Electron bombardment cesium ion engine system Summary report, 3 May 1965 - 16 Dec. 1966

Design, development, and life tests of electron bombardment cesium ion engine system, permanent magnet engine, and ac discharge engin

Extending Phenomenological Crystal-Field Methods to C1C_1 Point-Group Symmetry: Characterization of the Optically-Excited Hyperfine Structure of 167^{167}Er3+^{3+}:Y2_2SiO5_5

We show that crystal-field calculations for $C_1$ point-group symmetry are possible, and that such calculations can be performed with sufficient accuracy to have substantial utility for rare-earth based quantum information applications. In particular, we perform crystal-field fitting for a C$_1$-symmetry site in $^{167}$Er$^{3+}$:Y$_2$SiO$_5$. The calculation simultaneously includes site-selective spectroscopic data up to 20,000 cm$^{-1}$, rotational Zeeman data, and ground- and excited-state hyperfine structure determined from high-resolution Raman-heterodyne spectroscopy on the 1.5 $\mu$m telecom transition. We achieve an agreement of better than 50 MHz for assigned hyperfine transitions. The success of this analysis opens the possibility of systematically evaluating the coherence properties, as well as transition energies and intensities, of any rare-earth ion doped into Y$_2$SiO$_5$ .Comment: 6 pages, plus 5 pages in supplementary information, 4 figures tota

Uso de energía solar para la cocción de pan sustituido parcialmente por harina de quinoa (Chenopodium Quinoa Wild.)

Objetivos: 1) Estudiar las condiciones de funcionamiento de dos hornos solares: tipo caja y tipo tambor; 2) Evaluar la cocción de panes elaborados con harina de quinoa y 3) Estudiar la respuesta del consumidor en su aceptabilidad. Los panes con 0, 10, 15 y 20% de sustitución se hornearon y se midió radiación (W/m2 ), temperatura ambiente (°C) y temperatura interna del pan durante la cocción. Se realizaron pruebas de aceptabilidad con 112 consumidores. La hora local en que se alcanza la máxima temperatura interna del pan (tT°max), la velocidad de aumento de ésta (Va), el tiempo de duración de la cocción (Tdur) y el área bajo la curva (ABC) fueron las variables más afectadas por las condiciones de radiación y temperatura ambiente. El tipo de horno y el porcentaje de sustitución no fueron significativos en la aceptabilidad. Se observó una tendencia a valorar más el pan con 10% de quinoa.Aims: 1) to study the behavior of the working conditions of box type and drum solar cookers; 2) evaluate the cooking process of breads with quinoa flour and 3) study the consumer’s acceptability response. Four formulations were established with 0, 10, 15 and 20% of wheat flour substitution, and they were cooked into the cookers. Cookers working conditions–radiation (W/m2 ) and environment temperature (°C)- and internal temperature of the breads were measured during cooking process. Sensory acceptability tests were performed with 112 consumers. The cooking variables mostly affected by daily conditions of radiation and environment temperature were: local time at which the maximum temperature (tT°max) of breads was reached, rate of increase (Va), duration time (tdur) and area under the curve (ABC). The cooker type and % of quinoa were not significant on the sensory acceptability; therefore it was observed a tendency to prefer the bread with 10% of quinoa.Fil: Passamai, Victor Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigaciones en Energía no Convencional; Argentina. Universidad Nacional de Salta. Facultad de Cs.exactas. Departamento de Fisica; ArgentinaFil: Armada, M.. Universidad Nacional de Salta. Consejo de Investigacion; Argentina. Universidad Nacional de Salta. Facultad de Ingenieria; ArgentinaFil: del Castillo, V.. Universidad Nacional de Salta. Consejo de Investigacion; ArgentinaFil: Goldner, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigación para la Industria Química (i); Argentina. Universidad Nacional de Salta; Argentin

Finite size effects on measures of critical exponents in d=3 O(N) models

We study the critical properties of three-dimensional O(N) models, for N=2,3,4. Parameterizing the leading corrections-to-scaling for the $\eta$ exponent, we obtain a reliable infinite volume extrapolation, incompatible with previous Monte Carlo values, but in agreement with $\epsilon$-expansions. We also measure the critical exponent related with the tensorial magnetization as well as the $\nu$ exponents and critical couplings.Comment: 12 pages, 2 postscript figure

Parametric generation of second sound in superfluid helium: linear stability and nonlinear dynamics

