Analysis of a communication satellite for lunar far-side exploration

Analysis of communication satellite for lunar far-side exploration relaying color television, voice, high-bit-rate telemetry data, and ranging code from command and service, and lunar module

Radiation testing of composite materials, in situ versus ex situ effects

The effect of post irradiation test environments on tensile properties of representative advanced composite materials (T300/5208, T300/934, C6000/P1700) was investigated. Four ply (+ or - 45 deg/+ or - 45 deg) laminate tensile specimens were exposed in vacuum up to a bulk dose of 1 x 10 to the 10th power rads using a mono-energetic fluence of 700 keV electrons from a Van de Graaff accelerator. Post irradiation testing was performed while specimens were being irradiated (in situ data), in vacuum after cessation of irradiation (in vacuo data), and after exposure to air (ex situ data). Room temperature and elevated temperature effects were evaluated. The radiation induced changes to the tensile properties were small. Since the absolute changes in tensile properties were small, the existance of a post irradiation test environment effect was indeterminate

Ground state spin and Coulomb blockade peak motion in chaotic quantum dots

We investigate experimentally and theoretically the behavior of Coulomb blockade (CB) peaks in a magnetic field that couples principally to the ground-state spin (rather than the orbital moment) of a chaotic quantum dot. In the first part, we discuss numerically observed features in the magnetic field dependence of CB peak and spacings that unambiguously identify changes in spin S of each ground state for successive numbers of electrons on the dot, N. We next evaluate the probability that the ground state of the dot has a particular spin S, as a function of the exchange strength, J, and external magnetic field, B. In the second part, we describe recent experiments on gate-defined GaAs quantum dots in which Coulomb peak motion and spacing are measured as a function of in-plane magnetic field, allowing changes in spin between N and N+1 electron ground states to be inferred.Comment: To appear in Proceedings of the Nobel Symposium 2000 (Physica Scripta

Finite Size Corrections for the Pairing Hamiltonian

We study the effects of superconducting pairing in small metallic grains. We show that in the limit of large Thouless conductance one can explicitly determine the low energy spectrum of the problem as an expansion in the inverse number of electrons on the grain. The expansion is based on the formal exact solution of the Richardson model. We use this expansion to calculate finite size corrections to the ground state energy, Matveev-Larkin parameter, and excitation energies.Comment: 22 pages, 1 figur

Do published guidelines for evaluation of Irritable Bowel Syndrome reflect practice?

BACKGROUND: The only US guidelines listed in the National Guideline Warehouse for the diagnosis of Irritable Bowel Syndrome (IBS) are the expert opinion guidelines published by The American Gastroenterology Association. Although the listed target audience of these guidelines includes family physicians and general internists, the care recommended in the guidelines has not been compared to actual primary care practice. This study was designed to compare expert opinion guidelines with the actual primary care provided and to assess outcomes in the 3 years following the IBS diagnosis. METHODS: This is a retrospective medical record review study using a random sample of incident IBS cases from all Olmsted County, Minnesota providers diagnosed between January 1, 1993 and December 31, 1995. Data was collected on all care and testing provided to the subjects as well as 3-year outcomes related to the IBS diagnosis. RESULTS: Of the 149 IBS patients, 99 were women and the mean age was 47.6 years. No patient had all of the diagnostic tests recommended in the guidelines. 42% had the basic blood tests of CBC and a chemistry panel. Sedimentation rate (2%) and serum thyroxine level (3%) were uncommon. Colon imaging studies were done in 41% including 74% of those over the age of 50. In the 3 years following the diagnosis, only one person had a change in diagnosis and no diagnoses of gastro-intestinal malignancies were made in the cohort. CONCLUSIONS: Primary care practice based diagnostic evaluations for IBS differ significantly from the specialty expert opinion-based guidelines. Implementation of the specialty guidelines in primary care practice would increase utilization with apparent limited improvement in diagnostic outcomes

Role of a parallel magnetic field in two dimensional disordered clusters containing a few correlated electrons

An ensemble of 2d disordered clusters with a few electrons is studied as a function of the Coulomb energy to kinetic energy ratio r_s. Between the Fermi system (small r_s) and the Wigner molecule (large r_s), an interaction induced delocalization of the ground state takes place which is suppressed when the spins are aligned by a parallel magnetic field. Our results confirm the existence of an intermediate regime where the Wigner antiferromagnetism defavors the Stoner ferromagnetism and where the enhancement of the Lande g factor observed in dilute electron systems is reproduced.Comment: 4 pages, 3 figure

Discrete charging of metallic grains: Statistics of addition spectra

We analyze the statistics of electrostatic energies (and their differences) for a quantum dot system composed of a finite number $K$ of electron islands (metallic grains) with random capacitance-inductance matrix $C$, for which the total charge is discrete, $Q=Ne$ (where $e$ is the charge of an electron and $N$ is an integer). The analysis is based on a generalized charging model, where the electrons are distributed among the grains such that the electrostatic energy E(N) is minimal. Its second difference (inverse compressibility) $\chi_{N}=E(N+1)-2 E(N)+E(N-1)$ represents the spacing between adjacent Coulomb blockade peaks appearing when the conductance of the quantum dot is plotted against gate voltage. The statistics of this quantity has been the focus of experimental and theoretical investigations during the last two decades. We provide an algorithm for calculating the distribution function corresponding to $\chi_{N}$ and show that this function is piecewise polynomial.Comment: 21 pages, no figures, mathematical nomenclature (except for Abstract and Introduction