Collection efficiency of a monitor parallel plate ionization chamber for pencil beam scanning proton therapy

The collection efficiency of monitor parallel plate ionization chambers is the main uncertainty in the beam control of pencil beam scanning systems.Existing calculation methods for collection efficiency in photon or passive scattering proton systems have not considered the characteristics of non-uniform charge density in pencil beam scanning systems.In this study,Boag’s theory was applied to a proton pencil beam scanning system.The transverse distribution of charge density in the ionization chamber was considered to be a Gaussian function and an analytical solution was derived to calculate collection efficiency in the beam spot area.This calculation method is called the integral method and it was used to investigate the effects of beam parameters on collection efficiency.It was determined that collection efficiency is positively correlated with applied voltage,beam size,and beam energy,but negatively correlated with beam current intensity.Additionally,it was confirmed that collection efficiency is improved when the air filling the monitor parallel plate ionization chamber is replaced with nitrogen.

Collecting aerosol in airflow with a magnetically stabilized fluidized bed

A magnetically stabilized fluidized bed (MSB) is a highly efficient filter that takes the advantage of both fluidized beds and fixed beds. This paper presents the research to collect aerosol in airflow with a MSB. The filtering model of MSB is established with its parameters including magnetic Geld intensity, gas superficial velocity, average grain-size, and bed height on the collection efficiency of MSB. The model is verified by experiments.

Effects of Different Rainwater Diversion Patterns on Rainwater Collection Efficiency and Water Utilization Efficiency in Cornfield

Four rainwater diversion patterns including undisturbed soil ditch （T1）, slope compaction （T2）, asbestos sheet covering after compac- tion （T3） and plastic film covering after compaction （T4） were set in cornfield in arid areas of Yunnan Province, and effects of various patterns on rainwater collection efficiency, water utilization efficiency and corn yield were studied. The results shows that rainwater collection efficiency, water utilization efficiency and corn yield of the four diversion patterns presented the same trend, namely T4 〉T3 〉T2 〉T1. Overall, rainwater collection efficiencies of the four diversion patterns ranged from 41.7% to 58.7% ; compared with T1, water utilization efficiencies of T2 ,T3 and T4 increased by 34.9%, 53.5% and 92.5%, and maize yields of them improved by 1 767.0, 1 981.5 and 2 385.0 kg/hm2.

Efficiency of collective myosin Ⅱ motors studied with an elastic coupling power-stroke ratchet model

We proposed a modified ratchet model including power-stroke and elastic coupling to study the efficiency of collective non-processive motors such as myosin Ⅱ in muscle. Our theoretical results are in good agreement with the experimental data. Our study not only reveals that the maximum efficiency depends on elasticity and is independent of transition rates but also indicates that the parameters fitted to fast muscle are different from those fitted to a slow one. The latter may imply that the structure of the fast muscle is different from that of the slow one. The main reason that our model succeeds is that velocity in this model is an independent variable.

Optimal Design of Aperture Illuminations for Microwave Power Transmission with Annular Collection Areas

This work presents an optimal design method of antenna aperture illumination for microwave power transmission with an annular collection area.The objective is to maximize the ratio of the power radiated on the annular collection area to the total transmitted power.By formulating the aperture amplitude distribution through a summation of a special set of series,the optimal design problem can be reduced to finding the maximum ratio of two real quadratic forms.Based on the theory of matrices,the solution to the formulated optimization problem is to determine the largest characteristic value and its associated characteristic vector.To meet security requirements,the peak radiation levels outside the receiving area are considered to be extra constraints.A hybrid grey wolf optimizer and Nelder–Mead simplex method is developed to deal with this constrained optimization problem.In order to demonstrate the effectiveness of the proposed method,numerical experiments on continuous apertures are conducted;then,discrete arrays of isotropic elements are employed to validate the correctness of the optimized results.Finally,patch arrays are adopted to further verify the validity of the proposed method.

