Variation Of Momentum Research Articles

Cut-continuity of twistor angular momentum

Chen et al. argued recently that, in Bondi-Sachs space-times, the angular momentum at scri (null infinity) should vary continuously with the position of the cut (but not depend sensitively on its derivatives); they showed that this property was enjoyed by some definitions but not others. I show here that the twistor definition has this continuity. The argument is rather different from Chen et al.'s, with the invariant geometry of scri at the forefront. The flux, in the sense of the angular momentum emitted between two infinitesimally separated cuts, is calculated; this flux can be interpreted as the first variation of the angular momentum with respect to the cut. Examining the second variation, one finds that the twistor definition, unlike most others, responds to correlations in radiation between different asymptotic directions. The twistor angular momentum is thus sensitive to qualitatively different structure in the asymptotic field than are the currently more used ones.

Particle momentum variation under interaction with wavepackets of finite spatial width

The single and collective particle interaction with spatially localized wavepackets is analytically and numerically studied. The role of the finite spatial width of the wavepacket on the momentum and energy variation of particles passing through the wavepacket is investigated. The range of validity of analytical results, based on a perturbative approach, is investigated and clearly defined. Strongly nonlinear effects are shown to qualitatively differentiate the collective particle dynamics, for larger interaction strengths. These effects are manifested through the complex dependency of averaged momentum variations on the initial particle momentum, as shown by dissecting a particle distribution in terms of partitioning the ensemble of particles with respect to their initial momentum. The results provide understanding on the relation between single and collective particle dynamics and the emerging of complexity for weak and strong particle interactions with localized wavepackets.

Acoustic radiation torque on an interface reflecting acoustic vortex beams

Torque exerted by acoustic waves to rotate objects can result from asymmetry such as the case of an averaged torque on a Rayleigh disk exerted by an ordinary acoustic field. In the absence of asymmetry, acoustic torque can occur by viscous absorption either in the object or in the adjacent boundary layer of the object when using specific types of acoustic fields such as acoustic vortex beams carrying twisted wave fronts [Zhang and Marston, Phys. Rev. E 84, 065601 (2011)] or two orthogonal standing wave fields [Zhang and Marston, J. Acoust. Soc. Am. 136, 2917 (2014)]. Recent study suggested a torque on a flat water-air interface exerted by an ultrasonic vortex beam obliquely incident and reflecting off the interface [Zou, Lirette, and Zhang, Phys. Rev. Lett. 125, 074301 (2020)]. This torque is not associated with viscous absorption and instead results from variation of orbital angular momentum carried by the vortex beam during the reflection. The torque would otherwise disappear in normal incidence or using ordinary beams. The investigations advance understanding of radiation torque physics and approaches for non-contact manipulations using acoustic waves.

A simplified formula to estimate the load history due to ballistic impacts with bullet splash. Development and validation for finite element simulation of 9x21mm full metal jacket bullets

An original simplified formula is proposed to estimate the load history caused by ballistic impacts characterized by the so-called bullet splash phenomenon, consisting in the complete bullet fragmentation with no penetration of the target. The formula is based on the progressive momentum variation of the mass of the bullet impacting on a planar plate normal to the impact direction. The method aims at creating a simplified approach to assess the response of structures by means of explicit finite element simulations without the need of modelling the interaction between impactor and target. The results demonstrate that the proposed method can be used to estimate the forces generated by bullet-splash phenomena of 9x21mm full metal jacket bullets and effectively applied to finite element simulations allowing significant reductions in computational cost.

Advancing 3D shaping of vectorial light by counter-propagation of self-healing scalar and vector Bessel–Gaussian beams

It is well known that counter-propagation of structured light fields allows shaping of three-dimensional (3D) structures in amplitude, phase, or polarization. Here, we numerically demonstrate the potential of implementing non-diffracting Bessel–Gaussian (BG) beams for advancing this approach by taking advantage of its characteristic propagation behavior. In this context, we investigate the self-healing property in this counter-propagating configuration, observing a spin angular momentum (SAM) variation and the formation of a continuous orbital angular momentum (OAM) gradient in longitudinal direction. Additionally, by counter-propagation of BG beams of different types, namely, scalar and vector BG beams, we are able to increase the complexity of accessible 3D structured fields, revealing combined amplitude, phase, and polarization modulation in all spatial dimensions. Thereby, the SAM and OAM of the input light fields can be used to design the resulting 3D structure and its angular momenta. The presented light fields open new possibilities for customized optical trapping potentials and allow new insights into fundamental spin–orbit interaction in counter-propagating superpositions of structured fields.

