bluuebunny/crossref_metadata_2025 huggingface dataset:
The critical role of synthesis conditions on small polaron carrier concentrations in hematite—A first-principles study
Authors: Smart Tyler J. , Chen Mingpeng , Grieder Andrew C. , Urena Baltazar Valentin , Bridges Frank , Li Yat , Ping Yuan
Published: December 2021

Achieving highly efficient energy conversion with transition metal oxides necessitates overcoming conductivity limitations due to the formation of small polarons. Detailed understanding of the interplay among intrinsic defects, dopants, and electron polarons can help devise strategies for achieving higher carrier concentrations, therefore improving carrier conductivity. This work employs first-principles calculations to reliably predict electron polaron concentrations in a prominent polaronic oxide, hematite (Fe2O3), by resolving interactions between charged defects and electron polarons and keeping charge neutrality condition among all charged species. This work addresses that both VO and Fei can be primary donors in undoped hematite depending on the synthesis conditions, such as synthesis temperature and oxygen partial pressure, despite the fact that VO owns an extremely high ionization energy compared to kBT. Furthermore, from calculations of a plethora of n-type dopants (group IV and V elements), we find that Ti, Ge, Sb, and Nb are able to raise electron polaron concentrations in hematite significantly without considering dopant clustering. However, the magnitude of electron polaron concentration increase would be smaller if the dopant has a high tendency of clustering, such as Ti. We reveal the critical role of synthesis conditions on tuning electron polaron concentrations of both undoped and doped hematite. Our theoretical analysis provides important insights and general design principles for engineering more conductive polaronic oxides.
Density maximum and finite Darcy–Prandtl number outlooks on Gill's stability problem subject to a lack of thermal equilibrium
Authors: Shankar B. M. , Shivakumara I. S. , Naveen S. B.
Published: December 2021

The Gill stability problem encompasses the investigation of stability of natural convection flow in a vertical porous layer governed by Darcy's law under a local thermal equilibrium (LTE) perspective and was proved analytically by Gill [Gill, J. Fluid Mech. 35, 545–547 (1969)] that the flow is always stable. The present study deals with the simultaneous influence of the Darcy–Prandtl number and the density maximum property on Gill's stability problem subject to a lack of thermal equilibrium. The density variation with fluid temperature is assumed to be pure quadratic, and it is established that the linear stability of the basic state for a three-dimensional problem can be Squire-transformed. It is observed that Gill's proof of linear stability cannot be extended to the present model and hence we approached numerically by evaluating the growth rate of normal mode perturbations. The neutral stability curves are obtained, and the critical parameters at the onset of instability are determined. Even though the isolation presence of time-dependent velocity term and the density maximum property evidence the basic flow to be stable for all infinitesimal perturbations, their simultaneous occurrence induces instability under certain parametric conditions. The finite range of values of the scaled interphase heat transfer coefficient within which the flow is stable is found to increase with increasing Darcy–Prandtl number but vanishes with increasing porosity-modified conductivity ratio. Moreover, the basic state becomes stable when the Darcy–Prandtl number is larger than 7.08. The results of LTE model are delineated as a particular case from the present study.
Unidirectional transparency in epsilon-near-zero based rectangular waveguides induced by parity-time symmetry
Authors: Nicolussi Martin , Riley Joseph Arnold , Pacheco-Peña Victor
Published: December 2021

Epsilon-near-zero (ENZ) metamaterials present exciting features such as an almost infinite effective wavelength and phase velocity. However, a major challenge when using such artificial media is to achieve impedance matching due to their vanishing permittivity. To address this, it has recently been shown that wave propagation within ENZ media combined with parity-time (PT) symmetry concepts can exhibit asymmetric reflection and enhanced transmission. Here, we exploit this technique by studying a PT-symmetric ENZ structure consisting of a rectangular waveguide operating near the cutoff frequency of the dominant TE10 mode (emulating an ENZ metamaterial) and placed between balanced thin loss and gain blocks. Theoretical studies based on the transmission line theory, eigenvalue problems, and full-wave numerical simulations are performed. It is shown how unbroken and broken PT-symmetric phases can exist with exceptional points in between, demonstrating asymmetric reflection and enhanced transmission while preserving the ENZ behavior of the system.
Exceptional thermoelectric power factors in hyperdoped, fully dehydrogenated nanocrystalline silicon thin films
Authors: Narducci Dario , Zulian Laura , Lorenzi Bruno , Giulio Federico , Villa Elia
Published: December 2021

Single-crystalline silicon is well known to be a poor thermoelectric material due to its high thermal conductivity. Most excellent research has focused on ways to decrease its thermal conductivity while retaining acceptably large power factors (PFs). Less effort has been spent to enhance the PF in poly- and nanocrystalline silicon, instead. Here, we show that in boron-hyperdoped nanocrystalline thin films, the PF may be increased up to 33 mW K−2 m−1 at 300 K when hydrogen embedded in the film during deposition is removed. The result makes nanocrystalline Si a realistic competitor of Bi2Te3 for low-temperature heat harvesting, also due to its greater geo-availability and lower cost.
Modeling of spontaneous Raman scattering for detonation wave imaging
Authors: Tan Yaqin , Mével Rémy , Huang Yue
Published: December 2021

