bluuebunny/crossref_metadata_2025 huggingface dataset:
C2-Si: A novel silicon allotrope in monoclinic phase
Authors: Fan Qing-yang , Sun Yi-chao , Yang Fang , Song Yan-xing , Yu Xin-hai , Yun Si-ning
Published: June 2021

Based on density functional theory (DFT), a new silicon allotrope C2-Si is proposed in this work. The mechanical stability and dynamic stability of C2-Si are examined based on the elastic constants and phonon spectrum. According to the ratio of bulk modulus and shear modulus, C2-Si has ductility under ambient pressure; compared with Si64, Si96, I4/mmm and h-Si6, C2-Si is less brittle. Within the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional, C2-Si is an indirect narrow band gap semiconductor, and the band gap of C2-Si is only 0.716 eV, which is approximately two-thirds of c-Si. The ratios of the maximum and minimum values of the Young’s modulus, shear modulus and Poisson’s ratio in their 3D spatial distributions for C2-Si are determined to characterize the anisotropy. In addition, the anisotropy in different crystal planes is also investigated via 2D representations of the Young’s modulus, shear modulus, and Poisson’s ratio. Among more than ten silicon allotropes, C2-Si has the strongest absorption ability for visible light.
Biaxial modulus in fiber-textured thin films: Coinciding Voigt and Reuss bounds and planes of isotropy
Authors: Shrikanth S. , Prasad Rajesh , Neelakantan Suresh
Published: June 2021

The anisotropy of crystals necessitates the use of effective biaxial moduli for practical applications of fiber-textured thin films and coatings. The coincidence of the widely used Voigt and Reuss bounds of the effective moduli gives exact relations between the moduli of the polycrystal and the single crystal. It was known that only planes normal to three-, four-, and sixfold axes have coinciding bounds.1 The present study reports that planes without symmetry can also have coinciding bounds. A general mathematical framework to identify such planes in any crystal system is established. It is shown that the Voigt assumption of identical strain states in each grain cannot be made, as has been done in previous studies, for a general {hkl} fiber-textured thin film where the free surface boundary conditions are assumed. The conditions under which the Voigt average can be defined are also identified. For the textures where the Voigt average is invalid, a new method to estimate the polycrystalline average of the biaxial modulus under equibiaxial strain is defined. Another aspect of interest is that, the biaxial modulus, although generally anisotropic, is isotropic along certain planes. This is known for planes with three-, four-, and sixfold symmetry. However, here we demonstrate the existence of isotropy in planes without symmetry. A method to identify such planes under both equibiaxial strain and equibiaxial stress states are presented. Novel three-dimensional surfaces representing the averages of the biaxial moduli as functions of the orientation of the fiber axis are illustrated.
A convolutional neural network algorithm for breast tumor detection with magnetic detection electrical impedance tomography
Authors: Chen Ruijuan , Zhao Songsong , Wu Weiwei , Sun Zhihui , Wang Jinhai , Wang Huiquan , Han Guang
Published: June 2021

Breast cancer is a malignant tumor disease for which early detection, diagnosis, and treatment are of paramount significance in prolonging the life of patients. Magnetic Detection Electrical Impedance Tomography (MDEIT) based on the Convolutional Neural Network (CNN), which aims to realize non-invasive, high resolution detection of breast tumors, is proposed. First, the MDEIT forward problem of the coronal and horizontal planes of the breast was simulated and solved using the Finite Element Method to obtain sample datasets of different lesions. Then, the CNN was built and trained to predict the conductivity distribution in different orientations of the breast model. Finally, noise and phantom experiments were performed in order to assess the anti-noise performance of the CNN algorithm and its feasibility of detecting breast tumors in practical applications. The simulation results showed that the reconstruction relative error with the CNN algorithm can be reduced to 10%, in comparison with the truncated singular value decomposition algorithm and back propagation algorithm. The CNN algorithm had better stability in the anti-noise performance test. When the noise of 60 dB was added, the shape of the breast tumor could still be restored by the CNN algorithm. The phantom experimental results showed that through the CNN based reconstruction algorithm, the reconstruction conductivity distribution image was legible and the position of the breast tumor could be determined. It is reasonable to conclude that the MDEIT reconstruction method proposed in this study has practical importance for the early and non-invasive detection of breast tumors.
Realization of invariant-based shortcuts to population inversion with a superconducting circuit
Authors: Han Zhikun , Dong Yuqian , Yang Xiaopei , Song Shuqing , Qiu Luqing , Zheng Wen , Xu Jianwen , Huang Tianqi , Wang Zhimin , Lan Dong , Tan Xinsheng , Yu Yang
Published: June 2021

Shortcuts to adiabaticity have been proved an effective routine for precise quantum state manipulation. Here, we experimentally demonstrate invariant-based shortcuts to adiabaticity to speed up the population transfer in a superconducting circuit. Through inverse engineering of the Hamiltonian, we realize this protocol in a single-qubit and a two-qubit system. The Lewis–Risenfeld phase is characterized experimentally. Furthermore, we investigate the robustness of the scheme against amplitude and frequency errors.
Dosimetric calibration of GafChromic HD-V2, MD-V3, and EBT3 films for dose ranges up to 100 kGy
Authors: Abe Y. , Morace A. , Arikawa Y. , Mirfayzi S. R. , Golovin D. , Law K. F. F. , Fujioka S. , Yogo A. , Nakai M.
Published: June 2021

