bluuebunny/crossref_metadata_2025_split huggingface dataset:
W-band circular TM11 mode converter for gyrotrons
Authors: Chao Hsien-Wen , Huang Ren-Jun , Li Yi-Chin , Chang Tsun-Hsu 
Published: May 2021

This work proposes a methodology to convert a rectangular TE10 mode to a circular TM11 mode using an H-plane power divider at W-band. The divider evenly splits the input signal into two parts with the same amplitude and phase. One of the waves then goes through a wider rectangular waveguide with a lower cutoff frequency. After propagating through a specific length, the two waves differ by 180°. The two out-of-phase waves can jointly synthesize the circular TM11 mode with high mode purity. This power divider is structurally simple and capable of high-power operation. The full-wave simulation shows that the metal’s conductivity affects the transmission of two-mode converters joined back-to-back. The measured back-to-back transmission agrees with the simulation result except for minor quantitative differences. The measured 3-dB bandwidth is 2.8 GHz with a center frequency of 93.6 GHz, which warrants the success of the TM11 mode gyrotrons.
Output characteristics and experimental study of a highly linear and large-range force sensor based on the Villari effect
Authors: Shi Rui , Wang Chuanli , Yu Caofeng , Xiong Meijun , Wang Yu , Chen Zhuo 
Published: May 2021

Based on the principle of the Villari effect, a force sensor with a giant magnetostrictive material (GMM) as the sensitive element, high linearity, and a large range was studied. A Hall element integrated into the structure was used to detect the magnetic flux density and measure the external force. First, the finite element method was used to verify the validity of the intended magnetization process. Second, an equation for GMM magnetization was derived based on the Jiles–Atherton (J–A) model and the magneto-mechanical coupling effect. The relationships between magnetization and the biased magnetic field, and magnetization and the external force were analyzed under the dynamic coupling model of positive and negative effects. Finally, the influences of various biased magnetic fields and external forces on the sensor output characteristics were determined experimentally. The sensitivity of the designed force sensor was 0.337 mV/N when the bias current was 1.2 A and the preload was 120 N. When a force of 1000 N was applied, the linearity was 0.82%. The experimental results are consistent with the theoretical design values. These research results aid in the development of a highly linear, large-range force sensor. This study provides the theoretical and technical foundations for a high-performance force sensor that can be used in industrial testing.
Resistance of African tropical forests to an extreme climate anomaly
Authors: Bennett Amy C. , Dargie Greta C. , Cuni-Sanchez Aida , Tshibamba Mukendi John , Hubau Wannes , Mukinzi Jacques M. , Phillips Oliver L. , Malhi Yadvinder , Sullivan Martin J. P. , Cooper Declan L. M. , Adu-Bredu Stephen , Affum-Baffoe Kofi , Amani Christian A. , Banin Lindsay F. , Beeckman Hans , Begne Serge K. , Bocko Yannick E. , Boeckx Pascal , Bogaert Jan , Brncic Terry , Chezeaux Eric , Clark Connie J. , Daniels Armandu K. , de Haulleville Thales , Djuikouo Kamdem Marie-Noël , Doucet Jean-Louis , Evouna Ondo Fidèle , Ewango Corneille E. N. , Feldpausch Ted R. , Foli Ernest G. , Gonmadje Christelle , Hall Jefferson S. , Hardy Olivier J. , Harris David J. , Ifo Suspense A. , Jeffery Kathryn J. , Kearsley Elizabeth , Leal Miguel , Levesley Aurora , Makana Jean-Remy , Mbayu Lukasu Faustin , Medjibe Vincent P. , Mihindu Vianet , Moore Sam , Nssi Begone Natacha , Pickavance Georgia C. , Poulsen John R. , Reitsma Jan , Sonké Bonaventure , Sunderland Terry C. H. , Taedoumg Hermann , Talbot Joey , Tuagben Darlington S. , Umunay Peter M. , Verbeeck Hans , Vleminckx Jason , White Lee J. T. , Woell Hannsjoerg , Woods John T. , Zemagho Lise , Lewis Simon L. 
Published: May 2021

