Velocity Expansion Research Articles

Fragmentation function of g \u2192 Qoverline{Q} (3 {S}_1^{left[8right]} ) in soft gluon factorization and threshold resummation

We study the fragmentation function of the gluon to color-octet 3S1 heavy quark-antiquark pair using the soft gluon factorization (SGF) approach, which expresses the fragmentation function in a form of perturbative short-distance hard part convoluted with one-dimensional color-octet 3S1 soft gluon distribution (SGD). The short distance hard part is calculated to the next-to-leading order in αs and all orders in velocity expansion. By deriving and solving the renormalization group equation of the SGD, threshold logarithms are resummed to all orders in perturbation theory. The comparison with gluon fragmentation function calculated in NRQCD factorization approach indicates that the SGF formula resums a series of velocity corrections in NRQCD which are important for phenomenological study.

Classical Gravitational Bremsstrahlung from a Worldline Quantum Field Theory.

Using the recently established formalism of a worldline quantum field theory description of the classical scattering of two spinless black holes, we compute the far-field time-domain waveform of the gravitational waves produced in the encounter at leading order in the post-Minkowskian (weak field but generic velocity) expansion. We reproduce the previous results of Kovacs and Thorne in a highly economic way. Then, using the waveform, we extract the leading-order total radiated angular momentum and energy (including differential results). Our work may enable crucial improvements of gravitational-wave predictions in the regime of large relative velocities.

Big data analytics capabilities and organizational performance: the mediating effect of dual innovations

PurposeFollowing the rapid expansion of data volume, velocity and variety, techniques and technologies, big data analytics have achieved substantial development and a surge of companies make investments in big data. Academics and practitioners have been considering the mechanism through which big data analytics capabilities can transform into their improved organizational performance. This paper aims to examine how big data analytics capabilities influence organizational performance through the mediating role of dual innovations.Design/methodology/approachDrawing on the resource-based view and recent literature on big data analytics, this paper aims to examine the direct effects of big data analytics capabilities (BDAC) on organizational performance, as well as the mediating role of dual innovations on the relationship between (BDAC) and organizational performance. The study extends existing research by making a distinction of BDACs' effect on their outcomes and proposing that BDACs help organizations to generate insights that can help strengthen their dual innovations, which in turn have a positive impact on organizational performance. To test our proposed research model, this study conducts empirical analysis based on questionnaire-base survey data collected from 309 respondents working in Chinese manufacturing firms.FindingsThe results support the proposed hypotheses regarding the direct and indirect effect that BDACs have on organizational performance. Specifically, this paper finds that dual innovations positively mediate BDACs' effect on organizational performance.Originality/valueThe conclusions on the relationship between big data analytics capabilities and organizational performance in previous research are controversial due to lack of theoretical foundation and empirical testing. This study resolves the issue by provides empirical analysis, which makes the research conclusions more scientific and credible. In addition, previous literature mainly focused on BDACs' direct impact on organizational performance without making a distinction of BDAC's three dimensions. This study contributes to the literature by thoroughly introducing the notions of BDAC's three core constituents and fully analyzing their relationships with organizational performance. What's more, empirical research on the mechanism of big data analytics' influence on organizational performance is still at a rudimentary stage. The authors address this critical gap by exploring the mediation of dual innovations in the relationship through survey-based research. The research conclusions of this paper provide new perspective for understanding the impact of big data analytics capabilities on organizational performance, and enrich the theoretical research connotation of big data analysis capabilities and dual innovation behavior.

Laser Ablation of Aluminum Near the Critical Regime: A Computational Gas-Dynamical Model with Temperature-Dependent Physical Parameters

The complexity of the phenomena simultaneously occurring, from the very first instants of high-power laser pulse interaction with the target up to the phase explosion, along with the strong changes in chemical-physical properties of matter, makes modeling laser ablation a hard task, especially near the thermodynamic critical regime. In this work, we report a computational model of an aluminum target irradiated in vacuum by a gaussian-shaped pulse of 20 duration, with a peak intensity of the order of . This continuum model covers laser energy deposition and temperature evolution in the irradiated target, along with the mass removal mechanism involved, and the vaporized material expansion. Aluminum was considered to be a case study due to the vast literature on the temperature dependence of its thermodynamic, optical, and transport properties that were used to estimate time-dependent values of surface-vapor quantities (vapor pressure, vapor density, vapor and surface temperature) and vapor gas-dynamical quantities (density, velocity, pressure) as it expands into vacuum. Very favorable agreement is reported with experimental data regarding: mass removal and crater depth due to vaporization, generated recoil momentum, and vapor flow velocity expansion.