Enhancing betavoltaic nuclear battery performance with 3D P^(+)PNN^(+)multi-groove structure via carrier evolution

Betavoltaic nuclear batteries offer a promising alternative energy source that harnesses the power of beta particles emitted by radioisotopes.To satisfy the power demands of microelectromechanical systems(MEMS),3D structures have been proposed as a potential solution.Accordingly,this paper introduces a novel 3D^(63)Ni–SiC-based P^(+)PNN^(+)structure with a multi-groove design,avoiding the need for PN junctions on the inner surface,and thus reducing leakage current and power losses.Monte Carlo simulations were performed considering the fully coupled physical model to extend the electron–hole pair generation rate to a 3D structure,enabling the efficient design and development of betavoltaic batteries with complex 3D structures.As a result,the proposed model produces the significantly higher maximum output power density of 19.74μW/cm^(2) and corresponding short-circuit current,open-circuit voltage,and conversion efficiency of 8.57μA/cm^(2),2.45 V,and4.58%,respectively,compared with conventional planar batteries.From analysis of the carrier transport and collection characteristics using the COMSOL Multiphysics code,we provide deep insights regarding power increase,and elucidate the discrepancies between the ideal and simulated performances of betavoltaic batteries.Our work offers a promising approach for the design and optimization of high-output betavoltaic nuclear batteries with a unique 3D design,and serves as a valuable reference for future device fabrication.

Bipolar charged aerosol agglomeration and collection by a two-zone agglomerator

In older to collect fine particles more efficiently, a new-type electrostatic agglomerator with two zones was developed. The distinguishing feature of this electrostatic agglomerator is that the particles are bipolarly charged and coagulated in the same alternating electric field simultaneously. The silica flour with 2 fun mass median diameter and the smoke from burning wood powder were used as test aerosol. The comparison experimental results have shown that when the mean electric field is 4 kV/cm the collection efficiency of the new electrostatic agglomerator was 98.2% for silica flour and 67.4% for wood powder smoke, Under the same experimental condition. the collection efficiency of the electrostatic agglomerator with three zones was 97.4% for collecting silica flour and the collection efficiency of the electrostatic precipitator was 56.3% for wood powder smoke.

Photoelectrochemical evaluation of SILAR-deposited nanoporous BiVO4 photoanodes for solar-driven water splitting

We report a photoelectrochemical investigation of BiVO4 photoanodes prepared by successive ionic layer adsorption and reaction(SILAR),a facile method that yields uniform nanoporous films.After characterization of the phase,morphology,composition,and optical properties of the prepared films,the efficiencies of charge separation(ηsep)and water oxidation(ηox)in solar water splitting cells employing these photoanodes were estimated following a previously reported procedure.Unexpected wavelength and illumination direction dependencies were discovered in the derived efficiencies,casting doubt on the validity of the analysis.An alternative approach using a diffusion–reaction model that explicitly considers the efficiency of electron collection resolved the discrepancies and explained the illumination direction dependence of the photocurrent.Electron diffusion lengths(Ln)of 0.45μm and 0.55μm were derived for pristine and cobalt phosphate(Co-Pi)modified BiVO4,respectively,which are much shorter than the film thickness of^2.1μm.The Co-Pi treatment also increasedηoxfrom 0.86 to^1,which is the main reason for the overall performance enhancement caused by adding Co-Pi.These findings suggest that there is little scope for improving the performance of SILAR-deposited BiVO4 photoanodes by further catalyzing water oxidation,but enhanced performance is achievable if electron transport can be improved.

NUMERICAL SIMULATION OF THREE DIMENSIONAL GAS-PARTICLE FLOW IN A SPIRAL CYCLONE

The three-dimension gas-particle flow in a spiral cyclone is simulated nu- merically in this paper. The gas flow field was obtained by solving the three-dimension Navier-Stokes equations with Reynolds Stress Model （RSM）. It is shown that there are two regions in the cyclone, the steadily tangential flow in the spiral channel and the combined vortex flow in the centre. Numerical results for particles trajectories show that the initial position of the particle at the inlet plane substantially affects its trajectory in the cyclone. The particle collection efficiency curves at different inlet velocities were obtained and the effects of inlet flow rate On the performance of the spiral cyclone were presented. Numerical results also show that the increase of flow rate leads to the increase of particles collection efficiency, but the pressure drop increases sharply.

Assessment of CH4 and C 2 surface emissions from Polesgo’s landfill(Ouagadougou, Burkina Faso) based on static chamber method

Methane (CH4) and carbon dioxide (C02) surface emissions from Polesgo's landfill (Ouagadougou, Burkina Faso) were measured using the static chamber technique in 2017 and 2018. The Polesgo's landfill was composed of four zones: Phase I, II, Phase III, and SP. The surface of Phase I was fully covered and its conditions are better for surface emission measurements. As results concerning the Phase I zone, the geospatial means flux rates of CH4 (657 mg m-2 h l in 2017 and 1210 mg m 2 h_, in 2018, respectively) are measured higher than the tolerable value reported in literature. The emitted CH4 or C 02 have permitted to locate higher surface emissions which are related to the cover state. The calculated gas collection efficiency (27.4% in 2017 and 23.0% in 2018) is low compared to those reported for landfills integrating landfill gas (LFG) extraction system. The carbon footprint calculations (24,966 tC02-eq 2017 and 40,025 tC02-eq in 2018, respectively) shown that Polesgo's landfill is a significant source of greenhouse gases (GHG) and its important potential for organic recovery can contribute to reduce the carbon footprint.

