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Applied Energy 01/2013; · 5.11 Impact Factor
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ABSTRACT: Hypertension is asymptomatic until late stages of pathogenesis, rendering an effective means of detection for early diagnosis essential. The current method of diagnosing hypertension requires two or more sphygmomanometric readings over two or more office visits, which potentially hinders early detection. Though retinopathy is an indicator of vascular damage, it generally presents in later stages of hypertension. Previous and related studies have suggested that the microvasculature in the bulbar conjunctiva may be a sensitive site to assess vasculopathy. Conjunctival microangiopathy was assessed using CAIM and reported on a severity index (SI). Images of the retinal fundus were taken via non-mydriatic fundus photography and graded using the Scheie scale in the same subjects to compare with CAIM. Conjunctival microangiopathy was significantly elevated in hypertensive subjects (SI = 5.35 ± 1.04, n = 20) compared to control subjects (SI = 1.75 ± 1.39, n = 8; p ≤ 0.05), and correlated with time since disease diagnosis (R2 = 0.33). Hypertensive subjects with Grade 1 retinopathy displayed increased conjunctival microangiopathy (SI = 5.85 ± 0.90, n = 13) compared to those without retinopathy (SI = 4.43 ± 0.53, n = 7; p ≤ 0.05). These data indicate a possible pre-retinopathy time window during which conjunctival microangiopathy may indicate the risk of organ damage, supporting the hypothesis that the conjunctival microcirculation may serve as a platform for early detection and monitoring disease progression.
Clinical hemorheology and microcirculation 07/2012; · 3.40 Impact Factor
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ABSTRACT: In this study, we verified the treatment planning calculations of skin doses with the incorporation of the bolus effect due to the intervening alpha-cradle (AC) and carbon fiber couch (CFC) using radiochromic EBT2 films. A polystyrene phantom (25 × 25 × 15 cm(3)) with six EBT2 films separated by polystyrene slabs, at depths of 0, 0.1, 0.2, 0.5, 1, 1.4 cm, was positioned above an AC, which was 1 cm thick. The phantom and AC assembly were CT scanned and the CT-images were transferred to the treatment planning system (TPS) for calculations in three scenarios: (A) ignoring AC and CFC, (B) accounting for AC only, (C) accounting for both AC and CFC. A single posterior 10 3 10 cm(2) field, a pair of posterior-oblique 10 × 10 cm(2) fields, and a posterior IMRT field (6 MV photons from a Varian Trilogy linac) were planned. For each radiation field configuration, the same MU were used in all three scenarios in the TPS. Each plan for scenario C was delivered to expose a stack of EBT2 films in the phantom through AC and CFC. In addition, in vivo EBT2 film measurement on a lung cancer patient immobilized with AC undergoing IMRT was also included in this study. Point doses and planar distributions generated from the TPS for the three scenarios were compared with the data from the EBT2 film measurements. For all the field arrangements, the EBT2 film data including the in vivo measurement agreed with the doses calculated for scenario (C), within the uncertainty of the EBT2 measurements (4%). For the single posterior field (a pair of posterior-oblique fields), the TPS generated doses were lower than the EBT2 doses by 34%, 33%, 31%, 13% (34%, 31%, 31%, 11%) for scenario A and by 27%, 25%, 22%, 8% (25%, 21%, 21%, 6%) for scenario B at the depths of 0, 0.1, 0.2, 0.5 cm, respectively. For the IMRT field, the 2D dose distributions at each depth calculated in scenario C agree with those measured data. When comparing the central axis doses for the IMRT field, we found the TPS generated doses for scenario A (B) were lower than the EBT2 data by 35%, 34%, 31%, 16% (29%, 26%, 23%, 10%) at the depths of 0, 0.1, 0.2, 0.5 cm, respectively. There were no significant differences for the depths of 1.0 and 1.4 cm for all the radiation fields studied. TPS calculation of doses in the skin layers accounting for AC and CFC was verified by EBT2 film data. Ignoring the presence of AC and/or CFC in TPS calculation would significantly underestimate the doses in the skin layers. For the clinicians, as more hypofractionated regimens and stereotactic regimens are being used, this information will be useful to avoid potential serious skin toxicities, and also assist in clinical decisions and report these doses accurately to relevant clinical trials/cooperative groups, such as RTOG.
