bluuebunny/crossref_metadata_2025 huggingface dataset:
Generating random Gaussian states
Authors: Leppäjärvi Leevi , Nechita Ion , Sengupta Ritabrata
Published: August 2024

We develop a method for the random sampling of (multimode) Gaussian states in terms of their covariance matrix, which we refer to as a random quantum covariance matrix (RQCM). We analyze the distribution of marginals and demonstrate that the eigenvalues of an RQCM converge to a shifted semicircular distribution in the limit of a large number of modes. We provide insights into the entanglement of such states based on the positive partial transpose criteria. Additionally, we show that the symplectic eigenvalues of an RQCM converge to a probability distribution that can be characterized using free probability. We present numerical estimates for the probability of a RQCM being separable and, if not, its extendibility degree, for various parameter values and mode bipartitions.
Evaluation of microgravity level for the 2.0 s vacuum drop tower at the National Precise Gravity Measurement Facility (PGMF)
Authors: Liu Ruiqi , Bai Yanzheng , Huang Tong , Li Qing , Mao Qiangbing , Wang Liang , Wu Shuchao , Yu Jianbo , Zhang Yitian , Zhou Zebing
Published: August 2024

The drop tower is an important experimental facility to provide a microgravity environment on the ground. The National Precise Gravity Measurement Facility has built a vacuum drop tower at Wuhan in China. The vacuum drop tower has a falling-height of 20 m, a free falling-time of 2.0 s, and a pressure of ∼6.15 Pa after 1 h pumping. The microgravity level of the vacuum drop tower is analyzed in this paper. The error sources include the aerodynamic drag, the difference of gas pressure around the gaps, the misalignment, the rotation, the magnetic field, etc. The evaluated microgravity level of the vacuum drop tower is better than (4.80 ± 3.31) × 10−7g, which is mainly limited by the aerodynamic drag and the rotation of the capsule. In addition, the microgravity level is measured to be better than 3.22 × 10−5g by using the quartz-flexure accelerometer. The vacuum drop tower provides a ground-based public service platform with a microgravity environment on the order of magnitude of 10−7g for further experiments.
Magnetic topological Kondo semimetal phases of matter
Authors: Ok Seulgi , Legner Markus , Vergniory Maia G. , Neupert Titus , Cook Ashley M.
Published: August 2024

Kondo physics has long been interesting for studying correlated topology in isolation, as it occurs in heavy fermion compounds where myriad phenomena are well-separated in energy. We introduce magnetic topological Kondo semimetal phases of matter into the literature in this work to advance the understanding of correlated topological semimetal physics by studying a layered three-dimensional heterostructure in which two types of Kondo insulators are stacked alternatingly. In the heterostructures considered, one of these Kondo insulators is SmB6, a potential topological Kondo insulator, and the other one is an isostructural Kondo insulator AB6, where A is a rare-earth element, e.g., Eu, Yb, or Ce. We find that if the latter Kondo insulator orders ferromagnetically, the heterostructure generically becomes a magnetic Weyl Kondo semimetal, while antiferromagnetic order can yield a magnetic Dirac Kondo semimetal. We also confirm the realization of the magnetic Weyl (Dirac) Kondo semimetal phase in density functional theory calculations of the heterostructure of SmB6 and EuB6 (CeB6). Our results demonstrate that Kondo insulator heterostructures are a versatile platform for realizing correlated topological semimetal phases.
An analytical modeling study on yaw-based wake redirection control for large-scale offshore wind farm annual energy power improvement
Authors: Tan Junyao , Wang Qiang , Luo Kun , Fan Jianren
Published: August 2024

Active yaw control (AYC) can effectively improve offshore wind farm power generation performance. This work aims to study the sensitivity of full wind conditions and different yaw offset threshold settings to active yaw control for wake redirection, power generation efficiency, and annual energy production at a large-scale wind farm in Hangzhou Bay in Zhejiang Province, China. The results demonstrated that the optimization of AYC largely depends on the wind direction, which determines the wake strength of the wind farm. In the medium-speed environment, AYC is not sensitive to the wind speed variation and a similar yaw angle can be implemented on the wind turbines in these conditions. Moreover, the performance of AYC under different yaw offset threshold settings is approximately the same at low and high wind speeds and the optimal yaw offset threshold is about ±25° for all turbines. Compared with the aligned condition, AYC can achieve a contribution rate of more than 15% for a total power increase at medium wind speed and eventually gains an annual energy production of 0.32%, which will promote the efficient development and utilization of offshore wind power.
Vibrational polaritons with broken in-plane translational symmetry
Authors: Li Tao E.
Published: August 2024

