Self-organization as the driving force for the evolution of the biosphere

In this paper we present a space-time model of urban ecosystems as conjugate active media. This approach is based on the representation of urban ecosystems as self-organizing systems; it aims at identifying the threshold values of control parameters and is considered promising in assessing system stability to internal and external fluctuations.     

Autowave self-organization in heterogeneous natural–anthropogenic ecosystems

This article considers the spatio–temporal model of natural–anthropegenic ecosystems as a conjugated active media that takes the heterogeneity of anthropogenic and natural factors into account. The approach aims to identify the threshold values of the control parameters. The theoretical basis of the system analysis of the sustainability of the ecosystems is synergistic data on autowave self-organization in active media. The mathematical model is based on the modified FitzHugh–Nagumo system of equations.     

Photocounting statistics of radiation propagating through passive and active random media

The photocounting statistics of radiation propagating through active, quadratic random media and through passive media are considered on the basis of a recently developed quantum dynamic theory. We show that the counting statistics for lossless random active media and those for passive weakly-inhomogeneous random media are similar, although there are some differences. The peak of the photocounting distribution shifts to lower count numbern and is found to broaden with increasing turbulence level, as in the case of passive media. In lossy active media, the shift of the peak to lowern is more pronounced, in pumped active media below threshold it is less so, and in pumped active media above threshold, there is a shift of the peak to highern as a consequence of self-radiation. Severe broadening occurs in this latter case. Photocounting statistics for special states of the incident field are also discussed.     

Optical theorem detectors for active scatterers

We develop a new theory of the optical theorem for scalar fields in nonhomogeneous media which can be bounded or unbounded. It applies to arbitrary lossless backgrounds and quite general probing fields. The derived formulation holds for arbitrary passive scatterers, which can be dissipative, as well as for the more general class of active scatterers which are composed of a (passive) scatterer component and an active, radiating (antenna) component. The generalization of the optical theorem to active scatterers is relevant to many applications such as surveillance of active targets including certain cloaks and invisible scatterers and wireless communications. The derived theoretical framework includes the familiar real power optical theorem describing power extinction due to both dissipation and scattering as well as a novel reactive optical theorem related to the reactive power changes. The developed approach naturally leads to three optical theorem indicators or statistics which can be used to detect changes or targets in unknown complex media. The paper includes numerical simulation results that illustrate the application of the derived optical theorem results to change detection in complex and random media.     

活性无序介质中泵浦功率对局域模发射的影响

基于具有局域-非周期-类结构的活性无序介质中的复杂局域模与合适泵浦光的相互作用模型,研究活性无序介质中泵浦功率对局域模发射的影响,定性解释了泵浦功率对局域模发射的影响.结果表明,局域-非周期-类结构的无序介质的透射谱只与介质的结构有关,而与介质的损耗和增益无关,不同的激发模具有不同的泵浦功率阈值.     

New spectroscopic method for the determination of optical rotatory dispersion

A new spectroscopic methodology is proposed to measure optical rotatory dispersion(ORD)of optically active media.ORD is obtained from a three-step phase shifting algorithm using transmission spectra taken at three independent probing angles.Optical rotation angles of four sugar solutions are investigated.The results obtained by using the new method show excellent agreement with the reference data,indicating the new method can be used as a reliable way for studying ORD of optically active media.     

The Dynamics of the Autowave Front in a Model of Urban Ecosystems

A nonlinear singularly perturbed system of parabolic equations in a two-dimensional domain is considered. The system can be used to simulate the motion of an autowave front in a model of the evolution of urban ecosystems in the case of an inhomogeneous medium whose parameters vary with time. An asymptotic analysis of the problem is performed using methods of the theory of contrast structures. An asymptotic approximation of a front-type solution of the zero and first orders is obtained.     

Effect of absorption on the spreading of a laser beam

The propagation characteristics of the fundamental Gaussian laser beam in absorptive and active media are investigated. There is a general reduction in the spreading of the beam on propagation in both absorptive and active media. In addition, in an active medium there is a shift of the focal plane and a reduction in the waist size of the beam.     

Effect of ionization-recombination process on fluorescent and laser properties of complex organic molecules in buffer gases

It is shown that the stepwise ionization of active organic molecules under UV pump radiation is responsible in a large part for poor lasing properties of dye-vapour active media as compared with liquid ones.     

