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If a ball were given an initial velocity in excess of its terminal velocity, would the upward force of air resistance (a function of velocity) be greater than the downward force of gravity and thus push the ball back upwards? An answer to this question is provided. (JN)

Discusses the velocity of an orbiting satellite. Knowledge of the kinematics of falling objects is the only prerequisite for understanding the concepts considered. (DH)

Discusses and clarifies the relationship between the energy-momentum tensor and the velocity of energy flow. (Author/GA)

This research established a systematic method to generate various pore-size distributions (PSDs) and studied the effect of PSDs on the shock compaction response of granular materials using two-dimensional mesoscale simulations under identical porosity. Simulations utilized various PSDs for three particle shapes (circle, ellipse, and square). Contacting particle configurations using three PSDs, characterized by spatially uniform distributed pores to heterogeneous distributed pores, and non-contacting particle configurations under a single case of PSD were tested. The PSD of generated particle sets was characterized using coordination number, mean diameter, and bimodality coefficient as statistical metrics. Mesoscale simulations showed that regardless of the conditions of pore distributions, shock compaction of granular materials consistently demonstrates a precursor, shock compaction front, and end. However, the shock compaction velocity of contacting particles was dependent on the PSDs despite the constant initial porosity. The compaction velocity was faster in particle configurations with relatively uniform pore distributions than in heterogeneous pore distributions, which our study demonstrated can be attributed to particle rearrangement during compaction. Circular-shaped particles had high sensitivity in shock compaction response to the various PSDs. Furthermore, a contacting particle configuration tended to propagate the shock compaction wave relatively faster than particles that were in a non-contact configuration. This study established the relative importance of considering PSD as a metric over the coordination number in studies of the shock compaction response of granular materials. Further, insights are provided on the evolving shock substructure to characterize the shock compaction response of granular materials. [ABSTRACT FROM AUTHOR]

We perform large-scale atomistic simulations of a system containing 12 × 106 atoms, comprising an oxygen gas-filled bubble immersed in water, to understand the stability and cavitation induced by ultrasound. First, we propose a method to construct a bubble/water system. For a given bubble radius, the pressure inside the bubble is estimated using the Young–Laplace equation. Then, this pressure is used as a reference for a constant temperature, constant pressure simulation of an oxygen system, enabling us to extract a sphere of oxygen gas and place it into a cavity within an equilibrated water box. This ensures that the Young–Laplace equation is satisfied and the bubble is stable in water. Second, this stable bubble is used for ultrasound-induced cavitation simulations. We demonstrate that under weak ultrasound excitation, the bubble undergoes stable cavitation, revealing various fluid velocity patterns, including the first-order velocity field and microstreaming. These fluid patterns emerge around the bubble on a nanometer scale within a few nanoseconds, a phenomenon challenging to observe experimentally. With stronger ultrasound intensities, the bubble expands significantly and then collapses violently. The gas core of the collapsed bubble, measuring 3–4 nm, exhibits starfish shapes with temperatures around 1500 K and pressures around 6000 bar. The simulation results are compared with those from Rayleigh–Plesset equation modeling, showing good agreement. Our simulations provide insights into the stability and cavitation of nanosized bubbles. [ABSTRACT FROM AUTHOR]

Velocity autocorrelation functions (VACFs) were calculated using the molecular dynamics method in the TIP4P/2005 and SPC/E water models of 157 464 molecules at temperatures ranging from 250 to 370 K. The large size of the models and the high accuracy of the calculations allow us to reliably compute the long-time tails of the VACFs, showing that they systematically change shape from hydrodynamic (argon-like) at high temperatures to that typical of supercooled liquids at low temperatures. These tails in the range of 2–10 ps can be well fitted by a combination of two power functions: At−3/2 – Bt−β (A, B > 0, β ≈ 2). It is found that the amplitude of the hydrodynamic asymptote, A, approaches zero as the temperature decreases, thereby rendering the negative power-law decay,−Bt−2, the dominant term within the specified time interval. The presence of a negative −Bt−2 decay in the time interval of 2–10 ps determines the specific shape of the VACF long-time tail of water, distinguishing it from ordinary simple liquids. The amplitude B, which is always non-zero, demonstrates a slight increase with rising temperature. At medium temperatures, weak but well-defined damped oscillations are observed on the VACF in the 0.5–2 ps interval. [ABSTRACT FROM AUTHOR]

We present a simple implicit solution for the time-dependent trajectory of a thin Asay foil ejecta diagnostic for the general case where the impinging ejecta cloud is generated by a source function characterized by an arbitrary (sustained) time dependence and a time-independent (stationary) particle velocity distribution. In the limit that the source function time dependence becomes a delta function, this solution—which is amenable to rapid numerical calculations of arbitrary accuracy—exactly recovers a previously published solution for the special case of instantaneous ejecta production. We also derive simple expressions for the free-surface arrival (catch-up) time as well as the true ejecta areal mass accumulation on the accelerating foil and place bounds on the level of error incurred when applying instant-production mass solutions to a sustained-production trajectory. We demonstrate these solutions with example calculations for hypothetical source functions spanning a wide range of ejecta production durations, velocity distributions, and temporal behaviors. These calculations demonstrate how the foil trajectory is often insensitive to the temporal dependence of the source function, instead being dominated by the velocity distribution. We quantify this insensitivity using a "compatibility score" metric. Under certain conditions, one may capitalize upon this insensitivity to obtain a good approximation of the second integral of the velocity distribution from the observed foil trajectory. [ABSTRACT FROM AUTHOR]

