Modulation of third-harmonic generation conversion in the presence of a rotational wave packet

We report a modulation of third-harmonic generation (THG) owing to a rotational coherence in CO(2). The variation in conversion efficiency is mostly attributed to the dependence of chi(3)(tau) on the molecular alignment. THG via type I processes mainly depends on chi(3)(tau), while type II processes are influenced by the wave packet owing to both chi(3)(tau) and Delta k(tau). Observation of the generated third harmonic also shows significant changes of the polarization state owing to the birefringence induced by the rotational wave packet. Numerical modeling shows good qualitative agreement with the experimental data.     

Experimental estimates of dephasing time in molecular magnets

Muon spin relaxation measurements in isotropic molecular magnets (MM) with a spin value S ranging from 7/2 to 27/2 are used to determine the magnitude and origin of dephasing time tau(phi) of molecular magnets. It is found that tau(phi) approximately 10 nsec with no S or ligand dependence. This indicates a nuclear origin for the stochastic field. Since tau(phi) is a property of the environment, we argue that it is a number common to similar types of MM. Therefore, tau(phi) is shorter than the Zener and tunneling times of anisotropic MM such as Fe(8) or Mn(4) for standard laboratory sweep rates. Our findings call for a stochastic Landau-Zener theory in this particular case.     

Unified description of aging and rate effects in yield of glassy solids

The competing effects of slow structural relaxations (aging) and deformation at constant strain rate on the shear yield stress tau(y) of simple model glasses are examined using molecular simulations. At long times, aging leads to a logarithmic increase in density and tau(y). The yield stress also rises logarithmically with rate but shows a sharp transition in slope at a rate that decreases with increasing age. We present a simple phenomenological model that includes both intrinsic rate dependence and the change in properties with the total age of the system at yield. As predicted by the model, all data for each temperature collapse onto a universal curve.     

Large force fluctuations in a flowing granular medium

We study fluctuations in the force at the boundary of a 2D granular flow. The forces are mainly impulsive at all flow rates. The probability distribution of impulses decays exponentially at large impulses, as do the forces in a static granular medium. At small impulses, the distribution evolves continuously with flow rate with no indication of the transition from collisional flow to intermittently jamming flows. However, the distribution of the time interval between collisions tends to a power law, P(tau) - tau(-3/2), showing a clear dynamical signature of the approach to jamming.     

The modulation of coupled relaxation in porous media.

This work investigates the effects of modulation of the transverse and longitudinal relaxation of the surface-fluid/pore-fluid spin system in porous media. Important new NMR well logging applications identify pore fluids by varying the CPMG T(2) pulse spacing to discriminate on the basis of fluid diffusivities in applied and local static magnetic field gradients. However, anomalous laboratory CPMG T(2) results have been reported repeatedly over 25 years for various porous media filled with a single fluid. In relatively large pores, at near bulk conditions, the transverse relaxation of diffusing molecular spins should be proportional to the square of the CPMG pulse spacing tau, the susceptibility contrast at the pore wall and the applied gradient. Observed is a markedly linear tau dependence that saturates at a plateau for large tau. The effect is not quadratic in applied gradient or susceptibility. For large pores, the tau dependence and the saturation value are proportional to the surface-to-volume ratio of the pores. This is in distinct contrast to the behavior observed by Borgia, Brown and Fantazzini for systems with much smaller pores at higher magnetic fields. The large-pore anomalous behaviors can be explained as a modulation of the exchange between surface-fluid and pore-fluid spins, such as observed by Luz and Meiboom in 1963 for water enriched with quadrupolar 17O. Scalar coupling of the solid-surface spins to the fluid-surface spins was postulated by Kleinberg, Kenyon and Mitra as a dominant relaxation mechanism for the surface fluid. The CPMG tau effect can be described as the modulation of the exchange coupling by the CPMG pi pulses, which mix the magnetizations between the exchanging, strongly coupled spin systems of the pore-fluid and the surface-fluid, which is, in turn, weakly coupled by scalar or pseudo-scalar interactions to the fast-relaxing solid surface.     

