bluuebunny/crossref_metadata_2025 huggingface dataset:
Probing itinerant carrier dynamics at the diamond surface using single nitrogen vacancy centers
Authors: Mahdia Marjana , Allred James , Yuan Zhiyang , Rovny Jared , de Leon Nathalie P.
Published: February 2023

Color centers in diamond are widely explored for applications in quantum sensing, computing, and networking. Their optical, spin, and charge properties have extensively been studied, while their interactions with itinerant carriers are relatively unexplored. Here, we show that NV centers situated 10 ± 5 nm of the diamond surface can be converted to the neutral charge state via hole capture. By measuring the hole capture rate, we extract the capture cross section, which is suppressed by proximity to the diamond surface. The distance dependence is consistent with a carrier diffusion model, indicating that the itinerant carrier lifetime can be long, even at the diamond surface. Measuring dynamics of near-surface NV centers offers a tool for characterizing the diamond surface and investigating charge transport in diamond devices.
Stress–stress correlations reveal force chains in gels
Authors: Vinutha H. A. , Diaz Ruiz Fabiola Doraly , Mao Xiaoming , Chakraborty Bulbul , Del Gado Emanuela
Published: February 2023

We investigate the spatial correlations of microscopic stresses in soft particulate gels using 2D and 3D numerical simulations. We use a recently developed theoretical framework predicting the analytical form of stress–stress correlations in amorphous assemblies of athermal grains that acquire rigidity under an external load. These correlations exhibit a pinch-point singularity in Fourier space. This leads to long-range correlations and strong anisotropy in real space, which are at the origin of force-chains in granular solids. Our analysis of the model particulate gels at low particle volume fractions demonstrates that stress–stress correlations in these soft materials have characteristics very similar to those in granular solids and can be used to identify force chains. We show that the stress–stress correlations can distinguish floppy from rigid gel networks and that the intensity patterns reflect changes in shear moduli and network topology, due to the emergence of rigid structures during solidification.
Coexistence of three heteroclinic cycles and chaos analyses for a class of 3D piecewise affine systems
Authors: Wang Fanrui , Wei Zhouchao , Zhang Wei , Moroz Irene
Published: February 2023

Our objective is to investigate the innovative dynamics of piecewise smooth systems with multiple discontinuous switching manifolds. This paper establishes the coexistence of heteroclinic cycles in a class of 3D piecewise affine systems with three switching manifolds through rigorous mathematical analysis. By constructing suitable Poincaré maps adjacent to heteroclinic cycles, we demonstrate the occurrence of two distinct types of horseshoes and show the conditions for the presence of chaotic invariant sets. A family of attractors that satisfy the criteria are presented using this technique. It is shown that the outcomes of numerical simulation accurately reflect those of our theoretical results.
A von Hamos full-cylindrical spectrometer based on striped Si/Ge crystal for advanced x-ray spectroscopy
Authors: Guo Zhiying , Zhang Yujun , Xu Wei , Jin ShuoXue , Gan Xiaolong , Zhang Han , Chen Dongliang , Jia Quanjie
Published: February 2023

High-energy resolution core-level spectroscopies, including a group of different techniques to obtain element-specific information of the electronic structure around an absorption site, have become powerful tools for studying the chemical state, local geometric structure, and the nature of chemical bonding. High-resolution x-ray absorption and x-ray emission spectroscopies are well-established experimental techniques but have always been limited by the number of emitted photons and the limited acceptance of solid angles, as well as requiring high energy stability and repeatability for the whole experimental setup. A full-cylindrical x-ray spectrometer based on flexible HAPG (highly annealed pyrolitic graphite) mosaic crystals is an effective solution for the above issues. However, large-area HAPG remains expensive and is often not easy to access. Here, we present an alternative approach by using segmented single crystals (Si and Ge) with different orientations instead of the HAPG as a dispersive element. The proposed method drastically improved the energy resolution up to 0.2–2 eV in the range of 2–10 keV. High-pressure x-ray emission and resonant x-ray emission spectra are presented to demonstrate the capabilities of the instrument. The new design is particularly suitable for high-resolution spectroscopy applications at fourth-generation synchrotron radiation sources or free-electron lasers.
Computationally efficient Monte Carlo electron transport algorithm for nanostructured thermoelectric material configurations
Authors: Priyadarshi Pankaj , Neophytou Neophytos
Published: February 2023

Monte Carlo statistical ray-tracing methods are commonly employed to simulate carrier transport in nanostructured materials. In the case of a large degree of nanostructuring and under linear response (small driving fields), these simulations tend to be computationally overly expensive due to the difficulty in gathering the required flux statistics. Here, we present a novel Monte Carlo ray-tracing algorithm with computational efficiency of at least an order of magnitude compared to existing algorithms. Our new method, which is a hybrid of the analytical Boltzmann transport equation and Monte Carlo used a reduced number of ray-tracing particles, avoids current statistical challenges, such as the subtraction of two opposite going fluxes, the application of a driving force altogether, and the large simulation time required for low-energy carriers. We demonstrate the algorithm’s efficiency and power in accurate simulations in large domain nanostructures with multiple defects. We believe that the new method we present is indeed more robust and user friendly compared to common methods and can enable the efficient study of transport in nanostructured materials under low-field steady-state conditions.
Dynamic behavior of droplets impacting cylindrical superhydrophobic surfaces with different structures
Authors: Qian Lijuan , Huang Cong , Lv Li , Fu Qingfei , Fu Chao
Published: February 2023

