems can offer significant benefits. One such strategy, upper-room Ultraviolet Germicidal Irradiation (UVGI), relies on a collimated irradiance field which works in conjunction with ventilation patterns to disinfect the air. The focus of this study is to predict the UVGI system performance within a naturally ventilated hospital ward, for a range of ambient conditions using Computational Fluid Dynamics (CFD). A computer model of an open-plan six-bed Nightingale-style hospital ward was generated based on the dimensions of a former hospital building situated in Bradford, UK. With a total volume of 200 m3, natural ventilation is supplied through three casement windows and a further three openings on the leeward side ensure steady cross-ventilation. Boundary conditions are based on experimental measurements of the ventilation rate which were determined using a tracer technique. An experimentally-determined irradiance field is included in the model and stored as a fixed-value scalar field. A total of fifty steady-state CFD simulations show that disinfection performance depends on the ventilation rate, the degree of mixing present and the position of the UVGI fixture within the ward. The results underline the potential performance gains from UVGI installations and how they could be integrated within existing healthcare facilities as an infection control measure.
... Radiação Ultravioleta Germicida é a radiação normalmente gerada por lâmpadas com pico de emissão no comprimento de onda de 253,7 nm (UV-C) com ação germicida. Matam ou neutralizam bactérias, vírus e outros organismos primitivos (Wladyslaw, 2009). A radiação ultravioleta, ao contrário de outros desinfetantes que têm ação química, atua por meio físico, atingindo principalmente os ácidos nucléicos dos microorganismos, promovendo reações fotoquímicas que inativam os vírus e as bactérias (Daniel et al, 2001). ...
... It has been verified that ultraviolet germicidal irradiation (UVGI) does disinfect specific bioaerosols in laboratory experimentation (Kujundzic et al., 2006; Xu et al., 2005). By destroying the DNA of microorganisms, UVGI could inactivate and stop the reproduction of the bioaerosols (Kowalski, 2009). UV light has been installed in the upper part of rooms to reduce the concentration of airborne cultruable microorganisms in the indoor environment (Peccia et al, 2001). ...
... Usually the tube was made from fuses quartz that is transparent to the UV light. The main property of germicidal lamp is the 254 nm that are effective for destruction of most microorganisms (Kowalski 2009; Miller, Linnes et al. 2013).Figure 1 shows the experimental setup for this experiment. Four type fluorescent lamps include 10 W Reno blacklight lamp, 10 W Sonic aquarium lamp, 10 W Senkyo germicidal lamp and 10 W Hitachi insect lamp were placed in a box of 10x12x12 cm. ...
Conference Paper
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Ultraviolet light is the electromagnectic radiation in the range of 100 nm to 400 nm. The UV light spectrum consists of electromagnetic waves with frequencies higher than those that humans can identify as the violet in colour. These frequencies are invisible to most humans except those with aphakia (the absence of the lens of the eye). There are two sources of UV light; natural and artifical sources. The sunlight is the main source of the natural UV ligth. On the other hand, the artifical source could be generated by florescent lamp, gas-discharge lamp, laser, and LED. In this paper, the spectrum of the common ultraviolet light in the market such as the black light lamp, germicidal lamp, aquarium lamp and insect lamp will be discussed. The spectrum of UV light for each lamp was placed in a box of 10x12x12 cm and detected by a special spectrometer that directly connected to a computer via USB connection. The result shows that the main spectral lines of all fluorescent lamps are 254 nm, 313 nm, 404 nm, 437 nm, and 546 nm. The information of the various spectrums of the UV lamp is very important for the user. This information can be used to prevent over exposure of UV lights to humans that may potentially cause skin cancer.
... RNA, causing them to form covalent bonds with each other and interrupting hydrogen bonds with adenine bases in the cDNA/ RNA strain (13, 18). Pyrimidine dimers of thymine/uracil bases distort the shape of DNA/RNA, altering the double-helical structure and preventing the cell's accurately transcribing or replicating its genetic material, which ultimately leads to the death of the cell (13, 18, 19). Extending the irradiation time increased the IE in the droplets absorbs UV (13, 18), and shielding of viruses near the center of the aggregate likely also contributes to this trend. ...
Article
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Although respirators and filters are designed to prevent the spread of pathogenic aerosols, a stockpile shortage is anticipated during the next flu pandemic. Contact transfer and reaerosolization of collected microbes from used respirators are also a concern. An option to address these potential problems is UV irradiation, which inactivates microbes by dimerizing thymine/uracil in nucleic acids. The objective of this study was to determine the effects of transmission mode and environmental conditions on decontamination efficiency by UV. In this study, filters were contaminated by different transmission pathways (droplet and aerosol) using three spraying media (deionized water [DI], beef extract [BE], and artificial saliva [AS]) under different humidity levels (30% [low relative humidity {LRH}], 60% [MRH], and 90% [HRH]). UV irradiation at constant intensity was applied for two time intervals at each relative humidity condition. The highest inactivation efficiency (IE), around 5.8 logs, was seen for DI aerosols containing MS2 on filters at LRH after applying a UV intensity of 1.0 mW/cm(2) for 30 min. The IE of droplets containing MS2 was lower than that of aerosols containing MS2. Absorption of UV by high water content and shielding of viruses near the center of the aggregate are considered responsible for this trend. Across the different media, IEs in AS and in BE were much lower than in DI for both aerosol and droplet transmission, indicating that solids present in AS and BE exhibited a protective effect. For particles sprayed in a protective medium, RH is not a significant parameter.