To determine if spontaneous Raman scattering can be employed to perform temperature measurements in detonation waves propagating in a stoichiometric hydrogen–air mixture, a detailed rotational–vibrational Raman scattering model for nitrogen has been implemented. The Raman scattering cross-sections were calculated over the wavelength range 337–532 nm and show reasonable agreement with experimental data. The Raman model was coupled to steady one-dimensional and unsteady two-dimensional simulations of detonation to determine under which conditions temperature measurement can be performed with an appropriate signal-to-noise ratio. Based on the calculated Raman signal and signal-to-noise ratio fields, it was concluded that, through an integrated intensity ratio of Stokes Raman scattering and anti-Stokes Raman scattering, the Raman scattering temperature measurement might be possible for large incident laser light intensity and minimized background emission noise.
Introduction to Optical Coherence Elastography
Authors: Kennedy Brendan F. , Bamber Jeffrey C.
Published: December 2021

Optical coherence elastography (OCE) is an emerging variant of elastography, based on optical coherence tomography (OCT) that provides microscale resolution to depths of several millimeters in dense tissue. OCE was first proposed in 1998 but has undergone extensive development only in the past ten years. Several implementations of OCE are now approaching technical maturity, and initial clinical studies have demonstrated its potential in a number of clinical applications, particularly in ophthalmology, oncology, and cardiology. In this chapter, we provide context for the development of OCE by first describing the clinical basis for elastography, and providing an overview of ultrasound elastography and magnetic resonance elastography, both of which are mature elastography techniques routinely deployed in clinical medicine. We then introduce various optical elastography techniques that have been developed in parallel with OCE, e.g., laser speckle elastography and Brillouin microscopy. Finally, we provide an introductory description of OCE as a precursor to more detailed analyses in subsequent chapters.
Tissue Mechanics
Authors: Wĳesinghe Philip , Chin Lixin , Oberai Assad A. , Kennedy Brendan F.
Published: December 2021

The mechanics of tissue are exceptionally complex. They reflect the diverse composition and architecture of many tissues, and have a profound role in regulating a multitude of biochemical and molecular processes. As a consequence, the understanding and quantification of tissue mechanics has been, and still remains, an important century-long pursuit. A main challenge in this area is the formalization of biological complexity into mathematical relations that are at once simple, as to be readily interpretable, and accurate, such that they confer key information on a broad variety of tissues. In elastography, as well as in many other mechanical imaging and metrology methods, this challenge is often approached by codifying tissue mechanics using the principles of continuum mechanics. There, the biological complexity is distilled to a few relations by using assumptions that are motivated by the composition, and observed behavior of tissues, as well as the measurement method used. In this chapter, we describe and reconcile this close relationship between the tissue biology, the measurement method, and the continuum mechanics models used to quantify measurements in elastography. Specifically, we focus on those principles that have founded many of the compelling demonstrations of optical coherence elastography.
Speckle in Optical Coherence Tomography
Authors: Hepburn Matt S. , Foo Ken Y. , Curatolo Andrea , Munro Peter R. T. , Kennedy Brendan F.
Published: December 2021

Speckle is a characteristic granular texture inherent to optical coherence tomography (OCT) images of turbid media, such as biological tissues. Speckle is a consequence of the coherent nature of OCT, and results from the interference of light scattered by sub-resolution scatterers. As deformation can rearrange these scatterers, consequently changing the realization of speckle, an understanding of speckle is required to understand elastogram formation in optical coherence elastography (OCE). In this chapter, we analyze speckle using both 1D and 3D models of OCT image formation, and we use these models to describe key concepts, including statistics of the OCT amplitude, intensity, and phase; speckle size; and speckle contrast. The chapter concludes with a description of techniques developed to reduce speckle contrast, including digital image processing, and speckle-modulation techniques.
Measuring Deformation in Optical Coherence Elastography
Authors: Hepburn Matt S. , Foo Ken Y. , Chin Lixin , Munro Peter R. T. , Kennedy Brendan F.
Published: December 2021

Deformation is the change in size and shape of a sample in response to an applied load. Accurately measuring deformation is critical in optical coherence elastography (OCE), as along with the validity of the mechanical model of the sample, it determines the accuracy of the measurement of mechanical properties. In this chapter, we describe prominent methods to measure deformation in OCE, including phase-sensitive detection and cross-correlation-based approaches such as speckle tracking. We describe the working principles of these methods and analyze their advantages and disadvantages in the context of performance metrics including sensitivity, accuracy, and spatial resolution. In addition, we briefly describe several less prominent methods such as morphological tracking, correlation stability, digitally shifted complex cross-correlation, and Doppler spectrum detection.
Nanotwin orientation on history-dependent stress decay in Cu nanopillar under constant strain
Authors: Shen Yu-An , Chang Li , Chang Shou-Yi , Chou Y-C , Tu K N , Chen Chih
Published: December 2021

