33,555 research outputs found
Solar flare ionization in the mesosphere observed by coherent-scatter radar
The coherent-scatter technique, as used with the Urbana radar, is able to measure relative changes in electron density at one altitude during the progress of a solar flare when that altitude contains a statistically steady turbulent layer. This work describes the analysis of Urbana coherent-scatter data from the times of 13 solar flares in the period from 1978 to 1983. Previous methods of measuring electron density changes in the D-region are summarized. Models of X-ray spectra, photoionization rates, and ion-recombination reaction schemes are reviewed. The coherent-scatter technique is briefly described, and a model is developed which relates changes in scattered power to changes in electron density. An analysis technique is developed using X-ray flux data from geostationary satellites and coherent scatter data from the Urbana radar which empirically distinguishes between proposed D-region ion-chemical schemes, and estimates the nonflare ion-pair production rate
Thermal model of a 75 watt/e/ space power planar RTG system
Planar type radioisotope thermoelectric generator with beryllium plate for spacecraft powe
Double Ionisation in R-Matrix Theory Using a 2-electron Outer Region
We have developed a two-electron outer region for use within R-matrix theory
to describe double ionisation processes. The capability of this method is
demonstrated for single-photon double ionisation of He in the photon energy
region between 80 eV to 180 eV. The cross sections are in agreement with
established data. The extended RMT method also provides information on
higher-order processes, as demonstrated by the identification of signatures for
sequential double ionisation processes involving an intermediate He state
with .Comment: 5 pages, 4 figure
Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors
A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions
Fire retardant foams developed to suppress fuel fires
Heat insulating polyurethane foam retards and suppresses fuel fires. Uniformly dispersed in the foam is a halogenated polymer capable of splitting off hydrogen halide upon heating and charring of the polyurethane
After heat distribution of a mobile nuclear power plant
A computer program was developed to analyze the transient afterheat temperature and pressure response of a mobile gas-cooled reactor power plant following impact. The program considers (in addition to the standard modes of heat transfer) fission product decay and transport, metal-water reactions, core and shield melting and displacement, and pressure and containment vessel stress response. Analyses were performed for eight cases (both deformed and undeformed models) to verify operability of the program options. The results indicated that for a 350 psi (241 n/sq cm) initial internal pressure, the containment vessel can survive over 100,000 seconds following impact before creep rupture occurs. Recommendations were developed as to directions for redesign to extend containment vessel life
Dynamical formation and interaction of bright solitary waves and solitons in the collapse of Bose-Einstein condensates with attractive interactions
We model the dynamics of formation of multiple, long-lived, bright solitary
waves in the collapse of Bose-Einstein condensates with attractive interactions
as studied in the experiment of Cornish et al. [Phys. Rev. Lett. 96 (2006)
170401]. Using both mean-field and quantum field simulation techniques, we find
that while a number of separated wave packets form as observed in the
experiment, they do not have a repulsive \pi phase difference that has been
previously inferred. We observe that the inclusion of quantum fluctuations
causes soliton dynamics to be predominantly repulsive in one dimensional
simulations independent of their initial relative phase. However, indicative
three-dimensional simulations do not support this conclusion and in fact show
that quantum noise has a negative impact on bright solitary wave lifetimes.
Finally, we show that condensate oscillations, after the collapse, may serve to
deduce three-body recombination rates, and that the remnant atom number may
still exceed the critical number for collapse for as long as three seconds
independent of the relative phases of the bright solitary waves.Comment: 14 pages, 5 figure
Alkali oxide-tantalum, niobium and antimony oxide ionic conductors
The phase equilibrium relations of four systems were investigated in detail. These consisted of sodium and potassium antimonates with antimony oxide and tantalum and niobium oxide with rubidium oxide as far as the ratio 4Rb2O:llB2O5 (B=Nb, Ta). The ternary system NaSbO3-Sb2O4-NaF was investigated extensively to determine the actual composition of the body centered cubic sodium antimonate. Various other binary and ternary oxide systems involving alkali oxides were examined in lesser detail. The phases synthesized were screened by ion exchange methods to determine mobility of the mobility of the alkali ion within the niobium, tantalum or antimony oxide (fluoride) structural framework. Five structure types warranted further investigation; these structure types are (1) hexagonal tungsten bronze (HTB), (2) pyrochlore, (3) the hybrid HTB-pyrochlore hexagonal ordered phases, (4) body centered cubic antimonates and (5) 2K2O:3Nb2O5. Although all of these phases exhibit good ion exchange properties only the pyrochlore was prepared with Na(+) ions as an equilibrium phase and as a low porosity ceramic. Sb(+3) in the channel interferes with ionic conductivity in this case, although relatively good ionic conductivity was found for the metastable Na(+) ion exchanged analogs of RbTa2O5F and KTaWO6 pyrochlore phases
A momentum-space representation of Green's functions with modified dispersion on ultra-static space-time
We consider the Green's functions associated to a scalar field propagating on
a curved, ultra-static background, in the presence of modified dispersion
relations. The usual proper-time deWitt-Schwinger procedure to obtain a series
representation of the Green's functions is doomed to failure, because of higher
order spatial derivatives in the Klein-Gordon operator. We show how to overcome
this difficulty by considering a preferred frame, associated to a unit
time-like vector. With respect to this frame, we can express the Green's
functions as an integral over all frequencies of a space-dependent function.
The latter can be expanded in momentum space, as a series with geometric
coefficients similar to the deWitt-Schwinger's ones. By integrating over all
frequencies, we finally find the expansion of the Green's function up to four
derivatives of the metric tensor. The relation with the proper-time formalism
is also discussed.Comment: revtex, version accepted for publication in Phys. Rev.
- …