Publications

This letter presents an adaptive coverage control strategy for multi-agent systems with obstacle avoidance in the presence of actuator faults and time-varying uncertainties. The strategy is based on a leader-follower approach. Assuming that the motion of the leader is given, one distributes the followers within the leader’s obstacle-free sensing range so that collisions with obstacles can be avoided. An optimized distribution is achieved through the Centroidal Voronoi Tessellation (CVT) and a function approximation technique based immersion and invariance (FATII) coverage controller is constructed to realize the CVT. The stability of the FATII coverage controller is established and its validity is tested by simulations.

Lead-free double perovskites hold promise for stable and environmentally benign solar cells; however, they exhibit low efficiencies because defects act as charge recombination centers. Identifying trap-assisted loss mechanisms and developing defect passivation strategies constitute an urgent goal. Applying unsupervised machine learning to density functional theory and nonadiabatic molecular dynamics, we demonstrate that negatively charged Br vacancies in Cs2AgBiBr6 create deep hole traps through charge redistribution between the adjacent Ag and Bi atoms. Vacancy electrons are first accepted by Bi and then shared with Ag, as the trap transforms from shallow to deep. Subsequent charge losses are promoted by Ag and Bi motions perpendicular to rather than along the Ag–Bi axis, as can be expected. In contrast, charge recombination in pristine Cs2AgBiBr6 correlates most with displacements of Cs atoms and Br–Br–Br angles. Doping with In to replace Ag at the vacancy maintains the electrons at Bi and keeps the trap shallow.

The paper presents experimental studies of the radiation-protective properties of a material based on a modified titanium hydride with respect to gamma and neutron radiation of point radioisotope sources in barrier and continuous protection geometries. The calculation models of the problem of solving the radiation transport equation for the Monte Carlo method and a comparative assessment of experimental and calculation results are given. The assessment of the amplitude distribution of gamma radiation in the thickness of the material of protection showed a significant reduction in the power of the equivalent dose of gamma radiation in the energy range of 180–250 keV, which is due to the Compton scattering effect. The relaxation length of the dose of γ radiation in 137Сs by the protective material was 4.80 ± 0.18 cm. The relaxation length of the flux of fast neutrons from the Pu-α-Be source was 6.20 ± 0.18 cm. Comparative analysis of the experimental and calculation data of the protective properties of the material based on modified titanium hydride in relation to radioisotope sources has shown high convergence of the results obtained and the adequacy of the application of the calculation model of the task for the MCNP program used.

Developing robust electrocatalysts and advanced devices is important for electrochemical carbon dioxide (CO2) reduction toward the generation of valuable chemicals. We present herein a carbon-confined indium oxide electrocatalyst for stable and efficient CO2 reduction. The reductive corrosion of oxidative indium to the metallic state during electrolysis could be prevented by carbon protection, and the applied carbon layer also optimizes the reaction intermediate adsorption, which enables both high selectivity and activity for CO2 reduction. In a liquid-phase flow cell, the formate selectivity exceeds 90 % in a wide potential window from −0.8 V to −1.3 V vs. RHE. The continuous production of ca. 0.12 M pure formic acid solution is further demonstrated at a current density of 30 mA cm−2 in a solid-state electrolyte mediated reactor. This work provides significant concepts in the parallel development of electrocatalysts and devices for carbon-neutral technologies.

Graphitic carbon nitride (GCN) has attracted significant attention due to its excellent performance in photocatalytic applications. Non-metal doping of GCN has been widely used to improve the efficiency of the material as a photocatalyst. Using a combination of time-domain density functional theory with nonadiabatic molecular dynamics, we study the charge carrier dynamics in oxygen and boron doped GCN systems. The reported simulations provide a detailed time-domain mechanistic description of the charge separation and recombination processes that are of fundamental importance while evaluating the photovoltaic and photocatalytic performance of the material. The appearance of smaller energy gaps due to the presence of dopant states improves the visible light absorption range of the doped systems. At the same time, the nonradiative lifetimes are shortened in the doped systems as compared to the pristine GCN. In the case of boron doped at a carbon (B–C–GCN), the charge recombination time is very long as compared to the other two doped systems owing to the smaller electron–phonon coupling strength between the valence band maximum and the trap state. The results suggest B–C–GCN as the most suitable candidate among three doped systems studied in this work for applications in photocatalysis. This work sheds light into the influence of dopants on quantum dynamics processes that govern GCN performance and, thus, guides toward building high-performance devices in photocatalysis.

