Broken Regime Research Articles

Jacobi crossover ensembles of random matrices and statistics of transmission eigenvalues

We study the transition in conductance properties of chaotic mesoscopic cavities as time-reversal symmetry is broken. We consider the Brownian motion model for transmission eigenvalues for both types of transitions, namely, orthogonal-unitary and symplectic-unitary crossovers depending on the presence or absence of spin-rotation symmetry of the electron. In both cases the crossover is governed by a Brownian motion parameter τ, which measures the extent of time-reversal symmetry breaking. It is shown that the results obtained correspond to the Jacobi crossover ensembles of random matrices. We derive the level density and the correlation functions of higher orders for the transmission eigenvalues. We also obtain the exact expressions for the average conductance, average shot-noise power and variance of conductance, as functions of τ, for the arbitrary number of modes (channels) in the two leads connected to the cavity. Moreover, we give the asymptotic result for the variance of shot-noise power for both the crossovers, the exact results being too long. In the τ → 0 and τ → ∞ limits, the known results for the orthogonal (or symplectic) and unitary ensembles are reproduced. In the weak time-reversal symmetry breaking regime, our results are shown to be in agreement with the semiclassical predictions.

Breakdown of potential vorticity–based equivalent latitude as a vortex‐centered coordinate in the polar winter mesosphere

Potential vorticity (PV) and stream function (ψ) are useful vortex‐centered coordinates for studying the winter stratosphere, since both exhibit monotonic relationships with tracer constituents. At each isentropic level in the stratosphere and mesosphere, ψ varies monotonically normal to the jet axis and to tracer contours, and can thus be considered vortex‐centered. In the stratosphere, PV is anticorrelated with ψ and is also vortex‐centered. We show that, contrary to this, above ∼3000 K (∼60 km) the PV‐ψ anticorrelation breaks down up to 80% of the time. Over five years of Goddard Earth Observing System analyses are used to depict the seasonal and spatial variation of the relationship between PV and ψ. The deviation of PV from a vortex‐centered coordinate is estimated by calculating differences between the mean latitude of the highest PV band and the most polar mean latitude for any PV band in the hemisphere. If PV is anticorrelated with ψ, and thus vortex centered, these differences should be small. In both winter hemispheres, latitude differences are less than 5° below 55 km but exceed 15° above 60 km (∼0.5 hPa, ∼3000 K). In the mesosphere, regions of small PV are usually found in the vortex core and the largest PV values are located along the subtropical jet. The relationship between PV and ψ in the polar lower mesosphere is interpreted in the context of the gravity wave driven warm anomaly, the associated wave breaking regime, and local static stability anomalies which affect PV much more than ψ.

Rheology of worm-like micelles composed of tri-block copolymer in the limit of slow dynamics

We study the influence of micellar kinetics on the rheological behavior of worm-like micelles composed of tri-block copolymers of ethylene oxide and propylene oxide (EO20PO70EO20) in an aqueous solution containing KCl and ethanol. The kinetics of the micelles are adjusted by changing the ethanol concentration, according to a previous study in which the lifetime of the micelles was shown to decrease exponentially with increasing ethanol concentration. At higher ethanol concentrations (15 vol % EtOH), the worm-like micelles behave like Maxwell fluids at low frequencies, but have an upturn at higher frequencies, probably due to Rouse or breathing relaxation modes. At low ethanol concentrations (5 and 8 vol % EtOH) where the lifetime of the micelles is long, the rheological behavior is clearly non-Maxwellian, revealing a spectrum of relaxation times. The slow, block copolymer dependent growth of the micelles leads to scaling of viscosity with surfactant concentration, which varies with time. In this slow breaking regime, stirring of the solutions causes an increase of the viscosity, which slowly decreases once stirring is stopped. This apparent increase of the viscosity may be induced by the linking of ring-like micelles or by the formation of clusters of worm-like micelles (non-equilibrium structures), which disassemble when stirring is stopped.