Vibrational polaritons form in a planar Fabry–Pérot microcavity when a vibrational mode of a layer of molecules is near resonant with an infrared cavity mode. Here, dispersion relations of vibrational polaritons are studied when the molecular density distribution breaks the macroscopic translational symmetry along the cavity mirror plane. Both perturbative theory and numerical calculations show that, if a homogeneous in-plane molecular distribution is modulated by sinusoidal fluctuations, in addition to a pair of upper and lower polariton branches, a discrete number of side polariton branches may emerge in the polariton dispersion relation. Moreover, for a periodic Gaussian in-plane density distribution, only two, yet significantly broadened polariton branches exist in the spectra. This polariton linewidth broadening is caused by the scattering between cavity modes at neighboring in-plane frequencies due to the symmetry breaking, which is distinguished from known origins of polariton broadening such as the homogeneous broadening of molecules, the cavity loss, or the large energetic disorder of molecules. Associated with the broadened polariton branches, under the periodic Gaussian in-plane inhomogeneity, a significant number of the vibrational strong coupling eigenstates contain a non-zero contribution from the cavity photon mode at zero in-plane frequency, blurring the distinction between the bright and the dark modes. Looking forward, our theoretical investigation should facilitate the experimental exploration of vibrational polaritons with patterned in-plane molecular density distributions.
High-order LG vortex Pr:YLF laser emitting in the visible wavelength range for the measurement of angular velocity
Authors: Zhang Yu , Yan Aoyu , Qi Yaoyao , Lü Jia-Qi , An Jiashuo , Sheng Quan , Bai Zhenxu , Wang Yulei , Lu Zhiwei
Published: August 2024

High-order vortex beams carrying orbital angular momentum in the visible wavelength range are of tremendous interest for a diversity of applications, including super-resolution imaging, microfabrication, and underwater communications. Such beams can be generated directly from compact solid-state lasers; however, they generally have low topological charge number. In this work, we demonstrate the generation of high-order Laguerre–Gaussian (LG) modes from a simple Pr:YLF laser cavity and demonstrate its application in the measurement of angular velocity. We utilize enhanced intracavity spherical aberration to generate LG0,±m modes with m selectable up to 34, directly from a Pr:YLF laser operating at 640 nm. We utilize this laser beam in an off-axis illumination geometry in conjunction with the rotational Doppler effect, to measure the angular velocity of a spinning object. The demonstration highlights a potential application for these types of vortex laser.
Rotating spintronic terahertz emitter optimized for microjoule pump-pulse energies and megahertz repetition rates
Authors: Vaitsi Alkisti , Sleziona Vivien , Parra López Luis E. , Behovits Yannic , Schulz Fabian , Martín Sabanés Natalia , Kampfrath Tobias , Wolf Martin , Seifert Tom S. , Müller Melanie
Published: August 2024

Spintronic terahertz emitters (STEs) are powerful sources of ultra-broadband single-cycle terahertz (THz) field transients. They work with any pump wavelength, and their polarity and polarization direction are easily adjustable. However, at high pump powers and high repetition rates, STE operation is hampered by a significant increase in the local temperature. Here, we resolve this issue by rotating the STE at a few 100 Hz, thereby distributing the absorbed pump power over a larger area. Our approach permits stable STE operation at a fluence of ∼1 mJ/cm2 with up to 18 W pump power at megahertz repetition rates, corresponding to pump-pulse energies of a few 10 μJ and pump power densities approaching 1 kW/cm2. The rotating STE is of interest for all ultra-broadband high-power terahertz applications requiring high repetition rates. As an example, we show that terahertz pulses with peak fields of 10 kV/cm can be coupled to a terahertz-light wave-driven scanning tunneling microscope at 1 MHz repetition rate, demonstrating that the rotating STE can compete with standard terahertz sources such as LiNbO3.
Investigating nonlinear magnetohydrodynamics in an optimized, reactor-scale quasi-axisymmetric stellarator
Authors: Wright A. M. , Ferraro N. M.
Published: August 2024

We use the new simulation capabilities of the extended-magnetohydrodynamic (MHD) code, M3D-C1, to investigate the nonlinear MHD properties of a reactor-scale quasisymmetric stellarator equilibrium. Our model captures the self-consistent evolution of the magnetic field, temperature, density, and flow profiles without imposing restrictions on the structure of the first. We include the effects of resistivity using a realistic temperature-dependent Spitzer model, along with a model for heat transport that captures the key physical characteristic, namely, strongly anisotropic diffusion in directions perpendicular and parallel to the magnetic field. We consider a quasi-axisymmetric, finite-pressure equilibrium that was optimized for self-consistent bootstrap current, quasi-symmetry, and energetic particle confinement. Our assessment finds that the equilibrium is highly unstable to interchange-like pressure-driven instabilities near the plasma edge. The initially unstable modes rapidly destabilize other modes in the direction of the N-fold rotational symmetry (toroidal, in this case). For this equilibrium, N = 2, meaning destabilization of a large number of even-numbered toroidal Fourier modes. Thus, field-periodicity is likely to be an important factor in the nonlinear MHD stability characteristics of optimized stellarators.
Photoluminescence study of MgGa2O4 spinel oxide films grown by molecular beam epitaxy
Authors: Yang Tianchen , Shou Chengyun , Tran Jason , Almujtabi Abdullah , Mahmud Quazi Sanjid , Zhu Edward , Li Yuan , Wei Peng , Liu Jianlin
Published: August 2024

