972 research outputs found
Discrete Dirac system: rectangular Weyl functions, direct and inverse problems
A transfer matrix function representation of the fundamental solution of the
general-type discrete Dirac system, corresponding to rectangular Schur
coefficients and Weyl functions, is obtained. Connections with Szeg\"o
recurrence, Schur coefficients and structured matrices are treated.
Borg-Marchenko-type uniqueness theorem is derived. Inverse problems on the
interval and semiaxis are solved.Comment: Section 2 is improved in the second version: some new results on
Halmos extension are added and arguments are simplifie
A Study of the Efficacy of Unit Contingency Contracting Training
This research is a follow-on effort to Capt Pete Lasch\u27s thesis, which examined the Air Force training needs of contingency contracting officers (CCOs). Through this study, Lasch (2002) identified a list of critical training tasks for CCO training. This study investigates how units currently conduct training and to what extent the recommended tasks are being addressed in training. Interviews, surveys, and archival training logs were used to capture data for the study. CCO demographic information and recommendations were collected through these interviews and surveys. Interviews were used as a pre-test and later were combined with the electronic survey responses. Surveys were sent in two phases to CCOs who deployed in the period of interest from September 11th of 2001 to December 15th of 2002. Phase one described the purpose of the study and phase two involved collection of surveys from population of interest. Training logs or plans were also requested from the units survey participants deployed from. These logs provided insight into the content of training and allowed the researcher to investigate which of the recommended tasks from Lasch (2002) were included in unit training programs across the Air Force. Descriptive statistics and pattern matching were used to analyze the data. This analysis resulted in recommendations to both improve training programs and to provide relevant training material for future unit level CCO training programs
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Magmatism in southern Uruguay and the early rifting of the South Atlantic
A suite of early Cretaceous vo1canic rocks (Puerto GOmez and Arequita FIm.) are preserved within the N60° E trending Santa Lucia Basin, southern Uruguay which lies at the southern margin of the Parana - Etendeka continental flood basalt province. New Ar- Ar ages of the basalts range from 134 to 130 Ma while ages from the rhyolites range from 130 to 124 Ma. This magamtism was contemporaneous with the main flood basalt event, although rhyolite activity continued after rifting (127 - 126 Ma). The province therefore contains unique information about melting conditions at the periphery of the influence of the Tristan da Cunha plume.
The volcanic rocks of southern Uruguay are bimodal in silica, and the majority of basalts of the Puerto G6mez Fm., herein termed the Treinte Y Tres magma type, have major-, trace- element and initial isotope ratios similar to the low -Ti/Y Gramado-Tafelberg magma types of the Paranl-Etendeka. There are also a number of unique basalt samples termed the Santa Lucia magma type. which have low La/Nb, and are considered to have been generated by mixing between lithosphere - and asthenosphere - derived melts. These magmas represent the first sampling of true plume material in this CFB province. The rhyolites of the Arequita Fm. are relatively evolved with variably sized euhedral to anbedral quartz phenocrysts, and ignimbritic textures that are the first described from this province. The rhyolites have lower magmatic temperatures (850 - 950°C) than those of the Parana-Etendeka, and are divided into two geochemical series, the Lascano Series and the Aigtia Series. The rhyolites of the Lascano and Aigua Series are not related to the Puerto Gomez Fm. basaks, but rather they originated from separate sources in the mid to lower crust. where melting was facilitated by mid-crustal level intrusions of basaJtic material as recognised from a large gravity anomaly. Melt production rates in southern Uruguay were low (0.01 km3 yr-1) similar to the rates ca1cuIated for the waning stages of magmatism on the Serra Geral escarpment, southern Brazil. These rates are consistent with the notion that by this time the principal melt production was located in the newly forming ocean with Uruguay at the margins of the influence of the plume
Inhomogeneous nuclear spin polarization induced by helicity-modulated optical excitation of fluorine-bound electron spins in ZnSe
Optically-induced nuclear spin polarization in a fluorine-doped ZnSe epilayer
is studied by time-resolved Kerr rotation using resonant excitation of
donor-bound excitons. Excitation with helicity-modulated laser pulses results
in a transverse nuclear spin polarization, which is detected as a change of the
Larmor precession frequency of the donor-bound electron spins. The frequency
shift in dependence on the transverse magnetic field exhibits a pronounced
dispersion-like shape with resonances at the fields of nuclear magnetic
resonance of the constituent zinc and selenium isotopes. It is studied as a
function of external parameters, particularly of constant and radio frequency
external magnetic fields. The width of the resonance and its shape indicate a
strong spatial inhomogeneity of the nuclear spin polarization in the vicinity
of a fluorine donor. A mechanism of optically-induced nuclear spin polarization
is suggested based on the concept of resonant nuclear spin cooling driven by
the inhomogeneous Knight field of the donor-bound electron.Comment: 12 pages, 11 figure
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