bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse leakage and breakdown mechanisms of vertical GaN-on-Si Schottky barrier diodes with and without implanted termination
Authors: Guo Xiaolu , Zhong Yaozong , Chen Xin , Zhou Yu , Su Shuai , Yan Shumeng , Liu Jianxun , Sun Xiujian , Sun Qian , Yang Hui
Published: June 2021

This Letter studies the reverse leakage and breakdown mechanisms of vertical GaN-on-Si Schottky barrier diodes (SBDs) with and without argon-implanted termination (ArIT). The electrical leakage characteristics in the vertical GaN-on-Si SBD without edge termination sequentially go through the thermionic field emission, variable range hopping (VRH), and trap-assisted tunneling conduction mechanisms as the reverse bias increases gradually. Its leakage and breakdown mechanisms are limited by the edge electric field crowding effect. While for the vertical GaN-on-Si SBD with ArIT (ArIT-SBD), the electrons conduction at a low reverse bias, following the space-charge-limited conduction (SCLC) model, is limited by the damage-induced traps in the implanted GaN. As the reverse bias increases up to the occurrence of breakdown, the VRH and SCLC dominate the leakage mechanism of the ArIT-SBD, which stem from intrinsic traps in GaN grown on Si. A rapidly growing leakage under a low reverse bias and enhanced breakdown voltage performance in the ArIT-SBD is attributed to the charging of the damage-induced traps in implanted GaN. This Letter not only gives in-depth insights of vertical GaN-on-Si SBDs but also provides a useful design guidance of implanted termination for high-voltage power devices.
Combination of recommender system and single-particle diagnosis for accelerated discovery of novel nitrides
Authors: Koyama Yukinori , Seko Atsuto , Tanaka Isao , Funahashi Shiro , Hirosaki Naoto
Published: June 2021

Discovery of new compounds from wide chemical space is attractive for materials researchers. However, theoretical prediction and validation experiments have not been systematically integrated. Here, we demonstrate that a new combined approach is powerful in significantly accelerating the discovery rate of new compounds, which should be useful for exploration of a wide chemical space in general. A recommender system for chemically relevant composition is constructed by machine learning of Inorganic Crystal Structure Database using chemical compositional descriptors. Synthesis and identification experiments are made at the chemical compositions with high recommendation scores by the single-particle diagnosis method. Two new compounds, La4Si3AlN9 and La26Si41N80O, and two new variants (isomorphic substitutions) of known compounds, La7Si6N15 and La4Si5N10O, are successfully discovered. Finally, density functional theory calculations are conducted for La4Si3AlN9 to confirm the energetic and dynamical stability and to reveal its atomic arrangement.
Natural convection from discrete reactions on the bottom wall of an enclosure
Authors: Roy Nepal Chandra
Published: June 2021

Natural convection resulting from discrete reactive heat sources on the bottom wall of an enclosure is investigated. The rest of the bottom wall apart from the heat sources, the top wall, and the vertical walls are kept at the surrounding temperature. The remarkable findings, which have not been reported in any study, are that the flow field and temperature distribution are quite distinct depending on the odd and even number of reactive heat sources on the bottom wall. For odd numbers of heat sources, the vortices have a quite sharp corner near the center of the middle source and the base of the thermal plume is in the middle heat source. Contrary to this, for even numbers of reactive heat sources, the vortices have a blunt corner near the middle two heat sources and it seems that the thermal plume evolves from the coalescence of the middle two heat sources. Whatever the number of heat sources, for increasing the Rayleigh number, the maximum value of the stream function increases and the maximum temperature decreases. However, both of them are increased for higher values of the Frank–Kamenetskii number. It is also observed that the heat loss to the environment through the walls of the enclosure is stronger with the increase in the Rayleigh number and Frank–Kamenetskii number.
Low communication high performance ab initio density matrix renormalization group algorithms
Authors: Zhai Huanchen , Chan Garnet Kin-Lic
Published: June 2021

There has been recent interest in the deployment of ab initio density matrix renormalization group (DMRG) computations on high performance computing platforms. Here, we introduce a reformulation of the conventional distributed memory ab initio DMRG algorithm that connects it to the conceptually simpler and advantageous sum of the sub-Hamiltonian approach. Starting from this framework, we further explore a hierarchy of parallelism strategies that includes (i) parallelism over the sum of sub-Hamiltonians, (ii) parallelism over sites, (iii) parallelism over normal and complementary operators, (iv) parallelism over symmetry sectors, and (v) parallelism within dense matrix multiplications. We describe how to reduce processor load imbalance and the communication cost of the algorithm to achieve higher efficiencies. We illustrate the performance of our new open-source implementation on a recent benchmark ground-state calculation of benzene in an orbital space of 108 orbitals and 30 electrons, with a bond dimension of up to 6000, and a model of the FeMo cofactor with 76 orbitals and 113 electrons. The observed parallel scaling from 448 to 2800 central processing unit cores is nearly ideal.
High magneto-Seebeck effect at room temperature in Bi1.8Sb0.2Te3-ySey crystal
Authors: Ghose P. K. , Dalui T. K. , Chatterjee A. , Majumdar S. , Giri S.
Published: June 2021