Purpose: To compare the kinematic profile of 2 underwater pullout breaststroke techniques. Methods: Sixteen swimmers (9 men, 20.67 [2.71] y old; 7 women, 18.86 [0.83] y old) performed 3 × 25-m breaststroke using 2 pullout breaststroke techniques: Fly-Kick first and Combined. A speedometer was used to assess the peak and the mean velocity during the glide, propulsion, and recovery phases of both techniques, as well as for the total underwater sequence. The underwater distance was retrieved from video footage and was considered for each pullout technique. The range of motion of the knee during the fly-kick was also retrieved, and the time to complete the 25 m was considered the performance outcome, accompanied by the mean velocity, stroke rate, stroke length, and stroke index. Results: Velocity–time series showed different profiles between pullout techniques (P ≤.05) mostly in the glide and propulsion phases for males and females, respectively. The mean velocity of 25 m was shown to be greater in females when using the Fly-Kick first technique (P =.05, d = 0.36). Greater values in total underwater distance and knee range of motion were also observed for this technique in both cohorts. Conclusions: Female swimmers presented a higher performance when using the Fly-Kick first technique. Different kinematic profiles arise when swimmers use different underwater pullout techniques where the Fly-Kick first may allow them to reach higher kinematical standard. [ABSTRACT FROM AUTHOR]

We measured the austenitic FeCr18Ni12.5 stainless steel Hugoniot as a function of crystallographic direction to approximately 60 GPa. We shock-compressed FeCr18Ni12.5 samples oriented along ⟨ 100 ⟩ , ⟨ 110 ⟩ , and ⟨ 111 ⟩ to mean stresses ranging 30.5–58.1 GPa via Ta plate impact in a large-bore powder gun and measured the free-surface velocities with laser interferometry. We unambiguously observed the largest post-shock free-surface velocity along ⟨ 100 ⟩ in each experiment, which consequently produced the lowest shock velocity along that orientation. However, the propagation of experimental uncertainties through the impedance matching scheme used to compute the shock velocity produced sufficient uncertainty overlap to preclude definitive conclusion of Hugoniot anisotropy. [ABSTRACT FROM AUTHOR]

Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure. [ABSTRACT FROM AUTHOR]

In living and synthetic active matter systems, the constituents can self-propel and interact with each other and with the environment through various physicochemical mechanisms. Among these mechanisms, chemotactic and auto-chemotactic effects are widely observed. The impact of (auto-)chemotactic effects on achiral active matter has been a recent research focus. However, the influence of these effects on chiral active matter remains elusive. Here, we develop a Brownian dynamics model coupled with a diffusion equation to examine the dynamics of auto-chemotactic chiral active droplets in both quasi-two-dimensional (2D) and three-dimensional (3D) systems. By quantifying the droplet trajectory as a function of the dimensionless Péclet number and chemotactic strength, our simulations well reproduce the curling and helical trajectories of nematic droplets in a surfactant-rich solution reported by Krüger et al. [Phys. Rev. Lett. 117, 048003 (2016)]. The modeled curling trajectory in 2D exhibits an emergent chirality, also consistent with the experiment. We further show that the geometry of the chiral droplet trajectories, characterized by the pitch and diameter, can be used to infer the velocities of the droplet. Interestingly, we find that, unlike the achiral case, the velocities of chiral active droplets show dimensionality dependence: its mean instantaneous velocity is higher in 3D than in 2D, whereas its mean migration velocity is lower in 3D than in 2D. Taken together, our particle-based simulations provide new insights into the dynamics of auto-chemotactic chiral active droplets, reveal the effects of dimensionality, and pave the way toward their applications, such as drug delivery, sensors, and micro-reactors. [ABSTRACT FROM AUTHOR]

Chemical shakers are active particles with zero propulsion velocity whose activity derives from chemical reactions on portions of their surfaces. Although they do not move, except through Brownian motion, the nonequilibrium concentration and velocity fields that they generate endow them with properties that differ from their equilibrium counterparts. In particular, collections of such shakers can actively move, reorient, and self-assemble into various cluster states, which are the subject of this paper. Elongated chemical shakers constructed from linked catalytic and noncatalytic spheres are considered, and it is shown how hydrodynamic, chemotactic, and shape-dependent interactions give rise to various self-assembled shaker structures. The chemical forces responsible for cluster formation are described in terms of a model based on pair-wise additive contributions. The forms of the self-assembled structures can be varied by changing the chemostat concentrations that control the nonequilibrium state. The resulting structures and their manipulation through chemical means suggest ways to construct a class of active materials for applications. [ABSTRACT FROM AUTHOR]

We present comprehensive numerical results from a study of model H, which describes phase separation kinetics in binary fluid mixtures. We study the pattern dynamics of both density and velocity fields in d = 2, 3. The density length scales show three distinct regimes, in accordance with analytical arguments. The velocity length scale shows a diffusive behavior. We also study the scaling behavior of the morphologies for density and velocity fields and observe dynamical scaling in the relevant correlation functions and structure factors. Finally, we study the effect of quenched random field disorder on spinodal decomposition in model H. [ABSTRACT FROM AUTHOR]

As markerless motion capture systems become more affordable than ever, it is becoming far easier to collect and analyze kinematic data on baseballers. To ensure this data can be used impactfully, coaches and practitioners should possess a good understanding of specific technique characteristics that are associated with enhanced performance in pitchers and hitters. This study used the open-source data provided by Driveline Baseball's OpenBiomechanics Project to evaluate the contribution of lower-body kinematics to pitch velocity and bat speed. In addition to correlational analyses to examine the association between discrete kinematic variables and performance, statistical nonparametric mapping was used to compare slow and fast velocity groups across the entirety of pitching and hitting motions from peak knee height to ball release/contact. It was found that rotation of the trail leg and extension of the lead knee were both associated with performance in pitchers and hitters. Consequently, coaches and practitioners should ensure that individuals possess an adequate level of strength and flexibility to facilitate optimal movement of the trail hip and lead knee during pitching and hitting movements. If deficiencies exist, then training programs should be designed to address these issues and eventually bring about an improvement in performance. [ABSTRACT FROM AUTHOR]

