Possibility of the levitation of droplets in the atmosphere when they are charged by induction in an electric field under nonuniform evaporation conditions

The behavior of droplets in the atmosphere in an electric field has important bearing on the theory of thunderstorms. One of the possible mechanisms by which droplets become charged—the induction mechanism in the presence of nonuniform evaporation—is investigated in greater detail on the basis of recent experimental results (V. A. Saranin, Zh. Tekh. Fiz. 65(6), 21 (1995) [Tech. Phys. 40, 332 (1995)]). Zh. Tekh. Fiz. 68, 16–21 (February 1998)     

Microscopic theory of the electro-acoustic echo in order-disorder antiferroelectrics

A microscopic theory of the electro-acoustic echo (EAE) is proposed for the case in which two pulses of a variable electric field act on an antiferroelectric. This theory augments the phenomenological theory proposed for the purpose of interpreting experiments on the main regularities of the electro-acoustic echo in order-disorder antiferroelectrics. The deuterization effect and “pre-polarization” effect are explained. The shape of the echo signal is derived analytically and it is shown that this shape depends on the time interval between pump pulses. Fiz. Tverd. Tela (St. Petersburg) 40, 118–121 (January 1998)     

Exact solution of the problem of the equilibrium configuration of the charged surface of a liquid metal

A broad class of exact solutions is obtained for the problem of the equilibrium configuration of the charged surface of a conducting liquid allowing for capillary forces. An analysis of the solutions showed that when the amplitudes of the perturbations reached certain critical values, the region occupied by the liquid ceases to be singly connected, which corresponds to the formation of liquid metal droplets. It is shown that a steady-state liquid metal profile may exist for which appreciable local amplification of the electric field can be achieved. Zh. éksp. Teor. Fiz. 116, 1990–2005 (December 1999)     

Water droplets in a spherically confined nematic solvent: A numerical investigation

Recently, it was observed that water droplets suspended in a nematic liquid crystal form linear chains [Poulin et al., Science 275, 1770 (1997)]. The chaining occurs, e.g., in a large nematic drop with homeotropic boundary conditions at all the surfaces. Between each pair of water droplets a point defect in the liquid crystalline order was found in accordance with topological constraints. This point defect causes a repulsion between the water droplets. In our numerical investigation we limit ourselves to a chain of two droplets. For such a complex geometry we use the method of finite elements to minimize the Frank free energy. We confirm an experimental observation that the distance d of the point defect from the surface of a water droplet scales with the radius r of the droplet like .When the water droplets are moved apart, we find that the point defect does not stay in the middle between the droplets, but rather forms a dipole with one of them. This confirms a theoretical model for the chaining. Analogies to a second order phase transition are drawn. We also find the dipole when one water droplet is suspended in a bipolar nematic drop with two boojums, i.e., surface defects at the outer boundary. Finally, we present a configuration where two droplets repel each other without a defect between them. Received 11 December 1998     

Coalescence of polymer droplets: experiments on collision

The coalescence of polymer droplets is a fundamental phenomenon which appears for example when mixing two polymers. When two polymeric droplets collide, a transient regime appears, which results from a competition between interfacial and viscoelastic effects: the spherical droplets deform to give birth to a new drop in a short time (t_c) and the drop shape stabilizes after a long time.A new method is proposed to study experimentally under a microscope the collision between two droplets of polymer, with different viscosity ratios. This allows to détermine the characteristic time t_c. which defines this phenomenon. The experiments actually show that t_c varies like the geometric mean of the viscosities of the two polymers, for the case of a polydimethylsiloxane/polyisobutylene system.     