A dosimetric calibration of three types of radiochromic films (GafChromicTM HD-V2, MD-V3, and EBT3) was carried out for absorbed doses (D) ranging up to 100 kGy using a 130 TBq Co60 γ-ray source. The optical densities (ODs) of the irradiated films were acquired with the transmission-mode flatbed film scanner EPSON GT-X980. The calibration data were cross-checked using the 20-MeV proton beam from the azimuthally varying field cyclotron at the Research Center for Nuclear Physics in Osaka University. These experimental results not only present the measurable dose ranges of the films depending on the readout wavelength, but also show consistency with our hypothesis that the OD response curve [log(OD)–log(D) curve] is determined by the volumetric average of the absorption dose and does not strongly depend on the type of radiation for the excitation.
Analytic quasi-steady evolution of marginally unstable kinetic plasma instabilities in the presence of drag and scattering
Authors: Lestz J. B. , Duarte V. N.
Published: June 2021

The 1D bump-on-tail problem is studied in order to determine the influence of drag on quasi-steady solutions near marginal stability (1−γd/γL≪1) when effective collisions are much larger than the instability growth rate (ν≫γ). In this common tokamak regime, it is rigorously shown that the paradigmatic Berk–Breizman cubic equation for the nonlinear mode evolution reduces to a much simpler differential equation, dubbed the time-local cubic equation, which can be solved directly. It is found that in addition to increasing the saturation amplitude, drag introduces a shift in the apparent oscillation frequency by modulating the saturated wave envelope. Excellent agreement is found between the analytic solution for the mode evolution and both the numerically integrated Berk–Breizman cubic equation and fully nonlinear 1D Vlasov simulations. Experimentally isolating the contribution of drag to the saturated mode amplitude for verification purposes is explored but complicated by the reality that the amount of drag cannot be varied independently of other key parameters in realistic scenarios. While the influence of drag is modest when the ratio of effective drag to effective scattering α/ν is very small, it can become substantial when α/ν≳0.5, suggesting that drag should be accounted for in quantitative models of fast-ion-driven instabilities in fusion plasmas.
Negative hydrogen ion dynamics inside the plasma volume of a linear device: Estimates from particle-in-cell calculations
Authors: Fubiani G. , Agnello R. , Furno I. , Garrigues L. , Guittienne Ph. , Hagelaar G. , Howling A. , Jacquier R. , Reman B. , Simonin A. , Taccogna F.
Published: June 2021

Negative hydrogen or deuterium ions are the precursor particles used to generate a high power beam of neutrals in order to heat the tokamak plasma core of magnetic fusion devices, inject current, and to some extent control instabilities. In the case of ITER, for instance, the negative ions are produced inside a high power large volume low-pressure tandem type magnetized ion source and extracted toward an electrostatic accelerator which accelerates them to 1 MeV before entering a neutralizer converting the ions into a neutral beam. This so-called neutral beam injector relies on the production of negative ions on the surface facing the plasma of the ion source extraction electrode. The latter is covered by a cesium layer in order to increase the negative ion yield. The use of cesium is currently an issue as it may diffuse outside of the source and induce secondary particle production or voltage breakdowns inside the accelerator vessel requiring a regular maintenance in a nuclear environment. In this work, we analyze numerically with a 2.5D particle-in-cell model the production rate and transport of negative ions in a linear device used as an ion source. The negative ions are generated via a dissociative attachment process with a hydrogen molecule in the volume of a magnetized cesium-free plasma. The linear device in the model has a large aspect ratio with a radius of 5 and a length of 100 cm and the magnetic field strength ranges from 100 to 400 G. We show that the shape and depth of the plasma potential profile may be controlled by biasing the end-plates which in turn strongly influence the residence time of the electrons and hence the negative ion yield. We observe the formation of large-scale rotating structures when the positive ions become magnetized with a rotation velocity in the kHz range.
Heterogeneous assembly of water from the vapor phase—Physical experiments and simulations with binding trifunctional organosilanes at the vapor/solid interface
Authors: Senadheera D. I. I. , Kuruppu Arachchige Neepa M. K. , Subasinghege Don Visal , Kumar Revati , Garno Jayne C.
Published: June 2021

