bluuebunny/crossref_metadata_2025_split huggingface dataset:
Failure analysis and lifetime assessment of IGBT power modules at low temperature stress cycles
Authors: Hernes Magnar , D'Arco Salvatore , Antonopoulos Antonios , Peftitsis Dimosthenis 
Published: April 2021

AbstractLifetime models of high‐power Insulated Gate Bipolar Transistors modules express the number of cycles to end of life as a function of stress parameters. These models are normally developed based on experimental data from accelerated power‐cycling tests performed at predefined temperature stress conditions as, for example, with temperature swings above 60 °C. However, in real power converters applications, the power modules are usually stressed at temperature cycles not exceeding 40 °C. Thus, extrapolating the parameters of lifetime models developed using data from high‐temperature stress cycles experiments might result in erroneous lifetime estimations. This paper presents experimental results from power cycling tests on high‐power Insulated Gate Bipolar Transistors modules subjected to low temperature stress cycles of 30 and 40 °C. Therefore, devices experience still accelerated aging but with stress conditions much closer to the real application. Post‐mortem failure analysis has been performed on the modules reaching end‐of‐life in order to identify the failure mechanism. Finally, the number of cycles to end‐of‐life obtained experimentally is fit with a state‐of‐the‐art lifetime model to assess its validity at low temperature stress cycles. Challenges and limitations on data fitting to this lifetime model and the impact of various stress parameters on the anticipated failure are also presented.
Black hole parameter estimation with synthetic very long baseline interferometry data from the ground and from space
Authors: Roelofs Freek , Fromm Christian M. , Mizuno Yosuke , Davelaar Jordy , Janssen Michael , Younsi Ziri , Rezzolla Luciano , Falcke Heino 
Published: April 2021

Context.The Event Horizon Telescope (EHT) has imaged the shadow of the supermassive black hole in M 87. A library of general relativistic magnetohydrodynamics (GMRHD) models was fit to the observational data, providing constraints on black hole parameters.Aims.We investigate how much better future experiments can realistically constrain these parameters and test theories of gravity.Methods.We generated realistic synthetic 230 GHz data from representative input models taken from a GRMHD image library for M 87, using the 2017, 2021, and an expanded EHT array. The synthetic data were run through an automated data reduction pipeline used by the EHT. Additionally, we simulated observations at 230, 557, and 690 GHz with the Event Horizon Imager (EHI) Space VLBI concept. Using one of the EHT parameter estimation pipelines, we fit the GRMHD library images to the synthetic data and investigated how the black hole parameter estimations are affected by different arrays and repeated observations.Results.Repeated observations play an important role in constraining black hole and accretion parameters as the varying source structure is averaged out. A modest expansion of the EHT already leads to stronger parameter constraints in our simulations. High-frequency observations from space with the EHI rule out all but ∼15% of the GRMHD models in our library, strongly constraining the magnetic flux and black hole spin. The 1σconstraints on the black hole mass improve by a factor of five with repeated high-frequency space array observations as compared to observations with the current ground array. If the black hole spin, magnetization, and electron temperature distribution can be independently constrained, the shadow size for a given black hole mass can be tested to ∼0.5% with the EHI space array, which allows tests of deviations from general relativity. With such a measurement, high-precision tests of the Kerr metric become within reach from observations of the Galactic Center black hole Sagittarius A*.
Nonthermal phenomena in the center of Abell 1775
Authors: Botteon A. , Giacintucci S. , Gastaldello F. , Venturi T. , Brunetti G. , van Weeren R. J. , Shimwell T. W. , Rossetti M. , Akamatsu H. , Brüggen M. , Cassano R. , Cuciti V. , de Gasperin F. , Drabent A. , Hoeft M. , Mandal S. , Röttgering H. J. A. , Tasse C. 
Published: April 2021