Technology in cancer research & treatment 06/2012; · 2.02 Impact Factor
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ABSTRACT: Purpose: Electronic portal imaging devices (EPID) have been used for both in vivo dosimetry and in vitro dose verification in intensity modulated radiotherapy (IMRT). This study is to investigate the effect of EPID mechanical precision on the accuracy of measured dose distribution. Methods: EPID energy fluences (dicom images) of H&N IMRT fields were collected daily on two Varian LINACs (Clinac-iX & Trilogy) over 4-week period. The energy fluences were converted to doses using EPIDoseTM (Sun Nuclear Corp). Mechanical deviations of EPIDs could be divided into two components: one with inherent detector center misalignment from the beam central axis, another caused by the 'sagging effect' from gantry rotation. The first component was detected by 'best matching' of the measured and calculated dose at zero gantry angle (G=0). The second component was computed by 'best matching' the 10×10cm field defined by MLC at G=0, 90,180, and 270, separately. A 'shift' was generated by the combination of these two components and then applied to correct the measured dose at the corresponding gantry angle for the IMRT field. Results: Inherent misalignment of the detector's center and the 'sagging' deviation were found to be 1-2 mm and 1-5 mm, respectively for both LINACs. Each component was found very stable (change < 1mm) over the 4-week observational period. Using a Gamma index of 2%/2mm (DD/DTA), the 'shift' increased the average passing rate from 59% to more than 92%. On the other hand, blindly applying 'auto-shift' from commercially available software to obtain the best match would compound true QA issues with units' misalignments. Conclusions: A false 'mismatch' between measured and calculated dose distribution caused by mechanical inaccuracies of EPID could be avoided by measuring the two components identified in this study. One should examine the mechanical precision of equipment prior to clinical use of EPID dosimetry.
Medical Physics 06/2012; 39(6):3655. · 2.83 Impact Factor
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ABSTRACT: Purpose: VMAT involves multi-parameter modulations, thus presenting multi-dimensional challenges. Here, we present a viable approach to VMAT patient specific QA using EPID-based dosimetry for spine VMAT SRS casesMethods: Our spine VMAT SRS plans consisted of two full arcs and were optimized with 6 MV photons for a Varian Trilogy LINAC. The QA plans were computed by resetting all control points to 0° gantry angle while keeping the MLC apertures and corresponding MU weights intact. The dose distribution at the depth of clinical significance was calculated in a solid water phantom. EPIDose (Sun Nuclear Corp) was used to convert MV EPID images into absolute dose in a plane of interest in a homogeneous medium. During measurements, the source-to-detector distance (SDD) was set to 105 cm and the VMAT QA plan was delivered with 600 MU/min. For each QA plan, three measurements were made. The average pass rate (thresholds: 2%/2 mm) was then calculated. In addition, the dose at the isocenter or other points of clinical significance was also measured and the mean was calculated. Results: Our current institutional QA acceptance criteria for VMAT plans are: pass rate 90% for 2%/2mm with a dose threshold of 10% and the discrepancy between the measured and planned doses at the isocenter or other points of clinical significance 2%. Our preliminary investigation indicated that the pass rate was normally greater than 95.0% with a total number of valid detection points of ∼30000. The dose difference at the point of interest was, in general, around ±1.0 %. Sharp dose gradients were accurately detected at the PTV-cord interface. Conclusions: EPID- based dosimetry is real-time and financially viable. It can achieve sub- millimeter dosimetry accuracy without extensive inter-diode interpolations. We believe that EPID-based VMAT dosimetry offers a competitive alternative to other competing dosimetry technologies.
Medical Physics 06/2012; 39(6):3742. · 2.83 Impact Factor
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ABSTRACT: Purpose: Radiotherapy techniques for sparing the hippocampus during cranial irradiation are emerging. This work is to study dose-painting with volumetric modulated arc therapy (VMAT) in the setting of oligo brain metastases and the clinically relevant dose QA. Methods: A patient having 3 brain metastases was re-planned using 2-arc 6 MV photons with in-house VMAT treatment planning system (TPS). The clinical goal is to dose paint the whole brain and brain metastases to 32 Gy and 63 Gy in 15 fractions, respectively while keeping the mean dose to the hippocampus less than 6 Gy. The VMAT dose QA was carried out using ArcCHECK (AC) and 3DVH (Sun Nuclear Corp) on a Varian Trilogy LINAC. The AC Planned-Dose-Perturbation (ACPDP) algorithm was employed to estimate the actual patient dose distribution, at the same grid resolution as that from the TPS calculation. The patient's DICOM RT dose/plan/structures/CT images were loaded into the software. The measured doses and TPS calculated doses for relevant structures were compared. Their differences represented systematic errors induced from the combination of TPS dose calculation algorithm and beam-delivery. Results: Clinical planning criteria were all satisfied. A 99.5% 3D matching rate for 2%/2mm DD/DTA was observed between the ACPDP reconstruction and TPS-calculated dose. Despite the excellent agreement, the relative dose differences for patient's critical structures between measurements and TPS are: 0.8%, mean brain lesions; 0.7%, mean whole brain; 9% (<3% of prescription), mean L_hippocampus; 9% (<3% of prescription), mean R hippocampus; 0.1%, max cord; 1.8%, max chiasm; 3.7%, max brainstem; 0.5%, max L_OpticN; 1.9%, max R OpticN, 0.2%. Conclusions: For the application of dose painting VMAT planning for patients with oligo brain metastases, the patient relevant dose QA result has demonstrated the capability and the accuracy of our VMAT technique, allowing for 3-level dose-painting to spare critical structures with acceptable target coverage and homogeneity.