A trace amount of interfacial water is required to initiate hydrosilation reactions of trifunctional organosilanes to form surface assemblies. In recent studies, we have learned that water also has a critical role in directing molecular placement on surfaces because water can react with silicon to provide oxygenated sites for surface binding. Consequently, the wettability nature of substrates influences the placement and density of organosilane films formed by vapor-phase reactions. Nanopatterning protocols were designed using vapor-phase organosilanes and colloidal lithography to compare the wettability differences of hydrophilic mica(0001) compared to relatively hydrophobic Si(100) as a strategy for tracking the location of water on surfaces. The competition between hydrophobic and hydrophilic domains for the adsorption and coalescence of water condensed from vapor can be mapped indirectly by mapping the organosilanes, which bind to water at the solid interface, using atomic force microscopy. Trifunctional octadecyltrichlorosilane (OTS) was used as a marker molecule to map out the areas of the surface where water was deposited. The effect of systematic changes in film thickness and surface coverage of OTS was evaluated at the vapor/solid interface by adding an incremental amount of water to sealed reaction vessels to wet the surface and assessing the outcome after reaction with vapor-phase trichlorosilane. Reactive molecular dynamics simulations of the silicon–water vapor interface combined with electronic structure calculations of oxygenated silicon clusters with methyltrichlorosilane provided insight of the mechanism for surface binding, toward understanding the nature of the interface and wettability factors, which influence the association and placement of silane molecules on surfaces.
Neutron irradiation induced defects in oxides and their impact on the oxide properties
Authors: Haseman M. , Somodi C. B. , Stepanov P. , Wall D. E. , Boatner L. A. , Hosemann P. , Wang Y. Q. , Uberuaga B. P. , Selim F. A.
Published: June 2021

Understanding the irradiation-induced defects in oxides is of interest for a wide range of applications. ZnO is an interesting oxide with mixed ionic and covalent bonding that contains a variety of point defect structures—making it an excellent model for studying irradiation-induced defects and their impact on properties. Here, we investigate the effects of neutron irradiation on the formation of defects and on the structural, optical, and electrical properties of ZnO single crystals. We observe the formation of vacancies and voids via positron annihilation spectroscopy. Neutron irradiation led to a significant deterioration of the ZnO structure and formed a high concentration of point defects, vacancy clusters, and voids with large disparities in their structure across variable irradiation times. It also led to significant changes in the optical properties and sample color. Irradiation for 444 h induced a high concentration of Cu acceptors as well as a high concentration of Ga donors. Temperature-dependent Hall effect measurements revealed the competing production of donors and acceptors and showed an increase in the slope of the carrier freeze-out curve with increasing irradiation dose. This work demonstrates the combined effects of neutron irradiation in producing a wide range of structural defects, impurities, and dopants in oxides and their enormous impact on modifying the oxide structure and both the optical and electronic properties. It particularly emphasizes the importance of considering the production of new impurities and dopants during the neutron irradiation of oxides.
Numerical investigation of flow separation control over an airfoil using fluidic oscillator
Authors: Xia L. , Hua Y. , Zheng J. G.
Published: June 2021

Leading edge flow separation control over a stalled National Advisory Committee for Aeronautics 0015 airfoil using a fluidic oscillator (FO) is investigated by means of numerical simulation possibly for the first time to elucidate the flow control mechanism and evaluate control authority. The flow is assumed to be two-dimensional and fully turbulent and resolved using unsteady Reynolds-averaged Navier–Stokes calculations with the elaborate Reynolds stress turbulence model employed. Our simulation is proved to be able to successfully resolve the basic characteristics of a FO operating in quiescent air, which include both the qualitative prominent flow structures and quantitative jet oscillation frequency. It is seen that the driving force behind the self-induced and self-sustaining oscillation of jet flow inside the oscillator is Coanda effect induced alternating development of a recirculation bubble on either side of the mixing chamber walls. We provide a comprehensive analysis of the flow control procedure over an airfoil at Reynolds number of Re = 4.8 × 105 and an elucidation of the flow control mechanism. It is found that the most prominent flow feature resulting from the interplay between an oscillating jet and external crossflow over an airfoil is the production of spanwise vortices. The strong entrainment effect of the induced spanwise vortices is the dominant mechanism leading to the mitigation of flow separation. Periodic jet oscillation generates a series of downstream moving vortices over an airfoil surface and results in a greatly delayed flow separation. The recovery of a strong suction pressure peak near the leading edge and significant lift enhancement and drag reduction reflects the improvement of an aerodynamic performance of the airfoil under control. Also observed is the phenomenon of local flow frequency lock-in to forcing frequency near the leading edge region. Moreover, the mass supply rate at the inlet of the oscillator is found to have an appreciable effect on the flow control authority. A higher mass flow usually leads to a better flow control performance.
Measuring the effective height for atom gravimeters by applying a frequency jump to Raman lasers
Authors: Xu Yao-Yao , Deng Xiao-Bing , Zhou Hang , Qi Kun , Chen Xin-Ke , Luo Hua-Qing , Zhou Min-Kang , Duan Xiao-Chun , Hu Zhong-Kun
Published: June 2021

As the existence of the gravity gradient, the output of gravimeters is actually the gravitational acceleration at the reference instrumental height. Precise knowledge of the reference height is indispensable in the utilization of gravity measurements, especially for absolute gravimeters. Here, we present an interferometric method to measure the distance between the atomic cloud and a reflecting mirror directly, which consequently determines the reference height of our atom gravimeter. This interferometric method is based on a frequency jump of Raman lasers applied at the π pulse of the atom interferometer, which induces an additional phase shift proportional to the interested distance. An uncertainty of 2 mm is achieved here for the distance measurement, and the effect of the gravity gradient on absolute gravity measurements can thus be constrained within 1 μGal. This work provides a concrete-object-based measurement of the reference height for atom gravimeters.
Influence of an atomistic protrusion at the tip apex on enhancing molecular emission in tunnel junctions: A theoretical study
Authors: Zhu Jia-Zhe , Chen Gong , Ijaz Talha , Li Xiao-Guang , Dong Zhen-Chao
Published: June 2021

