bluuebunny/crossref_metadata_2025 huggingface dataset:
A comprehensive approach to convolutional neural networks‐based condition monitoring of permanent magnet synchronous motor drives
Authors: Pasqualotto Dario , Zigliotto Mauro
Published: March 2021

The increasing complexity of modern industrial systems calls for automatic and innovative predictive maintenance techniques. As suggested by the Industry 4.0 process, this demand translates in the need of more‐intelligent drives. Herein, the use of a special kind of neural networks to interpret the data from motor currents for diagnostic purposes is described. The early detection of possible faults in the electrical motor allows programmed maintenance and reduces the risk of unplanned shutdowns. The innovation is in the overall approach to the neural network training, which does not call anymore for a large set of faulty motors. A large training dataset generated using a combination of tuned motor models and some data augmentation techniques is proposed. The result is a comprehensive and effective motor condition monitoring algorithm, whose hearth is a convolutionary neural network trained by a safe and cheap simulation‐based dataset. The details of the design are fully reported here. The method has been implemented in the laboratory and fully tested on both healthy and faulty permanent magnet synchronous motors. The generality of the proposed method also paves the way for the detection of other failures and the application to different electrical motors.
Comparative analysis of the operating performance, magnetic field, and temperature rise of the three‐phase permanent magnet synchronous motor with or without fault‐tolerant control under single‐phase open‐circuit fault
Authors: Li Weili , Tang Haoyue , Luo Shifan , Yan Xin , Wu Zhigang
Published: March 2021

In the power transmission system, the semiconductor device in the inverter is one of the main fault points. When the open‐ or short‐circuit fault occurs in the semiconductor device, the motor can be turned into the operation with open‐phase fault. To take into account the non‐ideal factors existing in the calculation, this study establishes a system‐level calculation model including the permanent magnet synchronous motor (PMSM), inverter, and different control strategies, which is used to analyse the operating performance of the PMSM with or without fault‐tolerant control under single‐phase open‐circuit fault. In addition, based on the finite element method, the current fault characteristic and the change of the internal magnetic field distribution before and after the fault are studied, and the temperature rise of the PMSM with and without fault‐tolerant control is compared. The aim of this study is to compare the operating performance of the three‐phase PMSM under two common fault conditions, and quantitatively give the variation range of magnetic flux density and temperature rise. The theoretical analysis in this study is verified by building a systematic experiment platform.
Novel methodology for direct speed control of a permanent magnet synchronous motor with sensorless operation
Authors: Sahebjam Mehdi , Sharifian Mohammad B. B. , Feyzi M. Reza , Sabahi Mehran
Published: March 2021

A new formulation of the direct speed control (DSC) method for permanent magnet synchronous motor (PMSM) is proposed. The proposed DSC method employs a direct voltage control to synthesise the d and q axes stator voltage. In this method, no q‐axis current loop regulation is required. Thus, a new concept of the dynamic limiter (DL) is proposed to limit the undesirable current rises. The mathematical analyses, frequency and time domain simulations, and experimental test results highlight the simplicity and effectiveness of the proposed DSC method. Furthermore, sensorless operation of the method can make it a reliable alternative for low‐cost drive of PMSM.
Current Commutation in a Switched Lithium‐Ion Cell used in Cascaded Half‐Bridge Multilevel Inverters
Authors: Hanzl Christian , Hartmann Christoph , Hölzle Markus , Liebhart Bernhard , Schmid Michael , Endisch Christian
Published: March 2021

In order to improve the efficiency of battery electric vehicles, the utilization of reconfigurable batteries and multilevel inverters based on low‐voltage Si MOSFETs gains growing attention. Focusing on the half‐bridge as basic switching unit, this paper examines voltage and current waveforms during switching. It is shown that the current commutation speed depends on various factors such as sign and amplitude of the current as well as the particular switching scenario. For instance, turning off a positive cell current takes 0.21 s while turning it on takes 0.9 s. In addition, it is revealed that depending on the switching scenario and current direction, the lithium‐ion cell supports or opposes the remagnetization of the parasitic inductances and therefore the switching losses of the MOSFETs. Switching a positive load current of 125 A from active to bypass converts 276 J into heat while switching from bypass to active converts merely 32.5 J into heat.
Binding energies and sticking coefficients of H2 on crystalline and amorphous CO ice
Authors: Molpeceres G. , Zaverkin V. , Watanabe N. , Kästner J.
Published: March 2021

Context. Molecular hydrogen (H2) is the most abundant interstellar molecule and plays an important role in the chemistry and physics of the interstellar medium. The interaction of H2 with interstellar ices is relevant for several processes (e.g., nuclear spin conversion and chemical reactions on the surface of the ice). To model surface processes, quantities such as binding energies and sticking coefficients are required.

Aims. We provide sticking coefficients and binding energies for the H2/CO system. These data are absent in the literature so far and could help modelers and experimentalists to draw conclusions on the H2/CO interaction in cold molecular clouds.

Methods. Ab initio molecular dynamics simulations, in combination with neural network potentials, were employed in our simulations. Atomistic neural networks were trained against density functional theory calculations on model systems. We sampled a wide range of H2 internal energies and three surface temperatures.

