Twist in chiral interaction between biological helices

Using an exact solution for the pair interaction potential, we show that long, rigid, chiral molecules with helical surface charge patterns have a preferential interaxial angle approximately sqrt[RH]/L, where L is the length of the molecules, R is the closest distance between their axes, and H is the helical pitch. Estimates based on this formula suggest a solution for the puzzle of small interaxial angles in alpha-helix bundles and in cholesteric phases of DNA.     

Self-assembly and nonlinear dynamics of dimeric colloidal rotors in cholesterics

We study by simulation the physics of two colloidal particles in a cholesteric liquid crystal with tangential order parameter alignment at the particle surface. The effective force between the pair is attractive at short range and favors assembly of colloid dimers at specific orientations relative to the local director field. When pulled through the fluid by a constant force along the helical axis, we find that such a dimer rotates, either continuously or stepwise with phase-slip events. These cases are separated by a sharp dynamical transition and lead, respectively, to a constant or an ever-increasing phase lag between the dimer orientation and the local nematic director.     

Azimuthal anisotropy of K(0)(S) and Lambda+Lambda production at midrapidity from Au+Au collisions at sqrt[s(NN)]=130 GeV

We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K(0)(S), Lambda, and Lambda at midrapidity in Au+Au collisions at sqrt[s(NN)]=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t) approximately 3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed.     

Azimuthal anisotropy and correlations at large transverse momenta in p + p and Au + Au collisions at square root sNN=200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au + Au collisions at square root s(NN)=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au + Au collisions to those in p + p at the same energy. The elliptic anisotropy v(2) is found to reach its maximum at p(t) approximately 3 GeV/c, then decrease slowly and remain significant up to p(t) approximately 7-10 GeV/c. Stronger suppression is found in the back-to-back high-p(t) particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v(2) at intermediate p(t) is compared to simple models based on jet quenching.     

Velocity statistics in excited granular media

We present an experimental study of velocity statistics for a partial layer of inelastic colliding beads driven by a vertically oscillating boundary. Over a wide range of parameters (accelerations 3-8 times the gravitational acceleration), the probability distribution P(v) deviates measurably from a Gaussian for the two horizontal velocity components. It can be described by P(v) approximately exp(-mid R:v/v(c)mid R:(1.5)), in agreement with a recent theory. The characteristic velocity v(c) is proportional to the peak velocity of the boundary. The granular temperature, defined as the mean square particle velocity, varies with particle density and exhibits a maximum at intermediate densities. On the other hand, for free cooling in the absence of excitation, we find an exponential velocity distribution. Finally, we examine the sharing of energy between particles of different mass. The more massive particles are found to have greater kinetic energy. (c) 1999 American Institute of Physics.     

表面上方微粒及微粗糙度偏振光散射特性

为了区分由表面上方微粒和表面微粗糙度两种散射机理引起的散射光,利用偏振双向反射分布函数,并借助于由,■,■组成的正交右手基组表示了入射电场和散射电场。从理论上给出了两种不同散射机理在不同偏振状态下的双向反射分布函数与入射面外方位角之间的变化关系,并通过对这两种散射机理下的偏振双向反射分布函数的比较发现,利用p偏振入射产生的p偏振散射光(BRDFpp)可以将表面上方微粒和表面微粗糙度两种散射机理区分开来。     

Switchable two-dimensional gratings based on field-induced layer undulations in cholesteric liquid crystals

We propose switchable two-dimensional (2D) diffractive gratings with periodic refractive-index modulation arising from layer undulations in cholesteric liquid crystals. The cholesteric cell can be switched between two states: (1) flat layers of a planar cholesteric texture and (2) a square lattice of periodic director modulation associated with layer undulations that produces 2D diffraction patterns. The intensities of the diffraction maxima can be tuned by changing the applied field. The diffractive properties can be optimized for different wavelengths by appropriately choosing cholesteric pitch, cell thickness, and surface treatment.     

Surface plasmon dispersion for very small metallic spheres: A quantum mechanical formulation

We have derived a pair of matrix equations describing the surface plasmon dispersion for a very small spherical metal particle, using the quantum mechanical random-phase approximation (RPA). The surface of the sphere is represented by an infinite spherical potential well for the conduction electrons and the positive ions are assumed to be uniformly distributed into a “jellium”. The dispersion relation is obtained as the condition that a solution of the RPA integral equation for charge fluctuation would exist for the particle.     

Liquid-crystalline phases formed by DNA duplexes containing pyrophosphate groups

We have studied the interaction between synthetic DNA molecules containing pyrophosphate (PP) groups in various positions, which makes it possible to control the charge distribution along the DNA chain. The PP groups were either symmetrically arranged at the ends or at the center of DNA molecules or uniformly distributed along these molecules. It is shown that, similar to nonmodified DNA, the synthetic PP-modified DNA molecules can form cholesteric liquid crystals. Minima of the pair interaction potential are found, conditions of the symmetry of this potential are formulated, and the dependence of conformation angles on the effective charge is determined. The results of calculations show that the system exhibits polymorphism (i.e., several phases of cholesteric liquid crystals can exist in DNA solutions).     

