Polarization and transmission of microwaves in the magnetic suspension in the applied magnetic field

The production method of magnetic suspension consisting of ferromagnetic particles dispersed in cedarwood oil is presented at the beginning of this article. Next, the set-up for microwaves generation using a klystron is described. The main part of this paper concerning microwave transmission and polarization during its passage in samples of the produced magnetic suspension placed in a magnetic field is based on the following parameters: induction of this field, filling factor of magnetic suspension by ferromagnetic particles, dimensions of particles, viscosity of liquid carrier, and ratio of the magnetic field changes. Conducted investigations show that microwaves are damped and polarized in these magnetic suspensions. Obtained results are discussed and observed effects are explained by ordering of ferromagnetic particles in magnetic suspension by applied magnetic field.     

Spin diffusion and nuclear spin-lattice relaxation in irradiated solids: a multiple-pulse NQR study

We present a detailed theoretical and experimental NQR multiple-pulse spin-locking study of spin-lattice relaxation and spin diffusion processes in the presence of paramagnetic impurities in solids. The relaxation function of the nuclear spin system at the beginning of the relaxation process is given by exp , where T_1ρ is spin-lattice relaxation time in rotating frame and =d/6, d is the sample dimensionality. Then the relaxation proceeds asymptotically to an exponential function of time, which was attributed to the spin-diffusion regime. Using the experimental data obtained from the analysis of those two relaxation regimes in γ-irradiated powdered NaClO₃, spin diffusion coefficient has been determined and the radius of the diffusion barrier has been estimated.     

Polarization in organic molecular crystals and charge-transfer salts

Polarization in insulators is a general phenomenon that extends over nanometer distances. Two special cases illustrate recent theoretical progress. Polarization energies of localized charges in organic molecular crystals exceed the bandwidth and redistribute the charge density. A systematic treatment of electronic polarization is summarized in the limit of zero intermolecular overlap for pentacene crystals or thin films on metallic substrates, with special attention to the transport gap for producing a separated electron–hole pair and the optical dielectric tensor of the crystal. When overlap cannot be neglected, the general formulation of polarization in extended insulators is in terms of the exact ground state's phase. This formulation is applied to organic charge-transfer (CT) salts whose correlated electronic structure is described by one-dimensional Peierls–Hubbard models. Near the Peierls instability, coupling to lattice modes generates large peaks in the dielectric response that is primarily due to lattice vibrations. Comparisons with experiment are mentioned for both organic molecular crystals and CT salts.     

Influence of line defects on relaxation properties of graphene: A molecular dynamics study

The relaxation properties of single layer graphene sheets containing line defects were investigated using molecular dynamics simulation with AIROBE bond-order interatomic potential. The dynamic evolution of graphene sheets during relaxation condition was analyzed. The simulation results show that the single layer graphene sheets are not perfectly flat in an ideal state, and the graphene sheet shows a significant corrugations at the verge of sheet. The graphene sheet is bent with the line defects at the end of the sheet, and the extent of this bend also increases with the increase of the defect number. Furthemore, the graphene sheet transforms into a paraboloid with the line defects at the middle of the sheet.     

Polymers and molecular solids: New frontiers in surface science

A brief review is given of the present state of knowledge of the surface properties of polymers and molecular solids. These materials are shown to exhibit surface phenomena which are dramatically different from those characteristic of metals and covalent solids. The origin of these differences resides in the combined occurrence both of large electronic and atomic polarizabilities and of small probabilities for the transfer of an electronic excitation from one molecular site to another. The interplay of these two quantities leads to a diversity in the character of the resulting electronic excitations, ranging from localized molecular ion states in aromatic pendant-group polymers to quasi-one-dimensional metallic behavior in certain charge transfer salts and polymers. The primary role of the surface in such materials is the introduction of large, inhomogeneous fluctuations in the relaxation energies associated with the polarization of the solid by an excitation. These fluctuations produce a number of novel phenomena including localized surface states in the absence of dangling bonds, inhomogeneous broadening of photo-emission spectra, and alterations of the charge state of surface molecules. A simple, unified theoretical framework is developed for the interpretation of these phenomena.     