Article
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The article’s main goal is to describe the system design for the analysis of disinfection automated guided vehicle (AGV) utilisation so that the AGV’s optimal number can be determined. The simulation was used as the system’s main tool, allowing a relatively objective approach to imitate real system behaviour. With the proposed system, it is possible to determine the utilisation of AGVs and the number of necessary AGVs that carry out disinfection of the premises through the superstructure platforms. In the simulation model, two main modes of disinfection of ground AGV were tested. A regular circuit is carried out at specific intervals as well as a dynamic evaluation of the area and its possible contamination. When the area reaches a certain threshold, the instruction to disinfect the area is triggered. Experiments were carried out for a different number of AGVs, with the possible restriction of entry in the presence of the patient, and for a combination of specialised AGVs. Based on the results, we can conclude that the use of only surface-disinfecting AGVs is limited by the movement of patients and does not bring the same results as the use of a combination of surface- and air-disinfecting specialised AGVs.
Article
Treatment with ultraviolet (UV) light has been shown to be effective for disinfection of pathogens. For pathogenic risk management, it would be effective to estimate the UV sensitivity of unknown pathogenic microorganisms from their nucleotide sequences. In this study, we designed and used synthetic DNA molecules, 100–150 bases in length, to investigate not only the DNA sequences but also the secondary structures of the DNA as determinants of UV sensitivity of microorganisms. We showed that dimer-forming DNA by UV irradiation was undetectable by quantitative polymerase chain reaction (qPCR) when performed on all DNA bases. The undetectability ratio of PCR after UV irradiation indicated that UV reactivity tends to increase with the number of consecutive thymine pairs within DNA. In addition, UV reactivity was not influenced by increasing the number of complementary bonds in the DNA and the estimated free energy, indicating that complementary bonds in the DNA have no influence on the UV reactivity. The results of this study provide important information about the necessary factors determining UV sensitivity of microorganisms such as the number of consecutive thymine pairs within the DNA, which was the main driver regardless of the presence of secondary structures.
Article
Ozone and ultraviolet light are techniques used for microbiological control in foods that use different mechanisms of action to complement their antibacterial action. This study aimed to evaluate the complementarity of these antimicrobial techniques in the food safety of beef contaminated with Escherichia coli. The treatments of aqueous ozone and UV-C were evaluated in cycles, with each cycle having a dose of 69 mJ/cm² of light and 30 s of ozone spray at a concentration of 0.9 ppm, the time between each cycle was one hour and repeated ten times. The 1.7 Log total of E. coli reductions corresponds to the colony sum of the amount reduced by treatments from the amount proliferated without treatment. The techniques were also evaluated in isolation, obtaining a significant reduction for UV-C Light and for aqueous ozone it maintained the microbial load controlling proliferation. The organoleptic properties of the meat were evaluated by checking the pH, quantification of proteins, and lipid oxidation. It was observed that the treatments did not cause significant changes in the meat samples, showing that the technologies have the potential to preserve food by avoiding an exponential proliferation of microorganisms without modification of their organoleptic properties.
Article
Nanomaterial has diverse applications in electronics, catalysis, energy, materials chemistry and even biology due to the special properties endowed by their high specific surface ratio. However, nanoparticles can easily get agglomerated and lose their original properties, which has become one critical issue and limits its application in nanotechnology. Various surface modification methods were used to reduce its surface energy and prevent the agglomeration. While physical methods use surfactants to prevent the latter, chemical methods are more favorable, since the strong covalent bonds are more durable under wide range of conditions. Among these chemical modifications, chemical vapor deposition is extensively studied. Here we introduced nanomaterial’s characterization and reviewed different categories of chemical vapor deposition methods that have been used for nonmaterial’s surface modification. We showed that photo-induced chemical vapor deposition (PICVD) is an attractive strategy that could be carried out under normal temperature and pressure conditions; it might be the best potential candidate to be used widely in large-scale processes. Finally, we discussed the factors affecting functionalization process of PICVD and the research progress of its application in surface modification of nanoparticles.