Nonconservative dipole forces on an excited two-atom system

We compute the nonconservative electric dipole forces between the atoms of a suddenly excited binary system. These forces derive from the time variation of the longitudinal electromagnetic momentum. In contrast to the conservative van der Waals forces, the nonconservative forces possess components orthogonal to the interatomic axis. Thus, despite being several orders of magnitude smaller than van der Waals', they might be accessible experimentally. For the case of a binary system of identical atoms in Dicke states, these forces are reciprocal. However, when only one of the atoms is initially excited, as with the van der Waals forces, the nonconservative ones are nonreciprocal, which results in a net force on the two-atom system. We offer an estimate of the spatial displacement caused by the nonconservative forces on a binary system of hydrogen atoms.

Evidence for Corotation Origin of Super-metal-rich Stars in LAMOST-Gaia: Multiple Ridges with a Similar Slope in the ϕ versus L z Plane

Super-metal-rich (SMR) stars in the solar neighborhood are thought to be born in the inner disk and come to their present location by radial migration, which is most intense at the corotation resonance (CR) of the Galactic bar. In this work, we show evidence for the CR origin of SMR stars in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Gaia by detecting six ridges and undulations in the ϕ versus L z space coded by median V R, following a similar slope of −8 km s−1 kpc deg−1. The slope is predicted by Monario et al.'s model for CR of a large and slow Galactic bar. For the first time, we show the variation in the angular momentum with azimuths from −10° to 20° for two outer and broad undulations with negative V R around − 18 km s−1 following this slope. The wave-like pattern with large amplitude outside CR and a wide peak of the second undulation indicate that minor merger of the Sagittarius dwarf galaxy with the disk might play a role besides the significant impact of the CR of the Galactic bar.

Relativistic dilation and contraction of the probabilities of quantum states of light at angular incidence

In this work we propose a formulation for the treatment of quantized states of light in photon-matter interaction. It is built in the multidimensional Hilbert space to describe the orbital angular momentum states, in such that probabilities naturally arise in a relativistic setting. Our findings indicate that the classical-relativistic variability of the probabilities can describe the quantized states of light, with the state variable being the variation of the photon angular momentum. It was verified that the probability to find a specific quantized state of light at angular incidence can be treated by relativistic probabilities. Interestingly, our results indicate that, when both states have equal odds, there is a synchronization between source and observer. We found that the relativistic effect in the perspective of the source referential is able to change the odds of an event occurring, dilating and contracting the probabilities of finding a quantized state of light at angular incidence.

QUANTUM STATISTICAL PERSPECTIVE TO EXAMINE THE SOURCE CHAOS FRACTION THROUGH BOSON FEMTOSCOPY

Bose–Einstein correlations of identical particles reveal the shape and size of the particle emitting source of the given boson. These correlations are pivotal for a better understanding of the source dynamics and developing techniques to examine the propagation of quantum chaos in the presence of coherence at a certain temperature and momentum. Femtoscopy is of the utmost importance during this transformation for data processing and coherence-chaos analysis discrepancies. We introduced an evolving source to describe chaotic information inside quantum entanglement and the impact of the coherence order is discussed in this research. We also investigate the role of source size parameter and particle number in the dynamics of the temperature profiles with the function of momentum variation. The influences of the modeling factors on the correlations with their normalized correlator in the perspective of source coherence have been evaluated and the orientation of the source has an effect on the diffusivity of the fluid under consideration. Such consequences can cause an increase or decrease the genuine correlations due to the distributions of velocity and temperature. The main findings of the paper have been illustrated using the graphical representations of the considered correlations according to the geometry of the expanding source. Such results reveal the lucrativeness in the field of engineering applications.