Dielectric barrier discharge in needle-to-plane configuration: Model of surface charge relaxation

Relaxation process of surface charge owing to dielectric barrier discharge (DBD) in “needle – air gap – polyethylene terephthalate film – plane” configuration is considered. Experimental data of the surface charge relaxation (SCR) are obtained by means of the rotating capacitive probe. Taking into account Gaussian radial distribution of accumulated charge density, effective surface and volume electrical conductivities of a barrier dielectric, phenomenological model of SCR for any dielectric thickness is proposed and exact solutions are obtained. The adequacy of the model is confirmed by the numerical computation. There is a good agreement between the experimental results and the model calculations.     

基于偏振菲涅尔反射比分布的主动偏振成像目标辨别方法

由于偏振特性是材料自身所决定的物理特性,其偏振图像含有丰富的目标信息,利用偏振信息对目标进行识别一直是国内外目标探测领域的研究热点,而主动偏振成像较之被动偏振成像更具有信噪比高以及可控性好等优势。在详细分析了偏振菲涅尔反射比分布的理论基础上,提出了一种利用探测物体表面的偏振菲涅尔反射比的主动偏振成像方法。该方法在发射端将偏振方向正交的两种偏振态的光源交替照射到目标场景中,在探测端用分别装有两个偏振方向垂直的偏振片的CCD采集偏振图像。同时,将探测端架构在不同的探测方向采集目标经主动光源照射后的偏振数据,最后将这些数据传输到计算中心,通过最优化拟合技术反演出不同目标的光学常数,由于不同目标的表面材质不同,其反映出的光学常数就不同,从而达到辨识不同材质目标的目的。实验分别采用了仿真数据和实测数据来验证该方法的有效性。仿真实验显示,所提出的方法利用材料的光学常数对不同材料进行区分不仅是科学的而且更方便有效。实测数据进一步验证了该方法能够较好的恢复出目标的相关光学常数,尤其在区分金属和非金属材料方面表现突出,并且探测方法结构简单实用,在目标探测、伪装识别等领域中有较大应用前景。     

Electronic decoupling of surface layers from bulk and its influence in oxidation catalysis: A molecular beam study

Interactions between oxygen and Pd-surfaces have important implications, especially towards oxidation reactions, and influence of subsurface oxygen to oxidation reactions is the focus of the present study. In our efforts to understand the above aspects, CO oxidation reactions have been carried out with mixed molecular beam (MB), consisting CO and O₂, on Pd(1 1 1) surfaces under a wide variety of conditions (T = 400-900 K, CO:O₂ = 7:1 to 1:10). A new aspect of the above reaction observed in the transient kinetics regime is the evidence for oxygen diffusion into Pd subsurface layers, and its significant influence towards CO oxidation at high temperatures (≥600 K). Interesting information derived from the above studies is the necessity to fill up the subsurface layers with oxygen atoms to a threshold coverage (θ_O-sub), above which the reactive CO adsorption occurs on the surface and simultaneous CO₂ production begins. There is also a significant time delay (Γ) observed between the onset of oxygen adsorption and CO adsorption (and CO₂ production). Above studies suggest an electronic decoupling of oxygen covered surface and subsurface layers, which is slightly oxidized, from the metallic bulk, which induces CO adsorption at high temperatures and simultaneous oxidation to CO₂.     