Article
The United Nations Environment Programme (UNEP) convened the Minamata Convention on Mercury in 2013 to ban mercury-containing products in order to ensure human and environmental health. It will be effectuated in 2020 to discontinue use of low-pressure mercury lamps and new UV-emitting sources have to replace this conventional technology. However, the UV germicidal irradiation (UVGI) system still uses conventional UV lamps, and no research has been conducted for air disinfection using UVC LEDs. The research reported here investigated the inactivation effect of aerosolized microorganisms, including viruses, bacteria, and fungi, with an UVC LED module. The results can be utilized as a primary database to replace conventional UV lamps with UVC LEDs, a novel type of UV emitter. Implementation of UVC LED technology is truly expected to significantly reduce the extent of global mercury contamination, and this study provides important baseline data to help ensure a healthier environment and increased health for humanity.
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Background: Pathogen transmission from contaminated surfaces can cause hospital-associated infections. Although pulsed xenon ultraviolet (PX-UV) light devices have been shown to decrease hospital room bioburden in the United States, their effectiveness in United Kingdom (UK) hospitals is less understood. Methods: Forty isolation rooms at the Queens Hospital (700 beds) in North London, UK, were sampled for aerobic bacteria after patient discharge, after manual cleaning with a hypochlorous acid-troclosene sodium solution, and after PX-UV disinfection. PX-UV device efficacy on known organisms was tested by exposing inoculated agar plates in a nonpatient care area. Turnaround times for device usage were recorded, and a survey of hospital staff for perceptions of the device was undertaken. Results: After PX-UV disinfection, the bacterial contamination measured in colony forming units (CFU) decreased by 78.4%, a 91% reduction from initial bioburden levels prior to terminal cleaning. PX-UV exposure resulted in a 5-log CFU reduction for multidrug-resistant organisms (MDROs) on spiked plates. The average device turnaround time was 1 hour, with minimal impact on patient throughput. Ward staff were enthusiastic about device deployment, and device operators reported physical comfort in usage. Conclusions: PX-UV use decreased bioburden in patient discharge rooms and on agar plates spiked with MDROs. The implementation of the PX-UV device was well received by hospital cleaning and ward staff, with minimal disruption to patient flow.
Article
Among different physical and chemical agents, the UV radiation appears to be an important route for inactivation of resistant microorganisms. The present study introduces a new mercury free Dielectric Barrier Discharge (DBD) flat lamp, where the biocide action comes from the UV emission produced by rare earth phosphor obtained by spray pyrolysis, following plasma excitation. In this study, the emission intensity of the prototype lamp is tuned by controlling gas pressure and electrical power, 500 mbar and 15 W, corresponding to optimal conditions. In order to characterize the prototype lamp, the energetic output, temperature increase following lamp ignition and ozone production of the source were measured. The bactericidal experiments carried out showed excellent results for several gram-positive and gram-negative bacterial strains, thus demonstrating the high decontamination efficiency of the DBD flat lamp. Finally, the study of the external morphology of the microorganisms after the exposure to the UV emission suggested that other mechanisms than the bacterial DNA damage could be involved in the inactivation process.This article is protected by copyright. All rights reserved.
Article
Continuous flow (CF) dipper wells, or small countertop sinks, are used in the foodservice industry for rinsing utensils such as stirring spoons and dishers. In addition, these dipper wells are designed as continuous flow not only to rinse and clean but to also control for the buildup of microorganisms. Here, we evaluate a reduced water (RW) dipper well – with and without ultraviolet subtype C (UV-C) disinfection – for control and inactivation of Escherichia coli present on a stainless steel utensil. Overall, the RW dipper well (with and without UV-C) performed significantly better than the CF dipper well for removal of E. coli in 10% skim milk medium at various exposure and rinse times. More specifically, at 5, 10, and 30 s, the RW dipper well without UV-C achieved 1.04, 1.72, and 2.03 greater log10 (CFU/ml) reduction in E. coli compared to the CF dipper well at the same treatment times, respectively. When combined with UV-C, the RW dipper well increased reduction of E. coli by 0.36–1.68 log10 (CFU/ml) over prolonged use (i.e. 2 h continuous use). Moreover, the RW dipper well combined with UV-C may provide a preventative step to reduce the growth and/or persistence of bacteria on the utensil as well as the dipper well reservoir, especially for E. coli in 10% skim milk medium. To our knowledge this is the first study to evaluate the efficacy of dipper wells – both RW and CF systems – in the removal of E. coli on a stainless steel utensil.
Article
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This study evaluated the use of pulsed-xenon ultraviolet (PX-UV) room disinfection by sampling frequently touched surfaces in vancomycin-resistant enterococci (VRE) isolation rooms. The PX-UV system showed a statistically significant reduction in microbial load and eliminated VRE on sampled surfaces when using a 12-minute multiposition treatment cycle.
