Reduction In Collection Efficiency Research Articles

Ion recombination correction factors and detector comparison in a very-high dose rate proton scanning beam

PurposeAccurate dosimetry is paramount to study the FLASH biological effect since dose and dose rate are critical dosimetric parameters governing its underlying mechanisms. With the goal of assessing the suitability of standard clinical dosimeters in a very-high dose rate (VHDR) experimental setup, we evaluated the ion collection efficiency of several commercially available air-vented ionization chambers (IC) in conventional and VHDR proton irradiation conditions. MethodsA cyclotron at the Orsay Proton Therapy Center was used to deliver VHDR pencil beam scanning irradiation. Ion recombination correction factors (ks) were determined for several detectors (Advanced Markus, PPC05, Nano Razor, CC01) at the entrance of the plateau and at the Bragg peak, using the Niatel model, the Two-voltage method and Boag’s analytical formula for continuous beams. ResultsMean dose rates ranged from 4 Gy/s to 385 Gy/s, and instantaneous dose rates up to 1000 Gy/s were obtained with the experimental set-up. Recombination correction factors below 2 % were obtained for all chambers, except for the Nano Razor, at VHDRs with variations among detectors, while ks values were significantly smaller (0.8 %) for conventional dose rates. ConclusionsWhile the collection efficiency of the probed ICs in scanned VHDR proton therapy is comparable to those in the conventional regime with recombination coefficiens smaller than 1 % for mean dose rates up to 177 Gy/s, the reduction in collection efficiency for higher dose rates cannot be ignored when measuring the absorbed dose in pre-clinical proton scanned FLASH experiments and clinical trials.

Fragmentation and abrasion of solid particles in cyclones of CFB reactors: Phenomenology and kinetic model constitution

Particulate material in gas-solid flow systems is under constant mechanical stress due to the collisions of solid particles with the internal walls of the equipment and inter-particle collisions. These collisions cause attrition, resulting in a reduction in particle diameter. This study aims to analyze this phenomenon by evaluating the particle size distribution flowing in a loop in a cyclone. Samples were collected after each pass in the cyclone to obtain the temporal variation of particle size distribution. Increases in the inlet velocity increased the generation of fine particles, consequently reducing the collection efficiency in the cyclone. In addition, a kinetic model was built from the experimental database, and it enabled the prediction of a size reduction of FCC catalyst particles in a CFB reactor. • Effects of fragmentation and abrasion on the cyclone performance. • Phenomenology of fragmentation and abrasion in cyclones operating at high inlet velocities. • Reduction of collection efficiency in cyclones due to particles fragmentation. • Kinetic model constitution for fragmentation and abrasion in cyclones. • Prediction of fragmentation in cyclones operating in a circulating fluidized beds.

Effects of p-layer hole concentration and thickness on performance of p-i-n InGaN homojunction solar cells

In this paper, the effects of p-layer hole concentration and p-layer thickness on the performances of InGaN p-i-n homojunction solar cells with different indium components and their intrinsic mechanisms are investigated by numerical simulations. it is found that the conversion efficiency of solar cells first increases and then decreases slightly with the increase of p-layer hole concentration and p-layer thickness. Moreover, the change of p-layer hole concentration and p-layer thickness will cause great changes of the conversion efficiency of the solar cells, especially as the indium composition increases. In order to better clarify and understand the physical mechanism of this phenomenon, the collection efficiency, <i>I</i>-<i>V</i> characteristic, built-in electric field and carrier transport of solar cells are analyzed in this paper. When the hole concentration is insufficient, the build-in electric filed is not strong enough to separate the most of the electric-hole pairs. This will reduce the collection efficiency. In addition, the lower the hole concentration, the higher the series resistance of solar cells will be and the more the power loss. So a conclusion can be drawn that the lower hole concentration of p-layer would be accompanied by the reduction of collection efficiency and the increase of series resistance, thus resulting in a lower conversion efficiency. With the increase of the hole concentration which is below an optimal value, the built-in electric field reaches the threshold, which can improve the collection efficiency. At the same time, although the series resistance is reduced to a certain extent, it still reduces the effective output power and limits the conversion efficiency. When the hole concentration is higher than the optimal value, the carrier mobility becomes the main factor limiting the conversion efficiency. As for the p-layer thickness, the simulation results indicate that the lateral transport of carriers from the p-layer to the anode electrodes becomes more obstructive with the thinning of p-layer thickness. This is because when the p-layer thickness decreases, thus causing the p-layer sectional area to decrease, the lateral series resistance becomes higher. It is clear that when the p-layer is too thin, the lateral series resistance is one of the main limiting factors affecting the conversion efficiency of solar cells.