As a promising ultrawide bandgap oxide semiconductor material in the spinel family, magnesium gallate (MgGa2O4) exhibits great potential applications in power electronics, transparent electronics, and deep ultraviolet optoelectronics. However, few studies reveal its photoluminescence (PL) properties. In this work, MgGa2O4 films were grown by using oxygen plasma assisted molecular beam epitaxy. The bandgap of MgGa2O4 spinel films is determined to be around 5.4–5.5 eV, and all samples have transmittance over 90% in the visible spectral range. X-ray diffraction patterns confirmed that the spinel films were grown highly along ⟨111⟩ oriented. Power and temperature dependent PL studies were investigated. Optical transitions involving self-trapped hole, oxygen vacancy deep donor, and magnesium atom on gallium site deep acceptor levels were revealed.
Topology optimization of acoustic mirror-symmetric waveguides for interface states in Bragg and non-Bragg gaps
Authors: Liu Ting , Wang Linge , Liu Hongwei , Yin Jingwei
Published: August 2024

Topology optimization, as a scientific and efficient intelligence algorithm, can be used to distribute the structures or materials with periodic units within the design domain to obtain the desired properties or functions. To induce interface states with high transmission and localization at the specified objective frequency, we propose a topology optimization design of the mirror-symmetric periodic waveguides based on the combination of the multiple population genetic algorithm and the finite element method. In addition to the traditional Bragg gaps, which are generated by the same low-order mode resonances, interface states can also be induced through the proposed topology optimization method in the non-Bragg gaps formed by the resonances of the more complex modes. The non-Bragg interface states possess higher localization due to the involvement of high-order modes in the non-Bragg resonances. This topology optimization method is expected to realize the wavefield manipulation of sound wave localization from a new perspective and provide a novel method for the design of devices for intense localization and high transmission.
Low-temperature growth of high-quality VO2 epitaxial film on c-plane sapphire by reactive magnetron sputtering
Authors: Liu Chang , Zheng Zhi , Li Xing , Wang Yang , Dong Xiang , Huang Gaoshan , Mei Yongfeng
Published: August 2024

The growth of VO2 epitaxial films has been researched extensively for obtaining excellent phase-transition performance. However, previous methods typically necessitate high temperatures or post-annealing processes, which elevate both experimental complexity and cost. In this work, we prepared high-quality VO2 epitaxial films by reactive magnetron sputtering directly under a low growth temperature. Benefiting from the determination of the oxygen pressure ratio from the theoretical analysis of the sputtering process model, single-stoichiometric VO2 epitaxial films could be prepared under 450 °C with a resistance change of 103, and above 500 °C with a resistance change exceeding 104. The mechanism of achieving low-temperature growth of VO2 epitaxial films was analyzed utilizing Thornton's zone model; finally, the epitaxial characteristics of VO2 on the sapphire substrate were confirmed from in-plane and out-of-plane directions. This work presents a guideline for the low-temperature growth of VO2 epitaxial films with enhanced phase-transition performance, thereby reducing both the cost and the requirements associated with the epitaxial growth of VO2 films.
Controlled flow around a finite square cylinder through suction at the side and free-end leading edge
Authors: Jin Xiaowei , Dai Mingwei , Zou Xuchao , Laima Shujin
Published: August 2024

The flow around a finite square cylinder with suction control at the side and a free-end leading edge is investigated through direct numerical simulations at a Reynolds number of 250. The absolute value of the ratio (Γ) between the suction velocity and the free-stream velocity is in the range of 0<Γ≤2. The results show that suction reduces the drag and fluctuating lift on the square cylinder. The optimal control effectiveness for reducing the fluctuating lift coefficient Cl′ and the average drag coefficient Cd¯ is achieved at Γ=0.375 and 0.75, respectively (Cl′ reduced by over 70% and Cd¯ reduced by nearly 20%). This is superior to the control effect achieved by active suction control only at the side leading edge. Compared to suction applied only at the side leading edge, adding suction at the free-end leading edge suppresses the flow separation on the top surface of the square cylinder. Moreover, with increasing suction ratios, the tornado-like Tip Vortex scale at the free-end of the square cylinder decreases, and the root mean square of streamwise velocity fluctuation at various spanwise planes decreases. Additionally, a data-driven balanced model-based dominant flow mode identification method is adopted to identify the dominant modes of the flow field at the z/d=0 plane at different suction ratios. The results show that suction can suppress the influence of the square cylinder on the far wake, and as the suction ratio increases, the area of the free flow expands.
Effects of entry angle on the water-entry cavity and motion hydrodynamics of a hollow cylinder
Authors: Huang Zhengui , Hou Yu , Cai Xiaowei , Chen Zhihua , Xu Yiming , Qin Jian
Published: August 2024

The oblique water entry of a hollow cylinder at various entry angles is numerically studied. The formation characteristics of the internal and external cavities, the curling splash, and the underwater rotation of the cylinder are revealed and analyzed. Our results show that asymmetric left- and right-attached cavities form near both the inner and outer walls of the cylinder. There are different formation patterns for the internal cavity between the left and right sides. The left internal cavity is mainly formed by the cavity shrinkage after closure, whereas the right internal cavity is formed by internal flow separation at small water-entry angles. An inclined concavity forms on the through-hole jet tip, induced by the rightward-curling splash. The rotation direction of the cylinder varies with entry angles and a critical angle exists. A periodic hydrodynamic force and moment are observed as the cylinder swings from side to side, resulting in a steady tail-slap motion.
Reduction of spin backflow with underlying bulk WSe2 in Pt/Py/Al trilayers
Authors: Chiu Kuan-Chia , Chu Yu-Hsun , Lin Minn-Tsong
Published: August 2024