Results. Our results show that the binding energy for the H2/CO system is low on average, − 157 K for amorphous CO and −266 K for crystalline CO. This carries several implications for the rest of the work. H2 binding to crystalline CO is stronger by 109 K than to amorphous CO, while amorphous CO shows a wider H2 binding energy distribution. Sticking coefficients are never unity and vary strongly with surface temperature, but less so with ice phase, with values between 0.95 and 0.17. With the values of this study, between 17 and 25% of a beam of H2 molecules at room temperature would stick to the surface, depending on the temperature of the surface and the ice phase. Residence times vary by several orders of magnitude between crystalline and amorphous CO, with the latter showing residence times on the order of seconds at 5 K. H2 may diffuse before desorption in amorphous ices, which might help to accommodate it in deeper binding sites.

Conclusions. Based on our results, a significant fraction of H2 molecules will stick on CO ice under experimental conditions, even more so under the harsh conditions of prestellar cores. However, with the low H2–CO binding energies, residence times of H2 on CO ice before desorption are too short to consider a significant population of H2 molecules on pure CO ices. Diffusion is possible in a time window before desorption, which might help accommodate H2 on deeper binding sites, which would increase residence times on the surface.
Characterizing the astrometric instability of extragalactic radio source positions measured with geodetic VLBI
Authors: Gattano C. , Charlot P.
Published: March 2021

Context. Geodetic very long baseline interferometry (VLBI) has been used to observe extragalactic radio sources for more than 40 yr. The absolute source positions derived from the VLBI measurements serve as a basis to define the International Celestial Reference Frame (ICRF). Despite being located at cosmological distances, an increasing number of these sources are found to show position instabilities, as revealed by the accumulation of VLBI data over the years.

Aims. We investigate how to characterize the astrometric source position variations, as measured with geodetic VLBI data, in order to determine whether these variations occur along random or preferential directions. The sample of sources used for this purpose is made up of the 215 most observed ICRF sources.

Methods. Based on the geodetic VLBI data set, we derived source coordinate time series to map the apparent trajectory drawn by the successively measured positions of each source in the plane of the sky. We then converted the coordinate time series into a set of vectors and used the direction of these vectors to calculate a probability density function (PDF) for the direction of variation of the source position. For each source, a model that matches the PDF and that comprises the smallest number of Gaussian components possible was further adjusted. The resulting components then identify the preferred directions of variation for the source position.

Results. We found that more than one-half of the sources (56%) in our sample may be characterized by at least one preferred direction. Among these, about three-quarters are characterized by a unique direction, while the remaining sources show multiple preferred directions. The analysis of the distribution of these directions reveals an excess along the declination axis that is attributed to a VLBI network effect. Whether single or multiple, the identified preferred directions are likely due to source-intrinsic physical phenomena.
Discovery of the propargyl radical (CH2CCH) in TMC-1: One of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds
Authors: Agúndez M. , Cabezas C. , Tercero B. , Marcelino N. , Gallego J. D. , de Vicente P. , Cernicharo J.
Published: March 2021

We present the first identification in interstellar space of the propargyl radical (CH2CCH). This species was observed in the cold dark cloud TMC-1 using the Yebes 40 m telescope. The six strongest hyperfine components of the 20, 2–10, 1rotational transition, lying at 37.46 GHz, were detected with signal-to-noise ratios from 4.6σto 12.3σ. We derived a column density of 8.7 × 1013cm−2for CH2CCH, which translates to a fractional abundance relative to H2of 8.7 × 10−9. This radical has a similar abundance as methyl acetylene, with an abundance ratio CH2CCH/CH3CCH close to one. The propargyl radical is thus one of the most abundant radicals detected in TMC-1, and it is probably the most abundant organic radical with a certain chemical complexity ever found in a cold dark cloud. We constructed a gas-phase chemical model and find calculated abundances that agree with, or fall two orders of magnitude below, the observed value depending on the poorly constrained low-temperature reactivity of CH2CCH with neutral atoms. According to the chemical model, the propargyl radical is essentially formed by the C + C2H4reaction and by the dissociative recombination of C3$ \rm{H}_n^+ $ ions withn= 4−6. The propargyl radical is believed to control the synthesis of the first aromatic ring in combustion processes, and it probably plays a key role in the synthesis of large organic molecules and cyclization processes to benzene in cold dark clouds.
Second order optimality conditions for periodic optimal control problems governed by semilinear parabolic differential equations
Authors: Liu Hanbing , Wang Gengsheng
Published: March 2021

In this paper, we study second-order optimality conditions for some optimal control problems governed by some semi-linear parabolic equations with periodic state constraint in time. We obtain a necessary condition and a sufficient condition in terms of the second order derivative of the associated Lagrangian. These two conditions correspond to the positive definite and the nonnegativity of the second order derivative of the Lagrangian on the same cone, respectively.
Use of Performance Criteria in Calibrating Methods for Modeling and Simulating the Pollution Phenomena of Surface Waters
Authors: Toth Lorand , Artur Găman George , Pupăzan Daniel , Nicolescu Cristian , Kovacs and Marius
Published: March 2021

