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A major obstacle hindering further development of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is the inherent recombination losses that occur both via bulk defects and charge extraction interfaces. Herein, we propose a generic Ag, Ge dual-gradient absorber architecture, involving a downshift of absorber VBM at the front contact and an upshift of absorber CBM at the back contact, to improve device performance. We experimentally show that the substitution of Cu by Ag allows for larger band bending at the p–n junction, and the substitution of Sn by Ge imposes an additional drift field within the quasi-neutral region. Additionally, the Ag and Ge ions diffusing into the bulk absorber passivate the deleterious CuZn and CuSn deep-level defects. In turn, accelerated charge extraction, transport and minimized recombination loss offered surprising gains in Voc and Jsc, and the dual-gradient device achieved a maximum efficiency of 12.26% with an improved Voc,deficit of 553 mV. This Ag, Ge graded-substitution approach offers an alternative absorber architecture to improve the Voc,deficit in future high-efficiency kesterite PV cells.

Motivated by the study of a Mean Field Game toy model called the “seminar problem”, we consider the Fokker–Planck equation in the small noise regime for a specific drift field. This gives us the opportunity to discuss the application to diffusion problem of the WKB approach “a la Maslov (Maslov and Fedoriuk, 1981)”, making it possible to solve directly the time dependent problem in an especially transparent way.

A systematic study is performed to measure ion backflow fraction with GEM-based detectors. The ion current along with detector gain is measured with various voltage configurations and with different gas proportions. The observed ion backflow fraction is found to be very sensitive toward the applied drift field and the effective gain of the detector. The charge transparency in the GEM also depends on the gas mixtures. Here our main goal is to optimize the detector for the minimum ion backflow current at an optimized detector gain. So the gain and ion backflow values are calculated for a single and a quadruple GEM setups. It is observed that the ion backflow is very much dependent on the configuration of drift field and the GEM voltage. The induction field has a minor effect on ion backflow value. With an increase in gain, the ion backflow fraction decreases proportionally. From the scanning over gas ratios, we also observed that with increasing quencher proportion the gain decreases and ion backflow value is quite high.

The PICOSEC Micromegas detector can time the arrival of Minimum Ionizing Particles with a sub-25 ps precision. A very good timing resolution in detecting single photons is also demonstrated in laser beams. The PICOSEC timing resolution is determined mainly by the drift field. The arrival time of the signal and the timing resolution vary with the size of the pulse amplitude. Detailed simulations based on GARFIELD++ reproduce the experimental PICOSEC timing characteristics. This agreement is exploited to identify the microscopic physical variables, which determine the observed timing properties. In these studies, several counter-intuitive observations are made for the behavior of such microscopic variables. In order to gain insight on the main physical mechanisms causing the observed behavior, a phenomenological model is constructed and presented. The model is based on a simple mechanism of "time-gain per interaction" and it employs a statistical description of the avalanche evolution. It describes quantitatively the dynamical and statistical properties of the microscopic quantities, which determine the PICOSEC timing characteristics, in excellent agreement with the simulations. In parallel, it offers phenomenological explanations for the behavior of these microscopic variables. The formulae expressing this model can be used as a tool for fast and reliable predictions, provided that the input parameter values (e.g. drift velocities) are known for the considered operating conditions., Comment: Corresponding author S. E. Tzamarias, 47 pages, 19 figures, 2 appendices, 8 tables

We present a comprehensive analysis of electronic recoil vs. nuclear recoil discrimination in liquid/gas xenon time projection chambers, using calibration data from the 2013 and 2014-16 runs of the Large Underground Xenon (LUX) experiment. We observe strong charge-to-light discrimination enhancement with increased event energy. For events with S1 = 120 detected photons, i.e. equivalent to a nuclear recoil energy of $\sim$100 keV, we observe an electronic recoil background acceptance of $, 29 pages, 33 figures; minor typos corrected, references updated

International audience; The monolithic CMOS pixel sensor for charged particle tracking has already become a mainstream technology in high energy particle physics (HEP) experiments. During the last decade, progressive improvements have been made for CMOS pixels to deal with the high-radiation and high-rate environments expected, for example, at the future High Luminosity LHC. One of the key ingredients of these improvements is to achieve a fully depleted sensitive layer, where the charge collection is guided by strong drift field lines. CMOS sensors incorporating such charge collection property, often referred to as DMAPS (Depleted Monolithic Active Pixel Sensor), have been recently demonstrated in several large-scale monolithic prototypes with integrated fast readout architectures. This contribution summarizes the recent progress made on the large-scale DMPAS development, focusing on two demonstrator chips designed in the LFoundry 150 nm and the TowerJazz 150 nm CMOS processes, namely LF-Monopix1 and TJ-Monopix1.