Influence of sub-bandgap illumination on space charge distribution in CdZnTe detector

The space charge accumulation in CdZnTe crystals seriously affects the performance of high-flux pulse detectors.The influence of sub-bandgap illumination on the space charge distribution and device performance in CdZnTe crystals were studied theoretically by Silvaco TCAD software simulation.The sub-bandgap illumination with a wavelength of 890 nm and intensity of 8×10−8 W/cm2 were used in the simulation to explore the space charge distribution and internal electric field distribution in CdZnTe crystals.The simulation results show that the deep level occupation faction is manipulated by the sub-bandgap illumination,thus space charge concentration can be reduced under the bias voltage of 500 V.A flat electric field distribution is obtained,which significantly improves the charge collection efficiency of the CdZnTe detector.Meanwhile,premised on the high resistivity of CdZnTe crystal,the space charge concentration in the crystal can be further reduced with the wavelength of 850 nm and intensity of 1×10−7 W/cm2 illumination.The electric field distribution is flatter and the carrier collection efficiency of the device can be improved more effectively.

Recombination-induced voltage-dependent photocurrent collection loss in CdTe thin film solar cell

Recently, the efficiency of CdTe thin film solar cell has been improved by using new type of window layer Mg_(x)Zn_(1-x)O(MZO). However, it is hard to achieve such a high efficiency as expected. In this report a comparative study is carried out between the MZO/CdTe and CdS/CdTe solar cells to investigate the factors affecting the device performance of MZO/CdTe solar cells. The efficiency loss quantified by voltage-dependent photocurrent collection efficiency(ηC(V′)) is 3.89% for MZO/CdTe and 1.53% for CdS/CdTe solar cells. The higher efficiency loss for the MZO/CdTe solar cell is induced by more severe carrier recombination at the MZO/CdTe p-n junction interface and in CdTe bulk region than that for the CdS/CdTe solar cell. Activation energy(Ea) of the reverse saturation current of the MZO/CdTe and CdS/CdTe solar cells are found to be 1.08 e V and 1.36 e V, respectively. These values indicate that for the CdS/CdTe solar cell the carrier recombination is dominated by bulk Shockley-Read-Hall(SRH) recombination and for the MZO/CdTe solar cell the carrier recombination is dominated by the p-n junction interface recombination. It is found that the tunneling-enhanced interface recombination is also involved in carrier recombination in the MZO/CdTe solar cell. This work demonstrates the poor device performance of the MZO/CdTe solar cell is induced by more severe interface and bulk recombination than that of the CdS/CdTe solar cell.

Development of Evaluation Method of Daylighting Duct System Considering Inner Light Flux

Currently, daylighting ducts system is widely used as a daylighting device. Generally, daylighting duct system efficiently takes light from outside during the day, and conveys daylight to required location through light duct manufactured by high reflectance mirror. Daylighting duct system can convey daylight to underground space that has no windows opening to external space. Daylighting system is composed of light collection part, light guide part and light emission part. Efficiency of daylighting system is depending on type of each part used in the system. However, it is very difficult to estimate exact light flow in the system considering type of the parts. Authors performed measurement experiments to make clear the light flow with real-size model and miniature model of daylighting duct system. We discussed effect of type of the parts on efficiency of daylighting duct system.

Modeling Submicron Particles Collection in Laminar Forced Convection Gas Flow by a Rectangular Venturi Scrubber

Venturi scrubbers are usually used for large particles cleaning in turbulent gaseous flow. In this work, submicron particles scrubbing in laminar forced convection dusty air flow in a rectangular venturi scrubber have been numerically simulated. Hydrodynamics effects and scrubbing process are investigated in detail. Results are presented as flow velocity, axial pressure, streamlines pattern, particles and droplets mass fraction profile, and collect efficiency. They show that venturi scrubbers can be efficient for submicron particles scrubbing. In fact, a better collect efficiency is obtained at high particles-droplets residence time, high ratio droplets concentration/particles concentration, low venturi diameter ratioand low Reynolds numbers. There is a critical Reynolds number value for which the collect efficiency becomes very low and tends to be constant.

