bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress wave propagation and fracture formation in cyclotetramethylene tetranitramine (HMX)-Estane polymer bonded explosive under impact loading: A mesoscale numerical simulation
Authors: Ge Siyu , Yuan Shuai , Yang Guoli , Zhu Qing , Li Shangbin , Dou Yusheng
Published: April 2021

The stress wave propagation and fracture formation in HMX-Estane polymer-bonded explosive under an impact loading were studied using material point method mesoscale simulation. The stress wave propagation, temperature localizations, and material fracture behaviors were analyzed for various impact velocities, porosities, and binder volume fractions. The peak value of local longitudinal stress, due to stress wave propagation and reflection upon impact loading, was found to be higher for a larger impact velocity but lower for a greater porosity or a binder volume fraction. A spall fracture was observed in the strong tensile zones formed by the reflected wave. Greater damage was observed for either a higher impact velocity or a larger porosity. The plastic dissipation, frictional dissipation, and viscoelastic dissipation were all found to be a lead for hotspots. This study provides mesoscale explanations for stress wave propagation, the fracture mechanism, and the formation of hotspots in energetic materials.
Design of JT-60SA core Thomson scattering diagnostic system
Authors: Tojo H. , Pasqualotto R. , Fassina A. , Giudicotti L. , Sasao H. , Homma H. , Oyama N.
Published: April 2021

An incoherent Thomson scattering diagnostic will be installed in the JT-60SA tokamak to measure electron temperature and electron density profiles. The target radial spatial resolution is 25 mm with 46 spatial channels. The accuracy in electron temperature and density is a few percent at ne = 7.5 × 1019 m−3, which is the expected value in the plasma core. This paper presents the designs of collection optics, fibers with their alignment system, and polychromators. The collection optics overcomes unique issues for superconducting fusion devices, i.e., limited design space, high-temperature measurements, and harsh radiation condition. When in several years the more performing plasma will generate intense nuclear radiation, the lens materials of the optics can be replaced by radiation resistant glasses without major changes in the lens holder. It will prevent transmission degradation and keep stable measurement accuracy.
Homogenous nucleation rate of CO2 hydrates using transition interface sampling
Authors: Arjun A. , Bolhuis Peter G.
Published: April 2021

Carbon dioxide and water can form solid clathrate structures in which water cages encapsulate the gas molecules. Such hydrates have sparked much interest due to their possible application in CO2 sequestration. How the solid structure forms exactly from the liquid phase via a homogenous nucleation process is still poorly understood. This nucleation event is rare on the molecular timescale even under moderate undercooling or supersaturation conditions because of the large free energy barrier toward crystallization, rendering a brute force simulation of hydrate nucleation unfeasible for moderate undercooling or supersaturation. Here, we perform transition interface sampling simulations to quantify the homogenous nucleation rate for CO2 hydrate formation using accurate atomistic force fields at 500 bars for three different temperatures between 260 and 273 K. Collecting more than 100 000 pathways comprising roughly two milliseconds of simulation time, we computed a nucleation rate in the amorphous phase of ∼1021 nuclei s−1 cm−3 for a temperature of 260 K and a rate of ∼1012 nuclei s−1 cm−3 for a temperature of 265 K. For a temperature of 273 K, we find that the hydrate forms an sI crystalline phase with a rate of order of ∼101 nuclei s−1 cm−3. We compare these rates to classical nucleation theory estimates as well as experiments, and to nucleation rate estimates for methane hydrates and discuss possible causes of the observed differences. Our findings shed light on the kinetics of this important clathrate and should assist in future hydrate formation investigation.
Electronic properties and tunability of the hexagonal SiGe alloys
Authors: Wang Zhen , Zhang Zhaofu , Liu Sheng , Robertson John , Guo Yuzheng
Published: April 2021

Hexagonal (2H) germanium is found to be a direct bandgap semiconductor, showing the potential of efficient light emission. Based on 2H–Ge, the structure and electronic properties of 2H–SiGe alloys are studied in detail by hybrid functional calculations. By varying the Si content of the 2H–SiGe alloys, the bandgap is found to be direct for Si contents smaller than 0.35. We find that the key factor in determining the indirect-to-direct transition of the band structures for 2H–SiGe alloys originates from the variation of lattice constant. Furthermore, the Si-rich 2H–SiGe alloy can be changed from indirect to direct bandgap by strain engineering. Furthermore, we consider the effective electron masses (me), band alignments with several oxides, optical absorption properties, and vacancy formation energies of 2H–SiGe alloys, which show that the direct-gap 2H–SiGe alloys have the potential for optoelectronic applications.
Detection of ultra-weak laser pulses by free-running single-photon detectors: Modeling dead time and dark counts effects
Authors: Georgieva Hristina , Meda Alice , Raupach Sebastian M. F. , Hofer Helmuth , Gramegna Marco , Degiovanni Ivo Pietro , Genovese Marco , López Marco , Kück Stefan
Published: April 2021

