One-dimensional strings, random fluctuations, and complex chaotic structures

The effect of random fluctuations on the set of equations resulting from coupling 200 points with one-dimensional maps is studied. This dynamical system exhibits a spatial exponential growth in fluctuations, resulting in a complex chaotic structure. The system suggests a closer look at stability in complex systems.     

Modeling cities

Cities are systems with a large number of constituents and agents interacting with each other and can be considered as emblematic of complex systems. Modeling these systems is a real challenge and triggered the interest of many disciplines such as quantitative geography, spatial economics, geomatics and urbanism, and more recently physics. (Statistical) Physics plays a major role by bringing tools and concepts able to bridge theory and empirical results, and we will illustrate this on some fundamental aspects of cities: the growth of their surface area and their population, their spatial organization, and the spatial distribution of activities. We will present state-of-the-art results and models but also open problems for which we still have a partial understanding and where physics approaches could be particularly helpful. We will end this short review with a discussion about the possibility of constructing a science of cities.     

Scaling properties of the growing monolayer on the disordered substrate

We present results of theoretical and numerical studies the pattern formation processes in adsorptive system with the disordered substrate, representing high-entropy alloy. The lateral diffusivity of adatoms on the substrate is represented as a quenched spatial disorder. By taking into account a transference of adsorbate between first two layers we construct the reaction-diffusion model, describing evolution of adsorbate concentration on the disordered substrate. It will be shown, that at elevated values of the pressure inside a chamber the quenched spatial disorder will induce pattern formation in the system. We will show that the strength of the spatial disorder can control dynamics of nanostructured film growth, type of surface structures and scaling properties of the growing layer. This study provides an insight into details of self-organization of adatoms on the high-entropy alloys in adsorptive systems.     

复杂氧化物中电子相分离的量子调控

复杂氧化物可以呈现出高温超导、庞磁阻以及多铁效应等诸多新奇的物理现象.这类材料中的电荷/自旋/轨道和晶格自由度之间的强耦合相互作用,可以导致多种相互竞争且能量非常接近的电子态的空间共存,这就是电子相分离现象.如果可以将材料的空间尺寸缩小到电子相分离的特征长度,其物理性质甚至电子关联作用本身都会发生根本的变化,从而有可能实现复杂氧化物中的量子调控.本文综述了我们课题组在过去几年中针对复杂氧化物中电子相分离的量子调控取得的进展,内容包括：发现了锰氧化物边缘电子态,通过氧化物微纳加工技术,实现了量子态空间分布的调控,提高了庞磁阻锰氧化物的临界温度;研究了当材料空间尺度小于其电子相分离特征尺度时电子相分离的表现,确定了在电子相分离消失以后体系的磁结构;通过超晶格生长技术调控了材料中的掺杂有序度,对锰氧化物中大尺度的电子相分离的物理机理从实验上给出了解释.     

Superresolution imaging of scatterers in ultrasound B-scan imaging

A number of imaging systems exhibit speckle, which is caused by the interaction of a coherent pulse reflecting off of random reflectors. The limitations of these systems are quite serious because the speckle phenomenon creates a pattern of nulls and peaks from subresolvable scatterers or targets that are difficult to interpret. Another limitation of these pulse-echo imaging systems is that their resolution is dependent on the full spatial extent of the propagating pulse, usually several wavelengths in the axial or propagating dimension and typically longer in the transverse direction. This limits the spatial resolution to many multiples of the wavelength. This paper focuses on the particular case of ultrasound B-scan imaging and develops an inverse filter solution that eliminates both the speckle phenomenon and the poor resolution dependency on the pulse length and width to produce super-resolution ultrasound (SURUS) images. The key to the inverse filter is the creation of pulse shapes that have stable inverses. This is derived by use of the standard Z-transform and related properties. Although the focus of this paper is on examples from ultrasound imaging systems, the results are applicable to other pulse-echo imaging systems that also can exhibit speckle statistics.     