In this work, we detail a novel application of inverse design and advanced manufacturing to rapidly develop and experimentally validate modifications to a shaped charge jet analog. The shaped charge jet analog comprises a copper liner, a high explosive (HE), and a silicone buffer. We apply a genetic algorithm to determine an optimal buffer design that can be placed between the liner and the HE that results in the largest possible change in jet velocity. The use of a genetic algorithm allows for discoveries of unintuitive, complex, yet optimal buffer designs. Experiments using the optimal design verified the effectiveness of the buffer and validated the machine learning approach to hydrodynamic design optimization. [ABSTRACT FROM AUTHOR]

The so-called velocity correlated cluster emission (VCCE) effect is the recently reported emission of large clusters with nearly the same velocity from an atomically heavy target (such as coinage metals) following a single C 60 − impact at the keV kinetic energy range. The effect was observed to get weaker for a meaningfully lighter target (Al) down to its complete disappearance for C60–Be impact. Microscopic insight into the subpicosecond evolution and thermalization of the impact induced energy spike (driving the effect) is achieved using molecular dynamics simulations. It is shown that the weakening of the VCCE effect for aluminum (toward its complete disappearance for Be) is due to ultrafast decay of the atomic number density within the spike nanovolume, thus not enabling the buildup of sufficient subsurface pressure as required for driving the correlated emission. For the Be target, an extremely rapid decay of nearly 90% of the initial density within 200 fs from impact is observed. This finding provides further support for the conclusion that the emission of the velocity correlated clusters as observed for the heavier targets takes place within an ultra-short time window of only a few hundreds of femtoseconds, roughly extending from 200 to 500 fs from impact. The lower bound is dictated by the requirement for a relatively slow rate of decay of number density, enabling the buildup of a sufficiently intense pressure spike. The upper bound is dictated by the cooling rate of the spike (still maintaining an extremely high temperature of kT ≥ 1 eV, as experimentally observed) and the onset of the evolution of the impact crater. [ABSTRACT FROM AUTHOR]

Objectives: This study sought to report the reliability (intrasession) values of initial maximum push-rim propulsion (IMPRP) and sprint performance in elite wheelchair basketball (WB) players and to assess the involvement of strength in sprint capacity. Methods: Fifteen Spanish international WB male players participated in this study. The maximum single wheelchair push from a stationary position (IMPRP) and the sprint performance (ie, 3, 5, and 12 m) of WB players were measured in this study. Results: IMPRP mechanical outputs V, Vmax, P, Rel. P, F, and Rel. F variables presented high reliability values (intraclass correlation coefficient [ICC] ≥.92; coefficient of variation [CV] ≤ 8.04 ± 7.37; standard error of measurement [SEM] ≤ 29.92), but the maximum strength variables Pmax, Rel. Pmax, Fmax, and Rel. Fmax (ICC ≥.63; CV ≤ 13.19 ± 16.63; SEM ≤ 203.76) showed lower ICC values and by contrast higher CV and SEM values. The most substantial correlations were identified between maximum IMPRP values (ie, V, Vmax, P, Rel. P, F, and Rel. F) and sprint performance in 3 m (r ± confidence limits ≥ −0.74 ± 0.22, very large; R2 ≥.55), 5 m (r ± confidence limits ≥ −0.72 ± 0.24, very large; R2 ≥.51), and 12 m (r ± confidence limits ≥ −0.67 ± 0.27, large; R2 ≥.44). Conclusions: The IMPRP test and sprint tests (3, 5, and 12 m) are practical and reliable for measuring strength and speed in WB players. In addition, there were large to very large associations among strength variables (ie, P, Rel. P, F, and Rel. F) and all sprint variables. This could indicate a need to implement specific strength exercises in WB players to improve sprint capacity. [ABSTRACT FROM AUTHOR]

The study of granular avalanches in rotating drums is not only essential to understanding various complex behaviors of interest in granular media from a scientific perspective; it also has valuable applications in regard to industrial processes and geological catastrophes. Despite decades of research studies on avalanches, a proper understanding of their dynamic properties still remains a great challenge to scientists due to a lack of state-of-the-art techniques. In this study, we accurately predict the avalanche dynamic features of three-dimensional granular materials in rotating drums, by using graph neural networks on the basis of their initial static microstructures alone. We find that our method is robust to changes in various model parameters, such as the interaction potential, size polydispersity, and noise in particle coordinates. In addition, with the grain-scale velocities obtained either from our network or from numerical simulations, we find an approximately equal and strong correlation between the global velocity and global velocity fluctuation in our 3D granular avalanche systems, which further demonstrates the predictive power of our trained graph neural networks to uncover the fundamental physics of granular avalanches. We expect our method to provide more insight into the avalanche dynamics of granular materials and other amorphous systems in the future. [ABSTRACT FROM AUTHOR]

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum. [ABSTRACT FROM AUTHOR]