The fifth-order post-Newtonian Hamiltonian dynamics of two-body systems from an effective field theory approach: Potential contributions

We calculate the potential contributions of the motion of binary mass systems in gravity to the fifth post–Newtonian order ab initio using coupling and velocity expansions within an effective field theory approach based on Feynman amplitudes starting with harmonic coordinates and using dimensional regularization. Furthermore, the singular and logarithmic tail contributions are calculated. We also consider the non–local tail contributions. Further steps towards the complete calculation are discussed. We calculate all but the rational O ( ν 2 ) contributions to the bound state energy for circular motion and periastron advance K ( E ˆ , j ) . Comparisons are given to results in the literature.

Enhanced fluidization of group A particles modulated by group C powder

Geldart Group A powders are utilized in various industrial processes because of their good fluidization quality, which is closely related to fine content (≤ 45 μm). This work systematically investigated the effect of fine powders (≤ 20 μm) as additives on the fluidization quality of Group A powders. Three types of additives, Coal-15, GB-6, and SiO 2 -5 were added into the base powder FCC-76 (Group A) in various volume fractions. Among them, the addition of SiO 2 -5 showed a significant improvement on the fluidization quality of Group A powder, exhibiting lower minimum fluidization velocity and higher bed expansion, while the addition of Coal-15 slightly improved the fluidization quality. The addition of a high-volume fraction of GB-6 would turn Group A into Group C/A, exhibiting some fluidization characteristics of Group C particles. Overall, the fluidization advancement of Group A powders modulated by Group C additives has advantages for industrial processes, especially for gas-phase catalytic reactions. • Group A particles modulated by Group C powder showed better fluidization quality. • SiO 2 -5 particles were most effective among three types of Group C additives. • The bed expansion was increased with the modulation of Group C additives. • A higher volume fraction of Group C additives was more effective. • Both particle cohesion and bulk density affected the fluidization quality.

Power expansion for heavy quarkonium production at next-to-leading order in e+e\u2212 annihilation

We study heavy quarkonium production associated with gluons in e+e− annihilation as an illustration of the perturbative QCD (pQCD) factorization approach, which incorporates the first nonleading power in the energy of the produced heavy quark pair. We show how the renormalization of the four-quark operators that define the heavy quark pair fragmentation functions using dimensional regularization induces “evanescent” operators that are absent in four dimensions. We derive closed forms for short-distance coefficients for quark pair production to next-to-leading order ( {alpha}_s^2 ) in the relevant color singlet and octet channels. Using non-relativistic QCD (NRQCD) to calculate the heavy quark pair fragmentation functions up to v4 in the velocity expansion, we derive analytical results for the differential energy fraction distribution of the heavy quarkonium. Calculations for {}^3{S}_1^{left[1right]} and {}^1{S}_0^{left[8right]} channels agree with analogous NRQCD analytical results available in the literature, while several color-octet calculations of energy fraction distributions are new. We show that the remaining corrections due to the heavy quark mass fall off rapidly in the energy of the produced state. To explore the importance of evolution at energies much larger than the mass of the heavy quark, we solve the renormalization group equation perturbatively to two-loop order for the {}^1{S}_0^{left[8right]} case.

Evolution of exploding granules from coordinated observations by THEMIS, IRIS, SDO/HMI, and HINODE, and a simulation

