bluuebunny/crossref_metadata_2025 huggingface dataset:
Forced convection heat transfer around a circular cylinder in laminar flow: An insight from Lagrangian coherent structures
Authors: Cao Sheng-Li , Sun Xu , Zhang Jia-Zhong , Zhang Yi-Xin
Published: June 2021

The Lagrangian coherent structure (LCS) method is introduced to the convection heat transfer problem, and the forced convection heat transfer around a circular cylinder in laminar flow regime is analyzed from the Lagrangian viewpoint. First, the mechanics model of forced convection heat transfer around a circular cylinder is introduced along with the mathematical formulations. Subsequently, an implicit flow solver based on the characteristic-based split finite element method and the dual-stepping method is proposed to solve the flow and heat transfer equations, and the computation of LCS employing the finite-time Lyapunov exponent is discussed in detail. The accuracy and stability of the flow solver are examined carefully utilizing the data reported in the literature, and the grid-independence test is conducted. Finally, the mass and energy transport features around the circular cylinder at Pr (Prandtl number) = 0.7 and Re (Reynolds number) = 20–180 are investigated by relating the instantaneous thermal and vorticity patterns, lift coefficient, drag coefficient, and Nusselt number to the LCSs in the flow field. The results obtained may improve the existing understanding of forced convection heat transfer around a circular cylinder and pave the road for the application of LCSs in convection heat transfer problems.
Influence of a Cu–zirconia interface structure on CO2 adsorption and activation
Authors: Gell Lars , Lempelto Aku , Kiljunen Toni , Honkala Karoliina
Published: June 2021

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Straining of the Cu nanorod influences CO2 adsorption energy but does not change the preferred nanorod position on zirconia. Altogether, our results highlight that CO2 adsorption and activation depend sensitively on the chemical composition and atomic structure of the interface used in the calculations. This structure sensitivity may potentially impact further catalytic steps and the overall computed reactivity profile.
Self-intercalated two-dimensional magnetic semiconductor V8(S1-xSex)15
Authors: Yao Yuyu , Wen Yao , Wang Feng , Li Ningning , Wang Junjun , Wang Yanrong , Yang Jia , Zhan Xueying , Wang Zhenxing , He Jun
Published: June 2021

The exploration of two-dimensional (2D) magnets has attracted considerable attention due to their potential applications in spintronic devices over the past few years. Recently, a variety of 2D vanadium-based (V-based) chalcogenides have been demonstrated to own fascinating magnetic properties by both the theoretical predication and experimental realization. However, ternary V-based compounds have rarely been studied. Here, we synthesized three kinds of ultrathin ternary self-intercalated V8(S1-xSex)15 sheets with different Se contents by the atmospheric pressure chemical vapor deposition method. The Se content x is 8.7%, 12.1%, and 19.7%. The Raman spectra indicate that these three kinds of self-intercalated V8(S1-xSex)15 nanosheets with a different Se content own the same crystal structure. All self-intercalated V8(S1-xSex)15 nanosheets exhibit a semiconducting behavior, and the conducting type transits from ambipolar to p-type as the Se content increases. The spin Hall magnetoresistance (SMR) signal can be detected in the Pt/V8(S1-xSex)15 bilayer structure, and SMR signals (amplitudes) gradually weaken with the increasing temperature. These results manifest that self-intercalated V8(S1-xSex)15 own both semiconducting and magnetic characteristics.
Numerical and analytical study of undular bores governed by the full water wave equations and bidirectional Whitham–Boussinesq equations
Authors: Vargas-Magaña Rosa María , Marchant T. R. , Smyth Noel F.
Published: June 2021

Undular bores, also termed dispersive shock waves, generated by an initial discontinuity in height as governed by two forms of the Boussinesq system of weakly nonlinear shallow water wave theory, the standard formulation and a Hamiltonian formulation, two related Whitham–Boussinesq equations, and the full water wave equations for gravity surface waves are studied and compared. It is found that the Whitham–Boussinesq systems give solutions in excellent agreement with numerical solutions of the full water wave equations for the positions of the leading and trailing edges of the bore up until the onset on modulational instability. The Whitham–Boussinesq systems, which are far simpler than the full water wave equations, can then be used to accurately model surface water wave undular bores. Finally, comparisons with numerical solutions of the full water wave equations show that the Whitham–Boussinesq systems give a slightly lower threshold for the onset of modulational instability in terms of the height of the initial step generating the undular bore.
Numerical study of thermocapillary migration behaviors of droplets on a grooved surface with a three-dimensional color-gradient lattice Boltzmann model
Authors: Fu Xiaojin , Ba Yan , Sun Jinju
Published: June 2021

