Relative Separation Distance Research Articles

Impacts of an Upper Tropospheric Cold Low on Tropical Cyclone Intensity

Abstract Following a previous study examining the influence of an upper tropospheric cold low (CL) on the track of a nearby tropical cyclone (TC), this study investigates the impacts of a CL on TC intensity. The results suggest that the relative position and separation distance between the CL and TC are the key factors affecting TC intensity. When located outside the CL’s radius of maximum wind (RMW) but within its circulation, TCs initially in the northwest quadrant of the CL intensify faster than those in the other quadrants. The β effect causes the CL to move northwestward toward the TC and enhances eddy momentum flux convergence. Meanwhile, the upper-level TC outflow erodes the CL and reduces the associated vertical wind shear, promoting TC intensification. In contrast, for TCs initially located southeast of the CL, the attraction of Fujiwhara effect between the two entities counteracts the CL’s β drift and helps to maintain their separation distance. Moreover, Rossby wave energy dispersion induces an anticyclone southeast of the CL, which transports lower-θe air toward the TC and hinders the TC development. Furthermore, TCs within the CL’s RMW reach a similar intensity due to their PV superposition, irrespective of their relative positions to the CL. For TCs located outside the CL circulation, the CL’s impacts are largely negligible for TCs located northwest of CL, but TCs located southeast of the CL may still be affected by the CL-induced anticyclone.

Soliton molecules in Fermi–Pasta–Ulam–Tsingou lattice: Gardner equation approach

We revisit the Fermi–Pasta–Ulam–Tsingou lattice (FPUT) with quadratic and cubic nonlinear interactions in the continuous limit by deducing the Gardner equation. Through the Hirota bilinear method, the fundamental as well as multi-soliton, particularly two-, three- and four-soliton, solutions are obtained for the Gardner equation. Based on these multi-soliton solutions, we show the excitation of an interesting class of table-top soliton molecules in the FPUT lattice through the velocity resonance mechanism. Depending on the condition on the free parameters, which determine the bond length between the soliton atoms, we classify them as dissociated and synthetic type molecules. The main feature of the table-top soliton molecules is that they do not exhibit oscillations in the coalescence region. This property ensures that they are distinct from the soliton molecules, having retrieval force, of the nonlinear Schrödinger family of systems. Further, to study the stability of the soliton molecule we allow it to interact with a single (or multi) soliton(s). The asymptotic analysis shows that their structures remain constant, though the bond length varies, throughout the collision process. Then, from the relative separation distance calculation we also observe that the bond length of each of the soliton molecules is not maintained during soliton molecule–molecule interaction while their structures are preserved. In addition, we consider the FPUT lattice with quadratic nonlinear interaction and FPUT lattice with cubic nonlinearity as sub-cases and point out the nature of the soliton molecules for these cases also systematically. We achieve this based on the interconnections between the solutions of the Gardner, modified Korteweg–de Vries and Korteweg–de Vries equations. Finally, in order to validate the existence of all the soliton structures, especially reported for the Gardner equation in the continuous limit, we simulate the corresponding FPUT chain and verified these various structures numerically and analytically as well. We believe that the present study can be extended to other integrable and non-integrable systems with applications in fluid dynamics, Bose–Einstein condensates, nonlinear optics, and plasma physics.

Universality of cutoff for exclusion with reservoirs

We consider the exclusion process with reservoirs on arbitrary networks. We characterize the spectral gap, mixing time, and mixing window of the process, in terms of certain simple spectral statistics of the underlying network. Among other consequences we establish a nonconservative analogue of Aldous’s spectral gap conjecture, and we show that cutoff occurs if and only if the product condition is satisfied. We illustrate this by providing explicit cutoffs on discrete lattices of arbitrary dimensions and boundary conditions which substantially generalize recent one-dimensional results. We also obtain cutoff phenomena in relative entropy, Hilbert norm, separation distance, and supremum norm. Our proof exploits negative dependence in a novel, simple way to reduce the understanding of the whole process to that of single-site marginals. We believe that this approach will find other applications.

