Anomalous, quasilinear, and percolative regimes for magnetic-field-line transport in axially symmetric turbulence

We studied a magnetic turbulence axisymmetric around the unperturbed magnetic field for cases having different ratios l( ||)/l( perpendicular). We find, in addition to the fact that a higher fluctuation level deltaB/B(0) makes the system more stochastic, that by increasing the ratio l( ||)/l( perpendicular) at fixed deltaB/B(0), the stochasticity increases. It appears that the different transport regimes can be organized in terms of the Kubo number R=(deltaB/B(0))(l( ||)/l( perpendicular)). The simulation results are compared with the two analytical limits, that is the percolative limit and the quasilinear limit. When R<1 weak chaos, closed magnetic surfaces, and anomalous transport regimes are found. When R approximately 1 the diffusion regime is Gaussian, and the quasilinear scaling of the diffusion coefficient D( perpendicular) approximately (deltaB/B(0))(2) is recovered. Finally, for R>1 the percolation scaling of the diffusion coefficient D( perpendicular) approximately (deltaB/B(0))(0.7) is obtained.     

标准映象的周期分岔及其向混沌的过渡

本文研究了标准映象的周期轨道在其余数R=1和R=0附近的行为,对于前者出现倍周期分岔序列,其分岔率δ及标度因子α和β与其它二维保面积映象的结果一致;对于后者发生同周期分岔,这与标准映象的奇对称性有关。文中还计算了混沌轨道的李雅普诺夫指数,发现在倍周期分岔序列的聚点k_∞附近,存在标度关系: λ=λ_∞+A(k—k_∞)+B(k—k_∞)^τ, 其中因子τ=0.32。这与理论推断的结果τ=(ln(2))/(l 关键词：     

Tilt modulus of a lipid monolayer

In addition to the familiar bending and stretching deformations, lipid monolayers and bilayers in their disordered state are often subjected to tilt deformations, occurring for instance in structural rearrangements accompanying membrane fusion, or upon insertion of oblique hydrophobic proteins into lipid bilayers. We study the elastic response of a flat lipid monolayer to a tilt deformation, using the spatial and conformational average of the chain end-to-end vector from the membrane normal to define a macroscopic membrane tilt. The physical origin and magnitude of the corresponding tilt modulus is analyzed using two complementary theoretical approaches. The first is a phenomenological model showing that the tilt and bending deformations are decoupled and the effects of inter-chain correlations on the tilt modulus is small. The second is based on a molecular-level mean-field theory of chain packing, enabling numerical evaluation of the tilt modulus for realistic, multi-conformation, chain models. Both approaches reveal that the tilt modulus involves two major contributions. The first is elastic in origin, arising from the stretching of the hydrocarbon chains upon a tilt deformation and reflecting the loss of chain conformational freedom associated with chain stretching. The second, purely entropic, contribution results from the constraints imposed by a tilt deformation on the fluctuations of chain director orientations. Using the chain-packing theory we compute the two contributions numerically as a function of the cross-sectional area per chain. The elastic and entropic terms are shown to dominate the value of for small and large areas per chain, respectively. For typical cross-sectional areas of lipid chains in biological membranes they areof comparable magnitude, yielding .Received: 12 May 2004, Published online: 3 August 2004PACS: 87.16.-b Subcellular structure and processes - 61.20.Gy Theory and models of liquid structure - 61.30.St Lyotropic phases     

Inter-ELM power decay length for JET and ASDEX upgrade: measurement and comparison with heuristic drift-based model

Experimental measurements of the SOL power decay length (λ(q)) estimated from analysis of fully attached divertor heat load profiles from two tokamaks, JET and ASDEX Upgrade, are presented. Data was measured by means of infrared thermography. An empirical scaling reveals parametric dependency λ(q) in mm = 0.73B(T)(-0.78)q(cyl)(1.2)P(SOL)(0.1)R(geo)(0), where B(T)(T) describes the toroidal magnetic field, q(cyl) the cylindrical safety factor, P(SOL)(MW) the power crossing the separatrix and R(geo)(m) the major radius of the device. A comparison of these measurements to a heuristic particle drift-based model shows satisfactory agreement in both absolute magnitude and scaling. Extrapolation to ITER gives λ(q) ? 1 mm.     

On classification ofN=2 supersymmetric theories

We find a relation between the spectrum of solitons of massiveN=2 quantum field theories ind=2 and the scaling dimensions of chiral fields at the conformal point. The condition that the scaling dimensions be real imposes restrictions on the soliton numbers and leads to a classification program for symmetricN=2 conformal theories and their massive deformations in terms of a suitable generalization of Dynkin diagrams (which coincides with the A-D-E Dynkin diagrams for minimal models). The Landau-Ginzburg theories are a proper subset of this classification. In the particular case of LG theories we relate the soliton numbers with intersection of vanishing cycles of the corresponding singularity; the relation between soliton numbers and the scaling dimensions in this particular case is a well known application of Picard-Lefschetz theory.     