Significance
The responses of tropical forests to heat and drought are critical uncertainties in predicting the future impacts of climate change. The 2015–2016 El Niño Southern Oscillation (ENSO) resulted in unprecedented heat and low precipitation across the tropics, including in the very poorly studied African tropical forest region. We assess African forest ENSO responses using on-the-ground measurements. Across 100 long-term plots, record high temperatures did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality. Overall, despite the climate anomaly, forests continued to gain live biomass over the ENSO period. Our analyses, while limited to African tropical forests, suggest that they may be more resistant to climate extremes than Amazonian and Asian forests.
Quantifying collective intelligence in human groups
Authors: Riedl Christoph , Kim Young Ji , Gupta Pranav , Malone Thomas W. , Woolley Anita Williams 
Published: May 2021

Significance
Collective intelligence (CI) is critical to solving many scientific, business, and other problems. We find strong support for a general factor of CI using meta-analytic methods in a dataset comprising 22 studies, including 5,279 individuals in 1,356 groups. CI can predict performance in a range of out-of-sample criterion tasks. CI, in turn, is most strongly predicted by group collaboration process, followed by individual skill and group composition. The proportion of women in a group is a significant predictor of group performance, mediated by social perceptiveness.
Oligomodal metamaterials with multifunctional mechanics
Authors: Bossart Aleksi , Dykstra David M. J. , van der Laan Jop , Coulais Corentin 
Published: May 2021

Significance
Mechanical metamaterials are man-made materials with extraordinary properties that come from their geometrical structure rather than their chemical composition. For instance, they can be engineered to be extremely light and stiff; to shrink sideways when compressed, instead of expanding; or to exhibit programmable shape changes. Such properties often rely on zero-energy modes. In this work, we created a class of mechanical metamaterials with zero-energy modes that can exhibit multiple properties at the same time within a single structure. In particular, we created a metamaterial that can either shrink or expand on the side when compressed, depending on how fast it is compressed. These metamaterials could lead to novel adaptable devices for, for example, robotics and energy absorption applications.
Short hydrogen bonds enhance nonaromatic protein-related fluorescence
Authors: Stephens Amberley D. , Qaisrani Muhammad Nawaz , Ruggiero Michael T. , Díaz Mirón Gonzalo , Morzan Uriel N. , González Lebrero Mariano C. , Jones Saul T. E. , Poli Emiliano , Bond Andrew D. , Woodhams Philippa J. , Kleist Elyse M. , Grisanti Luca , Gebauer Ralph , Zeitler J. Axel , Credgington Dan , Hassanali Ali , Kaminski Schierle Gabriele S. 
Published: May 2021

Significance
Intrinsic fluorescence of nonaromatic amino acids is a puzzling phenomenon with an enormous potential in biophotonic applications. The physical origins of this effect, however, remain elusive. Herein, we demonstrate how specific hydrogen bond networks can modulate fluorescence. We highlight the key role played by short hydrogen bonds, present in the protein structure, on the ensuing fluorescence. We provide detailed experimental and molecular evidence to explain these unusual nonaromatic optical properties. Our findings should benefit the design of novel optically active biomaterials for applications in biosensing and imaging.
Global abundance estimates for 9,700 bird species
Authors: Callaghan Corey T. , Nakagawa Shinichi , Cornwell William K. 
Published: May 2021

Significance
For the fields of ecology, evolutionary biology, and conservation, abundance estimates of organisms are essential. Quantifying abundance, however, is difficult and time consuming. Using a data integration approach integrating expert-derived abundance estimates and global citizen science data, we estimate the global population of 9,700 bird species (∼92% of all extant bird species). We conclude that there are many rare species, highlighting the need to continue to refine global population estimates for all taxa and the role that global citizen science data can play in this effort.
Plant species richness at archaeological sites suggests ecological legacy of Indigenous subsistence on the Colorado Plateau
Authors: Pavlik Bruce M. , Louderback Lisbeth A. , Vernon Kenneth B. , Yaworsky Peter M. , Wilson Cynthia , Clifford Arnold , Codding Brian F. 
Published: May 2021