We report thermoelectric and electrical transport properties of Bi1.8Sb0.2Te3-ySey by tuning y. In contrast to the reported p-type conductivity of the end compounds with y = 0 and 3, a dominant n-type conduction mechanism is observed for y = 1.5 from the Hall measurement. Intriguingly, the magneto-Seebeck consequence is enhanced up to ∼ 20 times for y = 1.5 compared to the end members. The reasonable value of magnetoresistance with an anisotropic character with respect to the direction of the magnetic field is observed at low temperature, which decreases with increasing temperature. The density of state at the Fermi level near room temperature correlates high Seebeck coefficient as well as magneto-Seebeck effect. High magneto-Seebeck effect at room temperature is promising for the application.
New soliton configurations for two different models related to the nonlinear Schrödinger equation through a graded-index waveguide
Authors: Almusawa Hassan , Nur Alam Md. , Fayz-Al-Asad Md. , Osman M. S.
Published: June 2021

The present paper studies two various models with two different types: the nonlinear Schrödinger equation with power-law nonlinearity and the (3 + 1)-dimensional nonlinear Schrödinger equation. We perform the modified (G′G)-expansion method to find some exact solutions and to construct various types of solitary wave phenomena for each equation. The received aspects contribute to the firm mathematical foundation and might be essential to the soliton waves. As a result, we obtain all the solutions from Wazwaz [Math. Comput. Modell. 43, 178–184 (2016)] and also obtain some new soliton solutions.
Compatibility of C5F10O with common-used sealing materials: An experimental study
Authors: She Congdong , Tang Ju , Cai Rijian , Li Haotian , Li Long , Yao Qiang , Zeng Fuping , Li Chen
Published: June 2021

C5F10O has been widely studied as a promising environmentally friendly substitute to SF6 in power equipment. Up to now, the environmentally friendly gas insulated equipment developed still uses the same sealing materials as SF6 gas insulation equipment. However, whether these sealing materials are chronically compatible with C5F10O has always been a fundamental problem that perplexes the industry and academia. In this study, a thermally accelerated aging experiment on four rubber materials contacted with C5F10O/N2 was carried out. During the experiment, aged rubbers were analyzed using scanning electron microscopy and x-ray photoelectron spectroscopy to obtain the surface morphology characteristic and element composition. The gas samples were collected periodically and detected through gas chromatography mass spectrometry. Meanwhile, the degradation of the rubbers’ mechanical property is tested to figure out their long-term compatibility with C5F10O/N2 mixtures. Surface analysis of the rubber samples showed that after thermal accelerated aging, F in the form of C–F bonding and metal fluorides were detected on the surface of the ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), chloroprene rubber (CR), and methyl vinyl silicone rubber (VMQ), which did not exist in origin samples. The main gaseous decomposition products of C5F10O include CO, CO2, C3F6, and C3F7H, and the concentration when coexisting with rubber is significantly higher than that in the control group. The compression performance of aged rubbers all reduced, and the compression performance of EPDM and NBR is better than that of CR and VMQ. The experimental results proved the incompatibility between C5F10O and these four rubbers, while EPDM and NBR showed less deterioration in compression properties and could be more suitable for the C5F10O power equipment.
Ultimate detectivity of multiple-stage interband cascade infrared photodetectors
Authors: Yang Rui Q. , Hinkey Robert T.
Published: June 2021

In this work, we theoretically demonstrate that the ultimate detectivities in multi-stage interband cascade infrared photodetector configurations are higher than what can be achieved in a conventional single-absorber detector structure in any circumstance even including where carrier diffusion length is very long. Detailed derivations are provided to analytically show that in the limit of an infinite diffusion length, the ultimate detectivity of a multiple-stage device is about 11% higher than that of an optimized single-stage device. Furthermore, how the sequence of absorber thicknesses is optimized for maximizing the detectivity is described and discussed. Insights and explanations to the results are presented to improve the understanding, clarify possible confusion with different perspectives in the technical community, and to generate more interest in the development of advanced multi-stage interband cascade infrared photodetectors for various applications.
Evaluating the effects of the invasive cane toad (
Authors: Harvey Jeffrey A. , Ambavane Priyanka , Williamson Mark , Diesmos Arvin
Published: June 2021