To enhance spin–orbit torque (SOT) efficiency, various approaches exist, including the modification of spin mixing conductance through interface engineering. Recent studies have highlighted that transition metal dichalcogenides with strong spin–orbit couplings serve as spin sources and sinks even in few-layer configurations. In this study, we carry out spin torque ferromagnetic resonance measurements on SOT devices with insertion of a bulk WSe2 underlayer and reveal a notable increase in their spin mixing conductance and damping-like torque efficiency. Using the spin transparency model, we quantitatively unveil the reduction of the spin backflow factor, verifying the role of spin sink layers in SOT modification.
A nonlinear seepage theory model is developed using nuclear magnetic experiment and fractal theory
Authors: Dong Shuai , Liu Zhen , Yang He , Zhu Muyao , Li Zheng , Sun Zhaohui
Published: August 2024

The threshold pressure gradient becomes notably evident during water injection in soft, low-permeability coal seams. This phenomenon reduces the pressure hydrodynamic force and limits the effectiveness of dust reduction measures in coal mines through water injection. In this study, several mathematical models were developed to clarify the mechanism behind the threshold pressure gradient and identify the key parameters affecting permeability changes during this process. This model combines the stress sensitivity properties of the fluid boundary layer and coal body with fractal theory. The validity of the mathematical model was confirmed by comparing it with both visual experimental results from nuclear magnetic resonance water injection and other theoretical models. Particularly, the Bingham model effectively predicts the effective permeability of coal. Through the analysis of the influencing factors, it is found that the effective permeability increases with the pressure difference, pore compression coefficient, porosity, and maximum pore radius. Conversely, it decreases as the yield stress, fluid viscosity, tortuosity fractal dimension, and pore size distribution fractal dimension increase. Upon considering the impact of various factors, the pore compression coefficient was identified as having the most significant effect on coal permeability, whereas the yield stress has the greatest influence on the threshold pressure gradient. Collectively, our findings provide a theoretical foundation for enhancing the efficacy of water injection in soft, low-permeability coal seams.
Capturing the illusive ring-shaped intermediates in Aβ42 amyloid formation
Authors: Yuan Yu , Dong Xiaozhe , Wang Huan , Gai Feng
Published: August 2024

Protein/peptide amyloid fibril formation is associated with various neurodegenerative diseases and, hence, has been the subject of extensive studies. From a structure-evolution point of view, we now know a great deal about the initial and final states of this process; however, we know very little about its intermediate states. Herein, we employ liquid-phase transmission electron microscopy to directly visualize the formation of one of the intermediates formed during the aggregation process of an amyloid-forming peptide. As shown in figure, we find that Aβ42, the amyloid formation of which has been linked to the development of Alzheimer's disease, can populate a ring-shaped intermediate structure with a diameter of tens of nanometers; additionally, the air–liquid interface can “catalyze” the formation of amyloid fibrils.
A model with coupled Maxwell modes using Giesekus' postulate
Authors: Stephanou Pavlos S.
Published: August 2024

Relaxation modes must be considered coupled on several occasions, such as in polymer blends. Edwards et al. [J. Rheol, 40, 917–942 (1996)], using the generalized bracket formalism of non-equilibrium thermodynamics, provided the first thermodynamically derived constitutive model with coupled Maxwell modes by introducing relaxation coupling between the modes. In this work, we derive a similar model wherein coupling is introduced by using Giesekus' postulate to the mobility tensor and its introduction in the relaxation matrices, without considering cross-relaxation matrices. Our approach bears the following advantages over the work of Edwards et al.: (a) it derives the coupling term, instead of simply invoking it, by using the Giesekus postulate, (b) it is more in line with rheological experimental data for polymer blends, and (c) the proof of thermodynamic admissibility is easier to perform.
Persistent species relationships characterize migrating bird communities across stopover sites and seasons
Authors: DeSimone Joely G. , DeGroote Lucas W. , MacKenzie Stuart A. , Owen Jennifer C. , Patterson Andrea J. , Cohen Emily B.
Published: August 2024

Global migrations of diverse animal species often converge along the same routes, bringing together seasonal assemblages of animals that may compete, prey on each other, and share information or pathogens. These interspecific interactions, when energetic demands are high and the time to complete journeys is short, may influence survival, migratory success, stopover ecology, and migratory routes. Numerous accounts suggest that interspecific co-migrations are globally distributed in aerial, aquatic, and terrestrial systems, although the study of migration to date has rarely investigated species interactions among migrating animals. Here, we test the hypothesis that migrating animals are communities engaged in networks of ecological interactions. We leverage over half a million records of 50 bird species from five bird banding sites collected over 8 to 23 y to test for species associations using social network analyses. We find strong support for persistent species relationships across sites and between spring and fall migration. These relationships may be ecologically meaningful: They are often stronger among phylogenetically related species with similar foraging behaviors and nonbreeding ranges even after accounting for the nonsocial contributions to associations, including overlap in migration timing and habitat use. While interspecific interactions could result in costly competition or beneficial information exchange, we find that relationships are largely positive, suggesting limited competitive exclusion at the scale of a banding station during migratory stopovers. Our findings support an understanding of animal migrations that consist of networked communities rather than random assemblages of independently migrating species, encouraging future studies of the nature and consequences of co-migrant interactions.
Expressing gratitude in Nigerian English
Authors: Gut Ulrike , Unuabonah Foluke Olayinka
Published: August 2024