In quantum communication systems, the precise estimation of the detector´s response to the incoming light is necessary to avoid security breaches. The typical working regime uses a free-running single-photon avalanche diode in combination with attenuated laser pulses at telecom wavelength for encoding information. We demonstrate the validity of an analytical model for this regime that considers the effects of dark counts and dead time on the measured count rate. For the purpose of gaining a better understanding of these effects, the photon detections were separated from the dark counts via a software-induced gating mechanism. The model was verified by experimental data for mean photon numbers covering three orders of magnitude as well as for laser repetition frequencies below and above the inverse dead time. Consequently, our model would be of interest for predicting the detector response not only in the field of quantum communications, but also in any other quantum physics experiment where high detection rates are needed.
Phase variation in the locked state of mutually synchronized spin torque nano-oscillators
Authors: Jenkins Alex. S. , Martins Leandro , Benetti Luana , Alvarez Lara San Emeterio , Freitas Paulo P. , Ferreira Ricardo
Published: April 2021

Spin torque nano-oscillators (STNOs) have been shown to efficiently “lock” to electrical signals whether these are from external sources, self-reflected signals, or other STNOs via mutual synchronization. Traditionally, the locked state of an STNO has been considered digital, either “ON” or “OFF.” In this report, we show how the phase in the locked state can vary significantly as a function of the applied dc to the STNO with the phase strongly affecting the emitted power. This phase dependence demonstrates the analogue nature of the locked state, offering an extra degree of freedom when designing STNO-based neural networks.
Automodulation instability in gyrotrons operating at the second cyclotron harmonic
Authors: Fokin A. P. , Bakunin V. L. , Glyavin M. Yu. , Nusinovich G. S.
Published: April 2021

Interest in gyrotron operation at cyclotron harmonics is motivated by the users' desire to reduce the magnetic fields required for operation at a given frequency. However, operation at harmonics is more complicated than at the fundamental resonance because in harmonic gyrotrons there are many parasitic modes at the fundamental, which can be prone to excitation. The present study is devoted to the analysis of automodulation instability in harmonic gyrotrons. Such instability may occur, for example, when in the vicinity of the desired second harmonic mode there is a pair of parasitic modes at the fundamental, for the frequencies and azimuthal indices of which some specific conditions are met. In this paper, the equations describing this instability are derived in the cold-cavity approximation. The study is then focused on a second harmonic gyrotron with the parameters optimal for efficient operation. For such a gyrotron, the region of instability is determined in the plane of frequency mismatches between the operating and parasitic modes. This treatment performed within the framework of the general theory is complemented by consideration of some gyrotrons operating in specific modes, which are surrounded by specific sideband modes at the fundamental.
Point defects in crystals of charged colloids
Authors: Alkemade Rinske M. , de Jager Marjolein , van der Meer Berend , Smallenburg Frank , Filion Laura
Published: April 2021

Charged colloidal particles—on both the nano and micron scales—have been instrumental in enhancing our understanding of both atomic and colloidal crystals. These systems can be straightforwardly realized in the lab and tuned to self-assemble into body-centered-cubic (BCC) and face-centered-cubic (FCC) crystals. While these crystals will always exhibit a finite number of point defects, including vacancies and interstitials—which can dramatically impact their material properties—their existence is usually ignored in scientific studies. Here, we use computer simulations and free-energy calculations to characterize vacancies and interstitials in FCC and BCC crystals of point-Yukawa particles. We show that, in the BCC phase, defects are surprisingly more common than in the FCC phase, and the interstitials manifest as so-called crowdions: an exotic one-dimensional defect proposed to exist in atomic BCC crystals. Our results open the door to directly observe these elusive defects in the lab.
Magnonics in collinear magnetic insulating systems
Authors: Flebus B.
Published: April 2021

In the last decades, collinear magnetic insulating systems have emerged as promising energy-saving information carriers. Their elementary collective spin excitations, i.e., magnons, can propagate for long distances bypassing the Joule heating effects that arise from electron scattering in metal-based devices. This Tutorial article provides an introduction to theoretical and experimental advances in the study of magnonics in collinear magnetic insulating systems. We start by outlining the quantum theory of spin waves in ferromagnetic and antiferromagnetic systems, and we discuss their quantum statistics. We review the phenomenology of spin and heat transport of the coupled coherent and incoherent spin dynamics and the interplay between magnetic excitations and lattice degrees of freedom. Finally, we introduce the reader to the key ingredients of two experimental probes of magnetization dynamics, spin transport and NV-center relaxometry setups, and discuss experimental findings relevant to the outlined theory.
Dynamics of interfacial carriers and negative photoconductance in CH3NH3PbBr3-ZnO heterostructure
Authors: Chen Feng , Shi Zengliang , Chen Jinping , Cui Qiannan , Jian Aoqun , Zhu Yizhi , Xu Qingyu , Lou Zhidong , Xu Chunxiang
Published: April 2021

Understanding the interfacial charge transfer process and its dynamical mechanism is crucial to design efficient photoelectric devices. Methylammonium lead halide perovskite and zinc oxide (ZnO) have been demonstrated as promising candidates for excellent solar cells and photodetectors. However, the carrier transport process has not yet been fully explored on the perovskite surface and the perovskite/ZnO interface. Herein, a CH3NH3PbBr3-ZnO heterojunction was constructed as a quasi-phototransistor, where an apparent negative photoconductance was observed under illumination. Based on electrical and optical characterization, the photogenerated carrier transfer dynamics at CH3NH3PbBr3, ZnO, and their interface were investigated in detail. It can be assigned that the photogenerated electrons transfer toward the CH3NH3PbBr3 surface and the holes transfer to interior, so that the light-induced built-in electric field change would serve as the photogate to control the current flowing in the CH3NH3PbBr3-ZnO channel. These results provide clear images on the charge diffusion and drift process in the CH3NH3PbBr3-ZnO heterostructure. The study on the dynamics of negative photoconductivity of CH3NH3PbBr3-ZnO has great value for understanding the carrier transport properties and constructing perovskite heterostructure memory and optical switching devices.
Origins of the enhanced broadband absorption in black silicon
Authors: Kecebas Muhammed Ali , Pirouzfam Niloufar , Sendur Kursat
Published: April 2021

