Drift Field Research Articles

The XeBRA platform for liquid xenon time projection chamber development

XeBRA is a flexible cryogenic platform designed to perform research and development for liquid xenon detectors searching for rare events. Its extra-large outer cryostat makes it possible to install a wide variety of detector designs. We present the system, including its cryogenic, gas handling, data acquisition and slow control subsystems. Two dual phase time projection chambers with sensitive masses at the 1 kg scale have so far been operated in XeBRA. Using data from these, we determine the field-dependence of the electron drift velocity in liquid xenon. We also measure the relative charge and light yields for 41.5 keV energy deposits from 83mKr with electric drift fields between 50 V/cm and 677 V/cm.

Comparison between Drift Test Bench and Other Techniques in Spray Drift Evaluation of an Eight-Rotor Unmanned Aerial Spraying System: The Influence of Meteorological Parameters and Nozzle Types

In the past decade, an unmanned aerial spraying system (UASS) was applied more and more widely for low-volume aerial pesticides spraying operations in China. However, UASS have a higher drift risk due to more fine droplets sprayed with a higher working height and a faster driving speed than ground sprayers. Study on UASS spray drift is a new hot spot within the field of pesticide application technology. The field test bench was originally designed and applied for the measurement of the spray drift potential of ground sprayers. No methodology using the test bench for UASS drift evaluation was reported. Based on our previous study, field drift measurements of an eight-rotor UASS were conducted using three techniques (test bench, ground petri dish, and airborne collection frame) in this study, and the effects of meteorological parameters and nozzle types were investigated, to explore the applicability and the feasibility of the test bench used in UASS field drift evaluation. The test bench is proven promising for direct drift determination of UASS and the described methodology enabled classification of different UASS configurations. Higher wind speeds and finer droplets produced higher drift values. The faster the wind speed and the lower the humidity, the more the spray drift. The test bench can reduce the site requirements and improve the efficiency of the field drift test.

Coordinated drift of receptive fields in Hebbian/anti-Hebbian network models during noisy representation learning.

Recent experiments have revealed that neural population codes in many brain areas continuously change even when animals have fully learned and stably perform their tasks. This representational 'drift' naturally leads to questions about its causes, dynamics and functions. Here we explore the hypothesis that neural representations optimize a representational objective with a degenerate solution space, and noisy synaptic updates drive the network to explore this (near-)optimal space causing representational drift. We illustrate this idea and explore its consequences in simple, biologically plausible Hebbian/anti-Hebbian network models of representation learning. We find that the drifting receptive fields of individual neurons can be characterized by a coordinated random walk, with effective diffusion constants depending on various parameters such as learning rate, noise amplitude and input statistics. Despite such drift, the representational similarity of population codes is stable over time. Our model recapitulates experimental observations in the hippocampus and posterior parietal cortex and makes testable predictions that can be probed in future experiments.

Эффекты памяти и нелинейная электропроводность легированного перовскитоподобного ферритов лантана-стронция La-=SUB=-0.5-=/SUB=-Sr-=SUB=-0.5-=/SUB=-Fe-=SUB=-0.75-=/SUB=-Al-=SUB=-0.2-=/SUB=-Ni-=SUB=-0.05-=/SUB=-O-=SUB=-3-delta-=/SUB=-

Analysis of the existence of memory phenomena in model heterostructures based on doped ferrite La0.5Sr0.5Fe0.75Al0.2Ni0.05O3-δ with a perovskite structure has been carried out. It was demonstrated that one 5-10 μm thick ferrite layer sandwiched between Pt and Ni electrodes exhibits an analog memristor behavior. Under positive polarity, this heterostructure shows a smooth increase in electrical conductivity, with an opposite effect under negative polarity. Such phenomena are presumably associated with changing local concentrations of oxygen vacancies due to their drift in the electric field. Since lanthanum-strontium ferrites are sufficiently tolerant with respect to oxygen non-stoichiometry variations, no dendrite growth due to reductive decomposition is observed. The current vs. voltage dependencies display a strong nonlinearity resulting the Poole-Frenkel effect, namely, a decrease in the activation energy of electron holes trapped on oxygen vacancies. In addition to the Poole-Frenkel effect, pre-exponential factor of the conductivity vs. temperature dependence also increases under electric field, indicating an increase in the effective electron-hole mobility.