High output performance flutter-driven triboelectric nanogenerator

A key challenge that limits the actual application of flutter-driven triboelectric nanogenerators is the low electrical output. In this work, by deeply studying the vibrating process of flutter-driven triboelectric nanogenerator, we found that the inhomogeneous triboelectric charge distribution on the two face-to-face vibrating films and the inconsistent separation distance between different parts of these two films during vibrating process jointly lead to different driving effects of different parts of the films on the free electrons flowing in the external circuit, which are even opposite, thereby resulting in the low output of the flutter-driven triboelectric nanogenerators. To effectively avoid the cancellation and increase the output performance, the large area vibrating films are rationally separated into several parts with relative homogeneous triboelectric charge distribution and consistent separation distance with opposite film during vibrating process by the method of electrode segmentation and integration, which effectively makes the low output flutter-driven triboelectric nanogenerator into a high output contact-separated triboelectric nanogenerator composed of several integratable output units. By further optimization, the new developed flutter-driven TENG has the transferred charge density per time of 22.25 mC s−1 m−2, which is 2.8 times the record value (7.95 mC s−1 m−2), and 14 times of the value 1.57 mC s−1 m−2 of the general traditional structure flutter-driven TENG with the same area. It can light 2792 LEDs under a gentle wind (3.3 m s−1), which is 2.25 times of the maximum number (1240) reported in previous works under much stronger wind with speed of 15 m s−1.

Scaling of the B19 two-neutron halo properties close to unitarity

We explore the description of the bound $^{19}\mathrm{B}$ isotope in terms of a $^{17}\mathrm{B}+n+n$ three-body system where the two-body subsystems $^{17}\mathrm{B}+n$ and neutron-neutron ($nn$) have virtual states close to the continuum. Dimensionless scaling functions for the root-mean-square (rms) radii are defined and studied for different parameters of the neutron-core potential and considering three different models for neutron-neutron interaction. The scaling functions for the radii are rooted in the universal behavior of three-body systems close to the Efimov limit and depend only on dimensionless quantities formed by the two-neutron separation energies and scattering lengths. Our results show in practice the model independence of these scaling functions close to unitarity. We provide an estimation of the different rms relative separation distances between the constituents, as well as of the proton and matter radii.

Interactive Evaporation of Neighboring Pendant and Sessile Droplet Pair

Abstract In this article, we experimentally probe the vapor-mediated interaction behavior of evaporating sessile and pendant droplets in an interacting droplet (ID) system. For this purpose, a pendant droplet was introduced in the vapor diffusion domain of a sessile droplet and both were allowed to evaporate simultaneously. The evaporation dynamics were monitored using optical imaging techniques for varied separation (both horizontal and vertical) distances between them. Our observations reveal curtailed mass transfer rate from both the droplets although the evolution of droplet morphology (such as pendant droplet radius, contact radius, and contact angle of sessile droplet) at different stages of evaporation remain similar. The evaporative fluxes from these two droplets interact with one another and thereby reduce the diffusive mobility of vapor molecules in the liquid–vapor interface of both. This condition suppresses the diffusion mechanism and thereby impedes the evaporation rate. We show that the evaporation behavior for two droplets in an interacting droplet system is solely dictated by an effective external vapor concentration depending on the problem geometry. Therefore, to characterize the vapor diffusion domain we hypothesize a vapor front enfolding both the droplets and put forward a theoretical model by applying conservation of mass across it. We also propose a relationship to show the variation of the effective external vapor concentration with the relative separation distance between the droplets. The predictions from theoretical models are found to be in good agreement with our detailed experimental observations.

Flame interaction and tilting behavior of two tandem adjacent hydrocarbon turbulent diffusion flames in crosswind: An experimental quantification and characterization

This study presents an experimental investigation into the flame interaction and tilting behaviors of two tandem adjacent hydrocarbon turbulent diffusion flames in crosswind, which has not been well quantified in the past. Comprehensive experiments involving 204 tests were carried out employing two 15 cm square burners of various distances and two liquid fuels of representative soot production abilities, in crosswinds up to 6 m/s generated by a wind tunnel. The flame tilt angles were measured to quantify their interactions for flame merging and non-merging conditions. Results showed that the flame merging criterion extended under crosswind, especially for n-heptane fire with longer flame length. The tilt angles of merged flames were found to be smaller than that of single diffusion flame (SDF) and upstream diffusion flame (UDF) with the same crosswind speed for non-merging condition at relative larger separation distance. For flame non-merging condition, downstream diffusion flame (DDF)'s flame tilt angle values were lower than that of UDF due to the first flame shelter effect, and became smaller for larger separation distance at a given crosswind. According to their dynamic behaviors for non-merging condition, the ratio of flame tilt angle of DDF to that of UDF against a modified Fr* number fell into four regimes. The effective crosswind speed for DDF under crosswind momentum prevailed condition was proposed on account of the effects of the fire separation distance, the UDF's flame height and buoyancy flux. Non-dimensional formula was proposed to characterize their flame tilt angles for merging and non-merging flames respectively.