The dynamic behavior of droplets impacting cylindrical superhydrophobic surfaces with different structures (azimuthal groove, axial groove, pillar) is studied in this work. The rebound and splash thresholds with different structures were also proposed, which depended on D/D0 (where D is the cylinder diameter and D0 is the initial droplet diameter) and the surface structure of the substrate. Based on the energy conservation approach, a complete rebound threshold semi-empirical model is constructed for cylindrical superhydrophobic surfaces. The recovery coefficient is used to measure the energy loss during the droplet impacting the superhydrophobic cylindrical surface. At the same time, the energy loss was significant on the cylindrical superhydrophobic surface with different structures, and the surface structure of the substrate played a vital role in the energy loss of the collision process. Then, a prediction formula for the maximum spread diameter on the cylindrical superhydrophobic surface with different structures is presented to understand the droplet collision behavior further. In addition, a level wing-like splash morphology could reduce contact time on grooved superhydrophobic surfaces. Based on the contact time [(βamax/βzmax)1/2τ] as a function of the Weber number, the azimuthal grooved structure surface has the least contact time.
Downward quantum learning from element 118: Automated generation of Fermi–Löwdin orbitals for all atoms
Authors: Pederson Mark R. , Johnson Alexander I. , Withanage Kushantha P. K. , Dolma Sherab , Flores Gustavo Bravo , Hooshmand Zahra , Khandal Kusal , Lasode Peter O. , Baruah Tunna , Jackson Koblar A.
Published: February 2023

A new algorithm based on a rigorous theorem and quantum data computationally mined from element 118 guarantees automated construction of initial Fermi–Löwdin-Orbital (FLO) starting points for all elements in the Periodic Table. It defines a means for constructing a small library of scalable FLOs for universal use in molecular and solid-state calculations. The method can be systematically improved for greater efficiency and for applications to excited states such as x-ray excitations and optically silent excitations. FLOs were introduced to recast the Perdew–Zunger self-interaction correction (PZSIC) into an explicit unitarily invariant form. The FLOs are generated from a set of N quasi-classical electron positions, referred to as Fermi-Orbital descriptors (FODs), and a set of N-orthonormal single-electron orbitals. FOD positions, when optimized, minimize the PZSIC total energy. However, creating sets of starting FODs that lead to a positive definite Fermi orbital overlap matrix has proven to be challenging for systems composed of open-shell atoms and ions. The proof herein guarantees the existence of a FLOSIC solution and further guarantees that if a solution for N electrons is found, it can be used to generate a minimum of N − 1 and a maximum of 2N − 2 initial starting points for systems composed of a smaller number of electrons. Applications to heavy and super-heavy atoms are presented. All starting solutions reported here were obtained from a solution for element 118, Oganesson.
Grand canonical Brownian dynamics simulations of adsorption and self-assembly of SAS-6 rings on a surface
Authors: Gomez Melo Santiago , Wörthmüller Dennis , Gönczy Pierre , Banterle Niccolo , Schwarz Ulrich S.
Published: February 2023

The Spindle Assembly Abnormal Protein 6 (SAS-6) forms dimers, which then self-assemble into rings that are critical for the nine-fold symmetry of the centriole organelle. It has recently been shown experimentally that the self-assembly of SAS-6 rings is strongly facilitated on a surface, shifting the reaction equilibrium by four orders of magnitude compared to the bulk. Moreover, a fraction of non-canonical symmetries (i.e., different from nine) was observed. In order to understand which aspects of the system are relevant to ensure efficient self-assembly and selection of the nine-fold symmetry, we have performed Brownian dynamics computer simulation with patchy particles and then compared our results with the experimental ones. Adsorption onto the surface was simulated by a grand canonical Monte Carlo procedure and random sequential adsorption kinetics. Furthermore, self-assembly was described by Langevin equations with hydrodynamic mobility matrices. We find that as long as the interaction energies are weak, the assembly kinetics can be described well by coagulation-fragmentation equations in the reaction-limited approximation. By contrast, larger interaction energies lead to kinetic trapping and diffusion-limited assembly. We find that the selection of nine-fold symmetry requires a small value for the angular interaction range. These predictions are confirmed by the experimentally observed reaction constant and angle fluctuations. Overall, our simulations suggest that the SAS-6 system works at the crossover between a relatively weak binding energy that avoids kinetic trapping and a small angular range that favors the nine-fold symmetry.
Reformulation of the Ornstein–Zernike relation for a homogeneous isotropic fluid of spherical symmetry
Authors: Rivera-Cerecero Sócrates A. , Lozada-Cassou Marcelo
Published: February 2023