Superconductor Science and Technology Supercond. Sci. Technol. 35 (2022) 035003 (15pp) https://doi.org/10.1088/1361-6668/ac455e Current-induced self-organisation of mixed superconducting states Xaver S Brems1,2, Sebastian Mühlbauer1,∗, Wilmer Y Córdoba-Camacho3, Arkady A Shanenko3,4, Alexei Vagov4,5, José Albino Aguiar3 and Robert Cubitt2,∗ 1 Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, 85748, Germany 2 Institut Laue-Langevin, Grenoble, 38042, France 3 Departamento de Física, Universidade Federal de Pernambuco, Recife, PE, 50740-560, Brazil 4 HSE University, Moscow, 101000, Russia 5 Institut of Theoretical Physics III, University of Bayreuth, Bayreuth, 95440, Germany E-mail: sebastian.muehlbauer@frm2.tum.de and cubitt@ill.fr Received 19 September 2021, revised 8 December 2021 Accepted for publication 16 December 2021 Published 20 January 2022 Abstract Small-angle neutron scattering is used in combination with transport measurements to investigate the current-induced effects on the morphology of the intermediate mixed state (IMS) domains in the intertype superconductor niobium. We report the robust self-organisation of the vortex lattice domains to elongated parallel stripes perpendicular to the applied current in a steady-state. The experimental results for the formation of the superstructure are supported by theoretical calculations, which highlight important details of the vortex matter evolution. The investigation demonstrates a mechanism of a spontaneous pattern formation that is closely related to the universal physics governing the IMS in low-κ superconductors.

The changes in the mechanical properties and the texture of the surface layers in Cu–10Ga and Cu–10Ga–4Ni alloys are studied under the powerful pulsed radiation-thermal and shock-wave loads characteristic of pulsed thermonuclear fusion plants. Samples are irradiated by pulsed high-temperature plasma and ions in the 600-kJ Plasma Focus (PF) PF-1000 (Poland) plant, and deuterium is used as a working gas. The deuterium plasma power density is varied from 107 to 109 W/cm2 at the plasma pulse duration of ~10–7 s, and the deuterium ion flux power density is from 108 to 1011 W/cm2 at an ion flux incident time of ~5 × 10–8 s. Irradiation under the experimental conditions is found to change the texture of the surface layers to a depth of several micrometers, which is likely to be caused by directional solidification at a high temperature gradient oriented normal to the irradiated sample surface. There is a correlation between the type of texture formed in this case and the character of propagating slip lines with formation of a block structure. The lattice parameter in the irradiated surface layers decreases, which is related, supposedly, with the action of residual macroscopic stresses, since substantial changes in the surface layer composition have not been observed. A general tendency toward a decrease in the Vickers microhardness is noted in copper alloy samples as a result of their irradiation in the PF plant under the experimental conditions. A possible cause is thermal effect, since the concentration of alloying elements in the alloys decreases insignificantly after irradiation. The elastic modulus E of the Cu–10Ga alloy decreases insignificantly (to 14%) after irradiation. At the same time, in the Cu–10Ga–4Ni alloy, i.e., after alloying of the Cu–10Ga alloy with nickel (element with higher E as compared to that of copper), the elastic modulus of the initial surface layer remains almost the same after irradiation in PF.

MAPbBr3 (MA = CH3NH3+) doping with bismuth increases electric conductivity, charge carrier density and photostability, reduces toxicity, and expands light absorption. However, Bi doping shortens excited-state lifetimes due to formation of DY− charge recombination centers. Using nonadiabatic molecular dynamics and time−domain density functional theory, we demonstrate that the DY− center forms a deep, highly localized hole trap, which accelerates nonradiative relaxation ten-fold and is responsible for 90% of carrier losses. Hole trapping occurs by coupling between the valence band and the trap state, facilitated by the Br atoms surrounding the Bi dopant. Passivation of the DY− center with chlorines heals the local geometry distortion, eliminates the trap state, and makes the carrier lifetimes longer than even in pristine MAPbBr3. The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time, due to diminished electron−hole overlap around the passivated defect. Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr3, suggests a strategy for defect passivation and reduction of nonradiative energy losses, and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.

Запущенный в марте 2021 года наноспутник 3U CubeSat стал первым в истории, использующим сверхлегкую гармоническую дифракционную линзу для дистанционного зондирования Земли. В статье описывается платформа CubeSat, которая  использовала: синтез, проектирование и производство объективов диаметром 10 мм и фокусным расстоянием 70 мм; изготовленный на заказ корпус камеры с 3D-печатью, изготовленный из металлического сплава с нулевым тепловым расширением; и постобработку изображений на Земле с помощью сверточной нейронной сети, в результате чего получаются изображения, сопоставимые по качеству к классической рефракционной оптике, используемой ранее для дистанционного зондирования.