Aerothermodynamics of a sphere in a monatomic gas based onab initiointeratomic potentials over a wide range of gas rarefaction: transonic, supersonic and hypersonic flows

Aerothermodynamic characteristics of a sphere such as drag and energy transfer coefficients are calculated for Mach numbers varying from 1 to 10 over a wide range of the gas rarefaction degree spanning the free molecular, transitional and near hydrodynamic flow regimes. The effects of major factors determining the gas flow are studied using the direct simulation Monte Carlo method. To reveal the effect of gas species, the simulations are performed based onab initiointeratomic potentials for helium, neon, argon and krypton, as well as based on the hard sphere model. The impact of the accommodation coefficients is evaluated by applying the Cercignani–Lampis model of gas–surface interaction. The calculations are carried out for several values of the free stream and sphere temperatures. It is found that the effects of gas species on the drag and energy transfer coefficients are approximately 3 % and 6 %, respectively. The accommodation coefficients in the Cercignani–Lampis model strongly affect all aerothermodynamic characteristics. The drag and energy transfer coefficients calculated for different accommodation coefficients vary within 30 % and 200 %, respectively. It is found that the variation of the tangential momentum and normal energy accommodation coefficients can induce an increase of the drag coefficient compared to the case of diffuse gas–surface interaction. In hypersonic flows, the drag coefficient varies within 30 % when the sphere temperature varies from the free stream temperature to the stagnation temperature. The drag and energy transfer coefficients are found to be non-monotonic functions of the free stream temperature.

Theory of dispersive optical phonons in resonant inelastic x-ray scattering experiments

The community currently lacks a complete understanding of how resonant inelastic x-ray scattering (RIXS) experiments probe the electron-phonon interaction in solids. For example, most theoretical models of this process have focused on dispersionless Einstein phonons. Using a recently developed momentum average variational approximation for computing RIXS spectra of band insulators, we examine the influence of both electron and phonon dispersion in the intermediate state of the scattering process. We find that the inclusion of either, and their mutual interplay, introduces significant momentum variations in the RIXS intensity, even for momentum-independent electron-phonon coupling. The phonon dispersion also induces nontrivial changes in the excitation line shapes, which can have a quantitative impact on the data analysis. These results highlight the considerable challenges of interpreting RIXS data in actual materials.

Angular momentum transfer in direct numerical simulations of a laboratory model of a tropical cyclone

ABSTRACT Numerical simulations of a laboratory model of a tropical cyclone are carried out for different rotation rates. Particular attention is paid to the non-stationary stage of intensive cyclonic vortex formation. The transfer of angular momentum plays a key role in the formation of cyclonic and anticyclonic flows; therefore, a detailed analysis of the redistribution and variation of angular momentum is given. The time evolution of angular momentum fluxes and total angular momentum strongly depend on the rotation rate. It is shown that intensive cyclonic motion with velocity exceeding initial values substantially (ten or more times) is a result of accumulation in the centre of a small fraction of global angular momentum of a fluid layer (from 0.25% at fast rotation to 2% at slow rotation). The integral angular momentum of the anticyclonic flow is significantly larger than that of the cyclonic flow, mainly because of the relatively large fluid volume of the anticyclonic flow. Another important result is that the rotating fluid layer very quickly adapts to new boundary conditions (heating and cooling). Approximately two rotation periods are required to reach a quasi-stationary state. The application of the obtained results to the evolution of real tropical cyclones is discussed.

Dynamic characteristics of droplet impact on vibrating superhydrophobic substrate

The vibration of solids is ubiquitous in nature and in industrial applications and gives rise to alternative droplet dynamics during impact. Using many-body dissipative particle dynamics, we investigate the impact of droplets on superhydrophobic solid surfaces vibrating in the vertical direction at a vibration period similar to the contact time. Specifically, we study the influence of the impact phase and vibration frequency. We evaluate the influence from the aspects of maximum spreading diameter, the solid–liquid contact time and area, and the momentum variation during the impact. To quantitatively evaluate the solid–liquid contact, we introduce the area-time integral, which is the integral of the contact area over the whole contact time. It is meaningful when the heat exchange between solid and liquid is considered. One characteristic phenomenon of droplets impacting vibrating substrate is that multiple contacts may occur before the final rebound. Unlike previous studies defining the contact time as the time span from the first impact to the final detachment, we define the contact time as the summation of each individual contact time. Using this definition, we show that the discontinuity at the critical impact phase disappears. The fact that the area-time integral also changes continually with the impact phase supports the assumption that the effect of impact phase on the solid–liquid contact may be continuous. Moreover, we show that the probability of impact phase is affected by the vibrating frequency and use it to calculate the weighted averaged outcome when the impact phase is not controlled. This study not only offers insights into the physics of droplet impact on vibrating surfaces but also can be used to guide the design of surfaces to achieve manageable wetting using vibration.

