Volume-Charged Cones on a Liquid Interface in an Electric Field

In this study, we explore a novel type of slender conical liquid meniscus arisen in high electric field, which carries surface charge and net bulk charge of opposite sign. Stability of such dissipative structure is ensured by the balance between capillary and electrostatic forces and competition between the surface and bulk electric currents. The bulk charge is governed by the applied voltage being generated by the electric field of the cone due to dissociation/associations reactions at its apex. The effect of the physical parameters of the liquid on the microcone structure is elucidated. It is shown that the cone angle cannot exceed a critical value, which is a function of dielectric permittivity of the liquid. The electric current through the cone is found to be proportional to the square of the applied voltage. The obtained results can be applied for analysis of atomization processes of various liquids.     

Sink flow deforms the interface between a viscous liquid and air into a tip singularity

In our experiment, an interface between a viscous liquid and air is deformed by a sink flow of constant flow rate to form a sharp tip. Using a microscope, the interface shape is recorded down to a tip size of 1 microm. The curvature at the tip is controlled by the distance h between the tip and the sink. As a critical distance h*is approached, the curvature diverges like 1/(h-h*)3and the tip becomes cone shaped. As the distance to the sink is decreased further, the opening angle of the cone vanishes like h2. No evidence for air entrainment was found, except when the tip was inside the orifice.     

生物柴油高压共轨喷雾特性的试验研究

应用高速摄影系统与高压共轨系统,在高压定容器内研究了生物柴油的喷雾特性,并与柴油进行了对比。结果表明,生物柴油油束形态比柴油细且长,喷雾贯穿距离比柴油大,喷雾锥角比柴油小;高的运动黏度与表面张力导致生物柴油雾化性能比柴油差。随着喷油压力的升高,生物柴油喷雾贯穿距离变长,喷雾锥角增大;随着背压的升高,生物柴油喷雾贯穿距离...     

基于飞秒激光微加工的介质膜损伤修复研究

针对波长1053 nm, 0°高反介质膜元件, 采用有限时域差分法, 模拟分析了损伤修复点边缘与法线的夹角对膜层内电场强度分布的影响, 该角度越小, 修复点的损伤阈值越高. 通过优化飞秒激光微加工过程中的焦斑尺寸、脉冲能量、扫描步长和扫描次数等参数, 获得了夹角为25°、深度为14 μm的修复点. 该修复点典型的损伤阈值为21 J/cm², 是修复前的2.3倍, 50个修复点的测试结果表明该修复参数具有非常好的可重复性. 修复点的测试结果还验证了修复点边缘与法线的夹角大小与其损伤阈值的关系, 45°的电场强度最大值约为25°的2.5倍, 而45°的损伤阈值约为25°的1/2, 模拟和实验结果一致性较好. 同时, 实验验证了微加工的激光脉宽对修复点损伤阈值的影响, 在只改变脉宽的情况下, 脉宽越长, 损伤阈值越低.     

A controlled conical lens for the formation of Bessel light beams

The possibility of the formation of zero-order Bessel light beams using a uniaxial crystal with cylindrical electrodes is investigated. It is shown that, if a given polarization distribution is provided in the incident beam, a Bessel light beam with the cone angle controlled by an external electric field is formed. It is proposed to use this result for the matching of the axicon parameters and creation of conical lenses with an adjustable cone angle.     

Viscous entrainment from a nozzle: singular liquid spouts

We analyze a long-wavelength model of viscous entrainment from a nozzle and show that, when appropriate large-scale boundary conditions are imposed, the entrainment transition can become continuous. As the entrainment threshold is approached from above, the entrained steady-state spout becomes vanishingly thin compared to the nozzle radius and takes the form of a thin tendril emerging from a base profile whose tip is perfectly conical.     

Electrohydrodynamics of a Cone–Jet Flow at a High Relative Permittivity

We have proposed a new solution of the electrohydrodynamic equations describing a novel cone–jet flow structure formed at a conductive liquid meniscus in an electric field. Focusing on the liquids characterized by a high relative permittivity and using the slender body approximation, the cone–jet transition profiles and their characteristic radii are predicted in relation to the material parameters. The stable value of the cone angle is obtained using the Onsager’s principle of maximum entropy production. Three different regimes of the cone–jet flow behavior are identified depending on the relative importance of capillary, viscous and inertial stress contributions. The presented complete analytical solutions for the cone–jet transition zone and the far jet region yield several different laws of algebraic decrease for the radius, surface charge, and electric field of the jet.     