We present a methodology for generating built-in drift fields in large photodiodes. With the aid of TCAD we demonstrate how non-uniform doping profiles can be implemented in a standard CMOS process using a single additional mask and controlled using the implant conditions and mask geometry. We demonstrate that the resulting doping profile creates a built-in drift field and simulates the effect of the drift field on the charge transfer speed. We show that implementing a drift field can improve charge transfer characteristics of the photodiode.

On the basis of a 39-year record of satellite-based data, three basic types of large-scale structures of sea ice drift that are typical for the winter season have been distinguished. The types of atmospheric circulation that create the structure of sea ice drift fields have been revealed. The mechanism by which the drift field variations affect the interannual variations of the extent of sea ice in the Arctic Ocean has been described.

Estimating the sea ice drift field is of importance in both scientific study and activities in the polar ocean. Ice motion is being tracked at large scale (10 km and larger) on a daily basis; however, a higher resolution product is desirable for more reliable monitoring of rapid changes in sea ice. The use of wide-swath SAR has been extensively studied; yet, recent high-resolution X-band SAR sensors have not been tested enough. We examine the feasibility of KOMPSAT-5 and COSMO-SkyMed for retrieving sea ice motion by using the dataset of the MOSAiC expedition. The ice drift match-ups extracted from consecutive SAR image pairs and buoys for more than seven months in the central Arctic were used for a performance evaluation and validation. In addition to individual tests for KOMPSAT-5 and COSMO-SkyMed, a cross-sensor combination of two sensors was tested to overcome the drawback, a relatively long revisit time of high-resolution SAR. The experimental results show that higher accuracies are achievable from both single- and cross-sensor configurations of high-resolution X-band SARs compared to wide-swath C-band SARs, and that sub-daily monitoring is feasible from the cross-sensor approach.

For regional environmental studies it is important to know the location of the fast ice edge which affects the coastal processes in the Arctic. The aim of this study is to develop a new automated method for fast ice delineation from SAR imagery. The method is based on a fine resolution hybrid sea ice tracking algorithm utilizing advantages of feature tracking and cross-correlation approaches. The developed method consists of three main steps: drift field retrieval at sub-kilometer scale, selection of motionless features and edge delineation. The method was tested on a time series of C-band co-polarized (HH) ENVISAT ASAR and Sentinel-1 imagery in the Laptev and East Siberian Seas. The comparison of the retrieved edges with the operational ice charts produced by the Arctic and Antarctic Research Institute (Russia) showed a good agreement between the data sets with a mean distance between the edges of

Using sea ice information generated from Synthetic Aperture Radar (SAR) products can increase the safety and efficiency of ship operations in ice-infested waters. For the purpose of operational sea ice classification, the results need to be highly reliable. The combination of multiple SAR acquisitions can be used to estimate the reliability of sea ice classification and to overcome existing limitations. In this paper, we present a new approach for comparing sea ice classification results from pairs of independent TerraSAR-X acquisitions and additionally overlay it with information on sea ice movement. For this purpose, we combine our processors for estimating sea ice drift and classification. The sea ice drift field is used to compensate the ice movement between two SAR acquisitions and differentiate areas of homogeneous and inhomogeneous ice zones. The processing chain is developed for operational usage in near real-time.

This paper is concerned with the time-optimal coverage control problem for multiple unicycles in a drift field. Regarding the optimal time for each vehicle to reach an arbitrary point in the given region as a metric, a novel cost function is defined to evaluate the performance of the coverage network. Then, the time-optimal Voronoi partition is developed by using the optimal control theory and Lloyd's algorithms. On this basis, a distributed coverage control law is proposed to deploy the unicycles to the optimal positions. The stability of this coverage system is further analyzed. Finally, numerical simulations are provided to illustrate the effectiveness of the proposed approaches.

Industry-leading multi-crystalline PERC processing has been applied to kerfless wafers made directly from molten silicon using Direct Wafer™ technology, avoiding the need for ingot production and sawing of bricks into wafers, thus providing significant cost saving potential. Efficiency averaged 18,7% and a champion efficiency of 19,1% was achieved on wafers with uniform doping using only mass production tools and processes. An additional efficiency gain was obtained using non-uniform doping, with a higher dopant concentration on the backside of the wafers that we call “drift field wafers”. Simulations predict an efficiency increase of up to 0,9% in efficiency. In the first test, we demonstrated increased efficiency by 0,3% compared to uniformly doped wafers, leading to an average of 19,0%, with single cells > 19,3%. Further refinement of the wafer doping properties and co-optimization with mainstream cell process technologies will help accelerate the silicon PV learning curve and drive down costs for the prevailing multi-crystalline market.

