Dielectric spectroscopy of thixotropic dispersions

The full characterization of a dispersion requires measurement of the degree of dispersion and knowledge of the type of structuring assumed by the dispersed particles. Dielectric spectroscopy in the low frequency range is a promising experimental approach to this problem.     

Fabrication and characterization of Titanium Indiffused Proton Exchanged (TIPE) waveguides in lithium niobate

We report the fabrication and characterization of optical waveguides realized in LiNbO₃ by a combined titanium indiffusion proton exchange (TIPE) process. These guides provide several unique advantages which include permitting tailorong of guide birefringence, realizing proton exchanged Y-cut plates of good optical quality, and the realization of imbedded TM guides due to a lowering of n_o caused by proton exchange.     

The Dielectric Properties of Wet Materials

In microwave remote sensing, knowledge of the dielectric properties of the materials observed (vegetation, soils) is important for the interpretation of the recorded reflection or emission and for the design of models for this reflection or emission. Although there exists no simple law which describes the properties of a heterogeneous system when the properties of its components are known, boundaries can be indicated for the permittivity of such a system. Heterogeneous systems containing water, such as wet soils and plant material, have very complex dielectric properties due to the role of the conductivity. However, at the higher microwave frequencies, in particular above the S-band, these conductivity effects play only a minor role and the free water is most important. When knowing the permittivity of wet materials the penetration depth can be determined. In all practical cases this depth is smaller than the wavelength used for the observations.     

Surface relaxation and thermal expansion for the (001) face of α-Fe and Cu

The surface relaxation and the near-surface enhancement of thermal expansion have been calculated for the (001) face of a bcc crystal, α-Fe, and an fcc crystal, Cu. The calculations make use of the anharmonic perturbation formalism of Dobrzynski and Maradudin; the results for certain equal-time vibrational correlation functions which arise in this formalism are also presented. The crystal potential is described in terms of several kinds of short-range empirical interatomic potentials, such as have been used in studies of defects in bulk; in the near-surface region, the effects of surface redistribution of the electron distribution are modelled by the addition of a simple surface Madelung (SSM) force. The effect of the SSM force is to limit severely the usual outward relaxation driven by short-range interatomic potentials. For Fe(001), the five and one-half percent outward static relaxation driven by the short-range potentials acting alone is changed to a one percent inward static relaxation when the SSM force is incorporated; for Cu(001), the comparable change is from a one percent outward relaxation to a one-half percent outward relaxation. On the other hand, the SSM force makes only a small effect on the surface-enhanced thermal expansion coefficients (STEC) for interplanar spacings. The STEC for the outermost spacing is between 2.5. and 3.0 times of that for the bulk at the Debye temperature for both Fe(001) and Cu(001); for the second interplanar spacing, the STEC is smaller than 1.5 times of that of the bulk at the Debye temperature. The ratios of the near-surface mean-square amplitudes (MSA) to those of the bulk at high temperatures are, for Fe(001), about 1.75 for z-components (normal to surface) and 1.55 for x-components (parallel to surface) in the surface layer; for Cu(001), about 1.95 for z-components and 1.30 for x-components. The interplanar correlation functions, while smaller than the MSA on an absolute scale, do show considerable surface-enhancement, particularly for the zz-compoments. For example, the zz-correlation between an atom in the outermost layer and its nearest neighbor in the next layer is nearly twice the comparable bulk correlation above the Debye temperature for both Fe(001) and Cu(001).     

Sea Level Muon Spectrum Derived from Bugaev Model Using the Primary Cosmic Ray Energy Spectrum of Grigorov et al

In a recent paper BHATTACHARYYA has derived the pion and kaon production spectra in the atmosphere using a form of the primary nucleon energy spectrum of the measurements of GRIGOROV et al. and the interaction model of BUGAEV et al. The sea level muon spectrum derived from these meson spectra agrees with the magnetic spectrograph data of ALLKOFER et al. and AYRE et al. In this report a critical analysis of the paper has been made and some obvious mistakes in the formulation have been pointed out. The formulation of BUGAEV et al. and the data of GRIGOROV at al. have been misinterpreted by BHATTACHARYYA . The corrected results have been properly interpreted in this report.     

High molecular weight polyacetylenes from the nudibranch Peltodoris actromaculata and the sponge Petrosia ficiformis

Two series of high molecular weight straight chain polyacetylenes (C₄₆, C₄₉ and C₄₉, C₅₂, C₅₅) have been isolated from two marine invertebrates and partially characterized.