A reformulation of the Ornstein–Zernike equation for a homogeneous isotropic fluid composed of m species, with spherical symmetry, is formally derived. Based on a factorization of matrices of composed functions, this reformulation provides an interesting new set of functions. As a test to this reformulation, the resulting equations are solved for a binary mixture of hard spheres and compared to those obtained from the standard solution of the Ornstein–Zernike equation and with molecular dynamics simulations.
Local ordering in Ge/Ge–Sn semiconductor alloy core/shell nanowires revealed by extended x-ray absorption fine structure (EXAFS)
Authors: Lentz J. Zach , Woicik J. C. , Bergschneider Matthew , Davis Ryan , Mehta Apurva , Cho Kyeongjae , McIntyre Paul C.
Published: February 2023

Short-range atomic order in semiconductor alloys is a relatively unexplored topic that may promote design of new materials with unexpected properties. Here, local atomic ordering is investigated in Ge–Sn alloys, a group-IV system that is attractive for its enhanced optoelectronic properties achievable via a direct gap for Sn concentrations exceeding ≈10 at. %. The substantial misfit strain imposed on Ge–Sn thin films during growth on bulk Si or Ge substrates can induce defect formation; however, misfit strain can be accommodated by growing Ge–Sn alloy films on Ge nanowires, which effectively act as elastically compliant substrates. In this work, Ge core/Ge1−xSnx (x ≈ 0.1) shell nanowires were characterized with extended x-ray absorption fine structure (EXAFS) to elucidate their local atomic environment. Simultaneous fitting of high-quality EXAFS data collected at both the Ge K-edge and the Sn K-edge reveals a large (≈ 40%) deficiency of Sn in the first coordination shell around a Sn atom relative to a random alloy, thereby providing the first direct experimental evidence of significant short-range order in this semiconductor alloy system. Comparison of path length data from the EXAFS measurements with density functional theory simulations provides alloy atomic structures consistent with this conclusion.
Precision mapping of a silicon test mass birefringence
Authors: Jaberian Hamedan V. , Adam A. , Blair C. , Ju L. , Zhao C.
Published: February 2023

Excellent mechanical and thermal properties of silicon make it a promising material for the test masses in future gravitational wave detectors. However, the birefringence of silicon test masses, due to impurity and residual stress during crystal growth or external stress, can reduce the interference contrast in an interferometer. Using the polarization–modulation approach and a scanning system, we mapped the birefringence of a float zone silicon test mass in the ⟨100⟩ crystal orientation to assess the suitability of such material for future gravitational wave detectors. Apart from the stress-induced birefringence at the supporting area due to the weight of the test mass, the high resolution birefringence map of the silicon test mass revealed a high birefringence feature in the test mass. At the central 40 mm area, birefringence is in the range of mid 10−9 to low 10−8, which satisfy the requirement for future gravitational wave detectors.
Strain enhanced magnetism of V-implanted CrI3 monolayer
Authors: Xu Jinlin , Huang Xiaokun , Hu Jiangnan , Mo Yunying , Nie Xin , Chen Chao , Song Guang , Liu Jiaqian , Liu Liang , Jiang Xiangping , Liu Jun-Ming
Published: February 2023

In recent years, one of the urgent issues for two dimensional (2D) magnetic materials is to find efficient ways in enhancing the magnetic ordering temperature Tc. It is believed that an in-plane (IP) compressive strain can greatly enhance the interatomic interactions by shortening the chemical bond length if at all possible, leading to the enlarged spin exchange and possibly higher Tc. However, a large compressive strain usually favors antiferromagnetic (AFM) ordering due to growing dominance of the Pauli exclusion principle, in contradiction with the common requirement of nonzero magnetization. In compromise, ferrimagnetic (FiM) ordering can be alternated by synthesizing artificial 2D compound with two magnetic sublattices. In this work, we propose a V-implanted CrI3 monolayer, short for V-(CrI3)2, and study its FiM ordering under a series of IP biaxial strains using the first-principles calculations and Monte Carlo simulations. It is found that the V-(CrI3)2 monolayer may evolve from the stripy-type AFM insulator toward the FiM half-metal with net magnetic moment of 5.0 μB/f.u. aligned in parallel to the ab-plane upon increasing the IP biaxial strain up to ∼−3% (compressive strain) and beyond. As the IP biaxial strain increases up to ∼−5%, the Tc of the FiM state may be raised to room temperature. This work suggests that the IP strain engineering combined with spin implantation can be an alternative strategy for enhancing 2D magnetism.
An exact imaginary-time path-integral phase-space formulation of multi-time correlation functions
Authors: Videla Pablo E. , Batista Victor S.
Published: February 2023

An exact representation of quantum mechanics using the language of phase-space variables provides a natural starting point to introduce and develop semiclassical approximations for the calculation of time correlation functions. Here, we introduce an exact path-integral formalism for calculations of multi-time quantum correlation functions as canonical averages over ring-polymer dynamics in imaginary time. The formulation provides a general formalism that exploits the symmetry of path integrals with respect to permutations in imaginary time, expressing correlations as products of imaginary-time-translation-invariant phase-space functions coupled through Poisson bracket operators. The method naturally recovers the classical limit of multi-time correlation functions and provides an interpretation of quantum dynamics in terms of “interfering trajectories” of the ring-polymer in phase space. The introduced phase-space formulation provides a rigorous framework for the future development of quantum dynamics methods that exploit the invariance of imaginary time path integrals to cyclic permutations.
Fabrication of interdigitated electrodes of graphene oxide/silica by femtosecond laser-induced forward transfer for sensing applications
Authors: Paula Kelly T. , Santos Sabrina N. C. , Facure Murilo H. M. , Araujo Francineide L. , Andrade Marcelo B. , Correa Daniel S. , Mendonça Cleber R.
Published: February 2023