The negative ecological impacts of invasive species are well documented, although their effects are often more pronounced on islands than on the mainland. This is because many island species exhibit high degrees of endemism, have small geographic distributions, are rare, and exhibit low genetic diversity, which reduces their ability to respond to new emerging threats. One of the world’s most notorious invasive species is the cane toad (Rhinella marina), which is a voracious predator that is native to the neo-tropics but was intentionally introduced in the early 20th century to many warm regions and islands to control crop pests. Cane toads produce two kinds of toxins in neck glands that are often lethal to non-adapted predators in the invasive range. Although well-studied in Australia, their ecological impacts on many islands have received much less attention. Australia is the sixth largest country on Earth, so the effects of cane toads on small island nations may differ considerably from there. Here, we discuss the potential ecological impacts of cane toads in the Philippines and on other island nations. Cane toads were introduced onto the largest Philippine island, Luzon, in 1930 and have since spread over all but a few of the 7641 islands that make up the country. We speculate that, unlike most biological invasions with predators or herbivores where the ecological effects are strictly ‘top-down’, cane toads, by virtue of their biology and ecology, may have even more serious effects on island fauna because they exhibit both ‘top-down’ and ‘bottom-up’ effects.
Early role for a Na
+
,K
+
-ATPase (
ATP1A3
) in brain development
Authors: Smith Richard S. , Florio Marta , Akula Shyam K. , Neil Jennifer E. , Wang Yidi , Hill R. Sean , Goldman Melissa , Mullally Christopher D. , Reed Nora , Bello-Espinosa Luis , Flores-Sarnat Laura , Monteiro Fabiola Paoli , Erasmo Casella B. , Pinto e Vairo Filippo , Morava Eva , Barkovich A. James , Gonzalez-Heydrich Joseph , Brownstein Catherine A. , McCarroll Steven A. , Walsh Christopher A.
Published: June 2021

Significance

By evaluating children with a malformed cerebral cortex, we identified an ATPase pump (ATP1A3) with an early role in brain development. The ATP1A3 pump maintains the physiological concentration of sodium and potassium ions in cells, a process critical for osmotic equilibrium and membrane potential across several developing cell populations. We employed single-cell sequencing approaches to identify key enrichments for
ATP1A3
expression during human cortex development. Unravelling this early cell-type–specific pathophysiology in the developing brain offers a potential basis for the treatment of
ATP1A3
-related diseases affecting prenatal and early childhood development.
Long-read sequencing revealed cooccurrence, host range, and potential mobility of antibiotic resistome in cow feces
Authors: Qian Xun , Gunturu Santosh , Sun Wei , Cole James R. , Norby Bo , Gu Jie , Tiedje James M.
Published: June 2021

Significance

Estimating risk from environmental resistome is hindered by the lack of data on its mobility and host range, as well as whether it is likely functional. We developed an enrichment and analysis method using long-read sequencing technologies to link resistome and mobilome and correlate these with host range using a sample representative of an environmental source that had exposure to a medically important antibiotic. The long reads provide for detection of complete genes, direct evidence for their physical linkages important for assessing coselection, their chromosomal or plasmid location, and their likely hosts. The antibiotic-resistance gene, host, and potential transmissibility information can be assessed in the context of WHO-identified targets of concern and more directly contribute to the One Health vision.
Electrochemical quantification of accelerated FADGDH rates in aqueous nanodroplets
Authors: Vannoy Kathryn J. , Lee Inyoung , Sode Koji , Dick Jeffrey E.
Published: June 2021

Significance

For centuries, scientists have assumed that chemical reactivity in bulk, continuous water is conserved at all levels in nature, from reactions in the ocean to enzymatic digestion in a lysosome. There is growing evidence using mass spectrometry that chemical reaction rates are enhanced by orders of magnitude in micro- and nanodroplets. In this study, we use nanoelectrochemistry to track the enzymatic oxidation of glucose in single attoliter (10−18L) aqueous nanodroplets, one nanodroplet at a time. When a nanodroplet irreversibly adsorbs onto an ultramicroelectrode surface, the enzymatic reaction can be traced due to the electrochemical regeneration of the enzyme cofactor. We demonstrate the enzymatic reaction rate increases up to 100× for nanodroplets under 1 μm in radius.
A single-cell–resolution fate map of endoderm reveals demarcation of pancreatic progenitors by cell cycle
Authors: Yang Yun , Wang Hao , He Jia , Shi Wenchao , Jiang Zhanmei , Gao Lina , Jiang Yan , Ni Rui , Yang Qifen , Luo Lingfei
Published: June 2021

Significance

During embryonic development, an early-stage progenitor cell could generate different types of descendant cells. Developmental biologists keep dreaming of making all the descendant cell types generated by each early-stage progenitor cell clear. Here, we focus on one germ layer, the endoderm. Early foregut endoderm generates foregut digestive organs, including the pancreas, liver, and digestive tract. The central point of this work is the establishment of a full-coverage, single-cell–resolution fate map of zebrafish early foregut endoderm through unbiased labeling of every single endodermal progenitor cell and tracing its descendant cells. Based on the maps, we reveal a link of the cell cycle state and pancreatic fate propensity, providing an example of how the maps could facilitate understanding cell fate determination.
Groundwater dependence of riparian woodlands and the disrupting effect of anthropogenically altered streamflow
Authors: Rohde Melissa M. , Stella John C. , Roberts Dar A. , Singer Michael Bliss
Published: June 2021

Significance

Riparian ecosystems are biodiversity hotspots under intense pressure from multiple stressors. In most water-limited regions, high human water use from agricultural and urban development eclipses environmental water needs and intensifies ecosystem water stress. In particular, adequate consideration of riparian water needs in water resource management is lacking. Here, we show that in California, riparian vegetation exhibit: 1) seasonal canopy stress responses to deeper groundwater, and 2) greater groundwater coupling along streams with natural flow regimes compared with anthropogenically altered streams. We conclude that water subsidies in altered stream systems reduce groundwater dependence of riparian woodlands, undermine their adaptations and resilience to natural hydrologic variation, and ultimately threaten their sustainability under dual threats of increased water demand and a changing climate.
De novo determination of near-surface electrostatic potentials by NMR
Authors: Yu Binhan , Pletka Channing C. , Pettitt B. Montgomery , Iwahara Junji
Published: June 2021