This study explores nativisation processes in the area of pragmatics. Focussing on expressions of gratitude, more
than 1,300 thanking speech acts elicited from Nigerian speakers of English via Discourse Completion Tasks (DCTs) and 628 thanking
speech acts identified in various text categories of the International Corpus of English-Nigeria (ICE-Nig) were
analysed (i) regarding the use of thanking strategy, linguistic expression and structural form and (ii) compared with other
varieties of English. The results show distinct strategies and forms of expressing gratitude in Nigerian English (NigE) that
suggest nativisation processes as they reflect local cultural and communicative practices. Furthermore, systematic differences
between thanking speech acts in the corpus data and those elicited in the DCTs were observed.
English tough-constructions and their analogues in French and Russian
Authors: Tsikulina Alina , Tayalati Fayssal , Soroli Efstathia
Published: August 2024

Evaluative constructions involving tough-predicates (e.g., This hill is difficult to
climb) present atypical structure-to-meaning mappings and vary across languages: in some languages (e.g.,
English/French), speakers typically use so-called tough-constructions (TCs) in which the syntactic subject of the
matrix sentence is logically the missing object of the infinitive; in others (e.g., Russian), speakers opt for a variety of
functional analogues (e.g., passive, impersonal constructions). The aim of this paper is to explore English TCs involving
difficult and easy adjectives, compare them to French and Russian analogues based on a parallel-corpus, and investigate how
specific semantic properties (animacy, transitivity, adjective scope) relate to specific (more or less compact) configurations.
The results show that French and Russian have similar functional analogues and only partially share the structural properties of
English TCs. The findings support a multidimensional account based on the inherent semantic properties of evaluative constructions
and their degree of compactness.
Calibrating sensitive actions in palliative care consultations
Authors: Günthner Susanne
Published: August 2024

This article explores physicians’ uses of “honestly” wenn (‘if’)-clauses in
German palliative care interactions. In “stretching
the old linguistics to meet the challenge of talk-in-interaction” (Schegloff
1996: 114), the study aims to further our understanding of how routinized communicative practices are
mobilized in response to local interactional needs within institutional interaction. Using methods and concepts of Interactional Linguistics, Social Constructivism, and Linguistic
Anthropology, I will illustrate how doctors in German
palliative consultations reconfigure traditional conditional wenn (‘if’)-clauses to adjust to local needs. With its focus on the
interactional practices participants use in palliative consultations as well as the way in which these practices both
conform to and (re)construct the institutional order, the analysis contributes to “New Perspectives in Interactional
Linguistic Research” by heightening awareness of the communicative construction of social reality within institutional
(i.e., palliative) settings. Furthermore, in applying Interactional Linguistics to palliative interactions, this paper not only aims to shed light on the
reflexive relationship between (routinized) interactional practices and the “social field” (Hanks 2007) of palliative communication, but it also contributes insights into the field of
applied Interactional Linguistics.
How grammar-for-interaction emerges over time
Authors: Pekarek Doehler Simona
Published: August 2024

This paper argues for a broadening of the analytic scope of Interactional Linguistics (IL) to embrace systematic investigation into
how grammar grows out of social interaction longitudinally. While IL has amply documented the ways in which grammar structures interaction
and emerges locally in real time within and across turns-in-progress, evidence for how social interaction motivates
the routinization (or: sedimentation) of grammatical usage patterns over time is scarce due to
lack of diachronic interactional data. I review the few
existing diachronic and synchronic studies on the issue, and argue that the investigation of
second language (L2) interactions opens new avenues for IL research, enabling us to empirically document the over-time emergence of grammar-for-interaction. I then present an analysis of the developmental trajectory of je sais pas ‘I don’t know’
in French L2 interactions across four proficiency levels, showing that the expression
progressively routinizes as an interaction-organizational marker in ways that exhibit parallels to diachronic grammaticalization processes. This demonstrates how the study of L2
interactions can provide developmental evidence for how
grammatical patterns emerge and sediment over iterative social encounters as resources for social interaction. The
investigation of L2 data hence creates new opportunities for IL research in view of a better understanding of grammar as an outcome of peoples’ acting in the social world.
Introducing new perspectives in interactional linguistic research
Authors: Selting Margret , Barth-Weingarten Dagmar
Published: August 2024

Since Interactional Linguistics (IL) is still
a relatively recent approach to the study of language in talk-in-interaction, this introduction will first briefly outline how
IL came about, what its current state is, and what it is
characterized by. Then we will go into more detail on the new research perspectives that are highlighted by the contributions
to this collection.
Electronic and Thermoelectric Properties in SnS-Nanoribbon-Based Heterojunctions
Authors: Zhang 张 Kai-Bo 凯波 , Tan 谭 Shi-Hua 仕华 , Peng 彭 Xiao-Fang 小芳 , Long 龙 Meng-Qiu 孟秋
Published: August 2024