Enantioseparation on a chiral nanostructured surface: Effect of molecular shape

In this paper we use the Monte Carlo simulation method to study adsorption of chiral molecules on a solid surface with periodic distribution of active sites. Namely, equilibrium adsorption of a racemic mixture of enantiomers represented by homonuclear tetramers is modeled on a square lattice with a chiral pattern of active sites. We consider two possible chiral structures of the tetramers which differ only by chain geometry but have equal adsorption energies. The effect of the chain geometry on the effectiveness of separation is assessed by comparing the corresponding adsorption selectivities obtained from the simulations. We present results of model calculations in which the parameters do not refer to any particular experimental system. These results indicate that the model chiral surface can, in general, adsorb preferentially the complementary enantiomer, regardless of its chain conformation. Specifically, it was shown that changes in the tetramer geometry, from S-shaped to -shaped, lead to marginal changes in the shape of both single component and mixed adsorption isotherms calculated for the enantioselective surface. In this context, the enantiomer separation on the surface proposed in this work was shown to be insensitive to molecular shape of the adsorbing species.     

Effect of disorder on relaxation in the one-dimensional Glauber model

We study the long-time relaxation of magnetization in a disordered linear chain of Ising spins from an initially aligned state. The coupling constants are ferromagnetic and nearest-neighbor only, taking valuesJ ₀ andJ ₁ with probabilitiesp and 1–p, respectively. The time evolution of the system is governed by the Glauber master equation. It is shown that for large timest, the magnetizationM(t) varies as [exp(–₀ t](t), where ₀ is a function of the stronger bond strengthJ ₀ only, and (t) decreases slower than an exponential. For very long times, we find that ln (t) varies as –t ^1/3. For low enough temperatures, there is an intermediate time regime when ln (t) varies as –t ^1/2. The results can be extended to more general probability distributions of ferromagnetic coupling constants, assuming thatM(t) can only increase if any bond in the chain is strengthened. If the coupling constants have a continuous distribution in which the probability density varies as a power law near some maximum valueJ ₀, we find that ln (t) varies as –t ^1/3(lnt)^2/3 for large times.     

形状和原子数对纳米晶表面能的影响

确定了德拜温度与原子相互作用势的相互关系以及直角形纳米晶原子的平均配位数与形状和 原子数的关系.应用统计物理理论得到直角形纳米晶的表面能随温度、原子数和形状的变化 规律.以Ar纳米晶为例，讨论了形状和原子数对纳米晶表面能的影响. 关键词： 纳米晶 表面能 形状和线度     

Polarization relaxation in a ferroelectric crystal having different states of the domain structure and surface

Slow polarization relaxation of a ferroelectric in a weak electric field is investigated in triglycine sulfate crystals with different states of the domain structure and surface. An automated setup is described that allows one to register relaxation with record accuracy. It is shown that under conditions of little change in the “degree of metastability” of the structure, the variation of the polarization ΔP with time t follows the law ΔP=C/(1+t/ta)ⁿ in all cases, where the parameters C, a, and n depend on the state of the structure and the surface. We present a phenomenological analysis of the experimental data based on the assumption that the nuclei are independent and contribute additively to the total polarization of the crystal, and construct spectra of the energy barriers of the domain walls. Aspects of the transformation of the spectra with variation of the nature of the domain structure, depth of surface relief, and magnitude of the external electric field are elucidated. Fiz. Tverd. Tela (St. Petersburg) 39, 2046–2052 (November 1997)     

Polarization phenomena in the optical properties of porous silicon

We examine the polarization memory effect for porous Si excited by linearly polarized light. The various observations for the red-luminescing, slow band are discussed in the general framework of particle shape asymmetry. We show that because of the intrinsically nonlinear luminescence response, measurement parameters influence the polarization response. The preparation of porous Si with photoassisted etching is found to control the polarization retention parameter ρ. Using linearly polarized light during etching produces in-plane asymmetries. We find a substantial ρ-anisotropy linked to crystal symmetry planes and axes as a consequence of anisotropic etching. The effects are discussed with reference to current models of the light emission mechanism.     