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.     

锥顶碳纳米管的结构稳定性与场致发射性能

运用密度泛函理论研究了锥顶碳纳米管的结构稳定性与电子场致发射性能.结果表明:在外电场作用下,该体系的结构稳定性明显优于碳纳米锥体、C₃₀半球封口的碳纳米管,且电子发射性能与锥角大小、锥顶构型密切相关,特别是锥角38.9°及棱脊型顶部的cone₁@(6,6)综合性能最优,用其作为场致发射源的阴极时可显著提高发射电流密度并延长器件的使用寿命. 关键词： 锥顶碳纳米管 电子场致发射 结构稳定性 密度泛函理论     

On the possibility of corona initiation near a conducting drop nonlinearly vibrating in an external electrostatic field

An analytical asymptotic expression for the field strength near an ideal incompressible electrically conducting liquid drop nonlinearly vibrating in external electrostatic field E ₀ is found in an order of 5/2 in a small parameter. The small parameter here is the amplitude of deformation of the spherical shape of the drop. It is found that the strength of the electric field resulting at the tops of the drop exceeds the corona-initiating field even if E ₀ is one order of magnitude lower than the value at which the drop becomes unstable against the induced charge (that is, at such values of E ₀ as are observed in storm clouds in full-scale experiments).     

Analytical model of a corona discharge from a conical electrode under saturation

Exact partial solutions are found for the electric field distribution in the outer region of a stationary unipolar corona discharge from an ideal conical needle in the space-charge-limited current mode with allowance for the electric field dependence of the ion mobility. It is assumed that only the very tip of the cone is responsible for the discharge, i.e., that the ionization zone is a point. The solutions are obtained by joining the spherically symmetric potential distribution in the drift space and the self-similar potential distribution in the space-charge-free region. Such solutions are outside the framework of the conventional Deutsch approximation, according to which the space charge insignificantly influences the shape of equipotential surfaces and electric lines of force. The dependence is derived of the corona discharge saturation current on the apex angle of the conical electrode and applied potential difference. A simple analytical model is suggested that describes drift in the point-plane electrode geometry under saturation as a superposition of two exact solutions for the field potential. In terms of this model, the angular distribution of the current density over the massive plane electrode is derived, which agrees well with Warburg??s empirical law.     

Quantum dissociation of an edge of a Luttinger liquid

In a Luttinger liquid phase of one-dimensional molecular matter the strength of zero-point motion can be characterized by dimensionless De Boer's number quantifying the interplay of quantum fluctuations and two-body interactions. Selecting the latter in the Morse form we show that dissociation of the Luttinger liquid is a process initiated at the system edge. The latter becomes unstable against quantum fluctuations at a value of De Boer's number which is smaller than that of the bulk instability which parallels the classical phenomenon of surface melting.     

Instability of a spherical drop in the field of an electrical dipole

Analytical calculations show that, as a field in which an initially spherical charged conducting incompressible drop is placed becomes more and more nonuniform, coupling between the drop’s oscillation modes grows and the threshold of stability against the electrical field pressure declines. When an electrostatic parameter characterizing the electric field pressure exceeds a value that is critical for a certain mode to be unstable, the amplitude of this mode exponentially grows in an aperiodic manner and the amplitudes of modes coupled with this mode build up in an oscillatory manner, each mode having its own instability growth rate. In all cases, there exists a threshold value of the dimensionless electric parameter above which all oscillation modes are unstable.     

Interaction between laser beam and target in pulsed laser deposition: laser fluence and ambient gas effects

The most prominent phenomena on the target surface induced by laser irradiation in pulsed laser deposition is the formation of conical morphologies in the irradiated area. The conical morphologies formed under different laser fluences and the ambient oxygen pressures in KrF laser ablation of Pb(Zr_0.53Ti_0.47)O₃ were studied in detail by using scanning electron microscopy. The results indicate that, depending on the melting extent of the irradiated surface, there are two kinds of cones: one type with well-defined cone tip and cone body and the other having only a cone tip. Pb is very deficient in cone tip. The gas ambient pressure plays a remarkable role in the laser-target interaction. These results are interpreted by employing the impurity shielding mechanism and the surface instability mechanism.     