Context. Thermal gas in the center of galaxy clusters can show substantial motions that generate surface-brightness and temperature discontinuities known as cold fronts. The motions may be triggered by minor or off-axis mergers that preserve the cool core of the system. The dynamics of the thermal gas can also generate radio emission from the intra-cluster medium (ICM) and impact the evolution of clusters’ radio sources.
Aims. We aim to study the central region of Abell 1775, a system in an ambiguous dynamical state at z = 0.072 which is known to host an extended head-tail radio galaxy, with the goal of investigating the connection between thermal and nonthermal components in its center.
Methods. We made use of a deep (100 ks) Chandra observation accompanied by LOFAR 144 MHz, GMRT 235 MHz and 610 MHz, and VLA 1.4 GHz radio data.
Results. We find a spiral-like pattern in the X-ray surface brightness that is mirrored in the temperature and pseudo-entropy maps. Additionally, we characterize an arc-shaped cold front in the ICM. We interpret these features in the context of a slingshot gas tail scenario. The structure of the head-tail radio galaxy “breaks” at the position of the cold front, showing an extension that is detected only at low frequencies, likely due to its steep and curved spectrum. We speculate that particle reacceleration is occurring in the outer region of this tail, which in total covers a projected size of ∼800 kpc. We also report the discovery of revived fossil plasma with ultra-steep spectrum radio emission in the cluster core together with a central diffuse radio source that is bounded by the arc-shaped cold front.
Conclusions. The results reported in this work demonstrate the interplay between thermal and nonthermal components in the cluster center and the presence of ongoing particle reacceleration in the ICM on different scales.
Dynamics of Human–Water Interactions in the Kilombero Valley, Tanzania: Insights from Farmers’ Aspirations and Decisions in an Uncertain Environment
Authors: Höllermann Britta , Näschen Kristian , Tibanyendela Naswiru , Kwesiga Julius , Evers Mariele 
Published: April 2021

AbstractThe Kilombero Valley, one of East Africa’s largest seasonal wetlands, is a high-potential agricultural development corridor area in Tanzania. This seasonally flooded wetland is mainly used by smallholder farmers who cultivate during the rainy season, although there are some community-based irrigation systems that reduce hydro-climatic risks. In this study, we aim to understand how farmers’ aspirations and visions about the future are related to the current agricultural practices and human–water interaction. We specifically investigate the differences between farmers from rainfed and irrigated agriculture by using focus group discussions. Analysis of the in-depth interviews highlights how farmers’ actions both shape and respond to this highly dynamic and uncertain environment. Furthermore, we identify a close link, driven by the farmers’ level of agency, between aspirations and expected agro-economic development. The heterogeneity of farmers’ agency and hence their ability to cope with change is not only based on the socioeconomic status but also on their perception of the physical environment. We thus recommend that attention is also paid to the capacity for coping with environmental challenges that influences the level of farmers’ aspiration.
Strengthening the Resilience of Vulnerable Communities: Results from a Quasi-experimental Impact Evaluation in Coastal Bangladesh
Authors: Béné Christophe , Haque Mahfuzul A. B. M. 
Published: April 2021

AbstractAt present, no clear consensus exists on how to assess resilience interventions in the field. In this paper we propose to measure the impact of the ECOFISH project, the objective of which was to strengthen the resilience of local fishing communities affected by recurrent crises in Bangladesh. The evaluation was based on a difference-in-difference (DiD) framework. The DiD analysis indicates that households who benefited from ECOFISH have a higher propensity to adopt positive responses than non-beneficiaries when hit by a shock. Those beneficiaries also report a statistically higher recovery rate (resilience). The analysis indicates however that the project did not manage to reduce the propensity of households to engage in detrimental coping strategies and that the long-term food and nutritional security of the beneficiaries has not yet visibly improved compared to the control group. Those different results are discussed in the light of the wider literature on resilience evaluation.
Formation of ultra-high-resistance Au/Ti/p-GaN junctions and the applications in AlGaN/GaN HEMTs
Authors: Zhou Guangnan , Jiang Yang , Yang Gaiying , Wang Qing , Fan Mengya , Jiang Lingli , Yu Hongyu , Xia Guangrui 
Published: April 2021