Boundary spatiotemporal correlations in a self-organized critical model of punctuated equilibrium

In a semi-infinite geometry, a one-dimensional, M-component model of biological evolution realizes microscopically an inhomogeneous branching process for M-->infinity. This implies a size distribution exponent tau(')=7/4 for avalanches starting at a free, "dissipative" end of the evolutionary chain. A bulklike behavior with tau(')=3/2 is restored by "conservative" boundary conditions. These are such as to strictly fix to its critical, bulk value the average number of species directly involved in an evolutionary avalanche by the mutating species located at the chain end. A two-site correlation function exponent tau(')(R)=4 is also calculated exactly in the "dissipative" case, when one of the points is at the border. Together with accurate numerical determinations of the time recurrence exponent tau(')(first), these results show also that, no matter whether dissipation is present or not, boundary avalanches have the same space and time fractal dimensions as those in the bulk, and their distribution exponents obey the basic scaling laws holding there.     

Calculation of a "narrowed" autocorrelation function

A method of calculating an autocorrelation function with extremely narrow peaks is described. This is done by including terms in the autocorrelation expression corresponding to delays at 2 tau, 3 tau, etc., in addition to the usual term with delay tau. Implications in the frequency domain are explored. Graphs of this autocorrelation function for a number of violin sound samples, including a two-octave scale, vibrato, and glissando, are presented. Graphs of the autocorrelation function for some synthetic sound samples are also included.     

Heavy scalar tau decays in the complex MSSM: a full one-loop analysis

We evaluate all two-body decay modes of the heavy scalar tau in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) and no generation mixing. The evaluation is based on a full one-loop calculation of all decay channels, also including hard and soft QED radiation. The renormalization of the relevant sectors is briefly reviewed. The dependence of the heavy scalar tau decay on the relevant cMSSM parameters is analyzed numerically, including also the decay to Higgs bosons and another scalar lepton or to a tau and the lightest neutralino. We find sizable contributions to many partial decay widths and branching ratios. They are mostly of $\mathcal{O}(5\mbox{--}10~\%)$ of the tree-level results, but can go up to 20 %. These contributions are potentially important for the correct interpretation of scalar tau decays at the LHC and, if kinematically allowed, at the ILC or CLIC. The evaluation of the branching ratios of the heavy scalar tau will be implemented into the Fortran code FeynHiggs.     

Quantum correction to conductivity close to a ferromagnetic quantum critical point in two dimensions

We study the temperature dependence of the conductivity due to quantum interference processes for a two-dimensional disordered itinerant electron system close to a ferromagnetic quantum critical point. Near the quantum critical point, the crossover between diffusive and ballistic regimes of quantum interference effects occurs at a temperature T*=1/taugamma(E(F)tau)2, where gamma is the parameter associated with the Landau damping of the spin fluctuations, tau is the impurity scattering time, and E(F) is the Fermi energy. For a generic choice of parameters, T* is smaller than the nominal crossover scale 1/tau. In the ballistic quantum critical regime, the conductivity behaves as T1/3.     

Study of a spin-3/2 system by a quadrupolar-echo sequence: suppression of spurious signals.

The density matrix describing the evolution of a spin-3/2 system excited by a quadrupolar-echo sequence consisting of two rf pulses in quadrature phase, (X)-tau 2-(Y)-tau 4-[acquisition(y)], is calculated from the equilibrium state to the acquisition period. The interactions involved are the first-order quadrupolar interaction throughout the experiment and a local heteronuclear magnetic dipolar term between the two pulses and during the acquisition period. Three echoes, one due to a satellite transition at tau 4 = tau 2 and two due to the central transition at tau 4 = tau 2 and tau 4 = 3 tau 2, are predicted. They have similar expressions than those obtained with two rf pulses of the same phase, (X)-tau 2-(X)-tau 4-[acquisition(y)], except the signs. Moreover, it is shown experimentally that a combination of these two sequences, namely: (X)-tau 2-(X)-tau 4-[acquisition(y)]-recycle delay-(X)-tau 2-(-X)-tau 4-[acquisition(y)]-recycle delay-(X)-tau 2-(Y)-tau 4-[acquisition(-y)]-recycle delay-(X)-tau 2-(-Y)-tau 4-[acquisition(-y)]-recycle delay, cancels the spurious piezo-electric signals when studying a ferro-electric material in the single-crystal form.     

