17,746 research outputs found
Lightning induced currents in aircraft wiring using low level injection techniques
Various techniques were studied to predict the transient current induced into aircraft wiring bundles as a result of an aircraft lightning strike. A series of aircraft measurements were carried out together with a theoretical analysis using computer modeling. These tests were applied to various aircraft and also to specially constructed cylinders installed within coaxial return conductor systems. Low level swept frequency CW (carrier waves), low level transient and high level transient injection tests were applied to the aircraft and cylinders. Measurements were made to determine the transfer function between the aircraft drive current and the resulting skin currents and currents induced on the internal wiring. The full threat lightning induced transient currents were extrapolated from the low level data using Fourier transform techniques. The aircraft and cylinders used were constructed from both metallic and CFC (carbon fiber composite) materials. The results show the pulse stretching phenomenon which occurs for CFC materials due to the diffusion of the lightning current through carbon fiber materials. Transmission Line Matrix modeling techniques were used to compare theoretical and measured currents
Assumptions that imply quantum dynamics is linear
A basic linearity of quantum dynamics, that density matrices are mapped
linearly to density matrices, is proved very simply for a system that does not
interact with anything else. It is assumed that at each time the physical
quantities and states are described by the usual linear structures of quantum
mechanics. Beyond that, the proof assumes only that the dynamics does not
depend on anything outside the system but must allow the system to be described
as part of a larger system. The basic linearity is linked with previously
established results to complete a simple derivation of the linear Schrodinger
equation. For this it is assumed that density matrices are mapped one-to-one
onto density matrices. An alternative is to assume that pure states are mapped
one-to-one onto pure states and that entropy does not decrease.Comment: 10 pages. Added references. Improved discussion of equations of
motion for mean values. Expanded Introductio
Unified constitutive model for single crystal deformation behavior with applications
Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code
Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
Among the competing evolution theories for subdwarf-B (sdB) stars is the
binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary
system consisting of a pulsating sdB star and a late F main-sequence companion
(O'Donoghue et al. 1997), however the period and the orbit semi-major axes have
not been precisely determined. This paper presents orbital characteristics of
the EC 20117-4014 binary system using 20 years of photometric data. Periodic
Observed minus Calculated (O-C) variations were detected in the two highest
amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating
the binary system's precise orbital period (P = 792.3 days) and the
light-travel time amplitude (A = 468.9 s). This binary shows no significant
orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3
as an upper limit). This upper limit of the eccentricity is the lowest
among all wide sdB binaries with known orbital parameters. This analysis
indicated that the sdB is likely to have lost its hydrogen envelope through
stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB
stars. In addition to those results, the underlying pulsation period change
obtained from the photometric data was = 5.4 (0.7)
d d, which shows that the sdB is just before the end of the
core helium-burning phase
Lorentz transformations that entangle spins and entangle momenta
Simple examples are presented of Lorentz transformations that entangle the
spins and momenta of two particles with positive mass and spin 1/2. They apply
to indistinguishable particles, produce maximal entanglement from finite
Lorentz transformations of states for finite momenta, and describe entanglement
of spins produced together with entanglement of momenta. From the entanglements
considered, no sum of entanglements is found to be unchanged.Comment: 5 Pages, 2 Figures, One new paragraph and reference adde
Red Blood Cells from Individuals with Abdominal Obesity or Metabolic Abnormalities Exhibit Less Deformability upon Entering a Constriction.
Abdominal obesity and metabolic syndrome (MS) are multifactorial conditions associated with increased risk of cardiovascular disease and type II diabetes mellitus. Previous work has demonstrated that the hemorheological profile is altered in patients with abdominal obesity and MS, as evidenced for example by increased whole blood viscosity. To date, however, no studies have examined red blood cell (RBC) deformability of blood from individuals with obesity or metabolic abnormalities under typical physiological flow conditions. In this study, we pumped RBCs through a constriction in a microfluidic device and used high speed video to visualize and track the mechanical behavior of ~8,000 RBCs obtained from either healthy individuals (n = 5) or obese participants with metabolic abnormalities (OMA) (n = 4). We demonstrate that the OMA+ cells stretched on average about 25% less than the healthy controls. Furthermore, we examined the effects of ingesting a high-fat meal on RBC mechanical dynamics, and found that the postprandial period has only a weak effect on the stretching dynamics exhibited by OMA+ cells. The results suggest that chronic rigidification of RBCs plays a key role in the increased blood pressure and increased whole blood viscosity observed in OMA individuals and was independent of an acute response triggered by consumption of a high-fat meal
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