Significance
Identifying how past human populations altered ecosystems is critical for understanding current ecological diversity and for the management of both natural and cultural resources. This study presents evidence for an enduring ecological legacy of ancient people on the Colorado Plateau, where the complexity of archaeological sites correlates with the richness of culturally important plant species. This suggests the intentional or unintentional transport and cultivation of native plants on a scale that is often overlooked in the American Southwest, where exogenous domesticates (corn, beans, and squash) are emphasized. These results illustrate how even small-scale societies can affect ecosystems and highlight the importance of coupling archaeology, ecology, and tribal expertise for resource management.
Detection of differentially abundant cell subpopulations in scRNA-seq data
Authors: Zhao Jun , Jaffe Ariel , Li Henry , Lindenbaum Ofir , Sefik Esen , Jackson Ruaidhrí , Cheng Xiuyuan , Flavell Richard A. , Kluger Yuval 
Published: May 2021

SignificanceComparative analysis of samples from two biological states, such as two stages of embryonic development, is a pressing problem in single-cell RNA sequencing (scRNA-seq). A key challenge is to detect cell subpopulations whose abundance differs between the two states. To that end, we develop DA-seq, a multiscale strategy to compare two cellular distributions. In contrast to existing unsupervised clustering-based analysis, DA-seq can delineate cell subpopulations with the most significant discrepancy between two states and potentially reveal important changes in cellular processes that are undetectable using conventional methods.
Terahertz detection based on nonlinear Hall effect without magnetic field
Authors: Zhang Yang , Fu Liang 
Published: May 2021

Significance
Despite the enormous potential of terahertz technology, fast, sensitive, and broadband terahertz detection at room temperature has been a challenge. We propose a method for long-wavelength photodetection using topological quantum materials without invoking any diode or junction region. The inherently quadratic relation between transverse current and input voltage at zero magnetic field is used to rectify the incident terahertz or infrared electric field into a direct current. We identify the Weyl semimetal NbP and ferroelectric semiconductor GeTe for terahertz/infrared photodetection with large current responsivity without external bias.
Light extraction efficiency and internal quantum efficiency of fully UVC-transparent AlGaN based LEDs
Authors: Guttmann Martin , Susilo Anna , Sulmoni Luca , Susilo Norman , Ziffer Eviathar , Wernicke Tim , Kneissl Michael 
Published: May 2021

Abstract
The light extraction efficiency (LEE), external quantum efficiency (EQE), and current–voltage characteristics of deep ultraviolet light emitting diodes (DUV-LEDs) with different aluminum mole fractions in the p-AlGaN layers have been investigated. Optimizing the p-AlGaN layer composition requires a tradeoff between reducing the absorption losses and limiting the increases in the p-contact resistance and operation voltage. AlGaN multiple quantum well LEDs emitting around 263 nm with different AlGaN:Mg short period super lattices (p-SPSL) ranging from x = 33% (UV-absorbing) to x = 68% (UV-transparent) average aluminum mole fraction have been explored. DUV-LEDs with different p-contact metals and UV-reflectivities have been characterized by electroluminescence measurements and analyzed by ray-tracing simulations. The comparison shows an increased operating voltage and a five-fold increase of the on-wafer EQE with a maximum value of 3.0% for DUV-LEDs with UV-transparent p-SPSL (x = 68%) and UV-reflective indium contacts in comparison to LEDs with a UV-absorbing p-SPSL (x = 33%). Ray-tracing simulations show that the increase in EQE can be partially ascribed to a 2.5-fold improved LEE in combination with a two-fold increase in internal quantum efficiency.
Microscopic deformation mechanism and main influencing factors of carbon nanotube coated graphene foams under uniaxial compression
Authors: Wang Shuai , Wang Chao , Khan Muhammad Bilal , Chen Shaohua 
Published: May 2021

Abstract
Many experiments have shown that carbon nanotube-coated (CNT-coated) graphene foam (CCGF) has specific mechanical properties, which further expand the application of graphene foam materials in many advanced fields. To reveal the microscopic deformation mechanism of CCGF under uniaxial compression and the main factors affecting their mechanical properties, numerical experiments based on the coarse-grained molecular dynamics method are systematically carried out in this paper. It is found that the relative stiffness of CNTs and graphene flakes seriously affects the microscopic deformation mechanism and strain distribution in CCGFs. The bar reinforcing mechanism will dominate the microstructural deformation in CCGFs composed of relatively soft graphene flakes, while the microstructural deformation in those composed of stiff graphene flakes will be dominated by the mechanical locking mechanism. The effects of CNT fraction, distribution of CNTs on graphene flakes, the thickness of graphene flakes, and the adhesion strength between CNTs and graphene flakes on the initial and intermediate moduli of foam materials are further studied in detail. The results of this paper should be helpful for a deep understanding of the mechanical properties of CCGF materials and the optimization design of microstructures in advanced graphene-based composites.
RC time constant measurement using an INA219 sensor: creating an alternative, flexible, low-cost configuration that provides benefits for students and schools
Authors: El Hadi M , Ouariach A , Essaadaoui R , El Moussaouy A , Mommadi O 
Published: May 2021

