Initial Momentum Research Articles

Whole-body linear momentum control in two-foot running jumps in male basketball players

Running jumps that depart the ground from two feet require momenta redirection upward from initial momenta that are primarily horizontal. It is not known how each leg generates backward and upward impulses from ground reaction forces to satisfy this mechanical objective when jumping to maximize height. We examined whole-body linear momentum control strategies during these two-foot running jumps by uncovering the roles of each leg in impulse generation. 3D motion capture and force plates were used to record 14 male basketball players performing two-foot running jumps towards an adjustable basketball hoop. Total ground contact phase started from the first leg ground contact and ended at takeoff and was divided into center of mass descent and ascent subphases. During the total ground contact phase, all participants generated significantly more upward impulse with the first leg and ten participants generated significantly more backward impulse with the first leg compared to the second leg. During the descent subphase, all participants generated significantly more upward and backward impulses with the first leg. During the ascent subphase, all but one participant generated significantly more backward impulse with the second leg. In addition to group-level statistics, participant-specific strategies were described. Overall, this study revealed the fundamental whole-body momentum control strategies used in two-foot running jumps and supports future research into optimal jump techniques and training interventions that respect the need to satisfy the mechanical objectives of the movement.

Cosmic-Eν: An- emulator for the non-linear neutrino power spectrum

ABSTRACT Cosmology is poised to measure the neutrino mass sum Mν and has identified several smaller-scale observables sensitive to neutrinos, necessitating accurate predictions of neutrino clustering over a wide range of length scales. The FlowsForTheMasses non-linear perturbation theory for the the massive neutrino power spectrum, $\Delta ^2_\nu (k)$, agrees with its companion N-body simulation at the $10~{{\ \rm per\ cent}}-15~{{\ \rm per\ cent}}$ level for k ≤ 1 h Mpc−1. Building upon the Mira-Titan IV emulator for the cold matter, we use FlowsForTheMasses to construct an emulator for $\Delta ^2_\nu (k)$, Cosmic-Eν, which covers a large range of cosmological parameters and neutrino fractions Ων, 0h2 ≤ 0.01 (Mν ≤ 0.93 eV). Consistent with FlowsForTheMasses at the 3.5 per cent level, it returns a power spectrum in milliseconds. Ranking the neutrinos by initial momenta, we also emulate the power spectra of momentum deciles, providing information about their perturbed distribution function. Comparing a Mν = 0.15 eV model to a wide range of N-body simulation methods, we find agreement to 3 per cent for k ≤ 3kFS = 0.17 h Mpc−1 and to 19 per cent for k ≤ 0.4 h Mpc−1. We find that the enhancement factor, the ratio of $\Delta ^2_\nu (k)$ to its linear-response equivalent, is most strongly correlated with Ων, 0h2, and also with the clustering amplitude σ8. Furthermore, non-linearities enhance the free-streaming-limit scaling $\partial \log (\Delta ^2_\nu /\Delta ^2_{\rm m}) / \partial \log (M_\nu)$ beyond its linear value of 4, increasing the Mν-sensitivity of the small-scale neutrino density.

Coherent transient exciton transport in disordered polaritonic wires

Abstract Excitation energy transport can be significantly enhanced by strong light–matter interactions. In the present work, we explore intriguing features of coherent transient exciton wave packet dynamics on a lossless disordered polaritonic wire. Our main results can be understood in terms of the effective exciton group velocity, a new quantity we obtain from the polariton dispersion. Under weak and moderate disorder, we find that the early wave packet spread velocity is controlled by the overlap of the initial exciton momentum distribution and its effective group velocity. Conversely, when disorder is stronger, the initial state is nearly irrelevant, and red-shifted cavities support excitons with greater mobility. Our findings provide guiding principles for optimizing ultrafast coherent exciton transport based on the magnitude of disorder and the polariton dispersion. The presented perspectives may be valuable for understanding and designing new polaritonic platforms for enhanced exciton energy transport.

