15,362 research outputs found
Prospects of developing cage and pen culture in Sudan
This paper describes the prospects of cage and pen culture in Sudan and recommends that a project for developing pen and cage culture techniques be started for marine and freshwater aquaculture
Spin-filtering by field dependent resonant tunneling
We consider theoretically transport in a spinfull one-channel interacting
quantum wire placed in an external magnetic field. For the case of two
point-like impurities embedded in the wire, under a small voltage bias the
spin-polarized current occurs at special points in the parameter space, tunable
by a single parameter. At sufficiently low temperatures complete
spin-polarization may be achieved, provided repulsive interaction between
electrons is not too strong.Comment: 4 pages, 2 figure
Bulletin No. 273 - Drainage and Irrigation, Soil, Economic, and Social Conditions, Delta Area, Utah, Division 3: Economic Conditions
Project 90-A Study of Factors Influencing the Financial Condition of Certain Utah Irrigation and Drainage Projects-was undertaken in 1928 as an intensified study of local areas. This study was divided among four departments, with a project leader for each particular phase of the study. These four project leaders, guided by the Station Director, have constituted a committee in immediate charge of this project. Subprojects and their respective leaders have been: A-Engineering and Engineering Economic Aspects, O. W. Israelsen; B-Soil Productivity Aspects, D. S. Jennings; C-Contributing Sociological Aspects, J. A. Geddes; and D-Economic Aspects, W. Preston Thomas
Dynamic Analysis for a Geared Turbofan Engine with Variable Area Fan Nozzle
Aggressive design goals have been set for future aero-propulsion systems with regards to fuel economy, noise, and emissions. To meet these challenging goals, advanced propulsion concepts are being explored and current operating margins are being re-evaluated to find additional concessions that can be made. One advanced propulsion concept being evaluated is a geared turbofan with a variable area fan nozzle (VAFN), developed by NASA. This engine features a small core, a fan driven by the low pressure turbine through a reduction gearbox, and a shape memory alloy (SMA)-actuated VAFN. The VAFN is designed to allow both a small exit area for efficient operation at cruise, while being able to open wider at high power conditions to reduce backpressure on the fan and ensure a safe level of stall margin is maintained. The VAFN is actuated via a SMA-based system instead of a conventional system to decrease overall weight of the system, however, SMA-based actuators respond relatively slowly, which introduces dynamic issues that are investigated in this work. This paper describes both a control system designed specifically for issues associated with SMAs, and dynamic analysis of the geared turbofan VAFN with the SMA actuators. Also, some future recommendations are provided for this type of propulsion system
Non-thermal leptogenesis via direct inflaton decay without SU(2)(L) triplets
We present a non-thermal leptogenesis scenario following standard
supersymmetric hybrid inflation, in the case where light neutrinos acquire mass
via the usual seesaw mechanism and inflaton decay to heavy right-handed
neutrino superfields is kinematically disallowed, or the right-handed neutrinos
which can be decay products of the inflaton are unable to generate sufficient
baryon asymmetry via their subsequent decay. The primordial lepton asymmetry is
generated through the decay of the inflaton into light particles by the
interference of one-loop diagrams with exchange of different right-handed
neutrinos. The mechanism requires superpotential couplings explicitly violating
a U(1) R-symmetry and R-parity. We take into account the constraints from
neutrino masses and mixing and the preservation of the primordial asymmetry. We
consider two models, one without and one with SU(2)(R) gauge symmetry. We show
that the former is viable, whereas the latter is ruled out. Although the broken
R-parity need not have currently observable low-energy signatures, some
R-parity-violating slepton decays may be detectable in the future colliders.Comment: 22 pages including 9 figures, uses Revtex, version to appear in PR
Mitral Leaflet Separation Index in Assessing the Severity of Mitral Stenosis
Determining the severity of mitral stenosis (MS) is important for both prognostic and therapeutic reasons. The mitral valve area (MVA) can be measured by planimetry, pressure half-time, continuity equation, and proximal isovelocity surface area methods. In this study, we propose a novel yet simple, independent measure of MS severity–the mitral leaflet separation (MLS) index. This new index could be a useful surrogate measure of the MVA. This index would also help when there is a discrepancy between severities of MS estimated by existing methods, in the presence of atrial fibrillation and in the presence of mitral regurgitation
Determination of Interface Atomic Structure and Its Impact on Spin Transport Using Z-Contrast Microscopy and Density-Functional Theory
We combine Z-contrast scanning transmission electron microscopy with
density-functional-theory calculations to determine the atomic structure of the
Fe/AlGaAs interface in spin-polarized light-emitting diodes. A 44% increase in
spin-injection efficiency occurs after a low-temperature anneal, which produces
an ordered, coherent interface consisting of a single atomic plane of
alternating Fe and As atoms. First-principles transport calculations indicate
that the increase in spin-injection efficiency is due to the abruptness and
coherency of the annealed interface.Comment: 16 pages (including cover), 4 figure
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