On hydrodynamic characteristics of transient harbor resonance excited by double solitary waves

The harbor resonance triggered by double solitary waves (DSWs) with different wave parameters (including various wave heights and relative separation distances) is simulated based on the fully nonlinear Boussinesq model, FUNWAVE-TVD. A long and narrow harbor with different topographies is adopted. In the current study, effects of incident wave height, relative separation distance and bottom profile on hydrodynamic characteristics related to the transient oscillations are mainly investigated. The hydrodynamic characteristics considered include the evolution of the maximum free-surface elevation, the maximum runup, the wave energy distribution and the total wave energy inside the harbor. Results show that Green's law can accurately estimate the evolution of the maximum free-surface elevation in most part of the harbor area. The impacts of the topography on the maximum runup exhibit a strong dependence on the incident wave height. The smaller mean water depth inside the harbor, the larger relative separation distance, and the higher incident wave height tend to result in greater uniformity of the wave energy distribution. The normalized total wave energy is always shown to decrease gradually with the incident wave height, and to increase remarkably at first and then decrease slightly with the increase of the mean water depth.

Intersystem crossing effects on spin mixing in exciplex-based organic light-emitting devices

The electroluminescence (EL) efficiency in exciplex-based organic light-emitting devices (OLEDs) is seriously impacted by the spin sense of injected carriers that leads to spin correlated singlet and triplet polaron pairs, which subsequently form singlet and triplet exciplex, respectively. Magnetic field effect (MFE) measurements have been employed to investigate the intersystem crossing effects on spin mixing induced by hyperfine interaction (HFI), spin-orbit coupling (SOC) and Zeeman splitting on the fraction of singlets formed in the low efficiency exciplex-based OLEDs (electron donor-acceptor, <0.1 cd/A). Poly [ N , N ′-bis(4-butylphenyl)- N , N ′-bis(phenyl)-benzi （Poly-TPD）is selected as electron donor, and 2,5-bis(5- tert -butyl-2-benzoxazolyl) thiophene (BBOT) is used as the acceptor. BBOT: Poly-TPD film is sandwiched between PEDOT: PSS hole-transporting layer and aluminum cathode. In exciplex-based device, a relative larger electron-hole separation distance is obtained because the electrons and holes are located in different neighboring molecules. As a consequence, a small exchange energy ( Δ E S T ) can be achieved by modifying the electron-hole separation distance because the Δ E S T decreases exponentially with increasing its separation distance. We have obtained large (up to ≈ 28.6%) magneto-electroluminescence (MEL) upon the application of a relatively small field, B (<300 mT). In the meantime, its magneto-resistive (MR) exhibits a small value (MR ≈ −2.5%), suggesting that large EL changes are not simply caused by the magneto-resistive effect. Therefore, the external magnetic field influences primarily the radiative exciplex recombination rate but has a negligible effect on the total recombination rate. It is proved that MEL is independent on the reverse intersystem crossing (RISC) spin-mixing mechanism. We show that intersystem crossing (ISC) related spin-mixing process dominates the low efficiency response in the exciplex manifold. The triplet levels are very closer to the singlet level in the ISC process, leading to efficient conversion from singlets to triplets through the HFI and SOC. Therefore, many singlet exciplexes can convert into triplets with thermal energy release, resulting in lower EL efficiency of fluorescent exciplex-based device. • Magnetic field effect (MFE) measurements were used to investigate intersystem crossing effects on spin mixing. • A small exchange energy (△E ST ) can be achieved by separating the HOMO from the LUMO. • A large (up to ≈28.6%) MEL (magneto-electroluminescence) was obtained upon the application of a relatively small field. • Intersystem crossing (ISC) related spin-mixing process dominates the low efficiency response in the exciplex manifold.