Graphene-based materials, such as graphene oxide (GO), have been receiving much attention due to their graphene-like properties and compatibility with other materials. At the same time, novel printing methods have been developed for fabricating high-resolution patterns, such as Laser-Induced Forward Transfer (LIFT), which allows microscale transferring of a variety of materials to distinct substrates, enabling the design of micro- and nanodevices for biomedical and opto-electronic application. In this work, we propose the use of LIFT with fs-laser pulses for creating high-resolution interdigitated electrodes of tetraethyl orthosilicate functionalized with GO. The fs-LIFT approach successfully allowed micro-patterning of lines with widths on the order of 2 μm, with threshold energy of 70 nJ, and the reduction of graphene oxide to fabricate silica/GO films in an efficient, controlled, and localized way, without material degradation. As a proof of principle, interdigitated electrodes fabricated by fs-LIFT were successfully used as the sensing units of an impedimetric electronic tongue for taste recognition and heavy metals ions detection (Al3+, Hg2+, Co2+, and Cu2+) at different concentrations of 100 nmol l−1, 10 μmol l−1, and 1 mmol l−1.
Impact of the local atomic structure on the thermal conductivity of amorphous Ge2Sb2Te5
Authors: Guerboub Mohammed , Wansi Wendji Steve Dave , Massobrio Carlo , Bouzid Assil , Boero Mauro , Ori Guido , Martin Evelyne
Published: February 2023

Thermal properties are expected to be sensitive to the network topology, and however, no clearcut information is available on how the thermal conductivity of amorphous systems is affected by details of the atomic structure. To address this issue, we use as a target system a phase-change amorphous material (i.e., Ge2Sb2Te5) simulated by first-principles molecular dynamics combined with the approach-to-equilibrium molecular dynamics technique to access the thermal conductivity. Within the density-functional theory, we employed two models sharing the same exchange-correlation functional but differing in the pseudopotential (PP) implementation [namely, Trouiller–Martins (TM) and Goedecker, Teter, and Hutter (GTH)]. They are both compatible with experimental data, and however, the TM PP construction results in a Ge tetrahedral environment largely predominant over the octahedral one, although the proportion of tetrahedra is considerably smaller when the GTH PP is used. We show that the difference in the local structure between TM and GTH models impacts the vibrational density of states while the thermal conductivity does not feature any appreciable sensitivity to such details. This behavior is rationalized in terms of extended vibrational modes.
The dynamics of directional transport of a droplet in programmable electrowetting channel
Authors: Huo Xiaozhi , Li Long , Yang Yang , Liu Xuefeng , Yu Qiang , Wang Qinggong
Published: February 2023

Directional fluid transport by electrowetting is an effective method for fluid management both on Earth and in the space environment. Exact control of the process is always hard because the fundamental dynamics of fluid flow and interface are not well understood. In this study, we examine the process of a sensible droplet transported directionally in an electrowetting channel. The electrodes of the channel are programmed to actuate the droplet at the most effective manner. We build a numerical model based on the phase field method, and a dynamic contact angle model is incorporated in the model. Based on simulated results, the basic process of droplet deformation and motion is explained. Three different stages are observed when the droplet starts to move in the electrowetting channel. The droplet can be transported at a high velocity of 17 mm/s at a voltage of V = 80 V. A wide range of influence factors, including voltage, droplet size, friction factor, pinning force, channel height, gravity level, and tilted angle of the channel, are considered. The contact line friction increases almost linearly with the contact line friction coefficient and the pinning force, both retarding the motion of the droplet at parabolic relations. With an increase in the gravity level, the transport velocity of large droplet decreases. However, the droplet smaller than the capillary length shows quite good anti-gravity capability, which can be transported smoothly even when the channel is tilted by 90° in a normal gravity.
Hydrophobicity induced drag reduction: Perspectives from the slip length
Authors: Tao Zhi , Fang Weidong , Li Haiwang , Huang Yi , Xu Tiantong , Wu Hanxiao , Li Murun
Published: February 2023