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A number of different factors have contributed to an increased awareness of the threat posed by pathogenic microorganisms in indoor and outdoor environments and this in turn has led to renewed interest in ultraviolet germicidal irradiation (UVGI) as a potential control measure. This paper presents the results of a series of experiments carried out to determine the UV susceptibility of aerosolised Serratia marcescens and the effect of increased relative humidity on the UV susceptibility constant. Photoreactivation is a light induced DNA repair mechanism which enables microorganisms to recover from sub-lethal UV doses. Although this is an important issue it is often overlooked and not taken into account when estimating the UV susceptibility of microorganisms. This paper also presents data regarding the photoreactivation potential of Serratia marcescens and the effect that this can have on the UV susceptibility constant. INTRODUCTION In recent years a number of factors have stimulated an increased awareness of the presence of potentially pathogenic bioaerosols in indoor and outdoor environments and the detrimental health effects associated with them (Lin & Li, 2002). One of the main driving forces has been the re-emergence of tuberculosis as a major health concern mainly in the developing world but also more recently in the more developed countries of Europe. The situation has been compounded by the rise in the number of multi-drug resistant strains of Mycobacterium tuberculosis which has made antibiotic treatment of the disease increasingly problematic. There has also been an increase in the number of nosocomial infections (i.e. those acquired in hospital) and in the UK alone it is estimated that 1 in 10 patients will acquire some kind of infection during their stay in hospital (Beggs, 2000). Traditionally it has been thought that the main source of infection in healthcare facilities was person to person contact. However, it is now believed that the airborne transmission route accounts for as much as 10% of all nosocomial infections (Beggs, 2000).
Article
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Ultraviolet (UV) light disinfection has increasingly been used as an alternative method to replace conventional chlorine disinfection as it has been found to be a more efficient disinfection method. As UV disinfection only damages the nucleic acids of the microorganisms to prevent replication, there is a possibility of microorganisms repairing the damage sites. As few studies have investigated the reactivation of microorganisms after exposure to medium-pressure UV disinfection, it is essential for reactivation related to medium-pressure UV disinfection to be studied as medium-pressure lamps are gaining in popularity. Besides, disinfection by-products (DBPs) produced by UV disinfection have been discovered recently and may serve as a carbon source in the finished water, resulting in regrowth of the bacteria. It is therefore important to know the regrowth potential of bacteria with the existence of DBPs. In this study, the repair and regrowth of Escherichia coli after UV disinfection were investigated. Results showed that E. coli underwent photo repair (up to 5 log under fluorescent light conditions) more significantly than dark repair (up to 0.8 log in terms of bacterial count increase). The repair was generally found to be higher at low doses. At the same UV dose, it seems medium-pressure UV irradiation is able to control the repair to a lesser extent. In addition, the bacterial regrowth potential was studied with the addition of DBPs typically found in UV processes, such as acetic acid and formaldehyde. The maximum increase in bacterial count was found to be 0.3 log. Generally, the level of regrowth was insignificant compared with the increase of bacterial count due to bacterial repair.
Article
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Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m3 completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.
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A mathematical model is presented to explain the ultraviolet susceptibility of viruses in terms of genomic sequences that have a high potential for photodimerization. The specific sequences with high dimerization potential include doublets of thymine (TT), thymine-cytosine (TC), cytosine (CC), and triplets composed of single purines combined with pyrimidine doublets. The complete genomes of 49 animal viruses and bacteriophages were evaluated using base-counting software to establish the frequencies of dimerizable doublets and triplets. The model also accounts for the effects of ultraviolet scattering. Constants defining the relative lethality of the four dimer types were determined via curve-fitting. A total 77 water-based UV rate constant data sets were used to represent 22 DNA viruses. A total of 70 data sets were used to represent 27 RNA viruses. Predictions are provided for dozens of viruses of importance to human health that have not previously been tested for UV susceptibility.
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A rapid tool for the characterization of submicron particles is light spectroscopy. Rayleigh-Debye-Gans and Mie theories provide light scattering solutions that can be evaluated within the time constants required for continuous real time monitoring applications, as in characterization of biological particles. A multiwavelength assessment of Rayleigh-Debye-Gans theory for spheres was conducted over the UV-Vis wavelength range where strict adherence to the limits of the theory at a single wavelength could not be met. Reported corrections to the refractive indices were developed to extend the range of application of the Rayleigh-Debye-Gans approximation. The results of this study show that there is considerable disagreement between Rayleigh-Debye-Gans and Mie theory across the UV-Vis spectrum.
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Treatment of monkey kidney cells with low doses of carcinogen enhances the survival of UV-irradiated simian virus 40 (SV40). This is true for compounds with UV-like effects (metabolites of aflatoxin B1, N-acetoxyacetylaminofluorene) and compounds with x-ray-like effects (methyl methanesulfonate, ethyl methanesulfonate). This phenomenon resembles the UV-reactivation of viruses in eukaryotic cells. The carcinogen-induced enhancement of the survival of UV-irradiated SV40 is correlated with the inhibition of host-cell DNA synthesis, suggesting that the inhibition is an inducing agent. An enhancement of UV-irradiated SV40 survival is also obtained in cells treated with hydroxyurea or cycloheximide for long enough that there is still inhibition of host DNA synthesis during the early stage of SV40 infection. We hypothesize that treatment of host cells with carcinogens induces a new recovery pathway that facilitates the replication of damaged DNA, bypassing the lesions and resulting in the enhanced survival of UV-irradiated SV40. This inducible process might represent the expression of "SOS repair" functions in eukaryotic cells analogous to the previously demonstrated induction of SOS repair in bacteria after UV or carcinogen treatment.