上海城市植被光谱反射特征分析

地物光谱特征是遥感机理的重要内容,也是遥感应用研究的重要依据。城市植被作为城市中重要的生命支持系统,对于维持城市生态系统平衡起着核心的作用。文章以上海城市植被为研究对象,利用美国ASD公司生产的FieldSpec3便携式地物波谱仪,通过对2009年10月金边黄杨,金丝桃,圆柏,麦冬,珊瑚树,小叶黄杨等野外和室内光谱数据采集和处理,获得了这6种城市植被的高光谱数据。采用Savitzky Go-lay平滑方法进行光谱噪声去除和利用微分光谱技术进行植被环境背景影响消除,分别从植被冠层光谱和叶片光谱以及微分光谱,对这6种城市植被的光谱特征以及光谱曲线的差异和变化规律进行分析。可为今后进一步研究城市植被理化性能、参数反演、植被分类、植被调查以及城市环境监测等遥感应用服务。     

Negative refraction and focusing of circularly polarized waves in optically active media

Analysis indicates that certain types of optically active media are capable of producing negative refraction and focusing of circularly polarized waves. It is established that a slab of such material acts just as Veselago's hypothetical left-handed media lens, providing subwavelength resolution as Sir Pendry's ideal lens, but for circularly polarized waves.     

Calculation of the far-infrared spectrum of a water-vapor molecular laser

The theory of partial population inversion between vibrational-rotational states in molecular media is applied for a molecular laser using vapors of H₂O as active media. Two conditions of laser action in such media are discussed — population inversion and gain. The lines in the far-infrared at which such a laser can generate are predicted and the relative intensities of these lines, are calculated.The paper was mainly prepared during the author's stay at the University of Western Ontario, London (Ontario), Canada.     

A multiwave CuBr and PbBr2 laser with a sectioned active volume

The operation of a CuBr and PbBr₂ laser with a two-section gas-discharge tube with working media in different sections and an additional electrode between the sections was studied for the first time. Effective lasing was achieved in both media under control of time location of lasing pulses in different active media. The total mean lasing power equal to 1.5 W was distributed over wavelengths as follows: 1 W (510.6 nm), 0.3 W (578.2 nm), and 0.2 W (722.9 nm). The specific features of operation of the multicomponent laser and methods for its optimization are discussed. It is shown that the lasing power in a section is close to the power of an individual active element.     

Detonation waves in bubble-drop media

Wave processes in chemically active multicomponent media: liquid — gas bubbles — liquid drops have been studied experimentally. Existence of detonation waves in multicomponent (bubble-drop) media has been proved. Structure of detonation waves in bubble-drop and bubble media is qualitatively identical: detonation waves are solitary waves with pulsation profile the pressure behind which is close in value to the one in unperturbed medium. Propagation velocity of detonation waves in bubble and bubble-drop media drops with the increase in medium gas phase concentration and with the decrease in carrier liquid viscosity. Presence of liquid drops decreases detonation wave velocity compared with bubble medium that does not contain liquid drops. Detonation wave propagation in multicomponent media causes gas bubbles fragmentation as well as fragmentation of individual liquid drops. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-03-33106).     

Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses

The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and high-gain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed.     

本征态的局域化与增益介质中局域态的放大

用时域有限差分方法(FDTD)模拟了二维增益、非增益随机介质中的光学现象。在非增益介质中，观察到了局域态空间分布及其频率特征。在增益介质中，观察到局域态的放大过程。模拟结果显示非增益介质中的局域态相当于传统激光腔的腔模，随机激光是由局域态谐振产生的。     

Active media for lasers based on colored epoxy and triazine-containing polymers

The problems of the synthesis of active media for lasers based on colored thermoreactive polymers are examined, and the lasing characteristics of the active media are investigated. Zh. Tekh. Fiz. 67, 71–76 (October 1997)     

Characteristics of a multielectrode corona discharge in the working media of periodic-pulse XeCl* and KrCl* lasers

Results are reported from an investigation of the electrical and optical characteristics of a multielectrode negative-polarity corona discharge in He/Xe(Kr)/CCl₄ mixtures, which are used as the working media in inert-gas chloride lasers operating in the periodic-pulse mode. The corona discharge is studied in a needle-grid electrode system which is approximately as long as the active medium in a laser. Such a corona discharge is of interest for use in electrical modules for blowing the working media through XeCl* and KrCl* lasers, the working media of which contain vapors of liquid hydrocarbons of the CCl₄ type. Zh. Tekh. Fiz. 68, 48–51 (May 1998)     

On dissipative structures in nonuniform media

It is found that in many physical, chemical and biological systems the nonuniform active media may be considered as a “matrix” controlling the selection of the dissipative structures of definite type.     

Theoretical analysis of picosecond pulse development of passively mode-locked Nd-glass lasers

A realistic numerical theory of the temporal and spectral development of picosecond light pulses in a passively mode-locked Nd-glass laser is presented. The effects of the inhomogeneous gain profile of the active medium are considered. The calculations include the pulse development in the prelaser, the linear laser and the mode-locking region. In the mode-locking region twophoton absorption and self-phase modulation in the active medium as well as the bleaching dynamics of the mode-locking dye are included. The influence of self-phase modulation on the temporal pulse shape in active media of finite spectral gain width is analysed. The theoretical results are compared with the experimental findings.This paper is dedicated to Professor W.Kaiser for his 60th birthday.