Cu with nanotwin (NT) possesses great electrical, mechanical, and thermal properties and has potential for electronic applications. Various studies have reported the effect of NT orientation on Cu mechanical properties. However, its effect on Cu stress-relaxation behavior has not been clarified, particularly in nano-scale. In this study, Cu nanopillars with various orientations were examined by a picoindenter under constant strain and observed by in situ TEM. The angles between the twin plane and the loading direction in the examined nanopillars were 0°, 60°, to 90°, and a benchmark pillar of single-crystal Cu without NT was examined. The stress drops were respectively 10%, 80%, 4%, and 50%. Owing to the interaction by NT, the dislocation behavior in nanopillars was different from that in bulk or in thin film samples. Especially, the rapid slip path of dislocations to go to the free surface of the nanopillar induced a dislocation-free zone in the 0° nanopillar, which led to work-softening. On the contrary, a high dislocation density was observed in the 90° nanopillar, which was generated by dislocation interaction and obstruction of dislocation slip by twin planes, and it led to work-hardening. The findings reveal the NT orientation in Cu nanopillars affected stress relaxation significantly.
Infinity: some close encounters in physics teaching
Authors: Atkin Keith
Published: December 2021

This paper describes two examples of teaching situations in which the idea of infinity arises, and supports the conclusion that infinity is not a physical reality but a very powerful and useful mathematical device which facilitates modelling and the solution of problems in physics.
Physics experiments using arduino: determination of the air quality index
Authors: Singh Rohit , Singh Amit Kumar , Singhal Sonal
Published: December 2021

Air pollution is one of our day’s significant reasons for human health problems and affects every community throughout the world. Monitoring air pollution is a key aspect of raising awareness and pollution mitigation approaches followed by different nations. This paper targets to develop a low-cost Internet of things-based embedded system to measure and maintain air quality index (AQI) indicators at any locality. The system implemented here is minimal and can be deployed quickly and easily. The AQI measurement system was developed and tested for several periods, and recorded values of AQI were found to be in close agreement with actual values obtained from standard databases. In addition, several starting physics and electronics laboratory courses train students on measuring physical parameters over time. In this context, along with the introduction to the current pollution scenario and the challenges, this experiment will give a first-hand exposure of setting up a simple experiment and measuring a physical parameter to time. Students also learn to write simple programs and interface the experiment with a computer to record the results. The current work also demonstrates how to publish/subscribe the data using the message queue telemetry transport protocol.
Piloting a full-year, optics-based high school course on quantum computing
Authors: Walsh Joel A , Fenech Mic , Tucker Derrick L , Riegle-Crumb Catherine , La Cour Brian R
Published: December 2021

Quantum computing was once regarded as a mere theoretical possibility, but recent advances in engineering and materials science have brought practical quantum computers closer to reality. Currently, representatives from industry, academia, and governments across the world are working to build the educational structures needed to produce the quantum workforce of the future. Less attention has been paid to growing quantum computing capacity at the high school level. This article details work at The University of Texas at Austin to develop and pilot the first full-year high school quantum computing class. Over the course of two years, researchers and practitioners involved with the project learned several pedagogical and practical lessons that can be helpful for quantum computing course design and implementation at the secondary level. In particular, we find that the use of classical optics provides a clear and accessible avenue for representing quantum states and gate operators and facilitates both learning and the transfer of knowledge to other Science, Technology, and Engineering (STEM) skills. Furthermore, students found that exploring quantum optical phenomena prior to the introduction of mathematical models helped in the understanding and mastery of the material.
Online versus face-to-face learning in introductory university physics following COVID-19
Authors: Fouad Emadelden , Austin Robert , Kryger R A , Holton Doug , Srinivasan Sesha , Ngwa Wilfred
Published: December 2021

The use of technology in higher education science classrooms rose significantly in the advent of the COVID-19 pandemic. In many universities, academic programs including introductory physics classes were taken online. Some institutions adopted online learning but also maintained face-to-face (F2F) laboratories when COVID-19 restrictions began to ease. Here, the effectiveness of the online learning approach in comparison with F2F learning is explored. The percentage difference in performance for students who took the online introductory physics course, Physics for Scientists and Engineers, versus that of students simultaneously taking the same course F2F is reported. This is done both across different sections taught by different instructors, and for the same course taught online versus F2F by the same professor. Furthermore, a short survey was conducted to assess the student learning experience and opinion about online and F2F learning. The results show equal or better overall performance for online learning with 4.2% higher performance when comparing results across different sections taught by different instructors. A similar 6.1% performance improvement was seen when comparing results across different sections taught by the same instructor. In contrast with the performance outcomes, the survey results indicate that about 72% of students prefer F2F compared to online learning. The findings provide a useful reference as many institutions and programs transition back to more standard F2F or hybrid learning modes. The benefits and drawbacks of each mode are discussed in the specific context of student preferences and challenges faced in online learning during COVID-19.
Generation of quantification maps and weighted images from synthetic magnetic resonance imaging using deep learning network
Authors: Liu Yawen , Niu Haijun , Ren Pengling , Ren Jialiang , Wei Xuan , Liu Wenjuan , Ding Heyu , Li Jing , Xia Jingjing , Zhang Tingting , Lv Han , Yin Hongxia , Wang Zhenchang
Published: December 2021

