Materials Literature
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The low-frequency Raman spectrum of a single crystal of NaN${\mathrm{O}}_{3}$ has been measured for temperatures from 25 to 300\ifmmode^\circ\else\textdegree\fi{}C covering both ordered and disordered phases. The crystal is partially disordered below the transition temperature and the corresponding Raman spectra are i…
EPR studies of x-ray damaged crystals of (NH4)2SO4 show that long lived defects, NH3+ ions, are produced in two inequivalent sites with each site having two magnetically inequivalent orientations. All sites have approximately the same isotropic hyperfine splittings which are found to be 19.0 G for nitrogen and −24.6 G…
Measurements are reported of the frequency dependence of the conductivities σ⊥ and σ∥ in some nematic liquid crystals with strong positive dielectric anisotropy which are nematic at room temperature. The conductivity relaxation which causes σ∥ to increase already at frequencies <100 Hz in highly deionized liqui…
Thermal-conductance measurements on thin Mylar and glass plates indicate that abrasion of the plate surfaces does not suppress specular reflection of phonons, contrary to the behavior in crystalline materials. This reinforces the suggestion that nonspecular reflection at crystal surfaces is caused primarily by lattice…
The phonon dispersion curves, the temperature dependence of the Debye temperature, and the static elastic, dielectric, and piezoelectric constants of $\ensuremath{\alpha}$-Si${\mathrm{O}}_{2}$ have been calculated from a modified rigid-ion model with an effective charge, with short-range central forces for the two Si-…
We have measured the Young's modulus and internal friction in the two-dimensional layered dichalcogenides $2H$-Ta${\mathrm{Se}}_{2}$ and $2H$-Nb${\mathrm{Se}}_{2}$ using a vibrating reed technique. Weak elastic anomalies are observed at the incommensurate charge-density-wave transitions in Ta${\mathrm{Se}}_{2}$ and Nb…
A method is reported for the determination of the surface recombination velocity by scanning electron microscopy; this method is based on an established relationship between the effective diffusion length of the minority carriers, the penetration depth of the electron beam, and the surface recombination velocity. Valu…
An analysis of the second-order optical nonlinearities of crystalline substituted benzene is presented. A new irreducible tensor formalism for the decomposition of a crystal tensor as the sum of the contributions of microscopic units is developed and applied to the study of the second-order susceptibility in four benz…
The thermal conductivities of a borosilicate glass and a polycarbonate have been measured in the temperature range 0.04-60 K. Some samples contained well-defined holes to provide an additional source of phonon scattering. The results at low temperatures are consistent with the predictions of the Debye model using expe…
Photoelectric yields and directional photoemission spectra for clean (100) and (111) faces of copper measured with provision for varying the angle of incidence and the light polarization, and with photon energies up to 6.60 eV, are presented. Contrasting the structureless Fowler-like behavior of the (100) face, the (1…
Abstract A detailed study of the shrinkage behaviour of homopolymers and copolymers of acrylonitrile has been made. Apart from chemical shrinkage, a physical shrinkage, which is independent of temperature and oxidizing gas was observed. This shrinkage occurs even at temperatures below 180°C. The effect of temperature…
New optically active biphenyl compounds have been synthesised. Low-melting mixtures with biphenyl nematogens give stable, room-temperature cholesteric liquid crystals of positive dielectric anisotropy. These give the cholesteric-nematic electro-optical phase-change effect. Mixtures of the new compounds exhibit thermoc…
We have studied the behavior of several nematics in Couette flow with homeotropic boundary conditions. When Leslie's viscosity ${\ensuremath{\alpha}}_{3}>0$, the director tumbles at a critical shear rate, ${S}_{c}$. When $S>{S}_{c}$ a stable, stationary state is observed. When $S>{S}_{E}>{S}_{c}$, the flow…
A model is discussed which for the first time provides a unified description of many electrical and optical properties of chalcogenide glasses. It is proposed that localized gap states are at dangling bonds, and that lattice-distortion effects are sufficiently strong that these states exhibit an effective negative ele…
Comparing recent experimental results of the thermal and acoustic properties of glasses, it appears that the degree of purity and the method of sample preparation have a noticeable influence on the specific heat, but hardly any effect on the phonon transport properties such as the thermal conductivity, ultrasonic atte…
A model and an approximate theory is presented for conduction in solids which have a charge-ordered low-temperature phase and show a first-order phase transition of 'semiconductor-semimetal' type at a characteristic temperature T nu (e.g. Fe 3 O 4 ). The structure and the conduction mechanisms of the low-temperature p…
Measurements of the thermal conductivity of type I diamonds have been analysed in terms of various phonon-scattering processes. From the relations between the point-defect scattering rates and the total nitrogen contents, it appears that the nitrogen occurs in groups of approximately 10 atoms. The relation between nit…
Enol derivatives in the chlorophyll series. 13 2 ‐Desmethoxycarbonyl‐17 3 ‐desoxy‐13 2 ,17 3 ‐cyclochlorophyllide a‐enol and a method for the introduction of magnesium into porphinoid ligands under mild conditions Magnesium transfer from the iodo‐magnesium salt of 3,5‐di‐ t ‐butyl‐4‐hydroxy‐toluene (BHT) into methyl p…
Enol derivatives in the chlorophyll series. Preparation of 13 2 ,17 3 ‐cyclopheophorbide enols 13 2 ,17 3 ‐Cyclopheophorbide enols have been prepared as model systems for studying the effect of ring E enolization upon the properties of chlorophyll derivatives.
The structure of the variable portions of a K-type Bence-Jones protein REI forming a dimer has been determined by X-ray diffraction to a resolution of 2.0 A. The structure has been refined using a constrained crystallographic refinement procedure. The final R value is 0.24 for 15000 significantly measured reflections;…