保偏光纤和偏振器对传输光光谱的影响

保偏光纤和偏振器的参数以及它们之间的连接角度对传输光的光谱特性有重要的影响。利用琼斯矩阵建立了光波的传输模型,首次讨论了光波偏振度、光纤长度、光纤之间以及光纤与器件之间的对轴角度等对输出光谱的影响。研究表明,当光纤之间或光纤与器件之间的对轴角度不为零时,完全非偏振光的输出光谱形状不会发生改变,而偏振或部分偏振光波的输出光谱中叠加了周期函数。对轴角度一定时,光纤越长,周期函数的周期越小;光纤长度一定时,在一定的范围内,对轴角度越大,周期函数的幅值越大。通过实验对结论进行了验证。结论对采用保偏光纤和偏振器的系统具有理论指导意义。     

冰的热辐射偏振特性研究

冰作为全球能量平衡、气候、水文和生态模型中的重要参数,直接影响到地气系统能量平衡、天气和气候变化等,利用热红外波段对冰偏振特性研究国内外尚未见报道,运用热红外技术对冰热辐射偏振研究有重要意义。研究结果表明,波段、探测角、偏振角对冰热辐射偏振特性均有较大影响,而方位角影响不显著。振辐亮度表现为:LCH1LCH3LCH4LCH2,偏振亮温表现为TCH4TCH1TCH2TCH3,对冰热辐射偏振特性研究选择第三通道偏振亮温数据更优。探测角对冰热辐射特性影响极其显著且受偏振角影响,冰在探测角10°、偏振角30°处偏振亮温最低,这非偶然因素造成,与冰自身特性有关,探测角对冰偏振度影响表现为P0P40P10P20P50P30,偏振度大小与各偏振角的亮温差异大小直接相关,方位角对冰偏振亮温影响不显著,表面粗糙程度与组织结构差异直接导致冰在不同方位角发射辐射差异,利用偏振度对冰理化特性监测具有重要作用。     

Determination of effective atomic charge,extra-atomic relaxation and madelung energy in chemical compounds on the basis of X-ray photoelectron and auger transition energies

A new method is proposed for the determination of effective atomic charge, extra-atomic relaxation, and Madelung energy in chemical compounds, based on the experimentally measured energies of X-ray photoelectron and Auger transitions. The method has been applied to solid compounds of the elements from Na to Cl, and to a number of free sulfur-, phosphorus-, silicon-, and chlorine-containing molecules. The experimental energies are represented as consisting of two parts. The first part is determined by the ionization energy of a free ion with a given effective charge, and includes the intra-atomic relaxation. The second part is determined by the Madelung energy and the extra-atomic relaxation. The first contribution is calculated by using the Hartree-Fock method. The effective atomic charges required have been found from the shifts of Kα-lines in the X-ray spectra. The extra-atomic relaxations are obtained as the differences between experimental and theoretical Auger parameters, and the values calculated are the additive functions of ligands of the atom studied. The increments of the additive scheme correlate with the ligand refractions. The effective charges, extra-atomic relaxation energies and Madelung potentials obtained from ESCA and AES data agree well with both calculated and direct experimental results.     

Determining NMR flow propagator moments in porous rocks without the influence of relaxation

Flow propagators, used for the study of advective motion of brine solution in porous carbonate and sandstone rocks, have been obtained without the influence of Nuclear Magnetic Resonance (NMR) relaxation times, T₁ and T₂. These spin relaxation mechanisms normally result in a loss of signal that varies depending on the displacement ζ of the flowing spins, thereby preventing the acquisition of quantitative propagator data. The full relaxation behaviour of the system under flow needs to be characterised to enable the implementation of a true quantitative measurement. Two-dimensional NMR correlations of ζ − T₂ and T₁ − T₂ are used in combination to provide the flow propagators without relaxation weighting. T₁ − ζ correlations cannot be used due to the loss of T₁ information during the displacement observation time Δ. Here the moments of the propagators are extracted by statistical analysis of the full propagator shape. The measured displacements (first moments) are seen to correlate with the expected mean displacements for long observation times Δ. The higher order moments of the propagators determined by this method indicate those obtained previously using a correction were overestimated.