Double cascade turbulence and Richardson dispersion in a horizontal fluid flow induced by Faraday waves

We report the experimental observation of Richardson dispersion and a double cascade in a thin horizontal fluid flow induced by Faraday waves. The energy spectra and the mean spectral energy flux obtained from particle image velocimetry data suggest an inverse energy cascade with Kolmogorov type scaling E(k) ∝ k(γ), γ ≈ -5/3 and an E(k) ∝ k(γ), γ ≈ -3 enstrophy cascade. Particle transport is studied analyzing absolute and relative dispersion as well as the finite size Lyapunov exponent (FSLE) via the direct tracking of real particles and numerical advection of virtual particles. Richardson dispersion with <ΔR(2)(t)> ∝ t(3) is observed and is also reflected in the slopes of the FSLE (Λ ∝ ΔR(-2/3)) for virtual and real particles.     

Electron cotunneling transport in gold nanocrystal arrays

We describe current-voltage (I-V) characteristics of alkyl-ligated gold nanocrystals ~5 nm arrays in a long screening length limit. Arrays with different alkyl ligand lengths have been prepared to tune the electronic tunnel coupling between the nanocrystals. For long ligands, electronic diffusion occurs through sequential tunneling and follows activated laws, as a function of temperature σ∝e(-T(0)/T) and as a function of electric field I∝e(-E(0)/E). For better conducting arrays, i.e., with small ligands, the transport properties cross over to the cotunneling regime and follow Efros-Shklovskii laws as a function of temperature σ∝e(-(T(ES)/T)(1/2) and as a function of electric field I∝e(-(E)(ES)/E)(1/2). The data show that electronic transport in nanocrystal arrays can be tuned from the sequential tunneling to the cotunneling regime by increasing the tunnel barrier transparency.     

Power-law spin correlations in a perturbed spin model on a honeycomb lattice

We consider the spin-1/2 model on the honeycomb lattice in the presence of a weak magnetic field hα < 1. Such a perturbation destroys the exact integrability of the model in terms of gapless fermions and static Z2 fluxes. We show that it results in the appearance of a long-range tail in the irreducible dynamic spin correlation function: ∝ h(z)(2)f(t,r), where f(t,r) ∝ [max(t,r)]-4 is proportional to the density polarization function of fermions.     

液氦温区La2/3Ca1/3Mn1-xCuxO3(x=0.15)体系的磁电阻弛豫效应

实验上研究了液氦温区Ｌａ２／３Ｃａ１／３Ｍｎ１－ｘＣｕｘＯ３（ｘ＝０－１５）单相多晶样品给定磁场下的电阻随时间的变化,发现磁电阻随时间变化并非遵从对数规律而是呈指数型变化行为．对这一指数型磁电阻弛豫行为的可能起因进行了讨论,指出这是与Ｍｎ位上Ｃｕ掺杂将额外磁性杂质引入到样品中有关 关键词：     

Pair dispersion in turbulence: the subdominant role of scaling

The mixing properties of turbulent flows are, at first order, related to the dynamics of separation of particle pairs. Scaling laws for the evolution in time of the mean distance between particle pairs (t) have been proposed since the pioneering work of Richardson. We analyze a model which shares some features with 3D experimental and numerical turbulence, and suggest that pure scaling laws are only subdominant. The dynamics is dominated by a very wide distribution of "delay times" t(d), the duration for which particle pairs remain together before their separation increases significantly. The delay time distribution is exponential for small separations and evolves towards a flat distribution at large separations. The observed (t) behavior is best understood as an average over separations that individually follow the Richardson-Obukhov scaling, r(2) ∝ t(3), but each only after a fluctuating time delay t(d), where t(d) is distributed uniformly.     

Diffusion: A Layman's approach and its applications to one-dimensional random systems

Diffusion characteristics are reduced to the solution of a simple stationary equation. In classical one-dimensional random systems, time-irreversability (provided, e.g., by a magnetic field) implies L ∝ $\text{l}$nt, L is a diffusion length, t is time, while local space assymetry (provided by random fields) implies L ∝ $\text{l}$n²t; both cases are related to the localized particle distribution.     

G(E(p))/G(M(p)) ratio by polarization transfer in e-->p --> ep-->

The ratio of the proton's elastic electromagnetic form factors, G(E(p))/G(M(p)), was obtained by measuring P(t) and P(l), the transverse and the longitudinal recoil proton polarization, respectively. For elastic e-->p-->ep-->, G(E(p))/G(M(p)) is proportional to P(t)/P(l). Simultaneous measurement of P(t) and P(l) in a polarimeter provides good control of the systematic uncertainty. The results for the ratio G(E(p))/G(M(p)) show a systematic decrease as Q2 increases from 0.5 to 3.5 GeV2, indicating for the first time a definite difference in the spatial distribution of charge and magnetization currents in the proton.     