Relationships among Structures, Development Processes, and Heating Profiles for Two Mesoscale Convective Systems in Inactive Phase of a Large-Scale Disturbance over Northern Australia during the Southern Summer in 1998-1999

The relationships among structures, development processes, and diabatic heating profiles of a maritime mesoscale convective system (MCS) and a continental MCS in the inactive phase of a large-scale disturbance associated with Madden-Julian Oscillation (MJO) were studied mainly using dual-Doppler radar data around Darwin, Australia during the southern summer in 1998-1999. The maritime MCS (15 January 1999) formed in a west to southwesterly flow of moist air at the lowmid levels during the monsoon active regime, and had several convective lines oriented parallel to the mid-level shear in 1-2 hours cycle within an extensive stratiform region. Radar analyses revealed that a new convective line formed on a convergence between the outflow of a weak downdraft within the stratiform precipitation and the moist westerly in the low-level, and developed more deeply within a mid-level moist rear inflow. A cyclonic circulation (mesovortex) in the mid-level was subsequently found in the stratiform region. The analysis of heating profiles is indicative of a convective heating maximum at 6 km and a stratiform region with large heating and relatively small cooling above and below the melting level, respectively. The developments of the convective line and mesovortex are attributed to the small low-level cooling and convergence of moist air with the large mid-level heating, respectively, and both are considered to play a significant role in the maintenance of the MCS. The continental MCS (21 January 1999) formed in a strong mid-level east-southeasterly flow of dry air that was influenced by tropical depressions during the break regime. Radar analyses showed that the MCS formed a number of convective lines oriented parallel to low- and mid-level shears with relatively strong negative vortices and convergence in the low-mid level. Positive vorticity were found with a descending rear inflow in the rear of the lines and the stratiform region of the MCS below the mid-level. The heating profiles represented a convective heating maximum at 5.5 km, and a moderate stratiform cooling below the melting level. It is suggested that the stratiform cooling due to the mid-level dryness made a contribution to the advection of positive vorticity below about 5 km, resulting in the development of convective lines with a intensive vortex couplet. A comparison of the heating profiles in the stratiform parts of two MCSs indicated a larger low-level cooling in the continental MCS and a larger heating at the mid-upper level in the maritime MCS. It was suggested that the different stratiform heating of two MCSs in the inactive phase of the MJO played significant roles in their structures and development processes.

Sensitivity analysis of mountain waves using an adjoint model

An adjoint modeling system developed for the COAMPS nonhydrostatic model is used to explore the sensitivity of lee-side winds to the upstream atmospheric conditions for flow over a two-dimensional obstacle. For relatively small hills in the hydrostatic wave regime, the sensitivity patterns exhibit a dual lobed structure that is a manifestation of a superposition of internal gravity waves with downward-directed energy propagation. Nonhydrostatic waves generated by small terrain have corresponding sensitivities that are tilted vertically against the shear, which when introduced into the flow as perturbations, evolve into structures that resemble vertically decaying evanescent waves. Flow over higher obstacles near the gravity wave breaking threshold exhibits complex sensitivity patterns characterized by a wave-like packet of maxima and minima upstream of the middle- and upper-tropospheric region of wave breaking. In general, as the mountain height is increased, the tangent linear approximation becomes less accurate. However, the strongest nonlinearity occurs for flows very near the wave breaking threshold, rather than fully within the wave breaking regime forced by higher terrain.

Forecasting the duration of active and break spells in intrinsic mode functions of Indian monsoon intraseasonal oscillations

Several indices of the observed Indian summer monsoon intraseasonal oscillations (ISO) are decomposed into their respective intrinsic mode functions (IMFs). For each ISO index, it is shown that for most of the dominant IMFs, the peak in the active (break) regime may be used as a predictor for the duration of the subsequent break (active) regime. Similar results are also obtained for a Stochastic Forced Lorenz model proposed earlier as a paradigm model for ISO.

The Statistical Characteristics of Convective Cells in a Monsoon Regime (Darwin, Northern Australia)

Abstract A season of operational cell and track data from Darwin, Australia, has been analyzed to explore the statistical characteristics of the convective cell heights. The statistics for the monsoon and break regimes are significantly different with the break season cells being higher for a given reflectivity threshold. The monsoon cells produce more rain, but there are fewer intense cells and there is a much larger contribution from stratiform rain. The monsoon cells are also slightly larger, but shorter lived than the breaks. The shorter lifetime may reflect a more rapid transition to a longer-lived stratiform character. The monsoon regime is shown to be associated with large-scale ascent and higher humidity that may lead to more frequent, but weaker cells. Within regimes, the subset of intense cells generally reach near the tropopause or overshoot. However, there is little evidence in the data for a multimodal distribution of cell heights, except perhaps for the intense monsoon cases. Instead, the picture is a continuous distribution of cell heights with the peak of the distribution shifting to higher values as the distributions are conditioned on higher reflectivity.