Significance

Electrostatic potentials are important information for our understanding of biomolecular functions as well as for protein engineering and drug design. Typically, electrostatic potentials around biomolecules are computed from three-dimensional structures. However, the theory behind this computation is approximate with some limitations. Validation of the electrostatic theory through experiments is therefore essential yet remains inadequate. This paper presents a unique spectroscopic method to experimentally determine electrostatic potentials near the molecular surfaces without using any structural information. This method allows for examination of theoretical electrostatic potentials for many different regions of biomolecules. Structure-independent determination of electrostatic potentials for various biomolecular systems may lead to improvement of theoretical models, which would ultimately have broad impacts on basic research and pharmaceutical development.
Sensing of intracellular Hcp levels controls T6SS expression in
Vibrio cholerae
Authors: Manera Kevin , Caro Florence , Li Hao , Pei Tong-Tong , Hersch Steven J. , Mekalanos John J. , Dong Tao G.
Published: June 2021

Significance

Assembly, firing, and recycling of the type 6 secretion system (T6SS) organelle is a costly process as each secretion event ejects hundreds of inner-tube Hcp molecules. In comparison to bacteria whose T6SSs are tightly regulated, bacterial strains that constitutively display T6SS activity would seem inefficient in their deployment of T6SS, especially if secretion is interrupted by environmental conditions that reduce available cellular energy. Here we have discovered a quantity-sensing feedback control that avoids wasteful accumulation of secreted proteins in several pathogens that express the T6SS. By sensing the efficiency of secretion of its major substrate (Hcp), this regulatory mechanism likely conserves energy and would therefore be helpful in responding to a variety of stress conditions that interrupt T6SS secretion.
Electrophysiological insights into the role of proficiency in bilingual novel and conventional metaphor processing
Authors: Wang Xin , Jankowiak Katarzyna
Published: June 2021

While novel and conventional metaphor comprehension has received much attention in the monolingual context, thus far little electrophysiological research has been conducted with a view to examining how bilingual speakers process metaphors in their non-native language (L2) as well as how L2 proficiency level might modulate such processes. The present study aims to investigate the electrophysiological correlates of novel and conventional metaphor comprehension in intermediate and advanced Chinese-English bilingual speakers. The participants performed a semantic decision task to English (L2) novel metaphoric, conventional metaphoric, literal, and anomalous word pairs. The results showed a graded N400 effect from literal utterances, to conventional metaphors, novel metaphors, and finally to anomalous utterances in both groups of participants, indicating that both types of metaphors were more cognitively taxing than literal utterances, irrespectively of L2 proficiency level. Additionally, between-group differences that were irrespective of utterance type were found in the N400 time frame, indicating more extended lexico-semantic access in the intermediate relative to the advanced group. Finally, in both groups of participants, an anterior sustained negativity was found in response to anomalous, novel metaphoric, and conventional metaphoric word pairs, thus suggesting a continuing difficulty of meaning integration.
What is happening to insect numbers, and what does it mean?
Authors: Leather Simon R.
Published: June 2021

Reports of declines in abundance of a number of insect species have been increasing over the last two decades. These have variously been attributed to climate change, urbanisation, deforestation, agricultural intensification, habitat fragmentation and pesticide usage. The picture has been complicated by the fact that not all insect groups have shown the drastic declines reported for others, flawed methodology, paucity of long-term studies, the lack of data from the tropics with most long-term studies emanating from Europe and North America. In addition, the number of insect groups studied has largely been restricted to charismatic species such as Hymenoptera, Lepidoptera, Coleoptera and Odonata. Despite this, the evidence for long-term declines in insect abundance is incontrovertible. To aid in our understanding of the problem we need to set up more globally coordinated studies, use past data in innovative ways and convince policy makers and governments to support these studies.
Prevalence of disordered eating, eating disorders and risk of low energy availability in professional, competitive and recreational female athletes based in the United Kingdom
Authors: Sharps Francis Robert Jose , Wilson Laura Jane , Graham Catherine Anna‐Marie , Curtis Christopher
Published: June 2021

Eating disorders (ED), disordered eating (DE) and low energy availability (LEA) can be detrimental to health and performance. Previous studies have independently investigated the prevalence of ED, DE or LEA; however, few combined methods have identified risk within female athletes. The aim of this study was to identify the prevalence of ED, DE and LEA in UK‐based female athletes and investigate whether associations exist between age, competition level and primary sport. The Female Athlete Screening Tool (FAST) and Low Energy Availability in Females Questionnaire (LEAF‐Q) were used in a cross‐sectional study design. A total of 112 responses eligible for analysis were received. A total of 16%, 44% and 53% of female athletes were at risk of ED (FAST: >94), DE and LEA, respectively. Competition level (recreational, competitive or professional athletes; fishers, p ≤ 0.05) influenced and was a predictor of FAST (R 2 = 0.076, F (1,110) = 10.067, p ≤ 0.05, variance inflation value; VIF = 1.0) whereas age influenced (age: H (2) = 13.128, p ≤ 0.05), and was a predictor (R 2 = 0.144, F (2,109) = 9.170, p ≤ 0.05, VIF = 1.0) of LEAF‐Q. A positive correlation was observed between FAST and LEAF‐Q scores (R = 0.496, p ≤ 0.05). Age and competition level may be predicting risk factors of ED/DE and LEA within female athletes; however, further research is required to support the findings of this present study.
cMyBPC phosphorylation alters response to heart failure drug
Authors: Short Ben
Published: June 2021

