Thermodynamic Properties of Melts and Phase Equilibria in the Copper–Zirconium System

The vapor composition over and thermodynamic properties of Cu–Zr melts (5.1–85.0 at. % Zr) are studied by Knudsen cell mass spectrometry between 1191 and 1823 K. The data set obtained comprises more than 1100 activity values for various compositions and temperatures. The thermodynamic behavior of Cu–Zr melts is described in terms of the associated-solution approach with an accuracy no worse than the experimental accuracy. The melts are shown to contain two molecular species: CuZr and Cu₂Zr. The contributions of different types of chemical bonding to the Gibbs energy and enthalpy of formation of Cu–Zr melts are asymmetrical and shifted from the equiatomic composition in opposite directions: the extremum of covalent bonding is shifted to the Cu-rich side, while metallic bonding is more significant in Zr-rich alloys. The rapid temperature variation of covalent bonding leads to a large excess heat capacity C _p ^E of the melts and a negative excess entropy _f S ^E, which rapidly drops with decreasing temperature. It is shown that not only C _p ^E and _f S ^E but also their temperature variations are governed by the parameters of association reactions and depend more strongly on the entropy than on the enthalpy of complex formation. This indicates that, in the general case, the glass-forming capabilities of melts are independent of the interparticle interaction and accounts for the pronounced tendency of Cu–Zr melts toward amorphization.     

Multifilter Phase-Lock Loop Nonlinear Analysis and Design Criterion

In this paper a nonlinear analysis of a multifilter phase-lock loop (MPLL) by using the method of "harmonic balance" is presented. The particular MPLL considered has a low-pass filter and a bandpass filter in parallel. An analytic expression for the relationship between the input signal phase deviation and the phase error is determined for sinusoidal FM in the absence of noise. The expression is used to determine bounds on the proper operating region for the MPLL and to investigate the "jump phenomenon" previously observed. From these results the proper modulation index, modulating frequency, etc., used for the design of an MPLL is determined. Data for the loop unlock boundary obtained from the theoretical expression are compared to data obtained from analog computer simulations of the MPLL.     

Variational principles for steady heat conduction with mixed boundary conditions

Summary For the boundary value problem of steady heat conduction with general boundary conditions a variational problem is formulated by adding a simple surface integral to Butler's volume integral.This research was supported by the National Science Foundation, Grant GK-108.     

n-CdS/p-ZnIn2Se4 thin film solar cell

The photovoltaic behaviour of a CdS/ZnIn₂Se₄ vacuum-evaporated thin film solar cell is reported for the first time. Because of the band gap of ZnIn₂Se₄ (1.93 eV) this combination of semiconductor materials seems to be suitable for use as one of the junctions in tandem solar cell configurations. Uncoated cells exhibited efficiencies of the order of 1.5% under an illumination of 100 mW cm^-2.     

Deviation from stoichiometry in α-HgI2

Measurements of lattice constants, density and transition temperature have been carried out on α-HgI₂ single crystals grown both from vapor phase and from solution under different stoichiometric conditions. Stoichiometry deviations on both Hg- and I-rich sides were found. Large supersaturations extending on the Hg-rich side up to about 4 × 10^?2$\text{I}{}_{\mathrm{Hg}}\text{HgI}{}_2$ mole ratio and on the I-rich side up to about 10^?2$\text{I}{}^{\mathrm{?}}{}_3\text{HgI}{}_2$ mole ratio were accomodated by the crystals. The interpretation of the results supports the assumption of the presence of mercury interstitials in the Hg-rich crystals and of I^?₃ anions in the I-rich crystals. The large deviations from stoichiometry are attributed to the non-stoichiometry of the mother phase and to the easiness of the crystal structure for accomodating interstitials rather than to characteristic thermodynamic equilibria of interstitials in the lattice.     

Quasi-stationary multiple stimulated Raman generation in the visible using optical fibers

Several orders of stimulated Raman scattering (SRS) in monomode and multimode fibers have been observed. The relatively low power in the visible used in the quasi-stationary regime permitted observation of sharply defined Stokes and anti-Stokes spectral lines without any continua. Results of pump-to-Stokes power conversion in a monomode fiber indicate a striking equivalence between pump power and fiber length. The dependence of multiple SRS generation/amplification with these parameters is investigated up to the limit of near total pump extinction. We propose a qualitative explanation of these facts, although a detailed theory of nonlinear behavior of fibers is wanting. Parametric four-photon mixing is again confirmed to account for the generation of stimulated anti-Stokes radiation in multimode fibers and its absolute absence in monomode fibers.     

Hybrid Frenkel-Wannier-Mott excitons at interfaces and in microcavities

We discuss the linear and nonlinear optical properties of organic-inorganic nanostructures (quantum wells and superlattices) brought about by resonance interactions between Frenkel excitons in organic QWs and Wannier-Mott excitons in semiconductor QWs. We show that such a coupling (Coulomb dipole-dipole at an interface and through the cavity photons in a microcavity) is responsible for the appearance of mixed Frenkel-Wannier excitations. We demonstrate that the new hybrid states and their dispersion curves can be tailored to engineer the enhancement of resonant optical nonlinearity, fluorescence efficiency and relaxation processes.     

Counting of single protein molecules at interfaces and application of this technique in early-stage diagnosis

The fluorescence-based detection and counting of single protein molecules after specific binding to antibodies at interfaces is presented. A diode laser was used as the excitation source. The unspecific binding at the interface has been reduced to a level of only 0.1% of the maximum signal level. At present, the detection limit of this molecule-counting process is in the range of 10(-17) mol/L, and the dynamic range of the signal corresponds to 7 orders of magnitude of antigen concentration, but these values are not limiting. As a preliminary application in early-stage diagnosis, we have investigated the detection of a single cardiac actin molecule in human plasma, which is of interest in myocardial infarction diagnosis.