The release of certain substances into surface waters (lakes, rivers, estuaries and oceans) to the point where they interfere with beneficial use of water or with natural functioning of ecosystems defines the phenomenon of pollution. When stating aspects of pollution modelling, we refer to constitutive equations of the model, which may involve different values, so that the shape of equation is flexible while maintaining its structure. Quantifying the phenomenon of water pollution through simulation and spatial-temporal modelling requires the use of hydrological models that use characteristic parameters such as: bathymetry, hydrodynamic roughness, speed, Model Boundary Conditions, etc. The current paper is driven by lack of clear performance guidelines for pollution models for software users trying to demonstrate to customers and/or end users that a model is fit for purpose. Thus, common problems associated with data availability, errors and uncertainty as well as model examination will be addressed, including its calibration and validation on a case study materialized on a watercourse located in the Jiu Valley, Romania. The scientific article is intended to be a point of reference both for software users (numerical modelers) and for specialists in charge of interpreting the accuracy and validity of results from hydrodynamic models.
Sustainable Construction, LEED as a Green Rating System and the Importance of Moving to NZEB
Authors: Tabrizi Aydin
Published: March 2021

In this study, in order to evaluate the possibility of achieving the Net Zero Energy Building (NZEB) goal, the history of sustainable construction, and available green-rating systems with specific focus on Leadership in Energy & Environmental Design (LEED) rating system were explained. LEED rating system was selected as the most prevalent rating system in the industry to evaluate and analyze its efficiencies/drawbacks specifically in regards to the energy efficiency. The goal of this study is to answer an important question of the reasons to focus on NZEB concept when LEED rating has come up with a detailed certification process, which is somehow beneficial in regards to energy reduction. NZEB concept is defined as an evolution of very energy-efficient approach and it requires that the buildings have zero energy balance on an annual basis. This paper explains this questions in detail and it consists of three parts: in the first part sustainable building rating system including LEED certification is explained. The second part explains the deficiencies of LEED rating system in regards to the energy performance of buildings and the last part explains the NZEB concept and the movement towards the NZEB target.
Influence of the COVID-19 Pandemic Outbreak on Ground Transport CO2 Emission
Authors: Sikorski Michał , Majewski Jan , Snarski Wiktor
Published: March 2021

Coronavirus pandemic brought about stay-at-home strategies to diminish the danger of uncontrolled spread of the infection. This paper looks at the effect that these activities had on emissions caused by ground transport among different countries. CO2 emission year-to-date dropped by 5.4% with respect to the 2019 statistics, which means that the scope of the decrease is much more abrupt than during past financial crises or World War II. The circumstance of emissions relates to lockdown measures in every nation. By the beginning of July 2020, the pandemic’s impacts on worldwide emission reduced as lockdown limitations were loosened and some monetary exercises restarted, although the air pollution is still lower in contrast to 2019. The article traces back the reasons for the observed decline from the perspective of different countries and economy sectors. While there is no doubt that the major vector of changes was the COVID-19 pandemic, an increasingly important role of climate changes is also visible in the analysed data.
Analysis on parameter switching methods for hydropower dominant system
Authors: She Shengjing , Li Chongtao , Chen Yiping , Yang Rongzhao , Xiao Liang , Zeng Kehan , Gao Qin
Published: March 2021

With the rapid development of DC asynchronous interconnection, in order to ensure the frequency quality, higher requirements are put forward for the primary frequency control of hydropower units. In the high proportion hydropower system, it is difficult for the governor parameters to meet the requirements of primary frequency control and dynamic stability simultaneously. In order to solve the problem, this paper proposes a recommended parameter switching method by referring to the Nordic system. The parameter optimization methods before and after switching are proposed, and the effectiveness of the method is verified by time domain simulation.
Lightning Performance of Unshielded 220kV Transmission Lines Equipped with Metal-oxide Arresters
Authors: Xie Pengkang , Fang Zhen
Published: March 2021

Overhead ground wires have been proved to be effective to protect conductors from direct lightning strikes, but breakouts of ground wires have been frequently reported. In order to prevent ground wire breakout incidents to happen, unshielded 220kV lines equipped with metal oxide arresters (MOAs) whole line have been proposed in this paper. After cancelling ground wire, lightning strike risk of transmission lines becomes much higher. In order to improve the anti-lightning abilities of unshielded transmission lines, it is necessary to obtain the lightning energy absorption ability of these MOAs. In this paper, simulation model of MOA equipped unshielded 220kV transmission line was built, the influences of lightning parameters, striking occurrence point and grounding resistance of transmission tower on the absorbed energy of MOAs were calculated, and the suggested energy absorption ability of MOA was given, which can give references for the improvement of power supply reliability of transmission lines.
Behandlung pädiatrischer Patientinnen und Patienten in der Partikeltherapie
Authors: Rupprecht David , Humhal Stefanie
Published: March 2021