Mediation of resonance energy transfer by two polarisable particles.

The molecular quantum electrodynamics theory is employed to calculate the matrix element and Fermi golden rule rate for resonant transfer of electronic excitation energy between a donor and an acceptor in the vicinity of two neutral electric dipole polarizable particles, which play the role of bridging species. The emitter and absorber couple linearly to the electric displacement field via their electric dipole moments, while each mediator interacts quadratically with this field through its dynamic polarizability. This form of interaction Hamiltonian enables fourth-order perturbation theory to be used to compute the probability amplitude together with summation over 24 time-ordered diagrams representing a single virtual photon exchange between each pair of coupled particles. Expressions for the migration rate mediated by two inert molecules are obtained for an arbitrary arrangement of the four species that are in fixed mutual orientation or are freely tumbling. These formulae are valid for all interparticle separation distances outside the orbital overlap region. From the general result, rate equations applicable to an equidistant collinear configuration of the four bodies are evaluated. Near- and far-zone limiting forms of the transfer rate for the relay pathway are also calculated and exhibit inverse sixth and inverse square dependences on relative separation distances between pairs of particles, confirming the short-range (radiationless) and long-range (radiative) energy transfer mechanisms associated with two-body theory. The distance behavior of interference terms between two-, three-, and four-body terms is also examined, and the relative importance of each contribution to the total transfer rate is discussed.

Energy-sharing collisions and the dynamics of degenerate solitons in the nonlocal Manakov system

In this paper, by considering the degenerate two bright soliton solution of the nonlocal Manakov system, we bring out three different types of energy-sharing collisions for two different parametric conditions. Among the three, two of them are new which do not exist in the local Manakov equation. By performing an asymptotic analysis to the degenerate two-soliton solution, we explain the changes which occur in the quasi-intensity/quasi-power, phase shift and relative separation distance during the collision process. Remarkably, the intensity redistribution reveals that in the new types of shape-changing collisions, the energy difference of soliton in the two modes is not preserved during collision. In contrast to this, in the other shape-changing collision, the total energy of soliton in the two modes is conserved during collision. In addition to this, by tuning the imaginary parts of the wave numbers, we observe localized resonant patterns in both the scenarios. We also demonstrate the existence of bound states in the nonlocal Manakov equation during the collision process for certain parametric values.

Effective Radius of Curvature and Rayleigh Length of Partially-Coherent Array Beams Passing Through Oceanic Turbulence

Based on the spatial power spectrum of the refractive index of ocean water, we derive analytical expressions for the effective radius of curvature and Rayleigh length of partially-coherent Hermite–Gaussian linear array (PCHGA) beams propagating through oceanic turbulence. In addition, we discuss theoretically and analyze numerically the influence of oceanic turbulence and array parameters. The effective radius of curvature and Rayleigh length of PCHGA beams increase with the relative strength of temperature and salinity fluctuations, the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the array beam number, beam order, and relative separation distance, but decrease with the increase in the rate of dissipation of the mean-square temperature. The analysis provided here will help to understand the propagation of array beams through ocean turbulence.

Random sources generating far fields with ring-shaped array profiles

We introduce a class of planar random source generating ring-shaped array profiles in the far field. The model for spatial correlation function of this new source is composed by the Fourier transform of the Laguerre-Gaussian array function with circular symmetry. The analytical expressions for the spectral density (average intensity) in free space and atmospheric turbulence are derived. The effect of the source parameters on the propagation properties are investigated in detail. Numerical results show that the source can produce a ring-shaped optical array profile consisting of dark-hollow-shaped or Gaussian-like-shaped beamlets at some distance, and then keep shape-invariant for long distances in free space. The number of rings, the position of beamlets, and other features can be conveniently controlled by changing the initial source parameters. In addition, increasing the relative separation distance of each beamlet or decreasing the radius of beamlets can reduce the turbulence-induced degradation.

