174 research outputs found
Evolution user requirements for the restructured space station
Space Station Freedom (SSF) is designed to be an Earth orbiting multidisciplinary R&D facility capable of evolving to accommodate a variety of potential uses. In order to identify SSF evolution requirement and define potential growth configurations, NASA-Langley is analyzing user resource requirements for the post-PMC time frame. The analysis goal is to define resource levels, including crew, power, and volume, which allow full utilization of SSF capabilities commensurate with minimum essential user requirements. Multiple scenarios were studied including core R&D and combined SEI plus R&D utilization. An analysis is presented of a core R&D utilization scenario. Included are discussions of resource allocation assumptions for specific R&D disciplines, user requirements trends, and growth resource projections. These preliminary results show total resource requirements of 13 crew, 150 kW power, and additional lab volume equivalent to a second U.S. lab module. Additionally, orthogonal growth structure was identified as required to support SSF systems and users
Incidence of Bipolaris and Exserohilum Species in Corn Leaves in North Carolina
Samples of 42–60 corn leaves were collected without regard to disease symptoms at 2-m intervals in each of eight cornfields in western and two in eastern North Carolina in 1985. Sampling dates for the 10 fields ranged from 16 July to 8 August. The leaves were surface-sterilized and incubated in moist chambers for isolation of large-spored species of Bipolaris and Exserohilum. Incidence of B. zeicola infection was high (41–81%) in leaves from nine of the 10 fields. B. maydis and E. turcicum, which are more aggressive pathogens of hybrid corn than B. zeicola, occurred at lower incidences of 0–48% and 0–50%, respectively, in leaves from these fields at the time of sampling. This indicated that initial population densities of these aggressive pathogens were much lower than that of B. zeicola. Forty-five isolates of E. turcicum collected before 28 August were all race 1. Three isolates of race 2 were obtained later from fields of hybrids with the Ht 1 gene for resistance to race 1. All 75 isolates of B. maydis obtained from the 10 extensively sampled fields were race O; they were equally virulent on inbred line B73 with normal cytoplasm or B73 with C, S, or T male sterile cytoplasm. Frequencies of mating types of B. maydis and B. zeicola varied from field to field, with no correlation between the frequencies in the two species. Races 2 and 3 of B. zeicola, however, had similar mating type frequencies in these fields. B. sorokiniana was isolated from leaves from six of the 10 fields; the greatest incidence was 37%. E. rostratum was found in leaves from five fields at incidences up to 18%, and E. holmii occurred in leaves in one field at 11% incidence. These data indicate that a variety of species of Bipolaris and Exserohilum are able to infect green leaves of mature corn plants in the field. Thus, corn may contribute to the survival of species that are primarily pathogenic on other gramineous hosts
Percolation Threshold, Fisher Exponent, and Shortest Path Exponent for 4 and 5 Dimensions
We develop a method of constructing percolation clusters that allows us to
build very large clusters using very little computer memory by limiting the
maximum number of sites for which we maintain state information to a number of
the order of the number of sites in the largest chemical shell of the cluster
being created. The memory required to grow a cluster of mass s is of the order
of bytes where ranges from 0.4 for 2-dimensional lattices
to 0.5 for 6- (or higher)-dimensional lattices. We use this method to estimate
, the exponent relating the minimum path to the
Euclidean distance r, for 4D and 5D hypercubic lattices. Analyzing both site
and bond percolation, we find (4D) and
(5D). In order to determine
to high precision, and without bias, it was necessary to
first find precise values for the percolation threshold, :
(4D) and (5D) for site and
(4D) and (5D) for bond
percolation. We also calculate the Fisher exponent, , determined in the
course of calculating the values of : (4D) and
(5D)
Experimental evidence of a fractal dissipative regime in high-T_c superconductors
We report on our experimental evidence of a substantial geometrical
ingredient characterizing the problem of incipient dissipation in high-T_c
superconductors(HTS): high-resolution studies of differential
resistance-current characteristics in absence of magnetic field enabled us to
identify and quantify the fractal dissipative regime inside which the actual
current-carrying medium is an object of fractal geometry. The discovery of a
fractal regime proves the reality and consistency of critical-phenomena
scenario as a model for dissipation in inhomogeneous and disordered HTS, gives
the experimentally-based value of the relevant finite-size scaling exponent and
offers some interesting new guidelines to the problem of pairing mechanisms in
HTS.Comment: 5 pages, 3 figures, RevTex; Accepted for publication in Physical
Review B; (figures enlarged
Statistics of self-avoiding walks on randomly diluted lattice
A comprehensive numerical study of self-avoiding walks (SAW's) on randomly
diluted lattices in two and three dimensions is carried out. The critical
exponents and are calculated for various different occupation
probabilities, disorder configuration ensembles, and walk weighting schemes.