Study of tau decays to six pions and a neutrino

The tau decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(tau(-)-->2pi(-)pi(+)3pi(0)nu(tau)) = (2.2+/-0.3+/-0.4)x10(-4) and B(tau(-)-->3pi(-)2pi(+)pi(0)nu(tau)) = (1.7+/-0.2+/-0.2)x10(-4). A search for substructure in these decays shows that they are saturated by intermediate states with eta or omega mesons. We present the first observation of the decay tau(-)-->2pi(-)pi(+)omega(nu)tau and the branching fraction is measured to be (1.2+/-0.2+/-0.1)x10(-4). The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.     

Translocation of closed polymers through a nanopore under an applied external field

The dynamic behaviours of the translocations of closed circular polymers and closed knotted polymers through a nanopore, under the driving of an applied field, are studied by three-dimensional Langevin dynamics simulations. The power-law scaling of the translocation time τ with the chain length N and the distribution of translocation time are investigated separately. For closed circular polymers, a crossover scaling of translocation time with chain length is found to be τ～ N α , with the exponent α varying from α = 0.71 for relatively short chains to α = 1.29 for longer chains under driving force F = 5. The scaling behaviour for longer chains is in good agreement with experimental results, in which the exponent α = 1.27 for the translocation of double-strand DNA. The distribution of translocation time D(τ) is close to a Gaussian function for duration time τ < τ p and follows a falling exponential function for duration time τ > τ p . For closed knotted polymers, the scaling exponent α is 1.27 for small field force (F = 5) and 1.38 for large field force (F = 10). The distribution of translocation time D(τ) remarkably features two peaks appearing in the case of large driving force. The interesting result of multiple peaks can conduce to the understanding of the influence of the number of strands of polymers in the pore at the same time on translocation dynamic process and scaling property.     

From a simple liquid to a polymer melt: NMR relaxometry study of polybutadiene

We utilize NMR field cycling relaxometry to study the crossover from glassy dynamics (t approximately > tau alpha) through Rouse to reptation behavior in a series of monodisperse polybutadienes with molecular weights M=355 to 817,000 g/mol. We separate characteristic polymer dynamics from the total spectrum dominated by glassy dynamics. The polymer dynamics show typical Rouse relaxation features that grow with M and saturate at high M. Comparing to Rouse theory, we determine the Rouse unit size MR approximately = 500 and entanglement weight Me approximately = 2000; the Rouse spectrum saturates at Mmax approximately = 4000. The local order parameter S approximately 0.11 is relatively large, indicating noticeable local packing already in the Rouse regime. The M dependence of the glass transition temperature Tg, obtained from dielectric relaxation spectra, shows distinctive kinks at MR and Me.     

Defect production in nonlinear quench across a quantum critical point

We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory.     

Correlation time and diffusion coefficient imaging: application to a granular flow system

A parametric method for spatially resolved measurements for velocity autocorrelation functions, R(u)(tau) = , expressed as a sum of exponentials, is presented. The method is applied to a granular flow system of 2-mm oil-filled spheres rotated in a half-filled horizontal cylinder, which is an Ornstein-Uhlenbeck process with velocity autocorrelation function R(u)(tau) = e(- ||tau ||/tau(c)), where tau(c) is the correlation time and D = tau(c) is the diffusion coefficient. The pulsed-field-gradient NMR method consists of applying three different gradient pulse sequences of varying motion sensitivity to distinguish the range of correlation times present for particle motion. Time-dependent apparent diffusion coefficients are measured for these three sequences and tau(c) and D are then calculated from the apparent diffusion coefficient images. For the cylinder rotation rate of 2.3 rad/s, the axial diffusion coefficient at the top center of the free surface was 5.5 x 10(-6) m(2)/s, the correlation time was 3 ms, and the velocity fluctuation or granular temperature was 1.8 x 10(-3) m(2)/s(2). This method is also applicable to study transport in systems involving turbulence and porous media flows.     

Dynamics of fluctuations below a stationary bifurcation to electroconvection in the planar nematic liquid crystal N4

We fitted C(k,tau,epsilon) proportional to exp([-sigma(k,epsilon)tau] to time-correlation functions C(k,tau,epsilon) of structure factors S(k,t,epsilon) of shadowgraph images of fluctuations below a supercritical bifurcation at V(0)=V(c) to electroconvection of a planar nematic liquid crystal in the presence of a voltage V=sqrt[2]V(0)cos((2pift) [k=(p,q) is the wave vector and epsilon identical with V(2)(0)/V(2)(c)-1]. There were stationary oblique (normal) rolls at small (large) f. Fits of a modified Swift-Hohenberg form to sigma(k,epsilon) gave f-dependent critical behavior for the minimum decay rates sigma(0)(epsilon) and the correlation lengths xi(p,q)(epsilon).     