Book
Several general books are available on ultraviolet light and its applications. However, this is the first comprehensive monograph that deals with its application to water and wastewater treatment. There is a rapidly growing interest in using UV light in water sanitation due to the increased knowledge of the potential health and environmental impacts of disinfection byproducts. Ultraviolet Light in Water and Wastewater Sanitation integrates the fundamental physics applicable to water and wastewater sanitation, the engineering aspects, and the practical experience in the field. The text analyzes the concerns associated with this application of UV light and brings together comprehensive information on the presently available UV technologies applicable to water and wastewater treatment including: lamp technologies, criteria of evaluation and choice of technology; fundamental principles; performance criteria for disinfection; design criteria and methods; synergistic use of UV and oxidants (advanced oxidation); and functional requirements and potential advantages and drawbacks of the technique. Ultraviolet Light in Water and Wastewater Sanitation is the only treatise currently available combining fundamental knowledge, recommendations for design, evaluations of performance, and future prospects for this application. Water and wastewater treatment professionals, water utility employees, governmental regulators, and chemists will find this book an essential and unique reference for a technology which has received growing regulatory acceptance.
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Cryptosporidium parvum oocysts in water were exposed to distinct wavelength bands of collimated beam ultraviolet (UV) radiation across the germicidal UV wavelength range (210-295 nm) that were emitted from a medium pressure (MP) mercury vapour lamp. The dose of UV radiation transmitted though each narrow bandpass filter was measured utilising potassium ferrioxalate actinometry. Oocyst infectivity was determined using a cell culture assay and titre was expressed as an MPN. The log10 inactivation for each band of radiation was determined for a dose of 2 mJ/cm2. Doses from all wavelengths between 250-275 nm resulted in approximately 2 log10 inactivation of Cryptosporidium parvum oocyst infectivity while doses with wavelengths higher and lower than this range were less effective. Because polychromatic radiation from MP UV lamps had about the same germicidal activity between the wavelengths of 250-275 nm for inactivation of oocyst infectivity, there was no unique advantage of MP UV over low pressure (LP) UV except for the simultaneous delivery of a wide range of germicidal wavelengths.
Article
'Comprehensive virology 12' deals with several special groups of viruses showing properties that set them apart from the main virus families. The book comprises 5 chapters, all written by specialists, in which respectively 5 groups of viruses are discussed: in the 1st chapter, the viruses of invertebrates; chapter 2, the viruses of fungi; chapter 3, the cyanophages and viruses of eukaryotic algae; chapter 4, the viruses of fungi capable of replication in bacteria; and chapter 5, a view on lipid-containing bacteriophages. Each chapter has an impressive number of references. An index concludes this 12th volume in a series of 15.
Article
The detection and characterization of micro-particles, particularly airborne biological particles, is currently of great interest. We present a novel technique for recording the 2D angular scattering pattern from a single airborne microparticle. Angular scattering measurements were performed in both the near-forward and near-backward regions for a variety of particles including for ethanol droplets, single polystyrene latex spheres, psl clusters, and clusters of Bacillus subtilis spores, all of various sizes. Because the angular scattering pattern is sensitive to size, shape and refractive index, the angular feature associate with clusters may be used to better characterize such airborne micro-particles. A watershed image processing routine has also been implemented. Through this routine, the number of intensity patches per solid angles is found to increase with cluster diameter.
Article
Viruses represent one of the most abundant, ocean-borne particle types and have significant potential for affecting optical backscattering. Experiments addressing the light-scattering properties of viruses have heretofore not been conducted. Here we report the results of laboratory experiments in which the volume-scattering functions of several bacterial viruses (bacteriophages) were measured at varying concentrations with a laser light-scattering photometer using a He-Ne and/or Argon ion laser (632.8 and 514.0 nm, respectively). Four bacterial viruses of varying size were examined, including the coliphages MS-2 (capsid size 25-30 nm) and T-4 (capsid size ∼100 nm), and marine phages isolated from Saco Bay, Maine (designation Y-l, capsid size 50-80 nm) and Boothbay Harbor, Maine (designation C-2, capsid size -∼110 nm). Volume-scattering functions (VSFs) were fitted with the Beardsley-Zaneveld function and then integrated in the backward direction to calculate backscattering cross section. This was compared to the virus geometric cross section as determined by transmission electron microscopy and flow-field fractionation. Typical backscattering efficiencies varied from $20 \times 10^{-6}$ to 1,000 × 10-6. Data on particle size and backscattering efficiencies were incorporated into Mie scattering calculations to estimate refractive index of viruses. The median relative refractive index of the four viruses was ∼1.06. Results presented here suggest that viruses, while highly abundant in the sea, are not a major source of backscattering.