Although black silicon is utilized in a wide range of applications due to its broadband spectral emission and absorption, the underlying electromagnetic mechanisms are not well explored. In this study, the underlying phenomena that are responsible for these enhanced spectral features are investigated. The absorption spectra of the black silicon with random textures are analyzed, and the electromagnetic mechanisms that drive elevated absorption are explored. Our findings reveal that two separate electromagnetic phenomena occur in the textures, effective wavelength matching and waveguide modes. Detailed analysis reveals that the occurrence condition of those phenomena is highly dependent on the dimensions of the textures in the transverse direction. The effect of the texture dimensions and doping concentration both on absorption characteristics and physical phenomena is analyzed in detail. The findings of this study explain the absorption mechanisms of black silicon observed in experimental studies, which can lead to designer materials with rough surfaces for the desired spectral emissivity.
Interlayer configurations of self-assembled folded graphene
Authors: Bockhorn L. , Rode J. C. , Gnörich L. , Zuo P. , Brechtken B. , Haug R. J.
Published: April 2021

The relative orientation between atomic lattices in twisted bilayer graphene opens up a whole new field of rich physics. So, the study of self-assembled twisted bilayer graphene gives deep insight into its underlying growth process. Cuts in monolayer graphene via the atomic force microscopy technique are used to start self-assembly and to generate a folding process. The final configurations for this self-assembly process are investigated. Here, the focus is on structures that arise from one cut. During the self-assembly, these structures not only move forward but also rotate. As it turns out, the final positions for all studied structures can be assigned to commensurate interlayer configurations.
Flow in a ring-sheared drop: Drop deformation
Authors: Riley F. P. , McMackin P. M. , Lopez J. M. , Hirsa A. H.
Published: April 2021

The ring-sheared drop is a containerless system where shear is imparted by two contact rings, one rotating and the other stationary. In microgravity, aqueous drops can be studied in the air at the centimeter scale. Drops of this scale can also be studied experimentally on Earth, but the effects of gravity need to be mitigated by density matching the drop liquid and its surrounding fluid. The use of silicone oil drops surrounded by an aqueous solution allows density matching while retaining the viscosity ratio of the aqueous-air system in microgravity. The imposed shear drives a meridional flow in the drop which leads to a pear-shaped drop. A perturbation analysis with the capillary number as the small parameter is used to account for this mean drop deformation. The theory and time-averaged experiments agree, particularly at smaller ring rotation rates where the capillary number in the experiments is smaller. On top of the mean deformation, there is a smaller amplitude nonaxisymmetric deformation, which for slower ring rotation rates consists of a rotating wave with azimuthal wavenumber m = 1, that is, synchronous with the rotating ring. This is traced back to imperfections in the wetting and contact between the drop and the rotating ring in the experiment. At larger ring rotations, the experiments detect further unsteadiness with a broad frequency peak at about one third the ring rotation rate. Nonlinear simulations of the outer flow, assuming a nondeforming drop, find that at these ring rotations, the outer flow is unsteady with a similar frequency peak.
Characterization of MOCVD-grown AlSiO gate dielectric on β-Ga2O3 (001)
Authors: Jian Zhe (Ashley) , Sayed Islam , Liu Wenjian , Mohanty Subhajit , Ahmadi Elaheh
Published: April 2021

The interface and bulk properties of aluminum-silicon-oxide (AlSiO) dielectric grown by metal-organic chemical vapor deposition (MOCVD) on (001) β-Ga2O3 were investigated systematically using a deep UV-assisted capacitance–voltage methodology. The improved surface preparation with a combination of UV-ozone and wet chemical treatment reduced near-interface traps resulting in a negligible hysteresis. An average interface state density of 6.63 × 1011 cm−2 eV−1 and AlSiO bulk trap density of 4.65 × 1017 cm−3 eV−1 were quantified, which is half of that for Al2O3 deposited by atomic layer deposition (ALD). A net positive interface fixed charge of 1.56 × 1012 cm−2 was measured. In addition, a high dielectric breakdown field of ∼7.8 MV/cm and more effective suppression of gate leakage were achieved on these devices compared with ALD-Al2O3 on similar metal-oxide-semiconductor (MOS) structures.
Non-Bayesian social learning model with periodically switching structures
Authors: Ha Yuankai , Guo Yao , Lin Wei
Published: April 2021

