Astronomical adaptive optics in parameter space

We present a general, undiscretized formulation of astronomical adaptive optics that encompasses arbitrary guide star sources and deformable mirror configurations. It is shown that wave-front measurements can be represented as samples of an integral transform of the turbulence perturbation and also that the desired information for adaptive correction is a subset of this transformed space. Some properties of this space are explored, and their implications for adaptive optics are discussed.     

Holographic measurement of reverberation time

A system employing the radio frequency holographic method for the measurement of the reverberation time of an acoustic chamber is proposed. This system has the advantage of supplying visible information on the diminishing intensity of the acoustic wave. A simple mathematical model has been taken to discuss the basic principles involved in the system. A possible experimental set-up for the measurement of the reverberation time is described in detail.     

Modelling the behaviour of unemployment rates in the US over time and across space

This paper provides evidence that unemployment rates across US states are stationary and therefore behave according to the natural rate hypothesis. We provide new insights by considering the effect of key variables on the speed of adjustment associated with unemployment shocks. A highly-dimensional VAR analysis of the half-lives associated with shocks to unemployment rates in pairs of states suggests that the distance between states and vacancy rates respectively exert a positive and negative influence. We find that higher homeownership rates do not lead to higher half-lives. When the symmetry assumption is relaxed through quantile regression, support for the Oswald hypothesis through a positive relationship between homeownership rates and half-lives is found at the higher quantiles.     

空间光学的发展与波前传感技术

进入21世纪,国际上一些发达国家和有关部门都已制定了空间发展战略规划,如美国航空航天局(NASA)、欧洲空间局(ESA)和俄罗斯政府相关部门等都提出空间发展战略规划,这些规划提出了今后一段时间内空间科学要解决的问题和发展的方向,而解决这些问题并推进空间技术的发展很大程度上依赖于先进的光学和无线电望远镜及仪器设备。因此,本文介绍本世纪初国际上空间科学应用的大型天文望远镜的发展情况,重点描述了大口径光学望远镜的光学系统以及实现这类天文望远镜的关键技术之一—波前传感技术。     

Magneto optics and time resolved terahertz spectrocopy

Exploring, manipulating, and understanding new exotic quantum phenomena in condensed-matter systems have generated great interest in the scientific community. Static and time resolved optical spectroscopies after photoexcitations are important experimental tools for probing charge dynamics and quasiparticle excitations in quantum materials. In Synergetic Extreme Condition User Facility(SECUF), we shall construct magneto-infrared and terahertz measurement systems and develop a number of ultrafast femtosecond laser based systems, including intense near to mid-infrared pump terahertz probe. In this article, we shall describe several systems to be constructed and developed in the facilities, then present some examples explaining the application of magneto optics and time resolved spectroscopy techniques.     

Holographic coherence tomography for measurement of three-dimensional refractive-index space

A new tomographic method for the measurement of three-dimensional refractive-index fields of transparent media, which we call holographic coherence tomography and which combines double-exposure holographic interferometry with the detecting style of optical coherence tomography, has been developed. The three-dimensional refractive-index field can be achieved with a confocal lens system by continual longitudinal and horizontal scanning of the holographic reconstruction image.     

Dependence of the temperature behaviour of the sputtering ratio on the channelled fraction of the ion beam

A method of calculation is presented for the yield of an electron excitation process by a channelled particle in a single encounter with an atomic row or plane in a crystal. It is shown that, if ψ is the initial angle between the ion trajectory and the row or plane, the number of inner-shell electrons excited is an increasing function of ψ whereas the number of outer electrons excited may decrease with increasing ψ.     

Advection and dispersion in time and space

Previous work showed how moving particles that rest along their trajectory lead to time-nonlocal advection–dispersion equations. If the waiting times have infinite mean, the model equation contains a fractional time derivative of order between 0 and 1. In this article, we develop a new advection–dispersion equation with an additional fractional time derivative of order between 1 and 2. Solutions to the equation are obtained by subordination. The form of the time derivative is related to the probability distribution of particle waiting times and the subordinator is given as the first passage time density of the waiting time process which is computed explicitly.     