Thermocapillary actuation is used extensively in droplet-based microfluidic devices to manipulate the dynamic behaviors of droplets. In this study, a three-dimensional color-gradient lattice Boltzmann model is used to investigate the migration behaviors of droplets in the Wenzel state on a grooved surface that is subject to a uniform temperature gradient. On the solid surface, the wetting boundary condition is used to improve the accuracy of the simulations and to suppress spurious velocities at the contact line. The model is used to simulate the thermocapillary migration of a three-dimensional deformable droplet and the thermocapillary migration of a two-dimensional droplet on a solid substrate, and its accuracy is verified against theoretical predictions. The migration behavior of droplets on a smooth surface is investigated, and the flow field and corresponding temperature field around the droplets are analyzed. The experimental findings numerically confirm that a surface with micro-grooves parallel to the temperature gradient can accelerate thermocapillary migration to a greater extent than a smooth surface, indicating the influence of the grooves. The influence of the viscosity ratio is investigated, and it is found that the use of high-viscosity fluids is an effective means of obstructing migration. To determine the influence of surface roughness, a systematic and parametric study of groove depth and width is conducted. Finally, the influence of the orientation of the surface topography is investigated, and it is demonstrated that a surface with micro-grooves perpendicular to the temperature gradient can obstruct migration.
On the linear and non-linear fluid response to the circular forcing in a rotating spherical shell
Authors: Subbotin Stanislav , Shiryaeva Mariya
Published: June 2021

Fluid flow excited by a core oscillating in a rotating spherical cavity is experimentally investigated. Oscillations are set by an external inertial field so that in the reference frame of the cavity, the core moves along a circular trajectory around the rotation axis. Two situations are considered: when the core oscillations are co-directed or counter-directed with respect to the rotation of the cavity. The oscillating core is a source of non-axisymmetric inertial waves that form a system of cone-shaped shear layers in fluid bulk. Depending on the oscillation frequency, various inertial flow regimes arise, the spatial structure of which strongly depends on the sign of the oscillations. It is found that a strong non-linear response in the form of a steady zonal flow corresponds to each flow regime. The flow structure is a system of nested liquid geostrophic cylinders, one of which is associated with the critical latitude at the core boundary, where inertial waves are generated. The next one is associated with the wave reflection from the cavity boundary and is clearly manifested when they are focused on the wave attractor. The most intense zonal flow occurs when inertial waves are superposed and global vortex structures are resonantly excited.
Topological Josephson bifurcation amplifier: Semiclassical theory
Authors: Boutin Samuel , Lopes Pedro L. S. , Mu Anqi , Mendes Udson C. , Garate Ion
Published: June 2021

Amplifiers based on Josephson junctions allow for a fast and noninvasive readout of superconducting qubits. Motivated by the ongoing progress toward the realization of fault-tolerant qubits based on Majorana bound states, we investigate the topological counterpart of the Josephson bifurcation amplifier. We predict that the bifurcation dynamics of a topological Josephson junction driven in the appropriate parameter regime may be used as an additional tool to detect the emergence of Majorana bound states.
Experimental study of the flow regime effect on the stability of collapsible tubes conveying fluid
Authors: Podoprosvetova A. , Zayko J. , Yushutin V. , Vedeneev V.
Published: June 2021

Experimental studies of the stability of the collapsible tubes conveying fluid have been previously conducted in the context of cardiovascular mechanics mostly for turbulent flows, although blood flows are laminar under normal conditions. In this paper, the turbulent and laminar regimes with equal flow rates and pressure drops are investigated experimentally to identify the stability boundary and self-exciting oscillation modes of Penrose tubes conveying fluid in the Starling resistor. Four oscillation modes for laminar and for turbulent regimes were observed visually and by measuring the pressure drop and the output pressure. Comparison of amplitudes, frequencies, and boundaries between different oscillation modes for equivalent laminar and turbulent flow regimes is performed.
Ultrafast element-resolved magneto-optics using a fiber-laser-driven extreme ultraviolet light source
Authors: Möller Christina , Probst Henrike , Otto Johannes , Stroh Karen , Mahn Carsten , Steil Sabine , Moshnyaga Vasily , Jansen G. S. Matthijs , Steil Daniel , Mathias Stefan
Published: June 2021

We present a novel setup to measure the transverse magneto-optical Kerr effect in the extreme ultraviolet spectral range based on a fiber laser amplifier system with a repetition rate between 100 and 300 kHz, which we use to measure element-resolved demagnetization dynamics. The setup is equipped with a strong electromagnet and a cryostat, allowing measurements between 10 and 420 K using magnetic fields up to 0.86 T. The performance of our setup is demonstrated by a set of temperature- and time-dependent magnetization measurements with elemental resolution.
Electronic structure, optical properties, morphology and charge transport in naphthalenediimide (NDI)-based n-type copolymer with altered π-conjugation: A theoretical perspective
Authors: Ghosh Sarbani , Rolland Nicolas , Zozoulenko Igor
Published: June 2021