Numerical prediction of dust capture efficiency of a centrifugal wet scrubber

The gas, liquid, and dust particle behavior inside a centrifugal wet scrubber was simulated and a submodel for predicting its collection efficiency was developed that also takes in account the reduction in collection efficiency due to droplet carryover. Centrifugal wet scrubbers are used in many industries and deliver a high scrubbing efficiency at relatively low capital and operational costs. However, they often experience problems such as droplet carryover at high gas flows and reduced collection efficiency at low gas flows. An improved understanding of flow processes inside the scrubbers is needed to develop a better scrubber design. An experimental test facility was setup for this purpose which also served to validate the CFD modeling results. Ideal operating parameters for maximum scrubbing efficiency and minimum droplet carryover were identified. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1001–1012, 2018

A Study of the Effect of Different Inlet Vanes on Cyclone Pressure Drop and Collection Efficiency

Experimental studies have been conducted on pressure drop and collection efficiency of a cyclone separator with different inlet vanes. The results indicated that all the inlet vanes reduce the cyclone pressure drop and also influence the collection efficiency in various degrees. Cyclone pressure drop decreases when dust concentration in the gas increases, and when an inlet vane is installed. 3#, 4# inlet vanes cause a higher pressure drop reduction, and a lower collection efficiency than without an inlet vane; Of all the inlet vanes, the effect of 2# on pressure drop reduction is in the second place and has no reduction in collection efficiency; 1# inlet vane has effect on pressure drop within a limited certain conditions but has the highest collection efficiency.

Collection efficiency of scattered light in single-ended optical fiber sensors

Optical fibers allow a variety of spectroscopic sensing methods to be implemented in a single-ended backscattering geometry. Taking multimode fibers with surface-enhanced Raman scattering active tips as a model system, it is shown that the remote single-ended collection geometry can be relatively inefficient in comparison to the performance of the underlying sensor structure. Therefore the performance of the single-ended geometry has been compared to the analogous sensor structure on a nonguiding silica glass substrate. While part of the reduction in collection efficiency can be attributed to mismatches between the numerical aperture of the collection optics and that of the fiber, this study suggests that there can be an additional loss due to a mismatch between the confocal area of the collection optics and the area of the fiber core. This effect is most significant for high numerical aperture objectives. However, the collection efficiency is somewhat higher than would be expected from a simple area ratio analysis. This can be attributed to the graded-index fiber used in the model system and the relaxation of confocal requirements in the longitudinal direction.

Ion-recombination correction for different ionization chambers in high dose rate flattening-filter-free photon beams

Recently, there has been an increased interest in flattening-filter-free (FFF) linear accelerators. Removal of the filter results in available dose rates up to 24 Gy min−1 (for nominal energy 10 MV in depth of maximum dose, a source–surface distance of 100 cm and a field size of 10×10 cm2). To guarantee accurate relative and reference dosimetry for the FFF beams, we investigated the charge collection efficiency of multiple air-vented and one liquid ionization chamber for dose rates up to 31.9 Gy min−1. For flattened beams, the ion-collection efficiency of all air-vented ionization chambers (except for the PinPoint chamber) was above 0.995. By removing the flattening filter, we found a reduction in collection efficiency of approximately 0.5–0.9% for a 10 MV beam. For FFF beams, the Markus chamber showed the largest collection efficiency of 0.994. The observed collection efficiencies were dependent on dose per pulse, but independent of the pulse repetition frequency. Using the liquid ionization chamber, the ion-collection efficiency for flattened beams was above 0.990 for all dose rates. However, this chamber showed a low collection efficiency of 0.940 for the FFF 10 MV beam at a dose rate of 31.9 Gy min−1. All investigated air-vented ionization chambers can be reliably used for relative dosimetry of FFF beams. The order of correction for reference dosimetry is given in the manuscript. Due to their increased saturation in high dose rate FFF beams, liquid ionization chambers appear to be unsuitable for dosimetry within these contexts.

