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We experimentally address the long-time dynamics of an artificially curved growth interface in directional solidification. Repetitive cell nucleations are found to appear in a disordered way but to eventually organize themselves coherently, at long times. This behavior is recovered by simulation of a nonlinear advection-diffusion model for the phase dynamics. The existence of a periodic attractor is shown by deriving a Liapunov functional for the cellular pattern organization on time ranges that include the singular events of cell nucleation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The distortion and break-up of a thin planar liquid film impacted by two gas jets while discharging from a twin-fluid atomizer is studied numerically. The gas momentum vector has components normal and parallel to the liquid stream. Viscosity and compressibility are neglected in both the liquid phase and the gas phase. The reduced-dimension (lubrication) approximation is employed to describe the nonlinear distortion and breakup of the thin film. The gas-phase dynamics are modelled by using a boundary-element-method formulation. For the considered parameter range and for a given energy expenditure, direct modulation of liquid-phase velocities at the nozzle exit is found to be more effective in causing film rupture than indirect modulation via adjacent impacting gas jets. In the former case, dilational film modulation results in shorter breakup lengths than sinuous modulation. On the other hand, for gas-jet modulated films, sinuous mode forcing is more effective than dilational forcing for the same energy input. Co-flowing gas streams significantly alter wavelengths and amplitudes of film disturbances generated by direct film modulation. Large ratios of gas-jet momentum to liquid-film momentum result in "immediate" film rupture in response to the dynamics of the impacting gas jets, whereas for lower ratios films disintegration occurs further downstream after continuous growth of the initial disturbances. Film distortion is characterized by the formation of fluid blobs or long band-like films depending on Weber number values and density ratio. [ABSTRACT FROM AUTHOR]

We demonstrate that the direction of coupling of two interacting self-sustained electronic oscillators can be determined from the realizations of their signals. In our experiments, two electronic generators, operating in a periodic or a chaotic state, were subject to symmetrical or unidirectional coupling. In data processing, first the phases have been extracted from the observed signals and then the directionality of coupling was quantitatively estimated from the analysis of mutual dependence of the phase dynamics. [ABSTRACT FROM AUTHOR]

Transient phase dynamics, synchronization, and desynchronization which are stimulus-locked (i.e., tightly time-locked to a repetitively administered stimulus) are studied in two coupled phase oscillators in the presence of noise. The presented method makes it possible to detect such processes in numerical and experimental signals. The time resolution is enormous, since it is only restricted by the sampling rate. Stochastic stimulus locking of the phases or the n:m phase difference at a particular time t relative to stimulus onset is defined by the presence of one or more prominent peaks in the cross-trial distribution of the phases or the n:m phase difference at time t relative to stimulus onset in an ensemble of poststimulus responses. The oscillators' coupling may cause a transient cross-trial response clustering of the poststimulus responses. In particular, the mechanism by which intrinsic noise induces symmetric antiphase cross-trial response clustering in coupled detuned oscillators is a stochastic resonance. Unlike the presented approach, both cross-trial averaging (where an ensemble of poststimulus responses is simply averaged) and cross-trial cross correlation (CTCC) lead to severe misinterpretations: Triggered averaging cannot distinguish a cross-trial response clustering or decorrelation from a mean amplitude decrease of the single responses. CTCC not only depends on the oscillators' phase difference but also on their phases and, thus, inevitably displays "artificial" oscillations that are not related to synchronization or desynchronization. [ABSTRACT FROM AUTHOR]

In the presence of an inhomogeneous oscillatory electric field, charged particles experience a net force, averaged over the oscillatory timescale, known as the ponderomotive force. We derive a one-dimensional Hamiltonian model which self-consistently couples the electromagnetic field to a plasma which experiences the ponderomotive force. We derive a family of structure preserving discretizations of the model of varying order in space and time using conforming and broken finite element exterior calculus spectral element methods. In all variants of our discretization framework, the method is found to conserve the Casimir invariants of the continuous model to machine precision and the energy to the order of the splitting method used. [ABSTRACT FROM AUTHOR]

Low-temperature anomalies of dielectric permittivity of S n 2 P 2 S 6 crystals were investigated. It is shown that these phenomena have a relaxation character and the observed anomalies could be related to the small hole polarons dynamics with donor-acceptor compensation processes in lattice with tin and sulfur vacancies. To confirm it, we measured the dielectric properties of tin-enriched and sulfur-enriched crystals. It is shown that deviation from stoichiometry leads to a significant change in the low-temperature anomalies of dielectric losses. [ABSTRACT FROM AUTHOR]

Biomass straw fuel has the advantage of low-carbon sustainability, and therefore, it has been widely used in recent years in coupled blending combustion with coal-fired utility boilers for power generation. At present, the drag force FD, the lift force FL, and the torque T evaluation model are very limited. In this study, within a wide range of Reynolds numbers (10 ≤ Re ≤ 2000) and incident angles (0° ≤ θ ≤ 90°), the computational fluid dynamics open source code OpenFOAM-body-fitted mesh method is used to carry out the direct numerical simulation of the flow characteristics of large cylindrical biomass particles with a high aspect ratio of L/D = 9:1. The results show that (1) the projected area of the cylinder begins to decrease after reaching the maximum at θ = 15°, while the change in the incident angle causes the formation of a smaller recirculation zone on the leeward side of the structure, and the effect of the pressure difference on the drag coefficient (CD) is reduced. (2) The lift coefficient (CL) displays a parabolic symmetric distribution when θ = 45°, and then the distribution becomes asymmetrical when Re > 100. The torque coefficient (CT) exhibits a similar trend. (3) Based on the simulation data and the literature data, new models for CD, CL, and CT for cylinders with L/D = 9:1, 10 ≤ Re ≤ 2000 and 0° ≤ θ ≤ 90° are obtained, and the mean square errors are 2.4 × 10−2, 1.4 × 10−2, and 6.4 × 10−2, respectively. This new model can improve the accuracy and adaptability of the universal model of gas–solid dynamics for biomass particles. [ABSTRACT FROM AUTHOR]

