Formation of single-wall carbon nanotubes in Ar and nitrogen gas atmosphere by using laser furnace technique

The formation of single-wall carbon nanotubes (SWNTs) by using laser vaporization technique in different ambient gas atmosphere was investigated. SWNTs were prepared with Rh/Pd (1.2/1.2 atom%)-carbon composite rod in Ar and nitrogen gas atmosphere, respectively. Raman spectra of raw carbon materials including SWNTs and photoluminescence mapping of dispersed SWNTs in a surfactant solution demonstrate that the diameter distribution of SWNTs prepared in Ar atmosphere is narrower than those obtained by using CVD technique (e.g. HiPco nanotube), even when the ambient temperature is as high as 1150 ^○C. It was also found that nitrogen atmosphere gives wider diameter distribution of SWNTs than that obtained with Ar atmosphere. Furthermore, the relative yield of fullerenes (obtained as byproducts) is investigated by using HPLC (high-performance liquid chromatography) technique. It was found that the relative yield of higher fullerenes becomes lower, when nitrogen is used as an ambient gas atmosphere. Based on these experimental findings, a plausible formation mechanism of SWNTs is discussed.     

Propagation Characteristics of Infrared Pulse Waves through Windblown Sand and Dust Atmosphere

The physics characteristics of the windblown sand and dust atmosphere at the sand bench of Yellow River in China are discussed. The pulse distortion and time delay of infrared nanosecond pulse propagating through the atmosphere having sand and dust particles are investigated at 1.06 and 3.8 μm, respectively. It is shown that the delay of 10 ns laser pulse propagating through 5 km windblown sand and dust atmosphere are over 1 ns and 10 ns at 1.06 and 3.8 μm, respectively. The pulse spread increases slightly with wavelength increase. The pulse spread of a 10 ns laser pulse is over 40 ns at 3.8 μm. The pulse delay and spread increase rapidly with the sand particle density increasing in atmosphere. The narrower the pulse width is, the more the pulse distortion is. Hence, at infrared band, for a laser pulse propagating in sand and dust atmosphere, the pulse delay and spread are quite severe and need be taken into account for a narrower pulse laser system.     

Spectral shifts and spectral switches of elliptical Gaussian beam propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the spectrum of elliptical Gaussian beam (EGB) propagating through turbulent atmosphere can be derived analytically by tensor method. It can avoid time-consuming numerical integral that was commonly used in the previous study of spectral changes. Analytical results show that the on-axis normalized spectrum S(ω) of EGB propagating through turbulent atmosphere is different from the original spectrum S₀(ω) and there exist spectral shifts and spectral switches for EGB propagating through turbulent atmosphere. Besides, spectral shifts and spectral switches of EGB are closely related with the structure constant of the turbulent atmosphere, the beam parameters and the coordinate of observation point. Compared with the Gaussian beam, there are two spectral switches for EGB propagating through turbulent atmosphere.     

基于大气中性点的地-气分离方法空基验证探究

偏振遥感是遥感领域的一个新兴对地观测手段,地物反射的偏振效应是偏振遥感进行观测的基础。然而,地物反射具有偏振效应,大气粒子的反射与散射也具有偏振效应,并且大气的偏振效应往往大大强于地物偏振效应。当用偏振遥感器对地表目标进行观测时,大气的强偏振效应会干扰甚至覆盖地物的偏振信息。因此,如何最大限度地消除大气的偏振效应对地物偏振效应的影响是偏振遥感的一个关键性问题。大气中性点是大气中偏振度趋近为零的区域。利用大气中性点进行地-气分离理论的核心思想是将探测器放置于中性点区域进行对地观测,以减弱大气偏振对地物偏振的影响。基于国内首次大气中性点偏振遥感航空飞行实验,通过处理和分析实验所得影像数据,分别得到了中性点位置和非中性点位置影像偏振度分布,发现中性点位置偏振度集中分布区域要明显小于非中性点位置,验证了利用大气中性点进行地-气分离理论的合理性和可行性,提出了利用中性点进行偏振遥感实验所需要的条件,并初步分析出,波长较长的波段更适合于偏振遥感观测。     

Tethered Satellites in the geophysical environment

Summary A short presentation is given of the basic physical principle of a Tethered-Satellite System. The motion equations are summarized. A variety of physical phenomena in the upper atmosphere and ionosphere, as well as related to geomagnetism and gravity field will benefit by such type of missions; they are briefly illustrated and discussed. Near-term and far-term perspective applications are finally presented. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Theoretical study of defect formation processes in metals

Abstract

The equilibrium solute atmosphere around a straight edge dislocation in interstitial solid solutions has been investigated. A long-range deformation interaction among impurities is accounted for. Quantitative estimations have been given for the example of carbonaceous martensite. The impurity concentrations in an atmosphere around the dislocation core are calculated for a given temperature in dependence on its mean value in the specimen. For a dislocation with an impurity atmosphere stationary fluxes of interstitial atoms and vacancies on the dislocation are calculated; a concentration dependence of impurity parameters indicating a dislocation capture efficiency of the self-interstitial atoms and vacancies and the parameter of dislocation preference B are received; a radiation-induced deformation rate (swelling and creep) is determined.     