In this article, we investigate the dynamics of non-Bayesian social learning model with periodically switching structures. Unlike the strongly connectedness conditions set for the temporal connecting networks of the non-Bayesian social learning to guarantee its convergence in the literature, our model configurations are essentially relaxed in a manner that the connecting networks in every switching duration can be non-strongly connected. Mathematically and rigorously, we validate that, under relaxed configurations, dynamics of our model still converge to a true state of social learning in a particular sense of probability. Additionally, we provide estimations on the convergence rate for successful social learning in our model. Numerically, we demonstrate the efficacy of the analytically established conditions and estimations by using some representative examples with switching structures. We believe that our results could be potentially useful for illustrating the social activities in the real world.
Initial spreading dynamics of a liquid droplet: The effects of wettability, liquid properties, and substrate topography
Authors: Du Jiayu , Chamakos Nikolaos T. , Papathanasiou Athanasios G. , Min Qi
Published: April 2021

The initial spreading of glycerol and silicon oil droplets on smooth, corrugated, and orthogonal surfaces is numerically investigated by an effective, sharp-interface modeling method. In this study, the temporal evolution of spreading radius during the initial phase is scaled by R/R0 = C(t/τi)α for inertial regime and R/R0 = C(t/τμ)α for the viscous regime. We focus on exploring how wettability, liquid properties, and substrate topography influence the exponent α and coefficient C. Instead of discussing the effects of density, viscosity, and surface tension separately, we use the Ohnesorge number Oh = μ/(ρD0γ)1/2 to unify the combined influence of liquid properties. The results show that in the inertial regime (Oh ≪ 1), α is determined by wettability and the capillary wave is observed to propagate along the droplet interface, whereas in the viscous regime (Oh ≫ 1), α is determined by Oh and no capillary wave is observed. Consequently, both qualitative (propagation of capillary wave) and quantitative (Ohnesorge number) criteria to distinguish the two distinct regimes are provided. Regarding the coefficient C, it is found to increase with the increasing hydrophilicity and decreasing Oh in the inertial regime. A larger C is also observed in orthogonal microgrooves with wider gap or narrower width. Besides, the hydrophobicity and hydrophilicity can be enhanced by the corrugated surfaces, inducing a higher and lower α on hydrophilic and hydrophobic corrugated surfaces, respectively. Meanwhile, some interesting phenomena are also observed, such as the faster contact line velocity on the inside of a single corrugation and the “stick-jump” advancing mode of the contact line on orthogonal surfaces.
Wake structure characteristics of three tandem circular cylinders at a low Reynolds number of 160
Authors: Zhu Hongjun , Zhong Jiawen , Zhou Tongming
Published: April 2021

This paper reports the results of a numerical investigation into the flow around three isodiametric circular cylinders placed in an in-line configuration with identical spacing and the associated wake structures. The effect of spacing ratio (L/D, where L is the center-to-center spacing between two adjacent cylinders and D is the cylinder diameter) ranging from 1.5D to 10D with increment of 0.5D is examined at a low Reynolds number of 160. The results indicate that the wake structure experiences three evolutions as L/D increases, exhibiting four combined flow patterns: the overshoot, continuous reattachment-alternate reattachment (CR-AR), quasi-co-shedding (QCS), and co-shedding-co-shedding regimes. More than one frequency participates in the lift fluctuation for all three cylinders in the latter three patterns, signifying the wake interference. The evolution of the flow regime results in the variations of drag and lift coefficients, the alteration of pressure distribution around the cylinders' surface, and the switching of the phase lags of fluctuating lifts as well as the modification of vortex shedding characteristics, including the vortex formation location, wake width, and shedding frequencies. Particularly, the fluid forces and Strouhal number for the upstream and middle cylinders present a jump in the transition from the CR-AR to QCS regimes, while the fluid forces are reduced for the downstream cylinder. Furthermore, the transition from two layered vortices to the secondary vortex street is observed at 3.5 < L/D ≤ 6.5, where the downstream cylinder is sandwiched between the two shear layers detached from the middle cylinder, and two same-sign vortices in the same layer merge into a new vortex in the far wake.
Metabolic profiling of epidermal and mesophyll tissues under water-deficit stress in
Authors: Mayer Jesse A. , Wone Bernard W. M. , Alexander Danny C. , Guo Lining , Ryals John A. , Cushman John C.
Published: April 2021

Cactus pear (Opuntia ficus-indica) is a high productivity species within the Cactaceae grown in many semiarid parts of the world for food, fodder, forage, and biofuels. O. ficus-indica utilises obligate crassulacean acid metabolism (CAM), an adaptation that greatly improves water-use efficiency (WUE) and reduces crop water usage. To better understand CAM-related metabolites and water-deficit stress responses of O. ficus-indica, comparative metabolic profiling was performed on mesophyll and epidermal tissues collected from well-watered and water-deficit stressed cladodes at 50% relative water content (RWC). Tissues were collected over a 24-h period to identify metabolite levels throughout the diel cycle and analysed using a combination of acidic/basic ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) and gas chromatography/mass spectrometry (GC/MS) platforms. A total of 382 metabolites, including 210 (55%) named and 172 (45%) unnamed compounds, were characterised across both tissues. Most tricarboxylic acid (TCA) cycle and glycolysis intermediates were depleted in plants undergoing water-deficit stress indicative of CAM idling or post-idling, while the raffinose family oligosaccharides (RFO) accumulated in both mesophyll and epidermal tissues as osmoprotectants. Levels of reduced glutathione and other metabolites of the ascorbate cycle as well as oxylipins, stress hormones such as traumatic acid, and nucleotide degradation products were increased under water-deficit stress conditions. Notably, tryptophan accumulation, an atypical response, was significantly (24-fold) higher during all time points in water-deficit stressed mesophyll tissue compared with well-watered controls. Many of the metabolite increases were indicative of a highly oxidising environment under water-deficit stress. A total of 34 unnamed metabolites also accumulated in response to water-deficit stress indicating that such compounds might play important roles in water-deficit stress tolerance.
Global inequality remotely sensed
Authors: Mirza M. Usman , Xu Chi , Bavel Bas van , van Nes Egbert H. , Scheffer Marten
Published: April 2021