We report a dramatic current reduction, or a resistance increase, by a few orders of magnitude of two common-anode Au/Ti/p-GaN Schottky junctions annealed within a certain annealing condition window (600–700 °C, 1–4 min). Results from similar common-anode Schottky junctions made of Au/p-GaN, Al/Ti/p-GaN, and Au/Ti/graphene/p-GaN junctions demonstrated that all three layers (Au, Ti, and p-GaN) are essential for the increased resistance. Scanning-transmission electron microscopy, Hall, and Raman measurements have been performed to investigate the mechanisms. Moreover, this high-resistance junction structure was employed in p-GaN gate AlGaN/GaN high electron mobility transistors. It was shown to be an effective gate technology that was capable of boosting the gate breakdown voltage from 9.9 to 12.1 V with a negligible effect on the threshold voltage or the sub-threshold slope.
One-dimensional edge contact to encapsulated MoS2 with a superconductor
Authors: Seredinski A. , Arnault E. G. , Costa V. Z. , Zhao L. , Larson T. F. Q. , Watanabe K. , Taniguchi T. , Amet F. , Newaz A. K. M. , Finkelstein G. 
Published: April 2021

Establishing ohmic contact to van der Waals semiconductors such as MoS2 is crucial to unlocking their full potential in next-generation electronic devices. Encapsulation of few layer MoS2 with hBN preserves the material’s electronic properties but makes electrical contacts more challenging. Progress toward high quality edge contact to encapsulated MoS2 has been recently reported. Here, we evaluate a contact methodology using sputtered MoRe, a type II superconductor with a relatively high critical field and temperature commonly used to induce superconductivity in graphene. We find that the contact transparency is poor and that the devices do not support a measurable supercurrent down to 3 K, which has ramifications for future fabrication recipes.
Comparison of atmospheric pressure argon producing O(1S) and helium plasma jet on methylene blue degradation
Authors: Jaiswal S. , Aguirre E. M. 
Published: April 2021

A solution of methylene blue dye was degraded under an atmospheric pressure plasma jet operating in a linear field configuration with pure argon or pure helium as working gases. Optical emission spectroscopy was carried out to understand the reactive species present with and without dye treatment. Both plasma jets contain reactive species such as OH, N2, and atomic oxygen (O). However, atomic oxygen takes a greatly different form depending on the working gas. In the argon plasma jet, we observe that most of the atomic oxygen produced is the O(1S)–O(1D) transition that also leads to the green colored plasma plume. On the other hand, the helium plasma jet produces the well known triplet states of oxygen at 777 and 844 nm. The absorption spectra confirmed the faster and more energy efficient degradation of the methylene blue dye when treated by the argon plasma jet. Argon plasma with enhanced atomic oxygen content can be utilized as a cheaper and efficient method for waste water treatment.
Learning the molecular grammar of protein condensates from sequence determinants and embeddings
Authors: Saar Kadi L. , Morgunov Alexey S. , Qi Runzhang , Arter William E. , Krainer Georg , Lee Alpha A. , Knowles Tuomas P. J. 
Published: April 2021

Significance
The tendency of many cellular proteins to form protein-rich biomolecular condensates underlies the formation of subcellular compartments and has been linked to various physiological functions. Understanding the molecular basis of this fundamental process and predicting protein phase behavior have therefore become important objectives. To develop a global understanding of how protein sequence determines its phase behavior, we constructed bespoke datasets of proteins of varying phase separation propensity and identified explicit biophysical and sequence-specific features common to phase-separating proteins. Moreover, by combining this insight with neural network-based sequence embeddings, we trained machine-learning classifiers that identified phase-separating sequences with high accuracy, including from independent external test data.
Cotranscriptional R-loop formation by Mfd involves topological partitioning of DNA
Authors: Portman James R. , Brouwer Gwendolyn M. , Bollins Jack , Savery Nigel J. , Strick Terence R. 
Published: April 2021

Significance
R-loop structures pose a threat to genomic integrity because their formation can lead to mutagenesis. Mutagenesis drives antibiotic resistance in bacteria and chemotherapy resistance in human cancers; therefore, it is important to understand how R-loops form. Using a combination of in vitro single-molecule experimentation and in vivo mutagenesis assays, we have shown how Mfd, a bacterial protein known for its role in DNA repair, can interact with RNA polymerase to form R-loops. This interaction generates a topological domain in DNA that is highly prone to R-loop formation. The observed mechanism relies on properties of Mfd that are shared by many other proteins, hinting that this is a potentially universal model for R-loop formation.
BABEL enables cross-modality translation between multiomic profiles at single-cell resolution
Authors: Wu Kevin E. , Yost Kathryn E. , Chang Howard Y. , Zou James 
Published: April 2021

