Is there a fundamental limitation on the measurement of spatial coherence for highly incoherent fields?

We investigate a fundamental limitation on the measurement of spatial coherence for highly incoherent fields. We model the near-field detection scheme, required for such a measurement, with pointlike induced dipoles. We find that this fully vector model sets a characteristic length scale beyond which the spatial coherence of an optical field cannot be accurately measured. This length scale forms an uncertainty relationship with the photodetector integration time.     

Comments on the Paper astro-ph/0103335 by C. Rubano and P. Scudellaro

We briefly comment on a paper by Rubano and Scudellaro [Gen. Rel. Grav. 34 (2002) 307, astro-ph/0103335] where they found general exact solutions for two classes of exponential potentials in a scalar field model for quintessence. In that paper the authors were led to some interesting conclusions after a proper choice of the integration constants. By using dimensionless variables we show that the integration constants can be found explicitly without additional assumptions. In consequence we revise some results and conclusions in that paper. We also reproduce observations for Type-Ia supernovae with good accuracy.     

Efficient numerical integrators for stochastic models

The efficient simulation of models defined in terms of stochastic differential equations (SDEs) depends critically on an efficient integration scheme. In this article, we investigate under which conditions the integration schemes for general SDEs can be derived using the Trotter expansion. It follows that, in the stochastic case, some care is required in splitting the stochastic generator. We test the Trotter integrators on an energy-conserving Brownian model and derive a new numerical scheme for dissipative particle dynamics. We find that the stochastic Trotter scheme provides a mathematically correct and easy-to-use method which should find wide applicability.     

Directional control of optical power in integrated InP/InGaAsP extended cavity mode-locked ring lasers

We report on a passively mode-locked InP/InGaAsP multiple quantum well semiconductor ring laser that operates at a 20 GHz repetition rate and around 1575 nm wavelength. The device has been realized using the active-passive integration technology in a standardized photonic integration platform. We demonstrate experimentally for the first time to our knowledge that the relative positioning of the amplifier and absorber in a monolithically integrated ring laser can be used to control the balance of power between counterpropagating fields in the mode-locked state. The directional power balance is verified to be in agreement with a model previously reported.     

机载电子与维修系统仿真模型集成算法研究

随着飞机系统结构的复杂化,维修系统仿真模型的多样化,飞机维修系统仿真模型的集成存在基础层直接集成难度大和复用性差等问题。基于逆向推理的系统仿真模型集成算法以目标问题为导向逆向推理模型数据,经不同知识层次匹配查询目标模型,将模型集成过程转变为问题求解过程,降低了直接对目标建模的复杂程度,最终建立集成网络,实现决策、模型和数据的综合集成。经验证,该算法在飞机维修训练器的仿真系统模型集成中具有良好的性能。     

A nonlocal Poisson bracket of the sine-Gordon model

It is well known that the classical string on a two-sphere is more or less equivalent to the sine-Gordon model. We consider the non-abelian dual of the classical string on a two-sphere. We show that there is a projection map from the phase space of this model to the phase space of the sine-Gordon model. The corresponding Poisson structure of the sine-Gordon model is nonlocal with one integration.     

Modeling global vector fields of chaotic systems from noisy time series with the aid of structure-selection techniques

We address the problem of reconstructing a set of nonlinear differential equations from chaotic time series. A method that combines the implicit Adams integration and the structure-selection technique of an error reduction ratio is proposed for system identification and corresponding parameter estimation of the model. The structure-selection technique identifies the significant terms from a pool of candidates of functional basis and determines the optimal model through orthogonal characteristics on data. The technique with the Adams integration algorithm makes the reconstruction available to data sampled with large time intervals. Numerical experiment on Lorenz and Rossler systems shows that the proposed strategy is effective in global vector field reconstruction from noisy time series.     

One-loop-dimensional reduction of the linear σ model

We perform the dimensional reduction of the linear σ model at one-loop level. The effective potential of the reduced theory obtained from the integration over the nonzero Matsubara frequencies is exhibited. Thermal mass and coupling constant renormalization constants are given, as well as the thermal renormalization group equation which controls the dependence of the counterterms on the temperature. We also recover, for the reduced theory, the vacuum unstability of the model for large N.     

Superbosonization Formula and its Application to Random Matrix Theory

Starting from Gaussian random matrix models we derive a new supermatrix field theory model. In contrast to the conventional non-linear sigma models, the new model is applicable for any range of correlations of the elements of the random matrices. We clarify the domain of integration for the supermatrices, and give a demonstration of how the model works by calculating the density of states for an ensemble of almost diagonal matrices. It is also shown how one can reduce the supermatrix model to the conventional sigma model.     

Angle-Resolved Electron Spectra of F~- Ions by Few-Cycle Laser Pulses

The above-threshold detachment of F~- ions induced by a linearly polarized few-cycle laser pulse is investigated theoretically using the strong-field approximation model without considering the rescattering mechanism. We first derive an analytical form of transition amplitude for describing the strong-field photodetachment of F~- ions.The integration over time in transition amplitude can be performed using the numerical integration method or the saddle-point(SP) method of Shearer et al. [Phys. Rev. A 88(2013) 033415]. The validity of the SP method is carefully examined by comparing the energy spectra and photoelectron angular distributions(PADs) with those obtained from the numerical integration method. By considering the volume effect of a focused laser beam, both the energy spectra and the low-energy PADs calculated by the numerical integration method agree very well with the experimental results.     