JGP study shows that the phosphorylation state of cMyBPC modulates the ability of omecamtiv mecarbil to enhance myocardial force generation.
The response of optical fibres to gravitational waves
Authors: Mieling Thomas B
Published: June 2021

The response of optical fibre modes to plane gravitational waves (GW’s) of low frequency is computed. By solving perturbatively the Maxwell equations for step-index optical fibres in a GW background and implementing appropriate boundary conditions to describe single-mode fibres, explicit formulae for the perturbations of the phase and the polarisation of the fibre modes are obtained.
Systematic variation of design aspects for a significant increase in thermal fracture resistance of alumina microthrusters
Authors: Åkerfeldt Erika , Klintberg Lena , Thornell Greger
Published: June 2021

Because of thermal stresses occurring upon rapid heating or cooling, microcomponents made from high-temperature co-fired ceramics (HTCC) often fail at temperatures far below what the materials can withstand per se. This work investigates how resistance to thermal fracture in HTCC microcomponents can be increased by improving the component design, aiming at increasing the thermal performance of a microthruster with integrated heaters. The effect of four design parameters: component and cavity geometries (circular or square), heater location (central or peripheral), and addition of embedded platinum layers, on thermal fracture resistance was investigated through a full factorial designed experiment. Components of different designs were manufactured, and their thermal fracture resistance tested by rapid heating until failure. Peripheral heater location and presence of embedded platinum layers were seen to improve resistance to thermal fracture, whereas the shape of the component and the cavity did not significantly affect thermal performance. The most favourable design was then used for a cold gas microthruster that was fabricated and evaluated with respect to thermal fracture resistance. The microthruster survived rapid heating up to 1460 °C and was operated as a cold gas thruster at temperatures up to 772 °C, which is more than twice the maximum temperatures previously reported for alumina microthrusters.
Riemannian geometry and automatic differentiation for optimization problems of quantum physics and quantum technologies
Authors: Luchnikov Ilia A , Krechetov Mikhail E , Filippov Sergey N
Published: June 2021

Optimization with constraints is a typical problem in quantum physics and quantum information science that becomes especially challenging for high-dimensional systems and complex architectures like tensor networks. Here we use ideas of Riemannian geometry to perform optimization on the manifolds of unitary and isometric matrices as well as the cone of positive-definite matrices. Combining this approach with the up-to-date computational methods of automatic differentiation, we demonstrate the efficacy of the Riemannian optimization in the study of the low-energy spectrum and eigenstates of multipartite Hamiltonians, variational search of a tensor network in the form of the multiscale entanglement-renormalization ansatz, preparation of arbitrary states (including highly entangled ones) in the circuit implementation of quantum computation, decomposition of quantum gates, and tomography of quantum states. Universality of the developed approach together with the provided open source software enable one to apply the Riemannian optimization to complex quantum architectures well beyond the listed problems, for instance, to the optimal control of noisy quantum systems.
On the primordial information available to galaxy redshift surveys
Authors: McQuinn Matthew
Published: June 2021

We investigate the amount of primordial information that can be reconstructed from spectroscopic galaxy surveys, as well as what sets the noise in reconstruction at low wavenumbers, by studying a simplified universe in which galaxies are the Zeldovich displaced Lagrangian peaks in the linear density field. For some of this study, we further take an intuitive linearized limit in which reconstruction is a convex problem but where the solution is also a solution to the full nonlinear problem, a limit that bounds the effectiveness of reconstruction. The linearized reconstruction results in similar cross correlation coefficients with the linear input field as our full nonlinear algorithm. The linearized reconstruction also produces similar cross correlation coefficients to those of reconstruction attempts on cosmological N-body simulations, which suggests that existing reconstruction algorithms are extracting most of the accessible information. Our approach helps explain why reconstruction algorithms accurately reproduce the initial conditions up to some characteristic wavenumber, at which point there is a quick transition to almost no correlation. This transition is set by the number of constraints on reconstruction (the number of galaxies in the survey) and not by where shot noise surpasses the clustering signal, as is traditionally thought. We further show that on linear scales a mode can be reconstructed with precision well below the shot noise expectation if the galaxy Lagrangian displacements can be sufficiently constrained. We provide idealized examples of nonlinear reconstruction where shot noise can be outperformed.
The effect of finite halo size on the clustering of neutral hydrogen
Authors: Umeh Obinna , Maartens Roy , Padmanabhan Hamsa , Camera Stefano
Published: June 2021