Evaluation of Turbulence Depending Drag Coefficient in Plume Rise Model for Fire Smoke Dispersion

It is well-known that the correct modeling of the plume rise is fundamental for a proper description of pollutants dispersion, especially for highly buoyant plumes like those emitted by wildfires. In this work, we want to investigate the role of the drag coefficient (CD) in our plume rise scheme. We evaluate different formulations taken from the literature and suggest the best option for the plume rise scheme embedded in the Lagrangian Stochastic model SPRAY-WEB. As a matter of fact, previous works on plume rise models are based on the drag coefficient which is a quantity that should be determined. There is not a general consensus on the best values for CD. Some values suggested in the literature are simply constants that do not directly depend on the meteorological and turbulent variables. In order to evaluate the model performances obtained using different CD formulations we simulate a field experiment, carried out in August 2013 in Idaho (USA), in which prescribed fires were observed and the physical and chemical parameters were measured. As a matter of fact, plumes emitted from fires are affected by strong buoyancy and very low or even negligible initial vertical momentum. These conditions are very different from traditional plumes from stacks for which the classical plume rise models are built. For this reason, the case studies chosen for the tests are very challenging and they allow us to assess the scheme here proposed in the best way. Comparison among the results obtained with different CD parameterizations are presented and discussed. Three of the four CD models tested derive from an extension of the Stokes’ law; the fourth one is a more refined model derived from the Shanks transformation of the Goldstein series. This last model seems to give better results as regards the maximum height of the plume, but is the one that underestimates most CO concentrations.

Impact of Early Coherences on the Control of Ultrafast Photodissociation Reactions.

By coherent control, the yield of photodissociation reactions can be maximized, starting in a suitable superposition of vibrational states. In ultrafast processes, the interfering pathways are born from the early vibrational coherences in the ground electronic potential. We interpret their effect from a purely classical picture, in which the correlation between the initial position and momentum helps to synchronize the vibrational dynamics at the Franck-Condon window when the pulse is at its maximum intensity. In the quantum domain, we show that this localization in time and space is mediated by dynamic squeezing of the wave packet.

Spatial and temporal distribution of bioaerosols produced by patients with different postures in a negative pressure isolation ward under different ventilation modes

The high concentration of viral bioaerosols within the negative pressure isolation wards could pose a challenge to preventing potential cross-infection amongst healthcare workers (HCWs) and patients. Using the Euler–Lagrange methodology, this study numerically simulated the spatial and temporal distribution characteristics of bioaerosols in a typical negative pressure isolation ward as well as determined the interaction of ventilation mode and patient posture on ward ventilation performance. The removal effect of particle groups produced by two respiratory behaviours (breathing and coughing) was quantitatively analyzed, and the effect of exhaust air ratio and air exchange rate on particle distribution was discussed. The results showed that the migration characteristics of bioaerosol particles were sensitive to both the ventilation pattern and patient posture, which showed significant interactions. On this basis, the ventilation pattern with the best ventilation performance was evaluated, showing a particle removal effect of 70–85%. Due to the initial momentum difference, the diffusion behaviour of cough and breath particles was not consistent, but optimizing the airflow distribution near the exhaust outlet could improve their removal efficiency in the meantime. Further studies found that equal exhaust air velocity ratio facilitated the removal of aerosol particles, and an appropriate increase in the air exchange rate could also reduce the particle content.

Generative AI Images and Indian Media Industry: An Overview of Opportunities and Challenges

Artificial Intelligence (AI) has gained initial momentum in the past few years. Another side of this is Generative AI, which is growing and has the capacity to transform journalism and media content. There are speculations about the consequences of AI from creating warfare to the making of movies. This article considers notable platforms like Shutterstock, providers of stock photographs, music and editing tools and secondly, DALL.E 2-Open AI, a generative AI platform of Chat GPT.The proposed research article aims to find out the effects of generative AI images in the media industry, the opportunities of AI generative visuals and the challenges faced by the industry due to the innovative technology. This article will also try to demonstrate the capacity and the limitations of generative AI content and reflect on the implications of generative AI for media education and journalism.

Impact responses of the steel-PU foam-concrete-tube multilayer energy absorbing panel: Numerical and analytical studies

The enhancement of structural protection can be achieved by using energy absorbing structures as sacrificial layers. In this study, a new steel-PU foam-concrete-tube multilayer energy absorbing panel (SFCTMEAP) is developed to improve the impact resistance of buildings and infrastructures, and its behaviour under impact loading is numerically and analytically studied. A Finite Element (FE) model is established using LS-DYNA to further study the behaviours of SFCTMEAP, and its results (including the failure mode, displacement–time and impact force–time curves) agree well with the test data. The SFCTMEAP presents a deformation mode of local indentation of the front energy absorbing layer, flexure of the steel-concrete-steel panel and collapse of PU foam-filled steel tubes (PUFSTs). The energy dissipations of variant components of the SFCTMEAP are obtained through the FE model and the PUFSTs is the main energy absorbing component. In addition, parametric studies are performed to obtain the influences of the impact location, initial momentum of impactor and thickness of PU foam panel on the response of SFCTMEAP. The results indicates that the specimen with larger impact eccentric distance dissipates less impact energy, and raising the initial momentum of the impactor is benefit to the energy dissipation by the PUFSTs. Moreover, an analytical model is developed to calculate the displacement history of SFCTMEAP under the impact loading. The displacement responses predicted by the analytical model are found to be in good agreement with the test results.

A spherical version of Feynman’s static field momentum example

The Feynman demonstration that electromagnetic field momentum is real—even for static fields—can be made more pedagogically useful by simplifying its geometry. Instead of Feynman’s disk with charged balls on its surface, this article uses the geometry of a hollow non-conducting sphere with uniform surface charge density. With only methods available in a typical upper-division electrodynamics course, the initial field angular momentum and the final mechanical angular momentum can then be calculated in closed form and shown to be equal.

A Systematic Survey of Moon-forming Giant Impacts. I. Nonrotating Bodies

In the leading theory of lunar formation, known as the giant impact hypothesis, a collision between two planet-size objects resulted in a young Earth surrounded by a circumplanetary debris disk from which the Moon later accreted. The range of giant impacts that could conceivably explain the Earth–Moon system is limited by the set of known physical and geochemical constraints. However, while several distinct Moon-forming impact scenarios have been proposed—from small, high-velocity impactors to low-velocity mergers between equal-mass objects—none of these scenarios have been successful at explaining the full set of known constraints, especially without invoking controversial post-impact processes. In order to bridge the gap between previous studies and provide a consistent survey of the Moon-forming impact parameter space, we present a systematic study of simulations of potential Moon-forming impacts. In the first paper of this series, we focus on pairwise impacts between nonrotating bodies. Notably, we show that such collisions require a minimum initial angular momentum budget of approximately 2 J EM in order to generate a sufficiently massive protolunar disk. We also show that low-velocity impacts (v ∞ ≲ 0.5 v esc) with high impactor-to-target mass ratios (γ → 1) are preferred to explain the Earth–Moon isotopic similarities. In a follow-up paper, we consider impacts between rotating bodies at various mutual orientations.

Mechanism study on particle deposition and clogging characteristics in film cooling hole

The present study is focused on the problems of gas–solid two-phase flow transport in the film cooling hole that cause film flow obstruction and cooling failure. To study the unsteady development process of the deposition layer in the film hole, a simulation method combining computational fluid dynamics and the discrete element method was used, and a film hole flow model was established. The effect of gas phase and solid phase characteristics on clogging and deposition in the film hole was studied. The following conclusions are drawn: The inlet/outlet pressure ratio is inversely proportional to the clogging degree of the film hole. The inlet/outlet pressure determines the deposition behavior by affecting the initial momentum and drag force of particles. In the Stokes number range of 1.58–14.26, the deposition in the film hole first increases and then decreases. There is a Stokes number with the most severe clogging. The Stokes number determines the deposition pattern by affecting the relative magnitudes of the drag force and interaction forces of particles. The particle surface energy is positively correlated with film hole clogging. The particle surface energy determines the stability of the deposition layer by influencing the strength of the force chain network.