Fluid-based methods for particle sorting demonstrate increasing appeal in many areas of biosciences due to their biocompatibility and cost-effectiveness. Herein, we construct a microfluidic sorting system based on a swirl microchip. The impact of microchannel velocity on the swirl stagnation point as well as particle movement is analyzed through simulation and experiment. Moreover, the quantitative mapping relationship between flow velocity and particle position distribution is established. With this foundation established, a particle sorting method based on swirl induction is proposed. Initially, the particle is captured by a swirl. Then, the Sorting Region into which the particle aims to enter is determined according to the sorting condition and particle characteristic. Subsequently, the velocities of the microchannels are adjusted to control the swirl, which will induce the particle to enter its corresponding Induction Region. Thereafter, the velocities are adjusted again to change the fluid field and drive the particle into a predetermined Sorting Region, hence the sorting is accomplished. We have extensively conducted experiments taking particle size or color as a sorting condition. An outstanding sorting success rate of 98.75% is achieved when dealing with particles within the size range of tens to hundreds of micrometers in radius, which certifies the effectiveness of the proposed sorting method. Compared to the existing sorting techniques, the proposed method offers greater flexibility. The adjustment of sorting conditions or particle parameters no longer requires complex chip redesign, because such sorting tasks can be successfully realized through simple microchannel velocities control. [ABSTRACT FROM AUTHOR]

This study aims to analyze the effects of a training program based on practice variability on the speed and accuracy of the tennis forehand approach to the net shot. The study sample consisted of 35 players of both genders, 22 men and 13 women Cage 44 ± 10.9 years, height 1.73 ± 0.8 cm, and weight 74.7 ± 8,4 kg) Players were randomly distributed into two groups (control group = 18 and experimental group = 17). Both training groups worked a total volume of 4 weeks, seven sessions, and 15 min per session of forehand approach shot. Control group performed traditional training while experimental group trained with variability using wristband weights. The data obtained showed a large Group x Time interaction in the accuracy of the forehand approach shot, F(1, 16) = 28.034, p <.001. η =.637. Only the experimental group increased significantly in the accuracy after the program (51.4%. effect size = 1.3. p < .001). while no changes were achieved regarding hitting speed (1.2%, effect size =0.12, p=.62). The control group did not improve iii any of the tested variables. These results indicate that variability of training using wrist weights is a valid option to improve forehand approach shot accuracy in recreational-level players. Although stroke speed was not increased. this type of training may be interesting as accuracy and technical control is commonly the main goal of training at this level. [ABSTRACT FROM AUTHOR]

While characterizing space-charge-limited current (SCLC) is important for numerous applications, no analytical solutions for SCLC with monoenergetic initial velocity exist for two-dimensional (2D) geometries. Here, we derive approximate closed-form solutions for uniform SCLC with monoenergetic emission of electrons in a 2D planar diode, where emission is restricted to a long patch of width W for electrodes separated by a distance D. We also derive a semiempirical approach for estimating the SCLC for these cases by treating the geometric and velocity correction factors as multiplicative corrections to the SCLC for a one-dimensional vacuum diode given by the Child–Langmuir (CL) law. We show that the SCLC for a finite patch with nonzero velocity can exceed the CL law by three orders of magnitude. The theoretically calculated SCLCs for various emission widths and initial velocities in the 2D diode agree well with particle-in-cell simulations using the over-injection method in XOOPIC; they agree with the semiempirical relationship for lower initial velocities. In the limit of high initial velocity, the geometry and velocity corrections to the CL law cannot be decoupled, invalidating the assumption of the semiempirical approach and causing it to diverge from the theoretical solution and XOOPIC simulations. These results provide valuable estimates for determining the onset of virtual cathode formation for photocathodes and thermionic cathodes, which operate in the over-injection regime to avoid beam quality degradation. [ABSTRACT FROM AUTHOR]

Umbral flashes (UFs) are one of the most dynamic phenomena observed in the sunspot umbra at the chromospheric heights. In this paper, we present spectroscopic observations of UFs in the Ca  ii 8542 Å line recorded by a narrow-band imager working with the Multi-Application Solar Telescope (MAST). The deduced data are analysed to obtain various properties of the UFs occuring at different locations inside the umbral boundary. An intensity enhancement of up to 30% or more was observed at the location of UFs, with a periodicity |$\approx$| 3 min. The line-of-sight (LOS) velocity of UFs was estimated using bisector application to the emission profile resulting from the removal of mean umbral and the mean quiet Sun (QS) line profiles. The emission profiles resulting from removing the mean umbral profile were observed to better represent the emission component of the UF line profile. Both up-flows and down-flows of the order |$\approx$| 5 km s |$^{-1}$| were associated with the UFs with an average up-flow of |$\approx$| 1 km s |$^{-1}$|⁠. Out of all UFs analysed, 31% were observed to be associated with down-flows in case of removal of the mean umbral profile from the UF line profile. We observed multiple radially propagating LOS velocity disturbances (⁠|$\approx$| 20–40 km s |$^{-1}$|⁠) in the penumbra, which might be associated with the UFs, even though we could not establish a one-to-one correspondence. The horizontally propagating LOS velocity disturbances could produce the visual effect of running penumbral waves, which produce intensity fluctuations in intensity images when observed at the line-centre wavelength. The simultaneous photospheric HMI observations showed no distinct intensity or velocity signatures corresponding to the UFs observed in the chromospheric Ca  ii 8542 Å line. [ABSTRACT FROM AUTHOR]