Post-reionisation 21cm intensity mapping experiments target the spectral line of neutral hydrogen (HI) resident in dark matter haloes. According to the halo model, these discrete haloes trace the continuous dark matter density field down to a certain scale, which is dependent on the halo physical size. The halo physical size defines an exclusion region which leaves imprints on the statistical properties of HI. We show how the effect of exclusion due to the finite halo size impacts the HI power spectrum, with the physical boundary of the host halo given by the splashback radius. Most importantly, we show that the white noise-like feature that appears in the zero-momentum limit of the power spectrum is exactly cancelled when the finite halo size is taken into consideration. This cancellation in fact applies to all tracers of dark matter density field, including galaxies. Furthermore, we show that the exclusion due to finite halo size leads to a sub-Poissonian noise signature on large scales, consistent with the results from N-body simulations.
Self-similar orbit-averaged Fokker-Planck equation for isotropic spherical dense clusters (iii) Application to Galactic globular clusters
Authors: Ito Yuta
Published: June 2021

Fitting parametric models to globular clusters’ structural profiles has been essential for the study of stellar dynamics. It provides their important structural parameters, such as the concentrations and core radii of the clusters. However, existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution stage. Hence, a single parametric model cannot provide globular clusters’ structural parameters in both the early and late evolution stages. We have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck (OAFP) equation to model collapsingcore clusters at the late evolution stage. The present work establishes a new parametric model by combining the self-similar OAFP- and polytropic- models. Although it is a single-mass and isotropic model, the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution stages. As a main result, we show the characteristics of the relaxation times against the concentrations of the clusters. We also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.
A new class of viable and exact solutions of EFEs with Karmarkar conditions: an application to cold star modeling
Authors: Pant Neeraj , Govender Megandhren , Gedela Satyanarayana
Published: June 2021

In this work we present a theoretical framework within Einstein’s classical general relativity which models stellar compact objects such as PSR J1614–2230 and SAX J1808.4–3658. The Einstein field equations are solved by assuming that the interior of the compact object is described by a class I spacetime. The so-called Karmarkar condition arising from this requirement is integrated to reduce the gravitational behaviour to a single generating function. By appealing to physics we adopt a form for the gravitational potential which is sufficiently robust to accurately describe compact objects. Our model satisfies all the requirements for physically realistic stellar structures.
Physical and orbital properties of the stellar system HIP 43766
Authors: Widyan Hatem , Aljboor Hussam
Published: June 2021

In this paper, we present the analysis of the stellar binary system HIP 43766 to determine its properties. We rely on dynamical modeling and atmospheric modeling with recent data to determine the orbital solution and the physical properties of the system. There is a consistency between observed and synthetic photometry obtained using atmospheric modeling. The calculated dynamical mass sum of the system ranged between 1.691 and 2.609 solar masses, while it ranges between 2.0 and 2.1 as estimated utilizing atmospheric modeling. This could be due to inaccuracy in estimating the orbit, which could be modified with future observations with more relative positional measurements. The parameters of the system and the position of the components on the evolutionary tracks show that the system consists of F5 and G5 subgiant stars, mostly formed by fragmentation. A dynamical mass sum is predicted for the system.
Pollution tracks of r-process material in [Sr/Ba] vs. [Ba/Fe] space for the early Galaxy
Authors: Han Wan-Qiang , Yang Guo-Chao , Zhang Lu , Cui Wen-Yuan , Niu Ping , Wen Fang , Zhang Bo
Published: June 2021

In the early Galaxy, elemental abundances of the extremely metal-poor (EMP) stars contain abundant information about the neutron-capture nucleosynthesis and the chemical enrichment history. In this work, we study the abundance characteristics of Sr and Ba for the EMP stars in the [Sr/Ba] vs. [Ba/Fe] space. We find that there are three boundaries for the distribution region of the EMP stars. The weak r-process star CS 22897–008 lies on the upper end and the main r-process stars lie on the right end of the region. Near the right boundary of the distribution region, there is an Fe-normal belt. For the EMP stars in the belt, element Fe dominantly originates from the normal massive stars. The low-Sr stars ([Sr/Fe]≤−0.3) distribute in the region of the lower left of the Fe-normal belt and their Fe should originate partly from the prompt inventory. We find that the formation of the lower boundary of the distribution region is due to the pollution of the main r-process material and the formation of the right boundary could be explained by the combination of the weak r- and main r-process material. Furthermore, the formation of the left boundary is due to the pollution of the weak r-process material. Although the [Sr/Ba] ratios are related to the relative importance of the weak r-process material, the scatter of [Sr/Ba] ratios for the EMP stars mainly depends on the abundance ratio of the weak r-process.
Absolute parameters and observed flares in the M-type detached eclipsing binary 2MASS J04100497+2931023
Authors: Meng Gang , Zhang Li-Yun , Pi Qing-Feng , Long Liu , Han Xianming L. , Prabhakar Misra
Published: June 2021

