Properties of novel CVD graphite fibers and their bromine intercalation compounds

A hybrid fiber with a PAN core surrounded by a vapor grown carbon fiber (VGCF) sheath was fabricated using a proprietary process. The density, ultimate tensile strength, Young's modulus, and resistivity of pristine and bromine intercalated fibers made by this technique having diameters varying from 5 to 50 microns were compared with the values predicted from the rule of mixtures model. For both the pristine and intercalated fibers, the density, ultimate tensile strength, and Young's modulus of the fibers were lower than predicted, but the resistivity was measured to be consistent with predictions. The lower than theoretical mechanical properties may be evidence of a low density disordered interface between the core and the sheath which would lower the density and degrade the mechanical properties, but would leave the resistivity nearly unaffected. Intercalation had little if any effect on the ultimate tensile strength and Young's modulus, but raised the density by about 11 pct., and lowered the resistivity by an order of magnitude. The diameter dependence of the resistivity showed evidence of a depletion layer of the type found in VGCF

Microscopic non-equilibrium theory of quantum well solar cells

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the non-equilibrium Green's function formalism for a multi band tight binding Hamiltonian. The quantum kinetic equations for the single particle Green's functions of electrons and holes are self-consistently coupled to Poisson's equation, including inter-carrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering self energies. Photogeneration of carriers is described on the same level in terms of a self energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.Comment: 10 pages, 6 figures; corrected typos, changed caption Fig. 1, replaced Fig.

Microscopic theory of quantum-transport phenomena in mesoscopic systems: A Monte Carlo approach

A theoretical investigation of quantum-transport phenomena in mesoscopic systems is presented. In particular, a generalization to ``open systems'' of the well-known semiconductor Bloch equations is proposed. The presence of spatial boundary conditions manifest itself through self-energy corrections and additional source terms in the kinetic equations, whose form is suitable for a solution via a generalized Monte Carlo simulation. The proposed approach is applied to the study of quantum-transport phenomena in double-barrier structures as well as in superlattices, showing a strong interplay between phase coherence and relaxation.Comment: to appear in Phys. Rev. Let

Inelastic quantum transport in superlattices: success and failure of the Boltzmann equation

Electrical transport in semiconductor superlattices is studied within a fully self-consistent quantum transport model based on nonequilibrium Green functions, including phonon and impurity scattering. We compute both the drift velocity-field relation and the momentum distribution function covering the whole field range from linear response to negative differential conductivity. The quantum results are compared with the respective results obtained from a Monte Carlo solution of the Boltzmann equation. Our analysis thus sets the limits of validity for the semiclassical theory in a nonlinear transport situation in the presence of inelastic scattering.Comment: final version with minor changes, to appear in Physical Review Letters, sceduled tentatively for July, 26 (1999

Nutritional Management Post-AI to Enhance Pregnancy Outcomes

Effective replacement heifer development is a critical segment of the integrated management program in an efficient beef cow production system. The most critical factor determining the success of any heifer development program is nutrition. Most efforts are concentrated in providing the right amount and quality of feed to achieve gains from 1.5 to 2.0 lb/day, so heifers can reach 65% of their mature BW by the day of breeding. Approximately 80% of the U.S. cow-herds are spring calving, which means that producers utilizing estrous synchronization and AI are keeping their heifers in a feedlot environment until heifers are inseminated. Immediately following AI, heifers are typically moved to pasture. It is known that maternal recognition of pregnancy takes place around d 15 - 17 post-insemination and that transporting animals near this time compromises conception rates. However, moving heifers within the first 5 days post-insemination does not cause this reduction. Although, research suggests that conception rates are compromised when heifers are placed on early growth pasture forages. We hypothesized that feeding this high moisture pasture forage at turnout is limiting DMI which in turn causes a temporary energy deficiency that results in temporary heifer weight loss during the critical stages of early embryonic development and maternal recognition of pregnancy. Therefore, it is beneficial to ensure heifers maintain the same plane of nutrition after breeding, at least until day 25 when the embryo should be completely attached to the uterus. If this is true, maintaining a positive plane of nutrition on heifers after breeding will increase 1st service conception rates, improving herd fertility and longevity

Optical Spectroscopic Survey of High-latitude WISE-selected Sources

We report on the results of an optical spectroscopic survey at high Galactic latitude (|b| ≥ 30°) of a sample of WISE-selected targets, grouped by WISE W1 (λ_eff = 3.4 μm) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultraluminous infrared galaxy candidates using DEIMOS on Keck II. We find 0.30 ± 0.02 galaxies arcmin–2 with a median redshift of z = 0.33 ± 0.01 for the sample with W1 ≥ 120 μJy. The foreground stellar densities in our survey range from 0.23 ± 0.07 arcmin–2 to 1.1 ± 0.1 arcmin–2 for the same sample. We obtained spectra that produced science grade redshifts for ≥90% of our targets for sources with W1 flux ≥120 μJy that also had an i-band flux gsim 18 μJy. We used this for targeting very preliminary data reductions available to the team in 2010 August. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies