Primitive roles for inhibitory interneurons in developing frog spinal cord

Understanding the neuronal networks in the mammal spinal cord is hampered by the diversity of neurons and their connections. The simpler networks in developing lower vertebrates may offer insights into basic organization. To investigate the function of spinal inhibitory interneurons in Xenopus tadpoles, paired whole-cell recordings were used. We show directly that one class of interneuron, with distinctive anatomy, produces glycinergic, negative feedback inhibition that can limit firing in motoneurons and interneurons of the central pattern generator during swimming. These same neurons also produce inhibitory gating of sensory pathways during swimming. This discovery raises the possibility that some classes of interneuron, with distinct functions later in development, may differentiate from an earlier class in which these functions are shared. Preliminary evidence suggests that these inhibitory interneurons express the transcription factor engrailed, supporting a probable homology with interneurons in developing zebrafish that also express engrailed and have very similar anatomy and functions

Direct imaging of a digital-micromirror device for configurable microscopic optical potentials

Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.Comment: 9 page

Patterns from preheating

The formation of regular patterns is a well-known phenomenon in condensed matter physics. Systems that exhibit pattern formation are typically driven and dissipative with pattern formation occurring in the weakly non-linear regime and sometimes even in more strongly non-linear regions of parameter space. In the early universe, parametric resonance can drive explosive particle production called preheating. The fields that are populated then decay quantum mechanically if their particles are unstable. Thus, during preheating, a driven-dissipative system exists. In this paper, we show that a self-coupled inflaton oscillating in its potential at the end of inflation can exhibit pattern formation.Comment: 4 pages, RevTex, 6 figure

Semiclassical form factor for spectral and matrix element fluctuations of multi-dimensional chaotic systems

We present a semiclassical calculation of the generalized form factor which characterizes the fluctuations of matrix elements of the quantum operators in the eigenbasis of the Hamiltonian of a chaotic system. Our approach is based on some recently developed techniques for the spectral form factor of systems with hyperbolic and ergodic underlying classical dynamics and f=2 degrees of freedom, that allow us to go beyond the diagonal approximation. First we extend these techniques to systems with f>2. Then we use these results to calculate the generalized form factor. We show that the dependence on the rescaled time in units of the Heisenberg time is universal for both the spectral and the generalized form factor. Furthermore, we derive a relation between the generalized form factor and the classical time-correlation function of the Weyl symbols of the quantum operators.Comment: some typos corrected and few minor changes made; final version in PR

Resonant Production of Topological Defects

We describe a novel phenomenon in which vortices are produced due to resonant oscillations of a scalar field which is driven by a periodically varying temperature T, with T remaining much below the critical temperature $T_c$. Also, in a rapid heating of a localized region to a temperature {\it below} $T_c$, far separated vortex and antivortex can form. We compare our results with recent models of defect production during reheating after inflation. We also discuss possible experimental tests of our predictions of topological defect production {\it without} ever going through a phase transition.Comment: Revtex, 13 pages including 5 postscript figure

(Non)Invariance of dynamical quantities for orbit equivalent flows

We study how dynamical quantities such as Lyapunov exponents, metric entropy, topological pressure, recurrence rates, and dimension-like characteristics change under a time reparameterization of a dynamical system. These quantities are shown to either remain invariant, transform according to a multiplicative factor or transform through a convoluted dependence that may take the form of an integral over the initial local values. We discuss the significance of these results for the apparent non-invariance of chaos in general relativity and explore applications to the synchronization of equilibrium states and the elimination of expansions

A symmetric polymer blend confined into a film with antisymmetric surfaces: interplay between wetting behavior and phase diagram

We study the phase behavior of a symmetric binary polymer blend which is confined into a thin film. The film surfaces interact with the monomers via short range potentials. We calculate the phase behavior within the self-consistent field theory of Gaussian chains. Over a wide range of parameters we find strong first order wetting transitions for the semi-infinite system, and the interplay between the wetting/prewetting behavior and the phase diagram in confined geometry is investigated. Antisymmetric boundaries, where one surface attracts the A component with the same strength than the opposite surface attracts the B component, are applied. The phase transition does not occur close to the bulk critical temperature but in the vicinity of the wetting transition. For very thin films or weak surface fields one finds a single critical point at $\phi_c=1/2$. For thicker films or stronger surface fields the phase diagram exhibits two critical points and two concomitant coexistence regions. Only below a triple point there is a single two phase coexistence region. When we increase the film thickness the two coexistence regions become the prewetting lines of the semi-infinite system, while the triple temperature converges towards the wetting transition temperature from above. The behavior close to the tricritical point, which separates phase diagrams with one and two critical points, is studied in the framework of a Ginzburg-Landau ansatz. Two-dimensional profiles of the interface between the laterally coexisting phases are calculated, and the interfacial and line tensions analyzed. The effect of fluctuations and corrections to the self-consistent field theory are discussed.Comment: Phys.Rev.E in prin

Are Kaluza-Klein modes enhanced by parametric resonance?

We study parametric amplification of Kaluza-Klein (KK) modes in a higher $D$-dimensional generalized Kaluza-Klein theory, which was originally considered by Mukohyama in the narrow resonance case. It was suggested that KK modes can be enhanced by an oscillation of a scale of compactification by the $d$-dimensional sphere $S^d~(d=D-4)$ and by the direct product $S^{d_1}\times S^{d_2}~(d_1+d_2=D-4)$. We extend this past work to the more general case where initial values of the scale of compactification and the quantum number of the angular momentum $l$ of KK modes are not small. We perform analytic approaches based on the Mathieu equation as well as numerical calculations, and find that the expansion of the universe rapidly makes the KK field deviate from instability bands. As a result, KK modes are not enhanced sufficiently in an expanding universe in these two classes of models.Comment: 15 pages, 5 figure

Casimir forces in binary liquid mixtures

If two ore more bodies are immersed in a critical fluid critical fluctuations of the order parameter generate long ranged forces between these bodies. Due to the underlying mechanism these forces are close analogues of the well known Casimir forces in electromagnetism. For the special case of a binary liquid mixture near its critical demixing transition confined to a simple parallel plate geometry it is shown that the corresponding critical Casimir forces can be of the same order of magnitude as the dispersion (van der Waals) forces between the plates. In wetting experiments or by direct measurements with an atomic force microscope the resulting modification of the usual dispersion forces in the critical regime should therefore be easily detectable. Analytical estimates for the Casimir amplitudes Delta in d=4-epsilon are compared with corresponding Monte-Carlo results in d=3 and their quantitative effect on the thickness of critical wetting layers and on force measurements is discussed.Comment: 34 pages LaTeX with revtex and epsf style, to appear in Phys. Rev.

Particle production in the oscillating inflation model

We investigate the particle production of a scalar field $\chi$ coupled to an inflaton field $\phi$ ($g^2\phi^2\chi^2/2$) in the {\it oscillating inflation} model, which was recently proposed by Damour and Mukhanov. Although the fluctuation of the $\phi$ field can be effectively enhanced during a stage of the oscillating inflation, the maximum fluctuation is suppressed as the critical value $\phi_c$ which indicates the scale of the core part of the inflaton potential decreases, in taking into account the back reaction effect of created particles. As for the $\chi$ particle production, we find that larger values of the coupling constant $g$ are required to lead to an efficient parametric resonance with the decrease of $\phi_c$, because an effective mass of inflaton around the minimum of its potential becomes larger. However, it is possible to generate the superheavy $\chi$ particle whose mass is greater than $10^{14}$ GeV, which would result in an important consequence for the GUT baryogenesis.Comment: 18 pages, 14 figure