Single droplet impacts onto thin wall-films are a common phenomenon in many applications. For sufficiently high impact velocities, the droplet impact process consists of three phases, i.e., initial contact stage, droplet deformation with radial momentum transfer inducing an upward rising lamella, and crown propagation. Here, we present the results of a combined numerical and experimental study focusing on the early dynamics of the impact process. Specifically, the effects of the initial droplet shape, wall-film thickness, and contact line motion are analyzed. Prior to impact, an oblate spheroidal droplet shape was observed. Using direct numerical simulation, we show that the droplet shape affects the impact dynamics only during the first two phases, as it is one of the key parameter influencing the correct prediction of the impact zone. The contact line propagation is described by a square-root-time dependence R ¯ CL = α τ for both, dry and wetted surfaces. On dry surfaces, the advancement of the contact line is determined by the rolling motion of the truncated droplet. On wetted surfaces, the value of the α-parameter is controlled by two concurrent effects, namely, rolling motion and wall-film inertia. For impact onto thin films, the rolling motion prevails. With increasing wall-film height, the droplet penetrates into the soft substrates and wall-film inertia becomes the controlling factor. These insights into the early impact dynamics on wetted surface are important for the formulation of a unified modeling approach. [ABSTRACT FROM AUTHOR]

Networks of coupled nonlinear oscillators can display a wide range of emergent behaviors under the variation of the strength of the coupling. Network equations for pairs of coupled oscillators where the dynamics of each node is described by the evolution of its phase and slowest decaying isostable coordinate have previously been shown to capture bifurcations and dynamics of the network, which cannot be explained through standard phase reduction. An alternative framework using isostable coordinates to obtain higher-order phase reductions has also demonstrated a similar descriptive ability for two oscillators. In this work, we consider the phase-isostable network equations for an arbitrary but finite number of identical coupled oscillators, obtaining conditions required for the stability of phase-locked states including synchrony. For the mean-field complex Ginzburg–Landau equation where the solutions of the full system are known, we compare the accuracy of the phase-isostable network equations and higher-order phase reductions in capturing bifurcations of phase-locked states. We find the former to be the more accurate and, therefore, employ this to investigate the dynamics of globally linearly coupled networks of Morris–Lecar neuron models (both two and many nodes). We observe qualitative correspondence between results from numerical simulations of the full system and the phase-isostable description demonstrating that in both small and large networks, the phase-isostable framework is able to capture dynamics that the first-order phase description cannot. [ABSTRACT FROM AUTHOR]

Localized phenomena abound in nature and throughout the physical sciences. Some universal mechanisms for localization have been characterized, such as in the snaking bifurcations of localized steady states in pattern-forming partial differential equations. While much of this understanding has been targeted at steady states, recent studies have noted complex dynamical localization phenomena in systems of coupled oscillators. These localized states can come in the form of symmetry-breaking chimera patterns that exhibit coexistence of coherence and incoherence in symmetric networks of coupled oscillators and gap solitons emerging in the bandgap of parametrically driven networks of oscillators. Here, we report detailed numerical continuations of localized time-periodic states in systems of coupled oscillators, while also documenting the numerous bifurcations they give way to. We find novel routes to localization involving bifurcations of heteroclinic cycles in networks of Janus oscillators and strange bifurcation diagrams resembling chaotic tangles in a parametrically driven array of coupled pendula. We highlight the important role of discrete symmetries and the symmetric branch points that emerge in symmetric models. [ABSTRACT FROM AUTHOR]

We study macroscopic behavior of populations of quadratic integrate-and-fire neurons subject to non-Gaussian noises; we argue that these noises must be α -stable whenever they are delta-correlated (white). For the case of additive-in-voltage noise, we derive the governing equation of the dynamics of the characteristic function of the membrane voltage distribution and construct a linear-in-noise perturbation theory. Specifically for the recurrent network with global synaptic coupling, we theoretically calculate the observables: population-mean membrane voltage and firing rate. The theoretical results are underpinned by the results of numerical simulation for homogeneous and heterogeneous populations. The possibility of the generalization of the pseudocumulant approach to the case of a fractional α is examined for both irrational and fractional rational α. This examination seemingly suggests the pseudocumulant approach or its modifications to be employable only for the integer values of α = 1 (Cauchy noise) and 2 (Gaussian noise) within the physically meaningful range (0 ; 2 ]. Remarkably, the analysis for fractional α indirectly revealed that, for the Gaussian noise, the minimal asymptotically rigorous model reduction must involve three pseudocumulants and the two-pseudocumulant model reduction is an artificial approximation. This explains a surprising gain of accuracy for the three-pseudocumulant models as compared to the two-pseudocumulant ones reported in the literature. [ABSTRACT FROM AUTHOR]

Self-organization of radiation in random media is a key to controlling the optical energy flow and constitutes the basis of innovative cavity-free laser designs. Here, we theoretically demonstrate the existence of robust temporal dissipative soliton molecules in a graphene-based active disordered metamaterial. We observe that localized pulses with single and multiple peaks can coexist inside this metamaterial for a wide range of gain parameters, thereby exhibiting optical bistability. We further investigate the stability of such bound states under perturbation by analyzing their interaction force, finding stable tri-soliton molecule states with a periodically oscillating relative phase and a stable bi-soliton molecule. Our results offer a paradigm for mode-locking in active random metamaterials and pave the way for versatile applications such as multilevel encoding in optical communications, future designs of low-cost cavity-free lasers, and optical amplifiers. [ABSTRACT FROM AUTHOR]

We present trajectory simulation-based modeling to capture the interactions between ions and charged grains in dusty or complex plasmas. Our study is motivated by the need for a self-consistent and experimentally validated approach for accurately calculating the ion drag force and grain charge that determine grain collective behavior in plasmas. We implement Langevin dynamics in a computationally efficient predictor–corrector approach to capture multiscale ion and grain dynamics. Predictions of grain velocity, grain charge, and ion drag force are compared with prior measurements to assess our approach. The comparisons reveal excellent agreement to within ± 20 % between predicted and measured grain velocities [Yaroshenko et al., Phys. Plasmas 12, 093503 (2005) and Khrapak et al., Europhys. Lett. 97, 35001 (2012)] for 0.64 , 1.25 μ m grains at ∼ 20 − 500 Pa. Comparisons with the measured grain charge [Khrapak et al., Phys. Rev. E 72, 016406 (2005)] under similar conditions reveal agreement to within ∼ 20 % as well. Measurements of the ion drag force [Hirt et al., Phys. Plasmas 11, 5690 (2004); IEEE Trans. Plasma Sci. 32, 582 (2004)] are used to assess the viability of the presented approach to calculate the ion drag force experienced by grains exposed to ion beams of well-defined energy. Excellent agreement between calculations and measurements is obtained for beam energies >10 eV, and the overprediction below 10 eV is attributed to the neglect of charge exchange collisions in our modeling. Along with critical assessments of our approach, suggestions for future experimental design to probe charging of and momentum transfer onto grains that capture the effect of space charge concentration and external fields are outlined. [ABSTRACT FROM AUTHOR]