Response of multiple coupled dynamic systems

Analytical procedures are developed to investigate the nature of the response of multiple coupled dynamic systems. The dynamic systems are one-dimensional and are coupled at junctions. The spatial extents of the dynamic systems are determined by these junctions; a dynamic system terminates at these junctions. The junctions are characterized by assigning reflection and transmission coefficients at the terminal positions of the dynamic systems. In addition, a dynamic system is characterized by a single propagation wavenumber. The wavenumber may be complex, accounting for possible spatial attenuation and for distributed damping in the dynamic system. Further damping—edge damping—may be accounted for by assigning non-conservative coefficients at the junction. Quadratic forms describing the dynamics of multiple coupled dynamic systems are also presented and discussed. Relationship of such forms to the statistical energy analysis (SEA) of complex dynamic systems is touched upon. This paper is concerned chiefly with the development of analytical procedures. Examples of application of these procedures will be dealt with in subsequent publications.     

Ordering of defects in metal systems exposed to high-energy particles

A diffusion model for pore nucleation and growth in metal systems exposed to high-energy particles is proposed. The pore nucleation is seen as coagulation of excess vacancies. Our rough estimates correlate with experiment. A mechanism of radiation-induced pore formation and spatial ordering in metal systems is suggested. Altai State Technical University. Translated from Izvestiya Vysshikh Uchebnykh, Zevedenii, Fizika, No. 4, pp. 82–86, May, 2000.     

Spatial domain multiplexing: A new dimension in fiber optic multiplexing

A novel multiplexing technique for fiber optic communications has been developed that supports multiple channels of optical energy inside an optical fiber by confining each individual channel to a unique spatial location. These channels can operate at exactly the same wavelength as well as differing wavelengths. The basic operating principle and experimental results for spatial domain multiplexed fiber optic communication systems is presented here. This technique adds a new dimension to currently available multiplexing schemes and has the potential to increase the bandwidth of existing and futuristic optical fiber systems by multiple folds.     

辐射照相系统中转换屏的分辨率研究

 在高能X光辐射照相系统中，通常使用闪烁体材料的转换屏将X光转换为可见光进行探测。建立了转换屏空间分辨率的计算模型，模拟了转换屏的空间分辨率随屏的厚度、材料及X光子能量的变化关系，为系统的设计提供了参数。     

Growth of ordered domains beyond a dynamic instability in dissipative systems

We furnish evidence supporting our conjecture that the growth of structure which results at the onset of a center manifold in driven systems operating far from equilibrium can be described by a power law with a single exponent. More specifically, if the dissipative structure is contained in a center manifold and thus its stability is warranted, the linear dimensions for domains of organized spatial cells increase ast ^1/2.     

Geodesics in rotating systems

The paper investigates the equations for geodesics, null geodesics, and spatial geodesics in rotating systems. Geodesics and null geodesics have, as usual, been interpreted as the paths of free particles and of light rays, respectively. Spatial geodesics are given a firm interpretation as the shortest paths between points within the rotating system, where the path length is measured by an observer in the rotating system who moves along the spatial geodesic. The paper shows that equations for geodesics in rotating systems may be derived by the traditional method, i.e., from the flat-space metric of general relativity, or by means of the instantaneous Lorentz frames approach. This supports the use of instantaneous Lorentz frames as a valid method for the analysis of events in rotating systems.     

Physics,Mechanism, and Organization of Gravitational-Inertial Wave Orientation

The development of a fully autonomous all-weather high-precision orientation and navigation system capable of operating for a long time (hours, weeks, months, and years) by the existing methods is hampered due to the impossibility of forming a real-time starting reference coordinate system with stable orientation in the horizontal plane, relative to which an angular direction toward the object is determined (orientation) and running coordinates of the object are calculated (navigation), directly on board an object. The conventional methods of spatial orientation use information on a unidirectional vector to form reference coordinate systems (gyrocompasses, laser compasses, magnetic compasses, celestial reference systems, etc.). In this connection, information on the spatial orientation can be easily distorted by various physical factors, because it may be summed with them. Therefore, a fully autonomous high-precision global system of spatial orientation for mobile and fixed objects cannot be developed by these methods. This problem is solved in a system based on the biological principles of gravitational-inertial wave orientation. The present paper gives the physical and mathematical substantiation of these biological principles and describes their technical realization in navigation systems of a new generation.     

