A vapor barrier for cold testing printed circuit cards

Cold testing method prevents formation of frost on printed circuit boards and part holders during testing at sub-zero temperatures. Freon permits rapid attainment of the required testing temperature

Domain Coarsening in Systems Far from Equilibrium

The growth of domains of stripes evolving from random initial conditions is studied in numerical simulations of models of systems far from equilibrium such as Rayleigh-Benard convection. The scaling of the size of the domains deduced from the inverse width of the Fourier spectrum is studied for both potential and nonpotential models. The morphology of the domains and the defect structures are however quite different in the two cases, and evidence is presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende

The monoclinic phase in PZT: new light on morphotropic phase boundaries

A summary of the work recently carried out on the morphotropic phase boundary (MPB) of PZT is presented. By means of x-ray powder diffraction on ceramic samples of excellent quality, the MPB has been successfully characterized by changing temperature in a series of closely spaced compositions. As a result, an unexpected monoclinic phase has been found to exist in between the well-known tetragonal and rhombohedral PZT phases. A detailed structural analysis, together with the investigation of the field effect in this region of compositions, have led to an important advance in understanding the mechanisms responsible for the physical properties of PZT as well as other piezoelectric materials with similar morphotropic phase boundaries.Comment: 5 pages REVTeX file, 6 figures embedded. Presented at the Workshop on "Fundamental Physics of Ferroelectrics" held in Aspen, February 00. To appear in the proceeding

Effect of phonon scattering by surface roughness on the universal thermal conductance

The effect of phonon scattering by surface roughness on the thermal conductance in mesoscopic systems at low temperatures is calculated using full elasticity theory. The low frequency behavior of the scattering shows novel power law dependences arising from the unusual properties of the elastic modes. This leads to new predictions for the low temperature depression of the thermal conductance below the ideal universal value. Comparison with the data of Schwab et al. [Nature 404, 974 (2000)] suggests that surface roughness on a scale of the width of the thermal pathway is important in the experiment.Comment: 6 pages, 3 figure

The conceptual design of a 36 GHz RF undulator

The CompactLight project supported by European H₂020 is to design a hard X-ray FEL facility beyond today’s state of the art. The project integrates photo injector, X-band acceleration and innovative compact short-period undulators together to make the machine more compact. RF undulator has an extraordinary advantage of working at very short undulator period. A conceptual design for a RF undulator at 36 GHz using a corrugated cylindrical waveguide operating in the HE11 mode is presented in this paper. Based on beam dynamics simulation and photon beam radiation simulations, the possibility of RF undulator to be used in CompactLight project is evaluated

Superparaelectric phase in the ensemble of non-interacting ferroelectric nanoparticles

For the first time we predict the conditions of superparaelectric phase appearance in the ensemble of non-interacting spherical ferroelectric nanoparticles. The superparaelectricity in nanoparticle was defined by analogy with superparamagnetism, obtained earlier in small nanoparticles made of paramagnetic material. Calculations of correlation radius, energetic barriers of polarization reorientation and polarization response to external electric field, were performed within Landau-Ginzburg phenomenological approach for perovskites Pb(Zr,Ti)O3, BiFeO3 and uniaxial ferroelectrics rochelle salt and triglycine sulfate.Comment: 28 pages, 7 figures, 3 Appendices, to be submitted to Phys. Rev.

EXAFS study of lead-free relaxor ferroelectric BaTi(1-x)Zr(x)O3 at the Zr K-edge

Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi(1-x)Zr(x)O3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5 A around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm-3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.Comment: 13 pages, 12 figures, 4 tables. Submitted to Phys. Rev.