Scaling properties of three-dimensional magnetohydrodynamic turbulence

The scaling properties of three-dimensional magnetohydrodynamic turbulence with finite magnetic helicity are obtained from direct numerical simulations using 512(3) modes. The results indicate that the turbulence does not follow the Iroshnikov-Kraichnan phenomenology. The scaling exponents of the structure functions can be described by a modified She-Leveque model zeta(p) = p/9+1-(1/3)(p/3), corresponding to basic Kolmogorov scaling and sheetlike dissipative structures. In particular, we find zeta(2) approximately 0.7, consistent with the energy spectrum E(k) approximately k(-5/3) as observed in the solar wind, and zeta(3) approximately 1, confirming a recent analytical result.     

Consistent resolution of possible anomalies in B0-->phi K(S) and B+ --> eta'K+ Decays

In the framework of R-parity violating (R(p)) supersymmetry, we try to find a consistent explanation for both recently measured CP asymmetry in B0 --> phi K(S) decay and the large branching ratio of B+/- --> eta'K+/- decay, which are inconsistent with the standard model (SM) prediction. We also investigate other charmless hadronic B -- >PP and B --> VP decay modes whose experimental data favor the SM: for instance, recently measured CP asymmetries in B0 --> eta(')K(S) and B0 -- >J/Psi K(S). We find that all the observed data can be accommodated for certain values of R(p) couplings.     

Long range bond-bond correlations in dense polymer solutions

The scaling of the bond-bond correlation function P1(s) along linear polymer chains is investigated with respect to the curvilinear distance s along the flexible chain and the monomer density rho via Monte Carlo and molecular dynamics simulations. Surprisingly, the correlations in dense three-dimensional solutions are found to decay with a power law P1(s) approximately s(-omega) with omega=3/2 and the exponential behavior commonly assumed is clearly ruled out for long chains. In semidilute solutions, the density dependent scaling of P1(s) approximately g(-omega(0))(s/g)(-omega) with omega(0)=2-2nu=0.824 (nu=0.588 being Flory's exponent) is set by the number of monomers g(rho) in an excluded volume blob. Our computational findings compare well with simple scaling arguments and perturbation calculation. The power-law behavior is due to self-interactions of chains caused by the chain connectivity and the incompressibility of the melt.     

Exact maximal height distribution of fluctuating interfaces

We present an exact solution for the distribution P(h(m),L) of the maximal height h(m) (measured with respect to the average spatial height) in the steady state of a fluctuating Edwards-Wilkinson interface in a one dimensional system of size L with both periodic and free boundary conditions. For the periodic case, we show that P(h(m),L)=L(-1/2)f(h(m)L(-1/2)) for all L>0, where the function f(x) is the Airy distribution function that describes the probability density of the area under a Brownian excursion over a unit interval. For the free boundary case, the same scaling holds, but the scaling function is different from that of the periodic case. Numerical simulations are in excellent agreement with our analytical results. Our results provide an exactly solvable case for the distribution of extremum of a set of strongly correlated random variables.     

颗粒样品形变对声波传播影响的实验探究

为了更好地理解颗粒间接触结构的变化对通过颗粒介质中的声波的影响,本文利用单轴压缩实验,通过一系列增加的轴向压力使样品塑性应变不断增大,这在颗粒尺度上对应于颗粒间接触结构的改变.我们测量了此过程中通过颗粒样品的声波变化,结果表明颗粒体系内接触结构的变化对声波波形中的非相干波部分和频率有明显的影响,并且在样品接触结构变化的初始阶段声速是偏离有效介质理论的预测的.     

Pressure spectrum in homogeneous turbulence

The pressure spectrum in homogeneous steady turbulence is studied using direct numerical simulation with resolution up to 1024(3) and the Reynolds number R(lambda) between 38 and 478. The energy spectrum is found to have a finite inertial range with the Kolmogorov constant K = 1.65+/-0.05 followed by a bump at large wave numbers. The pressure spectrum in the inertial range is found to be approximately P(k) = B(p)epsilon;(4/3)k(-7/3) with B(p) = 8.0+/-0.5, and followed by a bump of nearly k(-5/3) at higher wave numbers. Universality and a new scaling of the pressure spectrum are discussed.     

Conformations of random polyampholytes

We study the size R(g) of random polyampholytes (i.e., polymers with randomly charged monomers) as a function of their length N. All results of our extensive Monte Carlo simulations can be rationalized in terms of the scaling theory we develop for the Kantor-Kardar necklace model, although this theory neglects the quenched disorder in the charge sequence along the chain. We find approximately N1/2. The elongated globule model, the initial predictions of both Higgs and Joanny ( approximately N1/3) and Kantor and Kardar ( approximately N), and previous numerical estimates are ruled out.     