Realization of free space optics with OFDM under atmospheric turbulence

Free space optics (FSO) technology provides a promising solution for future broadband networks, offering high data transmission compared to RF technology. This work is focused on investigating the performance of an FSO system with OFDM and QAM. A 10 Gbps data stream is transmitted using a 4-level QAM sequence through the FSO system under different atmospheric conditions. Results indicate that the integration of SOA prolongs the maximum achievable distance with acceptable SNR to 185 km under clear weather conditions whereas under atmospheric fog, the maximum distance is extended to 2.5 km.     

Quantum mechanics of space and time

A formulation of relativistic quantum mechanics is presented independent of the theory of Hilbert space and also independent of the hypothesis of spacetime manifold. A hierarchy is established in the nondistributive lattice of physical ensembles, and it is shown that the projections relating different members of the hierarchy form a semigroup. It is shown how to develop a statistical theory based on the definition of a statistical operator. Involutions defined on the matrix representations of the semigroup are interpreted in terms ofCPT conjugations. The theory of particles of spin one-half and systems with higher spin is developed from first principles. Methods are also developed for defining energy, momentum, orbital angular momentum, and weighted spacetime coordinates without reference to a manifold.     

Fractal time and space in complex fluids

Summary We investigate transport in complex fluids including glassy materials and turbulent flows. We focus on regimes where fractal hierarchical scaling exists in time, space or both simultaneously. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Physical defects in fiber optics: A theoretical framework in phase space

A Gaussian symplectic map is used to obtain the Wigner distribution function (WDF) of an optical fiber sectioned by a media with different refractive index. It is found that the WDF after the defect is simply the original Gaussian corrected by a polynomial term.     

Dynamics of water in real space and time

Owing to marked advances in instrumentation in X-ray and neutron scattering the time-dependent pair correlation function, the Van Hove function, can now be determined by inelastic X-ray and neutron scattering measurements. The local dynamics of water in real space and time is visualised by this approach. We discuss how the dynamic properties, such as viscosity and diffusion, can be elucidated through the Van Hove function of water.     

Holographic three-dimensional display synthesized from three-dimensional fourier spectra of real existing objects

A method of synthesizing computer-generated holograms of real existing objects is proposed that is based on a series of projection images of an incoherently illuminated object recorded from different perspectives. In accordance with the principles of computer tomography, the three-dimensional Fourier spectrum of the object is calculated by use of several projection images. A method of calculating a Fresnel hologram from the three-dimensional Fourier spectrum is proposed. Experimental results in the form of a computer simulation and optical reconstruction are presented.     

Asymptotic behaviour of self-avoiding walks in continuous space

The asymptotic behaviour of self-avoiding walks that do not lie on a lattice has been investigated by a Monte-Carlo procedure. Its dependence on the fine structure of the walk is discussed.     

Controlling and synchronizing space time chaos

Control and synchronization of continuous space-extended systems is realized by means of a finite number of local tiny perturbations. The perturbations are selected by an adaptive technique, and they are able to restore each of the independent unstable patterns present within a space time chaotic regime, as well as to synchronize two space time chaotic states. The effectiveness of the method and the robustness against external noise is demonstrated for the amplitude and phase turbulent regimes of the one-dimensional complex Ginzburg-Landau equation. The problem of the minimum number of local perturbations necessary to achieve control is discussed as compared with the number of independent spatial correlation lengths.     

Asymptotic behaviour of classical Yang-Mills fields in Minkowski space

We show how to define incoming and outgoing asymptotic fields for classical solutions of the Yang-Mills field equations without fixing the gauge. It is then seen that the Gribov ambiguities for putting the field in the Coulomb gauge reduce asymptotically to a field-independent, infinite parameter group of gauge transformations. This obscures the notion of color charge already at the classical level.