On the application of the single-phase level set method to naval hydrodynamic flows

The application of the single-phase level set approach to the numerical simulations of three-dimensional free surface flows around complex geometries, at both non-breaking and breaking regimes is presented. In this approach only the liquid phase is simulated and the level set function is used as tracking device to locate the free surface position. The extrapolation of the solution in the dummy points in the gaseous phase is such that second-order accuracy is maintained also in the points adjacent to the free surface; the time evolution of the level set function and the re-initialization step have been merged so to get a function which is a distance function everywhere, and satisfies, at the same time, the kinematic condition on the free surface. The implementation of this technique into a general purpose Reynolds averaged Navier–Stokes (RANS) equations solver developed at INSEAN [Di Mascio A, Broglia R, Favini B. A Second Order Godunov-type Scheme for Naval Hydrodynamics. Kluwer Academic/Plenum Publishers; 2001, p. 253–61], is described in details; capabilities of the algorithm in dealing with non-breaking and breaking flows in the naval hydrodynamic context will be demonstrated by using a submerged hydrofoil and two different ship hulls in straight course as test cases. Comparisons with both experimental data and numerical surface fitting computations are presented; convergence properties of the algorithm, as well as validation and verification assessment will be also discussed.

On the production of flat electron bunches for laser wakefield acceleration

We suggest a novel method for the injection of electrons into the acceleration phase of particle accelerators, producing low-emittance beams appropriate even for the demanding high-energy linear collider specifications. We discuss the injection mechanism into the acceleration phase of the wakefield in a plasma behind a high-intensity laser pulse, which takes advantage of the laser polarization and focusing. The scheme uses the structurally stable regime of transverse wakewave breaking, when the electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse elongated in the transverse direction with an underdense plasma, the electrons injected via the transverse wakewave breaking and accelerated by the wakewave perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with an asymmetric emittance (flat beam). An approach for generating flat laser-accelerated ion beams is briefly discussed.

Electron bunch acceleration in the wake wave breaking regime

Results are presented from theoretical analysis and 2D PIC simulations of electron acceleration in a breaking wake plasma wave generated by a short intense laser pulse during its interaction with a finite-length underdense plasma layer. The high energy electron energy spectrum and transverse emittance are obtained. It is shown that, for laser pulse lengths above the plasma wake wavelength, the wakefield-accelerated electrons are further accelerated by the electromagnetic wave.

Generation of Quasimonoenergetic Electron Bunches with 80-fs Laser Pulses

Highly collimated, quasimonoenergetic multi-MeV electron bunches were generated by the interaction of tightly focused, 80-fs laser pulses in a high-pressure gas jet. These monoenergetic bunches are characteristic of wakefield acceleration in the highly nonlinear wave breaking regime, which was previously thought to be accessible only by much shorter laser pulses in thinner plasmas. In our experiment, the initially long laser pulse was modified in underdense plasma to match the necessary conditions. This picture is confirmed by semianalytical scaling laws and 3D particle-in-cell simulations. Our results show that laser-plasma interaction can drive itself towards this type of laser wakefield acceleration even if the initial laser and plasma parameters are outside the required regime.

Impact of Orographically Induced Spatial Variability in PBL Stratiform Clouds on Climate Simulations

Abstract This paper examines the impact of orographically induced mesoscale heterogeneities on the macroscopic behavior of planetary boundary layer (PBL) stratiform clouds, and implements and tests a physically based parameterization of this effect in the University of California, Los Angeles (UCLA), atmospheric general circulation model (AGCM). The orographic variance and associated thermal circulations induce inhomogeneities in the cloud field that can significantly alter the PBL evolution; an effect that has been largely ignored in existing climate models. The impact of this effect on AGCM simulations is examined and the mechanisms at work are studied by analyzing a series of Cloud System Resolving Model (CSRM) simulations. Both the CSRM and AGCM results show that, in the absence of the orographic effect, the continental PBL tends to be in one of two regimes: the solid regime characterized by a cold and overcast PBL and the broken regime characterized by a low time-mean cloud incidence and a large-ampl...