The Spatial Arrangement of The Electric Field in the Needle-Plate Electrospinning

<p class="IJASEITAbtract">The electric field distribution of the Neddle-Plate (NP) electrospinning set up has reported due to the simple classical electrodynamics solutions. The charge is assumed to distribute uniformly in the needle (nozzle) and the collector (plate). The electric field has an influence only in the early stage of the electrospinning process. The electric field and the viscosity of the jet fluid have caused the bending of the straight jet. The high viscosity of the fluid can preserve the straight jet length much longer. The electric field gives the initial angular momentum of the jet due to the whipping motion of the jet. For the area away from the nozzle, the electric does not influence the whipping motion. Then the whipping motion solely due to the influence from the charge repulsion of the jet fluid and the evaporation of the solvent.</p>

Investigation on displacement efficiency and enhance oil recovery performance of CO2 and CO2-chemical additive composite system flooding using LBM simulation

CO2 flooding is a promising EOR method. Chemical additives reduce oil viscosity and CO2-oil interfacial tension. In this study, we propose a multiphase and multi-component model based on the LBM to examine the effectiveness of CO2 flooding and identify the factors that influence its performance. Additionally, we present a novel approach for simulating CO2-chemical additive composite system (CCAS) flooding by modifying fluid interaction parameters and reducing oil viscosity when exposed to chemicals. A comparison was conducted between the CO2 flooding approach and the CO2-chemical additive compound systems. The results show that the force between fluid molecules has a significant impact on interfacial tension and miscibility, affecting the displacement process. The viscosity and injection speed of the displaced fluid play a crucial role in determining the initial momentum and CO2 displacement performance. Additionally, reservoir rock morphology has an impact on the velocity of fluid molecules, and affects the displacement efficiency. The CCAS flooding has the potential to increase oil recovery by 15% compared to using CO2 flooding alone. Optimizing additive concentration, injection timing, and injection rate can further improve oil displacement efficiency by 5%-10%. Valuable theoretical guidance for applying CO2 chemical additives is provided by these research findings.

Nonextensive Behavior of Stellar Rotation in the Galactic Disk Components

The solar neighborhood is a unique stellar astrophysical laboratory formed by a variety of stars from different origins. In particular, two of the most notable populations known are the thick and thin disk stars, each characterized by distinct chemical compositions, ages, kinematics, and origins. Based on Tsallis nonextensive statistics, we investigate the observed distribution of the projected rotational velocity of the thin and thick disk component stars. Through Bayesian inference, our results show that the distributions of the Galactic disk populations selected from both kinematic and chemical criteria follow a nonextensive behavior, where non-Gaussian statistics provide a more accurate representation. We also observed an anticorrelation between the entropic index q and the age of disk components confirming the interpretation of initial angular momentum memory loss scaled by the parameter q. In contrast, a subextensivity case with q > 1 was found for the old high-α metal-rich subgroup hαmr, and due to their distinguished rotational behavior and atypical subextensive regime, we infer that thick disk and hαmr stars are, in fact, distinct objects. Our results also suggest that the rotational velocities of stars are defined not only by their evolutionary spin-down processes but also by their birth sites.

Generation of jet-forming plasma bunch with gigagauss axial magnetic field from impact of linearly polarized laser on microtube targets

Generation of a thin plasma jet with embedded gigagauss axial magnetic fields from the frontal impact of a short linearly polarized laser pulse on an overdense microtube target is considered. It is a new scheme of axial magnetic field generation without initial laser angular momentum. Three-dimensional particle-in-cell simulations show that the space-charge field of the laser expelled tube-front electrons will pull out carbon ions to form at the tube entrance a long-living low-density plasma bunch with gigagauss magnetic fields. The front center of the plasma bunch then stretches forward to form a thin gigagauss-magnetized plasma jet, which survives for sub-picosecond after the core of the laser has passed through the tube.

