Kinetic Energy Gain Research Articles

Sensitivity of the Energy Conversion Efficiency of Tropical Cyclones During Intensification to Sea Surface Temperature and Static Stability

AbstractIt is projected that the sea surface temperature (SST) increases under climate change and enhances tropical cyclone (TC) intensification directly. An opposing expected feature of climate change is the strengthening atmospheric static stability, which may suppress intensification. The intensity and diabatic heating are closely related through the secondary circulation, but it has been unclear whether both will change at the same rate. Here we show that they respond differently to stability changes. The efficiency of converting diabatic heating to kinetic energy (KE) of TCs to SST and static stability during the intensification stage is examined. In a set of idealised simulations, the efficiency does not have a significant relation with the SST. However the efficiency is found to decrease with increasing static stability at a rate of about K. It is shown that the KE increment declines, while the diabatic heating in the eyewall remains unchanged with larger static stability. The decrease in KE gain at the eyewall is associated with an enhanced outward advection of absolute angular momentum. The combined effect of enhanced water‐vapour supply and the slightly reduced updraft at the eyewall keeps the diabatic heating steady with varying static stability. This study demonstrates the complex effects of enhanced static stability, which is expected to accompany surface warming, on tropical cyclones.

Enhanced Subseasonal Variability of Spring Temperature Over Eastern China in 2022: Initial Role of Extremely Heavy Arctic Sea Ice in Previous Winter

AbstractIn spring 2022, strong temperature whiplash events occurred in eastern China (EC), characterized by enhanced subseasonal variability in surface air temperature (SAT). Our results show that extreme temperature fluctuations are dominated by the amplified Eurasian wave train on a biweekly timescale as a possible response to increased sea ice concentrations (SICs) over the Barents‐Kara Seas (BK) in previous winter. Increased winter SICs weaken the upward planetary waves and enhance the stratospheric polar vortex. In spring, the downward propagation of enhanced polar vortex intensifies the polar front jet, increasing kinetic energy gain of the North Atlantic wave train and guiding it to travel farther eastward. The Eurasian wave train strengthens through an upstream development and enhanced local baroclinicity and enhances subseasonal SAT variability over EC. Therefore, the state of BK SICs in previous winter could be a useful signal for the enhanced likelihood of spring extreme temperature whiplash events.

The Evolution of Ion Charge States in Coronal Mass Ejections

We model the observed charge states of the elements C, O, Mg, Si, and Fe in the ejecta of coronal mass ejections (CMEs). We concentrate on “halo” CMEs observed in situ by the Advanced Composition Explorer/Solar Wind Ion Composition Spectrometer to measure ion charge states, and also remotely by the Solar Terrestrial Relations Observatory when in near quadrature with the Earth, so that the CME expansion can be accurately specified. Within this observed expansion, we integrate equations for the CME ejecta ionization balance, including electron heating parameterized as a fraction of the kinetic and gravitational energy gain of the CME. We also include the effects of non-Maxwellian electron distributions, characterized as a κ function. Focusing first on the 2010 April 3 CME, we find a somewhat better match to the observed charge states with κ close to the theoretical minimum value of κ = 3/2, implying a hard spectrum of nonthermal electrons. Similar but more significant results come from the 2011 February 15 event, although it is quite different in terms of its evolution. We discuss the implications of these values, and of the heating required, in terms of the magnetic reconnection Lundquist number and anomalous resistivity associated with CME evolution close to the Sun.

Water Lifting and Outflow Gain of Kinetic Energy in Tropical Cyclones

Abstract While water lifting plays a recognized role in the global atmospheric power budget, estimates for this role in tropical cyclones vary from no effect to a major reduction in storm intensity. To better assess this impact, here we consider the work output of an infinitely narrow thermodynamic cycle with two streamlines connecting the top of the boundary layer in the vicinity of maximum wind (without assuming gradient-wind balance) to an arbitrary level in the inviscid free troposphere. The reduction of a storm’s maximum wind speed due to water lifting is found to decline with increasing efficiency of the cycle and is about 5% for maximum observed Carnot efficiencies. In the steady-state cycle, there is an extra heat input associated with the warming of precipitating water. The corresponding positive extra work is of an opposite sign and several times smaller than that due to water lifting. We also estimate the gain of kinetic energy in the outflow region. Contrary to previous assessments, this term is found to be large when the outflow radius is small (comparable to the radius of maximum wind). Using our framework, we show that Emanuel’s maximum potential intensity (E-PI) corresponds to a cycle where total work equals work performed at the top of the boundary layer (net work in the free troposphere is zero). This constrains a dependence between the outflow temperature and heat input at the point of maximum wind, but does not constrain the radial pressure gradient. We outline the implications of the established patterns for assessing real storms.

