Screening Distance Research Articles

Core hole electron screening in InSb

The application of a potential model to the analysis of differences between the Auger parameters of InSb and the elemental materials yields a value 1.82±0.07Å for the core hole screening distance in InSb. It also yields a value of 0.22 ± 0.49 e for the charge transfer in InSb. Shifts in the Auger parameters of elements between their metallic states and in a compound semiconductor are interpreted using a novel method based on quantifying atomic core potential, as a quantum mechanical observable, in terms of its dependence on the valence charge and the number of atomic core holes. The core hole screening distance is ∼30% larger than half the interatomic distance between the nearest neighbors and, by the equivalent cores model, is expected to be the screening radius of Sn and Te impurities in InSb.

String breaking and running coupling of [formula omitted] in a rotating media from holography

Through gravity/gauge duality, the string breaking and running coupling constant of heavy quark-antiquark pair are investigated in the rotating background. For the meson decay mode QQ¯→Qq¯+Q¯q, we discuss the string breaking and running coupling in the parallel and transverse case. It is found that the parallel case has a more significant on string breaking and running coupling constant than the transverse case in the confined phase. The string-breaking distance and the maximum value of running coupling will decrease with the increase of angular velocity in the parallel case. Besides, we also investigate the running coupling and screening distance at finite angular velocity in the deconfined phase. It is found that the maximum values of the running coupling and screening distance are decreasing functions of angular velocity. The parallel case has a more significant influence on the running coupling and screening distance than the transverse case in the deconfined phase.

Review and Analysis of the Vibration Assessment Procedures Advocated by the Railway Association of Canada

In the absence of government regulations, the Federation of Canadian Municipalities (FCM) and the Railway Association of Canada (RAC) espouse criteria for the assessment of vibration due to passing trains. Given that many municipalities follow these guidelines when considering the permitting of residential development, the effectiveness of the RAC vibration assessment methods are worth investigating. These include a limit of 0.14 mm/s RMS on amplitudes and a 75 m screening distance for triggering a detailed study of the impacts of railway vibration on developments in proximity to tracks. This paper provides a review of the criteria for their reasonableness at avoiding unwanted and/or undesirable vibration conditions for residential developments. This is accomplished through reference to the generic vibration propagation curves within the latest US Federal Railway/Transit Administrations noise and vibration guidelines and alternative parametric equations for estimating vibration propagation.

3D Monte-Carlo model to study the transport of hot electrons in the context of inertial confinement fusion. Part II

We describe two numerical investigations performed using a 3D plasma Monte-Carlo code, developed to study hot-electron transport in the context of inertial confinement fusion. The code simulates the propagation of hot electrons in ionized targets, using appropriate scattering differential cross sections with free plasma electrons and ionized or partially ionized atoms. In this paper, we show that a target in the plasma state stops and diffuses electrons more effectively than a cold target (i.e., a target under standard conditions in which ionization is absent). This is related to the fact that in a plasma, the nuclear potential of plasma nuclei has a greater range than in the cold case, where the screening distance is determined by the electronic structure of atoms. However, in the ablation zone created by laser interaction, electrons undergo less severe scattering, counterbalancing the enhanced diffusion that occurs in the bulk. We also show that hard collisions, i.e., collisions with large polar scattering angle, play a primary role in electron beam diffusion and should not be neglected. An application of the plasma Monte-Carlo model to typical shock ignition implosions suggests that hot electrons will not give rise to any preheating concerns if their Maxwellian temperature is lower than 25–30 keV, although the presence of populations at higher temperatures must be suppressed. This result does not depend strongly on the initial angular divergence of the electron beam set in the simulations.

Three-quark potential at finite temperature and chemical potential* *Supported by the NSFC (12175100, 11975132), the Research Foundation of Education Bureau of Hunan Province, China (21B0402, 20C1594) and the Natural Science Foundation of Hunan Province of China (2022JJ40344)

Using gauge/gravity duality, we study the potential energy and the melting of triply heavy baryon at finite temperature and chemical potential in this paper. First, we calculate the three-quark potential and compare the results with quark-antiquark potential. With the increase of temperature and chemical potential, the potential energy will decrease at large distances. It is found that the three-quark potential will have an endpoint at high temperature and/or large chemical potential, which means triply heavy baryons will melt at enough high temperature and/or large chemical potential. We also discuss screening distance which can be extracted from the three-quark potential. At last, we draw the melting diagram of triply heavy baryons in the plane.