Collection efficiency in a three-dimensional randomly arranged dual-layer granular bed filter

The dual-layer granular bed filter packed with randomly arranged granules was simulated to study the effects of bed depth of the lower layer of fine granules and the inlet gas velocity on the collection mechanism.The computational results show that the collection efficiency is much better from this granular bed than a single-layer granular bed,especially for particle diameters of 1-10μm.The inlet gas velocity has less effect on the grade collection efficiency of the dual-layer granular bed than of the single-layer granular bed.The dual-layer granular bed provides a high collection efficiency and low pressure drop.The relationship between the grade collection efficiency and the Stokes number(St)based on the inlet gas velocity is obtained.If St is below a threshold,the grade collection efficiency remains stable;if St is in value above threshold,the grade collection efficiency increases linearly with lg(St).As the bed depth of the lower layer of fine granules increases,the threshold for St shifts forward.

Collection efficiency and charge transfer optimization for a 4-T pixel with multi n-type implants

In order to increase collection efficiency and eliminate image lag, multi n-type implants were introduced into the process of a pinned-photodiode. For the purpose of improving the collection efficiency, multi n-type implants with different implant energies were proposed, which expanded the vertical collection region. To reduce the image lag, a horizontal gradient doping concentration eliminating the potential barrier was also formed by multi n-type implants. The simulation result shows that the collection efficiency can be improved by about 10% in the long wavelength range and the density of the residual charge is reduced from 2.59 × 10^9 to 2.62 × 10^7 cm^-3.

Experimental study on filtration performance of the moving bed granular filter with axial flow

The filtration performance of the moving bed granular filter with axial flow (MBGF-AF) is investigated through a large cold experiment. The effect of different operation parameters on the filtration performance (collection efficiency, pressure drop) of the axial-flow moving bed filter is investigated in combination with the dust deposition effect and the mechanism of trapping dust by the capturing particles. The results show that the collection efficiency of MBGF-AF is enhanced by decreasing the superficial gas velocity, increasing the inlet dust concentration properly, or decreasing the moving velocity of the capturing particles. A model covering the above operation parameters is established to calculate the collection efficiency of the moving bed granular filter. It is used in a wide range of operating parameters for the MBGFs.

Influence of wire spacing and plate spacing on electrostatic precipitation of nanoparticles: An approach involving electrostatic shielding and diffusion charging

Electrostatic precipitation is a process widely used as gas cleaning device,to removal particles from gas flows.However,in a conventional and well-sized precipitator,the collection efficiency decreases for ultrafine particles,making it difficult to employ this equipment for controlling nanoparticle pollution.This paper investigates the influence of plate spacing(4 and 6.5 cm)and wire spacing(4,6,and 12 cm)on the electric current and nanoparticle collection efficiency,considering the effect of diffusion charging and electrostatic shielding.Two laboratory-scale dry wire-plate electrostatic precipitators with different plate spacings were tested for the collection of nanoparticles(6.15–241.4 nm)at three air velocities(1.9,2.9,and 3.9 cm/s).The results demonstrated the effectiveness of the equipment in removing nanoparticles(99.9%)under the highest electric fields.Higher values of the wire spacing led to increases in the current and the collection efficiency.This was associated with reduced electrostatic shielding,which is more evident in smaller ducts with a higher density of field lines.It is expected that the findings should improve knowledge on electrostatic precipitation of nanoparticles,enabling optimization of collection efficiency by considering the effects of geometric parameters.

ANALYSIS ON CYCLONE COLLECTION EFFICIENCIES AT HIGH TEMPERATURES

In order to predict the influence of operating temperature on cyclone performance, an experimental investigation on particle separation was conducted in a 300 mm diameter, tangential volute-inlet and reverse flow cy-clone separator with air heated up to 973 K. The test powder silica has a mean mass diameter of 10 microns and the inlet velocity ranges from 12 m.s-1 to 36 m-s-1. Both the overall efficiency and fractionai efficiency of the cyclone were measured as a function of the inlet velocity and operating temperature. It is shown that at the same inlet velocity both the overall efficiency and fractionai efficiency decrease with an increase of temperature. An analysis of our own data and published results has shown that the fractionai efficiency of a cyclone is a defmite function of such dimensioniess numbers as Stokes number, Reynolds number, Froude number and dimensioniess cyclone inlet area and dimensioniess outlet diameter. A nondimensionai experimental correlation of the cyclone performance, including the influence of the temperature, was obtained on the basis of our own previous work. The prediction of the influence of temperature on separation efficiencies is in fairly good agreement with experimental results.