Objective. The generation of quantification maps and weighted images in synthetic MRI techniques is based on complex fitting equations. This process requires longer image generation times. The objective of this study is to evaluate the feasibility of deep learning method for fast reconstruction of synthetic MRI. Approach. A total of 44 healthy subjects were recruited and random divided into a training set (30 subjects) and a testing set (14 subjects). A multiple-dynamic, multiple-echo (MDME) sequence was used to acquire synthetic MRI images. Quantification maps (T1, T2, and proton density (PD) maps) and weighted (T1W, T2W, and T2W FLAIR) images were created with MAGiC software and then used as the ground truth images in the deep learning (DL) model. An improved multichannel U-Net structure network was trained to generate quantification maps and weighted images from raw synthetic MRI imaging data (8 module images). Quantitative evaluation was performed on quantification maps. Quantitative evaluation metrics, as well as qualitative evaluation were used in weighted image evaluation. Nonparametric Wilcoxon signed-rank tests were performed in this study. Main results. The results of quantitative evaluation show that the error between the generated quantification images and the reference images is small. For weighted images, no significant difference in overall image quality or signal-to-noise ratio was identified between DL images and synthetic images. Notably, the DL images achieved improved image contrast with T2W images, and fewer artifacts were present on DL images than synthetic images acquired by T2W FLAIR. Significance. The DL algorithm provides a promising method for image generation in synthetic MRI techniques, in which every step of the calculation can be optimized and faster, thereby simplifying the workflow of synthetic MRI techniques.
Mixed magnetic behavior in gadolinium and ruthenium co-doped nickel oxide nanoparticles
Authors: Abdallah A M , Awad R
Published: December 2021

Pure and different concentrations from (Gd, Ru) co-doped NiO nanoparticles, capped with Polyvinylpyrrolidone (PVP), were fabricated by the co-precipitation method. The nanoparticles were characterized by different techniques. The Rietveld refinements of x-ray Diffraction (XRD) patterns confirmed the formation of the pure face-centered-cubic NiO phase. The x-ray Photo-induced Spectroscopy (XPS) assured the trivalent oxidation state of the doped ions Gd3+ and Ru3+ and unveiled the multiple oxidation states of nickel ions (Ni2+ and Ni3+), emerging from the vacancies in the samples. The Transmission Electron Microscope (TEM) images showed the pseudospherical morphology of the samples and the Energy Dispersive x-ray permitted the quantitative analysis of the presented elements and their homogeneous distribution. The Raman and Fourier Transform Infra-Red (FTIR) spectra depicted the fundamental vibrational bands of NiO nanoparticles, confirming their purity. The UV-visible spectroscopy enabled the absorption measurements and the energy gap calculations. The co-dopants increased the energy bandgap of NiO nanoparticles from 3.15 eV for pure NiO to 3.62 eV with the highest concentration of the co-dopants (x = 0.02) The photoluminescence (PL) spectra gave insights into the possible defects present in the samples, such as nickel vacancies, single and double oxygen vacancies, and oxygen interstitials. The Vibrating Sample Magnetometer (VSM) studied the room temperature M-H loops of the co-doped samples. A combination of ferromagnetic, antiferromagnetic, and paramagnetic contributions was noticed and treated according to the law of approach to saturation and bound magnetic polaron (BMP) model. The magnetic parameters, such as the saturation magnetization, exchange and anisotropy field, and the BMP concentration were extracted from the fitted models and discussed in terms of the co-dopants’ concentration. The co-doped samples showed a softer magnetic behavior, which is recommended for data storage applications.
Anisotropic refraction and valley-spin-dependent anomalous Klein tunneling in a 1T′-MoS2-based p-n junction
Authors: Qi Fenghua , Zhou Xingfei
Published: December 2021

We investigate the transport properties of electron in a 1T′-MoS2-based p–n junction. The anisotropic refraction of electron is found when the electron beam crosses the p–n junction, which brings the phenomenon of valley splitting without any external fields. Moreover, it is found that the valley-spin-dependent anomalous Klein tunneling, i.e., the perfect transmission exists at a nonzero incident angle of valley-spin-dependent electron, happens when the vertical electric field is equal to the critical electric field. These two peculiar properties arise from the same reason that the tilted band structure makes the directions of wavevector and velocity different. Our work designs a special valley splitter without any external fields and finds a new type of Klein tunneling.
Multi-function terahertz wave manipulation utilizing Fourier convolution operation metasurface
Authors: Zhong Min , Li Jiu-Sheng
Published: December 2021