Disentangling the role of electrons and phonons in the photoinduced CO desorption and CO oxidation on (O,CO)-Ru(0001).

The role played by electronic and phononic excitations in the femtosecond laser induced desorption and oxidation of CO coadsorbed with O on Ru(0001) is investigated using ab initio molecular dynamics with electronic friction. To this aim, simulations that account for both kind of excitations and that only consider electronic excitations are performed. Results for three different surface coverages are obtained. We unequivocally demonstrate that CO desorption is governed by phononic excitations. In the case of oxidation the low statistics does not allow to give a categorical answer. However, the analysis of the adsorbates kinetic energy gain and displacements strongly suggest that phononic excitations and surface distortion also play an important role in the oxidation process.

A molecular simulation study on the sintering mechanism of TiO2

AbstractThe sintering process of TiO2 nanoparticles with different particle sizes and temperatures was studied thoroughly using equilibrium molecular dynamics simulations. The results show that when two nanoparticles contact, the sintering process was initiated by the merge of surface atoms of nanoparticles, and the process subsequently drives the internal atom to merge until two particles being merged homogeneously. There is mutual attraction between atoms and the particles gain kinetic energy to migrate due to the heating at high temperatures, leading to a faster sintering reaction. Moreover, there is a large difference in the sintering speed between 1600 and 1800 K. In the vicinity of the melting point, a small change in temperature makes a great impact on the sintering rate of TiO2 nanoparticles. Furthermore, by using the Lindemann index, it can be found that the larger particles have higher lattice structure stability compared to the smaller ones. The larger particle has a greater effect on the sintering behaviors when particles with different sizes’ contact. As a consequence, the sintering of two particles with different sizes is mainly initiated by the smaller particles moving toward the larger particle and is ended up with the atoms of smaller particle spreading around the larger particle. Therefore, the large nanoparticle size reduces the overall sintering rate.

Experimental investigation on flow boiling bubble motion under ultrasonic field in vertical minichannel by using bubble tracking algorithm

Bubble dynamics is important in flow boiling of minichannel, and ultrasonic field effects bubble behaviors. However, flow boiling bubble movements in minichannels under ultrasonic field have received little research attention and are still poorly understood. In this paper, the effects of ultrasonic field on bubble dynamics are experimentally studied by capturing the bubble motion behaviors of the flow boiling bubbles. The ultrasonic frequencies are set to 23, 28, 32, and 40kHz. Bubble tracking algorithm, which studies the growth, trajectories, velocities, and traveled distances for bubbles, is created to qualitatively describe bubble motion behavior of flow boiling in minichannel. It is found that after the application of ultrasound, the detachment frequency, velocity, and travel distance of the bubbles significantly increases, and the growth behavior and trajectory are extremely complex, the two-phase gas-liquid flow is extremely unstable. The bubbles gain kinetic energy as the ultrasound frequency increases. Finally, numerical simulations are used to quantitatively investigate the mechanism of bubble motion in microchannels under ultrasonic fields.

The fundamental concepts of the gravity-assist manoeuvre

A typical undergraduate course in mechanics does not cover the fascinating and important gravity-assist manoeuvre that allows satellites or other spacecrafts to navigate through our solar system on efficient and desired paths. Instead, it usually remains a mystery to students how energy is conserved when a spacecraft gains speed as it flies past a planet. Indeed, one might be led to believe that the curved path of the planet is the root cause for the gain in speed, requiring consideration of gravity-assist within the framework of the restricted three-body problem. This contribution will emphasize that this extension is not required to explain the gain in kinetic energy. Instead, a simple, scaffolded analysis of the planet-satellite system alone, using elementary physics, two reference frames and analytical methods, provides a sufficient explanation. Our simplified analysis is successfully validated against mission data from Voyager 2's gravity-assist manoeuvre around Jupiter.