Symmetry breaking regime in the nonlinear Hartree equation

The present article is concerned with minimizers of the attractive Hartree energy functional Hg[ψ̄,ψ]=12‖∇ψ‖22+(ψ,vψ)2+g(ψ,V * |ψ|2ψ)2 on Rd, d⩾2, for a general class of external potentials v and two-body interactions V of positive type, with g<0. We prove spontaneous symmetry breaking in the large coupling limit. A numerical investigation visualizes this regime in the example of an external double well potential.

Quantitative Photoperiodic Control of Erect Thallus Production in Sargassum muticum

A photoperiodic response of erect thallus production has been quantified in Sargassum muticum . Young germlings were cultured under long-day (LD; 16:8 h) conditions at 16 °C, 75 μmol m −2 s −1 until they had 4–5 early blades after 60 days in culture. The young thalli were transferred to short-day (SD; 8:16 h) and night break (NB; 8:7.5:1:7.5 h) regimes. Up to 34.7% of the plants had produced erect thalli after 140 days in culture in the SD regime, but no erect thalli were formed in the NB regime. When plants were transferred from NB to SD regimes, erect thalli were initiated within 10 days, but continued to be produced in plants transferred from SD to NB. Therefore, the development of erect thalli in S. muticum is a genuine photoperiodic response, which is inhibited by NB treatments, but continues in a NB regime after sufficient induction in SD.

Spectral signatures of chaotic diffusion in systems with and without spatial order

We investigate the two-point correlations in the spectra of extended systems exhibiting chaotic diffusion in the classical limit, in presence and in absence of spatial order. For periodic systems, we express the spectral two-point correlations in terms of form factors with the unit-cell index as a discrete spatial argument. For times below the Heisenberg time, they contain the full space–time dependence of the classical propagator. They approach constant asymptotes via a regime of quantum ballistic motion. In the opposite regime of strong disorder with localized eigenstates, we derive a semiclassical approximation of the form factor that spans the entire transition from metallic to isolating behaviour. The regime of weak breaking of periodicity is accessed from the side of exact order by a perturbation theory for the sets of, without disorder, symmetry-related periodic orbits.

A level set technique applied to unsteady free surface flows

An unsteady Navier–Stokes solver for incompressible fluid is coupled with a level set approach to describe free surface motions. The two-phase flow of air and water is approximated by the flow of a single fluid whose properties, such as density and viscosity, change across the interface. The free surface location is captured as the zero level of a distance function convected by the flow field. To validate the numerical procedure, two classical two-dimensional free surface problems in hydrodynamics, namely the oscillating flow in a tank and the waves generated by the flow over a bottom bump, are studied in non-breaking conditions, and the results are compared with those obtained with other numerical approaches. To check the capability of the method in dealing with complex free surface configurations, the breaking regime produced by the flow over a high bump is analyzed. The analysis covers the successive stages of the breaking phenomenon: the steep wave evolution, the falling jet, the splash-up and the air entrainment. In all phases, numerical results qualitatively agree with the experimental observations. Finally, to investigate a flow in which viscous effects are relevant, the numerical scheme is applied to study the wavy flow past a submerged hydrofoil. Copyright © 2001 John Wiley & Sons, Ltd.