On the time evolution of the liquid meniscus at the end of a capillary placed in an external electric field

Using a linearized set of equations of electrodynamics, the stability of the uniformly charged meniscus of a viscous conducting incompressible liquid at the end of a capillary is investigated and analytical expressions are derived for the electric field outside the meniscus, velocity fields in the liquid flow and meniscus, and generatrix of the meniscus shape. It is found that, if an external electric field near the meniscus exceeds that at which the free liquid surface becomes unstable against the surface charge, a finite number of longest waves become unstable with their instability growth rates nonmonotonically depending on the wavenumber. Analysis of the time evolution of the meniscus shape under various initial conditions shows that cylindrical waves with the highest instability growth rates play a decisive role in this process, while the influence of the initial deformation amplitude is insignificant.     

激光动态外锥折射实验研究

根据双轴晶体的锥形折射效应，提出锥角可控的动态外锥折射以及一种实现外锥折射的新方法；选用ＫＮｂＯ３晶体进行实验，不仅观察到外锥折射，而且实现了锥角在０°～８°范围内的外锥折射扫描控制     

Identification of molecules through the fluorescence enhancement by a metal tip

A fluorescence enhancement phenomenon, which is realized as a result of a sharp increase in the radiative decay rate of a quantum dipole emitter (QDE) is investigated theoretically in the vicinity of a conical metal tip. The QDE relaxation process is considered as a self-stimulated transition from an excited state into the ground state due to the feedback field formation from the tip. The dynamics of the system shows a stepped relaxation behavior that differs significantly from the conventional exponential decay. This effect can be observed in a small region of the resonance frequency, which is defined by an angle of conical tip. The increase of fluorescence when approaching of molecule to the metal tip on the surface enables one to determine its location.     

圆锥边界附近激光空泡溃灭行为的研究

为了研究刚性圆锥边界锥角对激光空泡溃灭行为的影响,文章建立了虚拟平面边界模型, 同时采用阴影摄影术、光偏转法以及数值计算的手段对边界附近空泡溃灭过程进行了研究. 结果表明边界的锥角对空泡的形状、溃灭时间以及液体射流形成均有明显影响. 空泡形状偏离球形的程度和溃灭时间均随锥角的增大而增大,且增大锥角度可以促使射流的形成. 空泡溃灭时间的实验值同理论值具有较高的一致性,验证了虚拟平面边界假设及无量纲距离修正的有效性.     

Optical absorption in a narrow-band InSb cylindrical layered nanowire in the presence of strong electrostatic field

On the example of InSb we consider the influence of a strong homogeneous electrostatic field on the state of carriers in a narrow-band quantized cylindrical layer in the case of Kaine dispersion law. Explicit expressions for the energy spectrum and wave function envelopes of charge carriers in the heterolayer are obtained. It is shown that under action of the strong external field the rotational motion, with respect to angular variables, of charge carriers becomes oscillatory in a narrow cone of the azimuth angle. We have obtained corresponding selection rules and calculated the threshold frequencies of absorption for interband and intraband electro-optical transitions in the layer. The threshold frequencies are determined by the geometric sizes of the sample and the magnitude of the external field.     

Numerical simulations of laser light guiding and focusing using an open hollow cone

An open hollow cone that can optically guide and focus a laser light into a small beam spot is proposed. The shaping and focusing effects are numerically demonstrated by finite-difference time-domain simulations. The results reveal that the cone-focused laser originates from the multi-beam interference and squeeze of two cone side walls acting like oblique targets. Moreover, the influences of oblique incident angle of laser light, cone angle and cone tip size on the focusing properties are discussed and the optimum cone geometry with cone angle of 16° and tip size of 4.5 wavelengths to achieve high energy concentration at the cone tip is also presented. It is shown that with an open hollow cone a laser light can be focused into a tiny highly localized beam spot of 1 µm diameter and keeps propagating forward for a distance of about 8 wavelengths with a tiny spot diameter remaining almost unchanged. The intensity almost increases up to twentyfold in a 1 µm focal spot.