String formation in sheared polymer blends: coalescence, breakup, and finite size effects

We have discovered a droplet-string transition in concentrated polymer blends which occurs when the size of the dispersed droplets becomes comparable to the gap width between the shearing surfaces. The transition is abrupt and proceeds via the coalescence of droplets in a four-stage kinetic process. Once formed, the strings are stable and exhibit pronounced hysteresis. The string state is stabilized by a suppression of the Rayleigh-Tomotika instability due to both finite size effects and to the shear-induced advection of small-amplitude disturbances.     

The Effect of Coagulation of Water Droplets on Their Size Distribution in the Operating Part of an Air-Cooler Device

Technical Physics - Mathematical simulation of coagulation of droplets of finite number of size fractions of a polydisperse mixture, injected by a nozzle into the region of an air-cooler unit along...     

Frequency-dependent deformation of liquid crystal droplets in an external electric field

Nematic droplets suspended in the isotropic phase of the same substance were subjected to alternating electrical fields of varying frequency. To keep the system at a constant nematic/isotropic volume ratio with constant droplet size, we carefully kept the temperature in the isotropic/nematic coexistence region, which was broadened by adding small amounts of a non-mesogenic liquid. Whereas the nematic droplets remained spherical at low (in the order of 10 Hz) and high frequencies (in the order of 1 kHz), at intermediate frequencies we observed a marked flattening of the droplets in the plane perpendicular to the applied field. Droplet deformation occurred both in liquid crystals (LCs) with positive and negative dielectric anisotropy. The experimental data can be quantitatively modelled with a combination of the leaky dielectric model and screening of the applied electric field due to finite conductivity.     

Variations in epidemic distribution with some characteristic parameters

Considering the spread of an epidemic among a population of mobile agents that can get infected and maintain the infection for a period, we investigate the variation in the homogeneity of the distribution of the epidemic with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that the inhomogeneity of epidemic distribution increases with an increase in τ for very low v, while it decreases with an increase in τ for moderate v. The epidemic distribution also tends to a homogeneous state as both v and α increase.     

25MeV/u40Ar+197Au反应中高激发热核的时空演化

报道了25MeV/u⁴⁰Ar+¹⁹⁷Au反应中从两粒子相对动量关联函数提取的发射时间随空间大小演化的规律.结果表明，即使发射源质量数减小50%，对计算的关联函数及提取的发射时间影响仍然很小.在短发射时间(τ≤100fm/c)情况下，较小的核物质密度，导致提取的发射时间变小.因此，在正常核物质密度参数下提取的τ值可作为发射时间的上限值.在长发射时间(τ≥300fm/c)情况下发射时间不随空间大小变化，提取的τ即为实际的发射时间. 关键词：     

Variations of the epidemic distribution with some characteristic parameters

Considering the epidemic spread among a population of mobile agents which can get infected and maintain the infection for a period, we investigate the variation of the homogeneity of the epidemic distribution with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that, the inhomogeneity of the epidemic distribution increases with the increase of τ for very low v, while decreases with the increase of τ for moderate v. And the epidemic distribution tends to a homogeneous state as both v and α increase.     

Contactless transport of matter in the first five resonance modes of a line-focused acoustic manipulator

The first five resonance modes for transport of matter in a line-focused acoustic levitation system are investigated. Contactless transport was achieved by varying the height between the radiating plate and the reflector. Transport and levitation of droplets in particular involve two limits of the acoustic forces. The lower limit corresponds to the minimum force required to overcome the gravitational force. The upper limit corresponds to the maximum acoustic pressure beyond which atomization of the droplet occurs. As the droplet size increases, the lower limit increases and the upper limit decreases. Therefore to have large droplets levitated, relatively flat radiation pressure amplitude during the translation is needed. In this study, using a finite element model, the Gor'kov potential was calculated for different heights between the reflector and the radiating plate. The application of the Gor'kov potential was extended to study the range of droplet sizes for which the droplets can be levitated and transported without atomization. It was found that the third resonant mode (H(3)-mode) represents the best compromise between high levitation force and smooth pattern transition, and water droplets of millimeter radius can be levitated and transported. The H(3)-mode also allows for three translation lines in parallel.     

Crossing the Coexistence Line at Constant Magnetization

Using Monte Carlo histogram methods, the microcanonical caloric curve is computed for the Ising model in two and three dimensions with fixed magnetization. Whereas the signatures of a possible first order phase transition are clearly visible for large systems, intriguing finite size effects are revealed for smaller system sizes. The behaviour of the caloric curve is studied in a systematic way. Furthermore, results for the thermal stability of three-dimensional droplets of minority spins inside the two-phase region are presented. The effect of the percolation transition on the stability of these droplets is discussed.     