Future developments of the thermoelectric technologies based on conducting polymer require to find n-type polymers with performance, especially electrical conductivity, comparable to the one of the state-of-the-art p-type conducting polymers. In this regard, naphthalenediimide based donor–acceptor copolymers have appeared as promising candidates. The backbone of the polymer can be engineered to control the electronic structure and the morphology of the chains in order to maximize both the charge carrier density and mobility. However, at the moment a complete theoretical insight from electronic structures to charge transport is missing. Here, we use a multiscale theoretical framework to study naphthalenediimide based donor–acceptor copolymers where the donor π-conjugated dithienylvinylene moieties are replaced by π non-conjugated dithienylethane in various amounts, and we show that this approach is in position to rationalize many experimental data. The resulting gradual change in electronic structure of polymer chains is investigated by the density functional theory and correlated with experimental absorption spectra. The morphology of a polymer film is studied by means of molecular dynamics simulations, showing that an extended network of inter-chain π–π stacking is preserved upon introduction of non-conjugated units in the polymer backbone. This finding is supported by a subsequent calculation of the charge transport, which shows only a moderate impact of the morphology on the mobility, while the experimental data can be retrieved by considering the effect of the π non-conjugated moiety on the electronic structure. Such a multiscale description of conducting polymers paves the way toward fully theoretical design of future high performances materials.
Exceptional degeneracy in a waveguide periodically loaded with discrete gain and radiation loss elements
Authors: Abdelshafy Ahmed F. , Mealy Tarek , Hafezi Ehsan , Nikzamir Alireza , Capolino Filippo
Published: June 2021

We demonstrate that a periodic waveguide comprising of uniform lossless segments together with discrete gain and radiating elements supports exceptional points of degeneracy (EPDs). We provide analytical expressions for all possible conditions that guarantee the occurrence of an EPD, i.e., the coalescence of eigenvalues and eigenvectors. We show that EPDs are not only achieved using symmetric gain and radiation periodic loading, but they are also obtained using asymmetric gain and radiation loss conditions. We illustrate the characteristics of the degenerate electromagnetic modes, showing the dispersion diagram and discussing the tunability of the EPD frequency. We show a special condition, and we refer to it as a parity-time-glide symmetry, which leads to a degeneracy that is occurring at all frequencies of operation. The class of EPDs proposed in this work is very promising for many applications that incorporate discrete-distributed coherent sources and radiation loss elements; operating in the vicinity of such special degeneracy conditions leads to a potential performance enhancement in a variety of microwave and optical resonators, antennas, and devices and can be extended to a new class of active integrated antenna arrays and radiating laser arrays.
A multi-sheath model for highly nonlinear plasma wakefields
Authors: Dalichaouch T. N. , Xu X. L. , Tableman A. , Li F. , Tsung F. S. , Mori W. B.
Published: June 2021

An improved description for nonlinear plasma wakefields with phase velocities near the speed of light is presented and compared against fully kinetic particle-in-cell simulations. These wakefields are excited by intense particle beams or lasers pushing plasma electrons radially outward, creating an ion bubble surrounded by a sheath of electrons characterized by the source term S≡−1enp(ρ−Jz/c), where ρ and Jz are the charge and axial current densities, respectively. Previously, the sheath source term was described phenomenologically with a positive-definite function, resulting in a positive definite wake potential. In reality, the wake potential is negative at the rear of the ion column which is important for self-injection and accurate beam loading models. To account for this, we introduce a multi-sheath model in which the source term, S, of the plasma wake can be negative in regions outside the ion bubble. Using this model, we obtain a new expression for the wake potential and a modified differential equation for the bubble radius. Numerical results obtained from these equations are validated against particle-in-cell simulations for unloaded and loaded wakes. The new model provides accurate predictions of the shape and duration of trailing bunch current profiles that flatten plasma wakefields. It is also used to design a trailing bunch for a desired longitudinally varying loaded wakefield. We present beam loading results for laser wakefields and discuss how the model can be improved for laser drivers in future work. Finally, we discuss differences between the predictions of the multi- and single-sheath models for beam loading.
Solution-processed amorphous p-type Cu-Sn-I thin films for transparent Cu-Sn-I/IGZO p–n junctions
Authors: Wu Haijuan , Liang Lingyan , Wang Xiaolong , Zhang Hengbo , Bao Jinbiao , Cao Hongtao
Published: June 2021

P-type Cu-Sn-I thin films with different Sn contents (CSn) were fabricated in air via a simple and low-cost spin-coating method. Sn additive facilitates the amorphization of CuI, and a complete amorphous phase of Cu-Sn-I film is achieved at CSn =15%. With increasing CSn, the optical bandgap increases and refractive index decreases, probably due to the influence of Sn-additive on both the electronic structure and phase state of the films. The air-processed Sn-free CuI films show p-type conduction with hole mobility and a concentration of 17.3 cm2/V−1 s−1 and 1.1 × 1019 cm−3, and an increasing trend of resistivity is observed along with a large drop in hole concentration during the Sn-inspired amorphization process. Moreover, transparent Cu-Sn-I/IGZO p–n junctions were constructed, exhibiting the optimum rectifying characteristic at CSn = 15% with a forward-to-reverse ratio of 6.2 × 103.
Vortex induced vibrations of a pivoted finite height cylinder at low Reynolds number
Authors: Cajas J. C. , Pastrana D. , Rodríguez I. , Lehmkuhl O. , Houzeaux G. , Vázquez M. , Treviño C.
Published: June 2021