The essence of wind-blown sand movement is a particle movement system driven by high Reynolds number wall turbulence in the atmospheric surface layer (ASL). Understanding this phenomenon is crucial as the law and mechanism of sand movement have not been effectively revealed at present. In this study, we utilize the high-frequency time series data from the Oceano site, a renowned location for such studies, which includes streamwise wind velocity (u), wall-normal wind velocity (w), temperature (T), and total saltation mass flux (q) to delve deeper into wind-blown sand movement. The results indicate a positive correlation between T and w. Interestingly, this correlation not only escalates with height but also intensifies with the increase of the stratification stability parameters (z/L). Sand influences the intensity ratio of each quadrant to Reynolds stress without altering the time ratio. Both the ejection and sweep processes correlate well with z/L. Similarly, q also exhibits a good correlation with z/L. The buoyancy's impact on the low-frequency fluctuations of q might be through its effect on the low-frequency fluctuations of w, enhancing the sand transport capacity of w. This discovery holds profound implications for the study of two-phase flow in ASL and the precise prediction of surface sediment transport. [ABSTRACT FROM AUTHOR]

Spheres are the most studied water entry projectile due to their symmetry and simplicity, but in practical applications, it is rare that an impacting body is perfectly spherical. Perturbations to the classical impactor are thus critical for aligning fundamental investigation with more advanced engineering applications. This study investigates the water entry of hydrophilic and hydrophobic spheres with through-channels along the water entry axis and producing deep seal cavities. The channels allow water to pass through the sphere to create a jet tailing the sphere and hastening cavity pinch-off. Channeled spheres produce smaller cavities than their intact counterparts and suppress the onset of cavity formation. Spheres with channels show similar drag coefficients as solid, intact spheres. [ABSTRACT FROM AUTHOR]

This work deals with planar dynamical systems with and without noise. In the first part, we seek to gain a refined understanding of such systems by studying their differential-geometric transformation properties under an arbitrary smooth mapping. Using elementary techniques, we obtain a unified picture of different classes of dynamical systems, some of which are classically viewed as distinct. We specifically give two examples of Hamiltonian systems with first integrals, which are simultaneously gradient systems. Potential applications of this apparent duality are discussed. The second part of this study is concerned with ruling out closed orbits in steady planar systems. We reformulate Bendixson's criterion using the coordinate-independent Helmholtz decomposition derived in the first part, and we derive another, similar criterion. Our results allow for automated ruling out of closed orbits in certain regions of phase space and could be used in the future for efficient seeding of initial conditions in numerical algorithms to detect periodic solutions. [ABSTRACT FROM AUTHOR]

Thermogenesis, electro-chemical physiology (ECP), and electro-mechanical activities (EMAs) are fundamental facets of cellular functioning that are associated with powering, coherence, homeostasis, sensing, and response to stimuli. The classical Hodgkin–Huxley–Katz purview of ECP is derived from Nernst-based foundations for dilute solutions, whereas cellular milieus are mostly highly packed colloidal coacervates, with various types/levels of macromolecules (ions), interactions, and ordering of water. It has also been established that trans-membrane potential (TMP) manifestation can also be affected by adsorption of ions and effective charge separation (1e processes), necessitating the questioning and expansion of classical purviews. Further, we have demonstrated that the traditional explanation of electrogenic/stoichiometric and vitally deterministic bidirectional pumping/channeling of ions by membrane proteins (such as Na,K-ATPase) as the rationale for resting/dynamic TMP variations is untenable. In stark contrast, the murburn purview of ECP-EMAs acknowledges the complexity and discretization of the organization of water, ions, and macromolecules within the cell and does not solicit selective ion-pumping or TMP-based powering/propagation rationales. Herein, we summarize the murburn rationale for the molecular to macroscopic integration of processes such as thermogenesis, kinetic Na–K differentiation at the cell membrane, visual signal transduction and neuronal impulse relay, Complex V mediated mechano-chemostat function, flagella-based motility, etc., and discuss the alteration of cellular volume/tenor in muscle cell contraction. We assert that the membrane-embedded proteins/enzymes cannot use ATP to work against the natural laws of physics. Therefore, the classical perception of membrane-based ion pumps must be jettisoned to make way for the thermodynamics-friendly murburn purview. [ABSTRACT FROM AUTHOR]

This paper presents a peculiar nodal-shaped oscillation in vortex-induced vibration (VIV). This response is distinct from the commonly observed limit cycle oscillation in VIV and other aeroelastic problems. To gain insight into the dynamics in nodal-shaped oscillation, we conduct wind tunnel tests to investigate the VIV response of a freely oscillating rectangular cylinder with various transverse structural natural frequencies fs and wind speeds. The evolution of the flow field during nodal-shaped oscillation was examined using time-frequency analysis and modal analysis. During the divergent stage of the nodal-shaped oscillation, two modes, namely, the wake mode with a frequency of f = 1.28fs and the structure mode with a frequency of f = fs, were found to dominate the response of the flow. The two modes in VIV are coupled and compete with each other, diverging the oscillation of the structure. As the oscillation diverges and the amplitude increases to the maximum, the wake mode vanishes, which disengages the coupling of the fluid and structure modes. This stops the VIV and the oscillation decays until the wake mode reappears at f = 1.28fs. The above processes cycle over and over again, resulting in nodal-shaped (divergent-decay-divergent-decay) oscillation cycles. This finding explains the underlying dynamical mechanism of nodal-shaped oscillation and demonstrates the strong relationship between the wake mode and VIV. [ABSTRACT FROM AUTHOR]