Memory effects and nonlinear electrical conductivity of doped perovskite-like lanthanum-strontium ferrite, La-=SUB=-0.5-=/SUB=-Sr-=SUB=-0.5-=/SUB=-Fe-=SUB=-0.75-=/SUB=-Al-=SUB=-0.2-=/SUB=-Ni-=SUB=-0.05-=/SUB=-O-=SUB=-3-delta-=/SUB=-

Analysis of the existence of memory phenomena in model heterostructures based on doped ferrite La0.5Sr0.5Fe0.75Al0.2Ni0.05O3-delta with a perovskite structure has been carried out. It was demonstrated that one 5-10 μm thick ferrite layer sandwiched between Pt and Ni electrodes exhibits an analog memristor behavior. Under positive polarity, this heterostructure shows a smooth increase in electrical conductivity, with an opposite effect under negative polarity. Such phenomena are presumably associated with changing local concentrations of oxygen vacancies due to their drift in the electric field. Since lanthanum-strontium ferrites are sufficiently tolerant with respect to oxygen non-stoichiometry variations, no dendrite growth due to reductive decomposition is observed. The current vs. voltage dependencies display a strong nonlinearity resulting from the Poole--Frenkel effect, namely, a decrease in the activation energy of electron holes trapped on oxygen vacancies. In addition to the Poole--Frenkel effect, pre-exponential factor of the conductivity vs. temperature dependence also increases under electric field, indicating an increase in the effective electron-hole mobility. Keywords: perovskite, lanthanum-strontium ferrites, memory effects, nonlinear electronic transport, memristors.

INVESTIGATION OF THE STRESS STATE OF MINE WORKINGS USING METHODS OF DEFORMABLE SOLID MECHANICS

The assessment of the reliability of a mining and technological scheme, taking into account the stress state of mine workings, depends on a combination of mining and geological, technical and technological factors. The article demonstrates the creation of a model of a rock mass and a scheme for calculating the stress state based on modern methods of mechanics of a deformable solid body.The object of study is a single mine working of great length, passed through the rock parallel to the strike of the coal seam (field drift) and located in the zone of influence of the support pressure. Due to the fact that the field drift is laid in the soil of the formation, which is a layered stratum in the zone of influence of clearing operations, the predominant load is the bearing pressure on the formation. The areas of application of the methods of complex potentials of integral equations and their combinations in solving applied problems are determined. The data of mine (field) measurements and observations, laboratory experiments and their generalizations are taken into account both when setting tasks and assigning boundary conditions, and when checking the results obtained. The mixed problem of the theory of elasticity about the contact stress on half-strips with varying along the longitudinal axis was solved; moving away from the ends, deformative properties, when these half-strips are clamped with friction between the layered half-planes.

Mathematical Model of Metal–Oxide Memristor Resistive Switching based on Full Physical Model of Heat and Mass Transfer of Oxygen Vacancies and Ions

Herein, a 1D mathematical model of memristor resistive switching that includes a full physical model of steady‐state heat and mass transfer is developed. The model considers ions and vacancies generation, recombination, and drift in an electric field in the memristor structure with dominant charge transport mechanism of electron tunnel hopping through vacancies. The distributions of vacancy concentration depending on the applied voltage and the given temperature of the memristor are found by numerical simulation. A good agreement is obtained between the part of the simulated current–voltage characteristics and the experimental one. There is no noticeable temperature gradient in a forming‐free nonfilament memristor. Therefore, the calculation of the vacancy concentration and the current–voltage characteristics in a forming‐free memristor with constant temperature over the film is appropriate. It is shown that the ion‐vacancy recombination can be neglected at temperatures over 600 K. In that case, the equation for ions, as well as the recombination term in the equation for vacancies can be neglected. The developed model at the same time consider all the processes occurring in the oxide layer and allow to reduce the computational complexity without significant loss of accuracy. The proposed model can be used to model large memristor arrays.

Validation of a drift-corrected 3D MR temperature imaging sequence for breast MR-guided focused ultrasound treatments

Real-time temperature monitoring is critical to the success of thermally ablative therapies. This work validates a 3D thermometry sequence with k-space field drift correction designed for use in magnetic resonance-guided focused ultrasound treatments for breast cancer. Fiberoptic probes were embedded in tissue-mimicking phantoms, and temperature change measurements from the probes were compared with the magnetic resonance temperature imaging measurements following heating with focused ultrasound. Precision and accuracy of measurements were also evaluated in free-breathing healthy volunteers (N = 3) under a non-heating condition.MR temperature measurements agreed closely with those of fiberoptic probes, with a 95% confidence interval of measurement difference from −2.0 °C to 1.4 °C. Field drift-corrected measurements in vivo had a precision of 1.1 ± 0.7 °C and were accurate within 1.3 ± 0.9 °C across the three volunteers. The field drift correction method improved precision and accuracy by an average of 46 and 42%, respectively, when compared to the uncorrected data. This temperature imaging sequence can provide accurate measurements of temperature change in aqueous tissues in the breast and support the use of this sequence in clinical investigations of focused ultrasound treatments for breast cancer.

