2,814 research outputs found
Application of numerical optimization to the design of wings with specified pressure distributions
A practical procedure for the optimum design of transonic wings is demonstrated. The procedure uses an optimization program based on the method of feasible directions coupled with an aerodynamic analysis program which solves the three-dimensional potential equation for subsonic through transonic flow. Two new wings for the A-7 aircraft were designed by using the optimization procedure to achieve specified surface pressure distributions. The new wings, along with the existing A-7 wing, were tested in the Ames 11 ft transonic wind tunnel. The experimental data show that all of the performance goals were met. However, comparisons of the wind tunnel results with the theoretical predictions indicate some differences at conditions for which strong shock waves occur
Computational wing optimization and comparisons with experiment for a semi-span wing model
A computational wing optimization procedure was developed and verified by an experimental investigation of a semi-span variable camber wing model in the NASA Ames Research Center 14 foot transonic wind tunnel. The Bailey-Ballhaus transonic potential flow analysis and Woodward-Carmichael linear theory codes were linked to Vanderplaats constrained minimization routine to optimize model configurations at several subsonic and transonic design points. The 35 deg swept wing is characterized by multi-segmented leading and trailing edge flaps whose hinge lines are swept relative to the leading and trailing edges of the wing. By varying deflection angles of the flap segments, camber and twist distribution can be optimized for different design conditions. Results indicate that numerical optimization can be both an effective and efficient design tool. The optimized configurations had as good or better lift to drag ratios at the design points as the best designs previously tested during an extensive parametric study
Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves
Transport currents can alter alter order parameter dynamics and change steady
states in superconductors, in ferromagnets, and in hybrid systems. In this
article we present a scheme for fully microscopic evaluation of order parameter
dynamics that is intended for application to nanoscale systems. The approach
relies on time-dependent mean-field-theory, on an adiabatic approximation, and
on the use of non-equilibrium Greens function (NEGF) theory to calculate the
influence of a bias voltage across a system on its steady-state density matrix.
We apply this scheme to examine the spin-transfer torques which drive
magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic
torques are peaked near Co/Cu interfaces, in agreement with most previous
pictures, but suprisingly act mainly on Co transition metal -orbitals rather
than on -orbitals as generally supposed.Comment: 9 pages, 5 figure
A comparison of theoretical and experimental pressure distributions for two advanced fighter wings
A comparison was made between experimental pressure distributions measured during testing of the Vought A-7 fighter and the theoretical predictions of four transonic potential flow codes. Isolated wind and three wing-body codes were used for comparison. All comparisons are for transonic Mach numbers and include both attached and separate flows. In general, the wing-body codes gave better agreement with the experiment than did the isolated wing code but, because of the greater complexity of the geometry, were found to be considerably more expensive and less reliable
Ab-initio GMR and current-induced torques in Au/Cr multilayers
We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities times smaller
than typical ferromagnetic metal circuit switching densities.Comment: 8 pages, 6 figure
Продукты ограниченного протеолиза: подходы к обнаружению и диагностические возможности в оценке тяжести патологии при эндогенной интоксикации
ПРОДУКТЫ ОГРАНИЧЕННОГО ПРОТЕОЛИЗАПРОТЕИНАЗО-ИНГИБИТОРНАЯ СИСТЕМАОТРАВЛЕНИЕ /ДИАГН /ОСЛЭНДОГЕННАЯ ИНТОКСИКАЦИЯ /ДИАГН /ОСЛСРЕДНЕМОЛЕКУЛЯРНАЯ ПЕПТИДНАЯ ФРАКЦИЯПАТОЛОГИЧЕСКИЕ ПРОЦЕССЫЛАБОРАТОРНЫЕ МЕТОДЫ И ПРОЦЕДУРЫБЕЛКОВО-ПЕПТИДНЫЕ КОМПОНЕНТ
Simulation of Dimensionally Reduced SYM-Chern-Simons Theory
A supersymmetric formulation of a three-dimensional SYM-Chern-Simons theory
using light-cone quantization is presented, and the supercharges are calculated
in light-cone gauge. The theory is dimensionally reduced by requiring all
fields to be independent of the transverse dimension. The result is a
non-trivial two-dimensional supersymmetric theory with an adjoint scalar and an
adjoint fermion. We perform a numerical simulation of this SYM-Chern-Simons
theory in 1+1 dimensions using SDLCQ (Supersymmetric Discrete Light-Cone
Quantization). We find that the character of the bound states of this theory is
very different from previously considered two-dimensional supersymmetric gauge
theories. The low-energy bound states of this theory are very ``QCD-like.'' The
wave functions of some of the low mass states have a striking valence
structure. We present the valence and sea parton structure functions of these
states. In addition, we identify BPS-like states which are almost independent
of the coupling. Their masses are proportional to their parton number in the
large-coupling limit.Comment: 18pp. 7 figures, uses REVTe
Spin transfer in an antiferromagnet
An electrical current can transfer spin angular momentum to a ferromagnet.
This novel physical phenomenon, called spin transfer, offers unprecedented
spatial and temporal control over the magnetic state of a ferromagnet and has
tremendous potential in a broad range of technologies, including magnetic
memory and recording. Recently, it has been predicted that spin transfer is not
limited to ferromagnets, but can also occur in antiferromagnetic materials and
even be stronger under some conditions. In this paper we demonstrate transfer
of spin angular momentum across an interface between ferromagnetic and
antiferromagnetic metals. The spin transfer is mediated by an electrical
current of high density (~10^12 A/m^2) and revealed by variation in the
exchange bias at the ferromagnet/antiferromagnet interface. We find that,
depending on the polarity of the electrical current flowing across the
interface, the strength of the exchange bias can either increase or decrease.
This finding is explained by the theoretical prediction that a spin polarized
current generates a torque on magnetic moments in the antiferromagnet.
Current-mediated variation of exchange bias can be used to control the magnetic
state of spin-valve devices, e.g., in magnetic memory applications.Comment: 5 pages, 3 figure
Wave functions and properties of massive states in three-dimensional supersymmetric Yang-Mills theory
We apply supersymmetric discrete light-cone quantization (SDLCQ) to the study
of supersymmetric Yang-Mills theory on R x S^1 x S^1. One of the compact
directions is chosen to be light-like and the other to be space-like. Since the
SDLCQ regularization explicitly preserves supersymmetry, this theory is totally
finite, and thus we can solve for bound-state wave functions and masses
numerically without renormalizing. We present an overview of all the massive
states of this theory, and we see that the spectrum divides into two distinct
and disjoint sectors. In one sector the SDLCQ approximation is only valid up to
intermediate coupling. There we find a well defined and well behaved set of
states, and we present a detailed analysis of these states and their
properties. In the other sector, which contains a completely different set of
states, we present a much more limited analysis for strong coupling only. We
find that, while these state have a well defined spectrum, their masses grow
with the transverse momentum cutoff. We present an overview of these states and
their properties.Comment: RevTeX, 25 pages, 16 figure
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