We report that the gas components in the N59 bubble suffered from sequential multiple cloud–cloud collision (CCC) processes. The molecular gas in the N59 bubble can be decomposed into four velocity components, namely Cloud A [95, 108] km s |$^{-1}$|⁠ , Cloud B [86, 95] km s |$^{-1}$|⁠ , Cloud C [79, 86] km s |$^{-1}$|⁠ , and Cloud D [65, 79] km s |$^{-1}$|⁠. Four CCC processes occurred among these four velocity components, i.e. Cloud A versus Cloud B, Cloud A versus Cloud C, Cloud C versus Cloud D, and Cloud A versus Cloud D. Using the near- and mid-infrared photometric point source catalogues, we identified 514 young stellar object (YSO) candidates clustered in 13 YSO groups, and most of them (⁠|$\sim 60~{{\ \rm per\ cent}}$|⁠) were located at the colliding interfaces, indicating that they were mainly triggered by these four CCC processes. We also found that these four collisions occurred in a time sequential order: the earliest and most violent collision occurred between Cloud A and Cloud D about 2 Myr ago, then Cloud B collided with Cloud A about 1 Myr ago, and finally, Cloud C collided with Clouds A and D simultaneously about 0.4 Myr ago. [ABSTRACT FROM AUTHOR]

We are concerned with the long time existence of smooth solutions to full compressible Navier-Stokes equations in 3D bounded domains with Dirichlet boundary conditions on the velocity and temperature. The smallness restriction on the initial data or time interval is unnecessary. Under the condition that the limiting system admits a reasonably smooth solution on a given time interval, we verify that the compressible system admits the smooth solution on the same interval as well, provided that the Mach number is sufficiently small. Moreover, as the Mach number goes to zero, the solution of the compressible system converges uniformly to that of the incompressible one. We utilize some geometric techniques to overcome difficulties introduced by non-slip boundary conditions. [ABSTRACT FROM AUTHOR]

Using the EXES instrument on SOFIA, we have obtained velocity-resolved spectra of several pure rotational lines of H2 toward shocked molecular gas within three Galactic sources: the supernova remnant (SNR) IC 443 (clump C), a protostellar outflow in the intermediate-mass star-forming region NGC 2071, and the SNR 3C 391. These observations had the goal of searching for expected velocity shifts between ortho- and para-H2 transitions emitted by C-type shocks. In contrast in our previous similar study of HH7, the result of our search was negative: no velocity shifts were reliably detected. Several possible explanations for the absence of such shifts are discussed: these include a preshock ortho-to-para ratio that is already close to the high-temperature equilibrium value of 3 (in the case of IC 443C), the more complex shock structures evident in all these sources, and the larger projected aperture sizes relative to those in the observations of HH7. [ABSTRACT FROM AUTHOR]

Iron partitioning among the main lower mantle phases, bridgmanite (Bm) and ferropericlase (Fp), has non‐monotonic behavior owing to the high‐spin to low‐spin crossover in ferrous iron (Fe2+) in Fp. Previously reported iron partitioning coefficient between these phases, KD ${K}_{D}$, still have considerable uncertainty. Here, we investigate the Fe2+ partitioning behavior using ab initio free energy results. Although we focus on Fe2+ only, we describe the effect of this iron spin crossover (ISC) on KD ${K}_{D}$ and of the latter on compositions and seismic velocities in a pyrolitic aggregate. Our results suggest that its velocities are mainly affected by the ISC and less so by the Fe2+ partitioning. In contrast, iron partitioning manifests in thermally induced velocity heterogeneity ratios. Prediction of the seismological parameter RS/P ${R}_{S/P}$∂lnVS/∂lnVP $\left(\partial \,\mathrm{ln}{V}_{S}/\partial \,\mathrm{ln}{V}_{P}\right)$ including iron partitioning effects resembles quantitatively RS/P ${R}_{S/P}$'s inferred from several tomographic studies down to 2,400 km depth. Plain Language Summary: Since the discovery of the iron spin crossover in lower mantle phases, its effect on mantle properties has been debated. The ferrous iron partitioning coefficient between bridgmanite (Bm) and ferropericlase (Fp), is the starting point for understanding these effects. Here, we show that iron partitioning changes due to the ISC in Fp do not affect significantly the velocities of a typical pyrolitic aggregate. However, its effect is perceptible on the thermally induced S‐ to P‐velocity heterogeneity ratio, that is, an undulated increase with depth similar to what is inferred from some tomography models down to 2,400 km depth. Key Points: The ferrous iron spin crossover (ISC) affects the iron partitioning between bridgmanite and ferropericlaseIron partitioning effects on mantle velocities are small but manifest clearly on thermally induced velocity heterogeneity ratiosThe predicted S‐ to P‐velocity heterogeneity ratio is similar to those inferred from tomography models down to 2,400 km depth [ABSTRACT FROM AUTHOR]

This study examined the acute effects of different loading protocols on 180° change of direction (COD) performance in eleven male handball players. Participants performed a 10-0-5 COD test under seven conditions: without an external load, and with 3, 6, and 9 kg loads applied under two modes—assisted into the COD and resisted out of it and resisted into the COD and assisted out of it. While total COD time was not affected (p = 0.098; η2 = 0.16), significant phase effects were observed (p < 0.001; η2 ≥ 0.55). Loading protocols significantly influenced velocity, acceleration, and their distances from COD (p < 0.001; η2 ≥ 0.37). Significant phase effects were observed for all step kinematic variables (p ≤ 0.037; η2 ≥ 0.67), except contact time, and significant interaction (phase*condition) effects for all variables (p ≤ 0.004; η2 ≥ 0.08), except for step frequency. Assisted-resisted protocols increased deceleration demands through higher COD entry velocities, displaying fewer but longer steps in the acceleration phase and greater steps taken during the deceleration phase. Resisted-assisted protocols decreased deceleration demands due to lower COD entry velocities, displaying shorter, but more steps taken in the acceleration phase, and fewer steps taken in the deceleration phase. These findings suggest that assisted-resisted and resisted-assisted loading protocols can be used to selectively overload specific phases of COD performance. [ABSTRACT FROM AUTHOR]