This article aims to optimize the drift field for the CEPC TPC to meet requirements from the CEPC baseline design. Simulations and analytic analysis have been done to give a preliminary result. Besides, a new TPC prototype with laser calibration system is being developed for further optimization by experiment and its progress will be introduced briefly.

A quadruple GEM detector has been assembled in a standalone configuration and operated using Ar and CO$_2$ gas mixtures in proportions of 70:30 and 90:10. Detailed performance study of the detector has been made by using $^{106}$Ru-Rh $\beta$-source and X-ray spectrum of $^{55}$Fe source. Results of these measurements are presented in terms of gain, efficiency, energy and time resolutions and also compared with our earlier triple GEM results. The energy resolution has been found to be somewhat worse compared with that of the triple-GEM detector. Effect of drift field on electron transparency and time resolution has been studied in detail., Comment: 8 pages, 13 figures

In this paper we address the regularity issue of weak solution for the following linear drift–diffusion system with pressure $$\begin{aligned} \partial _t u + b\cdot \nabla u -\Delta u + \nabla p = 0,\quad \mathrm {div}\,u=0,\quad u|_{t=0}(x)=u_0(x), \end{aligned}$$ where $$x\in \mathbb {R}^n$$ and b is a given divergence-free vector field. Under some assumptions of the drift field b in the critical sense, and for the initial data $$u_0\in (L^2(\mathbb {R}^n))^n$$ , we prove that there exists a weak solution u(t) to this system such that u(t) for any time $$t>0$$ is $$\alpha $$ -Holder continuous with $$\alpha \in (0,1)$$ . The proof of the Holder regularity result utilizes a maximum-principle type method to improve the regularity of weak solution step by step.

We calibrate a two-phase xenon detector at 0.27 keV in the charge channel and at 2.8 keV in both the light and charge channels using a $^{37}$Ar source that is directly released into the detector. We map the light and charge yields as a function of electric drift field. For the 2.8 keV peak, we calculate the Thomas-Imel box parameter for recombination and determine its dependence on drift field. For the same peak, we achieve an energy resolution, $E_{\sigma}/E_{mean}$, between 9.8% and 10.8% for 0.1 kV/cm to 2 kV/cm electric drift fields., Comment: 12 pages, 7 figures

A novel on-chip, customer-design spiral biasing adaptor (SBA) has been developed. A single SBA is used for biasing a Si drift detector (SDD) and SDD array. The use of an SBA reduces the biasing current. This paper shows the calculation of the geometry of an SBA and an SDD to get the best drift field in the SDD and SDD array. Prototype SBAs have been fabricated to verify the concept. Electrical measurements on these SBAs are in agreement with the expectations. The new SDD array with an SBA can be used for X-ray detection and in nuclear physics experiments.

An investigation was made on the energy resolution of an active-target type gas counter operating in low-pressure He/CO2 mixed gas for studies of nuclear reactions such as (?, n) and (?, p) using radioactive nuclear beams (RNBs). The dependencies of effective gain and energy resolution on different parameters such as drift field, induction field and GEM voltages were studied. The energy resolution with adequate electric field configuretaion was found to be 3% in ?. DOI: http://dx.doi.org/10.3329/jbas.v37i2.17553 Journal of Bangladesh Academy of Sciences, Vol. 37, No. 2, 139-144, 2013

We consider the optimal synthesis of the Zermelo–Markov–Dubins problem, that is, the problem of steering a vehicle with the kinematics of the Isaacs–Dubins car in minimum time in the presence of a drift field. By using standard optimal control tools, we characterize the family of control sequences that are sufficient for complete controllability and necessary for optimality for the special case of a constant field. Furthermore, we present a semianalytic scheme for the characterization of an optimal synthesis of the minimum-time problem. Finally, we establish a direct correspondence between the optimal syntheses of the Markov–Dubins and the Zermelo–Markov–Dubins problems by means of a discontinuous mapping.

