Roy B. Tumlos

University of the Philippines Manila | UPM · Department of Physical Sciences and Mathematics

Aspergillus flavus is a known source of aflatoxin and other carcinogens that contaminates perishable goods such as copra, one of the top exports of the Philippines. Fungal contamination in perishable products has caused post-harvest losses and a significant threat to food safety and security. Existing methods to control or prohibit the growth of fu...

Gamma irradiation as an alternative method to control or prohibit fungal contamination had been explored in this study. Locally acquired copra inoculated with Aspergillus flavus was irradiated with varying doses of gamma radiation. This resulted to the decreasing trend in the fungal count through increasing the absorbed dose of gamma radiation thus...

Strong emission from the auroral green line O(¹S)GO(¹D) at 557.7nm was observed in the afterglow of an atmospheric-pressure 2.45 GHz microwave-induced plasma jet. The device used Ar as the working gas for the plasma, and a surrounding N2 gas flow to stabilize the discharge. The characteristic line-shape of the peak at 557.7 nm indicated that the em...

This study is about using a composite of Tungsten Carbide (WC) powder and Styrene-butadiene rubber (SBR) as a gamma radiation shielding material. Eight different types of composite shield samples were fabricated via compression molding process, that is, four configurations of the samples defined based on the different WC:SBR weight ratios (0:1, 0.5...

This study aimed to evaluate the efficacy of ultraviolet-C irradiation and atmospheric pressure plasma jet treatment as inactivation methods of Salmonella spp. on stainless steel surfaces commonly used as food contact surfaces. Two types of stainless steel namely 304 and 316, were used as test surfaces with each type having three different finishes...

Roughness parameters are traditionally obtained for the surface characterization of microfluidic devices as these are easily computed from height profiles. However, these provide limited topological information on channel geometry needed for fluid flow or fluid retention optimization. In this study, topological measures from Minkowski functionals a...

A microwave-induced atmospheric-pressure plasma pencil was developed with an Ar-N₂ gas mixture supplied to a coaxial transmission line. High-frequency simulation showed sufficient high electric field at the tip of the inner conductor, which resulted to automatic plasma ignition and a stable operation. The dependence of the characteristics of the pl...

This study identified a reference organism for the establishment of microwave atmospheric pressure plasma jet treatment of young coconut liquid endosperm. Three different, predominant spoilage bacteria were isolated from spoiled liquid endosperm and identified through 16S rDNA sequencing, prior to propagation and eventual challenge studies. Basic L...

ZnO/Zn film was deposited on soda-lime glass substrate using a microwave atmospheric plasma jet. Energy dispersive spectroscopy showed that the Zn and O2 has an atomic ratio of 72:28. Zn (101) peak was also observed through X-ray Diffraction analysis. Annealing of the ZnO/Zn film at 400°C for 1h leads to the oxidation of Zn forming ZnO film. The ph...

This study established the efficacy of atmospheric pressure plasma jet on Pseudomonas aeruginosa on stainless steel types 316 and 304; with different finishes namely, mirror (MR), hairline (HL) and 2B surfaces. A cocktail of four strains of P. aeruginosa in the mid-stationary growth phase were allowed to attach on the test surfaces, and subjected t...

Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying ti...

Microalgae is one of the alternative feedstock for biofuel production with the highest yield per land area. However, current method in microalgae drying process requires high energy which accounts to about 60% of the total energy of the biofuel production chain. Moreover, conventional means of drying results to uneven drying of the microalgae with...

In this study, a hydrophobic coating on glass surfaces was fabricated by application of a silicone oil lubricant and activated using a microwave atmospheric plasma jet. Optimization of the treatment was done by variation of the working gas flow rates, input microwave power and plasma treatment time, based on contact angle measurements. In compariso...

Pictures of plasmas and deposits in a discharge chamber taken by varying shutter speeds have been integrated into high dynamic range (HDR) images. The HDR images of a graphite target surface of a compact planar magnetron (CPM) discharge device have clearly indicated the erosion pattern of the target, which are correlated to the light intensity dist...

High dynamic range (HDR) imaging was used to obtain a wide intensity map of a magnetized sheet plasma. A set of 12 low dynamic range (LDR) photographs with various shutter speeds (1/200-1/2 s) was captured with an Olympus FE-19 digital camera. The LDR images were processed to recover color channel response functions of the camera needed to produce...

Presented here is an image of a microwave air plasma produced from a 2.45-GHz source. To assist in the plasma ignition and confinement, a set of samarium-cobalt (Sm-Co) permanent magnets arranged in a double-hexapole configuration is used. In the image presented, air in the vacuum chamber is ignited into the plasma at a pressure of 3 × 10-3 torr. T...

The study to be presented is motivated by the need of certain industries to implement a cost-effective method of cleaning up wastewater from industrial processes, for example the clean-up of dye-tainted wastewater from textile mills. Biomass by-products, for a long time, have been the popular choice for the role of clean-up agents for certain appli...

This study deals with the enhancement of chromium (VI) removal by vacuum drying and plasma pre-treatments of cocolumber (Cocos nucifera) sawdust. For fixed adsorbent dose and pH, the effects of important parameters such as initial adsorbate concentration and contact time are determined. Results show that both pre-treatments increased the adsorption...

A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy contr...

Science Diliman (July-December 2004) 16:2, 31–35 A 2.45 GHz magnetron from a domestic microwave oven, with a power output rating of 1.5 kW, is utilized as the microwave source in the design of a multipurpose electron cyclotron resonance plasma device in the Plasma Physics Laboratory of the National Institute of Physics. Measurements of the power ou...

The results of an experimental study of the magnetic structure in the H-1 heliac are presented. Electron beam magnetic mapping has confirmed the existence of closed nested flux surfaces, in good agreement with a computer model. Measurements over a wide range of helical winding currents demonstrated a variety of attainable magnetic configurations wi...

A new, high-precision rotating wire grid apparatus for vacuum magnetic surface mapping of current-free toroidal plasma confinement geometries is described. This full-scaled version of the prototype apparatus1 developed on the SHEILA heliac has been tested and permanently installed on the H-1 heliac. Data of high quality are obtained with low electr...

We describe a new, fast, and accurate method for obtaining magnetic surface puncture plots by the use of a rotating grid of fine wires. Electrons launched from a small gun follow the magnetic field lines, and a fraction are intercepted by the wire grid. The current signals, chordal integrals of electron beam intensity, are inverted by an iterative...

A novel approach is used in studying the error fields in the heliac facility "H-lNF. in the plasma Research Laboratory of the Australian National University by an electron beam mapping technique using a rotating multi-wire grid collector and a reconstruction technique developed in tomography known as Algebraic Reconstruction Technique (ART). Some e...