Article
UV intensities on the surfaces of solid cylinders were measured in a disinfection chamber by means of a UV bioassay. The bioassay employed spores of the bacterium Bacillus subtilis (ATCC 6633) which had been deposited onto coupons of filter paper. These experimental measurements were then compared to surface intensity predictions obtained using an extense source with spherical emission (ESSE) model. Good agreement was obtained between both sets of data, with the predicted values lying between 75% and 95% of the experimental ones. The model was also applied to the prediction of UV intensities on the surfaces of an object of slab geometry travelling through a conceptualized disinfection facility having the con. guration of a tunnel in which UV sources were arranged on the walls of the tunnel. By assuming that the object was uniformly contaminated with spores of B. subtilis, estimates of the extent of disinfection achieved as the object travelled along the tunnel were made using previously published inactivation data for the spores. The versatility of the ESSE model was demonstrated by presenting three dimensional surface intensity plots of the various slab surfaces for both horizontal and vertical arrangements of UV sources in the tunnel. The model described here could prove useful in optimizing the arrangement and numbers of UV sources in surface disinfection facilities.
Article
Photons in the UV region of the spectrum are important for organisms since they are energy-rich and strongly absorbed by biological molecules having the potential to react with membranes, enzymes, and nucleic acids. These wavelengths can also be absorbed by specific molecules that undergo conversion to a more reactive state (light activation) which can then cause damage to molecules of critical physiological function (phototoxicity). The importance of pigments in two genera of the Citrus pathogens, Fusarium and Penicillium, was assessed for ability to protect against inactivation by UV-A, B, and C and two phototoxins activated by UV-A. Pigment-deficient mutants of both genera were isolated following UV-C mutagenesis. Direct exposure of fungal spores in suspension of wild type and pigment-deficient mutants was carried out under the appropriate light source. The UV-A activated phototoxins investigated were: alpha-terthienyl (alpha-T), which produces predominantly singlet oxygen (O-1(2)), an excited state of oxygen, which causes chiefly membrane damage; and 8-methoxypsoralen (8-MOP), which induces cycloadduct formation in DNA. For both genera, UV-A and UV-B alone were ineffective in causing inactivation of conidia at the fluences tested. Using appropriate Escherichia coli tester strains, it was demonstrated that the UV-B source was capable of inducing DNA lesions leading to lethality, presumably cyclobutane dimers in large measure. The carotenoids in one of the Fusarium species did not appreciably protect against lethal damage induced by UV-C, but the pigments of both Penicillium species were presumably able to screen UV-C and offer protection. It is assumed that the carotenoids in the wild type Fusarium species protected against UV-A activated alpha-T damage by quenching singlet oxygen. The blue-green pigment(s) in P. italicum prevent DNA damage caused by 8-MOP most probably by screening the UV-A wavelengths necessary to activate the phototoxin.
Article
The distribution of the energy of light waves during the interaction with suspensions of spherical bacteria obeys the Mie theory of scattering. In the visible range of the spectrum the Rayleigh-Gans theory cannot always be used for describing the scattering of light of bacterial suspensions.
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The scientific goals, instrumentation, and observational routine of the International Ultraviolet Explorer are described. The IUE, launched January 26, 1978, is in geosynchronous orbit, and there is continuous communication with ESA's ground station at Villafranca near Madrid and NASA's ground station at Goddard Space Flight Center during the observing shifts. Since the satellite can be commanded and data can be received in real time, the ground-based observer can make step-by-step decisions about his observing program in the same way as he would at a ground-based observatory. Among other goals, the project seeks to obtain high-resolution spectra of stars of all spectral types and to study gas streams in and around some binary systems. The format of the spectrum, which consists of a series of adjacent spectral orders displayed one above another in a rasterlike pattern, makes efficient use of the sensitive area of the SEC Vidicon television tubes used to integrate and record the spectrum. Preliminary studies are surveyed.
Article
Ultraviolet (UV) irradiation at 254 run and doses of 300 mWs/cm2 from a photochemical reactor (16.6 min at 300 μW/cm2) or 4.8 Ws/cm2 from a high intensity UV-C lamp (40 sec at 120–180 mW/cm2 reduced surface microbial count on mackerel by two to three log cycles. UV treated mackerel wrapped in 1 mil polyethylene and packed in -1°C ice had at least a 7 day longer shelf life than conventional ice-packed untreated controls. Spray washing with water containing 10 ppm chlorine by itself or in combination with UV irradiation was necessary to reduce surface counts on rough surfaced fish to the same extent as that on smooth surfaced fish. When UV irradiated and packed in 0°C ice, surface microbial counts on vacuum packaged mackerel lagged by 4 days those on mackerel wrapped in 1 mil polyethylene.