The vortex induced vibrations (VIVs) of a pivoted cylinder with finite height have been numerically investigated. A mathematical model is introduced and described, and the resulting equations are numerically solved for low Reynolds number Re = 100, 200 and several combinations of the governing parameters. Results on the solid body trajectories, the maximum amplitude of the oscillations, the hydrodynamic force coefficients, the wake structure, and details on the vortex shedding near the cylinder are presented and discussed. The numerical results compare reasonably well with the canonical system of VIV of two-degrees of freedom circular cylinder in the laminar regime. Also, qualitative similarities with closely related VIV systems at larger Re suggest interesting lines of future research. Analytical approximations for limiting cases are done and an excellent agreement with the numerical results is obtained.
Charge state control of the silicon vacancy and divacancy in silicon carbide
Authors: Son Nguyen T. , Ivanov Ivan G.
Published: June 2021

Color centers in silicon carbide (SiC), such as the negative silicon vacancy (VSi−) and neutral divacancy (VSiVC0), have recently been shown to be promising quantum bits (qubits) for a variety of applications in quantum communications and sensing. Considerable effort has been spent on improving the performance of these optical spin qubits, and the instability of their charge state is an important issue to be solved. Using electron paramagnetic resonance to monitor the charge state of dominant intrinsic defects in n-type, high-purity semi-insulating and p-type 4H-SiC, we reveal carrier compensation processes and the windows of the Fermi level that allow us to obtain stable VSi− and VSiVC0 in equilibrium. We show that stable VSi− and VSiVC0 ensembles can be obtained in n-type (p-type) via controlling the concentration of the Si vacancy (the C vacancy and the C antisite–vacancy pairs). The charge-state control of single VSi− and VSiVC0 emitters is expected to be possible in pure p-type layers by controlling the concentration of the C vacancy. In ultrapure materials, optical repumping is required for charge state control of single emitters.
Dynamics of a bubble in a liquid fully confined by an elastic boundary
Authors: Liu J. L. , Xiao W. , Yao X. L. , Huang X. H.
Published: June 2021

In order to investigate the dynamics of a bubble in a liquid fully confined by an elastic boundary, which are used for applications and research of cavitation bubbles in botanical and biomedical sciences, we establish a related numerical model by the boundary element method. The boundary is defined as an interface between two liquids with different densities to simulate the environment of biological tissue efficiently. Our numerical model is validated thanks to the results of an available related experiment and the calculations of a confined corrective Rayleigh–Plesset equation. Then, we focus on the dynamics of a non-spherical bubble caused by relative position of the bubble and confinement. The results show that the confinement can lead to a rapid oscillation of a bubble, and a jet will be generated along the eccentric direction because of the accumulation of high pressure and disturbance on one side of the spherical confinement. Furthermore, elastic modulus of the boundary, size of the confinement, and eccentric position of the bubble in the confinement are considered in this paper. The amplitude and cycle of a bubble oscillation will decrease with the increase of the elastic modulus and decrease of the size of the confinement. What's more, eccentricity leads to a strong restriction on the bubble surface near the boundary and obvious non-spherical deformation of the elastic boundary. The study can contribute to understandings and applications of cavitation bubbles in expulsion of spores, plant cell wall broken, thrombolysis, and other related botanical and biomedical fields.
Ultrafast spot-profile LEED of a charge-density wave phase transition
Authors: Storeck G. , Rossnagel K. , Ropers C.
Published: June 2021

We investigate the optically driven phase transition between two charge-density wave (CDW) states at the surface of tantalum disulfide (1T-TaS2). Specifically, we employ a recently improved ultrafast low-energy electron diffraction setup to study the transition from the nearly commensurate to the incommensurate (IC) CDW state. The experimental setup allows us to follow transient changes in the diffraction pattern with high momentum resolution and 1-ps electron pulse duration. In particular, we trace the diffraction intensities and spot profiles of the crystal lattice, including main and CDW superstructure peaks, as well as the diffuse background. Harnessing the enhanced data quality of the instrumental upgrade, we follow the laser-induced transient disorder in the system and perform a spot-profile analysis that yields a substantial IC-peak broadening for very short time scales followed by a prolonged spot narrowing.
A multiscale volume of fluid method with self-consistent boundary conditions derived from molecular dynamics
Authors: Liu Hanyi , Zhang Jun , Capobianchi Paolo , Borg Matthew K. , Zhang Yonghao , Wen Dongsheng
Published: June 2021

Molecular dynamics (MD) and volume of fluid (VOF) are powerful methods for the simulation of dynamic wetting at the nanoscale and macroscale, respectively, but the massive computational cost of MD and the sensitivity and uncertainty of boundary conditions in VOF limit their applications to other scales. In this work, we propose a multiscale simulation strategy by enhancing VOF simulations using self-consistent boundary conditions derived from MD. Specifically, the boundary conditions include a particular slip model based on the molecular kinetic theory for the three-phase contact line to account for the interfacial molecular physics, the classical Navier slip model for the remaining part of the liquid–solid interface, and a new source term supplemented to the momentum equation in VOF to replace the convectional dynamic contact angle model. Each slip model has been calibrated by the MD simulations. The simulation results demonstrate that with these new boundary conditions, the enhanced VOF simulations can provide consistent predictions with full MD simulations for the dynamic wetting of nanodroplets on both smooth and pillared surfaces, and its performance is better than those with other VOF models, especially for the pinning–depinning phenomenon. This multiscale simulation strategy is also proved to be capable of simulating dynamic wetting above the nanoscale, where the pure MD simulations are inaccessible due to the computational cost.
Influence of wetting behavior on the morphology of droplet impacts onto dry smooth surfaces
Authors: Foltyn P. , Ribeiro D. , Silva A. , Lamanna G. , Weigand B.
Published: June 2021