Light emission from the gap of a scanning tunneling microscope can be used to investigate many optoelectronic processes at the single-molecule level and to gain insight into the fundamental photophysical mechanisms involved. One important issue is how to improve the quantum efficiency of quantum emitters in the nanometer-sized metallic gap so that molecule-specific emission can be clearly observed. Here, using electromagnetic simulations, we systematically investigate the influence of an atomic-scale protrusion at the tip apex on the emission properties of a point dipole in the plasmonic nanocavity. We found that such an atomistic protrusion can induce strong and spatially highly confined electric fields, thus increasing the quantum efficiency of molecular fluorescence over two orders of magnitude even when its dipole is oriented parallel to the metal surface, a situation occurring in most realistic single-molecule electroluminescence experiments. In addition, our theoretical simulations indicate that due to the lightning rod effect induced by the protrusion in a plasmonic nanocavity, the quantum efficiency increases monotonically as the tip approaches the dipole to the point of contact, instead of being quenched, thus explaining previous experimental observations with ever-enhancing fluorescence. Furthermore, we also examine in detail how the protrusion radius, height, and material affect the protrusion-induced emission enhancement. These results are believed to be instructive for further studies on the optoelectronic properties of single molecules in tip-based plasmonic nanocavities.
Asymmetry between deuterium and tritium turbulent particle flows
Authors: Belli E. A. , Candy J.
Published: June 2021

The asymmetry between deuterium (D) and tritium (T) turbulent particle fluxes in mixed D–T plasmas is studied with numerical simulations of nonlinear gyrokinetic turbulence in ion temperature gradient-dominated and trapped electron mode-dominated regimes. At 50–50 D–T concentration, the asymmetry, or flow separation, between D and T fluxes is such that the tritium is better confined than the deuterium in both regimes. To supplement the nonlinear simulations, an analytic quasilinear theory of the particle flux symmetry breaking is developed and is valid for general electron dynamics. This theory correctly predicts the numerically computed deviation in the ion density fraction (from 50–50), or ion density gradient (from the electron gradient), required to restore equal deuterium and tritium fluxes.
Babinet's principle and saturation of the resonance frequency of scaled-down complementary metasurfaces
Authors: Ortiz Julián D. , Baena Juan D. , Marqués Ricardo , Enemuo Amarachukwu N. , Gollub Jonah , Akhmechet Roman , Penkov Boyan , Sarantos Chris , Crouse David T.
Published: June 2021

It has been previously demonstrated that the resonant frequency of the Split Ring Resonator (SRR) reaches a saturation value when its size is continuously scaled down, and at the same time, the resonance is attenuated. Now, it is demonstrated that similar saturation and attenuation phenomena happens to its complementary screen, which is commonly called a Complementary SRR (CSRR). It was found that the saturation frequency of the CSRR is near the saturation frequency of the SRR with equal geometrical dimensions. It is possible to control their saturation levels by tuning the geometry of the resonators. This work is relevant for the design of quasi-optical metamaterials based on one or both kinds of structures (i.e., SRRs and CSRRs) at once, especially when they both are required to resonate at the same frequency.
Effect of temperature on concentrated electrolytes for advanced lithium ion batteries
Authors: Mynam Mahesh , Kumari Surbhi , Ravikumar Bharath , Rai Beena
Published: June 2021

Salt-concentrated electrolytes are emerging as promising electrolytes for advanced lithium ion batteries (LIBs) that can offer high energy density and improved cycle life. To further improve these electrolytes, it is essential to understand their inherent behavior at various operating conditions of LIBs. Molecular dynamics (MD) simulations are extensively used to study various properties of electrolytes and explain the associated molecular-level phenomena. In this study, we use classical MD simulations to probe the properties of the concentrated electrolyte solution of 3 mol/kg lithium hexafluorophosphate (LiPF6) salt in the propylene carbonate solvent at various temperatures ranging from 298 to 378 K. Our results reveal that the properties such as ionic diffusivity and molar conductivity of a concentrated electrolyte are more sensitive to temperature compared to that of dilute electrolytes. The residence time analysis shows that temperature affects the Li+ ion solvation shell dynamics significantly. The effect of temperature on the transport and dynamic properties needs to be accounted carefully while designing better thermal management systems for batteries made with concentrated electrolytes to garner the advantages of these electrolytes.
Magneto-optical methods for magnetoplasmonics in noble metal nanostructures
Authors: Gabbani Alessio , Petrucci Gaia , Pineider Francesco
Published: June 2021