Linear optical coherence tomography system with a downconverted fringe pattern

Linear optical coherence tomography (LOCT) systems are a simple and robust alternative to time-domain optical coherence tomography systems, but a detector with approximately 10(4) pixels is needed for an imaging depth of 2 mm. We present a new system for LOCT with a special mask attached to the image sensor. The mask essentially performs a downconversion of the spatial frequencies by multiplication with a second spatial frequency. This reduces the fringe frequency of the optical coherence tomography signal so that the signal can be sampled with fewer pixels.     

Spatial-Variant Geometric Phase of Hybrid-Polarized Vector Optical Fields

We investigate a novel spatial geometric phase of hybrid-polarized vector fields consisting of linear, elliptical and circular polarizations by Young's two-slit interferometer instead of the widely used Mach-Zehnder interferometer.This spatial geometric phase can be manipulated by engineering the spatial configuration of hybrid polarizations,and is directly related to the topological charge, the local states of polarization and the rotational symmetry of hybrid-polarized vector optical fields. The unique feature of geometric phase has implications in quantum information science as well as other physical systems such as electron vortex beams.     

Particle Systems Analysis by Using Skeletonization and Exact Dilations

This paper describes how the formation of particle systems can be investigated by using computer vision techniques, namely effective exact dilations and multiscale skeletonization. By assuming that all particles started to grow at the same time and had the same growth rate, a hypothesis that can be validated later, it becomes possible to infer the shape and distribution of the particles in the initial system configuration. Multiscale skeletons are obtained for each individual particle, and a suitable overall spatial scale, i.e. those best approximating the initial configuration, is determined as that immediately before the smallest particle fades. The thus obtained skeletons provide an estimate of the shape and position of the initial particles before uniform expansion. By using exact dilations, a generalized Dirichlet tessellation reconstruction of the particle system is obtained from these skeletons, and the similarity between this reconstruction and the original system can be used to validate the assumptions about the growth conditions. The proposed methodology is illustrated with respect to KC1 polycrystalline thin films.     

Self-organized stable pacemakers near the onset of birhythmicity

General amplitude equations are derived for reaction-diffusion systems near the soft onset of birhythmicity described by a supercritical pitchfork-Hopf bifurcation. Using these equations and applying singular perturbation theory, we show that stable autonomous pacemakers represent a generic kind of spatiotemporal patterns in such systems. This is verified by numerical simulations, which also show the existence of breathing and swinging pacemaker solutions. The drift of self-organized pacemakers in media with spatial parameter gradients is analytically and numerically investigated.     

Spatial instabilities in reaction random walks with direction-independent kinetics

We study spatial instabilities in reacting and diffusing systems, where diffusion is modeled by a persistent random walk instead of the usual Brownian motion. Perturbations in these reaction walk systems propagate with finite speed, whereas in reaction-diffusion systems localized disturbances affect every part instantly, albeit with heavy damping. We present evolution equations for reaction random walks whose kinetics do not depend on the particles' direction of motion. The homogeneous steady state of such systems can undergo two types of transport-driven instabilities. One type of bifurcation gives rise to stationary spatial patterns and corresponds to the Turing instability in reaction-diffusion systems. The other type occurs in the ballistic regime and leads to oscillatory spatial patterns; it has no analog in reaction-diffusion systems. The conditions for these bifurcations are derived and applied to two model systems. We also analyze the stability properties of one-variable systems and find that small wavelength perturbations decay in an oscillatory manner.     

Real-time Fourier transformer based on fiber gratings

We use the well-known duality between paraxial diffraction in space and dispersion in time to propose a time-domain analog to spatial Fraunhofer diffraction. This analog permits the design of real-time optical Fourier-transformer systems. These systems are shown to be realizable by use of linearly chirped fiber gratings as dispersive media.