Exact results in modeling planetary atmospheres—II. Semi-gray atmospheres

We solve the radiative transfer equation for a semi-gray planetary atmosphere in radiative equilibrium, in an attempt to define an entirely analytical non-gray model atmosphere of finite optical thickness. The salient feature of the model is that the incident solar radiation is partitioned between two adjacent spectral domains—the “visible” and the “infrared”—in each of which the atmosphere's (effective) opacity is assumed to be independent of frequency (the semi-gray assumption). We envisage a plane-parallel atmosphere illuminated by a beam of parallel radiation and bounded below by a partially reflecting and emitting ground. The former emits infrared radiation, induced by the absorption of radiation both visible and infrared, deriving from the external irradiation as well as from the emission of the planet's surface layer. For an atmosphere with given single-scattering albedos and optical thicknesses in both the visible and infrared domains, we compute the temperature at every depth of the atmosphere, as well as the ground's temperature.     

Intrinsic room-temperature ferromagnetism of V-doped TiO2 (B) nanotubes synthesized by the hydrothermal method

Nanotubes of TiO₂(B) phase doped with 5 at.% of vanadium (V) have been synthesized by a hydrothermal method, followed by calcination at 300 °C in air and argon atmosphere, respectively. These nanotubes exhibit ferromagnetic character with clear hysteresis loop at room-temperature. X-ray diffraction and Fourier transform infrared spectroscopy confirm that the ferromagnetic behavior is intrinsic to the material and not due to other phases and/or metallic clusters. The photoluminescence and hysteresis loop characteristics are found to be dependent on calcination conditions, and implicate the role of oxygen vacancies. Existence of higher oxygen vacancies in V-doped TiO₂(B) nanotubes synthesized in argon than the air atmosphere is supported by the room-temperature photoluminescence spectra. The enhanced ferromagnetic behavior observed in V-doped TiO₂(B) nanotubes synthesized in argon than the air atmosphere is explained in terms of bound magnetic polaron (BMP) model.     

Internal friction in a magnetically treated material with dislocations

Internal friction of magnetically treated tin-bronze has been investigated as a function of the degree of dislocation pinning caused by an impurity-defect atmosphere. It is found that pulsed magnetic field treatment of this material can affect its internal friction in different ways. After pulsed magnetic field treatment the level of internal friction can be higher than in the untreated material if, as a result of aging processes preceding this treatment, a dislocation impurity-defect atmosphere is formed, and can be lower if a qualitatively new impurity-defect atmosphere is formed on the dislocations as a result of earlier treatment, or it can remain unchanged in the absence of atmospheres at the dislocations. The observed character of of internal friction in pulsed magnetic field treated material is linked with the presence of localized magnetically active centers excited by such treatment, which can lead to a change in the interaction energy of the atmosphere with a dislocation. Fiz. Tverd. Tela (St. Petersburg) 39, 1234–1236 (July 1997)     

1m反射式卡塞格伦系统的调试

介绍了高空大气探测激光雷达的接收物镜(卡塞格伦物镜)的光路及调试方法。给出30-60km的Rayleigh回波和80-110km钠层回波信号，与原来的离轴抛物物镜的回波信号相比，具有更高的Rayleigh回波高度、更高的信号值与信噪比。     

Analytical formula for a decentered elliptical Gaussian beam propagating in a turbulent atmosphere

Analytical formulas for the average intensity and decentered parameter of a decentered elliptical Gaussian beam (DEGB) propagating in a turbulent atmosphere are derived in a tensor form. The propagation properties of a DEGB in a turbulent atmosphere are investigated in detail, and found to be different from that in free space. Furthermore, as an application example, we investigate the propagation of a decentered elliptical flat-topped beam (DEFB) by expressing its electric field as a finite sum of DEGBs in a turbulent atmosphere. The properties of a DEGB or a DEFB in a turbulent atmosphere are closely related with the beam’s parameters and the structure constant of the turbulent atmosphere.     

Nonlinear power attenuation of the radiation of a pulsed CO2 laser in the atmosphere near the ground

Conclusion Thus, as a result of the natural investigations performed on the propagation of short (microsecond) pulses of CO₂ laser radiation in the near-ground atmosphere, quantitative data are obtained on the nonlinear power attenuation of powerful radiation by the atmosphere in the range of energy densities w = 3–18 J/cm² as a function of the meteorological conditions and the turbulent state of the atmosphere. It has been shown that the principal mechanism of nonlinearity of the medium along a 100–250 m path is the origin of low-threshold optical breakdown centers on solid aerosol particles. The initiation conditions and the main characteristics of an extended laser flash in the atmosphere have been investigated.Future work of interest is to obtain statistically justified dependences of the nonlinear power attenuation and distortions of the structure of beams of powerful pulsed radiation along extended paths on the basic opticometeorological parameters of the state of the atmosphere.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 5–13, February, 1983.     