Exploding granules constitute the strongest horizontal flows on the quiet Sun and contribute to the structure of the surface horizontal velocity fields which build the large-scale organization of the discrete magnetic field. In this work we explore exploding granule expansion through the observations of the ground-based THEMIS telescope, IRIS, SDO, and the Hinode space-borne instruments, and finally with the magnetohydrodynamics simulation. We evaluate the detection and the expansion of exploding granules at several wavelengths and at various spatial and temporal resolutions. To analyze the different temporal sequences, two methods of image segmentation are applied to select the granules. The first allows us to follow individually the exploding granules observed simultaneously by THEMIS, IRIS, and SDO. The second uses long time independent sequences from THEMIS, IRIS, SDO, Hinode, and a simulation. In the first method (called manual) the segmentation isolates the cell of the granules (bright granules and intergranular parts), while in the second method (called statistical) only the bright part of the granules are isolated. The results obtained with simultaneous or distinct temporal observations using the two methods of segmentation are in good agreement. The granule area evolves linearly with an expansion velocity that decreases with the radius. A rapid decrease in the velocity expansion in the first two minutes is observed. The detection and measurement of the dynamics of the explosive granules can be performed from ground- and space-based instruments. Our work reveals the usefulness of SDO data, with low spatial resolution, to study the dynamics of the exploding granules all over the solar surface.

Adaptive particle method based on moments for simulating the mass transport in natural flows

In this work, two modifications of an adaptive particle method based on the moments of the internal concentration of numerical particles are presented to introduce the effect of local shears on the mass transport in natural flows. This moment method uses a Taylor expansion of the flow velocity field to derive the transport equation of moments. The first modification is based on the introduction of a method of the local frame transport in order to perform an extension of the Taylor expansion of the flow velocity to a higher order. The second modification consists in applying a splitting or a merging to non-spherical numerical particles. When a non-spherical numerical particle becomes large compared to the scale of spatial variations of the velocity gradient, it is divided into two non-spherical numerical particles. On the contrary, when particles reach some other parts of the flow where they become small compared to spatial variations of the velocity gradient, then these particles should merge. The accuracy of both modifications is evaluated by simulating the mass transport in natural flows.

Fragmentation function of gluon into spin-singlet P -wave quarkonium

Following the operator definition of the fragmentation function developed by Collins and Soper, we compute the gluon-to-$h_c$ fragmentation function at the lowest order in the velocity expansion in NRQCD factorization approach. Utilizing some modern technique developed in the area of multi-loop calculation, we are able to analytically deduce the infrared-finite color-singlet short-distance coefficient associated with the fragmentation function. The fragmentation probability for gluon into $h_c$ is estimated to be order $10^{-6}$.

Intensification of the fluidization performances of polypropylene by using microwave absorbent

Abstract Fluidization is an effective method to better help the transfer and conversion of fuel particles. In this study, intensification of the fluidization performances of polypropylene was experimentally investigated by using microwave absorbent. The fluidization performances of polypropylene (PP) were initially presented and the effects of microwave absorbent (SiC) particle size, mass ratio of SiC to PP, and fluidization velocity on the co-fluidization performances were studied and presented. The results showed that the PP load significantly increased the initial bed height whereas slightly increased the critical fluidization velocity and bed expansion ratio. Adding microwave absorbent (SiC) can effectively improve the fluidization performance of PP particles. The smaller SiC particles (0.25−1 mm) had better fluidization performances than the larger ones (1–1.5 mm and 1.5−2 mm). The mass ratio of silicon carbide to polypropylene decreased the critical fluidization velocity. Fluidization velocity significantly affected the co-fluidization performance. For the co-fluidization of polypropylene and silicon carbide in the designed fluidized bed, the recommended fluidization parameters were: (a) the particle size of silicon carbide of 0.25–1 mm, (b) the mass ratio of silicon carbide to polypropylene of 3:2, and (c) the fluidization velocity of 0.66 m/s.

Consistent modeling of velocity statistics and redshift-space distortions in one-loop perturbation theory

The peculiar velocities of biased tracers of the cosmic density field contain important information about the growth of large scale structure and generate anisotropy in the observed clustering of galaxies. Using N-body data, we show that velocity expansions for halo redshift-space power spectra are converged at the percent-level at perturbative scales for most line-of-sight angles μ when the first three pairwise velocity moments are included, and that the third moment is well-approximated by a counterterm-like contribution. We compute these pairwise-velocity statistics in Fourier space using both Eulerian and Lagrangian one-loop perturbation theory using a cubic bias scheme and a complete set of counterterms and stochastic contributions. We compare the models and show that our models fit both real-space velocity statistics and redshift-space power spectra for both halos and a mock sample of galaxies at sub-percent level on perturbative scales using consistent sets of parameters, making them appealing choices for the upcoming era of spectroscopic, peculiar-velocity and kSZ surveys.