Characterization of thin films of Ga 2 Se 3 on Si fabricated using electron beam evaporation technique

Many studies have been conducted in the past on compound semiconductor and wide-gap semiconductor for their possible usage in place of oxide in metal-oxide-semiconductor structures for high-speed metal-oxide-semiconductor field-effect transistors application. The best candidates for this purpose, however, are compounds with stoichiometric vacant A 2 III B 3 VI type sites. A 2 III B 3 VI type compounds are wide-gap semiconductors with stoichiometric vacancies and low concentration of free and localized charged carriers. It has that gate insulators can be constructed from wide-gap semiconductor layers with thicknesses smaller than the Debye Screening distance. These new MS'S (metal-Wide bandgap semiconductor-semiconductor) with a good lattice match have less of interface states thus giving better stability to the structure. The idea was to use these MS'S structures for photovoltaic applications with insignificant number of interface states. During literature survey, it was also found that Ga2Se3 is the most prospective candidate for forming a heterostructure with Silicon because of its various properties. Structurally, perfect and homogeneous in thickness Ga2Se3 layers have already been formed in quasi-closed volume by the Hot Wall technique by B. I. Sysoev in the Voronezh Technological Institute, Russia. However, this technology is not cost-efficient for photovoltaic applications, although it has the advantage of better control of Ga and Se components. Over the last few years, many attempts have been made using many other techniques such as Sol-gel technique, vapour phase epitaxy, molecular beam epitaxy, etc. for preparing the thin film of GaSe. The current work is an attempt to prepare the Ga2Se3 film using the electron beam evaporation technique as it appeared to be much simpler. Film of thicknesses varying from 70 to 1000 Å were grown. The films have been studied for their morphology and properties for future use in photovoltaics and other device fabrication like IR detectors, etc. Various techniques were used to study the behavior of the films like XRD, SEM, and TEM.

Abnormal-Aware Multiperson Evaluation System with Improved Fuzzy Weighting

There exists a phenomenon that subjectivity highly lies in the daily evaluation process. Our research primarily concentrates on a multiperson evaluation system with anomaly detection to minimize the possible inaccuracy that subjective assessment brings. We choose the two-stage screening method, which consists of rough screening and score-weighted Kendall-τ distance to winnow out abnormal data, coupled with hypothesis testing to narrow global discrepancy. Then we use fuzzy synthetic evaluation method (FSE) to determine the significance of scores given by reviewers as well as their reliability, culminating in a more impartial weight for each reviewer in the final conclusion. The results demonstrate a clear and comprehensive ranking instead of unilateral scores, and we get to have an efficiency in filtering out abnormal data as well as a reasonably objective weight determination mechanism. We can sense that through our study, people will have a chance of modifying a multiperson evaluation system to attain both equity and a relatively superior competitive atmosphere. A preprint has previously been published (Ni, 2022).

Modeling particle-particle binary coagulation rate constants for spherical aerosol particles at high volume fractions using Langevin Dynamics simulations

Effect of volume-fraction and particle-particle hydrodynamic interactions on the coagulation rate of particles are investigated. Particle coagulation is modeled using Langevin Dynamics (LD) based trajectory simulations of N mono-sized spherical particles in a periodic domain. The extended Kirkwood-Risemann approach (J. Fluid Mechanics 855, 535 (2018)) is invoked to compute particle-particle hydrodynamic interactions whose effect is parameterized as a function of the momentum Knudsen number (Kn). The results are summarized as a model for coagulation rate constant (βij) that depends on the diffusive Knudsen number (KnD) used in prior work to parameterize coagulation in the dilute regime (Aerosol Sci. Tech. 45, 1499 (2011)), Kn and particle volume-fraction ηv. In the absence of hydrodynamic interactions, it is observed that the coagulation rate constant in the continuum limit for mass transfer (KnD→0) is significantly enhanced by a factor of ∼80 at ηv∼0.3 due to particle crowding. While considering hydrodynamic interactions for ηv≥0.05, we use a screening distance around each particle that scales inversely with ηv beyond which the contribution of farther neighbors is neglected owing to the rapid decay of hydrodynamic interactions with distance. We also present new LD calculations of βij and elucidate the dependence of the same on Kn1 and the particle radii ratio θr for the coagulation of two particles in the dilute limit ηv→0. It is observed that the reduction of βij becomes significant as Kn1→0: at the lowest momentum Knudsen number considered (Kn1=0.1): βij is reduced by a factor of ∼10 for equally sized particles (θr=0.5). At high KnD,Kn1, the particle size disparity is not significant, and it is seen that βij matches hard sphere predictions, indicating the insignificant contributions by hydrodynamic interactions. A series of animations of 2-particle simulations are presented as part of the Supplemental Information to illustrate the role of hydrodynamic interactions in particle coagulation. Computational results are summarized as regressions for convenient incorporation into particle/droplet growth sectional models.