The use of magneto-optical techniques to tune the plasmonic response of nanostructures—magnetoplasmonics—is a hot topic in active plasmonics, with fascinating implications for several plasmon-based applications and devices. In this exciting field, plasmonic nanomaterials with strong optical response to magnetic fields are desired, which is generally challenging to achieve with pure noble metals. To overcome this issue, several efforts have been carried out to design and tailor the magneto-optical response of metal nanostructures, mainly by combining plasmonic and magnetic materials or using ferromagnetic materials able to sustain a plasmonic response. However, despite their weak magneto-optical response, noble metals are a valuable model system allowing an accurate rationalization of magnetoplasmonic effects based on the interaction of magnetic fields with charge carriers. In addition, the emerging class of non-magnetic plasmonic heavily doped semiconductors is showing great potential for high performance magnetoplasmonics in the infrared range. In this Tutorial, the most common magneto-optical experimental methods employed to measure these effects are introduced, followed by a review of the major experimental observations that are discussed within the framework of an analytical model developed for the rationalization of magnetoplasmonic effects. Different materials are discussed, from noble metals to heavily doped semiconductors.
Vapor–liquid equilibrium of water with the MB-pol many-body potential
Authors: Muniz Maria Carolina , Gartner Thomas E. , Riera Marc , Knight Christopher , Yue Shuwen , Paesani Francesco , Panagiotopoulos Athanassios Z.
Published: June 2021

Among the many existing molecular models of water, the MB-pol many-body potential has emerged as a remarkably accurate model, capable of reproducing thermodynamic, structural, and dynamic properties across water’s solid, liquid, and vapor phases. In this work, we assessed the performance of MB-pol with respect to an important set of properties related to vapor–liquid coexistence and interfacial behavior. Through direct coexistence classical molecular dynamics simulations at temperatures of 400 K < T < 600 K, we calculated properties such as equilibrium coexistence densities, vapor–liquid interfacial tension, vapor pressure, and enthalpy of vaporization and compared the MB-pol results to experimental data. We also compared rigid vs fully flexible variants of the MB-pol model and evaluated system size effects for the properties studied. We found that the MB-pol model predictions are in good agreement with experimental data, even for temperatures approaching the vapor–liquid critical point; this agreement was largely insensitive to system sizes or the rigid vs flexible treatment of the intramolecular degrees of freedom. These results attest to the chemical accuracy of MB-pol and its high degree of transferability, thus enabling MB-pol’s application across a large swath of water’s phase diagram.
Correlation-driven phenomena in periodic molecular systems from variational two-electron reduced density matrix theory
Authors: Ewing Simon , Mazziotti David A.
Published: June 2021

Correlation-driven phenomena in molecular periodic systems are challenging to predict computationally not only because such systems are periodically infinite but also because they are typically strongly correlated. Here, we generalize the variational two-electron reduced density matrix (2-RDM) theory to compute the energies and properties of strongly correlated periodic systems. The 2-RDM of the unit cell is directly computed subject to necessary N-representability conditions such that the unit-cell 2-RDM represents at least one N-electron density matrix. Two canonical but non-trivial systems, periodic metallic hydrogen chains and periodic acenes, are treated to demonstrate the methodology. We show that while single-reference correlation theories do not capture the strong (static) correlation effects in either of these molecular systems, the periodic variational 2-RDM theory predicts the Mott metal-to-insulator transition in the hydrogen chains and the length-dependent polyradical formation in acenes. For both hydrogen chains and acenes, the periodic calculations are compared with previous non-periodic calculations with the results showing a significant change in energies and increase in the electron correlation from the periodic boundary conditions. The 2-RDM theory, which allows for much larger active spaces than are traditionally possible, is applicable to studying correlation-driven phenomena in general periodic molecular solids and materials.
Acoustic nonreciprocity
Authors: Rasmussen Curtis , Quan Li , Alù Andrea
Published: June 2021

Breaking acoustic reciprocity is essential to create robust one-way propagation where sound waves or elastic vibrations are permitted to travel in only one direction. This unidirectional response forms the basis for devices such as acoustic isolators and circulators, and it also unlocks new functionalities for complex systems such as acoustic topological insulators. After reviewing the principles of acoustic reciprocity, we look at techniques to achieve large reciprocity breaking, including nonlinearities, moving media, spatiotemporal modulation, and nonlinear bianisotropy. We then discuss the recent surge of progress in nonreciprocal surface acoustic wave devices and topological acoustic systems, areas which we predict will continue to flourish in the coming years. We anticipate that these and other applications of nonreciprocity will continue to enhance acoustic technology and form the basis for new acoustic devices. Reciprocity is a fundamental principle in wave manipulation, and techniques for breaking its symmetry will continue to be discovered, refined, optimized, and applied to several acoustic domains as the understanding of the underlying principles and new technologies mature.
Interplay of high-precision shock wave experiments with first-principles theory to explore molecular systems at extreme conditions: A perspective
Authors: Knudson M. D. , Desjarlais M. P.
Published: June 2021

Conventional methods for probing molecular changes in condensed matter systems, such as electronic and vibrational spectroscopy, are difficult to implement at the extreme conditions associated with dynamic compression experiments. This is particularly true for experiments in the multimegabar regime; to achieve the requisite energy density to produce such pressures, sample sizes are necessarily quite small and experimental timescales are, therefore, extremely short. Furthermore, these extreme pressure conditions also result in high temperatures and, therefore, significant thermal emission even in the visible to infrared regime and in some cases render the sample opaque or reflective, thereby precluding bulk spectroscopy techniques, such as Raman scattering. These experimental challenges require a different approach to evaluating shock-induced changes at the molecular or atomic level in the multimegabar or the so-called warm dense matter regime. The past few decades have seen significant advances in the use of first-principles methods to investigate materials under extreme conditions, enabling these methods to become a powerful tool for exploring molecular systems at extreme conditions. Here, we discuss the construct of combining high-precision shock wave experiments with first-principles theory to explore molecular systems at extreme conditions. The results from high-fidelity dynamic compression experiments are used to evaluate first-principles theoretical frameworks and identify the framework that best reproduces experimental results in the regime of interest. That validated framework is then used to perform detailed simulations of the system of interest, providing unique insight into the response of the system at the molecular level.
Experimental investigation on compression ramp shock wave/boundary layer interaction control using plasma actuator array
Authors: Tang Mengxiao , Wu Yun , Zong Haohua , Guo Shanguang , Liang Hua , Luo Yanhao
Published: June 2021