The eclipsing binary 2MASS J04100497+2931023 (J04100497+2931023) is classified its spectral type of M0 ± 2V on basis of a low-resolution spectral survey by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The low-resolution spectra exhibit strong single-peak emission in the Hα line. We obtained the radial velocities of this binary by means of the Cross-Correlation Function method from the LAMOST medium-resolution spectra. Both components of J04100497+2931023 indicate strong emissions in the Hα line. We performed follow-up photometric observations of J04100497+2931023 using the Xinglong 85 cm telescope of National Astronomical Observatories, Chinese Academy of Sciences. We obtained its full light curve in VRI filters. We first determined their absolute parameters from simultaneously radial velocity and light curves by the Wilson-Devinney program. From our new light curves, we detected three flares for the first time, including one convective flare. The amplitudes, durations, energies, and spectral indices of three flares were also determined. J04100497+2931023 was monitored for approximately 29 h, which indicates that the flare rate is 0.1 flare per hour. We conclude that J04100497+2931023 is a low-mass detached eclipsing binary with strong magnetic activity.
New open clusters found by manual mining of data based on Gaia DR2
Authors: Casado Juan
Published: June 2021

The physical nature of a series of 20 new open clusters is confirmed employing existing data on putative star members, mainly from the second Gaia Data Release (DR2). The clusters were discovered as overdensities of stars by visual inspection of either photographic DSS plates or proper motion plots of random source fields. The reported objects are not present in the most comprehensive or recent catalogs of stellar clusters and associations. For all of them, clumps of comoving stars are revealed in the proper motion space. The parallaxes of the clumped stars are compatible with the real existence of open clusters over narrow ranges of distances. Surface density calculations, free of most noise from non-member sources, allow differentiating a cluster core and an extended cluster corona in some instances. Color-magnitude diagrams generally show a definite main sequence that allows confirmation of the physical existence of the clusters and some of their characteristics. Two of the new clusters seem to form a double system with a common origin. Several of the new clusters challenge the claim of near completeness of the known OC population in the distance range from 1.0 to 1.8 kpc from the Sun (Kharchenko et al.).
Radio frequency interference detection based on the AC-UNet model
Authors: Yan Rui-Qing , Dai Cong , Liu Wei , Li Ji-Xia , Chen Si-Ying , Yu Xian-Chuan , Zuo Shi-Fan , Chen Xue-Lei
Published: June 2021

Radio frequency interference (RFI) is a serious issue in radio astronomy. This paper proposes a U-Net network model with atrous convolution to detect RFI. Using the ability of convolutional neural networks to extract image features of RFI, and learning RFI distribution patterns, the detection model of the RFI is established. We use observational data containing real RFIs obtained by the Tianlai telescope to train the model so that the model can detect RFI. Calculate the probability of a data point being RFI pixel by pixel, and set a threshold. At the same time the dropout layer was added to avoid overfitting problems. If the predicted probability of a data point exceeds the threshold, it is considered that there is RFI, and if the predicted probability of a data point does not exceed the threshold, then it is considered that there is no RFI, so that the part of the image with RFI is flagged. Experimental results show that this approach can achieve satisfactory accuracy in the detection of radio observation images with a small amount of RFI.
Methodology for in-flight flat-field calibration of the Lyman-alpha solar telescope (LST)
Authors: Li Jing-Wei , Li Hui , Li Ying , Feng Li , Huang Yu , Zhao Jie , Lu Lei , Ying Bei-Li , Xue Jian-Chao
Published: June 2021

Flat-field reflects the non-uniformity of the photometric response at the focal plane of an instrument, which uses digital image sensors, such as Charge Coupled Device (CCD) and Complementary Metal-Oxide-Semiconductor (CMOS). This non-uniformity must be corrected before being used for scientific research. In this paper, we assess various candidate methods via simulation using available data so as to figure the in-flight flat-field calibration methodology for the Lyman-alpha Solar Telescope (LST). LST is one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission and consists of three instruments: a White-light Solar Telescope (WST), a Solar Disk Imager (SDI) and a dual-waveband Solar Corona Imager (SCI). In our simulations, data from the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) mission are used. Our results show that the normal KLL method is appropriate for in-flight flat-field calibration of WST and implementing a transmissive diffuser is applicable for SCI. For the in-flight flat-field calibration of SDI, we recommend the KLL method with off-pointing images with defocused resolution of around 18″, and use the local correlation tracking (LCT) algorithm instead of limb-fitting to determine the relative displacements between different images.
The first photometric analysis and period investigation of the K-type W UMa type binary system V0842 Cep
Authors: Li Yu-Yang , Li Kai , Liu Yuan
Published: June 2021

V0842 Cep is a W UMa-type binary star that has been neglected since its discovery. We analysed theVRcIclight curves, obtained by the 1 m telescope at Weihai Observatory of Shandong University, using the Wilson-Devinney code. V0842 Cep was found to be a shallow contact binary system (f= 8.7%) with a mass ratio of 2.281. Because its orbital inclination is greater than 80°, the photometric results are reliable. A period study is included which reveals a continually decreasing orbital period (dpdt= 1.50(±0.42)×10−7d yr−1). This trend could be attributed to the angular momentum loss via stellar wind.
The HI gas and star formation in star-forming galaxies selected from ALFALFA
Authors: Lei Feng-Jie , Wu Hong , Zhu Yi-Nan , Lam Man I. , Zhou Zhi-Min
Published: June 2021