New data assimilation system DNDAS for high-dimensional models

The tangent linear(TL) models and adjoint(AD) models have brought great difficulties for the development of variational data assimilation system. It might be impossible to develop them perfectly without great efforts, either by hand, or by automatic differentiation tools. In order to break these limitations, a new data assimilation system, dual-number data assimilation system(DNDAS), is designed based on the dual-number automatic differentiation principles. We investigate the performance of DNDAS with two different optimization schemes and subsequently give a discussion on whether DNDAS is appropriate for high-dimensional forecast models. The new data assimilation system can avoid the complicated reverse integration of the adjoint model, and it only needs the forward integration in the dual-number space to obtain the cost function and its gradient vector concurrently. To verify the correctness and effectiveness of DNDAS, we implemented DNDAS on a simple ordinary differential model and the Lorenz-63 model with different optimization methods. We then concentrate on the adaptability of DNDAS to the Lorenz-96 model with high-dimensional state variables. The results indicate that whether the system is simple or nonlinear, DNDAS can accurately reconstruct the initial condition for the forecast model and has a strong anti-noise characteristic. Given adequate computing resource, the quasi-Newton optimization method performs better than the conjugate gradient method in DNDAS.     

Analytic structure of meson propagators in the proper-time regularized Nambu-Jona-Lasinio model

We analyze the analytic structure of meson propagators in the Nambu-Jona-Lasinio model with a proper-time regulator. We show that the regulator produces unphysical complex singularities. As a result the naive use of the Wick rotation is no longer allowed. Formulas involving integration over mesonic momenta, such as meson-loop contributions or dispersion relations for meson Green’s functions, cannot be written in usual forms.     

Self-organized synchronization and voltage stability in networks of synchronous machines

The integration of renewable energy sources in the course of the energy transition is accompanied by grid decentralization and fluctuating power feed-in characteristics. This development raises novel challenges for power system stability and design. We investigate power system stability from the viewpoint of self-organized synchronization aspects. In this approach, the power grid is represented by a network of synchronous machines. We supplement the classical Kuramoto-like network model, which assumes constant voltages, with dynamical voltage equations, and thus obtain an extended model, that incorporates the coupled categories voltage stability and rotor angle synchronization. We compare disturbance scenarios in small systems simulated on the basis of both classical and extended model and we discuss resultant implications and possible applications to complex modern power grids.     

On simulating complex actions

We describe and compare various methods to numerically simulate measures that are non-positive definite. We argue that variations of importance sampling will fail for large enough volume but some type of Riemann integration scheme might work. Using exact results for the three-dimensional Ising model, we show that to get anything distinguishable from noise, the phase of the measure must be known extremely precisely. We suggest that a recent method to compute the density of states may be the best method to use.     

Structure moyenne et analyse intégrale du panache thermique des convecteurs électriques

In this study, we present an experimental and numerical analysis of thermal plumes issued from electric convectors. The study of the mean velocity and temperature profiles measured within the thermal plume shows that the self-similarity of the profiles is only partly achieved. We developed an integral model that takes into account the settlement flow region by the variations of the entrainment coefficient and the ratio between the temperature and velocity profile widths. A comparison between computed and experimental results proves that the model gives a satisfactory prediction of the physical phenomena. We propose finally a simplified thermal plume model for an integration into a thermal building code.     

Ground-state energy and entropy of the two-dimensional Edwards-Anderson spin-glass model with different bond distributions

We study the two-dimensional Edwards-Anderson spin-glass model using a parallel tempering Monte Carlo algorithm. The ground-state energy and entropy are calculated for different bond distributions. In particular, the entropy is obtained by using a thermodynamic integration technique and an appropriate reference state, which is determined with the method of high-temperature expansion. This strategy provides accurate values of this quantity for finite-size lattices. By extrapolating to the thermodynamic limit, the ground-state energy and entropy of the different versions of the spin-glass model are determined.     

Continuous growth models in terms of generalized logarithm and exponential functions

Consider the one-parameter generalizations of the logarithmic and exponential functions which are obtained from the integration of non-symmetrical hyperboles. These generalizations coincide to the one obtained in the context of non-extensive thermostatistics. We show that these functions are suitable to describe and unify the great majority of continuous growth models, which we briefly review. Physical interpretation to the generalization function parameter is given for the Richards’ model, which has an underlying microscopic model to justify it.     

Drude model and Lifshitz formula

Since nearly 10 years, it has been known that inserting the permittivity of the Drude model into the Lifshitz formula for free energy causes a violation of the third law of thermodynamics. In this paper we show that the standard Matsubara formulation for free energy contains a contribution that is non-perturbative in the relaxation parameter. We argue that the correct formula must have a perturbative expansion and conclude that the standard Matsubara formulation with the permittivity of the Drude model inserted is not correct. We trace the non-perturbative contribution in the complex frequency plane, where it shows up as a self-intersection or a bifurcation of the integration path.     

The XXZ Heisenberg model on random surfaces

We consider integrable models, or in general any model defined by an R-matrix, on random surfaces, which are discretized using random Manhattan lattices. The set of random Manhattan lattices is defined as the set dual to the lattice random surfaces embedded on a regular d-dimensional lattice. They can also be associated with the random graphs of multiparticle scattering nodes. As an example we formulate a random matrix model where the partition function reproduces the annealed average of the XXZ Heisenberg model over all random Manhattan lattices. A technique is presented which reduces the random matrix integration in partition function to an integration over their eigenvalues.     

Time resolved pattern evolution in a large aperture laser

We have measured quasiinstantaneous transverse patterns in a broad aperture laser. Nonordered patterns yielding to boundary determined regular structures in progressive time-integrated recording are observed. The linear analysis and numerical integration of the full Maxwell-Bloch equations allow us to interpret the features of the experiment. We show that this system being far from threshold cannot be fully understood with a perturbative model.