Extremely low-mass white dwarfs (ELM WDs) with non-degenerate companions are believed to originate from solar-type main-sequence binaries undergoing stable Roche lobe overflow mass transfer when the ELM WD progenitor is at (or just past) the termination of the main-sequence. This implies that the orbital period of the binary at the onset of the first mass transfer phase must have been |$\lesssim 3-5$|  d. This prediction in turn suggests that most of these binaries should have tertiary companions since |$\approx 90$|  per cent of solar-type main-sequence binaries in that period range are inner binaries of hierarchical triples. Until recently, only precursors of this type of binaries have been observed in the form of EL CVn binaries, which are also known for having tertiary companions. Here, we present high-angular-resolution images of TYC 6992-827-1, an ELM WD with a sub-giant (SG) companion, confirming the presence of a tertiary companion. Furthermore, we show that TYC 6992-827-1, along with its sibling TYC 8394-1331-1 (whose triple companion was detected via radial velocity variations), are in fact descendants of EL CVn binaries. Both TYC 6992-827-1 and TYC 8394-1331-1 will evolve through a common envelope phase, which depending on the ejection efficiency of the envelope, might lead to a single WD or a tight double WD binary, which would likely merge into a WD within a few Gyr due to gravitational wave emission. The former triple configuration will be reduced to a wide binary composed of a WD (the merger product) and the current tertiary companion. [ABSTRACT FROM AUTHOR]

We present the results of an asteroseismic study of HD 118660 (TIC 171729860), being a chemically peculiar (mild Am) star exhibiting |$\delta$| Scuti (⁠|$\delta$|  Sct) pulsations. It is based on the analysis of two sectors of time-series photometry from the space mission TESS (Transiting Exoplanet Survey Satellite) and seismic modelling. It yielded the detection of 15 and 16 frequencies for TESS sectors 23 and 50, respectively. The identified pulsation modes include four radial (⁠|$\ell =0$|⁠) and five dipolar (⁠|$\ell =1$|⁠) ones. The radial modes are overtones with order n ranging from 3 and 6. Such high values of n are theoretically not expected for stars with the effective temperature of HD 118660 (⁠|$T_{\rm eff}\approx 7550\,\rm K$|⁠) located near the red edge of the |$\delta$|  Sct instability strip. To estimate the asteroseismic parameters, we have generated a grid of stellar models assuming a solar metallicity (⁠|$Z=0.014$|⁠) and different values for the convective overshooting parameter (⁠|$0.1\le \alpha _{\rm ov}\le 0.3$|⁠). We conclude that the analysis of the radial modes is insufficient to constrain |$\alpha _{\rm ov}$| and Z for |$\delta$|  Sct stars. The value for the equatorial velocity of HD 118660 derived from the seismic radius and the rotational frequency is consistent with values found in the literature. [ABSTRACT FROM AUTHOR]

In material handling, numerous solutions have been proposed to enhance the flexibility and adaptability of transport systems. Among these solutions, smart surfaces stand out as one of the most interesting responses, utilizing an array of actuators for common feeding tasks. The current paper focuses on a novel system within this category, notable for its distinguishing factor of being underactuated. With this characteristic, the concept leads to a simplified cost-effective design and a not actively driven functioning, leveraging gravity or object own velocity to manipulate the material flow maintaining top class performances, as the sorting rate reaches 4000 pcs/h. Specifically, the article begins with an introduction of the concept design and its digital model, followed by a description of the experimental setup built to test the surface's functionality and evaluate the predictions of the virtual counterpart. On top of that, a method to determine the essential parameters for the surface simulation is proposed and applied. As a result, the prototype successfully completed the three main intralogistic tasks experimented, i.e., sorting, slowing, and stopping of packages. Lastly, the digital model outcomes of the same operations were computed and compared with the measured results, demonstrating an accuracy of prediction with displacements and time errors below 7%. [ABSTRACT FROM AUTHOR]