We propose a novel metasurface based on a combined pattern of outer C-shaped ring and inner rectangular ring. By Fourier convolution operation to generating different predesigned sequences of metasurfaces, we realize various functionalities to flexible manipulate terahertz waves including vortex terahertz beam splitting, anomalous vortex terahertz wave deflection, vortex terahertz wave splitting and deflection simultaneously. The incident terahertz wave can be flexibly controlled in a single metasurface. The designed metasurface has an extensive application prospect in the field of future terahertz communication and sensing.
Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer
Authors: Shi Zhongyu , Wang Guanqing , Chen Xiangxiang , Wang Lu , Ding Ning , Xu Jiangrong
Published: December 2021

The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.
Fallback in bipolar planetary nebulae?
Authors: Baan Willem A. , Imai Hiroshi , Orosz Gabor
Published: December 2021

The subclass of bipolar Planetary Nebulae (PNe) exhibits well-defined low-power outflows and some shows shock-related equatorial spiderweb structures and hourglass structures surrounding these outflows. These structures are distinctly different from the phenomena associated with spherical and elliptical PNe and suggest a non-standard way to simultaneously energise both kinds of structures. This paper presents evidence from the published literature on bipolar PN Hb 12 and other sources in support of an alternative scenario for energising these structures by means of accretion from material shells deposited during earlier post-AGB and pre-PNe evolutionary stages. In addition to energising the bipolar outflow, a sub-Eddington accretion scenario could hydrodynamically explain the spiderweb and outer hourglass structures as oblique shockwaves for guiding the accreting material into the equatorial region of the source. Estimates of the accretion rate resulting from fallback-related spherical accretion could indeed help to drive a low-power outflow and contribute to the total luminosity of these sources.
Chemical abundances of three new Ba stars from the Keck/HIRES spectra
Authors: Liu Shuai , Wang Liang , Shi Jian-Rong , Wu Zhen-Yu , Yan Hong-Liang , Gao Qi , Li Chun-Qian
Published: December 2021

Based on high resolution, high signal-to-noise (S/N) ratio spectra from Keck/HIRES, we have determined abundances of 20 elements for 18 Ba candidates. The parameter space of these stars is in the range of 4880 ≤ T
eff ≤ 6050 K,

2.56
≤
log

g
≤
4.53

dex

and − 0.27 ≤ [Fe/H] ≤ 0.09 dex. It is found that four of them can be identified as Ba stars with [s/Fe] > 0.25 dex (s: Sr, Y, Zr, Ba, La, Ce and Nd), and three of them are newly discovered, which include two Ba giants (HD 16178 and HD 22233) and one Ba subgiant (HD 2946). Our results show that the abundances of α, odd and iron-peak elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, Mn, Ni and Cu) for our program stars are similar to those of the thin disk, while the distribution of [hs/ls] (hs: Ba, La, Ce and Nd, ls: Sr, Y and Zr) ratios of our Ba stars is similar to those of the known Ba objects. None of the four Ba stars show clear enhancement in carbon including the known CH subgiant HD 4395. It is found that three of the Ba stars present clear evidence of hosting stellar or sub-stellar companions from the radial velocity data.
New continuum and polarization observations of the Cygnus Loop with FAST I. Data processing and verification
Authors: Sun Xiao-Hui , Meng Mei-Niang , Gao Xu-Yang , Reich Wolfgang , Jiang Peng , Li Di , Yan Hui-Rong , Li Xiang-Hua
Published: December 2021

We report on the continuum and polarization observations of the Cygnus Loop supernova remnant (SNR) conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). FAST observations provide high angular resolution and high sensitivity images of the SNR, which will help to disentangle its nature. We obtained Stokes I, Q and U maps over the frequency range of 1.03 – 1.46 GHz split into channels of 7.63 kHz. The original angular resolution is in the range of

∼

3

′

−
∼

3

′

.8

, and we combined all the data at a common resolution of

4

′

. The temperature scale of the total intensity and the spectral index from the in-band temperature-temperature plot are consistent with previous observations, which validates the data calibration and map-making procedures. The rms sensitivity for the band-averaged total-intensity map is about 20 mK in brightness temperature, which is at the level of confusion limit. For the first time, we apply rotation measure (RM) synthesis to the Cygnus Loop to obtain the polarization intensity and RM maps. The rms sensitivity for polarization is about 5 mK, far below the total-intensity confusion limit. We also obtained RMs of eight extragalactic sources, and demonstrate that the wide-band frequency coverage helps to overcome the ambiguity of RM determinations.
Does ADS 9346 have a low-mass companion?
Authors: Kiyaeva Olga V. , Khovritchev Maxim Yu. , Kulikova Agrippina M. , Narizhnaya Natalya V. , Vasilyeva Tatyana A. , Apetyan Arina A.
Published: December 2021