Influence of wave height on round jet in regular waves: Direct numerical simulations

The influence of wave height on the dynamics of a turbulent round jet is analyzed using direct numerical simulation. The vortex dynamics associated with the interaction of the jet with waves of different heights is compared using the swirling strength criterion and the contours of vorticity. An analysis of the vortex roll-up frequency reveals that it increases with increasing wave height. With an increase in the wave height, the deflection of the jet elevates, and therefore, the span of the vortex rings in the near-field reduces in the direction of wave propagation. Further, an analysis of the braid region reveals that the number of lateral jets reduces to three with increasing wave height despite the number of counter-rotating vortex pairs remaining as four. The longer time evolution suggests that as the jet moves from the crest to the zero down-crossing, the fluid in the far-field gets detached from the main jet flow for the stronger waves. The evaluation of the preferred mode reveals that it remains helical for all wave heights. The proper orthogonal decomposition (POD) establishes that the highest energy is captured by the modes of the highest wave height. Also, as the wave height increases, a fewer number of modes capture 90% of the energy. Further, contours of POD modes represent the jet oscillations as well as the kinetic energy gain in the shear layer and the far-field. The time-averaged quantities quantitatively demonstrate an increase in mixing and entrainment in the jet as the wave height increases.

Ferromagnetic diagonal stripe states in the two-dimensional Hubbard model with U≲∞

We have performed a variational Monte Carlo simulation to study the ground state of a two-dimensional Hubbard model on a square lattice in the strong coupling region. The energy gain of possible inhomogeneous electron states are computed as a function of $U$ when the hole density $\epsilon=1/8$ and next nearest-neighbor hopping $t'/t=-0.30$. The bond-centered ferromagnetic diagonal stripe state is stabilized in the strong coupling region ($U/t\geq$16), which is due to the gain of both kinetic energy and on-site Coulomb interaction energy due to the holon moving over the ferromagnetic domain and the gain of kinetic-exchange-interaction energy at the antiferromagnetic domain wall.

Exclusion limits on dark matter-neutrino scattering cross section

We derive new constraints on combination of dark matter-electron cross section (${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$) and dark matter-neutrino cross section (${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$) utilizing the gain in kinetic energy of the dark matter (DM) particles due to scattering with the cosmic ray electrons and the diffuse supernova neutrino background (DSNB). Since the flux of the DSNB neutrinos is comparable to the cosmic ray (CR) electron flux in the energy range $\ensuremath{\sim}1\text{ }\text{ }\mathrm{MeV}--50\text{ }\text{ }\mathrm{MeV}$, scattering with the DSNB neutrinos can also boost low-mass DM significantly in addition to the boost due to interaction with the CR electrons. We use the XENON1T as well as the Super-Kamiokande data to derive bounds on ${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$ and ${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$. While our bounds for ${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$ are comparable with those in the literature, we show that the Super-Kamiokande experiment provides the strongest constraint on ${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$ for DM masses below a few MeV.

Interplay between adsorption, aggregation and diffusion in confined core-softened colloids

The behavior of colloidal particles with a hard core and a soft shell has attracted the attention for researchers in the physical-chemistry interface not only due to the large number of applications, but also owing to the unique properties of these systems, both in bulk and at interfaces. The adsorption at the two-phase boundary can provide information about the molecular arrangement. Thus, by Langevin Dynamics simulations, we have employed a recently obtained core-softened potential to analyze the relation between adsorption, structure and dynamic properties of the polymer-grafted nanoparticles near a solid repulsive surface. Two cases were considered: flat or structured walls. At low temperatures, a maximum is observed in the adsorption. It is related to a fluid to clusters transition and with a minimum in the contact layer diffusion - which is explained by the competition between the scales in the core-softened interaction. Due to the long range repulsion, the particles stay at the distance correspondent to this length scale at low densities, and overcome the repulsive barrier as the packing increases. However, by increasing the temperature, the gain in kinetic energy allows the colloids to overcome the long range repulsion barrier even at low densities. As a consequence, there is no competition and no maximum was observed in the adsorption.