Modeling and Understanding of External Latchup in CMOS Technologies—Part II: Minority Carrier Collection Efficiency

The n-wells of the parasitic p-n-p-n devices found in a CMOS layout will collect excess minority carriers from the chip substrate, potentially triggering latchup. This paper presents a model for the minority carrier collection efficiency of a given substrate current injector and collector pair; the model captures the effects of spacing, supply voltage, temperature, and current level. The model further describes the quantitative reduction in collection efficiency obtained by using guard rings. A good fit of the model to measurement results is observed in four different CMOS technologies.

Fabrication of adhesive coated swabs for improved swipe-based particle collection efficiency

Improving particle collection efficiency for swipe-based sampling systems can provide a better chance of detection when screening for trace explosives or narcotics particles. A technique was developed to improve the particle collection efficiency of commercially-available collection swabs used for field sampling of trace contraband materials. A silicone adhesive was added to Teflon-coated fiberglass swabs to aid in collecting trace levels of contamination from surfaces. Since the swabs are typically used for ion mobility spectrometry (IMS) analysis, it is important for them to produce no chemical background when heated. Results show that the adhesive swabs had a higher particle collection efficiency compared to the untreated swabs by a factor of 12, without negatively interfering with the IMS analysis. It was also found that the adhesive swabs could be reused 10 times without significant reduction in collection efficiency. While it is possible that the adhesive swabs may not be suitable for all surface types due to loss of adhesive material after multiple uses, the benefits of higher particle collection efficiency are extremely promising.

Entangled photons on demand: Erasing which-path information with sidebands

The biexciton cascade in a quantum dot can be used to generate entangled-photon pairs rapidly and deterministically (on demand). However, due to a large fine-structure splitting between intermediate exciton energy levels, which-path information encoded in the frequencies of emitted photon pairs leads to a small degree of entanglement. Here we show that this information can be efficiently erased by modulating the exciton and biexciton energy levels, giving rise to additional decay paths through sidebands. The resulting degree of entanglement is substantial and can be made maximal through spectral filtering, with only a nominal reduction in collection efficiency.

Permeability optimization and performance evaluation of hot aerosol filters made using foam incorporated alumina suspension

Porous ceramic samples were prepared from aqueous foam incorporated alumina suspension for application as hot aerosol filtering membrane. The procedure for establishment of membrane features required to maintain a desired flow condition was theoretically described and experimental work was designed to prepare ceramic membranes to meet the predicted criteria. Two best membranes, thus prepared, were selected for permeability tests up to 700 °C and their total and fractional collection efficiencies were experimentally evaluated. Reasonably good performance was achieved at room temperature, while at 700 °C, increased permeability was obtained with significant reduction in collection efficiency, which was explained by a combination of thermal expansion of the structure and changes in the gas properties.