Field Study of Vertical Screening Distance Criteria for Vapor Intrusion of Ethylene Dibromide

AbstractSeveral regulatory agencies recommend screening petroleum vapor intrusion (PVI) sites based on vertical screening distance between a petroleum hydrocarbon source in soil or groundwater and a building foundation. U.S. Environmental Protection Agency (U.S. EPA) indicate the risk of PVI is minimal at buildings that are separated by more than 6 feet (1.8 m) from a dissolved‐phase source and 15 feet (4.6 m) from a light nonaqueous phase liquid (LNAPL) source. This vertical screening distance method is not, however, recommended at sites with leaded gasoline sources containing ethylene dibromide (EDB) because of a lack of field data to document EDB attenuation in the vadose zone. To help address this gap, depth‐discrete soil‐gas samples were collected at a leaded gasoline release site in Sobieski, Minnesota (USA). The maximum concentration of EDB in groundwater (175 μg/L) at the site was high relative to those observed at other leaded gasoline release sites. Soil gas was analyzed for EDB using a modification of U.S. EPA Method TO‐14A that achieved analytical detection limits below the U.S. EPA Vapor Intrusion Screening Level (VISL) for EDB based on a 10−6 cancer risk (<0.16 μg/m3). Concentrations of EDB in soil gas above LNAPL reached as high as 960 μg/m3 and decreased below the VISL within a source‐separation distance of 7 feet. This result coupled with BioVapor model predictions of EDB concentrations indicate that vertical screening distances recommended by regulatory agencies at PVI sites are generally applicable for EDB over the range of anticipated source concentrations and soil types at most sites.

Evaluation of Vapor Intrusion Risk from Ethylene Dibromide Using the Vertical Screening Distance Approach

AbstractVapor intrusion (VI) occurs when volatile contaminants in the subsurface migrate through the vadose zone into overlying buildings. The 2015 U.S. EPA petroleum VI guidance recommends that additional investigation of the VI risk from gasoline hydrocarbons at the underground storage tank (UST) sites is not necessary where the vertical distance between a building and a vapor source exceeds a recommended vertical screening distance. However, due to the lack of soil‐gas data on the attenuation of ethylene dibromide (EDB), additional VI investigations to evaluate VI risk from EDB are recommended at UST sites with leaded gasoline releases containing EDB. We analyzed soil‐gas and groundwater concentrations of EDB from eight petroleum UST sites using a new analytical method with soil‐gas detection limit <0.16 μg/m3 EDB (VI screening level at the 10−6 risk level). The analysis included (1) assessing the frequency of EDB detections ≤0.16 μg/m3 at various vertical separation distances and (2) predicting vertical screening distances for EDB using the U.S. EPA PVIScreen model for different soil types in the vadose zone above dissolved‐phase and LNAPL sources. Ranges of estimated aerobic biodegradation rate constants for EDB, air exchange rates for residential buildings, and source vapor concentrations for other constituents were combined with conservative estimates of EDB source concentrations as model inputs. Concentrations of EDB in soil‐gas indicated that the U.S. EPA recommended vertical screening distances are protective of VI risk from EDB. Conversely, vertical screening distances predicted by modeling were >6 ft (1.8 m) for sites with sand and loam soil above dissolved phase sources and >15 ft (4.6 m) for sites with sand soil above LNAPL sources. This predicted dependence on the vapor source type and soil type in the vadose zone highlights the importance of soil characterization for VI screening at sites with EDB sources.