Particle image velocimetry measurement on shock wave/boundary layer interaction in a Mach 2.0 supersonic wind tunnel is performed to quantitatively reveal the plasma flow control effect in this paper. The typical flow structure is produced by a 24-degree compression ramp model and the streamwise plasma actuator array with five pulsed spark discharge plasma actuators is adopted as the control device. In the midspan plane, the results show that although the separation region exhibits an obvious extension, the foot of the separation wave moves upstream and the shock wave angle decreases from 41.6° to 22.3°, proving the decline in shock intensity. The shock wave drag is estimated to be reduced by 45%. According to the phase-averaged velocity field, the reason that the high-frequency actuation plays a key role in achieving the continuous control effect is revealed through the temporal evolution of the separation region area. Also, another interesting phenomenon that the flow deflects when passing through the actuation region is found, which may induce the upwash and downwash motions of the boundary layer and further reduce the flow separation on both sides of the actuation region. At last, a preliminary conceptual model is proposed to reveal the probable flow control mechanism.
Influence of the odd viscosity on a falling film down a slippery inclined plane
Authors: Chattopadhyay Souradip
Published: June 2021

The stability of a thin viscous Newtonian fluid with broken time-reversal-symmetry draining down a slippery inclined plane is examined. The presence of the odd part of the Cauchy stress tensor with an odd viscosity coefficient brings new characteristics in fluid flow as it gives rise to new terms in the pressure gradient of the flow. By odd viscosity, it is meant that apart from the well-known coefficient of shear viscosity, a classical liquid with broken time-reversal symmetry is endowed with a second viscosity coefficient. The model implements a Navier slip condition at the solid–liquid interface with the slip length being the parameter that measures the deviation from the no-slip condition. The classical long-wave expansion technique is performed and a nonlinear evolution equation of Benney-type is derived in terms of film thickness h(x, t), which is significantly modified due to the presence of odd viscosity in the liquid. The parameters governing the film flow system and the slippery substrate strongly influence the waveforms and their amplitudes and hence the stability of the fluid. The linear stability analysis is performed using the normal mode approach and a critical Reynolds number is obtained. The results of the linear stability analysis reveal that larger odd viscosity leads to the higher critical Reynolds number while the higher slip length makes the critical Reynolds number lower. In other words, odd viscosity has a stabilizing effect while the slip length promotes instability. Based on the method of multiple scales, a weakly nonlinear stability analysis is carried out, which shows that there is a range of wave numbers with a supercritical bifurcation and a range of larger wave numbers with a subcritical bifurcation. Different instability zones are also demarcated. The weakly nonlinear study shows that with an increase in the odd viscosity, the supercritical stable region and the explosion area shrink, whereas the unconditional stable and the subcritical unstable regions increase. It has also been shown that the spatial uniform solution corresponding to the sideband disturbance may be stable in the unstable region. The spatiotemporal evolution of the model has been analyzed numerically by employing the Crank–Nicolson method in a periodic domain for different values of the odd viscosity and slip length. The nonlinear simulations are found to be in good agreement with the linear and weakly nonlinear stability analysis.

The authors of the article agree to the retraction of the article effective 29 June 2022.
Uniaxial negative thermal expansion behavior of
β
-CuSCN
Authors: Wang Jiaqi , Gao Qilong , Gao Yaxing , Luo Yan , Guo Juan , Sun Qiang , Liang Erjun
Published: June 2021

Negative thermal expansion (NTE) as an interesting physical behavior is promising for thermal expansion control engineering. β-CuSCN consists of linear chain units with NTE along the c-axis. The NTE mechanism of β-CuSCN is investigated by variable temperature x-ray diffraction, temperature- and pressure-dependent Raman spectra, and first-principles calculations. It is found that the quasi rigid unit modes associated with the rotations of S–C≡N–Cu chains driven by Cu and S antiphase transverse vibrations and longitudinal acoustic and transverse acoustic modes involving the collective motions of atoms have large negative Grüneisen parameters, contributing significantly to the NTE of c-axis. Translational and librational motions of C≡N units, in which C and N atoms vibrate in the same and opposite directions have much smaller negative Grüneisen parameters, contribute only a minor part to the NTE, which is different from the known NTE mechanism of cyanides and Prussian blue analogous.
Elliptic solutions to matrix KP hierarchy and spin generalization of elliptic Calogero–Moser model
Authors: Prokofev V. , Zabrodin A.
Published: June 2021