Based on the photographic and CCD observations of the relative motion of the A and B components of the binary system ADS 9346 obtained with the 26-inch refractor of Pulkovo Observatory during 1979–2019, we discover an invisible companion associated with star A. Comparison of the ephemerides with the positional and spectroscopic observations allowed us to calculate the preliminary orbit of the photocenter (P = 15 yr). The minimal mass of the companion is approximately 0.13 M
⊙. The existence of the invisible low-mass companion is implied by the IR-excess based on IRAS data. To confirm this, additional observations of the radial velocity near the periastron need to be carried out.
LAMOST Time-Domain survey: first results of four K2 plates
Authors: Wang Song , Zhang Hao-Tong , Bai Zhong-Rui , Yuan Hai-Long , Xiang Mao-Sheng , Zhang Bo , Hou Wen , Zuo Fang , Du Bing , Li Tan-Da , Yang Fan , Cui Kai-Ming , Wang Yi-Lun , Li Jiao , Kovalev Mikhail , Li Chun-Qian , Tian Hao , Zong Wei-Kai , Han Heng-Geng , Liu Chao , Luo A-Li , Shi Jian-Rong , Fu Jian-Ning , Bi Shao-Lan , Han Zhan-Wen , Liu Ji-Feng
Published: December 2021

From Oct. 2019 to Apr. 2020, LAMOST performed a time-domain (TD) spectroscopic survey of four K2 plates with both low- and medium-resolution observations. The low-resolution spectroscopic survey acquired 282 exposures ( ≈ 46.6 h) over 25 nights, yielding a total of about 767 000 spectra, and the medium-resolution survey took 177 exposures ( ≈ 49.1 h) over 27 nights, collecting about 478 000 spectra. More than 70%/50% of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10. We determine stellar parameters (e.g., T
eff, log g, [Fe/H]) and radial velocity (RV) with different methods, including LASP, DD-Payne and SLAM. In general, these parameter estimations from different methods show good agreement, and the stellar parameter values are consistent with those of APOGEE. We use the Gaia DR2 RV values to calculate a median RV zero point (RVZP) for each spectrograph exposure by exposure, and the RVZP-corrected RVs agree well with the APOGEE data. The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters, multi-band magnitudes, distances and extinction values. Finally, we construct a binary catalog including about 2700 candidates by analyzing their light curves, fitting the RV data, calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3. The LAMOST TD survey is expected to represent a breakthrough in various scientific topics, such as binary systems, stellar activity, stellar pulsation, etc.
Deep double descent: where bigger models and more data hurt*
Authors: Nakkiran Preetum , Kaplun Gal , Bansal Yamini , Yang Tristan , Barak Boaz , Sutskever Ilya
Published: December 2021

We show that a variety of modern deep learning tasks exhibit a ‘double-descent’ phenomenon where, as we increase model size, performance first gets worse and then gets better. Moreover, we show that double descent occurs not just as a function of model size, but also as a function of the number of training epochs. We unify the above phenomena by defining a new complexity measure we call the effective model complexity and conjecture a generalized double descent with respect to this measure. Furthermore, our notion of model complexity allows us to identify certain regimes where increasing (even quadrupling) the number of train samples actually hurts test performance.
Augmenting physical models with deep networks for complex dynamics forecasting*
Authors: Yin Yuan , Le Guen Vincent , Dona Jérémie , de Bézenac Emmanuel , Ayed Ibrahim , Thome Nicolas , Gallinari Patrick
Published: December 2021

Forecasting complex dynamical phenomena in settings where only partial knowledge of their dynamics is available is a prevalent problem across various scientific fields. While purely data-driven approaches are arguably insufficient in this context, standard physical modeling-based approaches tend to be over-simplistic, inducing non-negligible errors. In this work, we introduce the APHYNITY framework, a principled approach for augmenting incomplete physical dynamics described by differential equations with deep data-driven models. It consists of decomposing the dynamics into two components: a physical component accounting for the dynamics for which we have some prior knowledge, and a data-driven component accounting for errors of the physical model. The learning problem is carefully formulated such that the physical model explains as much of the data as possible, while the data-driven component only describes information that cannot be captured by the physical model; no more, no less. This not only provides the existence and uniqueness for this decomposition, but also ensures interpretability and benefit generalization. Experiments made on three important use cases, each representative of a different family of phenomena, i.e. reaction–diffusion equations, wave equations and the non-linear damped pendulum, show that APHYNITY can efficiently leverage approximate physical models to accurately forecast the evolution of the system and correctly identify relevant physical parameters. The code is available at https://github.com/yuan-yin/APHYNITY.
Hausdorff dimension, heavy tails, and generalization in neural networks*
Authors: Şimşekli Umut , Sener Ozan , Deligiannidis George , Erdogdu Murat A
Published: December 2021