The influence of wettability on the morphology of droplet impacts onto dry surfaces is often neglected in the literature, despite its significant effect on the resulting morphology. In this work, the role of wettability is investigated systematically by considering droplet impact processes on smooth dry surfaces of two different materials. The wetting behavior is varied not only by employing two different fluids, but most importantly by varying the surface properties by plasma activation and polymerization. Overall, this leads to four different wetting behaviors for each surface. The changes in impact morphology are visualized by means of a three-perspective experimental facility. In particular, the bottom view employs a total internal reflection-configuration for visualizing the exact droplet contact area and contact time. This enables us to characterize the main features of the different wetting behaviors. Overall, we found that surface wettability mainly influences the receding phase, resulting in higher receding rates with decreasing wettability but also the maximum spreading diameter.
Spectroscopy of phase transitions for multiagent systems
Authors: Zagli Niccolò , Lucarini Valerio , Pavliotis Grigorios A.
Published: June 2021

In this paper, we study phase transitions for weakly interacting multiagent systems. By investigating the linear response of a system composed of a finite number of agents, we are able to probe the emergence in the thermodynamic limit of a singular behavior of the susceptibility. We find clear evidence of the loss of analyticity due to a pole crossing the real axis of frequencies. Such behavior has a degree of universality, as it does not depend on either the applied forcing or on the considered observable. We present results relevant for both equilibrium and nonequilibrium phase transitions by studying the Desai–Zwanzig and Bonilla–Casado–Morillo models.
Droplet fate, efficacy of face mask, and transmission of virus-laden droplets inside a conference room
Authors: Mirikar Dnyanesh , Palanivel Silambarasan , Arumuru Venugopal
Published: June 2021

The second and third waves of coronavirus disease-2019 (COVID-19) pandemic have hit the world. Even after more than a year, the economy is yet to return to a semblance of normality. The conference/meeting room is one of the critical sections of offices that might be difficult not to use. This study analyzes the distribution of the virus-laden droplets expelled by coughing inside a conference room, the effect of ventilation rates, and their positioning. The efficacy of masks is studied to get quantitative information regarding the residence time of the droplets. The effects of evaporation, turbulent dispersion, and external forces have been considered for calculating the droplets' trajectories. We have analyzed six cases, of which two are with masks. Change in the ventilation rate from four air changes per hour (ACH) to eight resulted in a 9% increment in the number of droplets entrained in the outlet vent, while their average residence time was reduced by ∼ 8 s. The shift in the vents' location has significantly altered droplets' distribution inside a conference room. It results in ∼ 1.5% of the injected droplets reaching persons sitting across the table, and a similar indoor environment is not recommended. Wearing a mask in the case of eight ACH has presented the best scenario out of the six cases, with a 6.5% improvement in the number of droplets entrained in the outlet vent and a 9 s decrease in their average residence time compared to the case without a mask. No droplets have reached persons sitting across the table when the infected person is wearing the mask, which follows that a social distancing of 6 ft with a mask is adequate in indoor environments.
Effects of (Ni0.8Fe0.2)100−xCrx seed layer on microstructure, magnetic properties, and giant magnetoresistance of [FeCoNi/Cu] multilayer films
Authors: Kulkarni Prabhanjan D. , Nakatani Tomoya , Sasaki Taisuke , Sakuraba Yuya
Published: June 2021

We studied the effect of the (Ni0.8Fe0.2)100−xCrx seed layer on the current-in-plane giant magnetoresistance (CIP-GMR) in Fe16Co66Ni18/Cu multilayer films. Both the GMR ratio (ΔR/R) and interlayer exchange coupling (IEC) between the FeCoNi layers showed strong dependences on the Cr concentration x in the seed layer. The highest ΔR/R of ∼30% was obtained for x = 38 (at. %) due to a comparatively strong antiparallel IEC resulting from a strong [111]-out-of-plane-texture of the [FeCoNi/Cu] multilayer. This confirms that a strong [111] texture is essential for the GMR in antiferromagnetically coupled multilayers as reported in previous works. However, we found that the strong [111] texture is not sufficient to obtain large ΔR/R. For x = 48, the [FeCoNi/Cu] multilayer showed a strong [111] texture as that for x = 38; however, the observed ΔR/R and antiparallel IEC for x = 48 were much smaller than those for x = 38. Detailed microstructural and chemical analyses by scanning transmission electron microscopy revealed that the fluctuation of the thickness of the Cu spacer layer can explain the reduction of antiparallel IEC that gave rise to the decrease in ΔR/R in the case of x = 48. We also discuss the effect of IEC energies on the sensitivity of GMR sensors.
A tunable phononic crystal system for elastic ultrasonic wave control
Authors: Song Yihao , Shen Yanfeng
Published: June 2021