Kinematic power corrections in off-forward hard reactions

We develop a general approach to the calculation of kinematic corrections ∝t/Q(2), m(2)/Q(2) in hard processes which involve momentum transfer from the initial to the final hadron state. As the principal result, the complete expression is derived for the time-ordered product of two electromagnetic currents that includes all kinematic corrections to twist-four accuracy. The results are immediately applicable, e.g., to the studies of deeply virtual Compton scattering.     

Pairing isomers

The formalism for quadrupole pairing forces acting simultaneously with monopole pairing and quadrupole particle-hole forces has been worked out in the framework of BCS and RPA. The low-lying 0⁺ states are studied. Expressions for E0 and E2 transition probabilities as well as spectroscopic amplitudes for (t, p) and (p, t) reactions are given. The formalism is applied to the actinide region and it is shown that the low-lying 0⁺ states strongly populated in (p, t) but not in (t, p) reactions can be explained as pairing isomers having an appreciably smaller value of the pairing gap Δ than the ground state. This phenomenon is similar to the phenomenon of gapless superconductivity in solid state physics, i.e. the pairing isomers are formed because of the inhomogeneity of oblate and prolate levels in the vicinity of the Fermi surface.     

1+1维和2+1维空间上定向聚合问题的数值研究

对1+1和2+1维空间上定向聚合问题的数值模拟结果显示,任意有限温度下的横向涨落和自由能涨落在聚合尺度t较大时都将趋于零温度时强耦合下的结果:Δx∝t^ν和ΔF∝t^ω(d=1+1时,ν=2/3,ω=1/3;d=2+1时,ν≈0.6,ω≈0.2).有限温度下,由于1+1维和2+1维空间上的比热C(T,t)∝t和1+1维空间上的熵涨落ΔS∝t^1/2,1+1维空间上的系综能量涨落和内能涨落以及2+1维空间上的系综能量涨落均趋于t^1/2而远强于自由能涨落.在2+1维空间上,定向聚合问题有发生相变的迹象:当熵涨落达到其最大值时,单位聚合尺度的熵涨落和内能涨落在聚合尺度t→∞时,可能会由低温下趋于有限值(零温度除外)转变为高温下趋于零 关键词： 定向聚合 表面生长现象 Kardar-Parisi-Zhang方程     

La0.822Sr0.178MnxO3薄膜的输运性质

本文报道了用La、Sr、Mn的环烷酸盐溶液,采用两次旋转覆盖的溶胶－凝胶方法,在LaA-lO3(100)基底上合成了La0.822Sr0.178MnxO3薄膜,Mn含量x在0．944－1．196范围内,电阻率随着温度的变化关系,是从绝缘体内金属导电行为转变;对x＝0．9样品则表现为绝缘体,对x＝0．944样品,当T／Tc时,ρ∝exp(E/kT),说明载流子的迁移是以热激活方式进行的,热激活能为21meV;当T＜Tc时,符合ρ＝ρ0＋AT^2．5,说明电子－声子和电子－磁极化子散射占主要,对x＝0．97、0．99、1．196样品,T／Tc时则更好地符合指数关系。     

Evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence

We study the evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence. By quasilinearizing the Navier-Stokes equation, we solve analytically the induction equation in the quasinormal approximation. We find that, if the magnetic field is not helical, the magnetic energy and correlation length evolve in time, respectively, as E(B) proportional to t(-2(1+p)/(3+p)) and xi(B) proportional to t(2/(3+p)), where p is the index of initial power-law spectrum. In the helical case, the magnetic helicity is an almost conserved quantity and forces the magnetic energy and correlation length to scale as E(B) proportional to (logt)(1/3)t(-2/3) and xi(B) proportional to (logt)(-1/3)t(2/3).     

Transient photodecay measurements as a probe of the density of localized states in amorphous semiconductors

We show that structure in the density of localized states of an amorphous semiconductor beyond the apparently ubiquitous exponential band tails yield deviations from the usual power-law decay of the photocurrent, i(t) ∝ t^α?1, which can be described analytically. With our expression, dispersive-transport results can be deconvoluted to provide a spectroscopy of the localized-state distribution when well-defined defect centers and band tails are simultaneously present.     