Transport and localization properties of excitations in one-dimensional lattices with diagonal disordered mosaic modulations

We present a numerical study of the transport and localization properties of excitations in one-dimensional lattices with diagonal disordered mosaic modulations. The model is characterized by the modulation period κ and the disorder strength W. We calculate the disorder averages , , and , where T is the transmittance and P is the participation ratio, as a function of energy E and system size L, for different values of κ and W. For excitations at quasiresonance energies determined by κ, we find power-law scaling behaviors of the form , , and , as L increases to a large value. In the strong disorder limit, the exponents are seen to saturate at the values , , and , regardless of the quasiresonance energy value. This behavior is in contrast to the exponential localization behavior occurring at all other energies. The appearance of sharp peaks in the participation ratio spectrum at quasiresonance energies provides additional evidence for the existence of an anomalous power-law localization phenomenon. The corresponding eigenstates demonstrate multifractal behavior and exhibit unique node structures. In addition, we investigate the time-dependent wave packet dynamics and calculate the mean square displacement , spatial probability distribution, participation number, and return probability. When the wave packet’s initial momentum satisfies the quasiresonance condition, we observe a subdiffusive spreading of the wave packet, characterized by where η is always less than 1. We also note the occurrence of partial localization at quasiresonance energies, as indicated by the saturation of the participation number and a nonzero value for the return probability at long times.

Formulation of causality-preserving quantum time of arrival theory

We revisit the quantum correction to the classical time of arrival to address the unphysical instantaneous arrival in the limit of zero initial momentum. In this study, we show that the vanishing of arrival time is due to the contamination of the causality-violating component of the initial wave packet. Motivated by this observation, we propose to update the temporal collapse mechanism in Galapon (2009) [18] to incorporate the removal of causality-violating spectra of the arrival time operator. We found that the quantum correction to the classical arrival time is still observed. Thus, our analysis validates that the correction is an inherent consequence of quantizing a time observable and is not just some mathematical artifact of the theory. We also discuss the possible application of the theory in describing point interactions in particle physics and provide a possible explanation to the observed neutron's lifetime anomaly.

Viscous QCD medium effects on the bottom quark transport coefficients

The bottom quark transport coefficients, i.e., drag and diffusion coefficients, have been studied for the collisional and soft gluon radiative processes within the viscous QCD medium. The thermal medium effects are incorporated using the effective fugacity quasiparticle model (EQPM). Both the shear and bulk viscous effects at leading order are embedded through the near-equilibrium distribution functions of the quark–gluon plasma (QGP) constituent quasiparticles. The transport coefficients’ dependence on the bottom quark’s initial momentum and QGP temperature have been investigated. The relative dominance of the radiative over the collisional process for the bottom quark seems to occur at a higher initial momentum compared to that of the charm quark. In contrast, the effect of the viscous corrections seems to be more for the charm quark. Furthermore, we also investigate the validity of the Einstein fluctuation–dissipation theorem for our analysis.

Study of the azimuthal asymmetry in heavy ion collisions combining initial state momentum orientation and final state collective effects

Study of the azimuthal asymmetry in heavy ion collisions combining initial state momentum orientation and final state collective effects

Aerodynamic effect on atomization characteristics in a swirl cup airblast fuel injector

To investigate the influence of swirling air flow field on the spray characteristics and the droplet behaviors of the swirl cup airblast fuel injector, a single swirler cup and a double swirlers cup airblast injector were operated in a wide range of fuel mass flow rates (mf) and relative air pressure drops (ΔPa). Various laser based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high speed particle imaging velocimetry, were employed to provide the information of spray angle, droplet Sauter mean diameter (SMD), droplet velocity, and air flow velocity. The results show that the air flow field was characterized by central toroidal recirculation zone (CTRZ), the double swirlers cup airblast injector generated stronger CTRZ than single swirlers cup airblast injector. The spray characteristics and the droplet behaviors with different size classes were significantly affected by the air flow field. The larger droplets (25–100 μm) with higher initial momentum were likely to keep its velocity when passing through CTRZ, when the mf increased, more large fuel droplets could pass through the CTRZ and expanded to both sides, resulting an increase in a spray angle. On the other hand, smaller droplets (<25 μm) with lower initial momentum were trend to be enrolled by the CTRZ; therefore, the spray droplets at lower mf were confined in the CTRZ. These droplets trend to coalesce with each other resulting in an increase of SMD in this region.