Asymptotic study of heat and mass transfer in weakly twisted jets

Jet flows of liquids and gases are used in various fields of technology as means of controlling the processes of heat and mass transfer, for the intensification and stabilization of the combustion process, as means of protecting structures from exposure to thermal fields, for coating, etc. The jets of liquids and gases in technology are formed by sources-nozzles of finite sizes with various distributions of the initial outflow velocities in the outlet section of the nozzle, therefore, the calculation of the aerodynamic and thermal characteristics of jet flows is reduced to solving non-self-similar problems. However, one of the methods for solving such problems is the method of asymptotic expansion of velocities and pressure in series in a small parameter, when the first member of this series is a self-similar solution to the jet source problem. This article proposes an asymptotic expansion for axisymmetric weakly swirling flows in a model of a viscous incompressible medium, which leads to nonlinear «boundary layer» equations that differ from the well-known classical equations [1]–[4] for flows with finite swirl. Self-similar solutions of these equations are constructed that describe the distribution of speed, pressure, and temperature in a weakly swirling jet. The results presented in the article complement the results of [3]–[7] by calculating the thermal field in the jet.

CFD modeling of a typical fluidized bed column

Abstract The hydrodynamic behavior of a 2-D gas–solid fluidized bed has been studied using computational fluid dynamics (CFD) software package ANSYS Fluent. The modeling results were validated using the experimental data carried out in a lab-scale perspex column based fluidized bed having a diameter of 0.1 m and height of 0.62 m. The modeling studies showed a very good resemblance with the experimental observations. Studies were carried out by using 0.0003 m biomass fine powder having a density of around 1242 kg/m3 at different inlet gas velocities. Eulerian-Eulerian model approach along with the kinetic theory of granular flow is used for simulating the gas–solid fluidization behavior. In the present work, the effects of inlet gas velocity, pressure drop and bed expansion ratio was studied. The minimum fluidization velocity condition was predicted by using the simulated contour plot of the computational software. The momentum exchange coefficients were calculated using Syamlal-O’Brien functions. The comparison study showed that the CFD simulation of a gas–solid fluidized bed can be used effectively for the designing and operation of a lab-scale fluidized bed column. Moreover the simulation studies would also help in the scaling up of the fluidized bed further for industrial usage.

Pulsating Flow of an Ostwald—De Waele Fluid between Parallel Plates

The flow between two parallel plates driven by a pulsatile pressure gradient was studied analytically with a second-order velocity expansion. The resulting velocity distribution was compared with a numerical solution of the momentum equation to validate the analytical solution, with excellent agreement between the two approaches. From the velocity distribution, the analytical computation of the discharge, wall shear stress, discharge, and dispersion enhancements were also computed. The influence on the solution of the dimensionless governing parameters and of the value of the rheological index was discussed.

Prompt {J/psi }-pair production at the LHC: impact of loop-induced contributions and of the colour-octet mechanism

Prompt double-J/psi production at high-energy hadron colliders can be considered as a golden channel to probe double parton scatterings (DPS)—in particular to study gluon–gluon correlations inside the proton—and, at the same time, to measure the distribution of linearly-polarised gluons inside the proton. Such studies, however, require a good control of both single parton scatterings (SPS) and DPS in the respective regions where they are carried out. In this context, we have critically examined two mechanisms of SPS that may be kinematically enhanced where DPS are thought to be dominant, even though they are either at higher orders in the strong-coupling or velocity expansion. First, we have considered a gauge-invariant and infrared-safe subset of the loop-induced contribution via colour-singlet (CS) transitions. We have found it to become the leading CS SPS contributions at large rapidity separation, yet too small to account for the data without invoking the presence of DPS yields. Second, we have surveyed the possible colour-octet (CO) contributions using both old and up-to-date non-perturbative long-distance matrix elements (LDMEs). We have found that the pure CO yields crucially depend on the LDMEs. Among all the LDMEs we used, only two result into a visible modification of the NRQCD (CS+CO) yield, but only in two kinematical distributions measured by ATLAS, those of the rapidity separation and of the pair invariant mass. These modifications, however, do not impact the control region used for their DPS study.