Significance

Reliable data on economic inequality are largely limited to North America and Western Europe. As a result, we know the least about areas where inequality presents the most serious developmental policy challenge. We demonstrate that spatial variation in night-light emitted per person can reflect the distribution of income. This allows us to map global patterns and trends in economic inequality using remote sensing.
Physical mixing in coastal waters controls and decouples nitrification via biomass dilution
Authors: Haas Sebastian , Robicheau Brent M. , Rakshit Subhadeep , Tolman Jennifer , Algar Christopher K. , LaRoche Julie , Wallace Douglas W. R.
Published: April 2021

Significance

Changes in both quantity and speciation of nitrogen in coastal waters impact phytoplankton communities, contributing to eutrophication and harmful algal blooms. Multidisciplinary oceanographic time series of high resolution are rare but crucial for identifying complex mechanisms that underlie such anthropogenic impacts. Analysis and modeling of such a time series from a seasonally stratified fjord showed that dilution of nitrifier biomass by variable winter mixing altered the timing and rates of nitrification, which converts ammonia to nitrite and nitrate. This reveals a link among climate-sensitive physical dynamics, nitrifier abundance, and diversity, with controls on phytoplankton ecology. The findings imply that explicit measurement and modeling of microbial communities will be required to project impacts of climate change on coastal ecosystems.
Supporting social hierarchy is associated with White police officers’ use of force
Authors: Swencionis Jillian K. , Pouget Enrique R. , Goff Phillip Atiba
Published: April 2021

Significance

We test whether White police officers who endorse social hierarchies are more likely than less hierarchy-supportive White police officers to use physical force when interacting with residents. In three United States cities, we found that White police officers with relatively higher social dominance orientation (SDO) were more likely than lower-SDO White officers to use force when interacting with residents. Black police officers, who hold a lower-status racial identity, showed nonsignificant or negative relationships between SDO and use of force. That White officers’ orientation toward enforcing hierarchies predicts their rate of force in three cities suggests the need for closer examination of how hierarchy maintenance relates to police use of force.
A multi-omics approach to lignocellulolytic enzyme discovery reveals a new ligninase activity from
Parascedosporium putredinis
NO1
Authors: Oates Nicola C. , Abood Amira , Schirmacher Alexandra M. , Alessi Anna M. , Bird Susannah M. , Bennett Joseph P. , Leadbeater Daniel R. , Li Yi , Dowle Adam A. , Liu Sarah , Tymokhin Vitaliy I. , Ralph John , McQueen-Mason Simon J. , Bruce Neil C.
Published: April 2021

Significance

Lignocellulose, in the form of crop residues, presents an attractive alternative to crude oil for both the production of renewable fuels and chemicals. Its large-scale application as a feedstock, however, remains limited. A bottleneck in its implementation is the presence of lignin that envelopes the structure, physically blocking access to sugar-rich polymers that lie beneath. Here, we describe the isolation of an exceptional lignocellulose-degrading fungus that produces new oxidase activity with no cofactor requirements. This enzyme cleaves β-ether units in lignin-releasing tricin, a flavonoid of pharmaceutical potential, from the lignin macromolecule. Furthermore, we demonstrate that treatments with this enzyme can increase the digestibility of lignocellulosic biomass, offering the possibility of producing a valuable product from lignin while decreasing processing costs.
Acquisition of optimal TFH cell function is defined by specific molecular, positional, and TCR dynamic signatures
Authors: Padhan Kartika , Moysi Eirini , Noto Alessandra , Chassiakos Alexander , Ghneim Khader , Perra Maria Maddalena , Shah Sanjana , Papaioannou Vasilis , Fabozzi Giulia , Ambrozak David R. , Poultsidi Antigoni , Ioannou Maria , Fenwick Craig , Darko Samuel , Douek Daniel C. , Sekaly Rafick-Pierre , Pantaleo Giuseppe , Koup Richard A. , Petrovas Constantinos
Published: April 2021

Significance

We characterized the heterogeneity of human TFH cells at a cellular, molecular, functional, and positional level and revealed possible mechanistic links between relevant determinants of this heterogeneity. Linking the topology with specific molecular profile and function is a key aspect in the understanding of the role of particular TFH cell subsets in the pathogenesis of relevant diseases and the delivery of optimal help to GC B cells for the development of potent neutralizing antibodies.
Thermal niches of planktonic foraminifera are static throughout glacial–interglacial climate change
Authors: Antell Gawain T. , Fenton Isabel S. , Valdes Paul J. , Saupe Erin E.
Published: April 2021