Medical Physics 06/2012; 39(6):3997. · 2.83 Impact Factor
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International Journal of Medical Physics, Clinical Engineering and Radiation Oncology. 05/2012;
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ABSTRACT: Protein tyrosine phosphatases (PTPs) are crucial regulators for numerous biological processes in nature. The dysfunction and overexpression of many PTP members have been demonstrated to cause fatal human diseases such as cancers, diabetes, obesity, neurodegenerative diseases and autoimmune disorders. In the past decade, considerable efforts have been devoted to the production of PTPs inhibitors by both academia and the pharmaceutical industry. However, there are only limited drug candidates in clinical trials and no commercial drugs have been approved, implying that further efficient discovery of novel chemical entities competent for inhibition of the specific PTP target in vivo remains yet a challenge. In light of the click-chemistry paradigm which advocates the utilization of concise and selective carbon-heteroatom ligation reactions for the modular construction of useful compound libraries, the Cu(I)-catalyzed azidealkyne 1,3-dipolar cycloaddition reaction (CuAAC) has fueled enormous energy into the modern drug discovery. Recently, this ingenious chemical ligation tool has also revealed efficacious and expeditious in establishing large combinatorial libraries for the acquisition of novel PTPs inhibitors with promising pharmacological profiles. We thus offer here a comprehensive review highlighting the development of PTPs inhibitors accelerated by the CuAAC click chemistry.
Current Medicinal Chemistry 03/2012; 19(15):2399-405. · 4.86 Impact Factor
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ABSTRACT: Purpose: To evaluate the measured dose distributions using radiochromic EBT2 films for small fields in iPlan (BrainLab) commissioning. Methods: Radiochromic EBT2 films were irradiated with 6 MV photons on a Varian Trilogy linac using polystyrene phantoms. The measurements included dose profiles and depth doses for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 10 × 10 cm2 etc. The dose profile measurements were taken at the depth of 5 cm. The calibration films were irradiated at dmax(1.4 cm) for doses up to 6 Gy. Films were scanned using an Epson 10,000 XL flatbed scanner with 72 dpi resolution. Pixel values were converted to doses using the established calibration-curve. The 2D dose dis-tributions were generated from the film data analysis. In-house software was utilized to compare the measured doses from films with the treatment planning data. In addition, selected patients’ SRS fields were also measured with the EBT2 films for comparison with iPlan. An EDGETM detector was also used to check the central-axis doses for the SRS patients’ measurements. Results and Discussion: The measured planar dose distributions achieved more than 98% and 95% passing rates with a set of 2%/2 mm dose and DTA criteria for all square fields and all patient treatment fields (<5 × 5 cm2), respectively. Agreement with measurement data with the EDGETM detector at the central axis (±1%) was found with the plan data. This is the first report for SRS small photon-field measurement using the latest radiochromic film, EBT2. The results shown in this work indicate that the use of EBT2 film provides accurate dosimetry measure-ments for small photon beams. The measurements show excellent agreement with the iPlan TP commissioning data. Conclusions: The patient-specific EBT2 film QA for iPlan SRS patients showed good results. The EBT2 films could potentially be a useful dosimeter in verification of commissioning as well as patient-specific QA for SRS cases.
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology. 01/2012; 1(1):1.