Significance
Simultaneous measurement of the DNA, RNA, and proteins of single cells can lead to important new insights but is experimentally challenging. This work introduces a deep learning algorithm that flexibly translates between chromatin, RNA, and protein profiles in single cells. This makes it possible to computationally synthesize matched multiomic measurements when only one modality is experimentally available. This algorithm complements experimental advances to efficiently achieve single-cell multiomic insight.
Riboflavin instability is a key factor underlying the requirement of a gut microbiota for mosquito development
Authors: Wang Yin , Eum Jai Hoon , Harrison Ruby E. , Valzania Luca , Yang Xiushuai , Johnson Jena A. , Huck Derek T. , Brown Mark R. , Strand Michael R. 
Published: April 2021

SignificanceMosquitoes are major disease vectors that require a gut microbiota for development into adults under some conditions but not others. To determine the underlying mechanisms for this variation, we determined that dietary riboflavin rapidly decays under most environmental conditions that mosquitoes experience, which makes larvae reliant on their gut microbiota for this essential micronutrient. Our findings illustrate the value of being able to both control and manipulate dietary nutrients, microbiota composition, and environmental conditions in studying the role of gut microbes in animal biology. Our results also suggest environmental conditions are an understudied variable in why the gut microbiota is essential for provisioning certain essential vitamins in aquatic organisms like mosquito larvae.
Design of 1300 nm spectral domain optical coherence tomography angiography system for iris microvascular imaging
Authors: Lan Gongpu , Xu Jingjiang , Hu Zhilin , Huang Yanping , Wei Yingzhao , Yuan Xing , Liu Huazong , Qin Jia , Wang Yicheng , Shi Qun , Zeng Jun , Shi Yue , Feng Jinping , Tan Haishu , An Lin , Wei Xunbin 
Published: April 2021

Abstract
Developing a high-resolution non-invasive optical coherence tomography angiography (OCTA) method for iris vasculature imaging is essential for diagnosing a wide range of ocular pathologies. However, the current iris-OCTA devices are still limited in imaging quality and penetration depth for dark-colored eyes ranging from brown to dark brown. A spectral domain iris-OCTA system is presented in this paper incorporating a 1300 nm wavelength for deeper tissue penetration, a linear-wavenumber spectrometer for better detection sensitivity, and an iris scan objective lens for better optical focusing across the entire iris over a 12 × 12 mm2 scan field. The −6 dB fall-off range is ∼3 mm, and the maximum sensitivity fall-off is −28.57 dB at 6.94 mm. The axial resolution is 15.1 ± 3.2 μm. The 40 mm focal-length iris scan objective is optimized based on the ocular parameters from 100 Asian participants’ left eyes, and it has a diffraction-limited lateral resolution (14.14 μm) for the iris, in general. OCT distortions were calibrated based on the average ocular parameters, and the maximum residual distortions in both the lateral and axial directions were <0.1 mm (2.0%) for all of the eyes. A pilot study on a constricted pupil was performed to demonstrate high-contrast, wide-field en face iris microvascular imaging by either a horizontal or vertical fast-scan protocol in a dark brown eye. The iris vessels are radially aligned, and each vessel is more visible when it has an angle of ∼65°–90° with respect to the fast-scan direction. A new circular fast-scan protocol could improve image quality for better visualization of the iris features or integration with image-registration algorithms and an eye-tracking system for eye-motion compensation.
Structure of levitated Si–Ge melts studied by high-energy x-ray diffraction in combination with reverse Monte Carlo simulations
Authors: Pozdnyakova Irina , Roik Oleksandr , Drewitt James W E , Bytchkov Aleksei , Kargl Florian , Jahn Sandro , Brassamin Séverine , Hennet Louis 
Published: April 2021