Tunable phononic crystals (PCs) are burgeoning within the engineering communities due to their adjustable capabilities for manipulating elastic waves. In this Letter, a shape memory alloy (SMA) stubbed PC is elaborated to achieve the tunable bandgaps for the control of ultrasonic waves. The tunable mechanism stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature. Both numerical modeling and experimental verification are conducted to validate the achievement of the controllable stop band properties. The proposed SMA PC design could be broadened to numerous promising applications, e.g., ultrasonic wave waveguiding, flat-lens focusing, and mechanical frequency filtering, possessing enabling potential for highly adjustable wave manipulation.
CO
2
reduction on pure Cu produces only H
2
after subsurface O is depleted: Theory and experiment
Authors: Liu Guiji , Lee Michelle , Kwon Soonho , Zeng Guosong , Eichhorn Johanna , Buckley Aya K. , Toste F. Dean , Goddard William A. , Toma Francesca M.
Published: June 2021

Significance

Electrochemical reduction of CO
2
to fuels and valuable chemicals is a global imperative to address energy and climate challenges. Despite enormous efforts, there is not yet a commercial process. The best catalyst remains Cu metal, but a great deal of controversy revolves around the role of the presence of oxygen in the material. We combine theory and experiments to show that pure Cu without subsurface oxygen leads to no organic products. Thus, maintaining substantial oxygen at Cu surfaces is essential for long-term reduction of CO
2
to organics.
The
Rhox
gene cluster suppresses germline
LINE1
transposition
Authors: Tan Kun , Kim Matthew E. , Song Hye-Won , Skarbrevik David , Babajanian Eric , Bedrosian Tracy A. , Gage Fred H. , Wilkinson Miles F.
Published: June 2021

Significance

Long interspersed element class 1 (
LINE1
) elements are transposable elements that comprise ∼20% of mammalian genomes. Their activity must be tightly controlled or genome integrity will be compromised, leading to DNA damage and cell death. Here, we report that several members of a rapidly evolving X-linked homeobox gene cluster suppress
LINE1
transposition. One family member of this
Rhox
gene cluster—
Rhox10
—silences
LINE1
expression and transposition in the male germline when it is hypomethylated and thus highly susceptible to
LINE1
activation.
Rhox10
acts by driving the expression of
Piwil2
, which encodes a key component in the Piwi-interacting RNA pathway. The ability of
Rhox
genes to suppress
LINE1
elements is evolutionarily conserved and perturbed by mutation in infertility patients.
Monitoring war destruction from space using machine learning
Authors: Mueller Hannes , Groeger Andre , Hersh Jonathan , Matranga Andrea , Serrat Joan
Published: June 2021

Significance

Satellite imagery is becoming ubiquitous. Research has demonstrated that artificial intelligence applied to satellite imagery holds promise for automated detection of war-related building destruction. While these results are promising, monitoring in real-world applications requires high precision, especially when destruction is sparse and detecting destroyed buildings is equivalent to looking for a needle in a haystack. We demonstrate that exploiting the persistent nature of building destruction can substantially improve the training of automated destruction monitoring. We also propose an additional machine-learning stage that leverages images of surrounding areas and multiple successive images of the same area, which further improves detection significantly. This will allow real-world applications, and we illustrate this in the context of the Syrian civil war.
Coevolutionary phage training leads to greater bacterial suppression and delays the evolution of phage resistance
Authors: Borin Joshua M. , Avrani Sarit , Barrick Jeffrey E. , Petrie Katherine L. , Meyer Justin R.
Published: June 2021

Significance

The evolution of antibiotic-resistant bacteria threatens to claim over 10 million lives annually by 2050. This crisis has renewed interest in phage therapy, the use of bacterial viruses to treat infections. A major barrier to successful phage therapy is that bacteria readily evolve phage resistance. One idea proposed to combat resistance is “training” phages by using their natural capacity to evolve to counter resistance. Here, we show that training phages by coevolving them with their hosts for 1 mo repeatably enhances their capacity for suppressing bacterial growth and delays the emergence of resistance. Enhanced suppression was caused by several mechanisms, suggesting that the coevolutionary training protocol produces a robust therapeutic that employs complementary modes of action.
Knowledge extraction and transfer in data-driven fracture mechanics
Authors: Liu Xing , Athanasiou Christos E. , Padture Nitin P. , Sheldon Brian W. , Gao Huajian
Published: June 2021

Significance

Data-driven approaches have launched a new paradigm in scientific research that is bound to have an impact on all disciplines of science and engineering. However, at this juncture, the exploration of data-driven techniques in the century-old field of fracture mechanics is highly limited, and there are key challenges including accurate and intelligent knowledge extraction and transfer in a data-limited regime. Here, we propose a framework for data-driven knowledge extraction in fracture mechanics with rigorous accuracy assessment which employs active learning for optimizing data usage and for data-driven knowledge transfer that allows efficient treatment of three-dimensional fracture problems based on two-dimensional solutions.
Ctf3/CENP-I provides a docking site for the desumoylase Ulp2 at the kinetochore
Authors: Quan Yun , Hinshaw Stephen M. , Wang Pang-Che , Harrison Stephen C. , Zhou Huilin
Published: June 2021