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ABSTRACT: Many global circulation models predict supersonic zonal winds and large vertical shears in the atmospheres of short-period Jovian exoplanets. Using linear analysis and nonlinear local simulations, we investigate hydrodynamic dissipation mechanisms to balance the thermal acceleration of these winds. The adiabatic Richardson criterion remains a good guide to linear stability, although thermal diffusion allows some modes to violate it at very long wavelengths and very low growth rates. Nonlinearly, wind speeds saturate at Mach numbers 2 and Richardson numbers 1/4 for a broad range of plausible diffusivities and forcing strengths. Turbulence and vertical mixing, though accompanied by weak shocks, dominate the dissipation, which appears to be the outcome of a recurrent Kelvin-Helmholtz instability. An explicit shear viscosity, as well as thermal diffusivity, is added to ZEUS to capture dissipation outside of shocks. The wind speed is neither monotonic nor single valued for a range of shear viscosities larger than about 10–3 of the sound speed times the pressure scale height. Coarsening the numerical resolution can also increase the speed. Hence global simulations that are incapable of representing vertical turbulence and shocks, either because of reduced physics or because of limited resolution, may overestimate wind speeds. We recommend that such simulations include artificial dissipation terms to control the Mach and Richardson numbers and to capture mechanical dissipation as heat.
The Astrophysical Journal 11/2010; 725(1):1146. · 6.02 Impact Factor
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ABSTRACT: Shortage of conventional raw material for the pulp and paper products together with the increasing world demand for paper has renewed interest in non-wood fibres. Non-wood pulping capacity has been increasing steadily over the last decade. A lot of crops grown for biomass, like switchgrass (Panicum virgatum L.), are good examples of plants with potential for pulp production. Raw material chemical composition, kraft pulp yield and properties, and fibre characteristics of elephant grass or hybrid pennisetum (Pennisetum purpureum Schum. cv. SDPN3) and switchgrass (cv. Cave-in-Rock) were determined in an effort to evaluate them as raw materials for pulp and paper production. Elephant grass had -cellulose and Klasson lignin contents of 45.6 and 17.7%, respectively. The respective values for switchgrass were 41.2 and 23.89 %. Pulp yields, following a mild kraft process, were 48 and 50% for switchgrass and elephant grass, respectively. The corresponding kappa numbers were 15.5 and 9.2. The weight-weighted fibre length averaged 1.32 mm. Pulp freeness was higher for switchgrass (330 mL) than for elephant grass (139 mL). Elephant grass had a burst index above 5.85 kP.m 2 g -1 . These characteristics demonstrate the suitability of both elephant grass and switchgrass for pulp production.
African Journal of Environmental Science and Technology. 08/2010; 4:465-470.
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ABSTRACT: Spontaneous inter-particle percolation is a mechanism of particle segregation which arises when a particle falls through the voids among large particles due to gravity or other applied force, the size difference being such that this can occur without the need for applying strain. It is a phenomenon arising in some packed bed processing operations and in some dispersers for particles. Here the mechanism is modelled by computer simulation. The model uses particle sizes, a coefficient of restitution and also, to cater for less elastic materials, a coefficient of friction. This yields percolation velocities quantitatively consistent with prior laboratory studies, showing the correct dependence on coefficient of restitution and particle size. The simulation clarifies the dependence of radial dispersion on packing height. The radial distributions are well described only at higher coefficients of restitution, pointing to the need for a better means of describing collisions between percolating and packed particles.
07/2010;
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ABSTRACT: A modular micro-TPV system was introduced in this work. Compared to the cylindrical structure, the modular TPV system has the advantages of easier fabrication and assembly. A micro combustor is a key component of the micro-TPV system. In order to maximize the power output, higher wall temperature and uniform distribution along the combustor wall is desirable. A micro cylindrical combustor (inner diameter d = 3.56 mm) and three kinds of micro modular combustors with the widths of 1.0 mm, 1.5 mm and 2.0 mm are experimented with. The results indicate that the micro modular combustor with a width of 1 mm has a much higher radiation efficiency than the micro cylindrical combustor. The wall temperature decreases with the increase of width due to the reduced heat transfer between the wall and hot gases. The performance of the micro modular TPV system is also predicted.