Copyright ©2012 by E. Bakolas and P. Tsiotras. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

We study quantitative asymptotics of planar random walks that are spatially non-homogeneous but whose mean drifts have some regularity. Specifically, we study the first exit time $\tau_\alpha$ from a wedge with apex at the origin and interior half-angle $\alpha$ by a non-homogeneous random walk on the square lattice with mean drift at $x$ of magnitude $O(1/|x|)$ as $|x| \to \infty$. This is the critical regime for the asymptotic behaviour: under mild conditions, a previous result of the authors (see arXiv:0910.1772) stated that $\tau_\alpha < \infty$ a.s. for any $\alpha$ (while for a stronger drift field $\tau_\alpha$ is infinite with positive probability). Here we study the more difficult problem of the existence and non-existence of moments $E[\tau_\alpha^s]$, $s>0$. Assuming (in common with much of the literature) a uniform bound on the walk's increments, we show that for $\alpha < \pi/2$ there exists $s_0 \in (0,\infty)$ such that $E[\tau_\alpha^s]$ is finite for $s < s_0$ but infinite for $s > s_0$; under specific assumptions on the drift field we show that we can attain $E[\tau_\alpha^s] = \infty$ for any $s > 1/2$. We show that for $\alpha \leq \pi$ there is a phase transition between drifts of magnitude $O(1/|x|)$ (the critical regime) and $o(1/|x|)$ (the subcritical regime). In the subcritical regime we obtain a non-homogeneous random walk analogue of a theorem for Brownian motion due to Spitzer, under considerably weaker conditions than those previously given (including work by Varopoulos) that assumed zero drift., Comment: 35 pages, 2 figures; most of the material in v1 (which had a different title) appears in revised form in v2 or the companion paper arXiv:0910.1772

With the help of Maxwell, Ansys and Garfield, a simulation of the electric field and the deviation of electron drift in the drift volume of a GEM-TPC prototype has been accomplished under the following conditions: Field Cages with one-side and double-side strips, with and without a guard ring. The advantage and necessity of a Field Cage with mirror strips and a guard ring were foreseen. According to the simulation results, TU-TPC was modified and tested; a larger effective area and better resolution were achieved.

We investigated the characteristics of a developed gas electron multiplier (GEM) detector by measuring the 5.9 keV X-ray of the Fe-55 isotope. The energy resolution linearly decreased with increasing GEM voltage. As the drift voltage increased up to 150 V, the energy resolution continuously decreased. The saturation value of the energy resolution was achieved at a drift voltage of over 150 V. In the case of the induction voltage (V[ind.]), when V[ind.] is smaller than 500 V and larger than 800 V, the eective gain increases. In our GEM detector, the energy resolution is stable at a drift field of above 1.35 kV/cm (400 V), a GEM voltage of above 480 V, and an induction voltage of around 600 V.

The transport of ions through multiple drift regions is modeled in order to develop an equation that is useful for an understanding of the resolving power of an overtone mobility spectrometry (OMS) technique. It is found that resolving power is influenced by a number of experimental variables, including those that define ion mobility spectrometry (IMS) resolving power: drift field (E), drift region length (L), and buffer gas temperature (T). However, unlike IMS, the resolving power of OMS is also influenced by the number of drift regions (n), harmonic frequency value (m), and the phase number (ϕ) of the applied drift field. The OMS resolving power dependence upon the new OMS variables (n, m, and ϕ) scales differently than the square root dependence of the E, L, and T variables in IMS. The results provide insight about optimal instrumental design and operation.

A novel ion mobility spectrometry instrument incorporating a cyclotron geometry drift tube is presented. The drift tube consists of eight regions, four curved drift tubes and four ion funnels. Packets of ions are propagated around the drift tube by changing the drift field at a frequency that is resonant with the ion's drift time through each region. The approach trims each packet of ions as it leaves and enters each new region. An electrostatic gate allows ions to be kept in the drift tube for numerous cycles, increasing the ability to resolve specified ions. We demonstrate the approach by isolating the [M + 2H](2+) or [M + 3H](3+) charge state of substance P as well as individual trisaccharide isomers from a mixture of melezitose and raffinose. Resolving powers in excess of 300 are obtainable with this approach.

We consider the steady state concentration of some diffusing substance, subject to a uniform drift field, past a circular obstacle. We obtain some exact representations of the concentration profile of the substance exterior to the obstacle. These representations are particularly useful for studying the solution in ranges of space where the concentration is very small (the “shadow” regions). We assume then that the drift dominates diffusion and obtain various asymptotic expansions in the shadow regions.

Floating strip Micromegas are intended for ion tracking in medical imaging applications. In the following chapter, the application of floating strip Micromegas as tracking detectors in high-intensity, low and medium energy ion beams, is presented.