The effects of laser polarization and wavelength on injection dynamics of a laser wakefield accelerator

Here, we investigate the effects of laser polarization and wavelength on electron injection dynamics in a laser wakefield accelerator. During the ionization process, electrons gain residual momentum and kinetic energy via above threshold ionization, which has a strong dependence on laser polarization. A circularly polarized laser pulse results in a much higher residual momentum and kinetic energy gain for the ionized electrons compared with the linearly polarized case. This residual momentum results in particle injection because of the sensitivity of particle trapping to the initial conditions and enhanced the total injected beam charge in both experiments and particle-in-cell simulations. Due to the strong correlation of above threshold ionization with laser wavelength, in this work we extended the investigation to long wavelength (up to 20 μm) drive pulses using particle-in-cell simulations. Owing to the gain in kinetic energy, it may be expected that the charge trapped would consistently increase for circular polarization with increasing laser wavelength, but this was not observed. Instead, there are oscillations with wavelength in the relative trapped charge between linear and circular polarization cases, which arise because of ionization and heating effects on the plasma. Our studies highlight the complex interplay between several different physical effects, including injection regimes—above threshold ionization assisted injection, wave-breaking injection by carrier-envelope-phase effects and ionization injection—ionization gradient induced laser pulse evolution, and thermal modifications to the wake structure that need considering when extrapolating laser wakefield acceleration to different wavelength regimes.

Coefficient of restitution: derivation of Newton’s experimental law from general energy considerations

In order to describe the velocity of two bodies after they collide, Newton developed a phenomenological equation known as ‘Newton’s experimental law’ (NEL). In this way, he was able to practically bypass the complication involving the details of the force that occurs during the collision of the two bodies. Today, we use NEL together with momentum conservation to predict each body’s velocity after collision. This, indeed, avoids the complication of knowing the forces involved in the collision, making NEL very useful. Whereas in Newton’s days the quantity of kinetic energy was not known, today it is a basic quantity that is in use. In this paper we will use the loss (or gain) of kinetic energy in a collision to show how NEL can be derived.

The Gauss pendulum

Recently, the Gauss rifle has gained attention as an interesting problem for physics and engineering education. In this manuscript we propose and analyze a novel problem that, while being related to the Gauss rifle, is rather simpler: the Gauss pendulum, which yields more consistent results and allows further agreement between model, simulation and experimental data. The Gauss pendulum, unlike the rifle, does not involve rotational movement of balls and the difference between the initial and final energy state of the system can be easily accessed by measuring the final height of the swinging projected ball. An extensive assessment of a Gauss pendulum has been developed using free software and accessible laboratory equipment. Focusing on the validation of the magnetic potential well model to understand the gain in kinetic energy, it was possible to obtain a remarkable agreement between the experimental and theoretically simulated data.

Direct Laser-Driven Electron Acceleration and Energy Gain in Helical Beams

A detailed study of direct laser-driven electron acceleration in paraxial Laguerre–Gaussian modes corresponding to helical beams LG0m with azimuthal modes m = {1,2,3,4,5} is presented. Due to the difference between the ponderomotive force of the fundamental Gaussian beam LG00 and helical beams LG0m, we found that the optimal beam waist leading to the most energetic electrons at full width at half maximum is more than twice smaller for the latter and corresponds to a few wavelengths Δw0 = {6,11,19}λ0 for laser powers of P0 = {0.1, 1,10} PW. We also found that, for azimuthal modes m ≥ 3, the optimal waist should be smaller than Δw0 < 19λ0. Using these optimal values, we have observed that the average kinetic energy gain of electrons is about an order of magnitude larger in helical beams compared to the fundamental Gaussian beam. This average energy gain increases with the azimuthal index m leading to collimated electrons of a few 100 MeV energy in the direction of the laser propagation.