Abstract
In this work, we have developed an alternative device composed by an Arduino board and an INA219 sensor to experimentally obtain the mathematical formulas describing the charge and discharge of the capacitor for educational proposes. We have obtained excellent agreement between theoretical prediction and experimental measurements. The INA219 DC sensor can measure direct current up to 26 V/3.2 A with a maximum error accuracy of 1%. The device makes it possible to follow the temporal evolution of the voltage and the current at a capacitor’s terminals. This platform can provide an alternative way for educational use compared to the expensive laboratory equipment (oscilloscope, voltmeter, generator). Indeed, we think that the presented device can play a dominant role in teaching and learning electricity courses in secondary schools due to its low cost, small size, reliability in measurements and good level of accuracy.
Optical scatter imaging of resected breast tumor structures matches the patterns of micro-computed tomography
Authors: Streeter Samuel S , Maloney Benjamin W , Zuurbier Rebecca A , Wells Wendy A , Barth Richard J , Paulsen Keith D , Pogue Brian W 
Published: May 2021

Abstract
In patients undergoing breast-conserving surgery (BCS), the rate of re-excision procedures to remove residual tumor left behind after initial resection can be high. Projection radiography, and recently, volumetric x-ray imaging are used to assess margin adequacy, but x-ray imaging lacks contrast between healthy, abnormal benign, and malignant fibrous tissues important for surgical decision making. The purpose of this study was to compare micro-CT and optical scatter imagery of surgical breast specimens and to demonstrate enhanced contrast-to intra-tumoral morphologies and tumor boundary features revealed by optical scatter imaging. A total of 57 breast tumor slices from 57 patients were imaged ex vivo by spatially co-registered micro-CT and optical scatter scanning. Optical scatter exhibited greater similarity with micro-CT in 89% (51/57) of specimens versus diffuse white light (DWL) luminance using mutual information (mean ± standard deviation of 0.48 ± 0.21 versus 0.24 ± 0.12; p < 0.001) and in 81% (46/57) of specimens using the Sørensen–Dice coefficient (0.48 ± 0.21 versus 0.33 ± 0.18; p < 0.001). The coefficient of variation (CV) quantified the feature content in each image. Optical scatter exhibited the highest CV in every specimen (optical scatter: 0.70 ± 0.17; diffuse luminance: 0.24 ± 01; micro-CT: 0.15 ± 0.03 for micro-CT; p < 0.001). Optical scatter also exhibited the highest contrast ratios across representative tumor boundaries with adjacent healthy/benign fibrous tissues (1.5–3.7 for optical scatter; 1.0–1.1 for diffuse luminance; 1.0–1.1 for micro-CT). The two main findings from this study were: first, optical scatter contrast was in general similar to the radiological view of the tissue relative to DWL imaging; and second, optical scatter revealed additional features associated with fibrous tissue structures of similar radiodensity that may be relevant to diagnosis. The value of micro-CT lies in its rapid three-dimensional scanning of specimen morphology, and combined with optical scatter imaging with sensitivity to fibrous surface tissues, may be an attractive solution for margin assessment during BCS.
Frozen-in fermionic singlet dark matter in non-standard cosmology with a decaying fluid
Authors: Arias Paola , Karamitros Dimitrios , Roszkowski Leszek 
Published: May 2021

Abstract
We perform a detailed study of dark matter production via freeze-in under the assumption that some fluid dominates the early Universe before depositing its energy to the plasma causing entropy injection.

As a dark matter candidate we consider a fermionic singlet that is produced through its interactions with a scalar particle in the thermal plasma.

The fluid alters the expansion rate of the Universe, as well as the scaling of the temperature, which significantly affects the evolution of both the number density and the mean momentum of the dark matter particle.

We identify and discuss in detail the effects of the evolution of these quantities by considering several examples representing dark matter production at different stages of expansion and entropy injection.