This paper presents the results of Hα imaging of 169 galaxies randomly selected from the α.40 - SDSS catalog. The sample has excluded all low surface brightness galaxies (LSBGs) whose central surface brightness in B band (μ0(B)) fainter than 22.5 mag arcsec−2. It can be used as the counterparts sample to LSBGs. We observed their Hα and R band images by using the 2.16 m telescope at the Xinglong Observatory of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC). The main goal of this work is to present the properties of those galaxies, together with Hα flux and star formation-, gas-, stellar mass- surface density. In addition, we confirm the correlations among HI content, stellar mass and star formation in ALFALFA galaxies. The HI mass increases with stellar mass, and the slope slows down at the higher stellar mass. The overall trend was that the specific star formation rate (sSFR) decreases with stellar mass, and the sSFR dropped sharply when the stellar mass is close to 1010.3 ∼ 1010.5
M
⊙. The weak correlation between SFR/MHI and M
HI implies the HI contribute little to star formation. Our sample, which are mostly star-forming galaxies, follows the revisited Kennicutt-Schmidt law as well as the Kennicutt-Schmidt law.
Spectral deconvolution analysis on Olivine-Orthopyroxene mixtures with simulated space weathering modifications
Authors: Han Hui-Jie , Lu Xiao-Ping , Jiang Te , Hsia Chih-Hao , Yang Ya-Zhou , Zhang Peng-Fei , Zhang Hao
Published: June 2021

Olivine and pyroxene are important mineral end-members for studying the surface material compositions of mafic bodies. The profiles of visible and near-infrared spectra of olivine-orthopyroxene mixtures systematically vary with their composition ratios. In our experiments, we combine the RELAB spectral database with new spectral data obtained from some assembled olivine-orthopyroxene mixtures. We found that the commonly-used band area ratio (BAR, Cloutis et al.) does not work well on our newly obtained spectral data. To investigate this issue, an empirical procedure based on fitted results by a modified Gaussian model is proposed to analyze the spectral curves. Following the new empirical procedure, the end-member abundances can be estimated with a 15% accuracy with some prior mineral absorption features. In addition, the mixture samples configured in our experiments are also irradiated by pulsed lasers to simulate and investigate the space weathering effects. Spectral deconvolution results confirm that low-content olivine on celestial bodies is difficult to measure and estimate. Therefore, the olivine abundance of space weathered materials may be underestimated from remote sensing data. This study may be utilized to quantify the spectral relationship of olivine-orthopyroxene mixtures and further reveal their correlation between the spectra of ordinary chondrites and silicate asteroids.
Partitioning the Galactic halo with Gaussian Mixture Models
Authors: Liang Xi-Long , Chen Yu-Qin , Zhao Jing-Kun , Zhao Gang
Published: June 2021

The Galactic halo is supposed to form from merging with nearby dwarf galaxies. In order to probe different components of the Galactic halo, we have applied the Gaussian Mixture Models method to a selected sample of metal poor stars with [Fe/H] < –0.7 dex in the APOGEE DR16 catalogue based on four-parameters, metallicity, [Mg/Fe] ratio and spatial velocity (VR,Vϕ). Nine groups are identified with four from the halo (group 1, 3, 4 and 5), one from the thick disk (group 6), one from the thin disk (group 8) and one from dwarf galaxies (group 7) by analyzing their distributions in the ([M/H], [Mg/Fe]), (VR,Vϕ), (Zmax,eccentricity), (Energy,Lz) and ([Mg/Mn], [Al/Fe]) coordinates. The rest of the two groups are respectively caused by observational effect (group 9) and the cross section component (group 2) between the thin disk and the thick disk. It is found that in the extremely outer accreted halo (group 1), stars born in the Milky Way cannot be distinguished from those accreted from other galaxies either chemically or kinematically. In the intermediate metallicity of −1.6 < [Fe/H] < –0.7 dex, the accreted halo is mainly composed of the Gaia-Enceladus-Sausage substructure (group 5), which can be easily distinguished from group 4 (the in-situ halo group) in both chemical and kinematic space. Some stars of group 4 may come from the disk and some disk stars can be scattered to high orbits by resonant effects as shown in theZmaxversus Energy coordinate. We also displayed the spatial distribution of main components of the halo and the ratio of accreted components do not show clear relation to the Galactic radius.
Time Borrowing Flip-Flop architecture for error masking in near threshold voltage regime
Authors: Raj Abhinav , Arora Diwakar , Chaurasia Aman , Indu S.
Published: June 2021

This As dynamic delay variability increases with near-threshold voltage operation, wide timing margins need to be integrated in DVFS (Dynamic Voltage and Frequency Scaling) when deciding the frequency of operation to ensure reliable and error-free operation. Hence the maximum frequency (which is already low) in near-threshold operation is limited by these timing margins. Online methodologies for the resilience of temporal arrangement errors facilitate the recovery of temporal arrangement margins, increasing efficiency and/or energy consumption. This study presents a method for the resilience of online temporal arrangement errors that masks temporal arrangement errors by borrowing time from the phases of serial pipelines. Planned style, while not instruction replay or roll-back support, will recover temporal arrangement margins.