Mechanisms of ion-beam-enhanced diffusion in amorphous silicon

We have investigated ion-beam-enhanced diffusion of Au in undoped and B doped amorphous Si. The diffusion coefficients depend linearly on ion flux and exibit an Arrhenius-like temperature dependence with an activation energy of 0.37 eV in the temperature range 200–350° C. Moreover the diffusivity is enhanced by a factor of 5 by B-doping at a concentration of 1×10²⁰ atoms/cm³. A similar enhancement is observed in thermal diffusion of Au which has an activation energy of 1.5 eV. On the basis of these results a model for the ion-beam-enhanced diffusion of Au is proposed where the high density of defects present in amorphous Si act as traps for the fast moving interstitial Au atoms. The effectiveness of this trapping process can be changed by the high concentration of mobile defects generated by the beam and also by a change in the charge state of the traps induced by the presence of B.     

New fir laser lines and frequency measurements from optically pumped13CD3OH3

We report the discovery of 57 new fir laser lines from¹³CD₃OH molecule optically pumped by a waveguide CO₂ laser of 300 MHz tunability. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorbing¹³CD₃OH line were performed using the transferred Lamb-Dip technique. We have also measured directly the frequency of seven FIR laser lines by heterodyning with already known laser lines. We present a complete list of all known laser lines (134) and frequency measurements (24) for this molecule.Work supported by CNPq, FAPESP, FAEP-Brasil, and CNR-Italia     

CO-laser photoacoustic detection of phosgene (COCl2)

Detection of COCl₂, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN₂ cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC     

Growth properties for solutions of differential equations defined in the disk

Summary We investigate the growth of solutions of a class of differential equations which are defined in the unit disk and for which the coefficients have slow growth in the unit disk as measured by the Nevanlinna characteristic. These results extend earlier work of S. Bank.     

Deformation of doped NaCl crystals during uniaxial compression at temperatures of 4.2–293 K

The impurity weakening of crystalline NaCl:Mg and NaCl:Mn associated with purification of the matrix in a melt is demonstrated. This effect is manifested in a consistent change in the yield strength and mobility of dislocations. Its unusual temperature dependence is determined: in a number of cases weakening becomes greater as the temperature is lowered within the interval 293–4.2 K. A deviation in the elastic region of the stress-strain curves is observed to increase as the temperature is lowered. Plasticizing of crystalline NaCl is established: when the deformation temperature is lowered from 293 to 77 and 4.2 K the rate of rise in the yield strength of Cd²⁺ and Sr²⁺ doped samples is lower than that of undoped samples. An explanation for this fact is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 313–317 (February 1997) Deceased.     

Optimal Server Acquisition in Open Queueing Networks

Several production and flexible manufacturing systems can naturally be modelled using queueing networks. In this paper, we consider the problem of acquiring servers for the nodes of an open queueing network, so as to optimize the steady-state mean virtual system parameters subject to a budget constraint. A partial enumeration scheme and a heuristic method have been proposed to solve this problem. Empirical results based on randomly generated test problems are used to identify a class of problems for which the heuristic performs well.     

Short-range order in miscible polymer blends: A monte carlo study

Local ordering in miscible binary polymer blends with strong attractive interactions between the two types of chains was investigated by computer simulation of allowable conformations on an incompressible cubic lattice. A tendency toward maximum ordering (in which chains pack in alternate parallel rows) is shown by the calculation of pair correlations and in “snapshots” of the mixtures. A specific directional interaction is not necessarily required for ordering. A comparison of these results with those recently obtained using mean-field theory is presented. The heat capacity of mixing was also calculated and found to be positive, with a value close to that reported experimentally.     

Intersegmental interaction and critical concentrations in PET–HFIP solutions

Spectroscopic determinations of the concentrations associated with the onset of intermolecular interaction in solutions of poly(ethylene terephthalate) (PET) are described. The intersegment forces perturb the electronic spectra and induce ground-state aggregation. These phenomena become observable at different chain densities, reflecting the influence of concentration on the coil dimensions, as well as the dynamical nature of the interactions. An estimate of the equilibrium constant for PET dimer formation in hexafluoroisopropanol is reported.     

Glass transitions in hydrogen-bonded polymer complexes

Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (T_g) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower T_g values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔC_p values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.