Article
Abstract— We have determined action spectra for pyrimidine dimer formation and loss of colony-forming ability in Chinese Hamster V-79 cells and have found a very strong correlation between the two. These data are consistent with the notion that damage to DNA is the principle cause of cell death and that the most important type of damage is the pyrimidine dimer. While the shape of the V-79 spectra mimics that of action spectra for bacteria. phage, and purified DNA, V-79 cells are about twice as sensitive to radiation at long wavelengths, relative to the sensitivity at 265 nm. However, if the action spectra are normalized to 297 nm. a wavelength included in the solar spectrum, the two sets of action spectra would coincide at wavelengths relevant to human skin-cancer. Thus an action spectrum based on microorganisms should be adequate for extrapolation to humans in terms of risk due to ozone depleteion.
Article
Ultraviolet light irradiation of bacterial spores in the presence of hydrogen peroxide has been shown to produce synergistic kills when compared with ultraviolet light (u.v.) and hydrogen peroxide used sequentially. This use in combination has been patented for the commercial sterilization of packaging before filling with UHT-processed products. Previous results have shown that lamps producing u.v. light with a maximum output at about 254 nm were extremely effective. Results obtained using a Synchrotron radiation source to produce a narrow band of irradiation now shows that the greatest kill of spores of Bacillus subtilis in the presence of hydrogen peroxide is obtained with radiation at ˜270 nm. Such results suggest that the action of the u.v. light is not directly on the spore DNA but may be related to the production of free hydroxyl radicals from hydrogen peroxide.
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The ultraviolet absorbance spectrum of a mixed culture of coliform bacilli is obtained and shown to be remarkably similar to recent measurements of the extinction curve of starlight.
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A comprehensive treatment of the mathematical basis for modeling the disinfection process for air using ultraviolet germicidal irradiation (UVGI). A complete mathematical description of the survival curve is developed that incorporates both a two stage inactivation curve and a shoulder. A methodology for the evaluation of the three-dimensional intensity fields around UV lamps and within reflective enclosures is summarized that will enable determination of the UV dose absorbed by aerosolized microbes. The results of past UVGI studies on airborne pathogens are tabulated. The airborne rate constant for Bacillus subtilis is confirmed based on results of an independent test. A re-evaluation of data from several previous studies demonstrates the application of the shoulder and two-stage models. The methods presented here will enable accurate interpretation of experimental results involving aerosolized microorganisms exposed to UVGI and associated relative humidity effects
Article
Recent enumeration and identification of marine particles that are less than 2μm in diameter, suggests that they may be the major source of light scattering in the open ocean. The living components of these small particles include viruses, heterotrophic and photoautotrophic bacteria and the smallest eucaryotic cells. In order to examine the relative contribution by these (and other) microorganisms to scattering, we have calculated a budget for both the total scattering and backscattering coefficients (at 550nm) of suspended particles. This budget is determined by calculating the product of the numerical concentration of particles of a given category and the scattering cross-section of that category. Values for this product are then compared to values for the particulate scattering coefficients predicted by the models of GORDON and MOREL (1983) and MOREL (1988).
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Hormesis is the application of potentially harmful agents at low doses to living organisms in order to induce stress responses. When fruit are exposed to low doses of UV a number of changes are induced including the production of anti-fungal compounds and delays in ripening. Both of these responses could be exploited by the horticultural sector to reduce postharvest losses. We review the results of UV treatment of a variety of fruits and the work done in identifying chemical changes in them. The prospects for treating fruits with UV on a commercial scale are considered.
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We investigated the detection of dielectric nanoparticles using static light scattering spectroscopy (LSS) in the UV range (from 250 to 390 nm). The light scattered by the polystyrene nanospheres in the backward direction were collected by means of an optical fiber probe and a charge-coupled device (CCD) spectrograph. The size distributions of the nanoparticles were obtained by a discrete inverse on the backscattering spectra using a theoretical model based on Mie theory. Our results show that UV LSS can be used to measure the sizes of nanoparticles with an accuracy far exceeding the diffraction limit and to study subwavelength structures at nanometer scale. This technique may find potential scientific and industrial applications including the study of macromolecular complexes at nanoscale, detection and identification of viral particles, non-invasive probing of nanoscale surface structures, and monitoring the processing of pharmaceutical nanoparticles.
Article
Ultraviolet (UV) light has become widely accepted as an alternative to chlorination or ozonation for wastewater disinfection. There are now over 2,000 wastewater treatment plants worldwide using either low- or medium-pressure UV technology. Recent studies investigating UV lamp technology, configuration, cleaning requirements and ageing, as well as long-term performance tests, have demonstrated beyond any doubt the effectiveness of UV in inactivating pathogens in wastewater. Research has also shown that, to ensure permanent inactivation and prevent the recovery of microorganisms following exposure to UV, a broad, "polychromatic" spectrum of UV wavelengths is necessary. These wavelengths inflict irreparable damage not only on cellular DNA, but on other molecules, such as enzymes, as well. Only medium-pressure UV lamps produce the necessary broad range of wavelengths; low-pressure lamps emit a single wavelength peak which only affects DNA. Polychromatic medium-pressure UV light is so effective because of the lamp's exceptionally high UV energy output at specific wavelengths across the UV spectrum. It has been shown, for example, that pathogenic E. coli O175:H7 was able to repair the damage caused by low-pressure UV, but no repair was detected following exposure to UV from medium-pressure lamps.