Today, a lab-on-a-chip is one of the most promising ways to create sensor devices for gas and liquid analysis for environmental monitoring, early diagnosis, and treatment effectiveness assessment. On the one hand, this requires a large number of measurements and, on the other hand, involves minimum consumption of the test analytes. Combination of highly sensitive photonic integrated circuits (PICs) with microfluidic channels (MFCs) is necessary to solve this problem. In this work, PICs based on a silicon nitride platform integrated with MFCs for studying liquids and gases were developed. Different concentrations of isopropanol in de-ionized water were used as the analyte. Based on this, the sensitivity (S) and detection limit (DL) of the analyzed solution were evaluated. Entire system calibration was carried out to calculate S and DL, considering experimental and numerical simulation data. This development may be of interest as a promising platform for environmental monitoring and realization of point-of-care strategy for biomedical applications.

Experiments on the irradiation of Cu–4 wt % Ni and Cu–4 wt % Ni–10 wt % Ga copper alloys by high-power pulsed flows of deuterium plasma and deuterium ions are carried out in the Plasma Focus PF- 1000 installation. The alloys are irradiated in two modes: the hard mode of combined action of deuterium plasma flows at qpl = 108–109 W/cm2, τpl = 100 ns and deuterium ions at qi = 109–1010 W/cm2, τi = 50 ns and also in more soft conditions: the Cu–4 wt % Ni alloy is irradiated with a deuterium plasma flow at a power density of qi = 2 × 107 W/cm2 and pulse duration of τpl = 100 ns; the Cu–4 wt % Ni–10 wt % Ga alloy, at qpl = 5 ×107–108 W/cm2 and qi = 108–109 W/cm2 and the same values of the pulse duration. The nature of the damage for Cu–4 wt % Ni and Cu–4 wt % Ni–10 wt % Ga alloys in the irradiation modes implemented is approximately the same and is determined by the wavy surface relief, the presence of craters, micropores, droplet-like fragments, and the absence of microcracks. Unlike the Cu–4 wt % Ni alloy, the surface structure of the Cu–4 wt % Ni–10 wt % Ga copper alloys has, after irradiation, a cellular or cellular– dendritic character. The parameters of the formation of such a structure depend on the regime of pulsed irradiation of the sample target and the conditions of subsequent directed crystallization of the molten surface layer. The formation of this structure is also significantly affected by alloying of the binary copper–nickel alloy with a third element (gallium) and probably the dendritic structure of the alloy in the initial state of the alloys. Plastic deformation is observed in the surface layer of each of the studied alloys after exposure to the flows of deuterium plasma and deuterium ions, which proceed by the sliding mechanism along the planes of the densest packing {111}, typical of materials with a face-centered cubic (fcc) lattice. The ductile copper Cu– Ni and Cu–Ni–Ga alloys under study, as well as the Cu–10 wt % Ga alloy studied previously, exhibit very high crack resistance to the effects of high-power pulsed radiation-thermal loads generated in a Plasma Focus PF-1000 installation, as compared to the refractory metals W, Mo, and V.

Using the entire data sample of 980  fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− collider, we present measurements of the branching fractions of the Cabibbo-favored decays Ξ0c→ΛK0S, Ξ0c→Σ0K0S, and Ξ0c→Σ+K−. Taking the decay Ξ0c→Ξ−π+ as the normalization mode, we measure the branching fraction ratio B(Ξ0c→ΛK0S)/B(Ξ0c→Ξ−π+)=0.229±0.008±0.012 with improved precision, and measure the branching fraction ratios B(Ξ0c→Σ0K0S)/B(Ξ0c→Ξ−π+)=0.038±0.006±0.004 and B(Ξ0c→Σ+K−)/B(Ξ0c→Ξ−π+)=0.123±0.007±0.010 for the first time. Taking into account the branching fraction of the normalization mode, the absolute branching fractions are determined to be B(Ξ0c→ΛK0S)=(3.27±0.11±0.17±0.73)×10−3, B(Ξ0c→Σ0K0S)=(0.54±0.09±0.06±0.12)×10−3, and B(Ξ0c→Σ+K−)=(1.76±0.10±0.14±0.39)×10−3. The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty of the branching fraction of Ξ0c→Ξ−π+.

A model of thermofield electron emission from the metal cathode with a thin insulating film on the surface in gas discharge is developed. It describes the tunneling of electrons from the cathode substrate into the film, their motion in it, and their going out into the discharge volume. Expressions for the film emission efficiency and emission current density from the cathode are obtained, which are correct in wide ranges of variation of the cathode temperature and the electric field strength in the film. In limiting cases of low temperature and strong electric field in the film, and also high temperature and weak electric field in the film, the results agree with those obtained from the corresponding analytical formulas. The model can be used for simulation of different gas discharge modes under the existence of thin insulating films on the cathode.