Abiotic niche lability reduces extinction risk by allowing species to adapt to changing environmental conditions in situ. In contrast, species with static niches must keep pace with the velocity of climate change as they track suitable habitat. The rate and frequency of niche lability have been studied on human timescales (months to decades) and geological timescales (millions of years), but lability on intermediate timescales (millennia) remains largely uninvestigated. Here, we quantified abiotic niche lability at 8-ka resolution across the last 700 ka of glacial–interglacial climate fluctuations, using the exceptionally well-known fossil record of planktonic foraminifera coupled with Atmosphere–Ocean Global Climate Model reconstructions of paleoclimate. We tracked foraminiferal niches through time along the univariate axis of mean annual temperature, measured both at the sea surface and at species’ depth habitats. Species’ temperature preferences were uncoupled from the global temperature regime, undermining a hypothesis of local adaptation to changing environmental conditions. Furthermore, intraspecific niches were equally similar through time, regardless of climate change magnitude on short timescales (8 ka) and across contrasts of glacial and interglacial extremes. Evolutionary trait models fitted to time series of occupied temperature values supported widespread niche stasis above randomly wandering or directional change. Ecotype explained little variation in species-level differences in niche lability after accounting for evolutionary relatedness. Together, these results suggest that warming and ocean acidification over the next hundreds to thousands of years could redistribute and reduce populations of foraminifera and other calcifying plankton, which are primary components of marine food webs and biogeochemical cycles.
NMR unveils an N-terminal interaction interface on acetylated-α-synuclein monomers for recruitment to fibrils
Authors: Yang Xue , Wang Baifan , Hoop Cody L. , Williams Jonathan K. , Baum Jean
Published: April 2021

Significance

Cell-to-cell spreading of αS fibrils leads to amyloid seeding of endogenous monomer. Detailed atomic-level mechanistic understanding of the fibril seeding process of αS is essential for design of therapeutic approaches against Parkinson’s disease. In light of its complexity, this process remains ill defined at the molecular level. Using relaxation-based solution NMR experiments, we mapped a common N-terminal binding interface of the Ac-αS intrinsically disordered monomer with Ac-αS fibrils and off-pathway oligomers to elucidate critical monomer–aggregate interactions during seeded aggregation and in equilibrium with mature aggregates. From this work, we propose a paradigm in which Ac-αS monomer recruitment to the fibril is driven by interactions between the intrinsically disordered monomer N terminus and the flanking IDRs on the fibril surface.
Pinpointing the neural signatures of single-exposure visual recognition memory
Authors: Mehrpour Vahid , Meyer Travis , Simoncelli Eero P. , Rust Nicole C.
Published: April 2021

Significance

Humans have a remarkable ability to remember images they have seen, even after seeing thousands, each only once and for a few seconds. One important step toward understanding how the primate brain supports this remarkable form of memory involves pinpointing the neural activity patterns that enable image memory behavior. This paper presents evidence this neural activity pattern is sensory referenced suppression: reductions in population response magnitude, corrected for sensory modulation.
Transfer-printed, tandem microscale light-emitting diodes for full-color displays
Authors: Li Lizhu , Tang Guo , Shi Zhao , Ding He , Liu Changbo , Cheng Dali , Zhang Qianyi , Yin Lan , Yao Zhibo , Duan Lian , Zhang Donghao , Wang Chenggong , Feng Meixin , Sun Qian , Wang Qiang , Han Yanjun , Wang Lai , Luo Yi , Sheng Xing
Published: April 2021

Significance

Inorganic semiconductor based micro-LEDs have recently attracted tremendous interests of both industrial developers and academic researchers for the realization of next-generation displays. The reduction of LED sizes causes performance degradation and increased fabrication challenges. In this paper, we introduce a tandem device scheme based on stacked red, green, and blue (RGB) micro-LEDs for the realization of full-color lighting and displays. Thin-film micro-LEDs (size ∼100 μm, thickness ∼5 μm) based on III–V compound semiconductors are vertically assembled via epitaxial liftoff and transfer printing. A thin-film dielectric-based optical filter serves as a wavelength selective interface for performance enhancement. Furthermore, we prototype arrays of tandem RGB micro-LEDs and demonstrate display capabilities across the entire visible wavelength range.
Molecular analysis of black coatings and anointing fluids from ancient Egyptian coffins, mummy cases, and funerary objects
Authors: Fulcher Kate , Serpico Margaret , Taylor John H. , Stacey Rebecca
Published: April 2021

Significance

Previous studies of ritual black coatings on coffins from ancient Egypt have taken single small samples from objects of wide-ranging time periods and have conflated different types of application. This study takes 100 samples of black ritual liquids identified by type of application and precisely located on the objects, to allow the results to be fully contextualized within the wider discipline. It shows that black coatings on coffins were made using a remarkably consistent selection of natural products. The molecules identified in these black coatings overlap with those used in Egyptian mummification balms, which may suggest a link among separate applications: preparation of the body for burial, decoration of the coffin, and rites performed during the funeral.
Solar anti-icing surface with enhanced condensate self-removing at extreme environmental conditions
Authors: Zhang Hongqiang , Zhao Guanlei , Wu Shuwang , Alsaid Yousif , Zhao Wenzheng , Yan Xiao , Liu Lei , Zou Guisheng , Lv Jianyong , He Ximin , He Zhiyuan , Wang Jianjun
Published: April 2021