Electron Wing‐Like Structures Formed at a Negatively Charged Spacecraft Moving in a Magnetized Plasma

AbstractSpacecraft‐plasma interactions are studied with self‐consistent numerical simulations of magnetized plasmas, where electrons are strongly magnetized whereas ions are weakly magnetized. It is found that for a spacecraft in such a magnetized plasma corresponding to a low Earth orbit, electrons can be reflected from a negatively charged spacecraft and then guided by geomagnetic field lines. The reflected electrons can leave a sharp trail like wings if the spacecraft size is greater than an average electron gyroradius of the environment. Such an electron wing‐like structure is associated with propagating Langmuir waves. This results in nontrivial asymmetric electrostatic potentials close to the spacecraft and even farther than the Debye screening distance. The convective electric field also gives rise to a differential potential of the spacecraft with respect to the plasma, resulting in yet another asymmetry in the plasma dynamics and the potential distribution around the spacecraft. These asymmetries in the plasma dynamics can significantly influence in‐situ measurements of space plasma. The results show a good qualitative agreement with actual measurements by a satellite in the polar regions.

Vertical Screening Distance Criteria to Evaluate Vapor Intrusion Risk from 1,2‐Dichloroethane (1,2‐DCA)

AbstractVapor intrusion (VI) involves migration of volatile contaminants from subsurface through unsaturated soil into overlying buildings. In 2015, the US EPA recommended an approach for screening VI risks associated with gasoline releases from underground storage tank (UST) sites. Additional assessment of the VI risk from petroleum hydrocarbons was deemed unnecessary for buildings separated from vapor sources by more than recommended vertical screening distances. However, these vertical screening distances did not apply to potential VI risks associated with releases of former leaded gasoline containing 1,2‐dichloroethane (1,2‐DCA), because of a lack of empirical data on the attenuation of 1,2‐DCA in soil gas. This study empirically evaluated 144 paired measurements of 1,2‐DCA concentrations in soil gas and groundwater collected at 47 petroleum UST sites combined with BioVapor modeling. This included (1) assessing the frequency of 1,2‐DCA detections in soil gas below 10−6 risk‐based screening levels at different vertical separation distances and (2) comparing the US EPA recommended vertical screening distances with those predicted by BioVapor modeling. Vertical screening distances were predicted for different soil types using aerobic biodegradation rate constants estimated from the measured soil‐gas data combined with conservative estimates of source concentrations. The modeling indicates that the vertical screening distance of 6 feet (1.8 m) recommended for dissolved‐phase sources is applicable for 1,2‐DCA below certain threshold concentrations in groundwater, while 15 feet (4.6 m) recommended for light nonaqueous phase liquid (LNAPL) sources is applicable for sites with clay and loam soils in the vadose zone, but not sand, if 1,2‐DCA concentrations in groundwater exceed 150 μg/L. This dependence of the predicted vertical screening distances on soil type places added emphasis on proper soil characterization for VI screening at sites with 1,2‐DCA sources. The soil‐gas data suggests that a vertical screening distance of 15 feet (4.6 m) is necessary for both dissolved‐phase and LNAPL sources.

Heavy quarks in strongly coupled non-conformal plasmas with anisotropy

We analyze physical observables of heavy quarks in gravity models describing strongly coupled non-conformal plasmas with anisotropy via the gauge/gravity duality. The focus lies on the binding energy of static quark-antiquark ( qoverline{q} -)pairs, the maximum distance (screening distance) of a bound qoverline{q} -pair and the drag force on uniformly moving quarks in the hot plasma. In order to discover universal behavior in the observables, the computations are worked out in a two parameter deformation of pure gravity in AdS5 spacetime with a black brane which is assumed to be dual to a respective two parameter deformation of mathcal{N} = 4 supersymmetric Yang-Mills (SYM) theory at temperature T. The deformation is designed to break isotropy and conformal symmetry and is a solution to equations of motion of a gravity action.

Characteristics of ion-cyclotron surface waves in semi-bounded (r, q) distribution dusty plasmas

The influence of magnetic field strength, ion mass, and the non-thermal character on the dispersion properties of ion-cyclotron surface wave is investigated in a semi-bounded (r, q) distribution dusty plasma. In the limit of short wave number, the dispersion relation is derived by adopting the specular reflection boundary condition and the effective screening distance in (r, q) distribution dusty plasma. It is found that the stronger magnetic field strength suppresses the wave speed, but the heavier ions will enhance the wave propagation. To investigate the wave propagation in the non-Maxwellian plasma, the typical values of r and q are chosen and the dispersion relation is plotted to obtain the general character of wave propagation. The result would reduce to the case of Maxwellian plasma for r→0 and q→∞.