Hydrophobicity has been developed in many areas, whose potentials in drag reduction at microscale have attracted numerous attentions for expanding the practical applications in fields of on chip devices, materials synthesis, and enhanced heat transfer. In this article, we select polydimethylsiloxane (PDMS) as the base material, whose hydrophobic modifications have been well developed. Among them, hydrofluoric acid treated one shows great performance and leads us to two types of microchannels, the straight and U-shaped, with enhanced hydrophobicity (from 91° to 106°). The coefficients of the pressure drop are experimentally measured with the Reynolds number ranging from 0 to 300. The results illustrate that the drag reduction rate reaches at 37.8% for the straight microchannel and 26.8% for the U-shaped microchannel. With the increase in the Reynolds number, the drag reduction effect stays almost constant for the straight channel, while it decreases gradually for the U-shaped channel. The flow impingement induced by a centrifugal force has an important impact on the slip effect that grows with the Re. Next, we adopt the numerical method and the micro-particle imaging velocimetry measurement to analyze the drag reduction effect from perspectives of the slip length. We successfully derive the slip length model correlating the drag reduction effect. Our results not only achieve substantial drag reduction in PDMS microchannels, but also provide a quantitative correlation between hydrophobicity and drag reduction, offering a feasible strategy for extensive applications at microscale, such as fluid actuation, bio-chip analysis, and highly efficient cooling system.
Hippocampal–cortical coupling differentiates long-term memory processes
Authors: Dahal Prawesh , Rauhala Onni J. , Khodagholy Dion , Gelinas Jennifer N.
Published: February 2023

Reactivation of long-term memories enables experience-dependent strengthening, weakening, or updating of memory traces. Although coupling of hippocampal and cortical activity patterns facilitates initial memory consolidation, whether and how these patterns are involved in postreactivation memory processes are not known. Here, we monitored the hippocampal–cortical network as rats repetitively learned and retrieved spatial and nonspatial memories. We show that interactions between hippocampal sharp wave–ripples (SPW-R), cortical spindles (SPI), and cortical ripples (CXR) are jointly modulated in the absence of memory demand but independently recruited depending on the stage of memory and task type. Reconsolidation of memory after retrieval is associated with an increased and extended window of coupling between hippocampal SPW-Rs and CXRs compared to the initial consolidation. Hippocampal SPW-R and cortical spindle interactions are preferentially engaged during memory consolidation. These findings suggest that specific, time-limited patterns of oscillatory coupling can support the distinct memory processes required to flexibly manage long-term memories in a dynamic environment.
Phenomenological understanding of kappa-carbides on strengthening mechanism of low-density steel
Authors: Wei L. L. , Gao G. H. , Misra R. D. K.
Published: February 2023

We elucidate here the phenomenological understanding of deformation mechanisms over a wide range of strain rates (5.5 × 10–4s–1 to 5.5 × 10–1s–1) based on the evolution of microstructure. Atom probe tomography (APT), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) experiments were conducted to reveal the spatial distribution of precipitates and microstructure evolution. The ordered kappa-carbides were characterised by a layered-type structure, which made it difficult for dislocations to by-pass kappa-carbides in the same layer individually and the corresponding strengthening mechanism was cutting mechanism. Dislocations and microbands evolution analysis shows that compared to dislocations, slip band width was the key factor that governed the strength of the experimental steel at different strain rates.
Nanoindentation size effects of mechanical and creep performance in Ni-based superalloy
Authors: Huang Yanyan , Zhou Cheng , Chen Keyan , Yang Yuxin , Xiong Jiankun , Yang Jianping , Guo Yang , Mao Guijun , Yang Lin , Nie Fuheng , Li Xia , Zhou Qinghua
Published: February 2023

Nanoindentation technique was adopted to study indentation size effects of physical-mechanical and creep performance with various depths (200–2000 nm) in GH901 utilising sharp and spherical tip. Residual impressions of both indenters with pile-up patterns are discussed. Nanohardness, reduced modulus and elastic recovery rates curves versus maximum displacement of two tips are obtained and nanohardness size effects are discussed with different models for Berkovich tip. The data obtained with spherical indentation are analysed separately by establishing stress–strain diagram. The creep results using Berkovich tip indicate that creep strain rate declines while creep stress exponent first decreases and then increases with the increasing depth; the creep stress exponent ( n) values, 2.39–7.35, imply the dominant creep deformation mechanism is dislocation control.
Curvature and dynamical spacetimes: can we peer into the quantum regime?
Authors: Cardoso Vitor , Hilditch David , Marouda Krinio , Natário José , Sperhake Ulrich
Published: February 2023

Stationary compact astrophysical objects such as black holes and neutron stars behave as classical systems from the gravitational point of view. Their (observable) curvature is everywhere ‘small’. Here we investigate whether mergers of such objects, or other strongly dynamical spacetimes such as collapsing configurations, may probe the strong-curvature regime of general relativity. Our results indicate that dynamical black hole spacetimes always result in a modest increase

∼

3

in the Kretschmann scalar, relative to the stationary state. In contrast, we find that the Kretschmann scalar can dynamically increase by orders of magnitude, during the gravitational collapse of scalar fields, and that the (normalized) peak curvature does not correspond to that of the critical solution. Nevertheless, without fine tuning of initial data, this increase lies far below that needed to render quantum-gravity corrections important.
Quantum chemistry simulations in an undergraduate project: tellurophenes as narrow bandgap semiconductor materials
Authors: Walker Bethany , Finlayson Chris E
Published: February 2023