Die Partikeltherapie, vor allem die Protonentherapie, ermöglicht es pädiatrische Patientinnen und Patienten hinsichtlich einer Dosisminimierung des gesunden Gewebes optimal zu behandeln. Das oberste Ziel hierbei ist es, neurokognitive und endokrine Funktionseinschränkungen zu reduzieren und Langzeitfolgen wie Sekundärkarzinome bei gleichzeitiger optimaler Dosisapplikation im zu bestrahlenden Gebiet zu vermeiden.
Research of security and safety culture within an organization. The case study within the Slovak Republic
Authors: Veľas Andrej , Halaj Martin , Hofreiter Ladislav , Kampová Katarína , Zvaková Zuzana , Jankura Richard
Published: March 2021

Security and safety culture is an increasingly important term in assessing the security and safety of organizations. It is an internal security and safety factor of an organization that can directly influence its overall security and safety. In many cases, however, organizations do not know, nor do they have a way of assessing the level of their security and safety culture. It is therefore necessary to know the content, elements, and sectors in which it can be identified in order to gain a deeper knowledge of security and safety culture in more detail and be able to examine it. Firstly, we focused on creating a model for evaluating the safety and safety culture and its application in selected organizations. Secondly, we devoted to the description and design of an organization’s security and safety culture assessment model. The proposed model is based on the identification of subsectors and indicators of security and safety culture that will gain their value by using information obtained from combining the four proposed methods. Accordingly, six security and safety culture sectors were defined for the purposes of security and safety culture assessment in selected organizations. These were compared to each other to determine their mutual weight. Finally, using these research methods, security and safety culture indicators were also identified and included in the defined security and safety culture sectors. The research needed to design a security and safety culture assessment model was realized in six selected organizations, which wanted to participate in the research. These were divided according to the size of the organization into two small, two medium, and two large organizations. Crucial element in our research was data collection conducted by means of controlled interviews and questionnaire surveys in these organizations. Based on this survey, indicators of security and safety culture could be identified. As a result of this, security and safety culture values are determined for all analyzed organizations. The conclusions will point up the possible way of evaluating security and safety culture in organizations and it also contains a specific example of their usage in the practice. Thus, by using the resulting values, it is possible to decide the further direction for the organizations, focusing on the sectors of the security and safety culture, which yielded unsatisfactory results.
Synthetic forces induce complex dynamics in a photonic quantum walk
Authors: Ishimaru Matthew
Published: March 2021

Researchers observe Bloch-Landau-Zener dynamics in a photonic system that models the behavior of a quantum walk under a constant force.
A three-dimensional velocity-map imaging setup designed for crossed ion-molecule scattering studies
Authors: Zhang Guo-dong , Guan Li-chang , Yan Zi-feng , Cheng Min , Gao Hong
Published: March 2021

In this study, we report the design and simulation of an electrostatic ion lens system consisting of 22 round metal plates. The opening of the extractor plate is covered with metal mesh, which is for shielding the interaction region of the lens system from the high DC voltages applied to all other plates than the repeller and extractor plates. The Simion simulation shows that both velocity-mapping and time focusing can be achieved simultaneously when appropriate voltages are applied to each of the plates. This makes the ion lens system be able to focus large ionic volumes in all three dimensions, which is an essential requirement for crossed ion-molecule scattering studies. A three-dimensional ion velocity measurement system with multi-hit and potential multi-mass capability is built, which consists of a microchannel plate (MCP), a P47 phosphor screen, a CMOS camera, a fast photomultiplier tube (PMT), and a high-speed digitizer. The two velocity components perpendicular to the flight axis are measured by the CMOS camera, and the time-of-flight, from which the velocity component along the flight axis can be deduced, is measured by the PMT. A Labview program is written to combine the two measurements for building the full three-dimensional ion velocity in real time on a frame-by-frame basis. The multi-hit capability comes from the fact that multiple ions from the camera and PMT in the same frame can be correlated with each other based on their various intensities. We demonstrate this by using the photodissociation of CH3I at 304 nm.
Scanning Raman picoscopy: Ångström-resolved tip-enhanced Raman spectromicroscopy
Authors: Zhang Yao , Zhang Yang , Dong Zhen-chao
Published: March 2021

In this review, we present a brief overview on the recent advances in Ångström-resolved tip-enhanced Raman spectromicroscopy. We first introduce the theoretical understanding of the confinement of light at the atomistic scale, and explain how the Raman scattering from a single molecule happens under the “illumination” of such an atomically confined light. Then we describe the latest developments on Ångström-resolved tip-enhanced Raman spectromicroscopy, particularly on a new methodology called “scanning Raman picoscopy” for visually constructing the chemical structure of a single molecule in real space. Finally, we give a perspective of this technique in various applications where identifying the chemical structures of materials at the chemical bond level is required.
A low noise transimpedance amplifier for optical receiver
Authors: Li Chenming , Xie Sheng , Zhou Gaolei , Mao Luhong , Qiu Bowen
Published: March 2021