缺陷对滞后标度性的影响

对二维Ising铁磁系统中的非磁杂质，利用Monte Carlo方法，获得不同杂质浓度、不同磁场变化速率下的磁滞(?)线，从而得到滞后(?)线面积与磁场变化速率的关系．结果表明，在温度和缺陷浓度组成的相图上，存在一条相变线．低温和低浓度时，(?)线面积与磁场速率的标度指数约为1/3，只微弱地依赖于温度及杂质浓度；而对高温和高浓度的杂质，指数强烈地依赖于温度和浓度 关键词：     

Calculation of the persistence length of a flexible polymer chain with short-range self-repulsion

For a self-repelling polymer chain consisting of n segments we calculate the persistence length , defined as the projection of the end-to-end vector on the direction of the j-th segment. This quantity shows some pronounced variation along the chain. Using the renormalization group and -expansion we establish the scaling form and calculate the scaling function to order . Asymptotically, the simple result emerges for dimension d = 3. Also away from the excluded-volume limit is found to behave very similar to the swelling factor of a chain of length . We carry through simulations which are found to be in good accord with our analytical results. For d = 2 both our and previous simulations as well as theoretical arguments suggest the existence of logarithmic anomalies.Received: 17 November 2003, Published online: 30 March 2004PACS: 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 05.10.Cc Renormalization group methods     

Strong coupling for planar SYM theory: An all-order result

We propose a scheme for determining a generalised scaling function, namely the Sudakov factor in a peculiar double scaling limit for high spin and large twist operators belonging to the sl(2) sector of planar SYM. In particular, we perform explicitly the all-order computation at strong 't Hooft coupling regarding the first (contribution to the) generalised scaling function. Moreover, we compare our asymptotic results with the numerical solutions finding a very good agreement and evaluate numerically the non-asymptotic contributions. Eventually, we illustrate the agreement and prediction on the string side.     

Measurement of B(D+-->K(*0)l(+)nu(l))

Using 13.53 fb(-1) of CLEO data, we have measured the ratios of the branching fractions R(+)(e),R(+)(mu) and the combined branching fraction ratio R(+)(l), defined by R(+)(l)=[B(D+-->K(*0)l(+)nu(l))]/[B(D+-->K-pi(+)pi(+))]. We find R(+)(e)=0.74+/-0.04+/-0.05, R(+)(mu)=0.72+/-0.10+/-0.05, and R(+)(l)=0.74+/-0.04+/-0.05, where the first and second errors are statistical and systematic, respectively. The known branching fraction B(D+-->K-pi(+)pi(+)) leads to B(D+-->K(*0)e(+)nu(e))=(6.7+/-0.4+/-0.5+/-0.4)%, B(D+-->K(*0)mu(+)nu(mu))=(6.5+/-0.9+/-0.5+/-0.4)%, and B(D+-->K(*0)l(+)nu(l))=(6.7+/-0.4+/-0.5+/-0.4)%, where the third error is due to the uncertainty in B(D+-->K-pi(+)pi(+)).     

Aspect-ratio dependence of charge transport in turbulent electroconvection

We present measurements of the normalized charge transport or Nusselt number Nu as a function of the aspect ratio Gamma for turbulent convection in an electrically driven film. In analogy with turbulent Rayleigh-Bénard convection, we develop the relevant theoretical framework in which we discuss the local power-law scaling of Nu with a dimensionless electrical forcing parameter R. For these experiments where 10(4) less, similar R less, similar 2 x 10(5) we find that Nu approximately F(Gamma)Rgamma with either gamma=0.26 (+/-0.02) or gamma=0.20 (+/-0.03), in excellent agreement with the theoretical predictions of gamma=1/4 and 1/5. Our measurements of the aspect-ratio dependence of Nu for 0.3相似文献   

Scaling and universality in electrical failure of thin films

We describe the electrical failure of thin films as a percolation in two-dimensional random resistor networks. We show that the resistance evolution follows a scaling relation expressed as R approximately epsilon(-&mgr;) where epsilon = (1-t/tau), tau is the time of electrical failure of the film, and &mgr; is the same critical exponent appearing in the scaling relation between R and the defect concentration. For uniform degradation the value of &mgr; is universal. The validity of this scaling relation in the case of nonuniform degradation is proved by discussing the case in which the failure is due to a filamentary defect growth. The existence of this relation allows predictions of failure times from early time measurements of the resistance.     

Longitudinal relaxation of initially straight flexible and stiff polymers

The relaxation mechanism of an initially straight flexible or stiff polymer chain of length N in a viscous solvent is studied through Brownian dynamics simulations covering a broad range of time scales. After the short-time free diffusion, the chain's longitudinal reduction R2(0)-R2 approximately Nt1/2 at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasisteady T approximately Nt(-1/2) relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains with a persistence length E > or = N are shown to exhibit a late intermediate-time longitudinal reduction R2(0)-R2 approximately N2E(-3/4)t1/4 associated with a T approximately N2E(-3/4)t(-3/4) relaxation of tensions affected by the deforming Brownian and the restoring bending forces.     

Segment distributions of end-tethered polymers in a good solvent

We use confocal fluorescence microscopy to study the conformation of single DNA molecules end-tethered to a solid substrate. The segment distribution rho(z) measured for chains with contour lengths 15.4 microm 相似文献