Article
DDSCAT 7.1 is an open-source Fortran-90 software package applying the discrete dipole approximation to calculate scattering and absorption of electromagnetic waves by targets with arbitrary geometries and complex refractive index. The targets may be isolated entities (e.g., dust particles), but may also be 1-d or 2-d periodic arrays of "target unit cells", allowing calculation of absorption, scattering, and electric fields around arrays of nanostructures. The theory of the DDA and its implementation in DDSCAT is presented in Draine (1988) and Draine & Flatau (1994), and its extension to periodic structures (and near-field calculations) in Draine & Flatau (2008). DDSCAT 7.1 includes support for MPI, OpenMP, and the Intel Math Kernel Library (MKL). DDSCAT supports calculations for a variety of target geometries. Target materials may be both inhomogeneous and anisotropic. It is straightforward for the user to "import" arbitrary target geometries into the code. DDSCAT automatically calculates total cross sections for absorption and scattering and selected elements of the Mueller scattering intensity matrix. This User Guide explains how to use DDSCAT 7.1 to carry out electromagnetic scattering calculations. DDfield, a Fortran-90 code to calculate E and B at user-selected locations near the target, is included in the distribution. A number of changes have been made since the last release, DDSCAT 7.0 . Comment: 83 pages, 11 figures
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Dust from scarlet-fever wards was exposed to a controlled range of atmospheric humidities by enclosure in metal boxes containing anhydrous calcium chloride and saturated solutions of potassium carbonate, sodium nitrite, potassium bromide and sodium sulphate. The death-rate of total organisms, Staphylococcus aureus and Streptococcus pyogenes in the dust was assessed by periodic sampling of series of twenty 10mg. portions. A positive correlation between atmospheric humidity and death-rate was observed for the three groups of organisms counted in three specimens of dust.
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Ultraviolet light action spectra in the range 2250 to 3020 A have been determined for the plaque-forming ability of the following bacteriophage and animal viruses: T-2, varphix-174, R-17, fr, MS2, 7-S, fd, vesicular stomatitis, vaccinia, encephalomyocarditis, reovirus-3, and polyoma. Absolute quantum yields for the plaque-forming ability of MS2, fr, fd, varphix-174, and T-2 were determined over the range 2250 to 3020 A. Relative quantum yields for plaque-forming ability indicated that viruses with single-stranded nucleic acid were on the average ten times more sensitive to UV than double-stranded viruses. In addition for ten of the twelve viruses a relation existed between the shape of their action spectra and the stranded state of their nucleic acid. The ratio of the inactivation cross-section at 2650 A to that at 2250 A for these viruses was 1.0 for single-stranded viruses and 2.0 for viruses with double-stranded nucleic acid. The above relations were dependent on the stranded state of the nucleic acid not the ribose or deoxyribose form of the sugar present.
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Kinetics of the inactivation of phage T7 by six ultraviolet and visible light wavelengths of the far (below 320 nm) and the near uv (above 320 nm) were studied, with and without host-cell reactivation. Inactivations were always exponential with the three shorter wavelengths (254,313, and 334 nm), whereas with the longer wavelengths (365, 405, and 460 nm), a small shoulder (extrapolation number <2) was consistently obtained. The host-cell reactivation sector was prominent with 254 and 313 nm of radiation, reduced with 334 nm, and either trivial or absent with the three longer wavelengths. Action spectra for the inactivation revealed small shoulders in the near-uv region, both with and without host-cell reactivation. A comparison of single-strand break (alkali-labile bond) induction by 365 nm of radiation in phage T4, compared with lethality in phage T7, revealed that a frequency of 0.3 single-strand breaks may occur per lethal hit.
Article
We have investigated the B to A conformation change of DNA double helices by a new method “soft-mode analysis.” We find theoretically that a mode does soften when the vibration normal modes are perturbed by increasing the electrostatic interaction between the unbalanced charges on atoms in the double helix. The same mode also softens for enhanced van der Waals interactions. The mode softening indicates the onset of conformation change. The enhancing of the electrostatic and van der Waals interaction mimic the effect of decreasing the polar nature of the solvent or water of hydration associated with the B conformation DNA. We discuss qualitatively the concept of soft modes and their relation to conformation change as well as their applicability to macromolecules. We discuss previous work in which the normal vibrational modes have been calculated. We also discuss the displacement which comes from the soft mode and show that it correlates very well with that expected for the B to A conformation charge.