As an earth-abundant and environmentally friendly material, tin sulfide (SnS) is not only a high-performance photovoltaic material, but also a new promising thermoelectric material. Despite extensive research on the thermoelectric properties of this material in recent years, the room-temperature thermoelectric figure of merit (ZT) of SnS has not been broke through 2 [2022 Sci. China Mater.
65 1143]. In this work, based on a combination of density functional theory and non-equilibrium Green’s function method, the electronic and thermoelectric properties in SnS-nanoribbon-based heterojunctions are studied. The results show that although SnS nanoribbons (SNSNRs) with zigzag edges (ZSNSNRs) and armchair edges (ASNSNRs) both have semiconductor properties, the bandgaps of ASNSNRs are much wider than those of ZSNSNRs, which induces much wider conductance gaps of N-ASNSNR (N is the number of tin-sulfide lines across the ribbon width)). In the positive energy region, the ZT peaks of L-SNS-Au are much larger than those of L-SNS-GNR (L represents the number of longitudinal repeating units of SNSNR in the scattering region). While in the positive energy region, the ZT peaks of L-SNS-GNR are larger than those of L-SNS-Au. Further calculations reveal that the figure of merit will be over 3.7 in L-SNS-Au and 2.2 in L-SNS-GNR at room temperature, and over 4 in L-SNS-Au and 2.6 in L-SNS-GNR at 500 K.
Electrohydrodynamic jet printed templates for hot embossing of microfluidic devices
Authors: Choubey Anupam , Bahga Supreet Singh
Published: August 2024

Hot embossing is a scalable method of fabricating microfluidic devices involving precise replication of micrometer-sized features from a master mold onto a thermoplastic substrate. Typically, high-resolution master molds for hot embossing are fabricated using expensive, resource-intensive processes such as photolithography and electron-beam lithography. Here, we present a maskless, cost-effective, and rapid microfabrication process based on electrohydrodynamic jet printing (EJP) for fabricating high-resolution reusable master templates for hot embossing of thermoplastic microfluidic devices. Our method is based on EJP to fabricate intricate polymeric templates, with feature sizes of order 100 µm, followed by a double casting process to obtain stiff PDMS master molds. Using these PDMS molds, we demonstrate the hot embossing of microfluidic devices with excellent reproducibility across multiple embossing cycles. In particular, we demonstrate the fabrication of microfluidic devices with simple geometries of cross-shape and Y-shape to complex geometries of flow-focusing droplet generator and tree-shaped gradient generator. Subsequently, we demonstrate the use of hot-embossed microfluidic devices for hydrodynamic focusing, droplet generation, and stable concentration gradient generation. Our method offers a low-cost and rapid alternative to traditional lithographic processes for fabricating master molds for hot embossing with comparable feature resolution.
First-principles study of the interaction of solutes with ∑3(11-1) symmetric tilt grain boundaries in α-Fe
Authors: Meftakhutdinov R M
Published: August 2024

The structural, cohesive and magnetic properties of a symmetric Σ3(70.53)[011](11-1) tilt grain boundary in pure bcc iron and with commonly used alloying elements (Si, Co, Mn, Ti, Cu, Mo, Nb, V, Cr and Ni) by means of density functional theory calculations are studied. Solubility and segregation energies were calculated for different positions of dissolved atoms. Calculations show a tendency for impurities to segregate near the boundary. It was found that the substituting Co, Cu and Ni in the layer adjacent to the boundary have an embrittling effect, while other atoms enhance the cohesion of the grains. Magnetic moments on GB atoms are significantly higher than those on bulk atoms.
Orientation optimization for high performance Mg3Sb2 thermoelectric films via thermal evaporation
Authors: Zhang Yiming , Li Bo , Han Zhijia , Feng Tao , Liu Zhenghao , Wu Xinzhi , Wang Qianjin , Zhu Kang , Hou Pengfei , Liu Weishu
Published: August 2024

Low-cost, highly efficient thermoelectric thin-film materials are becoming increasingly popular as miniaturization progresses. Mg3Sb2 has great potential due to its low cost and high performance. However, the fabrication of Mg3Sb2 thin films with high power factors (PFs) poses a certain challenge. In this work, we propose a general approach to prepare Mg3Sb2 thin films with excellent thermoelectric properties. Using a two-step thermal evaporation and rapid annealing process, (001)-oriented Mg3Sb2 thin films are fabricated on c-plane-oriented Al2O3 substrates. The structure of the film orientation is optimized by controlling the film thickness, which modulates the thermoelectric performance. The PF of the Mg3Sb2 at 500 nm (14 μW·m−1·K−2) would increase to 169 μW·m−1·K−2 with Ag doping (Mg3Ag0.02Sb2) at room temperature. This work provides a new strategy for the development of high-performance thermoelectric thin films at room temperature.
Equilibrium states for hyperbolic potentials via inducing schemes
*
Authors: Alves José F , Oliveira Krerley , Santana Eduardo
Published: August 2024

In a context of non-uniformly expanding maps, possibly with the presence of a critical set, we prove the existence of finitely many ergodic equilibrium states for hyperbolic potentials. Moreover, the equilibrium states are expanding measures. This generalizes a result due to Ramos and Viana, where analytical methods are used for maps with no critical sets. The strategy here consists in using a finite number of inducing schemes with a Markov structure in infinitely many symbols to code the dynamics, to obtain an equilibrium state for the associated symbolic dynamics and then projecting it to obtain an equilibrium state for the original map. We apply our results to the important class of multidimensional Viana maps.
Rethinking introductory physics: an approach for improving student persistence and performance by removing the calculus prerequisite
Authors: Capece A M , Richards A J
Published: August 2024