Progressive friction mobilization and enhanced Janssen's screening in confined granular rafts

Confined two-dimensional assemblies of floating particles, known as granular rafts, are prone to develop a highly nonlinear response under compression. Here we investigate the transition to the friction-dominated jammed state and map the gradual development of the internal stress profile with flexible pressure sensors distributed along the raft surface. Surprisingly, we observe that the surface stress screening builds up much more slowly than previously thought and that the typical screening distance later dramatically decreases. We explain this behavior in terms of progressive friction mobilization, where the full amplitude of the frictional forces is only reached after a macroscopic local displacement. At further stages of compression, rafts of large length-to-width aspect ratio experience much stronger screenings than the full mobilization limit described by the Janssen's model. We solve this paradox using a simple mathematical analysis and show that such enhanced screening can be attributed to a localized compaction front, essentially shielding the far field from compressive stresses.

Experimental analysis of the flow near the boundary of random porous media

The aim of this work is to experimentally examine flow over and near random porous media. Different porous materials were chosen to achieve porosity ranging from 0.95 to 0.99. In this study, we report the detailed velocity measurements of the flow over and near random porous material inside a rectangular duct using a planar particle image velocimetry (PIV) technique. By controlling the flow rate, two different Reynolds numbers were achieved. We determined the slip velocity at the interface between the porous media and free flow. Values of the slip velocity normalized either by the maximum flow velocity or by the shear rate at the interface and the screening distance K1/2 were found to depend on porosity. It was also shown that the depth of penetration inside the porous material was larger than the screening length using Brinkman’s prediction. Moreover, we examined a model for the laminar coupled flow over and inside porous media and analyzed the permeability of a random porous medium. This study provided detailed analysis of flow over and at the interface of various specific random porous media using the PIV technique. This analysis has the potential to serve as a first step toward using random porous media as a new passive technique to control the flow over smooth surfaces.

Screening of Primary School Children for Amblyopia and Amblyogenic Factors in Central Cairo, Egypt.

Objective To measure the prevalence of amblyopia and amblyogenic factors among primary school children and to evaluate distance visual acuity (VA) as a screening test to detect amblyopia and define its cutoff value. Subjects and Methods A cross-sectional study was conducted on primary school children in two schools in Central Cairo. Children underwent assessment of visual acuity using Landolt broken ring. Comprehensive ophthalmologic examination was performed for amblyopia suspects at the Ophthalmology Department of Ain Shams University Hospitals, including reassessment of best-corrected visual acuity (BCVA) using the same chart. Results A total of 352 children were examined. Reduced screening VA (amblyopia suspect) was detected in 47 subjects (13.35%) proved amblyopia after comprehensive examination was 1.98% (7 cases). Refractive errors (REs) were present in all suspected and proved amblyopia cases (100%) but was only present in 11.6% of nonamblyopic students (P < 0.05). The prevalence of hyperopia in the whole sample was 3.6%, and was 27.6% in subjects with RE. Thirty percent of hyperopic eyes were amblyopic. The prevalence of myopia was 9.3% of the whole sample and 70% of students with RE. Only 9% of myopic eyes were amblyopic. Mild to moderate amblyopia (VA better than 0.2log MAR) was 42.9%, while severe amblyopia represented 57.1%. Conclusion This study emphasizes the importance of school-based eye care system targeting the detection of amblyopia by application of a fast screening distance VA test with a cutoff value of high sensitivity at log MAR 0.539 (Snellen′s VA equivalent 6/18).

