132,842 research outputs found

    A tensor-vector-scalar framework for modified dynamics and cosmic dark matter

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    I describe a tensor-vector-scalar theory that reconciles the galaxy scale success of modified Newtonian dynamics (MOND) with the cosmological scale evidence for CDM. The theory provides a cosmological basis for MOND in the sense that the predicted phenomenology only arises in a cosmological background. The theory contains an evolving effective potential, and scalar field oscillations in this potential comprise the cold dark matter; the de Broglie wavelength of these soft bosons, however, is sufficiently large that they cannot accumulate in galaxies. The theory predicts, inevitably, a constant anomalous acceleration in the outer solar system which, depending upon the choice of parameters, can be consistent with that detected by the Pioneer spacecrafts.Comment: minor corrections, numerical error corrected in eq. 37 and subsequent equations, accepted MNRA

    Transitions to Measure Synchronization in Coupled Hamiltonian Systems

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    Transitions to measure synchronization in two coupled ϕ4\phi ^{4} lattices are investigated based on numerical simulations. The relationship between measure synchronization (MS), phase locking and system's total energy is studied both for periodic and chaotic states. Two different scalings are discovered during the process to MS according to phase locking. Random walk like phase synchronization in chaotic measure synchronization is found, and phase locking interrupted by phase slips irregularly is also investigated. Meanwhile, related analysis is qualitative given to explain this phenomenon.Comment: 10 pages, 6 figure

    Observation of a single atom in a magneto-optical trap

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    Fluorescence from Cs atoms in a magneto-optical trap is detected under conditions of very low atomic density. Discrete steps are observed in the fluorescent signal versus time and are associated with the arrival and departure of individual trapped atoms. Histograms of the frequency of occurrence of a given level of fluorescence exhibit a series of uniformly spaced peaks that are attributed to the presence of N = 0, 1, 2 atoms in the trap

    Recent advances on recursive filtering and sliding mode design for networked nonlinear stochastic systems: A survey

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    Copyright © 2013 Jun Hu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Some recent advances on the recursive filtering and sliding mode design problems for nonlinear stochastic systems with network-induced phenomena are surveyed. The network-induced phenomena under consideration mainly include missing measurements, fading measurements, signal quantization, probabilistic sensor delays, sensor saturations, randomly occurring nonlinearities, and randomly occurring uncertainties. With respect to these network-induced phenomena, the developments on filtering and sliding mode design problems are systematically reviewed. In particular, concerning the network-induced phenomena, some recent results on the recursive filtering for time-varying nonlinear stochastic systems and sliding mode design for time-invariant nonlinear stochastic systems are given, respectively. Finally, conclusions are proposed and some potential future research works are pointed out.This work was supported in part by the National Natural Science Foundation of China under Grant nos. 61134009, 61329301, 61333012, 61374127 and 11301118, the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant no. GR/S27658/01, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany

    Wigner functions of thermo number state, photon subtracted and added thermo vacuum state at finite temperature

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    Based on Takahashi-Umezawa thermo field dynamics and the order-invariance of Weyl ordered operators under similar transformations, we present a new approach to deriving the exact Wigner functions of thermo number state, photon subtracted and added thermo vacuum state. We find that these Wigner functions are related to the Gaussian-Laguerre type functions of temperature, whose statistical properties are then analysed.Comment: 10 pages and 2 figure

    Stress-energy Tensor Correlators in N-dim Hot Flat Spaces via the Generalized Zeta-Function Method

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    We calculate the expectation values of the stress-energy bitensor defined at two different spacetime points x,xx, x' of a massless, minimally coupled scalar field with respect to a quantum state at finite temperature TT in a flat NN-dimensional spacetime by means of the generalized zeta-function method. These correlators, also known as the noise kernels, give the fluctuations of energy and momentum density of a quantum field which are essential for the investigation of the physical effects of negative energy density in certain spacetimes or quantum states. They also act as the sources of the Einstein-Langevin equations in stochastic gravity which one can solve for the dynamics of metric fluctuations as in spacetime foams. In terms of constitutions these correlators are one rung above (in the sense of the correlation -- BBGKY or Schwinger-Dyson -- hierarchies) the mean (vacuum and thermal expectation) values of the stress-energy tensor which drive the semiclassical Einstein equation in semiclassical gravity. The low and the high temperature expansions of these correlators are also given here: At low temperatures, the leading order temperature dependence goes like TNT^{N} while at high temperatures they have a T2T^{2} dependence with the subleading terms exponentially suppressed by eTe^{-T}. We also discuss the singular behaviors of the correlators in the xxx'\rightarrow x coincident limit as was done before for massless conformal quantum fields.Comment: 23 pages, no figures. Invited contribution to a Special Issue of Journal of Physics A in honor of Prof. J. S. Dowke