We consider solutions of the matrix Kadomtsev–Petviashvili (KP) hierarchy that are elliptic functions of the first hierarchical time t1 = x. It is known that poles xi and matrix residues at the poles ρiαβ=aiαbiβ of such solutions as functions of the time t2 move as particles of spin generalization of the elliptic Calogero–Moser model (elliptic Gibbons–Hermsen model). In this paper, we establish the correspondence with the spin elliptic Calogero–Moser model for the whole matrix KP hierarchy. Namely, we show that the dynamics of poles and matrix residues of the solutions with respect to the kth hierarchical time of the matrix KP hierarchy is Hamiltonian with the Hamiltonian Hk obtained via an expansion of the spectral curve near the marked points. The Hamiltonians are identified with the Hamiltonians of the elliptic spin Calogero–Moser system with coordinates xi and spin degrees of freedom aiα,biβ.
Electron attachment to tetrazoles: The influence of molecular structure on ring opening reactivity
Authors: Luxford T. F. M. , Fedor J. , Kočišek J.
Published: June 2021

The electron-induced reactivity of 5-(4-chlorophenyl)-1H-tetrazole and 5-chloro-1-phenyl-1H-tetrazole was studied using a trochoidal electron monochromator quadrupole mass spectrometer experimental setup. 5-(4-chlorophenyl)-1H-tetrazole underwent dissociative electron attachment to form Cl−, [M–HCl]−, and [M–H]−. 5-chloro-1-phenyl-1H-tetrazole underwent associative electron attachment to form the parent anion and dissociative electron attachment to form Cl−, CN2Cl−, [M–N2–Cl]−, and [M–HCl]−. For each anion product, the ion yield was measured as a function of incident electron energy. Density functional theory calculations were performed to support the experimental results with estimates of the energetic thresholds for the different reaction pathways. While the tetrazole group is susceptible to electron-induced ring opening in both molecules, this process was only observed for 5-chloro-1-phenyl-1H-tetrazole, indicating that this process is influenced by the structure of the molecule.
Circularly polarized high harmonic generation through virtual circular birefringence
Authors: Hareli Liran , Lerner Gavriel , Cohen Oren , Bahabad Alon
Published: June 2021

We suggest a macroscopic scheme for generating circularly polarized high harmonics. The scheme uses a superposition of circularly polarized pump beams with different spatial modes, realizing a perturbed linearly polarized field which rotates along the propagation axis due to virtual circular birefringence. This method provides a spectral selectivity for the harmonic orders which are generated efficiently and for their spacing. The scheme is investigated numerically with a good agreement with the theory.
Flow-induced cross-flow vibrations of long flexible cylinder with an upstream wake interference
Authors: Lin Ke , Wang Jiasong , Fan Dixia , Triantafyllou Michael S.
Published: June 2021

Flow-induced vibration (FIV) of a flexible cylinder with an upstream wake interference at a subcritical Reynolds number is numerically investigated in this study. Two cylinders are installed in a tandem arrangement with the tandem separation between the cylinder centers set at 5.0 diameters. The downstream cylinder is flexible and placed in the wake of the stationary rigid upstream cylinder. A quasi-three-dimensional fluid-structure interaction (FSI) numerical methodology that couples the strip theory-based Lagrangian discrete vortex method with the finite-element method (FEM) for structural dynamics is developed to simulate the FIV response of the flexible cylinder with the upstream wake interference. The vortex-induced vibration (VIV) of an identical isolated cylinder is also numerically simulated as a contrast. This numerical study characterizes the dynamic response of the cylinder FIV with the upstream wake interference and sheds light on the FSI mechanisms responsible for the structural dynamic response. With the upstream wake interference, the cylinder FIV response shows two features distinct from the isolated VIV response: the vibration of large amplitude during the modal resonance branch transition and the extension of the modal resonance branch. The hydrodynamic coefficients database is constructed by the rigid cylinder forced vibration experiment to help explain the FSI properties of the FIV dynamic response. The lower added mass coefficient for the FIV with the upstream wake interference than the VIV of the isolated cylinder guarantees the synchronization between the vortex shedding frequency and the “true” natural frequency of the structure persisting to higher reduced velocity in a certain modal resonance response branch. The excitation coefficient distribution indicates that the cylinder FIV with the upstream wake interference reaches higher amplitude at high reduced velocity, instead of ceasing resonance as the isolated cylinder. The numerical wake visualization is shown and used to explain the correlation between the distribution of hydrodynamic coefficients along the cylinder span and the wake vortex mode. It is found that the upstream wake interference effect is strongly correlated with the vortex–structure interaction pattern between the upstream wake vortices and the downstream motion. When the upstream vortex impinges on the downstream cylinder and splits into subvortices, the effect of the upstream wake interference acting on the downstream cylinder reduces. When the downstream cylinder enters the gap between the upstream vortices over the entire vibration process, the upstream wake has a stronger interference effect on the downstream FIV response.
Gyroscopic rotation of boiling droplets
Authors: Lin Yukai , Chu Fuqiang , Ma Qiang , Wu Xiaomin
Published: June 2021