Numerical study on transient harbor oscillations induced by successive solitary waves

Tsunamis are traveling waves which are characterized by long wavelengths and large amplitudes close to the shore. Due to the transformation of tsunamis, undular bores have been frequently observed in the coastal zone and can be viewed as a sequence of solitary waves with different wave heights and different separation distances among them. In this article, transient harbor oscillations induced by incident successive solitary waves are first investigated. The transient oscillations are simulated by a fully nonlinear Boussinesq model, FUNWAVE-TVD. The incident successive solitary waves include double solitary waves and triple solitary waves. This paper mainly focuses on the effects of different waveform parameters of the incident successive solitary waves on the relative wave energy distribution inside the harbor. These wave parameters include the incident wave height, the relative separation distance between adjacent crests, and the number of elementary solitary waves in the incident wave train. The relative separation distance between adjacent crests is defined as the ratio of the distance between adjacent crests in the incident wave train to the effective wavelength of the single solitary wave. Maximum oscillations inside the harbor excited by various incident waves are also discussed. For comparison, the transient oscillation excited by the single solitary wave is also considered. The harbor used in this paper is assumed to be long and narrow and has constant depth; the free surface movement inside the harbor is essentially one-dimensional. This study reveals that, for the given harbor and for the variation ranges of all the waveform parameters of the incident successive solitary waves studied in this paper, the larger incident wave heights and the smaller number of elementary solitary waves in the incident tsunami lead to a more uniform relative wave energy distribution inside the harbor. For the successive solitary waves, the larger relative separation distance between adjacent crests can cause more obvious fluctuations of the relative wave energy distribution over different resonant modes. When the wave height of the elementary solitary wave in the successive solitary waves equals to that of the single solitary wave and the relative separation distance between adjacent crests is equal to or greater than 0.6, the maximum oscillation inside the harbor induced by the successive solitary waves is almost identical to that excited by the single solitary wave.

Effect of the angle of attack on the transient lift during the interaction of a vortex with a flat plate. Potential theory and experimental results

The dynamics of a two-dimensional vortex interacting with a flat plate at different angles of attack α is analysed using potential flow theory based on conformal mapping varying the nondimensional separation distance h∕c of the upstream incoming vortex to the plate (c is the chord length of the plate) and the vortex intensity Γl. Transient lift forces measured in a wind tunnel are also compared with the potential theory results for a given Γl and several values of h∕c and α. For the Reynolds number considered in the experiments (about 25 000) it is found that the potential theory predicts reasonably well the transient fluctuation in the lift force provided that the separation distance is not too close to the critical one h∗∕c at which the vortex trajectory given by the potential theory bifurcates. We find that the separation distance generating the highest induced lift is around this critical value h∗∕c, which, according to the potential theory, is displaced about −2.3(1−0.07|Γl|1∕2)α in relation to the zero angle of attack for the same Γl. Potential theory also predicts that the maximum peak of the lift fluctuation depends on α only through the relative separation |h−h∗|∕c, and that the maximum lift is substantially larger when a clockwise vortex passes below the plate than when it passes above the plate, for the same vortex intensity Γl and relative separation distance. The opposite happens for a counter-clockwise vortex. This asymmetry in the maximum lift fluctuation increases slightly with |Γl|, approaching a ratio of almost two for large |Γl|.

Propagation properties of Gaussian Schell-model array beams in non-Kolmogorov turbulence

A stochastic beam generated by a recently introduced Gaussian Schell-model array (GSMA) source (2015 Opt. Lett. 40 5662) is investigated. We derive the analytical propagation formulae for the spectral density and the propagation factor in non-Kolmogorov turbulence by utilizing the extended Huygens–Fresnel principle and second-order moments of the Wigner distribution function. Numerical results show that the lattice patterns of GSMA beams, which keep propagation-invariant in free space, are destroyed by the turbulence at sufficiently large distances. The GSMA beams have significant advantage over the Gaussian Schell-model beam in the robustness of the destructive effect of non-Kolmogorov turbulence, especially for the GSMA beam with more lattice elements and bigger relative separation distance of each lattice element. The effects of beam parameters and non-Kolmogorov turbulence on the propagation factor are analyzed in detail.