The step-by-step process of chromosome segregation defines the stages of the cell cycle. In eukaryotes, signals controlling these steps converge upon the kinetochore, a multiprotein assembly that connects spindle microtubules to chromosomal centromeres. Kinetochores control and adapt to major chromosomal transactions, including replication of centromeric DNA, biorientation of sister centromeres on the metaphase spindle, and transit of sister chromatids into daughter cells during anaphase. Although the mechanisms that ensure tight microtubule coupling at anaphase are at least partly understood, kinetochore adaptations that support other cell cycle transitions are not. We report here a mechanism that enables regulated control of kinetochore sumoylation. A conserved surface of the Ctf3/CENP-I kinetochore protein provides a binding site for Ulp2, the nuclear enzyme that removes SUMO chains from modified substrates. Ctf3 mutations that disable Ulp2 recruitment cause elevated inner kinetochore sumoylation and defective chromosome segregation. The location of the site within the assembled kinetochore suggests coordination between sumoylation and other cell cycle–regulated processes.
Modification of the Hybridization Gap by Twisted Stacking of Quintuple Layers in a Three-Dimensional Topological Insulator Thin Film
Authors: Zhou Changyuan , Song Dezhi , Jiang Yeping , Zhang Jun
Published: June 2021

Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers (QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb2Te3 QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states. Signatures of gap-closing are found in 3-QL films. The successful in situ application of this approach opens a new route to search for exotic physics in topological insulators.
Anisotropic Superconducting Properties of Kagome Metal CsV3Sb5
Authors: Ni Shunli , Ma Sheng , Zhang Yuhang , Yuan Jie , Yang Haitao , Lu Zouyouwei , Wang Ningning , Sun Jianping , Zhao Zhen , Li Dong , Liu Shaobo , Zhang Hua , Chen Hui , Jin Kui , Cheng Jinguang , Yu Li , Zhou Fang , Dong Xiaoli , Hu Jiangping , Gao Hong-Jun , Zhao Zhongxian
Published: June 2021

We systematically measure the superconducting (SC) and mixed state properties of high-quality CsV3Sb5 single crystals with T
c ∼ 3.5 K. We find that the upper critical field H
c2(T) exhibits a large anisotropic ratio of

H

c
2

a
b

/

H

c
2

c

∼
9

at zero temperature and fitting its temperature dependence requires a minimum two-band effective model. Moreover, the ratio of the lower critical field,

H

c
1

a
b

/

H

c
1

c

, is also found to be larger than 1, which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy. Both H
c1(T) and SC diamagnetic signal are found to change little initially below T
c ∼ 3.5 K and then to increase abruptly upon cooling to a characteristic temperature of ∼2.8 K. Furthermore, we identify a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state. Interestingly, we find that, below the same characteristic T ∼ 2.8 K, the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60° characteristic of the Kagome geometry. Our results suggest an intriguing superconducting state emerging in the complex environment of Kagome lattice, which, at least, is partially driven by electron-electron correlation.
Electromagnetic wave induced resonance in infinitely long and hollow square cobalt nano-prisms
Authors: Aziz M M , McKeever C
Published: June 2021

Confined metallic ferromagnetic nano-structures are desirable constituents in magnetic composites and devices for applications in telecommunications and electromagnetic wave absorption. Removing the core of these elements or substituting with non-magnetic fillers leads to immediate reduction in their weight and potential for tailoring their magnetic, dielectric and geometrical properties to enable the development of light-weight, high-frequency and efficient composites and devices. However the effect of this geometry change on the electromagnetic wave absorption and magnetic response in these hollow structures is not clear in comparison to their solid counterparts. In this article, electromagnetic wave propagation in long and hollow square cobalt nano-prisms with side lengths of 100 and 500 nm and with different wall thicknesses in the range 25–200 nm is simulated by solving the coupled system of Maxwell’s equations and the Landau–Lifshitz–Gilbert equation using the finite-difference time-domain method. The simulated dynamic magnetisation and power dissipation spectra indicated that the core of the long cobalt prisms can be removed up to wall thicknesses equal to the magnetic skin depth (about 50 nm estimated for cobalt) without significantly impacting electromagnetic wave absorption at the fundamental resonance frequencies. The simulations also revealed prominent higher frequency corner resonance modes in the small 100 nm prism with 25 nm wall thickness, but whose contribution becomes negligible with increasing prism size.
Nanosecond resolved ro-vibrational CO2 excitation measurement
Authors: Du Yanjun , Tsankov Tsanko V , Luggenhölscher Dirk , Czarnetzki Uwe
Published: June 2021

We report first ns-resolved absorption measurements of the ro-vibrational excitation of CO2. The high temporal resolution of 8 ns is made possible by a fast detector (rise-time 5 ns), sensitive in the mid-infrared region. The resolution is achieved by a slow temperature scan of a quantum cascade laser and a segmented data capturing scheme. A repetitively pulsed ns discharge in 10% CO2 + 90% He at 150 mbar and a repetition rate of 2 kHz is investigated. The evolution of the population densities of the different vibration modes as well as the associated vibrational and rotational temperatures within the discharge pulse of only 150 ns length are simultaneously determined and provide valuable insight into the CO2 excitation dynamics. A preferential excitation in the asymmetric vibrational mode is observed in the discharge phase shortly after the breakdown.
Production of ibuprofen-magnetite nanocomposites by pulsed laser ablation
Authors: Gera Tamás , Smausz Tomi , Ajtai Tibor , Kurilla Boldizsár , Homik Zsolt , Kopniczky Judit , Bozóki Zoltán , Szabó-Révész Piroska , Ambrus Rita , Hopp Béla
Published: June 2021