The effects of Reynolds number (R e τ = 180 and 300), particle Stokes number (S t + = 0.5 , 50 , and 92), and fluid–solid phase coupling level (one-way, two-way, and four-way) on particle behavior in turbulent channel flows has been investigated using direct numerical simulation and Lagrangian particle tracking. Previous studies have used all these levels of coupling, but in terms of those employing four-way coupling, no consideration is given as to how emergent phenomena due to collision dynamics within a flow affect the way in which particles impart feedback to the continuous phase. In the present work, we relate the particle–particle interaction to particle–fluid coupling, as well as in assessing its relation to the Stokes number. As the Reynolds number increases and the turbulent region narrows, fewer particles retain their velocity as they migrate to the wall-region leading to reduced streamwise velocity fluctuations and preferential concentration. It is also evident that low Stokes number particles are capable of minor wall-accumulation at R e τ = 300. At this increased Reynolds number, four-way coupled simulations performed with moderate Stokes number particles (S t + = 50) are shown to diminish the effects of particle–fluid feedback, leading to similar fluid and particle statistics as the one-way coupled simulations. It is concluded that turbophoretic and preferential concentration effects are responsible for this phenomenon, since the increased collision rates due to larger concentrations of particles and velocity fluctuations in the wall-region correlate directly with the impact on the two-way coupling flow modifications. Analysis of the collision dynamics also indicates particles colliding with increased relative velocities and angles, which cause larger momentum transfer and directional redistribution, increasing and redirecting slip velocities. It is concluded that for midrange Stokes numbers, four-way coupling is imperative to increase simulation accuracy beyond that obtained assuming one-way coupling. [ABSTRACT FROM AUTHOR]

This study presents droplet dynamics in a rough capillary channel. Prior studies investigating the effect of roughness on fluid flow have mainly considered a continuous phase whose behavior is different from a discontinuous phase, i.e., an oil slug. To explore the dynamic behavior of droplet motion across a rough channel, a direct numerical simulation of in a three-dimensional channel is performed. Three models have been considered: model A had a rough surface only on the bottom walls, model B on both the bottom and top walls, and model C on all walls. The results show that in contrast with common observations, roughness promotes droplet mobility in comparison with smooth walls. The presence of roughness results to an additional energy required to move the droplet, and the degree of confinement increases with the roughness; thus, the difficult of mobilization increases with the increase in roughness. Different roughness parameter effects have been investigated. The results have shown that the critical pressure increases with the increase in the pillar's height and decreases with the pillars spacing. The offset leads to a decrease in flow resistance for larger contact angles. We noted also that it is more difficult to mobilize a discontinuous phase in a neutral-wet surface condition. Furthermore, discontinuous pillars in the lateral direction led to much higher resistance. Through our comprehensive numerical study, we provide valuable insights into the impact of roughness in capillary channels. These findings can be used as guidelines for designing droplet flow on complex and rough surfaces, such as microfluidic devices, and hold significant relevance in the optimization of droplet control strategies in enhanced oil recovery methods. [ABSTRACT FROM AUTHOR]

It has been a long-standing problem how schooling fish optimize their motion by exploiting the vortices shed by the others. A recent experimental study showed that a pair of fish reduce energy consumption by matching the phases of their tailbeat according to their distance. In order to elucidate the dynamical mechanism by which fish control the motion of caudal fins via vortex-mediated hydrodynamic interactions, we introduce a new model of a self-propelled swimmer with an active flapping plate. The model incorporates the role of the central pattern generator network that generates rhythmic but noisy activity of the caudal muscle, in addition to hydrodynamic and elastic torques on the fin. For a solitary fish, the model reproduces a linear relation between the swimming speed and tailbeat frequency, as well as the distributions of the speed, tailbeat amplitude, and frequency. For a pair of fish, both the distribution function and energy dissipation rate exhibit periodic patterns as functions of the front-back distance and phase difference of the flapping motion. We show that a pair of fish spontaneously adjust their distance and phase difference via hydrodynamic interaction to reduce energy consumption. [ABSTRACT FROM AUTHOR]

Synchronization study allows a better understanding of the exchange of information among systems. In this work, we study experimental data recorded from a set of Rössler-like chaotic electronic oscillators arranged in a complex network, where the interactions between the oscillators are given in terms of a connectivity matrix, and their intensity is controlled by a global coupling parameter. We use the zero and one persistent homology groups to characterize the point clouds obtained from the signals recorded in pairs of oscillators. We show that the normalized persistent entropy (N P E) allows us to characterize the effective coupling between pairs of oscillators because it tends to increase with the coupling strength and to decrease with the distance between the oscillators. We also observed that pairs of oscillators that have similar degrees and are nearest neighbors tend to have higher N P E values than pairs with different degrees. However, large variability is found in the N P E values. Comparing the N P E behavior with that of the phase-locking value (P L V , commonly used to evaluate the synchronization of phase oscillators), we find that for large enough coupling, P L V only displays a monotonic increase, while N P E shows a richer behavior that captures variations in the behavior of the oscillators. This is due to the fact that P L V only captures coupling-induced phase changes, while N P E also captures amplitude changes. Moreover, when we consider the same network but with Kuramoto phase oscillators, we also find that N P E captures the transition to synchronization (as it increases with the coupling strength), and it also decreases with the distance between the oscillators. Therefore, we propose N P E as a data analysis technique to try to differentiate pairs of oscillators that have strong effective coupling because they are first or near neighbors, from those that have weaker coupling because they are distant neighbors. [ABSTRACT FROM AUTHOR]

Nonadiabatic molecular dynamics occur in a wide range of chemical reactions and femtochemistry experiments involving electronically excited states. These dynamics are hard to treat numerically as the system's complexity increases, and it is thus desirable to have accurate yet affordable methods for their simulation. Here, we introduce a linearized semiclassical method, the generalized discrete truncated Wigner approximation (GDTWA), which is well-established in the context of quantum spin lattice systems, into the arena of chemical nonadiabatic systems. In contrast to traditional continuous mapping approaches, e.g., the Meyer–Miller–Stock–Thoss and the spin mappings, GDTWA samples the electron degrees of freedom in a discrete phase space and thus forbids an unphysical unbounded growth of electronic state populations. The discrete sampling also accounts for an effective reduced but non-vanishing zero-point energy without an explicit parameter, which makes it possible to treat the identity operator and other operators on an equal footing. As numerical benchmarks on two linear vibronic coupling models and Tully's models show, GDTWA has a satisfactory accuracy in a wide parameter regime, independent of whether the dynamics is dominated by relaxation or by coherent interactions. Our results suggest that the method can be very adequate to treat challenging nonadiabatic dynamics problems in chemistry and related fields. [ABSTRACT FROM AUTHOR]