The van der Waals force between arbitrary-shaped particle and a plane surface connected by a liquid bridge in humidity environment

The van der Waals force (vdW force) between particulate matters at low humid condition and short distance contact is of great scientific importance in surface science. Due to the conventional theory for the van der Waals force between particles in single (vacuum or water) medium can not be directly applied in the humid condition, we present a mathematical model to calculate the van der Waals force between particle and surface linked by a liquid bridge in atmospheric humidity based on the surface integration method. In our model, the integration calculated the vdW force is divided into a wetting and a dry integrating region, and their boundary point is the radius of the wetting portion of the particle which is expressed as a function of relative humidity, contact angles and separation distance between the particle surface and the plane. For three basic contact geometries (sphere, cone and cylinder), the computational expressions of van der Waals force derived from our model are consistent with that by Butt. Moreover, our calculation results of the parabola particle model agree well with the published experimental data, which validated the rationality of the proposed model. In addition, our model can accurately calculate the vdW force between arbitrary-shaped particle and a plane surface in humidity environment.

The influence of oceanic turbulence on the beam quality parameters of partially coherent Hermite–Gaussian linear array beams

Based on the spatial power spectrum of the refractive index of ocean water and the second-order moments, the influence of oceanic turbulence and array beam parameters on the beam quality parameters including the M2-factor and turbulence distance of partially coherent Hermite–Gaussian linear array (PCHGLA) beams is studied in detail. It has been shown that the M2-factor of PCHGLA beams propagating through oceanic turbulence apparently increases with the increasing propagation distance, the M2-factor and relative M2-factor of PCHGLA beams apparently decrease and the turbulence distance of PCHGLA beams increases with the decreasing rate of dissipation of mean-square temperature and the increasing relative strength of temperature and salinity fluctuation and rate of dissipation of turbulent kinetic energy per unit mass of fluid. For the case of PCHGLA beams with larger beam number and relative separation distance and worse coherence degree, the relative M2-factor is smaller and the turbulence distance is larger, implying that influence of oceanic turbulence on the beam quality becomes weaker under this conditions. The results are illustrated by numerical examples.

Slow motion of spherical droplet in a micropolar fluid flow perpendicular to a planar solid surface

The Stokes axisymmetrical flow problem of a viscous fluid sphere moving perpendicular to an impermeable bounding surface within a micropolar stagnant fluid as well as the related problem of a micropolar fluid sphere moving perpendicular to an impermeable planar surface within a stagnant viscous fluid are considered. The fluids are considered to be incompressible, and the deformation of the fluid particle is neglected. A general solution is constructed from fundamental solutions in both cylindrical and spherical coordinate systems. As boundary conditions, continuity of velocity, continuity of shear stress and the spin–vorticity relation at the droplet surface are applied. Also the no-slip and no-spin boundary conditions are used at the impermeable plane surface. A combined analytical-numerical procedure based on collocation technique is used. The drag acting, in each case, on the fluid particle is evaluated with good convergence. Numerical results for the normalized hydrodynamic drag force versus the relative viscosity, relative separation distance between the particle and wall, micropolarity parameter (a viscosity ratio characterizing micropolar fluids) and spin parameter (a non-dimensional scalar factor relating the microrotation and vorticity at the droplet surface) are presented both in tabular and graphical forms. The results for the drag coefficient are in good agreement with the available solutions in the literature for the limiting cases.

Fabrication of a new fluorescent polymeric nanoparticle containing naphthalimide and investigation on its interaction with bovine serum albumin

A new fluorescent nanoparticle was synthesized by chemical crosslinking of polyacrylic acid using 4-aminoethanol-N-hydroxyethanyl-1,8-naphthalimide as the crosslinker. The particle possesses excellent characteristics, including low cytotoxicity, water solubility and good fluorescence properties. The interaction of the particle with bovine serum albumin was investigated by absorbance, fluorescence and circular dichroism spectroscopic methods. The interaction mechanisms, binding model and reciprocal effects on structure and fluorescence between nanoparticle and protein are discussed. The spectral data indicated that the nanoparticle could spontaneously form a reversible complex with bovine serum albumin in solution used mainly by hydrogen bonds and van der Waals forces. Fluorescence resonance energy transfer from tryptophan to naphthalimide in the complex was demonstrated and employed to determine their relative separation distance. During the interaction process, unfolding of polypeptide chains in the protein occurred but no adjustments of local polarities around the tryptophan and tyrosine residues were observed. In addition, it was found that the presence of protein induced a notable enhancement in nanoparticle fluorescence and a blue-shift in the emission maximum. These results will be useful for further applications of the developed nanoparticle in biomedical areas.