Extension of the spin-statistics theorem to nonlocal fields

A new and more general derivation of the connection between spin and statistics that is applicable to nonlocal quantum fields with arbitrarily singular ultraviolet behavior is proposed. The derivation employs the concept of the analytical wave front of a distribution and makes it possible to characterize precisely the admissible degree of breakdown of locality for which there exists in the theory a Klein transformation which reduces the fields to normal commutation relations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 586–591 (25 April 1998)     

Thermal Analysis for Velocity,Kinetics, and Enthalpy Reaction Measurements in Microfluidic Devices

Abstract

The aim of this work is to present new devices for the measurement of velocity, kinetics, and enthalpy of chemical reactions occurring in a microfluidic chip, co-flow, or droplets flow. The thermal analysis goes from the macroscopic approach by microcalorimetry to microscopic analysis inside the microchannel by IR thermography. Concerning microcalorimetry, the enthalpy is deduced from the measurement of the global heat flux dissipated by the chemical reaction as a function of the molar flow rate. A validation is presented on a well-known acid-base reaction. This device can be combined with an IR camera for local characterization. The processing of the measured temperature fields allows the estimation of properties of great importance for chemical engineers, such as heating source distribution (i.e., the kinetics) of the chemical reaction along the channel. A validation experiment of a temperature field processing method is proposed with the Joule effect. From such a previous experiment, a Peclet field is estimated and used in a further step in order to study an acid-base co-flow configuration. Finally, a first tentative of thermal characterization inside droplets flow during an acid-base chemical reaction is also presented.     

Delayed coalescence of droplets with miscible liquids: Lubrication and phase field theories

Mixing of droplets with a body of different liquids shows an interesting behavior for small contact angles at solid substrate. The droplets interact with each other, a liquid exchange appears between the approaching drops owing to surface tension gradients at the droplets interface. But the drops remain separated for some seconds (up to minutes), until the merging into a single drop occurs (Langmuir 24, 6395 (2008)). We investigate this phenomenon using lubrication approximation and phase field approach. For both methods, 2D quantitative computer simulations for delayed fusion of perfectly miscible thin liquid films/droplets with low contact angles are reported.     

Wave vector,local momentum and local coordinate from the perspective of information theory

In the context of informational analysis of atomic and molecular systems, the connection between local quantum observables and information measures is of interest. In this paper, analytical relationships for the imaginary part of the total local momentum (coordinate) in terms of information theoretic measures have been established. Moreover, on the basis of another scheme in which the relationship among densities of information energy, Shannon entropy and Fisher information has been proposed [M. Alipour and A. Mohajeri, Mol. Phys. 110, 403 (2012)], the general formulae for the imaginary part of the total local momentum and the corresponding variance are expressed. The presented proof may be viewed in light of the relation between the local wave vector and the information energy density. Through this study, another noteworthy application of information theory is highlighted.     

Critical analysis of the modified firsov model. sensitivity to the choice of atomic wavefunctions

Abstract

The Firsov model for calculating the low-velocity e-lectronic stopping power (S_e) as modified by Cheshire, et al, is found to be extremely sensitive to the choice of atomic wave functions (ψ) when a minimum impact parameter is used in the calculations. Differences of a factor of ?2 are observed, for example, between the predicted value of S_e using a minimal basis set for ψ and the value obtained using an extended basis set. A systematic analysis to reduce the sources of uncertainty in calculations of S _e is proposed in order to have a unified set of criteria regarding the predictions of the theory.     

Formation of argon cluster with proton seeding

ABSTRACT

We employ force-field molecular dynamics simulations to investigate the kinetics of nucleation to new liquid or solid phases in a dense gas of particles, seeded with ions. We use precise atomic pair interactions, with physically correct long-range behaviour, between argon atoms and protons. Time dependence of molecular cluster formation is analysed at different proton concentration, temperature and argon gas density. The modified phase transitions with proton seeding of the argon gas are identified and analysed. The seeding of the gas enhances the formation of nano-size atomic clusters and their aggregation. The strong attraction between protons and bath gas atoms stabilises large nano-clusters and the critical temperature for evaporation. An analytical model is proposed to describe the stability of argon-proton droplets and is compared with the molecular dynamics simulations.     