A theoretical and experimental study of the gas phase and liquid acetic acid based on resonant inelastic x-ray scattering (RIXS) spectroscopy is presented. We combine and compare different levels of theory for an isolated molecule for a comprehensive analysis, including electronic and vibrational degrees of freedom. The excitation energy scan over the oxygen K-edge absorption reveals nuclear dynamic effects in the core-excited and final electronic states. The theoretical simulations for the monomer and two different forms of the dimer are compared against high-resolution experimental data for pure liquid acetic acid. We show that the theoretical model based on a dimer describes the hydrogen bond formation in the liquid phase well and that this bond formation sufficiently alters the RIXS spectra, allowing us to trace these effects directly from the experiment. Multimode vibrational dynamics is accounted for in our simulations by using a hybrid time-dependent stationary approach for the quantum nuclear wave packet simulations, showing the important role it plays in RIXS. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy is used to address the remarkable persistence of the native Arrhenius dependence of the 2-aminopropanol substrate radical rearrangement reaction in B12-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium from physiological to cryogenic (220 K) temperatures. Two-component TEMPOL spin probe mobility in the presence of 10 mM (0.08% v/v) 2-aminopropanol over 200–265 K demonstrates characteristic concentric aqueous-cosolvent mesodomain and protein-associated domain (PAD, hydration layer) solvent phases around EAL in the frozen solution. The mesodomain formed by the relatively small amount of 2-aminopropanol is highly confined, as shown by an elevated temperature for the order–disorder transition (ODT) in the PAD (230–235 K) and large activation energy for TEMPOL rotation. Addition of 2% v/v dimethylsulfoxide expands the mesodomain, partially relieves PAD confinement, and leads to an ODT at 205–210 K. The ODT is also manifested as a deviation of the temperature-dependence of the EPR amplitude of cob(II)alamin and the substrate radical, bound in the enzyme active site, from Curie law behavior. This is attributed to an increase in sample dielectric permittivity above the ODT at the microwave frequency of 9.5 GHz. The relatively high frequency dielectric response indicates an origin in coupled protein surface group–water fluctuations of the Johari–Goldstein β type that span spatial scales of ∼0.1–10 Å on temporal scales of 10−10–10−7 s. The orthogonal EPR spin probe rotational mobility and solvent dielectric measurements characterize features of EAL protein–solvent dynamical coupling and reveal that excess substrate acts as a fluidizing cryosolvent to enable native enzyme reactivity at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

In plasma–liquid interactions, the phenomenon of induced liquid flow that originates at the plasma–liquid contact point is important in that it influences mass, charge, and heat transport from the source to the surrounding bulk fluid. Such stimulated flows have been observed in 1 atm glows with a liquid anode. Because the plasma contact point in such discharges is patterned, a natural question is what is the relationship between the observed self-organized patterns and the induced flow field? It is, therefore, of great interest to investigate the coupling mechanism between the self-organization patterns in an atmospheric pressure dc helium glow discharge with a liquid anode and the induced flow circulation. Particle imaging velocimetry is used to probe the flow fields in the plane normal and parallel to the plasma–liquid interface. A strong ascending flow with maximum speed up to 1.5 cm/s and circulation vortices nearby are observed in the plane normal to the interface centered at the plasma attachment. The experiment results suggested that the ascending flow is caused by water evaporation and the vortices are formed by viscous stress. With a self-organization pattern formed, the flow structures become non-static and the circulation vortices are observed to periodically form and decay. In the plane parallel to the interface, a strong swirl flow was found to exist only when the plasma attachment is self-organized. The analysis revealed that the driving mechanism could be the electrohydrodynamics force. Averaged flow velocity over time in the field of view was found to scale linearly with increasing input power and increasing liquid conductivity. [ABSTRACT FROM AUTHOR]

Infrared spectroscopic studies of weakly bound clusters isolated in solid parahydrogen (pH2) that exhibit large-amplitude tunneling motions are needed to probe how quantum solvation perturbs these types of coherent dynamics. We report high resolution Fourier transform infrared absorption spectra of (HCl)2, HCl–DCl, and (DCl)2 isolated in solid pH2 in the 2.4–4.8 K temperature range. The (HCl)2 spectra show a remarkable amount of fine structures that can be rigorously assigned to vibration–rotation–tunneling transitions of (HCl)2 trapped in double substitution sites in the pH2 matrix where end-over-end rotation of the cluster is quenched. The spectra are assigned using a combination of isotopically (H/D and 35Cl/37Cl) enriched samples, polarized IR absorption measurements, and four-line combination differences. The interchange-tunneling (IT) splitting in the ground vibrational state for in-plane and out-of-plane H35Cl–H37Cl dimers is 6.026(1) and 6.950(1) cm−1, respectively, which are factors of 2.565 and 2.224 smaller than in the gas phase dimer. In contrast, the (DCl)2 results show larger perturbations where the ground vibrational state IT splitting in D35Cl–D37Cl is 1.141(1) cm−1, which is a factor of 5.223 smaller than in the gas phase, and the tunneling motion is quenched in excited intramolecular vibrational states. The results are compared to similar measurements on (HCl)2 made in liquid helium nanodroplets to illustrate the similarities and differences in how both these quantum solvents interact with large amplitude tunneling motions of an embedded chromophore. [ABSTRACT FROM AUTHOR]

We consider a network of coupled oscillating units, where each unit comprises a self-oscillating polymer gel undergoing the Belousov-Zhabotinsky (BZ) reaction and an overlaying piezoelectric (PZ) cantilever. Through chemo-mechano-electrical coupling, the oscillations of the networked BZ-PZ units achieve in-phase or anti-phase synchronization, enabling, for example, the storage of information within the system. Herein, we develop numerical and computational models to show that the introduction of capacitors into the BZ-PZ system enhances the dynamical behavior of the oscillating network by yielding additional stable synchronization modes. We specifically show that the capacitors lead to a redistribution of charge in the system and alteration of the force that the PZ cantilevers apply to the underlying gel. Hence, the capacitors modify the strength of the coupling between the oscillators in the network. We utilize a linear stability analysis to determine the phase behavior of BZ-PZ networks encompassing different capacitances, force polarities, and number of units and then verify our findings with numerical simulations. Thus, through analytical calculations and numerical simulations, we determine the impact of the capacitors on the existence of the synchronization modes, their stability, and the rate of synchronization within these complex dynamical systems. The findings from our study can be used to design robotic materials that harness the materials' intrinsic, responsive properties to perform such functions as sensing, actuation, and information storage. [ABSTRACT FROM AUTHOR]