Vertical screening distances for total petroleum hydrocarbon for vapour intrusion risk assessment at petroleum underground storage tank sites

The US Environmental Protection Agency Office of Underground Storage Tanks (US EPA OUST) and Interstate Technology and Regulatory Council (ITRC) have recently published guidance indicating that buildings separated from light non-aqueous phase liquid (LNAPL) sources by more than 15 ft (4.6 m) are not a concern for vapour intrusion at petroleum underground storage tank (UST) sites. At this distance, there is a greater than 95% probability that soil gas concentrations for all key constituents of potential concern are below risk-based screening levels (RBSLs) between the LNAPL source and building foundation. Vertical screening distances for bulk Total Petroleum Hydrocarbon (TPH), common TPH fractions (C 5 –C 8 aliphatics, C 9 –C 12 aliphatics, and C 9 –C 10 aromatics), and indicator compounds ( n -hexane and naphthalene) are less certain, however, because of a general lack of empirical data and highly variable soil-gas RBSLs. This study addresses these gaps through a statistical analysis of hundreds of soil-gas samples collected above LNAPL sources at more than 30 petroleum UST release sites. Resulting vertical screening distances for the various TPH fractions range between 0 and 7 ft (2.1 m) depending primarily on soil-gas RBSLs, which vary by over 5 orders of magnitude. Vertical screening distances for naphthalene are generally &lt;3 ft (0.91 m). Vertical screening distances for n -hexane range from 12 (3.7) to 16 ft (4.9 m) and vary geographically. Vertical screening distances for total (bulk) TPH generally exceed 15 ft (4.6 m). Petroleum vapour intrusion risk assessments involving total (bulk) TPH are not recommended, however, because of uncertainties in quantifying soil-gas and indoor-air concentrations and defining RBSLs for fuel mixtures with variable source composition, toxicity, and fate and transport properties. Overall, the findings of this study validate the 15-ft screening distance recommended by ITRC and US EPA for application at petroleum UST sites with LNAPL sources.

Results of a primary care–based quality improvement project to optimize chart-based vision screening for preschool age children

To design chart-based vision screening for preschool-aged children. Our program consisted of educational sessions for providers as well as hands-on training for practice staff. We evaluated the intervention through pre- and post-intervention review of medical records. Completion of full vision screening (distance visual acuity in each eye plus stereovision beginning at 3years of age, as recommended at the time of the project) at well-child visits improved for 5-year-olds (45.0% to 58.2%; risk difference +13.2% [95% CI, 1.7-24.7]) and 4-year-olds (39.3% to 51.4%; risk difference +12.0% [95% CI, 0.7-23.4]) but declined somewhat among 3-year-olds (23.1% to 14.3%; risk difference, -8.8% [95% CI, -17.7 to 0.0]). Risk factors for not being fully screened included being 3years old (risk ratio of 4.1 compared to 5-year-olds) and being a patient of a small practice (risk ratio of 1.9 compared to large practices). This quality improvement project showed that screening for visual acuity and stereovision among preschool-aged children using chart-based techniques is difficult to accomplish and unlikely to be consistently successful, especially among 3-year-olds.

Role of the source to building lateral separation distance in petroleum vapor intrusion

The adoption of source to building separation distances to screen sites that need further field investigation is becoming a common practice for the evaluation of the vapor intrusion pathway at sites contaminated by petroleum hydrocarbons. Namely, for the source to building vertical distance, the screening criteria for petroleum vapor intrusion have been deeply investigated in the recent literature and fully addressed in the recent guidelines issued by ITRC and U.S.EPA. Conversely, due to the lack of field and modeling studies, the source to building lateral distance received relatively low attention. To address this issue, in this work we present a steady-state vapor intrusion analytical model incorporating a piecewise first-order aerobic biodegradation limited by oxygen availability that accounts for lateral source to building separation. The developed model can be used to evaluate the role and relevance of lateral vapor attenuation as well as to provide a site-specific assessment of the lateral screening distances needed to attenuate vapor concentrations to risk-based values. The simulation outcomes showed to be consistent with field data and 3-D numerical modeling results reported in previous studies and, for shallow sources, with the screening criteria recommended by U.S.EPA for the vertical separation distance. Indeed, although petroleum vapors can cover maximum lateral distances up to 25–30m, as highlighted by the comparison of model outputs with field evidences of vapor migration in the subsurface, simulation results by this new model indicated that, regardless of the source concentration and depth, 6m and 7m lateral distances are sufficient to attenuate petroleum vapors below risk-based values for groundwater and soil sources, respectively. However, for deep sources (>5m) and for low to moderate source concentrations (benzene concentrations lower than 5mg/L in groundwater and 0.5mg/kg in soil) the above criteria were found extremely conservative as the model results indicated that for such scenarios the lateral screening distance may be set equal to zero.