Journal of Micromechanics and Microengineering 06/2010; 20(8):085003. · 2.11 Impact Factor
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ABSTRACT: Measurement of the flame temperature in a micro combustor is essentially difficult due to the size constraint. A one-dimensional (1D) flame model coupled with the heat conduction in the solid wall is employed to analyze the heat transfer occurring in a cylindrical micro combustor. The flame temperature is given explicitly by taking into account the effects of the heat loss (from the flame to the wall) in the reaction zone and heat recirculation through the solid wall. With the data obtained from the simulation results of the 1D adiabatic freely propagating CH4–air laminar flames, the flame temperature in a cylindrical micro combustor can be solved iteratively. In order to validate the 1D model, the two-dimensional (2D) numerical simulations of premixed combustion of the CH4–air mixtures are carried out in a 0.5 mm radius cylindrical micro combustor. The comparisons of the flame temperature and heat recirculation between the 1D model and 2D numerical simulation indicate that despite the simplifications and assumptions made in the present study, the 1D theoretical model is able to predict the flame temperature to a reasonable accuracy.
Heat Transfer Engineering 06/2010; 31(7):581-591. · 0.89 Impact Factor
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ABSTRACT: In this paper, we introduce an estimation technique for analyzing radial velocity data commonly encountered in extrasolar planet detection. We discuss the Keplerian model for radial velocity data measurements and introduce a technique named the iterative adaptive approach (IAA) to estimate the three-dimensional spectrum (power versus eccentricity, orbital period and periastron passage time) of the radial velocity data. We then discuss different ways to regularize the IAA algorithm in the presence of noise and measurement errors. We also discuss briefly the computational aspects of the method and introduce a computationally efficient version of IAA. Finally, we establish the significance of the spectral peaks by using a relaxation maximum likelihood algorithm and a generalized likelihood ratio test. Numerical experiments are carried out on both simulated and real life data sets to evaluate the performance of our method. The real life data sets discussed are radial velocity measurements of the stars HD 63454, HD 208487, and GJ 876.
The Astronomical Journal 01/2010; 139(2):783. · 4.03 Impact Factor
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ABSTRACT: Purpose: To develop a methodology of therapy portal imaging verification for volumetric modulated arc therapy (VMAT) and RapidArc treatments. Method and Materials: For Varian dynamic IMRT treatments the “DMLC aperture” or CIAO can be imaged by electronic portal imaging device (EPID) or with film. However, during VMAT and RapidArc treatment delivery, MLC leaves constantly move while gantry is rotating continuously. For quality assurance purpose for VMAT and RapidArc treatments we introduce the concept of “Dose Aperture”. In this approach a 3D isodose surface is created with a fixed beam direction, and a portal aperture is drawn around the projection of the isodose surface. For rotational modalities, such as VMAT and RapidArc, a standard orthogonal pair of beam directions can be selected on which the Dose Apertures are projected on the digitally reconstructed radiographs (DRRs). Portal images using these apertures can be obtained to verify the isocenter and location of the treatment with respect to the patient's bony anatomy. Results: For a VMAT plan the prescription isodose surface was generated using well established planning software tools. For the AP and LAT beams, two Dose Apertures were created, which were then projected on the corresponding DRRs for field matching and correlation. The Dose Apertures could be transferred to setup fields which are then readily available for portal imaging application of VMAT and RapidArc treatments. Conclusion: Although setup fields without the treatment apertures can be used to verify the location of the isocenter, the portal image generated with Dose Aperture is patient specific and can be used when weekly portal imaging is required.
Medical Physics 05/2009; 36(6):2818-2818. · 2.83 Impact Factor
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ABSTRACT: The micro combustor is a key component of the micro thermophotovoltaic (TPV) system. Premixed combustion of a hydrogen–air mixture in micro combustors with an inner diameter of 2 mm is studied experimentally and numerically. A backward-facing step (s = 0.5 mm) is employed in the cylindrical tube for flame stabilization. The effects of flow velocity, fuel–air equivalence ratio and combustor length on the wall temperature are investigated. Based on the measured wall temperature, the radiation heat flux through the combustor wall is quantified. The experimental results (measurements and direct photos) indicate that the position of the peak wall temperature is nearly localized within a narrow zone (4–6 mm from the step), independent of flow velocity, fuel–air equivalence ratio and combustor length. The combustion flows are numerically modeled by solving the 2D governing equations in both the gas phase and solid phase. The numerical results indicate that at Re > 500 (u0 = 8 m s−1) modeling the turbulence (k–ε model) is necessary to ensure good agreement with the experimental values. The numerical model is shown to be applicable over the full span of both flow velocity (8 ≤ u0 ≤ 16 m s−1) and fuel–air equivalence ratio (0.6 ≤ Φ ≤ 1.0).
Journal of Micromechanics and Microengineering 11/2008; 19(1):015019. · 2.11 Impact Factor
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11/2008;