The p53 transcription factor is a key mediator in cellular responses to various stress signals including DNA repair, cell cycle arrest, and apoptosis. In this work, we employ landscape and flux theory to investigate underlying mechanisms of p53-regulated cell fate decisions. Based on a p53 regulatory network, we quantified the potential landscape and probabilistic flux for the p53 system. The landscape topography unifies and quantifies three cell fate states, including the limit cycle oscillations (representing cell cycle arrest), high p53 state (characterizing apoptosis), and low p53 state (characterizing the normal proliferative state). Landscape and flux results provide a quantitative explanation for the biphasic dynamics of the p53 system. In the oscillatory phase (first phase), the landscape attracts the system into the ring valley and flux drives the system cyclically moving, leading to cell cycle arrest. In the fate decision-making phase (second phase), the ring valley shape of the landscape provides an efficient way for cells to return to the normal proliferative state once DNA damage is repaired. If the damage is unrepairable with larger flux, the system may cross the barrier between two states and switch to the apoptotic state with a high p53 level. By landscape-flux decomposition, we revealed a trade-off between stability (guaranteed by landscape) and function (driven by flux) in cellular systems. Cells need to keep a balance between appropriate speed to repair DNA damage and appropriate stability to survive. This is further supported by flux landscape analysis showing that flux may provide the dynamical origin of phase transition in a non-equilibrium system by changing landscape topography. [ABSTRACT FROM AUTHOR]

The linear and weakly nonlinear stability of flow in the Taylor-Dean system is investigated. The base flow far from the boundaries, is a superposition of circular Couette and curved channel Poiseuille flows. The computations provide for a finite gap system, critical values of Taylor numbers, wave numbers and wave speeds for the primary transitions. Moreover, comparisons are made with results obtained in the small gap approximation. It is shown that the occurrence of oscillatory nonaxisymmetric modes depends on the "anisotropy" coefficient in the dispersion relation, and that the critical Taylor number changes slightly with the azimuthal wave number for large absolute values of rotation ratio. The weakly nonlinear analysis is made in the framework of the Ginzburg-Landau equations for anisotropic systems. The primary bifurcation towards stationary or traveling rolls is supercritical when Poiseuille component of the base flow is produced by a partial filling. An external pumping can induce a subcritical bifurcation for a finite range of rotation ratio. Special attention is also given to the influence of anisotropy properties on the phase dynamics of bifurcated solution (Eckhaus and Benjamin-Feir conditions). [ABSTRACT FROM AUTHOR]

We investigate memory effects in barrier-crossing in the overdamped setting. We focus on the scenario where the hidden degrees of freedom relax on exactly the same time scale as the observable. As a prototypical model, we analyze tagged-particle diffusion in a single file confined to a bi-stable potential. We identify the signatures of memory and explain their origin. The emerging memory is a result of the projection of collective many-body eigenmodes onto the motion of a tagged-particle. We are interested in the "confining" (all background particles in front of the tagged-particle) and "pushing" (all background particles behind the tagged-particle) scenarios for which we find non-trivial and qualitatively different relaxation behaviors. Notably and somewhat unexpectedly, at a fixed particle number, we find that the higher the barrier, the stronger the memory effects are. The fact that the external potential alters the memory is important more generally and should be taken into account in applications of generalized Langevin equations. Our results can readily be tested experimentally and may be relevant for understanding transport in biological ion-channels. [ABSTRACT FROM AUTHOR]

Hybrid dynamic systems have recently gained interest with respect to both fundamental physics and device applications, particularly with their potential for coherent information processing. In this perspective, we will focus on the recent rapid developments of magnon-based hybrid systems, which seek to combine magnonic excitations with diverse excitations for transformative applications in devices, circuits, and information processing. Key to their promising potentials is that magnons are highly tunable excitations and can be easily engineered to couple with various dynamic media and platforms. The capability of reaching strong coupling with many different excitations has positioned magnons well for studying solid-state coherent dynamics and exploiting unique functionality. In addition, with their gigahertz frequency bandwidth and the ease of fabrication and miniaturization, magnonic devices and systems can be conveniently integrated into microwave circuits for mimicking a broad range of device concepts that have been applied in microwave electronics, photonics, and quantum information. We will discuss a few potential directions for advancing magnon hybrid systems, including on-chip geometry, novel coherent magnonic functionality, and coherent transduction between different platforms. As a future outlook, we will discuss the opportunities and challenges of magnonic hybrid systems for their applications in quantum information and magnonic logic. [ABSTRACT FROM AUTHOR]

Water is at the heart of almost all biological phenomena, without which no life that we know of would have been possible. It is a misleadingly complex liquid that exists in near coexistence with the vapor phase under ambient conditions. Confinement within a hydrophobic cavity can tip this balance enough to drive a cooperative dewetting transition. For a nanometer-scale pore, the dewetting transition leads to a stable dry state that is physically open but impermeable to ions. This phenomenon is often referred to as hydrophobic gating. Numerous transmembrane protein ion channels have now been observed to utilize hydrophobic gating in their activation and regulation. Here, we review recent theoretical, simulation, and experimental studies that together have started to establish the principles of hydrophobic gating and discuss how channels of various sizes, topologies, and biological functions can utilize these principles to control the thermodynamic properties of water within their interior pores for gating and regulation. Exciting opportunities remain in multiple areas, particularly on direct experimental detection of hydrophobic dewetting in biological channels and on understanding how the cell may control the hydrophobic gating in regulation of ion channels. [ABSTRACT FROM AUTHOR]

The characterization of an ionic liquid's properties based on structural information is a longstanding goal of computational chemistry, which has received much focus from ab initio and molecular dynamics calculations. This work examines kernel ridge regression models built from an experimental dataset of 2212 ionic liquid melting points consisting of diverse ion types. Structural descriptors, which have been shown to predict quantum mechanical properties of small neutral molecules within chemical accuracy, benefit from the addition of first-principles data related to the target property (molecular orbital energy, charge density profile, and interaction energy based on the geometry of a single ion pair) when predicting the melting point of ionic liquids. Out of the two chosen structural descriptors, ECFP4 circular fingerprints and the Coulomb matrix, the addition of molecular orbital energies and all quantum mechanical data to each descriptor, respectively, increases the accuracy of surrogate models for melting point prediction compared to using the structural descriptors alone. The best model, based on ECFP4 and molecular orbital energies, predicts ionic liquid melting points with an average mean absolute error of 29 K and, unlike group contribution methods, which have achieved similar results, is applicable to any type of ionic liquid. [ABSTRACT FROM AUTHOR]