We report the experimental studies of a parametric excitation of a second sound (SS) by a first sound (FS) in a superfluid helium in a resonance cavity. The results on several topics in this system are presented: (i) The linear properties of the instability, namely, the threshold, its temperature and geometrical dependencies, and the spectra of SS just above the onset were measured. They were found to be in a good quantitative agreement with the theory. (ii) It was shown that the mechanism of SS amplitude saturation is due to the nonlinear attenuation of SS via three wave interactions between the SS waves. Strong low frequency amplitude fluctuations of SS above the threshold were observed. The spectra of these fluctuations had a universal shape with exponentially decaying tails. Furthermore, the spectral width grew continuously with the FS amplitude. The role of three and four wave interactions are discussed with respect to the nonlinear SS behavior. The first evidence of Gaussian statistics of the wave amplitudes for the parametrically generated wave ensemble was obtained. (iii) The experiments on simultaneous pumping of the FS and independent SS waves revealed new effects. Below the instability threshold, the SS phase conjugation as a result of three-wave interactions between the FS and SS waves was observed. Above the threshold two new effects were found: a giant amplification of the SS wave intensity and strong resonance oscillations of the SS wave amplitude as a function of the FS amplitude. Qualitative explanations of these effects are suggested.Comment: 73 pages, 23 figures. to appear in Phys. Rev. B, July 1 st (2001

Scaling of the superfluid density in superfluid films

We study scaling of the superfluid density with respect to the film thickness by simulating the $x-y$ model on films of size $L \times L \times H$ ($L >> H$) using the cluster Monte Carlo. While periodic boundary conditions where used in the planar ($L$) directions, Dirichlet boundary conditions where used along the film thickness. We find that our results can be scaled on a universal curve by introducing an effective thickness. In the limit of large $H$ our scaling relations reduce to the conventional scaling forms. Using the same idea we find scaling in the experimental results using the same value of $\nu = 0.6705$.Comment: 4 pages, one postscript file replaced by one Latex file and 5 postscript figure

Scaling of the specific heat in superfluid films

We study the specific heat of the $x-y$ model on lattices $L \times L \times H$ with $L \gg H$ (i.e. on lattices representing a film geometry) using the Cluster Monte--Carlo method. In the $H$--direction we apply Dirichlet boundary conditions so that the order parameter in the top and bottom layers is zero. We find that our results for the specific heat of various thickness size $H$ collapse on the same universal scaling function. The extracted scaling function of the specific heat is in good agreement with the experimentally determined universal scaling function using no free parameters.Comment: 4 pages, uuencoded compressed PostScrip

Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

Tungsten trioxide adopts a variety of structures which can be intercalated with charged species to alter the electronic properties, thus forming `tungsten bronzes'. Similar optical effects are observed upon removing oxygen from WO_3, although the electronic properties are slightly different. Here we present a computational study of cubic and hexagonal alkali bronzes and examine the effects on cell size and band structure as the size of the intercalated ion is increased. With the exception of hydrogen (which is predicted to be unstable as an intercalate), the behaviour of the bronzes are relatively consistent. NaWO_3 is the most stable of the cubic systems, although in the hexagonal system the larger ions are more stable. The band structures are identical, with the intercalated atom donating its single electron to the tungsten 5d valence band. Next, this was extended to a study of fractional doping in the Na_xWO_3 system (0 < x < 1). A linear variation in cell parameter, and a systematic change in the position of the Fermi level up into the valence band was observed with increasing x. In the underdoped WO_3-x system however, the Fermi level undergoes a sudden jump into the conduction band at around x = 0.2. Lastly, three compounds of a layered WO_4&#215;a,wdiaminoalkane hybrid series were studied and found to be insulating, with features in the band structure similar to those of the parent WO_3 compound which relate well to experimental UV-visible spectroscopy results.Comment: 12 pages, 16 figure

On stability of the three-dimensional fixed point in a model with three coupling constants from the ϵ\epsilon expansion: Three-loop results

The structure of the renormalization-group flows in a model with three quartic coupling constants is studied within the $\epsilon$-expansion method up to three-loop order. Twofold degeneracy of the eigenvalue exponents for the three-dimensionally stable fixed point is observed and the possibility for powers in $\sqrt{\epsilon}$ to appear in the series is investigated. Reliability and effectiveness of the $\epsilon$-expansion method for the given model is discussed.Comment: 14 pages, LaTeX, no figures. To be published in Phys. Rev. B, V.57 (1998

Vortex Loop Phase Transitions in Liquid Helium, Cosmic Strings, and High-T_c Superconductors

The distribution of thermally excited vortex loops near a superfluid phase transition is calculated from a renormalized theory. The number density of loops with a given perimeter is found to change from exponential decay with increasing perimeter to algebraic decay as T_c is approached, in agreement with recent simulations of both cosmic strings and high-T_c superconductors. Predictions of the value of the exponent of the algebraic decay at T_c and of critical behavior in the vortex density are confirmed by the simulations, giving strong support to the vortex-folding model proposed by Shenoy.Comment: Version to appear in Phys. Rev. Lett, with a number of corrections and addition