In this work, the coupled generalized thermoelasticity of two-dimensional finite domain subjected to moving heat source is investigated. The generalized thermoelasticity is based on Lord–Shulman (LS) theory, and the moving heat source is considered to move along the x -axis at the middle of the domain with constant velocity. The meshless method, because of continuous moving of approximations over the problem domain, is the best numerical method for problems with moving loads. So, for solving the governing equations, the meshless Galerkin weak form is employed. In the applied meshless method, the moving least square (MLS) shape functions are used for approximating the field variables in each influence domain. Also, for solving the final equations in the time domain, the Newmark time marching method is used. The results show that a moving source with a velocity equal to the temperature's wave speed exhibit the maximum peak values of temperature, displacement and stress in the domain, and when the temperature wave speed and the elastic wave speed are equal, the moving heat source at this speed drastically increases the peak values of stress, displacement and temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A pilot-scale smouldering reactor with a height of 2.0 m is constructed. • Smouldering performance under long-term continuous operation is evaluated. • Effect of discharging residue interval and Darcy velocity is investigated. • 30 s for discharging residue interval and 3.5 cm/s for Darcy velocity are suggested. Smouldering is a novel, low-energy, low-cost technology for disposing of sludge with high moisture. Currently, related researches focus on the lab-scale with batch disposal, but more reports about the pilot-scale with continuous process need to be done. Based on our previous research, this study further enlarged the pilot-scale smouldering reactor height from 1.2 m to 2.0 m and provides insight into the smouldering performance under long-term continuous operation and the influence of the discharging residue interval and Darcy velocity. The temperate evolution shows that the discharging residue interval significantly affects the reaction location stability due to the difference between the smouldering upward velocity and the feed-stock descent velocity. Furthermore, the unburnout content, heavy metal in the smouldering-derived residue, the non-condensable flue gas concentrations (O 2 , CO, NO x , VOCs, dioxin), and the components of the condensable liquid are deeply investigated. The pilot-scale measurements show that 30 s and 40 s for the discharging residue interval under the studied operating condition may be reasonable for the high (3.5 cm/s and 5.0 cm/s) and low (2.5 cm/s) Darcy velocity, respectively. Comprehensively, the condition with 30 s for the discharging residue interval and 3.5 cm/s for the Darcy velocity is suggested in the future actual application. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying the initial-boundary value problem for the radiative full Euler equations, which are a fundamental system in the radiative hydrodynamics with many practical applications in astrophysical and nuclear phenomena, with the non-slip boundary condition on an impermeable wall. Due to the difficulty from the disappearance of the velocity on the impermeable boundary, quite few results for compressible Navier-Stokes equations and no result for the radiative Euler equations are available at this moment. So the asymptotic stability of the rarefaction wave proven in this paper is the first rigorous result on the global stability of solutions of the radiative Euler equations with the non-slip boundary condition. It also contributes to our systematical study on the asymptotic behaviors of the rarefaction wave with the radiative effect and different boundary conditions such as the inflow/outflow problem and the impermeable boundary problem in our series papers including [5,6]. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the long time existence of the classical solution to 2D one-fluid Euler-Poisson system of electrons with non-zero vorticity in the standard Sobolev spaces so that both the local solution and long time solution lie in the same Sobolev space framework without any extra restrictions of space-decay rates at infinity. It is shown that the lifespan of the classical solution is at least T ε , δ = min ⁡ { e ε − 2 | l n ε | − α , κ δ } , where ε > 0 is the size of the initial perturbed density and velocity, δ > 0 is the size of the initial vorticity, α > 0 is any fixed number, κ > 0 is a suitable constant. We decompose the Euler-Poisson system into three bilinear interaction parts: dispersion–dispersion, vorticity–dispersion, and vorticity–vorticity. Based on the Strichartz inequality, the related quartic energy estimates, the conservation of specific vorticity along the streamline and some delicate analysis, the precise bound of lifespan T ε , δ is obtained. By the way, for the 2D irrotational one-fluid Euler-Poisson system with small amplitude ε of the perturbed initial data in the Sobolev spaces, we obtain an interesting long time existence result with lifespan T ε ≥ e ε − 2 | l n ε | − α (α > 0 is any fixed constant). [ABSTRACT FROM AUTHOR]

The wind energy requirements for high temporal and spatial observations, unavailable in many countries, are met by reanalysed wind data, which are increasingly used in wind power assessments. However, these data also include unrealistic features, making their validation compulsory. The validation analysis of ERA5 and MERRA-2 wind data, two of the most successful wind reanalyses, with observations near Morocco's coast, highlighted the existence of bias in both datasets, and other shortcomings. The study was conducted at eight selected sites in the period 2011-2020 using linear and probability density function based statistical tests. The local ERA5-BA and MERRA-2 BA velocity fields were created using Bias Adjustment (BA) Techniques. Only part of the observed and modelled datasets (training period) were used to identify the transfer function. The BA fields were verified against observations during the remaining period (verification period). They outperformed their respective non-adjusted fields and also the WFDE5 (the global bias-corrected ERA5 wind field) in the wind potential assessments, represented by capacity factor and low-wind day. At every location, the relative errors in the latter's estimates using ERA5-BA were lowered to less than 10 %, and the same was true for MERRA-2-BA. Thus, an observational dataset of reduced length can help overcome some reanalysed wind data limitations for wind power estimations. Additionally, this methodology can be applied to the correction of each reanalysis update. [ABSTRACT FROM AUTHOR]

The increase in human activities and natural degradation often leads to tilting, collapsing, and other forms of deterioration in architectural heritage, posing significant threats to its safety. Therefore, timely detection of abnormal deformation signals in buildings is essential for the protection of architectural heritage. Spaceborne synthetic aperture radar interferometry (InSAR) can detect slight displacements over large areas. However, relying solely on annual mean velocity maps derived from InSAR may not accurately assess the stability of ancient buildings. In this study, we developed a framework that evaluates the stability of individual buildings by integrating the InSAR displacements with building footprints. Vertical and rotational deformations, along with the temporal evolution of these deformations, are combined to generate the results for building stability assessment. We used 74 TerraSAR-X images captured from August 2017 to November 2019 to evaluate the stability of Jianchuan Ancient Town, a renowned National Historical and Cultural City in China. The displacement result suggests that the majority of Jianchuan Ancient Town remains stable, with over 93% of coherent points (CTs) displaying displacement velocities ranging from −5 to 5 mm/yr. Out of the 1,891 buildings in Jianchuan Ancient Town, 1404 are considered stable, 352 are of moderate stability, and 12 are deemed unstable. This study showed the potential of InSAR applications in assessing the stability of architectural heritages, emphasizing its crucial role in heritage preservation and management. [ABSTRACT FROM AUTHOR]

The joint inversion of Rayleigh and Love waves plays a crucial role in mitigating the non‐uniqueness of surface wave inversion results and enhancing the stability of these inversions. Existing approaches to the joint inversion of Rayleigh and Love wave dispersion curves, which rely on conventional objective functions, often struggle with complex stratigraphic configurations and yield results of limited accuracy. This study introduces two novel nonlinear joint inversion techniques for Rayleigh and Love waves: Pearson correlation coefficient and thickness mean sharing. The Pearson correlation coefficient approach employs the Pearson correlation coefficient and alternating iterative objective functions to synchronize the shear wave velocity structures derived from Rayleigh and Love waves, thereby enhancing the accuracy of the joint inversion. Conversely, the thickness mean sharing method computes an average of the thickness values obtained in each iteration of the inversion, utilizing the traditional joint inversion objective function. Tests on three distinct stratigraphic structures—characterized by increasing velocity, high‐speed hard interlayers and low‐speed soft interlayers—as well as on measured data, demonstrate that the proposed methods significantly improve the stability and accuracy of nonlinear joint inversion. [ABSTRACT FROM AUTHOR]