Superradiance in molecular H aggregates

Direct evidence of superradiance from an organic semiconductor (quaterthiophene) whose molecules are arranged in a H aggregate fashion, is reported. Time resolved photoluminescence measurements show a linear correlation between the radiative lifetime (tau(rad)) of the purely electronic exciton recombination and the inverse of the number (N(C)) of the coherently emitting dipoles, i.e., tau(rad) proportional, variant 1/N(C). These data support the recently developed theoretical models describing the optical properties of H aggregates of rodlike molecules with a nonvanishing component of the perpendicular molecular transition dipole moment.     

Time course of adaptation and recovery from adaptation in the cat auditory-nerve neurophonic

The auditory-nerve neurophonic (ANN) reflects the ensemble response of phase-locked firing in single auditory-nerve fibers to sustained signals. Consequently, neural response properties such as adaptation and recovery from adaptation can be observed. In this study, ANN responses to 800-Hz, 100-ms tones presented at 10-30-dB SL were recorded using bipolar platinum-iridium electrodes placed on the auditory nerve of the cat. The cat ANN adaptation properties were determined and fit to the equation: A(tp) = Yre(-tp/tau Ar) + Yse(-tp/tau As) + Ass. The rapid time constant of adaptation (tau Ar) was invariant across stimulus level, with a mean value of 4.8 (+/- 2.1) ms. The short-term time constant (tau As) decreased approximately 21 ms for each 10-dB increase in probe amplitude. The mean tau As was 116 ms at 10 dB SL, 83.2 ms at 20 dB SL, and 73.5 ms at 30 dB SL. The ANN recovery from adaptation data was analyzed and fit to the equation: A(delta t) = Amax - Yre(-delta t/tau Rr) - Yse(-delta t/tau Rs). Here, tau Rr, the rapid time constant of recovery, and tau Rs, the short-term time constant, were independent of masker intensity in the studied range, with values of 16.2(+/- 9.8) and 125(+/- 50.1) ms, respectively. The results of this study indicate that ANN time constants are comparable to those measured for single units and that the adaptation behavior of phase-locked and nonphase-locked activity appears to be similar.     

A mass reconstruction technique for a heavy resonance decaying to τ+τ-

For a resonance decaying to τ⁺τ^-, it is difficult to reconstruct its mass accurately because of the presence of neutrinos in the decay products of the τ leptons. If the resonance is heavy enough, we show that its mass can be well determined by the momentum component of the τ decay products perpendicular to the velocity of the τ lepton, p_⊥, and the mass of the visible/invisible decay products, m_vis/inv, for τ decaying to hadrons/leptons. By sampling all kinematically allowed values of p_⊥ and m_vis/inv according to their joint probability distributions determined by the MC simulations, the mass of the mother resonance is assumed to lie at the position with the maximal probability. Since p_⊥ and m_vis/inv are invariant under the boost in the τ lepton direction, the joint probability distributions are independent upon the τ's origin. Thus this technique is able to determine the mass of an unknown resonance with no efficiency loss. It is tested using MC simulations of the physics processes m pp→Z/h(125)/h(750)+X→ ττ+X at 13 TeV. The ratio of the full width at half maximum and the peak value of the reconstructed mass distribution is found to be 20%-40% using the information of missing transverse energy.     

Stochastic resonance driven by time-modulated correlated coloured noise sources in a single-mode laser

This paper investigates the phenomenon of stochastic resonance in a single-mode laser driven by time-modulated correlated coloured noise sources. The power spectrum and signal-to-noise ratio R of the laser intensity are calculated by the linear approximation. The effects caused by noise self-correlation time τ₁, τ₂ and cross-correlated time τ₃ for stochastic resonance are analysed in two ways: τ₁, τ₂ and τ₃ are taken to be the independent variables and the parameters respectively. The effects of the gain coefficient Γ and loss coefficient K on the stochastic resonance are also discussed. It is found that besides the presence of the standard form and the broad sense of stochastic resonance, the number of extrema in the curve of R versus K is reduced with the increase of the gain coefficient Γ.