In this paper, a regulated cascode (RGC) structure and a shunt-feedback transimpedance amplifier are cascaded. By analyzing the average input-referred noise current, this paper used the method of adjusting the metal–oxide–semiconductor size and increasing the transimpedance gain to optimize the circuit noise characteristics without introducing redundant structures and noise sources. The measured results demonstrated that when the photodetector capacitance is 300 pF and the supply voltage is 1.8 V, the fabricated transimpedance amplifier has a transimpedance gain of 59.5 dBΩ and a −3 dB bandwidth of 4 GHz. Simultaneously, the average input-referred noise current spectral density is less than 7 pA/√Hz, and the data rate is as high as 5 Gb/s. The circuit takes advantage of the traditional shunt-feedback transimpedance amplifier and introduces a RGC structure between it and the input terminal as a current buffer structure. A π-type matching network was formed by adding an inductor between the shunt-feedback amplifier and the introduced RGC. All these structures can effectively improve the gain–bandwidth product of the designed amplifier.
Automated calibration of 3D-printed microfluidic devices based on computer vision
Authors: Wang Junchao , Liang Kaicong , Zhang Naiyin , Yao Hailong , Ho Tsung-Yi , Sun Lingling
Published: March 2021

With the development of 3D printing techniques, the application of it in microfluidic/Lab-on-a-Chip (LoC) fabrication is becoming more and more attractive. However, to achieve a satisfying printing quality of the target devices, researchers usually require quite an amount of work in calibration trials even for high-end 3D printers. To increase the calibration efficiency of the average priced printers and promote the application of 3D printing technology in the microfluidic community, this work has presented a computer vision (CV)-based method for rapid and precise 3D printing calibration with examples on cylindrical hole/post diameters of 0.2–2.4 mm and rectangular hole/post widths of 0.2–1.0 mm by a stereolithography-based 3D printer. Our method is fully automated, which contains five steps and only needs a camera at hand to provide photos for convolutional neural network recognition. The experimental results showed that our CV-based method could provide calibrated dimensions with just one print of the specific calibration ruler to meet user desire. The higher resolution of the photo provides a higher precision in calibration. Subsequently, only one more print for the target device is needed after the calibration process. Overall, this work has provided a quick and precise calibration tool for researchers to apply 3D printing in the fabrication of their microfluidic/LoC devices with average price printers. Besides, with our open source calibration software and calibration ruler design file, researchers can modify the specific setting based on customized needs and conduct calibration on any type of 3D printer.
A CMOS Hall sensor modeling with readout circuitry and microcontroller processing for magnetic detection
Authors: Fan Hua , Zhang Jiayi , Zuo Siming , Hu Qiang , Feng Quanyuan , Heidari Hadi
Published: March 2021

A Hall sensor array system for magnetic field detection and analysis is realized in X-FAB 0.18 μm CMOS technology. Magnetic field detection is attributed to the magnetization of metal coils to metal particles and the sensing characteristics of the Hall sensor array. The system puts forward a complete solution from Hall sensors, analog front-end circuit, analog-to-digital converter (ADC) to microcontroller unit. Using Ansoft Maxwell and COMSOL Multiphysics software for simulation verification, the minimum diameter of magnetic particles that can be detected in the system is 2 μm. The measured signal to noise and distortion ratio, spurious free dynamic range, and effective number of bits of the proposed ADC are 70.61 dB, 90.08 dB, and 11.44-bit, respectively. The microsystem based on STM32 combines hardware and software design, which can effectively adjust the motion parameters and realize the real-time display in the LCD screen of the magnetic field and voltage information. Compared to the prior system, the portability, cost, and efficiency have been considerably improved, which is aimed at the rapid measurement of heavy metal particles such as Fe, Co, and Ni in ambient air and blood.
Mechanisms to decrease the diseases spreading on generalized scale-free networks
Authors: Galiceanu Mircea , Mendes Carlos F. O. , M. Maciel Cássio , Beims Marcus W.
Published: March 2021

In this work, an epidemiological model is constructed based on a target problem that consists of a chemical reaction on a lattice. We choose the generalized scale-free network to be the underlying lattice. Susceptible individuals become the targets of random walkers (infectious individuals) that are moving over the network. The time behavior of the susceptible individuals’ survival is analyzed using parameters like the connectivity γ of the network and the minimum (Kmin) and maximum (Kmax) allowed degrees, which control the influence of social distancing and isolation or spatial restrictions. In all cases, we found power-law behaviors, whose exponents are strongly influenced by the parameter γ and to a lesser extent by Kmax and Kmin, in this order. The number of infected individuals diminished more efficiently by changing the parameter γ, which controls the topology of the scale-free networks. A similar efficiency is also reached by varying Kmax to extremely low values, i.e., the number of contacts of each individual is drastically diminished.
An unrestricted approach for the accurate calculation of the intermolecular potential of (O2)4: Implications for the solid epsilon phase
Authors: Valentín-Rodríguez Mónica A. , Bartolomei Massimiliano , Hernández Marta I. , Campos-Martínez José , Hernández-Lamoneda Ramón
Published: March 2021