Statistics of Stochastic Differential Equations on Manifolds and Stratified Spaces

Statistics for stochastic differential equations (SDEs) attempts to use SDEs as statistical models for real-world phenomena. This involves an understanding of qualitative properties of this class of stochastic processes which includes Brownian motion as well as estimation of parameters in the SDE or a nonparametric estimation of drift and diffusivity fields from obser- vations. Observations can be in continuous time, in high frequency discrete time considering the limit of small inter-observation times or in discrete time with constant inter-obseration times. Application areas of SDEs where state spaces are naturally viewed as manifolds or stratified spaces include multi- variate stochastic volatility models, stochastic evolution of shapes (e.g. of biological cells), time-varying image deformations for video analysis and phy- logenetic trees.

Sub‐second Lifetime of Photocarriers in Hybrid Lead Halide Perovskite

AbstractRecently lead halide perovskite based solar cells have rapidly advanced and their power conversion efficiency (PCE) increased to 25.7%. The progress has been attributed to the super‐long carriers’ lifetime (τ) and long diffusion length (LD) of the photocarriers, however it has been a challenge to precisely characterize and understand the super‐long τ and LD of photocarriers. Here, a MAPbI3 single crystal exhibits four different τ which increase with LD extending from nm scale to mm scale. The prior two lifetimes estimated by transient photoluminescence (TPL) spectra are in the range of ns which comes from the recombination of photocarriers in the tens of nm thick surface layer. In contrast, the third lifetime estimated by transient open‐circuit voltage is hundreds of µs, which is a result of the excess photocarriers diffusing hundreds of µm to electrodes. Finally, the fourth lifetime estimated from the transient photoconductance is as long as sub‐second since the low‐density photocarriers under an electric field drift across the mm‐scale high‐quality single crystal. This study not only clarifies the physical mechanisms of four different lifetimes of photocarriers but also facilitates the design of novel electronics with the halide perovskite semiconductors.

Analytical model of free charge transfer in charge-coupled devices

A one-dimensional analytical model of charge transfer in charge-coupled devices, which describes the spatial–temporal behavior of the charge carrier density in a potential well, is presented. The general solution of this model considers the transfer dynamics in terms of the electric drift field, i.e., self-induced drift and fringing-field drift, and yields an analytical solution for the total number of charge carriers. A comparison of the transfer efficiency for various electric drift fields is presented. The modulation transfer function in dependence on the transfer efficiency is analyzed, aiming especially at time-delay integration (TDI) applications. Finally, the results of this model are concluded and discussed in detail.

Simultaneous Cross‐Energy Ion Response and Wave Generation After the Impact of an Interplanetary Shock

AbstractInterplanetary (IP) shocks have substantial impact on particles and electromagnetic fields when arriving at the Earth's magnetosphere. In this study, we have examined the dynamics of cross‐energy ions and plasma waves observed by Van Allen Probe B near the equator at the noon sector inside the geosynchronous orbit after the impact of an IP shock on 27 February 2014. We found that the Ultra‐Low Frequency (ULF) and electromagnetic ion cyclotron (EMIC) waves are induced, and the differential fluxes of protons of various energies have different responses after the IP shock arrival. The perpendicular flux increased dramatically for low‐energy ions (10–100 eV) due to the electric field drift and betatron acceleration. These adiabatic processes also accounted for the evident proton flux decrease at 30–80 keV energies and increase at energies higher than 100 keV, caused by the positive or negative gradient in phase space density before the IP shock arrival. The short‐lived ULF waves triggered by the IP shock also interacted with the ∼100 keV protons, resulting in the stripes in their pitch angle distribution. The anisotropic distribution of >50 keV protons excited EMIC waves after the shock arrival. This study provides a comprehensive picture of the IP shock effects on the ions of different energies and plasma waves inside the geosynchronous orbit, which shed new lights on the cross‐energy responses of ions and plasma waves in the inner magnetosphere to solar wind discontinuities.