Abstract
The short-range order in liquid Si, Ge and binary Si
x
–Ge1−x
alloys (x = 0.25, 0.50, 0.75) was studied by x-ray diffraction and reverse Monte Carlo simulations. Experiments were performed in the normal and supercooled liquid states by using the containerless technique of aerodynamic levitation with CO2 laser heating, enabling deeper supercooling of liquid Si and Si–Ge alloys than previously reported. The local atomic structure of liquid Si and Ge resembles the β-tin structure. The first coordination numbers of about 6 for all compositions are found to be independent of temperature indicating the supercooled liquids studied retain this high-density liquid (HDL) structure. However, there is evidence of developing local tetrahedral ordering, as manifested by a shoulder on the right side of the first peak in S(Q) which becomes more prominent with increasing supercooling. This result is potentially indicative of a continuous transition from the stable HDL β-tin (high pressure) phase, towards a metastable low-density liquid phase, reminiscent of the diamond (ambient pressure) structure.
Effective velocities of polaron spin states in monolayer transition metal dichalcogenides
Authors: Sun Yong , Ma Xu-Fei , Liu Xiao-Yi , Cui Yu , Deng Jia-Pei , Xiao Yao , Li Zhi-Qing , Wang Zi-Wu 
Published: April 2021

Abstract
We propose a theoretical model for studying the effective velocities of polaron spin states in monolayer transition metal dichalcogenides (TMDS) on the substrate. It is found that the effective velocity of polaron shows the splitting with different magnitudes due to the Rashba spin–orbit coupling, which results in the reversed distribution of the effective velocities of polaron spin states. Moreover, the reversed points depend on the truncated wave-vector of optical phonon and can be modulated by the polarity of substrate and the internal distance between monolayer TMDS and substrate. These theoretical results enlighten some simple ways to distinguish and modulate the polaron spin states in two-dimensional heterostructures.
Torsional moduli of transition metal dichalcogenide nanotubes from first principles
Authors: Bhardwaj Arpit , Sharma Abhiraj , Suryanarayana Phanish 
Published: April 2021

AbstractWe calculate the torsional moduli of single-walled transition metal dichalcogenide (TMD) nanotubes usingab initiodensity functional theory (DFT). Specifically, considering forty-five select TMD nanotubes, we perform symmetry-adapted DFT calculations to calculate the torsional moduli for the armchair and zigzag variants of these materials in the low-twist regime and at practically relevant diameters. We find that the torsional moduli follow the trend: MS2> MSe2> MTe2. In addition, the moduli display a power law dependence on diameter, with the scaling generally close to cubic, as predicted by the isotropic elastic continuum model. In particular, the shear moduli so computed are in good agreement with those predicted by the isotropic relation in terms of the Young’s modulus and Poisson’s ratio, both of which are also calculated using symmetry-adapted DFT. Finally, we develop a linear regression model for the torsional moduli of TMD nanotubes based on the nature/characteristics of the metal-chalcogen bond, and show that it is capable of making reasonably accurate predictions.
High-sensitivity tactile sensor based on Ti2C-PDMS sponge for wireless human–computer interaction
Authors: Sun Peng , Wu Dongping , Liu Chaoran 
Published: April 2021

Abstract
Tremendous attention has been paid to high-performance flexible tactile sensors owing to their potential applications in bionic skin, wearable electronics, the Internet of Things, etc. However, the majority of pressure sensors require an intricately designed nanostructure requiring a high-cost complex manufacturing process. Therefore, the high-throughput and low-cost technology to produce high-sensitivity, flexible, pressure-sensitive materials with a large responding range is urgently needed. Herein, a novel flexible piezoresistive tactile sensor is fabricated based on the Ti2C-PDMS sponge as the conductive elastomer. The sensor exhibits a high sensitivity of 279 kPa−1 in a wide pressure range (0–34.4 kPa). The response time is as fast as 0.45 s with excellent durability over 4,000 cycles. Moreover, a 16-pixel wireless sensor system is fabricated and a series of applications have been demonstrated, including real-time force perception and pressure morphology feedback, which promote the potential applications in the visualizing of pressure distribution, human–machine communication and wearable devices.