Computer simulations of critical phenomena and phase behaviour of fluids

Computer simulation techniques such as Monte Carlo (MC) and Molecular Dynamics (MD) methods yield numerically exact information (apart from statistical errors) on model systems of classical statistical mechanics. However, a systematic limitation is the restriction to a finite (and often rather small) particle number N (or box linear dimension L, respectively). This limitation is particularly restrictive near critical points (due to the divergence of the correlation length of the order parameter) and for the study of phase equilibria (possibly involving interfaces, droplets, etc.). Starting out with simple lattice gas (Ising) models, finite size scaling analyses have been developed to overcome this limitation. These techniques work for both simple Lennard-Jones fluids and their mixtures, including generalizations to approximate models for quadrupolar fluids such as carbon dioxide, benzene etc. and various mixtures, whose phase behaviour can be predicted. A combination of MC and MD allows the study of dynamic critical phenomena, and specialised techniques (umbrella sampling plus thermodynamic integration) yield the surface free energy of droplets as function of droplet size. Thus, computer simulation has become a versatile and widely applicable tool for the study of fluids.     

Two Types of Electronic States in One-Dimensional Crystals of Finite Length

Exact and general results on the electronic states in one-dimensional crystals bounded at τ and τ+L, where L=Na, N is a positive integer, and a is the potential period, are presented. Corresponding to each energy band of the Bloch wave, there are N−1 states in the finite crystal whose energies are dependent on L but not on τ and map the energy band exactly. There is always one and only one electronic state corresponding to each band gap of the Bloch wave, whose energy is dependent on τ but not on L. This state is either a constant-energy confined band-edge state or a surface state in the band gap.     

Stagnation-point polydisperse spray flame ignition

A theory of stagnation-point flow polydisperse spray flame ignition by an isothermal hot surface is presented for the first time. The configuration investigated consists of a mixture of fuel droplets and air flowing against an isothermal hot surface (such as a hot ignition probe). The polydisperse spray of droplets is modelled using the sectional approach. A single global chemical reaction is assumed for the case when ignition occurs. The mathematical analysis makes use of a small parameter that is exploited for an asymptotic approach. An analytical criterion for ignition is derived which includes effects of the flow field, the reactants and all the fuel spray-related parameters, including the initial size distribution of the spray's droplets. Numerical calculations disclose how the actual droplet size distribution impacts on the critical stagnation point temperature necessary to promote ignition. Additionally, the analytical estimates are compared with predictions of a numerical finite difference code with very satisfactory agreement.     

全场彩虹技术测量喷雾浓度及粒径分布

喷雾颗粒的浓度、粒径等多参数的同时测量是研究喷雾的关键. 对应用全场彩虹技术测量双组分液滴的浓度及粒径分布进行了研究. 基于改进的Nussenzweig理论,对液滴折射率和粒径分布采用无分布函数算法进行最优化求解, 然后通过折射率与浓度的关系反推液滴浓度.用模拟全场彩虹信号对该算法进行了验证, 该算法可准确反演具有单峰分布、双峰分布粒径特征的液滴群的折射率与粒径分布. 并对体积分数从0%到100%的乙醇溶液喷雾进行了实验测量, 结果表明,所测得折射率与理论值符合,粒径分布稳定.该技术在喷雾浓度测量方面具有广阔的应用前景. 关键词： 全场彩虹技术 折射率 粒径 组分     

Surface free energy of the crystal-liquid interface on the metastable extension of the melting curve

The surface free energy γ, excess surface energy e, and excess surface stress τ at the crystal-liquid interface of a Lennard-Jones system have been determined by molecular dynamics simulation. The calculations have been performed for temperatures both above and below the triple-point temperature for the region where each of the coexisting phases is metastable and is at a negative pressure. The asymptotic behavior of γ, e, and τ has been analyzed near the endpoint of the melting curve, which is a point of the contact of the metastable extension of the melting curve and the spinodal of the stretched liquid [V.G. Baidakov and S.P. Protsenko, Phys. Rev. Lett. 95, 015701 (2005)]. It has been found that γ, e, and τ at this point are finite and the excess surface entropy is zero.     

Spectral characterization of diffusion with chemical shift resolution: Highly concentrated water-in-oil emulsion

We present a modulated gradient spin-echo method, which uses a train of sinusoidally shaped gradient pulses separated by 180° radio-frequency (RF) pulses. The RF pulses efficiently refocus chemical shifts and de-phasing due to susceptibility differences, resulting in undistorted, high-resolution diffusion weighted spectra. This allows for the simultaneous spectral characterization of the diffusion of several molecular species with different chemical shifts. The technique is robust against susceptibility artifacts, field inhomogeneity and imperfections in the gradient generating equipment. The feasibility of the technique is demonstrated by measuring the diffusion of water, oil, and water-soluble salt in a highly concentrated water-in-oil emulsion. The diffusion of water and salt reveal precise information about the droplet size distribution below the μm-range. Common droplet size distribution explains both the data for water with finite long-range diffusion and the data for salt with negligible long-range diffusion. The results of water diffusion show that the technique is efficient in deconvolving the effects of molecular exchange between droplets and restricted diffusion within droplets. The effects of water exchange suggest that droplets of different sizes are uniformly distributed within the sample.     