Photoelectron–photofragment coincidence (PPC) spectroscopy is used to study the photodetachment, photodissociation, and dissociative photodetachment (DPD) of I2Br−, IBr2−, I2Cl−, and ICl2− at 266 nm. The mixed trihalides are asymmetric analogs of the well-studied I3− anion, with distinguishable dissociation asymptotes and the potential for selective bond breaking. The high beam energy PPC spectrometer used in this study couples an electrospray ionization source, a hexapole accumulation ion trap, and a linear accelerator to produce a 21 keV beam of a particular trihalide. Total, stable, and dissociative photoelectron spectra have been recorded for all the anions, except ICl2− that does not photodetach at 266 nm. A bound ground state (X) is observed for all the anions, and a dissociative first excited (A) state is also seen for I2Br− and I2Cl− at low electron kinetic energies (eKE). A 258 nm photoelectron spectrum recorded for I2Br− and I2Cl− rules out autodetachment of a dipole-bound state as the origin of the low eKE feature. The threshold detachment energy (TDE) of I2X− to the X state of the radical is similar to I3−, whereas the TDE to the radical A state increases with substitution of iodine for a lighter halogen. Two-body DPD is observed for I2Br− and I2Cl−, resulting in IBr/ICl + I + e−. For IBr2− and ICl2−, the charge symmetric three-body photodissociation of [Br–I–Br]− and [Cl–I–Cl]− is seen yielding Br + Br and Br + Br*, and Cl + Cl and Cl + Cl* neutral fragments. Evidence for the minimum energy anion structure is observed in all cases, where the iodine atom is located at the center of the trihalide. [ABSTRACT FROM AUTHOR]

The low melting point of room temperature ionic liquids is usually explained in terms of the presence of bulky, low-symmetry, and flexible ions, with the first two factors related to the lattice energy while an entropic effect is attributed to the latter. By means of molecular dynamics simulations, the melting points of 1-ethyl-3-methyl-imidazolium hexafluorophosphate and 1-decyl-3-methyl-imidazolium hexafluorophosphate were determined, and the effect of the molecular flexibility over the melting point was explicitly computed by restraining the rotation of dihedral angles in both the solid and the liquid phases. The rotational flexibility over the bond between the ring and the alkyl chain affects the relative ordering of the anions around the cations and results in substantial effects over both the enthalpy and the entropy of melting. For the other dihedral angles of the alkyl group, the contributions are predominantly entropic and an alternating behavior was found. The flexibility of some dihedral angles has negligible effects on the melting point, while others can lead to differences in the melting point as large as 20 K. This alternating behavior is rationalized by the different probabilities of conformation defects in the crystal. [ABSTRACT FROM AUTHOR]

Rotationally resolved electronic spectra of two conformational isomers of jet-cooled indole-4-carboxylic acid (I4CA) and the deuterated forms of the acid (—COOD) and amide (—ND) groups have been obtained using a UV laser/molecular beam spectrometer. The in-plane orientation of the acid group defines the two lowest energy rotamers of I4CA. The S1 ← S0 origin bands of the two rotamers and four isotopologues have been fit to asymmetric rotor Hamiltonians in both electronic states. From the best-fit parameters, the positions of the H-atoms in the principal axis frames of each conformer have been determined and serve to unambiguously identify the syn forms (i.e., COH⋯O) of the cis and trans rotamers. The experimental S0 and S1 inertial parameters, hydrogen atom positions, and transition dipole moment (TDM) orientations are compared with the results of theoretical calculations. The TDM orientation indicates that the S1 state is the 1La state in contrast to most substituted indoles. The molecular orbital properties and natural charges are investigated to better understand the 1La/1Lb state reversal and the extent of photoinduced intramolecular charge transfer that impacts the rotamer-dependent fluorescence lifetimes. [ABSTRACT FROM AUTHOR]

Recent experiments have shown how nematically ordered tactoid shaped actin droplets can be reorganized and divided by the action of myosin molecular motors. In this paper, we consider how similar morphological changes can potentially be achieved under equilibrium conditions. Using simulations, both atomistic and continuum, and a simple macroscopic model, we explore how the nucleation dynamics, shape changes, and the final steady state of a nematic tactoid droplet can be modified by interactions with model adhesive colloids that mimic a myosin motor cluster. We show how tactoid reorganization may occur in an equilibrium colloidal-nematic setting. We then suggest based on the simple macroscopic model how the simulation models may be extended to potentially stabilize divided tactoids. [ABSTRACT FROM AUTHOR]

The influence of ring-puckering on the light-induced ring-opening dynamics of heterocyclic compounds was studied on the sample 5-membered ring molecules γ-valerolactone and 5H-furan-2-one using time-resolved photoelectron spectroscopy and ab initio molecular dynamics simulations. In γ-valerolactone, ring-puckering is not a viable relaxation channel and the only available reaction pathway is ring-opening, which occurs within one vibrational period along the C—O bond. In 5H-furan-2-one, the C=C double bond in the ring allows for ring-puckering which slows down the ring-opening process by about 150 fs while only marginally reducing its quantum yield. This demonstrates that ring-puckering is an ultrafast process, which is directly accessible upon excitation and which spreads the excited state wave packet quickly enough to influence even the outcome of an otherwise expectedly direct ring-opening reaction. [ABSTRACT FROM AUTHOR]

Granular aluminum (grAl) is an applied quantum material. We present nano-superconducting quantum interference devices (nanoSQUIDs) based on grAl thin films. These devices exhibit non-hysteretic behavior, allowing conventional SQUID readout down to temperatures well below the critical temperature as well as detection properties comparable to those of Dayem bridge-based devices of greater complexity. Despite being much longer than the coherence length, the current–phase relation of these grAl constrictions appears to be single valued at least down to half their critical temperature. This suggests that grAl thin films should be described as a network of inter-grain Josephson junctions. [ABSTRACT FROM AUTHOR]