Oxygen in its elemental form shows a variety of magnetic properties in its condensed phases; in particular, the epsilon solid phase loses its magnetism. These phenomena reflect the nature of the intermolecular forces present in the solid and the changes that arise with variations in pressure and temperature. In this study, we use intermolecular potentials obtained with unrestricted ab initio methods to model the singlet state of the oxygen tetramer [(O2)4], which is the unit cell, consistent with the non-magnetic character of this phase. To do this, we perform an analysis of the coupled–uncoupled representations of the spin operator together with a pairwise approximation and the Heisenberg Hamiltonian. We start from unrestricted potentials for the dimer calculated at a high level as well as different density functional theory (DFT) functionals and then apply a finite model to predict the properties of the epsilon phase. The results obtained in this way reproduce well the experimental data in the entire pressure range below 60 GPa. Additionally, we show the importance of calculating the singlet state of the tetramer as opposed to previous DFT periodic calculations, where the unrestricted description leads to a mixture of spin states and a poor comparison with the experiment. This point is crucial in the recent discussion about the coexistence of two epsilon phases: one where the identity of each O2 with spin S = 1 is retained within the tetramer unit vs another at higher pressures where the tetramer behaves as a single unit with a closed-shell character.
Trailing-edge boundary layer characteristics of a pitching airfoil at a low Reynolds number
Authors: Zhou Teng , Zhong Siyang , Fang Yi
Published: March 2021

The periodic variation of the flow pattern and the boundary layer characteristics near the trailing edge of a pitching NACA (National Advisory Committee for Aeronautics) 0012 airfoil are examined experimentally in this study. The mean pitching angle and pitching amplitude were 0° and 7.5°, respectively, and the reduced frequency varied from 0.094 to 0.157. Static cases with various angles of attack were tested for reference. All the tests were conducted at a low Reynolds number of 66000. Particle image velocimetry was used as the primary measurement for flow visualization and boundary layer analysis. The periodic development of the flow pattern close to the trailing edge within one pitching cycle was monitored. The instantaneous flow patterns acquired at certain phase angles are compared with the static cases, demonstrating the influences of the pitching motion, including the lag effect on the boundary layer. A vortex street is observed as the airfoil achieves certain pitching angles, leading to the largest boundary layer displacement thickness at the corresponding side. As the pitching angle increases, transition of the boundary layer at the trailing edge occurs at a higher incidence compared with the static cases. Increasing the pitching frequency would lead to the decrease in the vortex structure strength and delayed boundary layer transition near the trailing edge.
Coarse grained simulations of shock-driven turbulent material mixing
Authors: Grinstein Fernando F. , Saenz Juan A. , Germano Massimo
Published: March 2021

We revisit coarse-grained simulation strategies for turbulent material mixing applications involving shock-driven turbulence in the context of the Radiation Adaptive Grid Eulerian (xRAGE) hydrodynamics and Besnard–Harlow–Rauenzahn (BHR) Reynolds-averaged Navier–Stokes codes, using newly available Low-Mach-Corrected (LMC) xRAGE hydrodynamics. Impact assessments are based on comparisons with a relevant shock-tube experiment for which turbulent mixing and velocity data are available. xRAGE Implicit Large-Eddy Simulation (ILES) and a recently proposed xRAGE-BHR bridging paradigm are tested. Bridging models turbulent stresses dynamically, based on decomposing the full stress into modeled and resolved components, using a differential filter as a secondary filtering operation to define the resolved part, and additionally requiring the resolved stress to approach the full stress with grid resolution refinement to ensure realizability of the bridging-based large-eddy simulation. Much improved scale-resolving with LMC-xRAGE ILES and with dynamic LMC-xRAGE/BHR bridging enables higher simulated mixing and turbulence levels on coarser grids. For the tested planar shock-tube case, the more-accurate models can achieve the same level of accuracy with less resolution than required with the highest-fidelity turbulence simulation models typically used at scale with default xRAGE hydrodynamics; two-levels of grid-coarsening savings can be thus achieved for the mixing prediction in these comparisons: one associated with the more-accurate LMC xRAGE hydrodynamics and an additional one from using the dynamic xRAGE-BHR bridging.
Numerical simulation of the flow around two square cylinders using the lattice Boltzmann method
Authors: Zhou Yi , Wang Zhengdao , Qian Yuehong , Yang Hui , Wei Yikun
Published: March 2021

We present a numerical investigation on flow around two square cylinders in side-by-side, tandem, and staggered arrangements at Reynolds number Re = 100 (which is based on the side length of the square cylinder). The dimensionless spacing between the two cylinders are T/D < 5.0 and L/D < 10.0 in the transverse and longitudinal directions, respectively. Numerical results reveal various flow patterns depending on the spacing, including the single bluff-body, flip-flopping, in-phase synchronized, and anti-phase synchronized patterns for the side-by-side arrangement, type-I and type-II patterns for the tandem arrangement, and nine complex flow patterns for the staggered arrangement. Moreover, these flow patterns can be divided into three categories: single bluff-body flow, small incidence angle flow, and large incidence angle flow. The flow structures, lift coefficient, drag coefficient, and Strouhal number (St) are presented to demonstrate the dependence of these parameters on the spacing, and the relationship between the flow pattern and lift and drag coefficients is also explored.
Intrinsic losses in photovoltaic laser power converters
Authors: Lin Minshen , Sha Wei E. I. , Zhong Wenxing , Xu Dehong
Published: March 2021