We find that, since the dark matter density is reduced when the entropy injection to the plasma continues after freeze-in, in order to reproduce its observational value an enhanced rate of dark matter production is required relative to standard cosmology. Furthermore, the impact of the assumed non-standard cosmological history on the dark matter mean momentum can result in either a relaxed or a tightened bound on the dark matter mass from large structure formation data.
Recent progress of physical failure analysis of GaN HEMTs
Authors: Cai Xiaolong , Du Chenglin , Sun Zixuan , Ye Ran , Liu Haijun , Zhang Yu , Duan Xiangyang , Lu Hai 
Published: May 2021

Abstract
Gallium nitride (GaN)-based high-electron mobility transistors (HEMTs) are widely used in high power and high frequency application fields, due to the outstanding physical and chemical properties of the GaN material. However, GaN HEMTs suffer from degradations and even failures during practical applications, making physical analyses of post-failure devices extremely significant for reliability improvements and further device optimizations. In this paper, common physical characterization techniques for post failure analyses are introduced, several failure mechanisms and corresponding failure phenomena are reviewed and summarized, and finally device optimization methods are discussed.
Morphology and crystalline property of an AlN single crystal grown on AlN seed
Authors: Zhang Li , Qi Haitao , Cheng Hongjuan , Shi Yuezeng , Lai Zhanpin , Luo Muchang 
Published: May 2021

Abstract
AlN single crystal grown by physical vapor transport (PVT) using homogeneous seed is considered as the most promising approach to obtain high-quality AlN boule. In this work, the morphology of AlN single crystals grown under different modes (3D islands and single spiral center) were investigated. It is proved that, within an optimized thermal distribution chamber system, the surface temperature of AlN seed plays an important role in crystal growth, revealing a direct relationship between growth mode and growth condition. Notably, a high-quality AlN crystal, with (002) and (102) reflection peaks of 65 and 36 arcsec at full width at half maximum (FWHM), was obtained grown under a single spiral center mode. And on which, a high-quality Al
x
Ga1–

x
N epitaxial layer with high Al content (x = 0.54) was also obtained. The FWHMs of (002) and (102) reflection of Al
x
Ga1–

x
N were 202 and 496 arcsec, respectively, which shows superiority over their counterpart grown on SiC or a sapphire substrate.
A complete small-signal HBT model including AC current crowding effect
Authors: Huang Jinjing , Liu Jun 
Published: May 2021

Abstract
An improved small-signal equivalent circuit of HBT concerning the AC current crowding effect is proposed in this paper. AC current crowding effect is modeled as a parallel RC circuit composed of C
bi and R
bi, with distributed base-collector junction capacitance also taken into account. The intrinsic portion is taken as a whole and extracted directly from the measured S-parameters in the whole frequency range of operation without any special test structures. An HBT device with a 2 × 20 μm2 emitter-area under three different biases were used to demonstrate the extraction and verify the accuracy of the equivalent circuit.
WO3 passivation layer-coated nanostructured TiO2: An efficient defect engineered photoelectrode for dye sensitized solar cell
Authors: Babu Arya , Vasanth Arya , Nair Shantikumar , Shanmugam Mariyappan 
Published: May 2021

Abstract
Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide (TiO2) were controlled by RF-sputtered tungsten trioxide (WO3) passivation. X-ray photoelectron spectroscopy assured the coating of WO3 on the TiO2 nanoparticle layer by showing Ti 2p, W 4f and O 1s characteristic peaks and were further confirmed by X-ray diffraction studies. The coating of WO3 on the TiO2 nanoparticle layer did not affect dye adsorption significantly. Dye sensitized solar cells (DSSCs) fabricated using WO3-coated TiO2 showed an enhancement of ~10% compared to DSSCs fabricated using pristine TiO2-based photo-electrodes. It is attributed to the WO3 passivation on TiO2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules. It was further evidenced that there is an optimum thickness (duration of coating) of WO3 to improve the DSSC performance and longer duration of WO3 suppressed photo-electron injection from dye to TiO2 as inferred from the detrimental effect in short circuit current density values. RF-sputtering yields pinhole-free, highly uniform and conformal coating of WO3 onto any area of interest, which can be considered for an effective surface passivation for nanostructured photovoltaic devices.