New factorization theory for heavy quarkonium production and decay

The widely used nonrelativistic QCD (NRQCD) factorization theory now encounters some notable difficulties in describing quarkonium production. This may be due to the inadequate treatment of soft hadrons emitted in the hadronization process, which causes bad convergence of velocity expansion in NRQCD. In this paper, starting from QCD we propose a rigorously defined factorization approach, soft gluon factorization (SGF), to better deal with the effects of soft hadrons. After a careful velocity expansion, the SGF can be as simple as the NRQCD factorization in phenomenological studies, but has a much better convergence. The SGF may provide a new insight to understand the mechanisms of quarkonium production and decay.

Nonlinear gyrokinetic Coulomb collision operator

A gyrokinetic Coulomb collision operator is derived, which is particularly useful to describe the plasma dynamics at the periphery region of magnetic confinement fusion devices. The derived operator is able to describe collisions occurring in distribution functions arbitrarily far from equilibrium with variations on spatial scales at and below the particle Larmor radius. A multipole expansion of the Rosenbluth potentials is used in order to derive the dependence of the full Coulomb collision operator on the particle gyroangle. The full Coulomb collision operator is then expressed in gyrocentre phase-space coordinates, and a closed formula for its gyroaverage in terms of the moments of the gyrocentre distribution function in a form ready to be numerically implemented is provided. Furthermore, the collision operator is projected onto a Hermite–Laguerre velocity space polynomial basis and expansions in the small electron-to-ion mass ratio are provided.

Study on explosion characteristics of premixed hydrogen/biogas/air mixture in a duct

Hydrogen addition into biogas can improve the combustion performance. However, hydrogen addition will also pose higher explosion severity. In order to study the influence of hydrogen addition on the biogas explosion, the deflagration characteristics of premixed hydrogen/biogas/air mixtures with the unity equivalence ratio were evaluated in a 10 L transparent duct. The hydrogen fraction λ H 2 in the blended fuel and the methane fraction in biogas θ CH 4 were varied 0.1–0.6 and 0.4–1.0, respectively. The results show that when the mixture was less reactive, the low flame velocity facilitated the flame front deformation, leading to the more salient tulip flames. The profiles of the reduced flame velocity V / ES L (i.e., laminar burning velocity S L and expansion ratio E ) could be divided into three patterns, depending on the combination of λ H 2 and θ CH 4 . As the reactivity of the mixture increased, the flame velocity profile would shift from the first pattern to the second pattern then to the third one. However, the V / ES L was linearly scaled with the flame position Z tip irrespective of the biogas composition before the flame touched the sidewall, indicating that the effect of flame instability and acoustic wave on flame propagation was insignificant. The explosion parameters (e.g., the maximum flame velocity V m and the maximum overpressure P m ) were more sensitive to the hydrogen fraction than to the methane fraction. In addition, hydrogen addition was more effective in augmenting the explosion parameters for biogas with low methane fraction. For a fixed methane fraction, the V m and P m showed the linearly dependence on the hydrogen fraction defined by Yu et al. (Yu and Law 1986). Moreover, the increasing hydrogen fraction would gradually moderate the effect of the methane fraction in biogas on the explosion parameters. There was a good linear nexus between the P m and the V m irrespective of the composition of the mixtures. The V m was well scaled with the ES L or the maximum H radical [H] max in the reaction zone of laminar flame. Therefore, the ( ES L ) and [H] max provide the good indicators to predict the explosion parameters of the hydrogen/biogas fuel. • Combined effect of hydrogen and biogas is discussed through their effect on the mixture properties. • The effect of hydrogen on explosion parameters is greater than that of biogas. • Hydrogen shows a stronger effect on biogas with lower methane fraction. • The increasing hydrogen fraction moderates the effect of methane fraction on explosion parameters. • The explosion parameters were linearly scaled with ES L and [H] max .

Rotation errors in numerical manifold method and a correction based on large deformation theory

Numerical manifold method (NMM) is an effective method for simulating block system, however, significant errors are found in its simulation of rotation problems. Three kinds of errors, as volume expansion, stress vibration, and attenuation of angular velocity, were observed in the original NMM. The first two kind errors are owing to the small deformation assumption and the last one is due to the numerical damping. A large deformation NMM is proposed based on large deformation theory. In this method, the governing equation is derived using Green strain, the large deformation iteration and the open-close iteration are combined, and an updating strategy is proposed. The proposed method is used to analyze block rotation, beam bending, and rock falling problems and the results prove that all three kinds of errors are eliminated in this method.