In an effort to improve retention and persistence in the physics major, we implemented a curriculum change at our institution in which we enroll in our calculus-based Physics I course the first-year physics majors who placed into the pre-calculus level. Prior to the intervention, 12.5% of non-calculus-ready students were retained within the major. Following the intervention, 50% of these students have either successfully graduated with a physics degree from our institution or are progressing through the major. This intervention can help address demographic disparities in physics education, since female, African American, Hispanic, and multiracial students are overrepresented in the non-calculus-ready group. In this paper we present the outcomes of the intervention, describe the strategies employed to accommodate and support non-calculus-ready students, and offer recommendations for departments seeking to create more inclusive learning environments that lead to better retention.
Predicting time-of-flight with Cerenkov light in BGO: a three-stage network approach with multiple timing kernels prior
Authors: Feng Xuhui , Ran Hengjia , Liu Huafeng
Published: August 2024

Objective. In the quest for enhanced image quality in positron emission tomography (PET) reconstruction, the introduction of time-of-flight (TOF) constraints in TOF-PET reconstruction offers superior signal-to-noise ratio. By employing BGO detectors capable of simultaneously emitting prompt Cerenkov light and scintillation light, this approach combines the high time resolution of prompt photons with the high energy resolution of scintillation light, thereby presenting a promising avenue for acquiring more precise TOF information. Approach. In Stage One, we train a raw method capable of predicting TOF information based on coincidence waveform pairs. In Stage Two, the data is categorized into 25 classes based on signal rise time, and the pre-trained raw method is utilized to obtain TOF kernels for each of the 25 classes, thereby generating prior knowledge. Within Stage Three, our proposed deep learning (DL) module, combined with a bias fine-tuning module, utilizes the kernel prior to provide bias compensation values for the data, thereby refining the first-stage outputs and obtaining more accurate TOF predictions. Main results. The three-stage network built upon the LED method resulted in improvements of 11.7 ps and 41.8 ps for full width at half maximum (FWHM) and full width at tenth maximum (FWTM), respectively. Optimal performance was achieved with FWHM of 128.2 ps and FWTM of 286.6 ps when CNN and Transformer were utilized in Stages One and Three, respectively. Further enhancements of 2.3 ps and 3.5 ps for FWHM and FWTM were attained through data augmentation methods. Significance. This study employs neural networks to compensate for the timing delays in mixed (Cerenkov and scintillation photons) signals, combining multiple timing kernels as prior knowledge with DL models. This integration yields optimal predictive performance, offering a superior solution for TOF-PET research utilizing Cerenkov signals.
Noise characterization analysis of dynamic dual-energy CT and its advantage in suppressing statistical noise
Authors: Li Liang , Sun Huahai , Yao Yidi , Chen Zhiqiang
Published: August 2024

Objective. Multi-energy CT conducted by photon-counting detector has a wide range of applications, especially in multiple contrast agents imaging. However, static multi-energy (SME) CT imaging suffers from higher statistical noise because of increased energy bins with static energy thresholds. Our team has proposed a dynamic dual-energy (DDE) CT detector model and the corresponding iterative reconstruction algorithm to solve this problem. However, rigorous and detailed analysis of the statistical noise characterization in this DDE CT was lacked. Approach. Starting from the properties of the Poisson random variable, this paper analyzes the noise characterization of the DDE CT and compares it with the SME CT. It is proved that the multi-energy CT projections and reconstruction images calculated from the proposed DDE CT algorithm have less statistical noise than that of the SME CT. Main results. Simulations and experiments verify that the expectations of the multi-energy CT projections calculated from DDE CT are the same as those of the SME projections. Still, the variance of the former is smaller. We further analyze the convergence of the iterative DDE CT algorithm through simulations and prove that the derived noise characterization can be realized under different CT imaging configurations. Significance. The low statistical noise characteristics demonstrate the value of DDE CT imaging technology.
Turn-table micro-CT scanner for dynamic perfusion imaging in mice: design, implementation, and evaluation
Authors: Allphin A J , Nadkarni R , Clark D P , Gil C J , Tomov M L , Serpooshan V , Badea C T
Published: August 2024