Torque scaling in turbulent Taylor-Couette flow with co- and counterrotating cylinders

We analyze the global transport properties of turbulent Taylor-Couette flow in the strongly turbulent regime for independently rotating outer and inner cylinders, reaching Reynolds numbers of the inner and outer cylinders of Re(i) = 2×10(6) and Re(o) = ±1.4×10(6), respectively. For all Re(i), Re(o), the dimensionless torque G scales as a function of the Taylor number Ta (which is proportional to the square of the difference between the angular velocities of the inner and outer cylinders) with a universal effective scaling law G ∝ Ta(0.88), corresponding to Nu(ω) ∝ Ta(0.38) for the Nusselt number characterizing the angular velocity transport between the inner and outer cylinders. The exponent 0.38 corresponds to the ultimate regime scaling for the analogous Rayleigh-Bénard system. The transport is most efficient for the counterrotating case along the diagonal in phase space with ω(o) ≈ -0.4ω(i).     

Atomistic Simulation of the Equation of State of SrF 2 Using Electron Gas Interionic Potentials

We have determined the equation of state (EOS) of SrF 2 in the cubic (C1, Fm3m ) and orthorhombic (C23, Pbnm ) phases using Electron Gas Interionic Potentials (EGIP) that incorporate many-body energy components. Thermal effects are included by means of a quasi-harmonic Debye model. The zero pressure unit cell length ( a 0 ), lattice energy ( E latt ), bulk modulus ( B 0 ), and EOS of the C1 phase are predicted in good agreement with the observed data. Moreover, the computed EOS satisfy very well the empirical Vinet EOS. Fittings of m / m 0 m p data ( m = a, b, c ) to linear forms of the Vinet EOS reveal that SrF 2 (C23) is more compressible along the b and c axes than along the a direction. Finally, the {\rm C1}\rightleftharpoons {\rm C23} transition is predicted to occur at p t =3.92 GPa, which is between the observed direct ( p t =5.0 GPa) and reverse C1 ( p t =1.7 GPa) phase transitions.     

Development of high vorticity in incompressible 3D Euler equations: Influence of initial conditions

The incompressible three-dimensional ideal flows develop very thin pancake-like regions of increasing vorticity. These regions evolve with the scaling ω_max(t) ∝ l(t)^-2/3 between the vorticity maximum and pancake thickness, and provide the leading contribution to the energy spectrum, where the gradual formation of the Kolmogorov interval E _k ∝ k^?5/3 is observed for some initial flows. With the massive numerical simulations, we study the influence of initial conditions on the processes of pancake formation and the Kolmogorov energy spectrum development.     

Measurements of the proton elastic-form-factor ratio mu pG p E/G p M at low momentum transfer

High-precision measurements of the proton elastic form-factor ratio, mu pG p E/G p M, have been made at four-momentum transfer, Q2, values between 0.2 and 0.5 GeV2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q2 range the deviation from unity is primarily due to G p E being smaller than expected.     

Spin squeezing: transforming one-axis twisting into two-axis twisting

Squeezed spin states possess unique quantum correlation or entanglement and are significantly promising for advancing quantum information processing and quantum metrology. In recent back-to-back publications [C. Gross et al., Nature (London) 464, 1165 (2010) and Max F. Riedel et al., Nature (London) 464, 1170 (2010)], reduced spin fluctuations are observed leading to spin squeezing at -8.2 and -2.5 dB, respectively, in two-component atomic condensates exhibiting one-axis-twisting interactions. The noise reduction limit for the one-axis twisting scales as ∝1/N(2/3), which for a condensate with N～10(3) atoms is about 100 times below the standard quantum limit. We present a scheme using repeated Rabi pulses capable of transforming the one-axis-twisting spin squeezing into the two-axis-twisting type, leading to Heisenberg limited noise reduction ∝1/N or an extra tenfold improvement for N～10(3).     

A causal and fractional all-frequency wave equation for lossy media

This work presents a lossy partial differential acoustic wave equation including fractional derivative terms. It is derived from first principles of physics (mass and momentum conservation) and an equation of state given by the fractional Zener stress-strain constitutive relation. For a derivative order α in the fractional Zener relation, the resulting absorption α(k) obeys frequency power-laws as α(k) ∝ ω(1+α) in a low-frequency regime, α(k) ∝ ω(1-α/2) in an intermediate-frequency regime, and α(k) ∝ ω(1-α) in a high-frequency regime. The value α=1 corresponds to the case of a single relaxation process. The wave equation is causal for all frequencies. In addition the sound speed does not diverge as the frequency approaches infinity. This is an improvement over a previously published wave equation building on the fractional Kelvin-Voigt constitutive relation.     

Ground state proton radioactivity from 121Pr: when was this exotic nuclear decay mode first discovered?

Ground-state proton radioactivity has been identified from 121Pr. A transition with a proton energy of E(p)=882(10) keV [Q(p)=900(10) keV] and half-life t(1/2)=10(+6)(-3) ms has been observed and is assigned to the decay of a highly prolate deformed 3/2(+) or 3/2(-) Nilsson state. The present result is found to be incompatible with a previously reported observation of ground-state proton radioactivity from 121Pr, which would have represented the discovery of this phenomenon.