One of the research gaps is to understand the development of seismic characteristics of gas‐saturated rock along with the change in rock properties because of chemical reactions. We suggest a method to explain the change in elastic properties brought on by CO2 injection in a rock by capturing the physico‐chemical interactions observed in the laboratory in a theory of rock physics. To explain the laboratory‐measured physical characteristics and velocity of a dynamic rock–fluid system, we include a time‐dependent component in the existing cemented‐sand model. We demonstrate theoretically the rate of change of elastic moduli of the dry frame by incorporating the measured rate of change of cement due to chemical dissolution. We adapt the theory such that it can be applied to the field data and calibrate the theory using water‐saturated well log data from the Ankleshwar field, an established oil field in the Cambay basin, western India. Theoretical time‐lapse logs of velocity and density are then produced using the theory over a range of CO2 saturations, assuming cementing material in grain contacts and geochemical interactions comparable to those observed in the laboratory rock. Then, using theoretical logs, corresponding time‐lapse synthetic seismic data are produced for different saturation. These data clearly demonstrate that, for a uniform model, velocity decreases by up to 18% as CO2 saturation increases from 0% to 20% (ignoring the chemical effect), and that, for a specific saturation, say 20%, chemical effects result in a 17% decrease in velocity from the present to the end of 60 years. However, for the patchy model, velocity decreases maximum by 14% and 16% due to varying saturation and chemical reaction. Moreover, for a particular saturation of CO2, say 20%, velocity differs by 16% for different types of models. This research contributes to making strategy for CO2‐sequestration in a designated field. [ABSTRACT FROM AUTHOR]

The existing Pascal curve gears are limited by inflexible pitch curves and constrained transmission ratio changes, which hinders the application in a range of mechanical systems that require more adaptable gear solutions. To address this, a design procedure for higher-order multisegment denatured Pascal curve gear is proposed. A unified mathematical expression for the Pascal curve gear family is derived, enabling the construction of non-circular gears with free-form pitch curves by adjusting key parameters and offering more flexible pitch curve and a wider range of transmission ratios. Compared with elliptical gears and eccentric circular gears, its transmission ratio range can be expanded by up to 35%. Then the transmission characteristics of these gears are analyzed in detail. To validate the design, the visual analysis and design software of the gear is compiled based on Visual Basic, and is verified with the example. The novelty Pascal curve gears is applied to drive the differential velocity vane pump. The displacement, instantaneous flow rate, and pulsation rate of the differential velocity vane pump are calculated. The comparison with the differential pumps driven by eccentric non-circular gears and Fourier non-circular gears shows that when the pitch curves are not concave, the displacement driven by Pascal curve circular gears is the highest (compared to differential pumps driven by eccentric non-circular gears, and Fourier non-circular gears, their flow rates increased by 50.6%, and 175.7%, respectively), and the instantaneous flow pulsation rate of single pump is the smallest.This study shows that the higher-order multisegment denatured Pascal curve gear provides a viable solution for systems requiring flexible transmission mechanisms and improved operational performance. [ABSTRACT FROM AUTHOR]

Fluctuation dynamics of an experimentally measured observable offer a primary signal for nonequilibrium systems, along with dynamics of the mean. While universal speed limits for the mean have actively been studied recently, constraints for the speed of the fluctuation have been elusive. Here, we develop a theory concerning rigorous limits to the rate of fluctuation growth. We find a principle that the speed of an observable's fluctuation is upper bounded by the fluctuation of an appropriate observable describing velocity, which also indicates a tradeoff relation between the changes for the mean and fluctuation. We demonstrate the advantages of our inequalities for processes with non-negligible dispersion of observables, quantum work extraction, and the entanglement growth in free fermionic systems. Our results open an avenue toward a quantitative theory of fluctuation dynamics in various non-equilibrium systems encompassing quantum many-body systems and nonlinear population dynamics. Fluctuation dynamics of an observable offers a primary signal for understanding non-equilibrium statistical mechanics. Here, the author derives a principle that the speed of an observable's fluctuation is upper bounded by the fluctuation of an observable describing velocity, which is valid for various non-equilibrium systems from quantum many-body systems to nonlinear population dynamics. [ABSTRACT FROM AUTHOR]

The least squares vorticity stabilization (LSVS), proposed in N. Ahmed, G. R. Barrenechea, E. Burman, J. Guzmán, A. Linke, and C. Merdon (“A pressure-robust discretization of Oseen’s equation using stabilization in the vorticity equation,” SIAM J. Numer. Anal., vol. 59, no. 5, pp. 2746–2774, 2021) for the Scott–Vogelius finite element discretization of the Oseen equations, is studied as an augmentation of the popular grad-div stabilized Taylor–Hood pair of spaces. An error analysis is presented which exploits the situation that the velocity spaces of Scott–Vogelius and Taylor–Hood are identical. Convection-robust error bounds are derived under the assumption that the Scott–Vogelius discretization is well posed on the considered grid. Numerical studies support the analytic results and they show that the LSVS-grad-div method might lead to notable error reductions compared with the standard grad-div method. [ABSTRACT FROM AUTHOR]