The convenient graphical user-interfaces now available with advanced simulation software offer a powerful didactic tool for research-led teaching of methods in quantum chemistry and wider applications of quantum mechanics. In the student project work reported here, a homologous series of semiconducting chalcogenophenes (encompassing poly-thiophenes, poly-selenophenes and poly-tellurophenes) with varying polymer chain lengths were simulated in detail using density functional theory (DFT). Following geometry optimization, energy calculations reveal that increasing the length of the polymer chain (N) from a monomer to a hexamer leads to a narrowing and large-N convergence of the bandgap. It is found that hexa-tellurophene has significantly favourable electronic properties as compared to the other analogues, with a greatly enhanced electron affinity (−2.74 eV), and a corresponding bandgap energy of 2.18 eV, giving a superior matching to the solar spectrum.
Adaptive weight-based capsule neural network for bearing fault diagnosis
Authors: Zhao Xiaoqiang , Chai Jingxuan
Published: February 2023

In industrial systems, the vibration signals of rolling bearings are highly complex due to varying operating conditions and ambient noise. Presented with signals with a lack of features after being disturbed by a complex environment, traditional convolutional neural networks cannot diagnose bearing faults accurately and effectively. This paper proposes a dynamic capsule network (DCCN) based on adaptive shared weights to solve the above problems. To learn the features of the vibration signals, the convolution weights are adaptively adjusted and shared to different convolutional layers through an attention mechanism, which can effectively reduce the computational cost of the network. In addition, a dynamic routing algorithm is used to generate sub-capsules that share weights. These sub-capsules extract and transform the fault features into vector features information storage to reduce feature loss. Finally, the feature-extraction capability of the DCCN is enhanced by concatenating the dynamic convolution using skip connect lines. The effectiveness of the proposed method is verified by noise and variable-load experiments, and the DCCN exhibits a better generalization and diagnosis performance than current advanced deep-learning methods.
A new continuous dynamic system for measuring the sphericity error of bearing balls
Authors: Yang Ping , Yang Bingya , Kong Yangbo , Wang Bo
Published: February 2023

The sphericity error is one of the most important tolerances to evaluate the dimensional accuracy of bearing balls. A continuous dynamic measurement system based on an industrial camera and a Z-shaped transparent track is developed to measure the sphericity error of bearing balls. The Z-shaped track, which is considered for the parameter setting of length, width and inclination, is designed to achieve a pure rolling of the ball around three perpendicular axes. During the whole measurement process, 15 images are dynamically captured by an industrial camera and divided into three groups according to the three mutually perpendicular directions. Then, a sub-pixel edge contour of the bearing ball from each image is extracted by an image-processing step, such as image de-noising, contrast enhancement, region-of-interest extraction and edge detection. Finally, the roundness error and sphericity error, as defined by ISO 12181-1 and ISO 3290-1, are acquired from the extracted contour of each image. Three different diameter bearing balls with a precision grade of G1000, representing a sphericity error of approximately 25 μm, are applied as experimental objects. The two times standard deviation roundness error obtained from the contour of each image are all less than 7 μm after six repeated measurements. In addition, the two measurement results respectively acquired from the proposed method and a commercial projection measuring instrument have good consistency.
Restoration of motion-blurred star images with elliptical star streaks
Authors: Fan Qiao-yun , Zhang Miao , Xue Yao-ke
Published: February 2023

The restoration of motion-blurred star images under high dynamic conditions is important for the high-precision attitude measurement of star sensors. Through motion modelling analysis, it is found that the streak of the imaged star point (star streak) is an elliptical arc. However, existing star image restoration methods are only suitable for the case where the star streak is a straight line. For this reason, a star image restoration algorithm for elliptical star streaks is proposed in this paper. First, the elliptical star streak is transformed into a circular star streak by projective transformation. Then, the circular star streak is transformed into a straight star streak by polar coordinate transformation. Finally, the restored original star image is obtained by restoration methods for straight star streaks and coordinate inverse transformation. At the same time, the algorithm is further optimized by subdividing the polar coordinates. The experiment shows that the proposed algorithm is effective and the restoration accuracy is at the same level as that of existing star image restoration methods for straight star streaks.
A time asynchronous parameters calibration method of high-precision FOG-IMU based on a single-axis continuous rotation scheme
Authors: Chang Jiachong , Fan Shiwei , Zhang Ya , Li Jingchun , Shao Jianbo , Xu Dingjie
Published: February 2023

There is a time asynchronous problem with the output signals between each inertial sensor in an actual high-precision fiber optic gyro inertial measurement unit (FOG-IMU), which reduces the velocity update accuracy of the strap-down inertial navigation system in the actual applications. Firstly, the velocity error formulas are derived in the coordinate navigation system considering three time asynchronous errors between the three-axis accelerometers and gyros. Then an error-state Kalman filter is designed with respect to the time asynchronous parameters measurement model in angular dynamic environments. Afterward, a single-axis continuous rotation scheme is developed to calibrate the time asynchronous parameters. In particular, a simple observability analysis model is proposed to verify the rationality of the calibration scheme. Furthermore, the time asynchronous parameters are calculated effectively based on the proposed indirect calibration scheme. Finally, the proposed method is verified effectively through simulations and turntable experiments, which can significantly reduce the measurement errors of high-precision FOG-IMU. As a result, compared with the traditional three-parameter direct calibration method, the eastward and northward velocity errors are reduced by 7.01% and 2.48%, respectively.
On the potential biological impact of radiation-induced acoustic emissions during ultra-high dose rate electron radiotherapy: a preliminary study
Authors: Lascaud Julie , Parodi Katia
Published: February 2023