These results are analyzed and compared with those previously available.
Various subtleties in the calculation and definition of these exponents are
discussed. Precise numerical values are given for these exponents in most
cases, and many new properties are recognized for them.Comment: 34 pages (+ 12 figures), REVTEX 3.
Fast Algorithms For Josephson Junction Arrays : Bus--bars and Defects
We critically review the fast algorithms for the numerical study of
two--dimensional Josephson junction arrays and develop the analogy of such
systems with electrostatics. We extend these procedures to arrays with
bus--bars and defects in the form of missing bonds. The role of boundaries and
of the guage choice in determing the Green's function of the system is
clarified. The extension of the Green's function approach to other situations
is also discussed.Comment: Uuencoded 1 Revtex file (11 Pages), 3 Figures : Postscript Uuencode
Multifractal behavior of linear polymers in disordered media
The scaling behavior of linear polymers in disordered media modelled by
self-avoiding random walks (SAWs) on the backbone of two- and three-dimensional
percolation clusters at their critical concentrations p_c is studied. All
possible SAW configurations of N steps on a single backbone configuration are
enumerated exactly. We find that the moments of order q of the total number of
SAWs obtained by averaging over many backbone configurations display
multifractal behavior, i.e. different moments are dominated by different
subsets of the backbone. This leads to generalized coordination numbers \mu_q
and enhancement exponents \gamma_q, which depend on q. Our numerical results
suggest that the relation \mu_1 = p_ c \mu between the first moment \mu_1 and
its regular lattice counterpart \mu is valid.Comment: 11 pages, 12 postscript figures, to be published in Phys. Rev.
Driven Diffusion in the Two-Dimensional Lattice Coulomb Gas; A Model for Flux Flow in Superconducting Networks
We carry out driven diffusion Monte Carlo simulations of the two dimensional
classical lattice Coulomb gas in an applied uniform electric field, as a model
for vortex motion due to an applied d.c. current, in a periodic superconducting
network. A finite-size version of dynamic scaling is used to extract the
dynamic critical exponent z, and infer the non-linear response at the
transition temperature. We consider the f=0 and f=1/2 cases, corresponding to
no applied magnetic field, and to one half flux quantum per unit cell of the
network respectively.Comment: 25 pages, 7 figures (available from [email protected]),
RevTex3.0, URST12
Cutaneous skull metastasis from uterine leiomyosarcoma: a case report
<p>Abstract</p> <p>Background</p> <p>Cutaneous metastases in the facial region occur in less than 0.5% of patients with metastatic cancer.</p> <p>Case presentation</p> <p>A 52-year-old woman who admitted with a lung and a skull skin nodule is presented. She had a known diagnosis of uterine leiomyosarcoma following an extended total hysterectomy two years ago. Excision biopsy of both nodules revealed metastatic disease.</p> <p>Conclusion</p> <p>The appearance of a cutaneous nodule in a patient with a history of uterine leiomyosarcoma might indicate a metastatic tumor lesion. Biopsy and immunohistochemistry are essential for correct diagnosis.</p
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