Despite its success in a wide range of applications, characterizing the generalization properties of stochastic gradient descent (SGD) in non-convex deep learning problems is still an important challenge. While modeling the trajectories of SGD via stochastic differential equations (SDE) under heavy-tailed gradient noise has recently shed light over several peculiar characteristics of SGD, a rigorous treatment of the generalization properties of such SDEs in a learning theoretical framework is still missing. Aiming to bridge this gap, in this paper, we prove generalization bounds for SGD under the assumption that its trajectories can be well-approximated by a Feller process, which defines a rich class of Markov processes that include several recent SDE representations (both Brownian or heavy-tailed) as its special case. We show that the generalization error can be controlled by the Hausdorff dimension of the trajectories, which is intimately linked to the tail behavior of the driving process. Our results imply that heavier-tailed processes should achieve better generalization; hence, the tail-index of the process can be used as a notion of ‘capacity metric’. We support our theory with experiments on deep neural networks illustrating that the proposed capacity metric accurately estimates the generalization error, and it does not necessarily grow with the number of parameters unlike the existing capacity metrics in the literature.
Meta-optimization of the parameters for the gravitational search algorithm in chemical kinetics problems
Authors: Enikeeva L V , Shvareva E N , Dubovtsev D A , Gubaydullin I M
Published: December 2021

The paper considers the selection of the optimal parameters of the heuristic algorithm, which is used for mathematical modeling of the chemical-technological process. This adjustment of the algorithm parameters is called meta-optimization. The gravity search algorithm is used as a heuristic algorithm. Meta-optimization is performed by a genetic algorithm. The meta-optimization is tested on the problem of modeling the process of propane pre-reforming. It is shown that setting even one parameter of a heuristic algorithm is a time-consuming operation. The article presents the results of the numerical solution of the meta-optimization algorithm.
Computer simulation of block polymerization of 1,6-Hexanediol Diacrylate
Authors: Shakiryanov E D
Published: December 2021

In this paper, a computer model of the block three-dimensional free-radical polymerization of 1,6-Hexanediol Diacrylate (HDDA) is proposed. The model of the reaction system is based on an ideal mixing reactor. The reaction process is modeled by the Monte Carlo method. Accounting for the diffusion inhibition of the reaction is described using the free volume model. An adequate description of the experimental data of the calculated conversion rate curve is obtained. The nature of the change in the rate constant of the growth reaction with increasing conversion is shown.
Algorithm for numerical simulation of electron density and stochastically convecting high latitude ionosphere
Authors: Vlaskov G
Published: December 2021

The problem of modeling the inhomogeneities of the electron density in the polar ionosphere at the level of the F - layer is considered. It is known that the distribution of ionospheric plasma changes under the action of the electric field of large-scale magnetospheric convection. Since the electric field undergoes significant fluctuations in the auroral zone, it is proposed to use the Monte Carlo method to solve this problem, simulating the process of plasma motion, like the Wiener one with deterministic drift.
Vertical turbulent exchange structure and parametrization for 3D shallow water hydrodynamics models
Authors: Sukhinov A I , Chistyakov A E , Protsenko S V , Protsenko E A
Published: December 2021

The work describes research of vertical turbulent exchange structure and parametrization for 3D shallow water hydrodynamics models. In this paper, the coefficients of horizontal turbulent exchange are calculated using a whole set of averaging periods of turbulent velocity pulsations. Using experimental data on the pulsations of the velocity components, the coefficient of vertical turbulent exchange was calculated on the basis of various approaches to its parameterization, based on the analysis of the obtained coefficient distributions, the most adequate parameterization of the coefficient was selected, which is used in the software package. The distribution of the vertical turbulent exchange coefficient obtained in a numerical experiment was compared with the results of full-scale measurements, and the calculation results obtained using the mathematical statistics apparatus were analysed.
Research of strength capabilities of building steels under temperature effects
Authors: Vernezi N L , Kosenko E E , Kosenko V V , Demchenko D B , Cherpakov A V
Published: December 2021

The use of information technologies in construction makes it possible to assess the strength capabilities of various classes of reinforcement in order to use the full strength potential of steels laid down at the production stage. The information obtained during the study of the properties of steels is important both for building structures and for metals used in the manufacture of load-bearing car bodies, in the construction of which high-strength steels are also used. In terms of the quality of the steels produced, the Russian industry is among the leaders in the world along with the largest European companies. The high characteristics of steel make it possible to expand the range of their application, both in conditions of elevated and in conditions of low temperatures.
Stability of a nonlinear thermoelastic plate
Authors: Volokitin G I , Moiseev D V
Published: December 2021