Characterization of a low-pressure Micro-Megas-like gaseous detector with low energy x-ray sources

Within the family of the Micro Strip Gas Detectors (MSGD), the intrinsic characteristics of the bulk Micro-Megas (MM) device represent the most promising features for the construction of a new instrument to be operated as a TPC gas chamber in a low-pressure regime. In this study, we present the main properties of a low-pressure bulk MM detector in which the amplification gap was slightly increased to improve the gas gain. Two configurations have been deeply studied: the first one with a gap of 128μm and a second one with a 192μm gap, both filled and operated with a gas mixture (Ar-CO2) at pressures below 100 mbar. The dependence of the gain and the energy resolution on the amplification field, gas pressure and drift field have been evaluated. The reliability of the measured performance, combined with the simple and robust structure of the detector even with an increased length of amplification gap, make it an attractive choice for applications where the track length of low energy particles is detected by using a low-pressure filling gas.

Numerical Simulation and Forecasting Model of Snow Drift Hazard in Yanchong Expressway with Embankment Form

To reasonably predict the snow drift hazard of expressway embankment in alpine mountainous area, in this paper, the computational fluid dynamics (CFD) numerical simulation method is used to analyze the distribution law of flow field of snow drift, the regression orthogonal design method is used to establish the prediction model of snow drift hazard in the expressway with the embankment form. Results show that different factors have different effects on snow drift hazard, the influence of embankment slope is the largest, followed by the coupling term of embankment slope and wind speed, the wind speed, the coupling term of embankment height and embankment slope, the coupling term of the mountain relative height and embankment slope, and the embankment height, while the influence of the distance between embankment and mountain-embankment slope coupling is the smallest. Numerical simulation and field observation have confirmed that the combined action of the terrain and embankment of Yanchong expressway Chicheng branch line leads to great changes in wind speed, resulting in uneven distribution of snow. A large amount of snow can be accumulated at the foot of the leeward slope of the mountain and the windward slope of the embankment, and there is less snow on the embankment pavement. By comparing the snow drift prediction model and CFD numerical simulation results, the error of the prediction model established in this paper is only 8.67%, which has high applicability. The research of this paper can provide a theoretical reference for the prediction and prevention of snow drift hazard on expressway embankment in alpine mountainous area.

Two-dimensional particle simulation of the boundary between a hot pair plasma and magnetized electrons and protons: Out-of-plane magnetic field

By means of a particle-in-cell (PIC) simulation, we study the interaction between a uniform magnetized ambient electron–proton plasma at rest and an unmagnetized pair plasma, which we inject at one simulation boundary with a mildly relativistic mean speed and temperature. The magnetic field points out of the simulation plane. The injected pair plasma expels the magnetic field and piles it up at its front. It traps ambient electrons and drags them across the protons. An electric field grows, which accelerates protons into the pair cloud's expansion direction. This electromagnetic pulse separates the pair cloud from the ambient plasma. Electrons and positrons, which drift in the pulse's nonuniform field, trigger an instability that disrupts the current sheet ahead of the pulse. The wave vector of the growing perturbation is orthogonal to the magnetic field direction and magnetic tension cannot stabilize it. The electromagnetic pulse becomes permeable for pair plasma, which forms new electromagnetic pulses ahead of the initial one. A transition layer develops with a thickness of a few proton skin depths, in which protons and positrons are accelerated by strong electromagnetic fields. Protons form dense clumps surrounded by a strong magnetic field. The thickness of the transition layer grows less rapidly than we would expect from the typical speeds of the pair plasma particles and the latter transfer momentum to protons; hence, the transition layer acts as a discontinuity, separating the pair plasma from the ambient plasma. Such a discontinuity is an important building block for astrophysical pair plasma jets.

Development of a Persistent Current Mode 9.39 T (400 MHz) LTS/Bi-2223 NMR Magnet With a Bi-2223 Superconducting Joint

We developed and operated a persistent current (PC) mode 9.39 T (400 MHz for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR) LTS/Bi-2223 NMR magnet using a Bi-2223 insert coil with a superconducting joint. Firstly, we developed a basic joining procedure to achieve the superconducting joint for the high-strength Bi-2223 tape used for the insert coil. We applied this procedure to the coil. Secondly, a stand-alone PC mode operation test for the coil at 4.2 K was performed. No apparent field decay was observed owing to the superconducting joint. Finally, we installed the coil inside the LTS outer coil's bore to form a PC mode LTS/Bi-2223 NMR magnet system. We successfully demonstrated a 9.39 T PC mode operation of the magnet though the current of the insert coil was limited to 5 A. The field drift rate was as low as 0.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ppm h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The joint resistance was estimated to be < 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> Ω at 4.2 K and 0.26 T. To our best knowledge, this is the first demonstration of a Bi-2223 superconducting joint that realized a PC mode LTS/Bi-2223 NMR magnet. This is an important step towards full-scale PC mode Bi-2223 magnets, including a 30.5 T (1.3 GHz) LTS/HTS NMR magnet.

