Raman characterization of passivated GaAs surfaces

The technique of Raman scattering at room temperature, is used to investigate the effect of H₂S passivation of the surface of n-type GaAs. Well-defined LO, L^- and L⁺ features are distinguished in spectra which have been recorded in z(x, y)[ovbar|zovbar] scatte ring orientation. It is observed that the ratio of the LO to L^- peak is reduced by the effects of the passivation process and that the shift of the L⁺ feature from the laser line is decreased. This latter effect, it is suggested, is caused by a decrease in free-carrier concentration due to donor neutralization by hydrogen during passivation. This neutralization effect will also affect the LO to L^- ratio and so complicate a quantitative analysis of the influence of passivation on the surface barrier potential.     

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

A particle method with adjustable transport properties—the generalized consistent Boltzmann algorithm

The consistent Boltzmann algorithm (CBA) for dense, hard-sphere gases is generalized to obtain the van der Waals equation of state and the corresponding exact viscosity at all densities except at the highest temperatures. A general scheme for adjusting any transport coefficients to higher values is presented.     

Nonlocal character of the Rastall model

The discussion of whether quantum theory is compatible with the locality idea that no causal influence can act outside the forward light cone has recently been tightly linked to the corresponding question for a much simpler model theory that enjoys all of the pertinent properties of quantum theory but is much easier to fully comprehend. It is shown here that, contrary to recent claims, the model theory is incompatible with the locality idea mentioned above. The logical structure of the argument, which is similar to the one employed for quantum theory, is discussed.     

A fluorimetric kinetic method for the determination of tonin activity in rat submaxillary glands

A method for the kinetic determination of tonin activity in rat submaxillary gland extracts is described. The method is based on the fluorogenic reaction of o-phthalaldehyde with the dipeptide histidyl-leucine generated in the enzymatic hydrolysis of angiotensin I. The reaction is monitored by fluorescence at 440 nm. At pH 7.5, the method allows the determination of 2–15 nmol/ml histidyl-leucine with relative standard deviation of 6%.     

Novel FBG Writing System With Arbitrary Amplitude and Phase Control

FBGs with arbitrary apodization and phase have been fabricated by constantly moving fibers with a highly precision air bearing translation stage while a CW UV laser beam is switched on/off by triggers with nanosecond accuracy.     

Magnetization scaling in the ruthenate-cuprate RuSr2Eu1.4Ce 0.6Cu2O10-δ (Ru-1222)

The magnetic properties of the superconducting ruthenate-cuprate RuSr₂Eu _1.4Ce_0.6Cu₂O_10-δ (Ru-1222) have been studied by a scaling analysis of the dc magnetization and ac susceptibility measurements. Non-linear M(H) curves reveal the presence of nano-size clusters with a net magnetic moment of ∼10² μ_B at 180 K, near the deviation from a Curie-Weiss behavior. On cooling, no scaling was observed down to 90 K, discarding the possibility of magnetic phase separation of collinear ferromagnetic particles. We explain this result in terms of a variable number of contributing particles, with a temperature dependent net magnetic moment. For 70 K ≤T≤ 90 K the scaling plots evidence the emergence of a system of non-interacting particles, which couple on further cooling. The observed cluster-glass features are preserved down to the lowest measured temperature (10 K); no signature of long-range order was detected. The frequency shift of the peak in the real part of the ac susceptibility does not follow the Vogel-Fulcher type dependence, as previously reported. The puzzling temperature dependence of the coercive field, H_C(T), is correlated with the changes in the scaling factors.