Ionizing radiation pulses delivered at ultra-high dose rates in emerging FLASH radiotherapy can result in high-intensity low-frequency thermoacoustic emissions that may have a biological impact. This study aims at providing insights into the thermoacoustic emissions expected during FLASH radiotherapy and their likelihood of inducing acoustic cavitation. The characteristics of acoustic waves induced by the energy deposition of a pulsed electron beam similar to previous pre-clinical FLASH radiotherapy studies and their propagation in murine head-like phantoms are investigated in-silico. The results show that the generated pressures are sufficient to produce acoustic cavitation due to resonance in the irradiated object. It suggests that thermoacoustics may, in some irradiation scenarios, contribute to the widely misunderstood FLASH effect or cause adverse effects if not taken into account at the treatment planning stage.
Deep learning aided oropharyngeal cancer segmentation with adaptive thresholding for predicted tumor probability in FDG PET and CT images
Authors: De Biase Alessia , Sijtsema Nanna M , van Dijk Lisanne V , Langendijk Johannes A , van Ooijen Peter M A
Published: February 2023

Objective. Tumor segmentation is a fundamental step for radiotherapy treatment planning. To define an accurate segmentation of the primary tumor (GTVp) of oropharyngeal cancer patients (OPC) each image volume is explored slice-by-slice from different orientations on different image modalities. However, the manual fixed boundary of segmentation neglects the spatial uncertainty known to occur in tumor delineation. This study proposes a novel deep learning-based method that generates probability maps which capture the model uncertainty in the segmentation task. Approach. We included 138 OPC patients treated with (chemo)radiation in our institute. Sequences of 3 consecutive 2D slices of concatenated FDG-PET/CT images and GTVp contours were used as input. Our framework exploits inter and intra-slice context using attention mechanisms and bi-directional long short term memory (Bi-LSTM). Each slice resulted in three predictions that were averaged. A 3-fold cross validation was performed on sequences extracted from the axial, sagittal, and coronal plane. 3D volumes were reconstructed and single- and multi-view ensembling were performed to obtain final results. The output is a tumor probability map determined by averaging multiple predictions. Main Results. Model performance was assessed on 25 patients at different probability thresholds. Predictions were the closest to the GTVp at a threshold of 0.9 (mean surface DSC of 0.81, median HD95 of 3.906 mm). Significance. The promising results of the proposed method show that is it possible to offer the probability maps to radiation oncologists to guide them in a in a slice-by-slice adaptive GTVp segmentation.
A flexible 8.5 MHz litz wire receive array for field-cycling imaging
Authors: Stormont Robert S , Davies Gareth R , Ross P James , Lurie David J , Broche Lionel M
Published: February 2023

Objectives. Low frequency coils present unique challenges as loop losses, component losses, and the supporting electronics can significantly degrade the signal-to-noise ratio (SNR). SNR may already be a limiting factor with MRI at low field (and frequency), therefore the minimization of additional loss is particularly important. If interactions between loops are managed, array coils can provide increased SNR, coverage, and potentially imaging speed. In this work, we investigate methods to characterise and preserve SNR from a low frequency coil array, allowing a more geometrically conforming array for quick, no-tune application with various anatomies. Approach. Single and multi-turn, 16.2 cm diameter litz wire loops were constructed and characterised for losses under various loading conditions. Low noise preamplifiers were acquired and characterized, as well as interfacing electronics were developed and evaluated. A bench level SNR test was implemented to observe the effects of tuning and loading on individual coils. The results were used to select a design for construction of a 6-channel, flex array coil. Main results. Ultra fine strand litz wire exhibited lower losses than equivalent diameter solid wire which should translate to improved SNR and provides the mechanical flexibility needed in a conforming array. Single turn loop losses were dominant under all loading conditions; however, 2 and 3 turn loops were body loss dominated under modest loading conditions. Preamplifier blocking achieved was well short of our design goal and critical overlaps became necessary for coil-to-coil interaction control. Our finished array, a 3-channel posterior array coil and a 3-channel anterior array coil, conforms nicely to various anatomies and is providing consistent results in various volunteer study trials. Significance. Receive coils are challenging at low fields as loop losses often limit the final SNR. This is exacerbated in an array coil as loops may be smaller and not coupled well to the body. In this work we have demonstrated that body loss dominance is possible with 16.2 cm loops at 8.5 MHz. We have optimized, built, and tested low noise interfacing electronics and characterized the SNR penalties as the tuning and loading is varied, a key parameter in a geometrically flexible array designed for rapid setup. The resultant 6-channel, general-purpose array is supporting various Field-Cycling Imaging studies where body habitus and anatomies require a flexible, adaptable array coil which can be quickly positioned and utilized.
Spatially and temporally resolved atomic oxygen densities in a micro cavity plasma array
Authors: Steuer David , van Impel Henrik , Schulz-von der Gathen Volker , Böke Marc , Golda Judith
Published: February 2023

