Nonlinear optical characterization of cluster dynamic in water in oil microemulsion by a pump probe laser beam technique

We present a new pump probe laser beams configuration for the nonlinear optical characterization of microemulsions. We detect the variation of the on-axis optical intensity of the probe beam as generated by the concentration profile induced in an optically thin film of microemulsion by the pump beam. A mathematical model has been introduced to describe the phenomenon. The technique allows the determination of both Kerr-like optical nonlinearity and time constants and, therefore, it gives information both on cluster dimension and their shape. We discuss its application to WAD (water/AOT/decane, where AOT denotes sodium-bis-di-ethyl-sulfosuccinate) with the application of a strong electric field of optical source. Comparison between theoretical predictions and experimental results confirms the presence of giant optical nonlinearity in the absence of turbidity divergence. Chainlike shape of clusters, of the kind already reported with the application of strong electric field, could justify this result. Received 26 October 2002 RID="a" ID="a"e-mail: vicari@na.infn.it     

Functional Analysis of Tube Chain Conveyors

This paper describes some of the aspects necessary for the design and use of tube chain conveyors. It is based on the reports of experienced experts and recent tube chain conveyor experimental results. The aim of the research work is the formulation of general technical regulations for tube chain conveyors. Theoretical models were developed, which allow the calculation of the motion resistances in all parts of the conveyor by the use of empirical extracted correction factors. Specially designed measurement equipment enabled the measurement of the important chain tractive force from the closed tube system. The measurements show the influence of the major operational parameters and the bulk solid properties.     

Bulk and microscopic properties of copolymer networks in mixed aqueous solvents

Amphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon-grafted water-soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water-insoluble solutes. © 1992 John Wiley & Sons, Inc.     

Elastic constants of lead-bismuth alloys

A study of ultrasonic velocities and internal friction has been carried out in Pb-Bi alloys in the concentration range of 0 to 49.5 atomic % Bi using the composite oscillator technique. From the velocity and density data a set of elastic constants namely, Young’s modulus, rigidity modulus, bulk modulus and Poisson’s ratio are estimated. The results are interpreted in terms of the phase changes occurring in the alloy system. Internal friction is found to be more sensitive than the elastic constants to the phase changes.     

The Effect of Temperature on Lattice Mechanical Properties of Noble and Transition Metals

A simple pseudopotential model is used for the calculation of the temperature dependence of lattice mechanical properties which also depend on the phonon density of states such as lattice heat capacity C _V , Debye temperature _D, harmonic contribution to free energy, thermal pressure, isothermal bulk modulus corrected to the fourth order, volume thermal expansion coefficient , Debye-Waller factor, mean-square displacement, Debye-Waller temperature parameter, and X-ray characteristic temperature _M of Cu, Ag, Au, Ni, Pd, Pt, Rh, and Ir. The contribution of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer-like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings show the ability of our model potential to reproduce wide class of properties in noble and transition metals.     

Optical properties of the quasi-two-dimensional dichalcogenides 2H-TaSe and 2H-NbSe

We present a comprehensive analysis of the optical constants of the two-dimensional dichalcogenide materials 2 H - TaSe ₂ and 2 H - NbSe ₂ , in an attempt to address the physics of two-dimensional correlated systems. The title compounds were studied over several decades in frequency, from the far-infrared to the ultraviolet. Measurements with linearly polarized light have allowed us to obtain both the in-plane and out-of-plane components of the conductivity tensor. Although the electromagnetic response of dichalcogenides is strongly anisotropic, both the in-plane and out-of-plane components of the conductivity tensor share many common features, including the presence of a well-defined metallic component, as well as a “mid-infrared band”. We discuss the implications of these results in the context of the spectroscopic results of other classes of low-dimensional conductors such as the high-temperature superconducting cuprates. In particular, the analysis of the redistribution of the spectral weight as a function of temperature, as well as the behavior of the quasiparticles relaxation rate, points to significant distinctions between the charge dynamics of dichalcogenides and other classes of low dimensional conductors. Received 28 October 2002 / Received in final form 10 March 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: degiorgi@solid.phys.ethz.ch     

Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique

SiO₂/CdS-nanoparticle composite films (SiO₂:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural (XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E _d) effectively controlled the line shapes of the PL measurements. Received 24 May 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: msakp@mahendra.iacs.res.in     

磁场中夸克物质的黏滞系数

研究了磁场中夸克非轻子弱作用过程的反应率和黏滞系数. 改进了在弱磁场情况下的近似计算方法, 给出了非轻子过程的反应率与夸克物质的体黏滞系数的表达式, 显示出在弱磁场情况下, 黏滞系数的温度依赖关系与零磁场情况下一致, 但黏滞系数的大小依赖磁场的强度.     

Creation evidence of the second non-dispersive Zakharenko wave by helium atomic beams in superfluid helium-II at low temperatures

In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C _ph = C _g ≠ 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures ∼100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and negative roton signals together. It is natural that the negative roton creation by the beams requires the ⁴He-atom energies ∼12 K, while the positive roton creation by the atomic beams requires energies ∼35 K. Therefore, successive increase in the heater power resulting in an increase in the ⁴He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.      

Effective-medium approach for surface-localized magnetic polaritons in magnetic (ferromagnetic and antiferromagnetic) superlattices

The general effective-medium dispersion relations are derived for surface-localized magnetic polaritons which propagate parallel to the surface between a superlattice and semi-infinite bulk material, as applied to ferromagnetic and antiferromagnetic superlattices, in the situation when a static magnetic field is applied in the plane of the layers and parallel to the magnetization. The dependence of the energy of the surface waves on the volume fraction of the ferromagnetic superlattice component and the influence of the external magnetic field on the spectrum of the surface magnetic polaritons for the antiferromagnetic superlattice are investigated. The spectrum of the surface-localized magnetic polaritons which appear at the junction of the magnetic (ferromagnetic and antiferromagnetic) superlattice with the magnetic material are more complex, in contrast to the cases of semi-infinite magnetic material or semi-infinite magnetic SL. It is essential that in all cases in the presence of the external magnetic field the spectrum of the magnetic polaritons are non-reciprocal. The properties of surface polaritons are discussed in detail for the system ferromagnetic superlattice (YIG/non magnet)/YAG and the antiferromagnetic superlattice (MnF₂/ZnF₂)/FeF₂.