Particle dispersion and mixing induced by breaking internal gravity waves

The purpose of this paper is to analyze diapycnal mixing induced by the breaking of an internal gravity wave — the primary wave — either standing or propagating. To achieve this aim we apply two different methods. The first method consists of a direct estimate of vertical eddy diffusion from particle dispersion while the second method relies upon potential energy budgets [Winters, K.B., Lombard, P.N., Riley, J.J., D’Asaro, E.A., 1995. J. Fluid Mech. 289, 115–128; Winters, K.B., D’Asaro, E.A., 1996. J. Fluid Mech. 317, 179–193]. The primary wave we consider is of small amplitude and is statically stable, a case for which the breaking process involves two-dimensional instabilities. The dynamics of the waves have been previously analyzed by means of two-dimensional direct numerical simulations [Bouruet-Aubertot, P., Sommeria, J., Staquet, C., 1995. J. Fluid Mech. 285, 265–301; Bouruet-Aubertot, P., Sommeria, J., Staquet, C., 1996. Dyn. Atmos. Oceans 29, 41–63; Koudella, C., Staquet, C., 1998. In: Davis, P. (Ed.), Proceedings of the IMA Conference on Mixing and Dispersion on Stably-stratified Flows, Dundee, September 1996. IMA Publication]. High resolution three-dimensional calculations of the same wave are also reported here [Koudella, C., 1999]. A local estimate of mixing is first inferred from the time evolution of sets of particles released in the flow during the breaking regime. We show that, after an early evolution dominated by shear effects, a diffusion law is reached and the dispersion coefficient is fairly independent of the initial seeding location of the particles in the flow. The eddy diffusion coefficient , K , is then estimated from the diapycnal diffusive flux. A good agreement with the value inferred from particle dispersion is obtained. This finding is of particular interest regarding the interpretation of in situ estimates of K inferred either from tracer dispersion or from microstructure measurements. Computation of the Cox number, equal to the ratio of eddy diffusivity to molecular diffusivity, shows that the Cox number varies within the interval [9, 262], which corresponds to the range of vertical eddy diffusivity measured in the interior of the ocean. The Cox number is found to depend on the turbulent Froude number squared. We show eventually that mixing results in a weak distortion of the initial density profile and we relate this result to observations made at small scale in the ocean. Comparisons between the analysis of the two-dimensional and high resolution (256 3 ) three-dimensional direct numerical simulations of the primary wave were also conducted. We show that the energetics and the amount of mixing are very close when the primary wave is of small amplitude. This results from the fact that, for a statically stable wave, the dynamics of the initially two-dimensional primary wave remains mostly two-dimensional even after the onset of wavebreaking.

Determination of scalar meson masses in QCD-inspired quark models

We compare two QCD-inspired quark models with four-fermion interaction (with and without the remnant coupling to low-energy gluons) in the regime of dynamical chiral symmetry breaking (DCSB). The first one, the Nambu-Jona-Lasinio (NJL) model, ensures the factorization of scalar and pseudoscalar meson poles in correlators, the well-known Nambu relation between the scalar meson mass and the dynamical quark mass, mσ=2mdyn, and the residual chiral symmetry in coupling constants characteristic for the linear σ-model. The second one, the gauge NJL model (GNJL), happens to be qualitatively different from the NJL model, namely, the Nambu relation is not valid, and the factorization of light meson poles does not entail the residual chiral symmetry, i.e., it does not result in a linear σ-model. The more complicated DCSB pattern in the GNJL model is fully explained in terms of excited meson states with the same quantum numbers. The asymptotic restrictions on parameters of scalar and pseudoscalar meson states are derived from the requirement of chiral symmetry restoration at high energies. Bibliography: 13 titles.

Parity doublets and chiral symmetry restoration in baryon spectrum

It is argued that an appearance of the near parity doublets in the upper part of the light baryon spectrum is an evidence for the chiral symmetry restoration in the regime where a typical momentum of quarks is around the chiral symmetry restoration scale. At high enough baryon excitation energy the nontrivial gap solution, which signals the chiral symmetry breaking regime, disappears and the chiral symmetry should be restored. Thus one observes a phase transition in the upper part of the light baryon spectrum. The average kinetic energy of the constituent quarks in this region is just around the critical one 3 T c .

EXCITED SCALAR MESONS IN A CHIRAL QUARK MODEL

First radial excitations of the scalar and pseudoscalar meson nonets as well as their ground states are described as quark–antiquark bound systems in the framework of a nonlocal chiral quark model of the NJL type. Glueball states and their possible mixing with members of the [Formula: see text] multiplets are not considered. Radial excitations are described by means of simple polynomial form factors in the momentum–space which are introduced into the four-quark vertices of the quark Lagrangian. The form factors are chosen in the regime of spontaneous chiral symmetry breaking so that the gap equations do not change their standard form, which provides fulfillment of the low energy theorems. All free parameters of the form factors are fixed by experimentally observed masses of pseudoscalar mesons. All masses of the scalar mesons are predicted. The local six-quark 't Hooft interaction is introduced to solve the so-called UA(1)-problem. The (four particle) singlet–octet mixing for the ground and radially excited states of scalar and pseudoscalar mesons is taken into account. The widths of the main strong decays of the first radial excitation of the scalar meson nonet are calculatedin satisfactory agreement with experimental data. Classification of the considered meson nonets is given. It is shown that the meson states a0(1450), f0(1370), fJ(1710) and [Formula: see text] are the first radial excitations of a0(980), f0(400-1200), f0(980), [Formula: see text].