Cooper pair cotunneling in single charge transistors with dissipative electromagnetic environment

We observed current-voltage characteristics of superconducting single charge transistors with on-chip resistors of R approximately R(Q)=h/4e(2) approximately 6.45 kOmega, which are explained in terms of Cooper pair cotunneling. Both the effective strength of Josephson coupling and the cotunneling current are modulated by the gate-induced charge on the transistor island. For increasing values of the resistance R we found the Cooper pair current at small transport voltages to be dramatically suppressed.     

Elliptic flow of identified hadrons in Au+Au collisions at sqrt sNN =200 GeV

The anisotropy parameter (v(2)), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in Au+Au collisions at sqrt[s(NN)]=200 GeV for identified and inclusive charged particle production at central rapidities (|eta|<0.35) with respect to the reaction plane defined at high rapidities (|eta|=3-4 ). We observe that the v(2) of mesons falls below that of (anti)baryons for p(T)>2 GeV/c, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.     

RHIC和LHC能区两粒子关联函数研究

应用多源热模型研究了相对论性重离子对撞机（RHIC）上PHENIX合作组测得的每核子对质心能量√sNN=200 GeV的氘-金（d+Au）碰撞中快度长程方位角关联,和大型强子对撞机（LHC）上CMS合作组测得的质心能量√s=0.9,2.36,7 TeV的质子质子（p+p）碰撞中高多重数短程赝快度关联,在误差范围内模型结果很好地重现了实验数据。用4个参数分析了长程方位角关联,结果表明,参数可以清楚地显示出脊结构的变化趋势,说明脊结构与集体效应、流体力学流效应、粒子对的横动量及信号等有关。用3个参数分析了小系统高多重数短程赝快度关联,结果表明,参数σ和c₃与能量相关,能量越大,两粒子越靠近,关联越强。The multi-source thermal model is used in this paper to analyze the long-range azimuth correlation in deutron-gold (d+Au) collisions at center-of-mass energy per nucleon pair √sNN=200 GeV measured by the PHENIX Collaboration at the relativistic heavy ion collider (RHIC), and the short-range pseudorapidity correlation in high multiplicity event in proton-proton (p+p) collisions at center-of-mass energy √s=0.9, 2.36, 7 TeV measured by the CMS Collaboration at the large hadron collider (LHC). The modeling results are in approximately agreement with the experimental data in error ranges. Four parameters are used in the analysis of long-range azimuth correlation, which show that the parameters describe the change trend of ridge structure. The ridge structure is related to the collective effect, hydrodynamic flow effect, transverse momentum and signal of particle pair, and so forth. Three parameters are used in the analysis of the short-range pseudorapidity correlation in high multiplicity event in small system, which show that the parameters σ and c3 are related to collision energy. Large collision energy results in strong correlation due to close distance between particles.     

Does the Boltzmann Principle Need a Dynamical Correction?

In an attempt to derive thermodynamics from classical mechanics, an approximate expression for the equilibrium temperature of a finite system has been derived (M. Bianucci, R. Mannella, B. J. West and P. Grigolini, Phys. Rev. E 51: 3002 (1995)) which differs from the one that follows from the Boltzmann principle S = kln(E) via the thermodynamic relation 1/T=S / E by additional terms of dynamical character, which are argued to correct and generalize the Boltzmann principle for small systems (here (E) is the area of the constant-energy surface). In the present work, the underlying definition of temperature in the Fokker–Planck formalism of Bianucci et al., is investigated and shown to coincide with an approximate form of the equipartition temperature. Its exact form, however, is strictly related to the volume entropy S = k ln (E) via the thermodynamic relation above for systems of any number of degrees of freedom ((E) is the phase space volume enclosed by the constant-energy surface). This observation explains and clarifies the numerical results of Bianucci et al., and shows that a dynamical correction for either the temperature or the entropy is unnecessary, at least within the class of systems considered by those authors. Explicit analytical and numerical results for a particle coupled to a small chain (N~10) of quartic oscillators are also provided to further illustrate these facts.     

Scaling property in one-nucleon removal reactions induced by exotic nuclei

Assuming a core plus valence nucleon structure, one-nucleon removal reaction is investigated within the framework of few-body Glauber theory. Fermi-type distribution is used for the core density, while the wavefunction of the valence nucleon is calculated by solving the single particle eigeuvalue problem of the SchrSdinger equation with the Woods-Saxon potential. The parallel momentum distribution (P//) of the fragments is calculated for isotopes with 3 < Z < 18. A remarkable scaling property is observed from the dependence of the dimensionless quantity R2v/R2c on the full width at half maximum of the parallel momentum distribution (FWHMp//). R2v/R2c is a measure of the exotic extent of the nuclear halo. Based on the obtained scaling law, FWHMp// can be used as an experimental observable to extract R2v/R2c and measure the exoticextent for the nuclear halo.     