Quadrupolar forces and aggregation of nematic droplets

The electrostatic quadrupolar interaction between spherical nematic droplets in an isotropic (and nonconducting) liquid is calculated. It is found to have an anisotropic form U _q ∝1/R ⁵, where R is the distance between droplets, with repulsion for droplets having parallel orientation of the quadrupole moments and attraction at oblique angles around the orthogonal orientation. In an external magnetic field aligning the orientations of the quadrupole moments, a competition of the quadrupolar repulsion and van der Waals attraction (U _vdW∝ 1/R ⁶) leads to a specific spatial organization of droplets which is in fact often reported in experimental observations (see the monograph by P. Drzaic, Liquid Crystal Dispersions, World Scientific, Singapore (1995) and references cited therein). Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 747–752 (25 November 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Intramolecular association within the SAFT framework

A general theory for modelling intramolecular association within the SAFT framework is proposed. Sear and Jackson [Phys. Rev. E. 50 (1), 386 (1994)] and Ghonasgi and Chapman [J. Chem. Phys. 102 (6), 2585 (1995)] have previously extended SAFT to include intramolecular association for chains with two sites. We show that the resulting equations from the two approaches are equivalent, and use their work as a basis for developing a new general theory. The approach used by Ghonasgi and Chapman is based on mass balances and an infinite dilution result and provides the equations needed to determine the contribution to the Helmholtz free energy from association (inter- as well as intramolecularly) at equilibrium. Sear and Jackson rederived the contribution to the Helmholtz free energy from association from the theory by Wertheim [J. Stat. Phys. 42 (3–4), 459 (1986)] with inclusion of intramolecular association, and using this approach we obtain an expression for the Helmholtz free energy that is valid also at non-equilibrium states (with respect to hydrogen bonds), which is very useful when calculating derivatives.     

Large eddy simulations of partially premixed ethanol dilute spray flames using the flamelet generated manifold model

The paper presents Large Eddy Simulations (LESs) for the Sydney ethanol piloted turbulent dilute spray flames ETF2, ETF6, and ETF7. The Flamelet Generated Manifold (FGM) approach is employed to predict mixing and burning of the evaporating fuel droplets. A methodology to match the experimental inflow spray profiles is presented. The spray statistical time-averaged results show reasonable agreement with mean and RMS data. The Particle Size Distribution (PSD) shows a good match downstream of the nozzle exit and up to x/D = 10. At x/D = 20 and 30 the PSD is under-predicted for droplets with mean diameter D10 > 20μm and over-predicted for the smaller size droplets. The simulations reasonably predict the reported mean flame structure and length. The effect of increasing the carrier velocity (ETF2–ETF7) or decreasing the liquid fuel injection mass flow rate (ETF2–ETF6) is found to result in a leaner, shorter flame and stronger spray–flow interactions. Higher tendency to local extinction is observed for ETF7 which is closer to blow-off compared to ETF2 and has higher scalar dissipation rates, higher range of Stokes number, and faster droplet response. The possible sources of LES-FGM deviations from the measurements are discussed and highlighted. In particular, the spray time-averaged statistical error contribution is quantified and the impact of the inflow uncertainty is studied. Sensitivity analysis to the pre-vaporized nozzle fuel mass fraction show that such small inflow perturbations (by ±?2% for the ETF2 flame) have a strong impact on the flame structure, and the droplets’ dynamics. Conditional scatter plots show that the flame exhibits wide range of mixing conditions and bimodal mixing lines particularly at upstream locations (x/D?相似文献   

On the problem of the quantization of infinitely reducible first-class constraints

A manifestly covariant scheme in a Hamiltonian form of augmenting infinitely reducible first-class fermionic constraints (ICC1) up to irreducible constraints is proposed for a class of theories (including D=10 superstrings and superparticles in the covariant formulation). The modified formulation, which is obtained after the scheme is applied to a theory including only ICC1, contains irreducible first-class constraints and irreducible second-class constraints separated from them. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 673–678 (10 May 1996)     

Evidence of the harmonic Faraday instability in ultrasonic atomization experiments with a deep, inviscid fluid

A popular method for generating micron-sized aerosols is to submerge ultrasonic (ω~MHz) piezoelectric oscillators in a water bath. The submerged oscillator atomizes the fluid, creating droplets with radii proportional to the wavelength of the standing wave at the fluid surface. Classical theory for the Faraday instability predicts a parametric instability driving a capillary wave at the subharmonic (ω/2) frequency. For many applications it is desirable to reduce the size of the droplets; however, using higher frequency oscillators becomes impractical beyond a few MHz. Observations are presented that demonstrate that smaller droplets may also be created by increasing the driving amplitude of the oscillator, and that this effect becomes more pronounced for large driving frequencies. It is shown that these observations are consistent with a transition from droplets associated with subharmonic (ω/2) capillary waves to harmonic (ω) capillary waves induced by larger driving frequencies and amplitudes, as predicted by a stability analysis of the capillary waves.     