Objective. This study introduces a novel desktop micro-CT scanner designed for dynamic perfusion imaging in mice, aimed at enhancing preclinical imaging capabilities with high resolution and low radiation doses. Approach. The micro-CT system features a custom-built rotating table capable of both circular and helical scans, enabled by a small-bore slip ring for continuous rotation. Images were reconstructed with a temporal resolution of 3.125 s and an isotropic voxel size of 65 µm, with potential for higher resolution scanning. The system’s static performance was validated using standard quality assurance phantoms. Dynamic performance was assessed with a custom 3D-bioprinted tissue-mimetic phantom simulating single-compartment vascular flow. Flow measurements ranged from 1.5 1 to 9 ml min−1, with perfusion metrics such as time-to-peak, mean transit time, and blood flow index calculated. In vivo experiments involved mice with different genetic risk factors for Alzheimer’s and cardiovascular diseases to showcase the system’s capabilities for perfusion imaging. Main Results. The static performance validation confirmed that the system meets standard quality metrics, such as spatial resolution and uniformity. The dynamic evaluation with the 3D-bioprinted phantom demonstrated linearity in hemodynamic flow measurements and effective quantification of perfusion metrics. In vivo experiments highlighted the system’s potential to capture detailed perfusion maps of the brain, lungs, and kidneys. The observed differences in perfusion characteristics between genotypic mice illustrated the system’s capability to detect physiological variations, though the small sample size precludes definitive conclusions. Significance. The turn-table micro-CT system represents a significant advancement in preclinical imaging, providing high-resolution, low-dose dynamic imaging for a range of biological and medical research applications. Future work will focus on improving temporal resolution, expanding spectral capabilities, and integrating deep learning techniques for enhanced image reconstruction and analysis.
Transformer for low concentration image denoising in magnetic particle imaging
Authors: Liu Yuanduo , Zhang Liwen , Wei Zechen , Wang Tan , Yang Xin , Tian Jie , Hui Hui
Published: August 2024

Objective. Magnetic particle imaging (MPI) is an emerging tracer-based in vivo imaging technology. The use of MPI at low superparamagnetic iron oxide nanoparticle concentrations has the potential to be a promising area of clinical application due to the inherent safety for humans. However, low tracer concentrations reduce the signal-to-noise ratio of the magnetization signal, leading to severe noise artifacts in the reconstructed MPI images. Hardware improvements have high complexity, while traditional methods lack robustness to different noise levels, making it difficult to improve the quality of low concentration MPI images. Approach. Here, we propose a novel deep learning method for MPI image denoising and quality enhancing based on a sparse lightweight transformer model. The proposed residual-local transformer structure reduces model complexity to avoid overfitting, in which an information retention block facilitates feature extraction capabilities for the image details. Besides, we design a noisy concentration dataset to train our model. Then, we evaluate our method with both simulated and real MPI image data. Main results. Simulation experiment results show that our method can achieve the best performance compared with the existing deep learning methods for MPI image denoising. More importantly, our method is effectively performed on the real MPI image of samples with an Fe concentration down to 67 μgFe ml−1. Significance. Our method provides great potential for obtaining high quality MPI images at low concentrations.
Vertically aligned 2D tin sulfide (SnS) nanoplates for selective detection of ethanol gas at room temperature
Authors: Arora Hemant K , Jain Nikita , Kumar Sunil , Puri Nitin K
Published: August 2024

Detection of ethanol gas quickly and efficiently at room temperature is crucial for ensuring environmental, human as well as industrial safety. In this work, we have demonstrated a chemiresistive room temperature ethanol gas sensor based on vertically aligned tin sulfide (SnS) nanoplates. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) analysis have revealed the formation of orthorhombic, vertically aligned SnS nanoplates with high specific surface area. The sensor has been fabricated by depositing the SnS powder sample on ITO sheets using electrophoretic deposition (EPD), followed by the deposition of silver (Ag) electrodes using the thermal evaporation technique. The sensor obtained has exhibited a response value (R
g/R
a) of 17.4–400 ppm ethanol gas concentration, a quick response, and a recovery time of 12.4 s and 20.2 s at room temperature. The sensor has demonstrated long-term stability of 15 min, impressive selectivity, and remarkable repeatability across three successive test cycles of ethanol gas at 400 ppm. Based on the experimental sensing results, a plausible mechanism has been proposed for the sensor. The sensing response of SnS-based sensor at room temperature expands its potential for innovative applications across industries, marking a significant advancement in sensing technology.
Experimentally validated passive nonlinear capacitor in piezoelectric vibration applications
Authors: Ali Taşkıran M , Bülent Özer M
Published: August 2024

Piezoelectric vibration isolation and energy harvesting applications have been extensively studied in the literature. The studies include linear and nonlinear approaches. Linear methods are simpler but possess inherent limitations. On the other hand, nonlinear ones could perform better over a broader operating frequency range. Nonlinearity can be introduced in the mechanical domain or electrical domain actively or passively. Since electrical components can be on smaller scales compared to mechanical counterparts, inducing nonlinearity on the mechanical system through the electrical domain can be more practical. Moreover, passive structures require no energy supply and controller therefore they are simpler and more reliable than active ones. In this paper, a novel way to attain passive hardening stiffness was suggested by introducing an electrical component in a shunt circuit for passive nonlinear piezoelectric vibration isolation or energy harvesting applications and the induced structural non-linearity is demonstrated experimentally. A passive nonlinear component is suggested to be a hardening capacitor obtained by the P–N junction. An analytic model is derived for parallel connected macro-fiber composite (MFC) piezoelectric material attached bimorph configuration on a cantilever beam and the model is solved numerically. MFC integrated bimorph model, and P–N junction approximate model are presented. The frequency response of the coupled system is obtained by using numerical models and experiments. Both numerical analysis and experiments validated the hardening stiffness effect of the P–N junction. To the best of the authors’ knowledge, this study is the first study to demonstrate that nonlinear capacitance of P–N junctions can be used to attain nonlinearity in a mechanical system.