The self-propelled motion of boiling droplets has attracted strong interest, and major discoveries are concentrated in the film boiling regime, e.g., translational motion of Leidenfrost drops on ratchets, Leidenfrost wheels. However, little attention was paid to the boiling regimes below the Leidenfrost point. Here, we focus on those boiling regimes and discover a gyroscopic rotation phenomenon of boiling droplets that is ubiquitous on various types of surfaces with diverse wettability and microstructures. The occurrence of gyroscopic rotation can be attributed to the viscous stress from vapor/bubble flows in the gaps of surface microstructures, verified by the results that for the experimental surfaces, the rougher the surface structures and the larger the solid–liquid contact area, the more probable it is to generate gyroscopic rotations. A theoretical model is established to investigate the effect of substrate temperature (boiling regime) on the spinning rate of boiling droplets, and the results further approve the proposed mechanism of gyroscopic rotation. The outcomes of this work help to deepen the understanding of droplet boiling and the corresponding dynamics on surfaces with microstructures.
High-resolution asymmetric structure of a Fab–virus complex reveals overlap with the receptor binding site
Authors: Goetschius Daniel J. , Hartmann Samantha R. , Organtini Lindsey J. , Callaway Heather , Huang Kai , Bator Carol M. , Ashley Robert E. , Makhov Alexander M. , Conway James F. , Parrish Colin R. , Hafenstein Susan L.
Published: June 2021

Significance

Our study makes significant progress understanding asymmetry in icosahedral viruses that would be otherwise masked by forcing homogeneity through icosahedral averaging. Using an asymmetric approach revealed the atomic-resolution structure of a complex between canine parvovirus and a strain-specific neutralizing antibody. Since species jumping is a rare event in DNA viruses, the emergence of an antibody that binds more avidly to the canine-adapted virus (and not ancestral feline equivalent) is of special interest. The Fab-bound and -unbound epitopes were solved on the same virus capsid with an atomic-resolution asymmetric map. Fab 14 stabilizes a capsid loop within the same binding site used by the receptor, suggesting capsid conformational change or steric competition with the receptor contributes to the mechanism of antibody neutralization.
Mitochondria-dependent synthetic small-molecule vaccine adjuvants for influenza virus infection
Authors: Sato-Kaneko Fumi , Yao Shiyin , Lao Fitzgerald S. , Nan Jason , Shpigelman Jonathan , Cheng Annette , Saito Tetsuya , Messer Karen , Pu Minya , Shukla Nikunj M. , Cottam Howard B. , Chan Michael , Molina Anthony J. , Corr Maripat , Hayashi Tomoko , Carson Dennis A.
Published: June 2021

Significance

Effective vaccine strategies are needed to overcome genetic, physiologic, or age-related deficits in immune responses relevant to vulnerable populations. Vaccine adjuvants that overcome these variants and do not compromise safety are highly desirable. We identified a synthetic small-molecule compound 81 [
N
-(4-chloro-2,5-dimethoxyphenyl)-4-ethoxybenzenesulfonamide] and its derivative 2F52 [
N
-benzyl-
N
-(4-chloro-2,5-dimethoxyphenyl)-4-ethoxybenzenesulfonamide] as activators of innate immunity via mitochondrial stress pathways, circumventing classic pathogen-recognition receptors. Neither 81 nor 2F52 as adjuvants caused local or systemic toxicity in mice after injection. Moreover, in a mouse influenza challenge study, compound 2F52 demonstrated protective effects when used with inactivated virus. Thus, compound 2F52, acting through an unconventional pathway to stimulate innate immunity, could be a useful synthetic adjuvant to enhance current and future vaccines.
Genetic basis of variation in cocaine and methamphetamine consumption in outbred populations of
Drosophila melanogaster
Authors: Baker Brandon M. , Carbone Mary Anna , Huang Wen , Anholt Robert R. H. , Mackay Trudy F. C.
Published: June 2021

Significance

The use of cocaine and methamphetamine presents significant socioeconomic problems. However, identifying the genetic underpinnings that determine susceptibility to substance use is challenging in human populations. The fruit fly,
Drosophila melanogaster
, presents a powerful genetic model since we can control the genetic background and environment, 75% of disease-causing genes in humans have a fly counterpart, and flies—like humans—exhibit adverse effects upon cocaine and methamphetamine exposure. We showed that the genetic architecture underlying variation in voluntary cocaine and methamphetamine consumption differs between sexes and is dominated by variants in genes associated with connectivity and function of the nervous system. Results obtained from the
Drosophila
gene discovery model can guide studies on substance abuse susceptibility in human populations.
Simulating the directional translocation of a substrate by the AAA+ motor in the 26S proteasome
Authors: Saha Arjun , Warshel Arieh
Published: June 2021

Significance

The substrate translocation through the proteasomal AAA+ motor is central to the process of protein degradation. Emerging structural studies challenge one to advance a detailed knowledge of the energetics of the translocation process. Here, we generate the relevant free energy landscape using cryogenic electron microscopy structures of the substrate-bound 26S proteasome by using a combination of coarse-grained modeling, simplified atomistic binding free energy calculations, and ATP hydrolysis energies. This landscape successfully reproduces the unidirectionality of the biological process and reveals that the unidirectional motion can be significantly enhanced/tuned by electrostatic effect. Our mutagenesis analysis identifies key residues of pore loop 1 and estimates their contribution to the translocation process. This work provides a guidance for investigating ATP-driven translocation processes of proteasomes.