Using photovoltaic cells as photovoltaic laser power converters (PLPCs) is a potential technology for long-range wireless power transfer. Intrinsic processes that limit the performance of PLPCs have not been fully investigated. Based on a thermodynamic model, we categorize and calculate the intrinsic losses in PLPCs. We use the experimental data of silicon and gallium arsenide to take into account the unavoidable Auger process. We find that the entropic loss generated during the absorption and emission of radiation is the major loss mechanism. Importantly, we show that in the presence of nonideal absorptivity and volumetric entropy production via Auger recombination, using lasers with photon energy equal to the bandgap of the PLPC can be impractical, e.g., comparable efficiencies can be achieved in much thinner silicon PLPCs illuminated by lasers with higher photon energies. We also investigate the methods of diminishing the intrinsic losses with respect to the Auger process: by intensifying the laser irradiance, the proportion of entropic loss in input power can be arbitrarily reduced; by using spectral and angular filters, the intrinsic losses can be diminished via absorption enhancement or emission restriction. Additionally, we discuss the practical efficiency limit of PLPCs accounting for the entropy production due to finite carrier mobilities. The results in this work estimate the potentials for efficiency improvements, which are fundamental to the design of PLPCs.
Operator learning for predicting multiscale bubble growth dynamics
Authors: Lin Chensen , Li Zhen , Lu Lu , Cai Shengze , Maxey Martin , Karniadakis George Em
Published: March 2021

Simulating and predicting multiscale problems that couple multiple physics and dynamics across many orders of spatiotemporal scales is a great challenge that has not been investigated systematically by deep neural networks (DNNs). Herein, we develop a framework based on operator regression, the so-called deep operator network (DeepONet), with the long-term objective to simplify multiscale modeling by avoiding the fragile and time-consuming “hand-shaking” interface algorithms for stitching together heterogeneous descriptions of multiscale phenomena. To this end, as a first step, we investigate if a DeepONet can learn the dynamics of different scale regimes, one at the deterministic macroscale and the other at the stochastic microscale regime with inherent thermal fluctuations. Specifically, we test the effectiveness and accuracy of the DeepONet in predicting multirate bubble growth dynamics, which is described by a Rayleigh–Plesset (R–P) equation at the macroscale and modeled as a stochastic nucleation and cavitation process at the microscale by dissipative particle dynamics (DPD). First, we generate data using the R–P equation for multirate bubble growth dynamics caused by randomly time-varying liquid pressures drawn from Gaussian random fields (GRFs). Our results show that properly trained DeepONets can accurately predict the macroscale bubble growth dynamics and can outperform long short-term memory networks. We also demonstrate that the DeepONet can extrapolate accurately outside the input distribution using only very few new measurements. Subsequently, we train the DeepONet with DPD data corresponding to stochastic bubble growth dynamics. Although the DPD data are noisy and we only collect sparse data points on the trajectories, the trained DeepONet model is able to predict accurately the mean bubble dynamics for time-varying GRF pressures. Taken together, our findings demonstrate that DeepONets can be employed to unify the macroscale and microscale models of the multirate bubble growth problem, hence providing new insight into the role of operator regression via DNNs in tackling realistic multiscale problems and in simplifying modeling with heterogeneous descriptions.
Intermediate state representation approach to physical properties of molecular electron-attached states: Theory, implementation, and benchmarking
Authors: Dempwolff Adrian L. , Belogolova Alexandra M. , Trofimov Alexander B. , Dreuw Andreas
Published: March 2021

Computational schemes for comprehensive studies of molecular electron-attached states and the calculation of electron affinities (EAs) are formulated and implemented employing the intermediate state representation (ISR) formalism and the algebraic–diagrammatic construction approximation for the electron propagator (EA-ADC). These EA-ADC(n)/ISR(m) schemes allow for a consistent treatment of not only electron affinities and pole strengths up to third-order of perturbation theory (n = 3) but also one-electron properties of electron-attached states up to second order (m = 2). The EA-ADC/ISR equations were implemented in the Q-Chem program for Ŝz-adapted intermediate states, allowing also open-shell systems to be studied using unrestricted Hartree–Fock references. For benchmarking of the EA-(U)ADC/ISR schemes, EAs and dipole moments of various electron-attached states of small closed- and open-shell molecules were computed and compared to full configuration interaction data. As an illustrative example, EA-ADC(3)/ISR(2) has been applied to the thymine–thymine (6–4) DNA photolesion.
Motion of an active particle in a linear concentration gradient
Authors: Vinze Prathmesh M. , Choudhary Akash , Pushpavanam S.
Published: March 2021