Thermal relaxation of dark matter admixed neutron star

ABSTRACT Motivated by the various theoretical studies regarding the efficient capturing of dark matter by neutron stars, we explore the possible indirect effects of captured dark matter on the cooling mechanism of a neutron star. The equation of states for different configurations of dark matter admixed star at finite temperature is obtained using the relativistic mean-field formalism with the IOPB-I parameter set. We show that the variation in the dark matter momentum vastly modifies the neutrino emissivity through specific neutrino generating processes of the star. The specific heat and the thermal conductivity of a dark matter admixed star have also been investigated to explore the propagation of cooling waves in the interior of the star. The dependence of theoretical surface temperature cooling curves on the equation of state and chemical composition of the stellar matter has also been discussed along with the observational data of thermal radiation from various sources. We observed that the dark matter admixed canonical stars with $k_{f}^{\rm DM} \gt 0.04$ comply with the fast cooling scenario. Further, the metric for internal thermal relaxation epoch has also been calculated with different dark matter momentum and we deduced that increment of dark matter segment amplify the cooling and internal relaxation rates of the star.

Relativistic ro‐vibrational feature of electron in Bohr's orbits of hydrogen‐like atoms in Heisenberg picture

AbstractThe relativistic effects have been widely reported to affect the chemical and physical properties of the heavy elements such as lanthanides (), actinides (), and transactinides (). This effect is definitely weakened by reducing the atomic number in lighter elements such as hydrogen‐like atoms (HLAs). The aim of present paper is to investigate the relativistic effects of electron motion in Bohr orbits on the chemical and physical properties of HLAs. The theoretical model is based on the Heisenberg (rather than Schrodinger) picture where the relativistic vibrational Hamiltonian (RVH) is expanded as a power series of harmonic oscillator Hamiltonian for the first time. By applying the first‐order RVH (correct to ) to the Heisenberg equation, a pair of coupled equations is obtained for the relativistic position and linear momentum of electron. A simple comparison of the first‐order relativistic and nonrelativistic equations reveals that the relativistic natural frequency of an HLA (like entropy) is slowly raised by increasing beyond . In general, RVH plays a fundamental role because it specifies the temporal relativistic variations of position, velocity, and linear momentum of the oscillating electron. The results are finally verified by demonstrating energy conservation.

Deep Learning-Based Next-Generation Waveform for Multiuser VLC Systems.

Due to the growing number of users, power, and spectral effectiveness, most communication systems are complex and difficult to implement on a large scale. Artificial Intelligence (AI) has played an outstanding role in the implementation of theoretical systems in the real world, with less complexity achieving better results. In this direction, we compare the Non-Orthogonal Multiple Access (NOMA) technique for a multiuser Visible Light Communication (VLC) system with Successive Interference Cancellation (SIC) for two types of detectors: (1) the deep learning-based system and (2) the traditional maximum likelihood (ML) decoder-based system. For multiplexing, we compare the variations of novel Orbital Angular Momentum (OAM) multiplexing and Orthogonal Frequency Division Multiplexing (OFDM) with Index Modulation (IM). In this article, we implement OFDM-IM and OAM-IM for four users for the Gaussian fading MIMO Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) VLC channels. The suggested systems’ bit error rate (BER) performances are compared in simulations for a wide range of Signal-to-Noise Ratios (SNRs), which shows that deep learning-based systems outperform the ML-based system for both users to ensure better decoding at the receiver end, especially at higher SNR values. The detection error is lower in a deep learning-based system at around 20% and around 30% for low SNR and high SNR values, respectively.