We investigated the application of pulsed laser ablation (PLA) for the production of magnetic nanoparticles (MNPs)/drug nanocomposites. Magnetic drug delivery vehicles can provide a multifunctional theranostic platform and allow for a combination of diagnostics, monitoring and therapeutics. We applied nanosecond laser pulses at two different wavelengths (Nd:YAG laser, λ
1 = 532 nm/λ
2 = 1064 nm, FWHM = 6 ns) for the ablation of target tablets consisting of a mixture of ibuprofen (as a model drug) and magnetite NPs in various mass ratios. Fourier-transform infrared and Raman spectroscopy investigations of the ablated particles revealed that PLA induced no chemical changes in the pharmaceutical compound. The size distributions of the composite particles were established using a particle size analyzer (scanning mobility particle sizer), and 100–150 nm mean particle size values were obtained. SEM, energy dispersive x-ray spectroscopy and fast photography studies provided morphological and compositional information about the ablated particles. We demonstrated that PLA offers a simple and chemical free method for producing MNPs/drug nanocomposites, and it can be applied for the future development of new theranostic nanosystems.
Modelling of runaway electron dynamics during argon-induced disruptions in ASDEX Upgrade and JET
Authors: Insulander Björk K , Vallhagen O , Papp G , Reux C , Embreus O , Rachlew E , Fülöp T , Upgrade Team the ASDEX , contributors JET , MST1 Team the EUROfusion
Published: June 2021

Disruptions in tokamak plasmas may lead to the generation of runaway electrons that have the potential to damage plasma-facing components. Improved understanding of the runaway generation process requires interpretative modelling of experiments. In this work we simulate eight discharges in the ASDEX Upgrade and JET tokamaks, where argon gas was injected to trigger the disruption. We use a fluid modelling framework with the capability to model the generation of runaway electrons through the hot-tail, Dreicer and avalanche mechanisms, as well as runaway electron losses. Using experimentally based initial values of plasma current and electron temperature and density, we can reproduce the plasma current evolution using realistic assumptions about temperature evolution and assimilation of the injected argon in the plasma. The assumptions and results are similar for the modelled discharges in ASDEX Upgrade and JET. For the modelled discharges in ASDEX Upgrade, where the initial temperature was comparatively high, we had to assume that a large fraction of the hot-tail runaway electrons were lost in order to reproduce the measured current evolution.
Sex ratio, age group and length at first maturity of mackerel scad (Decapterus macarellus Cuvier, 1833) in the Southern waters of Ambon, Eastern Indonesia
Authors: Silooy F D , Tupamahu A , Ongkers O T S , Haruna  , Matrutty D D P , Pattikawa J A
Published: June 2021

The existence of mackerel scad in Ambon waters, Moluccas Indonesia has decreased from year to year mainly due to the over exploitation. This research aimed to study the biological aspects, in particular were sex ratio, age group and length at first maturity of mackerel scad (Decapterus macarellus) from this area. Sampling was done on September 2016 to July 2017 at the southern waters of Ambon Island. Samples collected were dissected to determine their sex and their gonad maturity level then measured. Bhattacharya method was used to determine age group while Spearman- Kaber method was used to identify length at the first maturity of this species. It was found that mackerel scad in the southern waters of Ambon Island had an equal number of male and female that consists of four age groups with length at first maturity for male and female were 24.9 cm and 24.8 cm, respectively.
Population dynamics of Strombus luhuanus, Linneaus 1758 from Oma coastal waters, Central Maluku, Eastern Indonesia
Authors: Haumahu S , Uneputty P A
Published: June 2021

Strombus luhuanus (strawberry conch), Linneaus 1758 is a marine mesogastropod belongs to Strombidae family. S. luhuanus is locally consumed by coastal communities in Maluku province to fulfill their protein needed, which will decreasing the stock in natural environment. The biological study including population dynamics needed to maintain S. luhuanus population. The research was conducted in Oma coastal water, Central Maluku, Eastern Indonesia during January to December 2019. The objectives of this research were to study the aspect of population dynamics of S. luhuanus such as asymptotic length (L∞), growth coeficient (K), natural mortality (Z), exploitation rate (E) and recruitment. A total of 1823 individual of S. luhuanus found in this study which consisted of 831 individual of males and 992 individual of females population. Shell size of S. luhuanus varied monthly. The result showed that in general, the male population showed five cohort, while the female showed six cohort. L∞ = 63.40 mm, K = 0.65 for females population; whilst for the males population, L∞ = 69.80 and K = 0.5. Total mortality (Z) for both population were Z = 3.03 and Z = 4.32, respectively. Exploitation rate of S. luhuanus in this study area showed that the population was overexploited (E = 0.64 and E = 0.79 for females and males population, respectively).