A viscous continuum traffic flow model with consideration of the coupling effect for two-lane freeways

In this paper, the viscous continuum traffic flow model for a single lane is extended to the traffic flow for two-lane freeways. The proposed model is a higher-order continuum model considering the coupling and lane changing effects of the vehicles on two adjacent lanes. It results from integrating the Taylor series expansion of the viscous continuum traffic flow model proposed by Ge (2006 Physica A 371 667) into the multi-lane model presented by Daganzo (1997 Transpn. Res. B 31 83). Our proposed model may be used to describe non-anisotropic behaviour because of lane changing in multi-lane traffic. A linear stability analysis is given and the neutral stability condition is obtained. Also, issues related to lane changing, shock waves and rarefaction waves, local clustering and phase transition are investigated through a simulation experiment. The simulation results show that the proposed model is capable of explaining some particular traffic phenomena commonly observable in real world traffic flow.     

Landau–Ginzburg theory for ‘star’-shaped droplets

ABSTRACT

Molecular simulations have shown that when a nano-drop comprising a single spherical central ion and a dielectric solvent is charged above a well-defined threshold, it acquires a stable star morphology. A linear continuum model of the ‘star’-shapes comprised electrostatic and surface energy is not sufficient to describe these shapes. We employ combined molecular dynamics, continuum electrostatics and macroscopic modelling in order to construct a unified free energy functional that describes the observed star-shaped droplets. We demonstrate that the Landau free energy coupled to the third-order Steinhardt invariant mimics the shapes of droplets detected in molecular simulations. Using the maximum likelihood technique we build a universal free energy functional that describes droplets for a range of Rayleigh fissility parameter. The analysis of the macroscopic free energy demonstrates the origin of the finite amplitude perturbations just above the Rayleigh limit. We argue that the presence of the finite amplitude perturbations precludes the use of the small parameter perturbation method for the analysis of the shapes above the Rayleigh limit of the corresponding spherical shape.     

Optical phase change in bismuth through structural distortions induced by laser irradiation

ABSTRACT

Semimetal bismuth (Bi) is known to possess a wide range of peculiar properties, owing to its unique electronic band structure. Its electronic band can easily be distorted by structural changes, and thereby undergo transitions between semimetal to either semiconductor or metal states. Utilising a focused laser beam, one can easily introduce structural defects, along with phase changes, oxidation, and morphological modifications. Confocal Raman microscopy indicated that the as-fabricated Bi droplets inhibit the Raman signal from the underlying silicon (Si) substrate. After a laser flash heating step, the intensity of Si optical phonons was strongly enhanced at the positions of Bi droplets, and exceeding the intensity from the bare Si substrate. Thus, such laser irradiating step on the Bi droplets induces an optical phase change. The optical phase change was detected as going from inhibition to strong enhancement of the underlying Si substrate Raman signal. From the observed Bi optical phonon modes (E_g and A_1g), alterations in the Raman peaks due to laser exposure indicated that the ordered crystallinity in pristine Bi droplets became deteriorated. The effects of atomic displacements and loss of structural order in Bi droplets impacts its dielectric response. The observed Si Raman signal enhancement is similar to the surface-enhanced Raman scattering effect typically known for noble metals.     

Attenuation of solar radiation by a water mist from the ultraviolet to the infrared range

A model is developed for the hemispherical transmittance of direct and scattered solar radiation from a cloudless atmosphere by a mist layer of water droplets in order to investigate the potential of water misting systems to serve as a protection from solar irradiation with particular emphasis on harmful UV radiation. The proposed model is based on published spectral experimental data for solar irradiation, Mie theory for interaction of the radiation with single spherical droplets, and radiative transfer theory. Known limiting solutions are employed to simplify the Mie calculations. The modified two-flux approximation is used to account for both direct and diffuse irradiation in lieu of a numerical solution for the full radiative transfer equation in anisotropically scattering media. The role of the governing parameters of a disperse water curtain of water droplets, water content, and droplet size for sample conditions is studied in some detail, particularly in the near-ultraviolet part of the spectrum where radiation can result in human tissue damage.