Resonant alpha particle loss in stellarators

Particle resonances in stellarators can produce islands in the space of passing particle orbits without the presence of an unstable Alfvén mode, provided the period of the resonance matches the period of the equilibrium magnetic field. In this case, the equilibrium itself plays the role of a mode amplitude, and the islands appear on surfaces where the orbital helicity matches the field period. At low energy, these surfaces are given by the field line helicity, but at higher energy, cross field drift causes them to move. The resonances are also felt by trapped particles bouncing back and forth on surfaces with matching helicity. The periodic variation of B along these orbits produces local wells, giving loss due to drift while trapped in a well. Stellarator designs that have equilibrium-induced resonance islands exhibit anomalous alpha particle loss and are unsuitable for reactors.

СВОЙСТВА ИОННЫХ ПОТОКОВ, СФОРМИРОВАННЫХ БЕССЕТОЧНЫМ ДВУХЭЛЕКТРОДНЫМ ИОННЫМ ЗАТВОРОМ ИОН-ДРЕЙФОВОГО СПЕКТРОМЕТРА ПРИ АТМОСФЕРНОМ ДАВЛЕНИИ. I. НЕПРЕРЫВНЫЙ ИОННЫЙ ПОТОК

The properties of the ion flow have been experimentally determined depending on the parameters of a gridless two-electrode ion shutter and the conditions of ion transport in the drift tube. The transverse structure of the ion flow in the plane of the collector is investigated using a collector consisting of concentric rings. The resulting ion current distributions have a radial structure that varies depending on experimental conditions. Theoretical estimates are given to take into account the degree of influence of the space charge on the transverse dimensions of the ion beam in the drift field. The agreement of experimental and theoretical results allows one to conclude that the observed phenomena are caused by a space charge.

A Study on Affordable Homestead Implements for Stress Reduction on Body Parts amongst Farm Workers of Khammam District, India

The rural populations consisting of marginal and poor farmers are dependent on labourers for all farm related activities like sowing / planting of paddy, harvesting of agricultural and horticultural produce and application of pesticides which can be very costly. These labourers also face a lot of problems in sowing / planting of paddy as it has to be done by bending down continuously or during application of pesticides to cotton fields drift can be major health concern and harvesting different produce like bhendi due to its thorny spikes and capsaicin content of chilies. In view of this, KVK, Wyra, Khammam has assessed cost effective homestead implements and is relentlessly trying to popularize them. These included use of protective clothing during application of pesticides, rolling stem applicator for controlling sucking pest in cotton, knitted gloves for bhendi plucking and chilli finger guard for its plucking. These simple and cost-effective farm implements helped farm women in drudgery reduction, ergonomic stress on various body parts, improved work efficiency, decreased labour cost and body allergies. Protective clothing reduced itching, irritation, skin allergies, burning, vomiting, headache and faintness over a month’s time, rolling stem applicator was ecofriendly and decreased the amount of chemicals, knitted gloves for bhendi plucking reduced the bruising and repeated damage to fingers during harvesting and chilli finger guard. The reduction in stress on body parts automatically improved the work efficiency among farm workers.

Sheath formation around a dielectric droplet in a He atmospheric pressure plasma

Interactions at the interface between atmospheric pressure plasmas and liquids are being investigated to address applications ranging from nanoparticle synthesis to decontamination and fertilizer production. Many of these applications involve activation of droplets wherein the droplet is fully immersed in the plasma and synergistically interacts with the plasma. To better understand these interactions, two-dimensional modeling of radio frequency (RF) glow discharges at atmospheric pressure operated in He with an embedded lossy dielectric droplet (tens of microns in size) was performed. The properties of the sheath that forms around the droplet were investigated over the RF cycle. The electric field in the bulk plasma polarizes the dielectric droplet while the electron drift in the external electric field is shadowed by the droplet. The interaction between the bulk and sheath electric fields produces a maximum in E/N (electric field/gas number density) at the equator on one side of the droplet where the bulk and sheath fields are aligned in the same direction and a minimum along the opposite equator. Due to resistive heating, the electron temperature Te is maximum 45° above and below the equator of the droplet where power deposition per electron is the highest. Although the droplet is, on the average, negatively charged, the charge density on the droplet is positive on the poles and negative on the equator, as the electron motion is primarily due to diffusion at the poles but due to drift at the equator.