Fermionic order by disorder in a van der Waals antiferromagnet

CeTe3 is a unique platform to investigate the itinerant magnetism in a van der Waals (vdW) coupled metal. Despite chemical pressure being a promising route to boost quantum fluctuation in this system, a systematic study on the chemical pressure effect on Ce3+(4f1) states is absent. Here, we report on the successful growth of a series of Se doped single crystals of CeTe3. We found a fluctuation driven exotic magnetic rotation from the usual easy-axis ordering to an unusual hard-axis ordering. Unlike in localized magnetic systems, near-critical magnetism can increase itinerancy hand-in-hand with enhancing fluctuation of magnetism. Thus, seemingly unstable hard-axis ordering emerges through kinetic energy gain, with the self-consistent observation of enhanced magnetic fluctuation (disorder). As far as we recognize, this order-by-disorder process in fermionic system is observed for the first time within vdW materials. Our finding opens a unique experimental platform for direct visualization of the rich quasiparticle Fermi surface deformation associated with the Fermionic order-by-disorder process. Also, the search for emergent exotic phases by further tuning of quantum fluctuation is suggested as a promising future challenge.

Bethe-Slater-curve-like behavior and interlayer spin-exchange coupling mechanisms in two-dimensional magnetic bilayers

Layered magnets have recently received tremendous attention, however, spin-exchange coupling mechanism across their interlayer regions is yet to be revealed. Here, we report a Bethe-Slater-curve (BSC) like behavior in nine transition metal dichalcogenide bilayers (MX2, M=V, Cr, Mn; X=S, Se, Te) and established interlayer spin-exchange coupling mechanisms at their van der Waals gaps using first-principle calculations. The BSC-like behavior offers a distance-dependent interlayer anti-ferromagnetic (AFM) to ferromagnetic (FM) transition. This phenomenon is explained with the spin-exchange coupling mechanisms established using bilayer CrSe2 as a prototype in this work. The Se pz wavefunctions from two adjacent interfacial Se sublayers overlap at the interlayer region. The spin alignment of the region determines interlayer magnetic coupling. At a shorter interlayer distance, Pauli repulsion at the overlapped region dominates and thus favors anti-parallel oriented spins leading to interlayer AFM. For a longer distance, kinetic energy gain of polarized electrons across the bilayer balances the Pauli repulsion and the bilayer thus prefers an interlayer FM state. In light of this, the AFM-FM transition is a result of competition between Pauli and Coulomb repulsion and kinetic energy gain. All these results open a new route to tune interlayer magnetism and the revealed spin-exchange coupling mechanisms are paramount additions to those previously established ones.

Blueshifts of high-order harmonic generation in crystalline silicon subjected to intense femtosecond near-infrared laser pulse

We present the generation of high order harmonics in crystalline silicon subjected to intense near-infrared 30fs laser pulses. The harmonic spectrum extends from the near infrared to the extreme ultraviolet spectral region. Depending on the pulsed laser intensity, we distinguish two regimes of harmonic generation: (i) perturbative regime: electron-hole pairs born during each half-cycle of the laser pulse via multiphoton and tunnel transitions are accelerated in the laser electric field and gain kinetic energy; the electron-hole pairs then recombine in the ground state by emitting a single high-energy photon. The resultant high harmonic spectrum consists of sharp peaks at odd harmonic orders. (ii) non-perturbative regime: the intensity of the harmonics increases, their spectral width broadens and the position of harmonics shifts to shorter wavelengths. The blueshifts of high harmonics in silicon are independent on the harmonic order which may be helpful in the design of continuously tunable XUV sources.

Nonadiabatic contributions to Bragg-regime dynamics in atomic Kapitza-Dirac scattering

Atomic Kapitza-Dirac Bragg regime scattering is a multiphoton process in which a neutral atom undergoes a change of momentum through an interaction with a coherent light source. When the Bragg conditions are met, the outgoing atom beams are spatially quantized. Counterpropagating lasers act as pump and probe scattering from far-off-resonant excited intermediate electronic states, leaving the atoms in the electronic ground state with quantized transverse momentum. Each nontrivial scattering event imparts transverse velocity and therefore kinetic energy to the deflected atoms through recoil. In the Bragg regime, the loss of energy in the light fields is equal to the gain of kinetic energy in the atom. Energy nonconserving intermediate states, which are described by nonadiabatic contributions, are not accounted for by first-order off-resonant states. By comparing the solutions of increasing orders of off-resonant intermediate states, it becomes clear that calculating the correct Pendell\"{o}sung frequencies and phases requires including an ever increasing number of off-resonant states in proportion to the square root of the field strength.