Janus particles self-propel by generating local tangential concentration gradients along their surface. These gradients are present in a layer whose thickness is small compared to the particle size. Chemical asymmetry along the surface is a prerequisite to generate tangential chemical gradients, which gives rise to diffusio-osmotic flows in a thin region around the particle. This results in an effective slip on the particle surface. This slip results in the observed “swimming” motion of a freely suspended particle even in the absence of externally imposed concentration gradients. Motivated by the chemotactic behavior of their biological counterparts (such as sperm cells, neutrophils, macrophages, bacteria, etc.), which sense and respond to external chemical gradients, the current work aims at developing a theoretical framework to study the motion of a Janus particle in an externally imposed linear concentration gradient. The external gradient along with the self-generated concentration gradient determines the swimming velocity and orientation of the particle. The dominance of each of these effects is characterized by a non-dimensional activity number A (ratio of applied gradient to self-generated gradient). The surface of Janus particle is modeled as having a different activity and mobility coefficient on the two halves. Using the Lorentz reciprocal theorem, an analytical expression for the rotational and translational velocity is obtained. The analytical framework helps us divide the parameter space of surface activity and mobility into four regions where the particle exhibits different trajectories.
A generic Slater–Koster description of the electronic structure of centrosymmetric halide perovskites
Authors: Kashikar Ravi , Gupta Mayank , Nanda B. R. K.
Published: March 2021

The halide perovskites have truly emerged as efficient optoelectronic materials and show the promise of exhibiting nontrivial topological phases. Since the bandgap is the deterministic factor for these quantum phases, here, we present a comprehensive electronic structure study using first-principle methods by considering nine inorganic halide perovskites CsBX3 (B = Ge, Sn, Pb; X = Cl, Br, I) in their three structural polymorphs (cubic, tetragonal, and orthorhombic). A series of exchange–correlation (XC) functionals are examined toward accurate estimation of the bandgap. Furthermore, while 13 orbitals are active in constructing the valence and conduction band spectra, here, we establish that a 4 orbital based minimal basis set is sufficient to build the Slater–Koster tight-binding (SK-TB) model, which is capable of reproducing the bulk and surface electronic structures in the vicinity of the Fermi level. Therefore, like the Wannier based TB model, the presented SK-TB model can also be considered an efficient tool to examine the bulk and surface electronic structures of the halide family of compounds. As estimated by comparing the model study and DFT band structure, the dominant electron coupling strengths are found to be nearly independent of XC functionals, which further establishes the utility of the SK-TB model.
Propagation of microwave breakdown in argon induced by a 28 GHz gyrotron beam
Authors: Shimamura Kohei , Yamasaki Junko , Miyawaki Kaisei , Minami Ryutaro , Kariya Tsuyoshi , Yang Juan , Yokota Shigeru
Published: March 2021

An atmospheric argon discharge plasma was induced by a high-power microwave beam using a 28 GHz gyrotron and investigated at pressures of 40 kPa–100 kPa and Gaussian peak intensities of 0.115 GW/m2 (0.204 MV/cm) and 0.168 GW/m2 (0.246 MV/cm). According to high-speed imaging results, the propagation velocity of the discharge front increased with the backpressure to maintain a range of 600 m/s–1000 m/s. The propagation velocity was 25 times larger in argon than in air. Applying the collisional-radiative (CR) model to the spectroscopic results showed that the electron density increases with the pressure from 5.0×1021 m−3 at 40 kPa to 5.0×1022 m−3 at 100 kPa and lies on the critical density curve. The electron temperature decreases as the background pressure increases from 2 eV to 0.5 eV, and the gas temperature was 300–400 K. According to CR analysis, the population densities of 3dn and 2sn excitation levels in the fast velocity condition are much lower than that in any other conditions. The results revealed that the energy transfer from electrons to ionized particles is more remarkable in the high background pressure and the fast velocity condition.
Zinc finger protein E4F1 cooperates with PARP-1 and BRG1 to promote DNA double-strand break repair
Authors: Moison Céline , Chagraoui Jalila , Caron Marie-Christine , Gagné Jean-Philippe , Coulombe Yan , Poirier Guy G. , Masson Jean-Yves , Sauvageau Guy
Published: March 2021

Significance

Cycling cells acquire numerous DNA lesions under physiological conditions and thus require functional DNA damage response (DDR) pathways to support proper DNA repair. Hundreds of proteins orchestrate the DDR in time and space from very early events, such as the sensing of DNA lesions by DNA-dependent poly(ADP-ribose) polymerases (PARPs) to late steps in chromatin restoration. Here we define a function of E4F1 in double-strand break repair. We show that E4F1 is rapidly recruited to DNA lesions by PARP-1, where it promotes γH2AX clearance, transcriptional silencing, DNA-end resection, and homologous recombination. These data provide an unsuspected molecular explanation for the essential role of E4F1 in DDR-associated cell cycle arrest and survival.
On a question of Mordell
Authors: Booker Andrew R. , Sutherland Andrew V.
Published: March 2021

Significance

A Diophantine equation is a polynomial equation to which one seeks solutions in integers. There is a notable disparity between the difficulty of stating Diophantine equations and that of solving them. This feature was formalized in the 20th century by Matiyasevich’s negative answer to Hilbert’s tenth problem: It is impossible to tell whether some Diophantine equations have solutions or not. One need not look very far to find examples whose status is unknown. A striking example was noted by Mordell in 1953: The equation

x

3

+

y

3

+

z

3

=
3

has the solutions

(

1,1,1

)

and

(

4,4
,
−
5

)

(and permutations); are there any others? This paper concludes a 65-y search with an affirmative answer to Mordell’s question and strongly supports a related conjecture of Heath-Brown.