The two-dimensional solutions and stability analysis are presented for an evaporating thin viscous liquid film flowing inside a uniformly heated rotating horizontal cylinder. A non-linear, fourth-order, partial differential evolution equation is obtained by simplifying mass, momentum, and energy conservation equations within the lubrication approximation. The effect of evaporation, gravity, viscous drag, surface tension, thermocapillary stress, and intermolecular forces has been taken into account. The numerical solutions of the model are validated against the existing experimental as well as the numerical results, along with the analytical result for the limiting cases of the present model. The film thickness model is solved to elucidate two-dimensional spatiotemporal solutions and their stability for a wide range of thermal and other parameters. The evaporative mass flux at the liquid–air interface results in unsteady solutions which are oscillatory in nature, and the amplitude of the oscillations increases with an increase in the evaporative flux. The film ruptures after some time and the rupture time is found to be inversely proportional to the evaporation number, a non-dimensional number quantifying the rate of evaporation. The linear stability analysis shows that the thermocapillary stresses as well as the long-range molecular forces destabilize the film. A negative disjoining pressure is shown to reduce the rupture time and vice versa. Evaporation (condensation) plays a destabilizing (stabilizing) role in the thin film flow. Non-linear computations are carried out for the steady profiles, validating the growth rates obtained from the linear stability analysis. [ABSTRACT FROM AUTHOR]

We present a phase-amplitude reduction framework for analyzing collective oscillations in networked dynamical systems. The framework, which builds on the phase reduction method, takes into account not only the collective dynamics on the limit cycle but also deviations from it by introducing amplitude variables and using them with the phase variable. The framework allows us to study how networks react to applied inputs or coupling, including their synchronization and phase locking, while capturing the deviations of the network states from the unperturbed dynamics. Numerical simulations are used to demonstrate the effectiveness of the framework for networks composed of FitzHugh–Nagumo elements. The resulting phase-amplitude equations can be used in deriving optimal periodic waveforms or introducing feedback control for achieving fast phase locking while stabilizing the collective oscillations. [ABSTRACT FROM AUTHOR]

Phase reduction is a general approach to describe coupled oscillatory units in terms of their phases, assuming that the amplitudes are enslaved. The coupling should be small for such reduction, but one also expects the reduction to be valid for finite coupling. This paper presents a general framework, allowing us to obtain coupling terms in higher orders of the coupling parameter for generic two-dimensional oscillators and arbitrary coupling terms. The theory is illustrated with an accurate prediction of Arnold's tongue for the van der Pol oscillator exploiting higher-order phase reduction. [ABSTRACT FROM AUTHOR]

The superthermality indices of positron (electron) contributions to the new nonlinear wave profiles characterized by the model as supersoliton, cnoidal, shocklike, and super-periodic wave propagation have been obtained in the superthermal ionosphere plasma pair. These profiles that exhibit critical behaviors are described by the modified KP equation. Furthermore, the novel solutions have been exposed and the super-solitary and period solutions are derived and explained using the Jacobi elliptic function expansion method for the Modified Korteweg–De Vries (MKdV) equation. These solutions may be useful in the space of ionosphere fluids. Indeed, the MKdV model is potent for the dynamics of fluid flow. The super propagating waves obtained under the influence of critical densities represent a source of forcing or collapsing energy waves in space plasma fluids. To check the impacts of superthermality on the progress of nonlinear formations, all the given solutions are deliberated by the superthermal factor in ionosphere fluid observations and applications. [ABSTRACT FROM AUTHOR]

The escape rate of S→R switching (from superconducting S state to unstable resistive R state) in an ac SQUID with Josephson junction based on single- and multi-band superconductors is investigated by taking the frustration effects in a multi-band superconducting state into account. Using the effective critical current approach, it is shown that the escape rate in thermal activation regime can manifest qualitative features caused by the frustration effects in two- and three-band superconductors. [ABSTRACT FROM AUTHOR]

The main contribution of this study is the effects of the operating conditions on the internal vapor pressure and temperature in an annular screen wick heat pipe, using distilled water as the working fluid. High-resolution pressure transducers, optical fiber distributed temperature sensors, and K-type thermocouples were employed to measure the internal and external temperatures as well as the local static pressures at different axial positions of the heat pipe. Temporal and frequency analysis using a one-dimensional continuous wavelet transform was performed on the differential pressure data to characterize flow behavior and infer the flow regime occurring within the heat pipe. The heat pipe was tested in multiple orientations with respect to the horizon (θ = 0 ° , 45 ° , and 90 °), heat loads (25, 50, and 75 W), and condenser coolant temperatures ( T w , i n = 10 ° C , 20 ° C , and 30 ° C). To estimate the vapor-phase flow friction factor for multiple Reynolds numbers, the Lockhart–Martinelli correlation was employed. This study provides critical experimental data and analyses for complex two-phase flow behavior in an annular wick heat pipe geometry. The thermal resistance and effective thermal conductivity were estimated as a function of the heat pipe orientation and power input. The experimental investigation revealed that power input and orientation influence both the internal vapor core and external surface temperatures, as well as the local pressure response. The outcomes from this study provide a valuable database that supports the advancement of heat pipe design, modeling, and validation. [ABSTRACT FROM AUTHOR]

How complex patterns generated by neural systems are represented in individual neuronal activity is an essential problem in computational neuroscience as well as machine learning communities. Here, based on recurrent neural networks in the form of feedback reservoir computers, we show microscopic features resulting in generating spatiotemporal patterns including multicluster and chimera states. We show the effect of individual neural trajectories as well as whole-network activity distributions on exhibiting particular regimes. In addition, we address the question how trained output weights contribute to the autonomous multidimensional dynamics. [ABSTRACT FROM AUTHOR]

One of the most characteristic features of relativistic particle dynamics at cyclotron resonances is the stepwise dependence of energy and momentum on time [V. A. Buts and A. G. Zagorodny, Phys. Plasmas 28(2), 022311 (2021)]. The reason for these steps is the phase synchronization of charged particles and waves. To describe other features, we introduce new dependent variables in this paper. These variables allow us to find a convenient representation of the relativistic resonance that fits the numerical results and thus establish new expressions for the stationary phase, as well as analytically describe effects that were previously visible only in numerical experiment. In particular, the temporal width of the steps, the dynamics of particles on the steps, and, most importantly, the moments of random jumps of particles from one step to another are determined. Analysis of the obtained results opens the possibility to find the conditions for the unlimited acceleration of electrons by transverse electromagnetic waves in a vacuum without an external magnetic field. [ABSTRACT FROM AUTHOR]