基于机器视觉的细水雾液滴尺寸测量与分析

为了满足科研与工程中对细水雾液滴尺寸测量的高精度低成本要求,对雾滴尺寸的机器视觉测量方法进行了深入研究.在自行建立的高压喷雾系统与雾滴采集装置上对细水雾液滴进行了采样,用显微镜及其CCD相机对雾滴样本进行了图像采集,用图像处理软件对采集的雾滴图像进行了处理与分析,测量并统计了5966个雾滴,得到了雾滴尺寸的频谱分布和累积分布以及雾滴平均直径和特征直径,将测量结果与相位多普勒粒子分析仪(PDPA)的测量结果进行了比较.结果表明,机器视觉方法町测量的最小雾滴直径约4.39 μm;机器视觉测量结果与PDPA测最结果相当接近,两种方法测得的细水雾液滴平均直径和特征直径的相对误差均在5%以内,雾滴尺寸均匀度指数的相对误差为0.27%.     

Effect of Mannosylerythritol lipid-A on light scattering of AOT/D<Subscript>2</Subscript>O/Octane

The light scattering technique is used for the study of interaction of Mannosylerythritol lipid-A on AOT/D₂O/Octane. The collective diffusion of AOT/D₂O droplets soluble in Octane mixed with lipid is founded from a correlation function of light scattering. We focus on the variation of the dynamic behavior of droplets as a function of the lipid concentrations and the size of droplets. The increase of concentration of Mannosylerythritol lipid-A on microemulsion decreases the dynamic of droplets. The SAXS experiment shows the size and the interaction of the droplets change by increase of Mannosylerythritol lipid-A concentration. A hard sphere model can describe the interaction of lipid with AOT/D₂O droplets.     

Generation of Monodisperse Micron‐Sized Droplets using Free Adjustable Signals

This paper describes the generation of small water droplets in the size range down to a few microns. Commercially available inkjet printing devices are not suitable for producing such droplets since they produce satellite droplets. Furthermore, standard drop‐on‐demand devices are normally restricted to the generation of droplets with the same size as the orifice diameter. Using a new and more sophisticated computer‐based signal generation system, smaller‐sized droplets can be generated from the same orifice. A key feature of the design is the generation of freely definable pulses. This enables the generation of acoustic modes within the fluid of the droplet generator, which leads to the generation of droplets without satellites. Only very few pulse forms enable the generation of suitable acoustic modes. Therefore, it is necessary to look for the specific pulse corresponding to the chosen droplet generator. Flexible pulse form generation appears to be more suitable than simple pulse forms for the generation of such droplets.     

Simulations of coulombic fission of charged inviscid drops

We present boundary-integral simulations of the evolution of critically charged droplets. For such droplets, small perturbations are unstable and eventually lead to the formation of a lemon-shaped drop with very sharp tips. For perfectly conducting drops, the tip forms a self-similar cone shape with a subtended angle identical to that of a Taylor cone, and quantities such as pressure and velocity diverge in time with power-law scaling. In contrast, when charge transport is described by a finite conductivity, we find that small progeny drops are formed at the tips, whose size decreases as the conductivity is increased. These small progeny drops are of nearly critical charge, and are precursors to the emission of a sustained flow of liquid from the tips as observed in experiments of isolated charged drops.     

An equal-time quantized field theory on the light cone

Semileptonic decays of polarized τ leptons are investigated and the most general angular distribution of two and three meson final states is derived. Emphasis is put on τ studies in electron positron annihilation where the neutrino escapes detection and the τ restframe cannot be reconstructed. It is shown that the most general distribution can be characterized by 16 structure functions, most of which can be determined in currently ongoing high statistics experiments. Of particular interest for the three meson case are the distribution of the normal to the Dalitz plane and the distribution around this normal. Predictions for the structure functions are given for the two and three pion case and forK ^*(→Kπ). Implications for an experiment where the τ restframe could be reconstructed are also considered.     

Einige Bemerkungen zur Theorie des Mößbauer-Effektes

Although the life-time τ of an excited nucleus is finite, and the coherence-length of the emitted γ-ray is of the order of 1/τ, the reaction of the γ-emission on the motion of the emitting nucleus is momentary. In a second remark some ?Mößbauer-experiments” are proposed by which properties of a crystal could be measured.