Growth process of nanostructured silver films pulsed laser ablated in high-pressure inert gas

The growth process of silver thin films deposited by pulsed laser ablation in a controlled inert gas atmosphere was investigated. A pure silver target was ablated in Ar atmosphere, at pressures ranging between 10 and 100 Pa, higher than usually adopted for thin film deposition, at different numbers of laser shots. All of the other experimental conditions such as the laser (KrF, wavelength 248 nm), the fluence of 2.0 J cm⁻², the target to substrate distance of 35 mm, and the temperature (295 K) of the substrates were kept fixed. The morphological properties of the films were investigated by transmission and scanning electron microscopies (TEM, SEM). Film formation results from coalescence on the substrate of near-spherical silver clusters landing as isolated particles with size in the few nanometers range. From a visual inspection of TEM pictures of the films deposited under different conditions, well-separated stages of film growth are identified.     

Influence of ambient atmosphere on charge transport in polycrystalline thin films of three simple aromatic hydrocarbons

Drift mobility of charge carriers in p-terphenyl, p-quaterphenyl and tetracene polycrystalline thin films was measured using the classical time-of-flight method. The measurements were carried out both in the atmosphere and in vacuum of the order of 10 ^{- 3} Torr. The mobility measured in the atmosphere is of the order of 10 ^-4cm²V^-1s^-1 and turns out to be about 1 order of magnitude higher than that measured in vacuum. It is suggested that the hopping transport of charge dominates in the structures investigated. The increase in the mobility for the measurements in the atmosphere probably results from the additional localized states due to water and other atmosphere molecules.     

Radiative transfer solutions for coupled atmosphere ocean systems using the matrix operator technique

Accurate radiative transfer models are the key tools for the understanding of radiative transfer processes in the atmosphere and ocean, and for the development of remote sensing algorithms. The widely used scalar approximation of radiative transfer can lead to errors in calculated top of atmosphere radiances. We show results with errors in the order of±8% for atmosphere ocean systems with case one waters. Variations in sea water salinity and temperature can lead to variations in the signal of similar magnitude. Therefore, we enhanced our scalar radiative transfer model MOMO, which is in use at Freie Universität Berlin, to treat these effects as accurately as possible. We describe our one-dimensional vector radiative transfer model for an atmosphere ocean system with a rough interface. We describe the matrix operator scheme and the bio-optical model for case one waters. We discuss some effects of neglecting polarization in radiative transfer calculations and effects of salinity changes for top of atmosphere radiances. Results are shown for the channels of the satellite instruments MERIS and OLCI from 412.5 nm to 900 nm.     

卷云短波红外辐射特性

 采用离散纵标法耦合大气分子吸收，模拟计算了卷云大气的反射特性。研究了在短波波段卷云辐射性质随波长、卷云光学厚度、卷云有效尺度、云高和卷云中冰晶粒子形状等的变化关系，分析了卷云对大气红外背景辐射的影响。结果表明：在2.7 μm的水汽强吸收带上，卷云的出现明显增强了该波段的大气背景辐射，反射率随光学厚度和云高增大而增大。     

Evaporation of an emulsion trapped in a yield stress fluid

The present work deals with emulsions of volatile alkanes in an aqueous clay suspension, Laponite, which forms a yield stress fluid. For a large enough yield stress (i.e. Laponite concentration), the oil droplets are prevented from creaming and the emulsions are thus mechanically stabilized. We have studied the evaporation kinetics of the oil phase of those emulsions in contact with the atmosphere. We show that the evaporation process is characterized by the formation of a sharp front separating the emulsion from a droplet-free Laponite phase, and that the displacement of the front vs. time follows a diffusion law. Experimental data are confronted to a diffusion-controlled model, in the case where the limiting step is the diffusion of the dissolved oil through the aqueous phase. The nature of the alkane, as well as its volume fraction in the emulsion, has been varied. Quantitative agreement with the model is achieved without any adjustable parameter and we describe the mechanism leading to the formation of a front.     

高空大气探测激光雷达的安装与调试

介绍了高空大气探测激光雷达的接收望远镜的光路及安装与调试的情况。对离轴抛物面主镜、凹抛物面副镜及转折平面镜的调校作了简要说明。给出了望远镜系统 60km附近的Rayleigh回波和 80～ 1 1 0km的钠层回波的结果。结果表明 ,回波的信噪比很高 ,如果使用更大的镜子的话 ,则会得到更好的结果     

弹性连续介质中氢致裂纹传播理论

弹性连续介质中的氢原子,在裂纹应力场的诱导下发生聚集,形成氢气团,本文计算了气团分布区平均氢浓度,并将该区看作沿裂纹尖端分布的弹性夹杂,确定了夹杂的本征应变,研究了夹杂的应力场P_ij对裂纹位错密度的影响,求得了裂纹尖端总的应力强度因子,认为氢脆机理是氢气团增大了裂纹尖端应力强度因子,最后还讨论了氢致开裂的物理过程及氢致裂纹扩展速率,所得结果与实验符合很好。 关键词：