The problem of loss of stability of a circular plate under lateral compression in an inhomogeneous temperature field is considered. The theory of superposition of a small deformation on a finite one is used. A similar approach to the study of the equilibrium bifurcation of nonlinear thermoelastic bodies was used in the following works.
Evaluation of the possibility of using pulp to improve the characteristics of various materials
Authors: Kuimov D N , Minkin M S
Published: December 2021

The article presents the results of the analytical review of the work on the possibility of using cellulose to improve the physical and chemical characteristics of various materials, including paper, cardboard, plastic and others. Unique chemical and physical properties of nanocellulose are shown.
Three-dimensional integro-differential model of unstationary hydrodynamic process in a liquid-metal pool of underwater arc welding
Authors: Rybalkin E , Yagyaev E , Bogutsky V , Shron L
Published: December 2021

Wet underwater arc welding is now widely used. At the same time, obtaining high-quality welds with this welding method is an urgent scientific and technical problem due to their saturation with hydrogen and oxygen and the formation of pores. One of the promising directions for solving this issue is the use of an external electromagnetic effect on the liquid metal in the weld pool in order to control the movements of the molten metal flows to improve the degassing processes of welded joints. It is possible to estimate the parameters and efficiency of external electromagnetic influence by means of mathematical modeling of related electromagnetic, hydrodynamic and thermal processes occurring in the welding installation. The article proposes a three-dimensional integro-differential model of a non-stationary hydrodynamic process occurring in the liquid metal of a weld pool in an underwater arc welding system with an external electromagnetic effect. For the equations of hydrodynamics boundary value problems are formed, which, using potential theory, are reduced to a system of integro-differential equations for the vorticity function in the volume of a liquid conductor and a simple vector layer on its surface. For a numerical solution, the resulting system of integro-differential equations is approximated by an algebraic system according to the Krylov-Bogolyubov method. This system of equations makes it possible to determine the velocity field in the liquid metal of the weld pool for any welding modes.
Formalization of requirements for assembly of high-precision units during process design of production of multi-product machining systems
Authors: Nazaryev A , Bochkarev P , Gumarov G
Published: December 2021

This article considers the improvement of mathematical and methodological support of the implementation of an enlarged block of design procedures of the analysis of requirements of the assembly of high-precision products of the complex of design procedures of the system of accounting requirements for the assembly in the design of manufacturing methods of machining. The proposed modernization will allow to more efficiently perform of the design dimensional analysis of a high-precision assembly unit in an automated fashion and choose rational manufacturing methods of machining of parts in the system of automated sequencing of manufacturing methods during process design of the production of multi-nomenclature machining complexes. In addition, the proposed solutions allow for the expansion of digitalization of designing preproduction and process design and the transition to intelligent production systems. The problem posed in the presented study is relevant, since the proposed solutions allow for the expansion of digitalization of designing preproduction and process design and the transition to intelligent production systems in the future.
Investigation of piston ring wear engines by the mathematical statistics method
Authors: Khachkinayan A , Zharkov Yu , Zubkov V , Novakovich V , Ermakov V
Published: December 2021

Improving the reliability and durability of internal combustion engines makes it possible to increase productivity and reduce the cost of operation. The study of nature and magnitude of piston rings wear is relevant and represents a scientific novelty. During the operation of internal combustion engines, it is almost impossible to determine the influence of various factors on the wear rate and the resource of piston rings. One of the most accurate ways to study the wear intensity and the service life values of internal combustion engines piston rings during operation is the statistical method. The method of mathematical statistics allows us to study the nature and magnitude of individual parts wear with a sufficient degree of accuracy, to determine the main causes of wear, to outline ways of increasing the parts wear resistance, to establish durability criteria, to reasonably assign standard service life of parts and plan the parts need for any period with a given probability, with climatic conditions being taking into account. The article presents the collected statistical material on the internal combustion engines piston rings wear of construction and road vehicles operated at construction sites of Rostov region. It has been processed according to the normal Gauss law and data on the wear and service life of piston rings are obtained. The obtained experimental data on the wear of piston rings in height are reliable to the distribution law and can be used to determine the intensity of engines piston rings wear at repair enterprises.
Experimental studies of vibroacoustic characteristics of the basic structure parts of the traction rolling stock and transportation technological vehicles
Authors: Yaitskov I , Nazaretov A , Kochetkov A
Published: December 2021

The paper presents the obtained results of the vibration studies, particularly, the structural elements of the railway rolling stock, created at the driver workplaces, structures of the internal combustion engines, hoods, frames while moving and a stationary machine, which determine the vibration spectral composition and propose the specific engineering solutions for the noise and vibration protection system.
Heat recovery in the refrigeration equipment of dining cars
Authors: Voron O A , Patenyan A A , Yu Rostokin A
Published: December 2021

The paper investigates the major parameters of the existing refrigeration equipment of dining cars, as well as analyzes the latest trends in the development of refrigeration equipment, taking into account the changing requirements of legislation and environmental standards. Besides, it compares several systems with different refrigerants. Finally, our study introduces the possibilities of exploiting a transcritical system with heat recovery.