Collection of biological and non-biological particles by new and used filters made from glass and electrostatically charged synthetic fibers

Synthetic filters made from fibers carrying electrostatic charges and fiberglass filters that do not carry electrostatic charges are both utilized commonly in heating, ventilating, and air-conditioning (HVAC) systems. The pressure drop and efficiency of a bank of fiberglass filters and a bank of electrostatically charged synthetic filters were measured repeatedly for 13 weeks in operating HVAC systems at a hospital. Additionally, the efficiency with which new and used fiberglass and synthetic filters collected culturable biological particles was measured in a test apparatus. Pressure drop measurements adjusted to equivalent flows indicated that the synthetic filters operated with a pressure drop less than half that of the fiberglass filters throughout the test. When measured using total ambient particles, synthetic filter efficiency decreased during the test period for all particle diameters. For particles 0.7-1.0 mum in diameter, efficiency decreased from 92% to 44%. It is hypothesized that this reduction in collection efficiency may be due to charge shielding. Efficiency did not change significantly for the fiberglass filters during the test period. However, when measured using culturable biological particles in the ambient air, efficiency was essentially the same for new filters and filters used for 13 weeks in the hospital for both the synthetic and fiberglass filters. It is hypothesized that the lack of efficiency reduction for culturable particles may be due to their having higher charge than non-biological particles, allowing them to overcome the effects of charge shielding. The type of particles requiring capture may be an important consideration when comparing the relative performance of electrostatically charged synthetic and fiberglass filters. Electrostatically charged synthetic filters with high initial efficiency can frequently replace traditional fiberglass filters with lower efficiency in HVAC systems because properly designed synthetic filters offer less resistance to air flow. Although the efficiency of charged synthetic filters at collecting non-biological particles declined substantially with use, the efficiency of these filters at collecting biological particles remained steady. These findings suggest that the merits of electrostatically charged synthetic HVAC filters relative to fiberglass filters may be more pronounced if collection of biological particles is of primary concern.

Influence of sebum and stratum corneum hydration on pesticide/herbicide collection efficiencies of the human hand.

The adhesion of house dust particles and chemical residues to the hands after contact with a variety of surfaces can yield significant exposures to children. Chemicals present on the surface or absorbed into house dust particles may adhere to the hands and subsequently are available for ingestion or absorption through the skin under normal physiological conditions. Contact of a hand with a surface occurs primarily through a thin layer of sebum and sweat on the skin surface. The study presented here examined the effect of the composition of the sebum and sweat layer on the adhesion of a mixture of pesticides and a herbicide to a hand after contact with a house-dust-laden surface. Collection efficiencies on the hand for atrazine and malathion were correlated with sebum levels on the palm of an individual hand. The increase in sebum values measured in this study caused a 13 percent and 8 percent reduction in collection efficiency, respectively, for atrazine and malathion applied to house-dust-laden surfaces. Diazinon and chlorpyrifos collection efficiencies were correlated with skin hydration levels measured on the palm of the individual's hand. The increased skin hydration measured in this study caused a 7 percent and 5 percent reduction in collection efficiency, respectively, for diazinon and chlorpyrifos.

A collector design study for GaAs/Ge/GaAs double heterojunction bipolar transistors

We analyze the effect of the conduction band offset in the collector heterojunction in NpN GaAs/Ge/GaAs double heterojunction bipolar transistors (DHBT). Despite excellent diode characteristics in both the emitter-base and base-collector diodes, the GaAs/Ge/GaAs DHBTs exhibit relatively low common-emitter dc current gains and a lack of collector current saturation with increasing collector-emitter bias. Simulations indicate that this is at least in part attributable to a reduction in collection efficiency caused by the large collector-base conduction band offset (0.26 eV) between the Ge base and the GaAs collector. A modified collector design, which incorporates higher doping in the region of the GaAs conduction band spike, is proposed to decrease the width of the barrier to electrons. Simulations predict that the collection efficiency will be greatly improved with the incorporation of a modified collector.

Cyclone pressure drop and efficiency with and without an inlet vane

Cyclone pressure drop decreases when dust concentration in the gas increases, when an inlet vane is installed. In this work, experimental data have been obtained for two different configurations (with and without inlet vane) in order to study these effects; these data have been compared with results published by other authors. Empirical correlations have been obtained to predict pressure drop as a function of dust load for these operating conditions. Finally, the influence of an inlet vane on cyclone collection efficiency has been studied; for large particles, the efficiency is not affected, but with smaller particle diameters, the inlet vane causes a slight reduction in collection efficiency.