Electromagnetohydrodynamic boundary layer flow in hybrid nanofluid with thermal radiation effect: Numerical simulation

AbstractHybrid nanofluid boundary layer flow past a stretching surface with zero mass flux boundary condition is explored in this article. The main aim of this article is to analyze the electromagnetohydrodynamic role in a hybrid nanofluid containing silver and molybdenum disulfide nanoparticles. The self‐similar solution is embedded to reduce the governing partial differential equation into algebraic equations and a shooting algorithm is applied to obtain the solution of the resultant boundary value problem. Variation in momentum, energy, and nanoparticle concentration is explained through graphical profiles. Nusselt number and drag force coefficients are computed for various flow parameters and their impact on the nanofluid and hybrid nanofluid is computed and presented and explained in a comparative fashion. It is observed that the velocity profile shows the opposite nature with respect to the electric field and magnetic field. For electric field parameter velocity accelerates whereas for magnetic parameter velocity diminishes. Nusselt number increases with electric field parameter and nanoparticle volume fraction.

Computational Analysis of Nanoparticle Shapes on Hybrid Nanofluid Flow Due to Flat Horizontal Plate via Solar Collector.

The present work discusses the 2D unsteady flow of second grade hybrid nanofluid in terms of heat transfer and MHD effects over a stretchable moving flat horizontal porous plate. The entropy of system is taken into account. The magnetic field and the Joule heating effects are also considered. Tiny-sized nanoparticles of silicon carbide and titanium oxide dispersed in a base fluid, kerosene oil. Furthermore, the shape factors of tiny-sized particles (sphere, bricks, tetrahedron, and platelets) are explored and discussed in detail. The mathematical representation in expressions of PDEs is built by considering the heat transfer mechanism owing to the effects of Joule heating and viscous dissipation. The present set of PDEs (partial differential equations) are converted into ODEs (ordinary differential equations) by introducing suitable transformations, which are then resolved with the bvp4c (shooting) scheme in MATLAB. Graphical expressions and numerical data are obtained to scrutinize the variations of momentum and temperature fields versus different physical constraints.

Analysis of Relationships Between ENSO Events and Atmospheric Angular Momentum Variations

AbstractThe El Niño–Southern Oscillation (ENSO) event has a long incubation process, during which the interannual variation of length‐of‐day (LOD) and the atmospheric angular momentum (AAM) series will be quickly affected due to the interaction between sea and air. Based on the comparisons between filtered interannual LOD variation, the AAM, the Oceanic Niño Index (ONI), and the Southern Oscillation Index (SOI) for the period of January 1953 and December 2013, the relationships among them and ENSO are studied. The results demonstrate that AAM changes and SOI/ONI series have similar waveform structures and trends. Interannual LOD variations, atmospheric LOD excitations, and ENSO indices such as the SOI and ONI are well correlated as a consequence of angular momentum conservation. AAMs can be accurately modeled at present, taking ESMGFZ as an example, its sampling interval can reach 3 hr, and can realize accurate prediction in the next 90 days. Consequently, AAM series also can be used as an index for ENSO events and has its own advantages compared with SOI/ONI.

Polarization-based transformations of linearly polarized quasi-Gaussian beams propagating in uniaxial crystals at an arbitrary angle

Studying the polarization of paraxial beams propagating through uniaxial anisotropic crystals at an arbitrary angle is a powerful feature to extend the range of utilization of these crystals. In this paper, we derive a general theoretical model, based on the existing theory, to describe the transformations of polarization state in cases of arbitrary beam propagation. Stokes parameters are employed for the determination of polarization state of the light beam. The derived model is applied to a linearly polarized quasi-Gaussian beam propagating through rutile crystal. The dependence of the polarization state of the beam on many parameters such as beam waist, angle of propagation, and thickness of the crystal is investigated. The variation of each of these parameters leads to an extensive and interesting change of the polarization state. Moreover, the results are employed to observe the variations of the spin angular momentum as a function of the above-mentioned parameters. Furthermore, we report on an interesting result regarding the longitudinal component of the propagating field, where we noticed the existence of clearly non negligible values of this component for certain propagation parameters. The results of the current work are promising and can be utilized to obtain the best functioning of the output beam depending on its shape and polarization. In addition, they are promising for other future applications such as designing polarization-based devices which are useful in many fields.