23,803 research outputs found
Stoner-Wohlfart model applied to bicrystal magnetoresistance hysteresis
We calculate numerically the magnetization direction as function of magnetic
field in the Stoner-Wohlfart theory and are able to reproduce the shape of the
low-field magnetoresistance hysteresis observed in manganite grain boundary
junctions. Moreover, we show that it is necessary to include biaxial
magnetocrystalline anisotropy to fully describe the grain boundary
magnetoresistance in LaSrMnO/SrTiO bicrystal tunnel
junctions.Comment: 5 pages, 4 figure
Kinetics of nitric oxide formation and decomposition
Experiments on shock wave structure were conducted in the 12 inch shock tube facility, and it is shown that this work was motivated by the need for improved kinetics for the modeling of NO production in space shuttle flow fields. The experiments on shock structure involved simultaneous observations of pressure and temperature on the wall of the shock tube during reflection of normal shock waves in inert gases
Dyadic Green's Functions and Guided Surface Waves for a Surface Conductivity Model of Graphene
An exact solution is obtained for the electromagnetic field due to an
electric current in the presence of a surface conductivity model of graphene.
The graphene is represented by an infinitesimally-thin, local and isotropic
two-sided conductivity surface. The field is obtained in terms of dyadic
Green's functions represented as Sommerfeld integrals. The solution of
plane-wave reflection and transmission is presented, and surface wave
propagation along graphene is studied via the poles of the Sommerfeld
integrals. For isolated graphene characterized by complex surface conductivity,
a proper transverse-electric (TE) surface wave exists if and only if the
imaginary part of conductivity is positive (associated with interband
conductivity), and a proper transverse-magnetic (TM) surface wave exists when
the imaginary part of conductivity is negative (associated with intraband
conductivity). By tuning the chemical potential at infrared frequencies, the
sign of the imaginary part of conductivity can be varied, allowing for some
control over surface wave properties.Comment: 9 figure
Ion Drift Meter for Dynamics Explorer
The ion drift meter for Dynamics Explorer B is discussed. It measures two mutually perpendicular angles of arrival of thermal ions with respect to the sensor look directions. These angles lie in the vertical and horizontal planes and may be thought of as pitch and yaw in the conventional aerodynamic sense. The components of the ion drift velocity along vertical and horizontal axes through the spacecraft body are derived to first order from knowledge of the spacecraft velocity vector and more accurately with additional knowledge of the component of ion drift along the sensor look direction
Planar ion trap (retarding potential analyzer) experiment for atmosphere explorer
The retarding potential analyzer and drift meter were carried aboard all three Atmosphere Explorer spacecraft. These instruments measure the total thermal ion concentration and temperature, the bulk thermal ion velocity vector and some limited properties of the relative abundance of H(+), He(+), O(+) and molecular ions. These instruments functioned with no internal failures on all the spacecraft. On AE-E there existed some evidence for external surface contamination that damaged the integrity of the RPA sweep grids. This led to some difficulties in data reduction and interpretation that did not prove to be a disastrous problem. The AE-D spacecraft functioned for only a few months before it re-entered. During this time the satellite suffered from a nutation about the spin axis of about + or - 2 deg. This 2 deg modulation was superimposed upon the ion drift meter horizontal ion arrival angle output requiring the employment of filtering techniques to retrieve the real data
Kinetics of the reaction of nitric oxide with hydrogen
Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles
A theoretical investigation of the aerodynamics of slender wing-body combinations exhibiting leading-edge separation
Theoretical investigation of aerodynamics of slender wing-body combinations exhibiting leading edge separatio
Outsourcing and Volatility
While outsourcing of production from the U.S. to Mexico has been hailed in Mexico as a valuable engine of growth, recently there have been misgivings regarding its fickleness and volatility. This paper is among the first in the trade literature to study the second moment properties of outsourcing. We begin by documenting a new stylized fact: the maquiladora outsourcing industries in Mexico experience fluctuations in value added that are roughly twice as volatile as the corresponding industries in the U.S. A difference-in-difference method is extended to second moments to verify the statistical significance of this finding. We then develop a stochastic model of outsourcing with heterogeneous firms that can explain this volatility. The model employs two novel mechanisms: an extensive margin in outsourcing which responds endogenously to transmit shocks internationally, and translog preferences which modulate firm entry.
Gravity from the extension of spatial diffeomorphisms
The possibility of the extension of spatial diffeomorphisms to a larger
family of symmetries in a class of classical field theories is studied. The
generator of the additional local symmetry contains a quadratic kinetic term
and a potential term which can be a general (not necessarily local) functional
of the metric. From the perspective of the foundation of Einstein's gravity our
results are positive: The extended constraint algebra is either that of
Einstein's gravity, or ultralocal gravity. If our goal is a simple modification
of Einstein's gravity that for example makes it perturbatively renormalizable,
as has recently been suggested, then our results show that there is no such
theory within this class.Comment: 34 page
Basic linear algebra subprograms for FORTRAN usage
A package of 38 low level subprograms for many of the basic operations of numerical linear algebra is presented. The package is intended to be used with FORTRAN. The operations in the package are dot products, elementary vector operations, Givens transformations, vector copy and swap, vector norms, vector scaling, and the indices of components of largest magnitude. The subprograms and a test driver are available in portable FORTRAN. Versions of the subprograms are also provided in assembly language for the IBM 360/67, the CDC 6600 and CDC 7600, and the Univac 1108
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