Significance

Among various anti-icing conditions, cold and humid environments are the most difficult to tackle. Although photothermal materials have been used to increase surface temperature for delaying freezing, severe condensation under cold and humid environments causes increased reflection, resulting in lower temperature rise and eventually condensate freezing. Ideal passive anti-icing surfaces should remove condensed water immediately, leaving no water for freezing. Herein, a condensate self-removing solar anti-icing/frosting surface is developed. With optimum hierarchical micro/nanostructures, it has excellent photothermal capability to elevate surface temperature and simultaneously can shed off condensed water effectively via coalescence-induced droplet jumping, providing continuously refreshed dry surface for sunlight absorption to maintain the elevated temperature under challenging environmental conditions, where condensation and fogging would otherwise be strongly promoted.
COVID-19 lockdowns show reduced pollution on snow and ice in the Indus River Basin
Authors: Bair Edward , Stillinger Timbo , Rittger Karl , Skiles McKenzie
Published: April 2021

Melting snow and ice supply water for nearly 2 billion people [J. S. Mankin, D. Viviroli, D. Singh, A. Y. Hoekstra, N. S. Diffenbaugh,
Environ. Res. Lett.
10, 114016 (2015)]. The Indus River in South Asia alone supplies water for over 300 million people [S. I. Khan, T. E. Adams, “Introduction of Indus River Basin: Water security and sustainability” in
Indus River Basin
, pp. 3−16 (2019)]. When light-absorbing particles (LAP) darken the snow/ice surfaces, melt is accelerated, affecting the timing of runoff. In the Indus, dust and black carbon degrade the snow/ice albedos [S. M. Skiles, M. Flanner, J. M. Cook, M. Dumont, T. H. Painter,
Nat. Clim. Chang.
8, 964−971 (2018)]. During the COVID-19 lockdowns of 2020, air quality visibly improved across cities worldwide, for example, Delhi, India, potentially reducing deposition of dark aerosols on snow and ice. Mean values from two remotely sensed approaches show 2020 as having one of the cleanest snow/ice surfaces on record in the past two decades. A 30% LAP reduction in the spring and summer of 2020 affected the timing of 6.6 km
3
of melt water. It remains to be seen whether there will be significant reductions in pollution post−COVID-19, but these results offer a glimpse of the link between pollution and the timing of water supply for billions of people. By causing more solar radiation to be reflected, cleaner snow/ice could mitigate climate change effects by delaying melt onset and extending snow cover duration.
Global and country-level estimates of human population at high altitude
Authors: Tremblay Joshua C. , Ainslie Philip N.
Published: April 2021

Estimates of the global population of humans living at high altitude vary widely, and such data at the country level are unavailable. Herein, we use a geographic information system (GIS)-based approach to quantify human population at 500-m elevation intervals for each country. Based on georeferenced data for population (LandScan Global 2019) and elevation (Global Multiresolution Terrain Elevation Data), 500.3 million humans live at ≥1,500 m, 81.6 million at ≥2,500 m, and 14.4 million at ≥3,500 m. Ethiopia has the largest absolute population at ≥1,500 m and ≥2,500 m, while China has the greatest at ≥3,500 m. Lesotho has the greatest percentage of its population above 1,500 m, while Bolivia has the greatest at ≥2,500 m and ≥3,500 m. High altitude presents a myriad of environmental stresses that provoke physiological responses and adaptation, and consequently impact disease prevalence and severity. While the majority of high-altitude physiology research is based upon lowlanders from western, educated, industrialized, rich, and democratic countries ascending to high altitude, the global population distribution of high-altitude residents encourages an increased emphasis on understanding high-altitude physiology, adaptation, epidemiology, and public health in the ∼500 million permanent high-altitude residents.
STARTRAC analyses of scRNAseq data from tumor models reveal T cell dynamics and therapeutic targets
Authors: Bhatt Dev , Kang Boxi , Sawant Deepali , Zheng Liangtao , Perez Kristy , Huang Zhiyu , Sekirov Laura , Wolak Dan , Huang Julie Y. , Liu Xian , DeVoss Jason , Manzanillo Paolo S. , Pierce Nathan , Zhang Zemin , Symons Antony , Ouyang Wenjun
Published: April 2021

Single-cell RNA sequencing is a powerful tool to examine cellular heterogeneity, novel markers and target genes, and therapeutic mechanisms in human cancers and animal models. Here, we analyzed single-cell RNA sequencing data of T cells obtained from multiple mouse tumor models by PCA-based subclustering coupled with TCR tracking using the STARTRAC algorithm. This approach revealed various differentiated T cell subsets and activation states, and a correspondence of T cell subsets between human and mouse tumors. STARTRAC analyses demonstrated peripheral T cell subsets that were developmentally connected with tumor-infiltrating CD8+ cells, CD4+ Th1 cells, and T reg cells. In addition, large amounts of paired TCRα/β sequences enabled us to identify a specific enrichment of paired public TCR clones in tumor. Finally, we identified CCR8 as a tumor-associated T reg cell marker that could preferentially deplete tumor-associated T reg cells. We showed that CCR8-depleting antibody treatment provided therapeutic benefit in CT26 tumors and synergized with anti–PD-1 treatment in MC38 and B16F10 tumor models.
Dark matter candidates in the NMSSM with RH neutrino superfields
Authors: López-Fogliani Daniel E. , Perez Andres D. , Ruiz de Austri Roberto
Published: April 2021

R-parity conserving supersymmetric models with right-handed (RH) neutrinos are very appealing since they could naturally explain neutrino physics and also provide a good dark matter (DM) candidate such as the lightest supersymmetric particle (LSP). In this work we consider the next-to-minimal supersymmetric standard model (NMSSM) plus RH neutrino superfields, with effective Majorana masses dynamically generated at the electroweak scale (EW). We perform a scan of the relevant parameter space and study both possible DM candidates: RH sneutrino and neutralino. Especially for the case of RH sneutrino DM we analyse the intimate relation between both candidates to obtain the correct amount of relic density.
Besides the well-known resonances, annihilations through scalar quartic couplings and coannihilation mechanisms with all kind of neutralinos, are crucial. Finally, we present the impact of current and future direct and indirect detection experiments on both DM candidates.
Crystal growth, structure and optical properties of Pr3+-doped yttria-stabilized zirconia single crystals*
Authors: Wang Dai-Ni , Xu Shou-Lei , Wang Xiang-Yu , Li Si-Yao , Hong Xing , A. Goodman Bernard , Deng Wen
Published: April 2021

The development of blue semiconductor light-emitting diodes (LEDs) has produced potential applications for Pr-doped materials that can absorb blue light, especially crystals, and we now report structure and optical properties for high-quality Pr-doped single crystals of yttria-stabilized zirconia (YSZ) grown by the optical floating zone (FZ) method. X-ray diffraction (XRD) and Raman spectroscopy showed that all of the single crystal samples were in the cubic phase, whereas the corresponding ceramic samples contained a mixture of monoclinic and cubic phases. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy showed that Pr was present as the Pr3+ ion in ceramic rods and single crystals after heating to high temperatures. The absorption and photoluminescence excitation (PLE) spectra of the Pr-doped YSZ crystals measured at room temperature showed strong absorption of blue light, while their photoluminescence (PL) spectra showed five emission peaks at 565 nm, 588 nm, 614 nm, 638 nm, and 716 nm under 450 nm excitation. The optimum luminescence properties were obtained with the crystal prepared using 0.15 mol% Pr6O11, and those with higher concentrations showed evidence of quenching of the luminescence properties. In addition, the color purity of Pr-doped YSZ single crystal reached 98.9% in the orange–red region.
Equilibrium folding and unfolding dynamics to reveal detailed free energy landscape of src SH3 protein by magnetic tweezers*
Authors: Su Huanhuan , Sun Hao , Hong Haiyan , Guo Zilong , Yu Ping , Chen Hu
Published: April 2021

Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics. Force spectroscopy experiments by optical tweezers and atomic force microscopy have measured the force-dependent unfolding rates with different kinds of pulling geometry. However, the equilibrium folding and unfolding dynamics at constant forces has not been reported. Here, using stable magnetic tweezers, we performed equilibrium folding and unfolding dynamic measurement and force-jump measurement of src SH3 domain with tethering points at its N- and C-termini. From the obtained force-dependent transition rates, a detailed two-state free energy landscape of src SH3 protein is constructed with quantitative information of folding free energy, transition state barrier height and position, which exemplifies the capability of magnetic tweezers to study protein folding and unfolding dynamics.
Substitution effect on the superconductivity in Mo3–x
Re
x
Al2C with β-Mn structure prepared by microwave method*
Authors: Sun Jun-Nan , Ruan Bin-Bin , Zhou Meng-Hu , Chen Yin , Yang Qing-Song , Shan Lei , Ma Ming-Wei , Chen Gen-Fu , Ren Zhi-An
Published: April 2021

We report the microwave synthesis and the doping effect of Mo3−x
Re
x
Al2C (0 ≤ x ≤ 0.3) superconductor. Re doping into Mo3Al2C results in a regular shrinkage of the lattice, marked by the linear decrease of lattice parameter a from 6.868(1) Å (for Mo3Al2C) to 6.846(2) Å (for Mo2.7Re0.3Al2C). Upon Re doping, T
c of Mo3−x
Re
x
Al2C first increases and then decreases, with the maximum T
c = 9.14 K at the optimal doping level of x = 0.09. Our report provides a convenient method to synthesize Mo3−x
Re
x
Al2C within minutes, and also marks the first Re doping study with enhanced superconductivity on the non-centrosymmetric superconductor Mo3Al2C.
Distributed optimization for discrete-time multiagent systems with nonconvex control input constraints and switching topologies*
Authors: Shen Xiao-Yu , Su Shuai , Hou Hai-Liang
Published: April 2021

This paper addresses the distributed optimization problem of discrete-time multiagent systems with nonconvex control input constraints and switching topologies. We introduce a novel distributed optimization algorithm with a switching mechanism to guarantee that all agents eventually converge to an optimal solution point, while their control inputs are constrained in their own nonconvex region. It is worth noting that the mechanism is performed to tackle the coexistence of the nonconvex constraint operator and the optimization gradient term. Based on the dynamic transformation technique, the original nonlinear dynamic system is transformed into an equivalent one with a nonlinear error term. By utilizing the nonnegative matrix theory, it is shown that the optimization problem can be solved when the union of switching communication graphs is jointly strongly connected. Finally, a numerical simulation example is used to demonstrate the acquired theoretical results.