Aspect sensitivity measurements of polar mesosphere summer echoes using coherent radar imaging

International audienceThe Esrange VHF radar (ESRAD), located in northern Sweden (67.88° N, 21.10° E), has been used to investigate polar mesosphere summer echoes (PMSE). During July and August of 1998, coherent radar imaging (CRI) was used to study the dynamic evolution of PMSE with high temporal and spatial resolution. A CRI analysis provides an estimate of the angular brightness distribution within the radar's probing volume. The brightness distribution is directly related to the radar reflectivity. Consequently, these data are used to investigate the aspect sensitivity of PMSE. In addition to the CRI analysis, the full correlation analysis (FCA) is used to derive estimates of the prevailing three-dimensional wind associated with the observed PMSE. It is shown that regions within the PMSE with enhanced aspect sensitivity have a correspondingly high signal-to-noise ratio (SNR). Although this relationship has been investigated in the past, the present study allows for an estimation of the aspect sensitivity independent of the assumed scattering models and avoids the complications of comparing echo strengths from vertical and off-vertical beams over large horizontal separations, as in the Doppler Beam Swinging (DBS) method. Regions of enhanced aspect sensitivity were additionally shown to correlate with the wave-perturbation induced downward motions of air parcels embedded in the PMSE

Analysis of path integrals at low temperature : Box formula, occupation time and ergodic approximation

We study the low temperature behaviour of path integrals for a simple one-dimensional model. Starting from the Feynman-Kac formula, we derive a new functional representation of the density matrix at finite temperature, in terms of the occupation times of Brownian motions constrained to stay within boxes with finite sizes. From that representation, we infer a kind of ergodic approximation, which only involves double ordinary integrals. As shown by its applications to different confining potentials, the ergodic approximation turns out to be quite efficient, especially in the low-temperature regime where other usual approximations fail

A short proof of stability of topological order under local perturbations

Recently, the stability of certain topological phases of matter under weak perturbations was proven. Here, we present a short, alternate proof of the same result. We consider models of topological quantum order for which the unperturbed Hamiltonian $H_0$ can be written as a sum of local pairwise commuting projectors on a $D$-dimensional lattice. We consider a perturbed Hamiltonian $H=H_0+V$ involving a generic perturbation $V$ that can be written as a sum of short-range bounded-norm interactions. We prove that if the strength of $V$ is below a constant threshold value then $H$ has well-defined spectral bands originating from the low-lying eigenvalues of $H_0$. These bands are separated from the rest of the spectrum and from each other by a constant gap. The width of the band originating from the smallest eigenvalue of $H_0$ decays faster than any power of the lattice size.Comment: 15 page

Distributed Approximate Dynamic Control for Traffic Management of Busy Railway Networks

Railway operations are prone to disturbances that can rapidly propagate through large networks, causing delays and poor performance. Automated re-scheduling tools have shown the potential to limit such undesirable outcomes. This study presents the network-wide effects of local deployment of an adaptive traffic controller for real-time operations that is built on approximate dynamic programming (ADP). The controller aims to limit train delays by advantageously controlling the sequencing of trains at critical locations. By using an approximation to the optimised value function of dynamic programming that is updated by reinforcement learning techniques, ADP reduces the computational burden substantially. This framework has been established for isolated local control, so here we investigate the effects of distributed deployment. Our ADP controller is interfaced with a microscopic railway traffic simulator to evaluate its effect on a large and dynamic railway system, which controls critical points independently. The proposed approach achieved a reduction in train delays by comparison with First-Come-First-Served control. We also found the improvements to be greater at terminal stations compared to the vicinity of our control areas

Comparison of test specificities of commercial antigen-based assays and in-house PCR methods for detection of rotavirus in stool specimens

Seven commercial rotavirus antigen assays were compared with in-house PCR methods for detecting rotavirus in stool specimens. The assay sensitivities were 80% to 100%, while the specificities were 54.3% for one commercial immunochromatographic (ICT) method and 99.4% to 100% for other assays. Thus, except for one commercial ICT, all the assays were generally reliable for rotavirus detection

Evidence of false-positive results in a commercially available rotavirus assay in the vaccine era, Australia, 2011 to 2012

Concerns were raised about specificity of the VIKIA Rota-Adeno immunochromatographic kit. Only 28-37% of samples positive with the VIKIA kit could be confirmed using two real-time RT-PCR assays and three ELISA kits. On re-analysis of a subset of the positive samples, 86% remained positive with the VIKIA kit, however, 90% remained negative in the other assays. In a highly vaccinated population we found a high number of false-positive rotavirus tests with a widely-used commercial kit

Global Equation of State of two-dimensional hard sphere systems

Hard sphere systems in two dimensions are examined for arbitrary density. Simulation results are compared to the theoretical predictions for both the low and the high density limit, where the system is either disordered or ordered, respectively. The pressure in the system increases with the density, except for an intermediate range of volume fractions $0.65 \le \nu \le 0.75$, where a disorder-order phase transition occurs. The proposed {\em global equation of state} (which describes the pressure {\em for all densities}) is applied to the situation of an extremely dense hard sphere gas in a gravitational field and shows reasonable agreement with both experimental and numerical data.Comment: 4 pages, 2 figure

The Origin of Spatial Intermittency in the Galaxy Distribution

The dynamical equations describing the evolution of a self-gravitating fluid can be rewritten in the form of a Schrodinger equation coupled to a Poisson equation determining the gravitational potential. This approach has a number of interesting features, many of which were pointed out in a seminal paper by Widrow & Kaiser (1993). In particular we show that this approach yields an elegant reformulation of an idea due to Jones (1999) concerning the origin of lognormal intermittency in the galaxy distribution.Comment: 4 pages, to appear in MNRAS, no figure