Micro cavity plasma arrays have numerous applications, such as the treatment of volatile organic compounds or the generation of new species. In recent years, the focus has also shifted to plasma catalysis, in which catalytic surfaces are combined with plasmas. The key to all of these applications is the generation of reactive species such as atomic oxygen within the plasma. Typically, atomic oxygen densities can be measured by laser spectroscopic methods. In the case of a micro plasma array, which consists of thousands of cavities with a diameter between 50 and 200 µm, optical access is limited. For this reason, an optical emission spectroscopy approach, helium state enhanced actinometry, is used. 2D resolved narrow bandwidth measurements are performed by using an ICCD camera in combination with a tunable bandpass filter (550–1000 nm). The discharge is operated in helium with an oxygen admixture of 0.1%. An argon admixture of 0.05% is used as actinometer gas. The triangular excitation voltage is varied between amplitudes of 400 and 800 V at a frequency of 15 kHz. Very high dissociation degrees up to nearly complete dissociation are observed. Time resolved measurements show significant differences in oxygen density between the increasing and the decreasing potential phase.
Cascode Configuration of GaN Static Induction Transistor for MHz Power Switch Applications
Authors: Li Wenwen , Ji Dong
Published: February 2023

A cascoded GaN static induction transistor (SIT) that combines a low voltage Si MOSFET at the input and a high voltage GaN SIT at the output has been simulated and evaluated. The Schottky-gate SIT is an ideal choice for the cascode configuration as it provides a parallel Schottky diode, enabling bi-directional conduction. Simulation results show that the device has great potential for MHz frequency switching applications. Additionally, power losses in the Si MOSFET and GaN SIT have been analyzed separately.
Gyrotropy and permittivity sensing driven by toroidal response
Authors: Marinov K , Fedotov V A
Published: February 2023

Using a quasi-static model of a toroidal metamaterial we demonstrate analytically that simultaneous excitation of the magnetic and toroidal dipoles in an array of subwavelength toroidal solenoids results in gyrotropic behaviour resembling conventional optical activity. We derive the polarization eigenstates of this uniaxial chiral toroidal metamaterial and show that such a medium is reciprocal, while the eigenstates are represented by two counter-rotating ellipses, one of which can be used for probing changes of the host permittivity in a manner exclusive to the toroidal metamaterial. We also show that the mechanism of permittivity sensing involving resonant toroidal response is fundamentally different from that, which has been exploited so far under the term ‘toroidal’.
Semi-empirical modeling of the temporal variation of indoor radon concentration over short periods
Authors: Orabi M
Published: February 2023

The time rate of change of the indoor radon concentration is studied in a semi-empirical frame. The differential equation that describes the radon mass-balance inside a room is used, with taking into account all sources of indoor radon. Rather than solving the equation numerically, an analytical form is obtained with applying some approximations that are based on experimental observations. This makes the describing model more realistic and updatable. After fitting some of the parameters to the experimental data, the model is found to be successful for describing the indoor radon concentration over a couple of days. Moreover, the model predicts some important characteristics of the radon flow to the indoors from the soil and from the building materials. For the room considered in this study, it is found that the radon diffusion transfer coefficient inside the building material is

2.06
×

10

−
6

m
h

,

while the radon diffusion and advection transfer coefficients inside the soil are

0.91
×

10

−
4

m
h

and

1.04
×

10

−
3

m

h
.
Pa

,

respectively. The model can also predict the amount of contribution to the indoor radon by any sources that may be unknown. It was found to be

30.61

Bq

m

3

.
h

.

The obtained results show the feasibility and convenience of the model.
Gravitational wave probes of massive gauge bosons at the cosmological collider
Authors: Niu Xuce , Rahat Moinul Hossain , Srinivasan Karthik , Xue Wei
Published: February 2023

We extend the reach of the “cosmological collider” for massive gauge boson production during inflation from the CMB scales to the interferometer scales. Considering a Chern-Simons coupling between the gauge bosons and the pseudoscalar inflaton, one of the transverse gauge modes is efficiently produced and its inverse decay leaves an imprint in the primordial scalar and tensor perturbations. We study the correlation functions of these perturbations and derive the updated constraints on the parameter space from CMB observables. We then extrapolate the tensor power spectrum to smaller scales consistently taking into account the impact of the gauge field on inflationary dynamics. Our results show that the presence of massive gauge fields during inflation can be detected from characteristic gravitational wave signals encompassing the whole range of current and planned interferometers.
How to use GP: effects of the mean function and hyperparameter selection on Gaussian process regression
Authors: Hwang Seung-gyu , L'Huillier Benjamin , Keeley Ryan E. , Jee M. James , Shafieloo Arman
Published: February 2023

Gaussian processes have been widely used in cosmology to reconstruct cosmological quantities in a model-independent way.
However, the validity of the adopted mean function and hyperparameters, and the dependence of the results on the choice have not been well explored.
In this paper, we study the effects of the underlying mean function and the hyperparameter selection on the reconstruction of the distance moduli from type Ia supernovae.
We show that the choice of an arbitrary mean function affects the reconstruction: a zero mean function leads to unphysical distance moduli and the best-fit ΛCDM to biased reconstructions.
We propose to marginalize over a family of mean functions and over the hyperparameters to effectively remove their impact on the reconstructions. We further explore the validity and consistency of the results considering different kernel functions and show that our method is unbiased.