一种体积物态方程物理基础的讨论

 对体积物态方程v-v_c=(R/p)(h-h_c)的物理基础进行了讨论。给出了该方程的一个统计力学形式证明,从而给出了方程中物质参数的微观定义,亦即给出了该方程的具体表达式。在R=R(p)假设下,给出了方程中物质参数的热力学表达式,通过分析其与Debye理论下的对应态定律的一致性,证明了该假设的近似合理性,从而也就证明了该方程的成立并不受其建立时所依据的定压比热为常数这一过强条件的限制。进一步地,通过与物质参数热力学表达式常压实验值的比较,指出了单纯的R=R(p)假定存在一定的局限,该局限引起的偏差随温度的升高而增大,在常压下的高温区间,该偏差在20%左右。     

Surface acoustic cavitation understood via nanosecond electrochemistry. Part III: Shear stress in ultrasonic cleaning

Acoustic cavitation is extensively used for cleaning purposes. However, little is known about the fundamental aspects of the cleaning process. Our previous electrochemical data suggested that acoustic bubbles were oscillating at a distance of only a few tens of nanometers above the surface [J. Phys. Chem. B 105 (2001) 12087; E. Maisonhaute, B.A. Brookes, R.G. Compton, J. Phys. Chem. B 106 (2002) 3166–3172]. The flow velocities resulting from the bubble collapse lead to important drag and shear forces on the surface, responsible for cleaning and/or eroding the latter. We review here the forces acting on an adsorbed particle located on the surface, and develop arguments to explain why small adsorbates are harder to remove by sonication. Then, experimental results on particle desorption and surface effects brought about by ultrasound are presented and shown to agree with our theoretical predictions.     

Temperature variations in the director orientation and anchoring energy at the surface of cholesteric layers

Slight changes with temperature in the director orientation at the surface of a perfect planar cholesteric liquid crystal (CLC) layer, which are precursors of a jump in the pitch of the cholesteric helix, are observed by measuring the temperature dependence of the optical transmission spectra of the layer. The observed changes in the director orientation are described in the framework of the continuum theory of CLCs, supplemented with allowance for the surface anchoring forces. In particular, the angle of deviation of the director at the surface from the alignment direction at the exact temperature of the jump in pitch is expressed in terms of the anchoring potential. The relation obtained is use to find the anchoring potential in the samples. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 37–42 (10 January 1996)     

Radiation reaction and the self-force for a point mass in general relativity

A point particle of mass mu moving on a geodesic creates a perturbation h(mu), of the spacetime metric g(0), that diverges at the particle. Simple expressions are given for the singular mu/r part of h(mu) and its quadrupole distortion caused by the spacetime. Subtracting these from h(mu) leaves a remainder h(R) that is C1. The self-force on the particle from its own gravitational field corrects the world line at O(mu) to be a geodesic of g(0)+h(R). For the case that the particle is a small nonrotating black hole, an approximate solution to the Einstein equations is given with error of O(mu(2)) as mu-->0.     

The high-frequency dispersion coefficient for the Rayleigh velocity in a vertically inhomogeneous anisotropic half-space

For an arbitrary anisotropic half-space with continuous vertical variation of material properties, an explicit closed-form expression for the coefficient B of high-frequency dispersion of the Rayleigh velocity v(R)(omega) approximately v(R)(0)(1+B/omega) is derived. The result involves two matrices, one consisting of the surface-traction derivatives in velocity and the other of its Wentzel-Kramers-Brillouin coefficients, which are contracted with an amplitude vector of the Rayleigh wave in the reference homogeneous half-space. The "ingredients" are routinely defined through the fundamental elasticity matrix and its first derivative, both taken at v=v(R)(0) and referred to the surface.     

High-Resolution Measurements of HBr Transitions in the First Overtone Band Using Tunable Diode Lasers

High-resolution absorption lineshapes of the R(7) and P(2) transitions in the first overtone (v = 0-2) band of H(79)Br have been recorded at room temperature using a pair of distributed feedback diode lasers operating near 1.95 and 2.00 μm, respectively. Spectral line intensities and self-broadening coefficients were determined by fitting the measured spectra (for various pressures P = 10-100 Torr) with Voigt profiles and compared with values in the literature. Measured line intensities for the P(2) and R(7) transitions are approximately 11 and 16% higher than those listed in the HITRAN database, respectively. The measured self-broadening coefficient of the P(2) transition is approximately 14% lower than the value listed in HITRAN. Measurements of the P(2) lineshapes at low pressure (100 mTorr) were modeled with eight-line Gaussian profiles based on ground state (v = 0) hyperfine constants to include the effects of nuclear electric quadrupole interactions. Copyright 2000 Academic Press.