We made numerical calculations of the radiation-induced conductivity by computing current densities, carrier concentrations, and internal electric fields in a disordered sample biased by constant applied voltage under a pulsed or step-function irradiation in a large-signal regime. For this purpose, we used the multiple trapping model featuring an exponential trap distribution with the dispersion parameter α. Calculations of radiation-induced conductivity were done with traditional simplifications (1D-analysis, one-carrier polymer, diffusion currents neglected, and non-injecting electrodes). The nonlinear effects accompanying the large-signal radiation-induced conductivity, such as an internal field variation, the bimolecular recombination, and the charge carrier extraction by electrodes, have been consistently accounted for. Numerical analysis agrees satisfactorily with the results of previously published analytical calculations.

Transcriptional pausing is crucial for the timely expression of genetic information. Biochemical methods quantify the half-life of paused RNA polymerase (RNAP) by monitoring restarting complexes across time. However, this approach may produce apparent half-lives that are longer than true pause escape rates in biological contexts where multiple consecutive pause sites are present. We show here that the 6-nitropiperonyloxymethyl (NPOM) photolabile group provides an approach to monitor transcriptional pausing in biological systems containing multiple pause sites. We validate our approach using the well-studied his pause and show that an upstream RNA sequence modulates the pause half-life. NPOM was also used to study a transcriptional region within the Escherichia coli thiC riboswitch containing multiple consecutive pause sites. We find that an RNA hairpin structure located upstream to the region affects the half-life of the 5′ most proximal pause site—but not of the 3′ pause site—in contrast to results obtained using conventional approaches not preventing asynchronous transcription. Our results show that NPOM is a powerful tool to study transcription elongation dynamics within biologically complex systems.

At present, the task of searching for compounds with a high superconducting transition temperature is a very relevant scientific direction. Usually, the calculation of is carried out by numerically solving the system of Eliashberg equations. In this paper, a set of programs for solving this system written in various forms on the imaginary axis is presented. As an example of the developed methods applications, calculations results of and thermodynamic properties of the metallic hydrogen I41/AMD phase and some other substances under high pressure are presented.

Terahertz (THz, 0.3 − 3 THz) wireless access is nowadays considered as a major enabling technology for sixth generation (6G) cellular systems. To compensate for high prop- agation losses, these systems will utilize antenna arrays with extremely directional beams. The performance of such systems will thus be heavily affected by micromobility such as shakes and rotations of user equipment (UE) even when user is in stationary position. The ultimate impact of micromobility is spontaneous degradation of signal-to-noise (SNR) level leading to outages. In this paper, we measure and statistically investigate the micromobility process of various applications including video viewing, phone calling, virtual reality viewing and racing game. Particularly, we characterize occupancy distributions and first- passage time (FPT) to outage for various antenna configurations. We also assess the radial symmetry in micromobility patterns and characterize distance-dependent velocity and drift to the origin parameters. The obtained results are essential for developing mathematical models of micromobility patterns that needs to be further used in system-level analysis of THz cellular systems. To this end, we also illustrate that Markov models are only suitable for applications with low and purely random micromobility dynamics such as video viewing and phone calling. When a user is controlled by the application, as in the case of gaming, Markov models overestimate FPT to outage.

We present a measurement of the branching fractions of the Cabibbo favored ¯B0→D+π− and the Cabibbo suppressed ¯B0→D+K− decays. We find B(¯B0→D+π−)=(2.48±0.01±0.09±0.04)×10−3 and B(¯B0→D+K−)=(2.03±0.05±0.07±0.03)×10−4 decays, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the D+→K−π+π+ branching fraction. The ratio of branching fractions of ¯B0→D+K− and ¯B0→D+π− is measured to be RD=[8.19±0.20(stat)±0.23(syst)]×10−2. These measurements are performed using the full Belle dataset, which corresponds to 772×106B¯B pairs and use the Belle II software framework for data analysis.

We propose a superconducting spin valve based on a Josephson junction with B20-family magnetic metal as a barrier material. Our analysis shows that the states of this element can be switched by reorienting the intrinsic non-collinear magnetization of the spiral magnet. This reorientation modifies long-range spin-triplet correlations and thereby strongly influences the critical Josephson current. Compared to superconducting spin valves proposed earlier, our device has the following advantages: (a) it contains only one barrier layer, which makes it easier to fabricate and control; (b) its ground state is stable, which prevents uncontrolled switching; (c) it is compatible with devices of low-T Josephson electronics. This device may switch between two logical states which exhibit two different values of critical current, or its positive and negative values. I.e. 0-π switch is achievable on a simple Josephson junction.