5,377 research outputs found
Analog MOS integrated circuits
The goal was to design single-chip lowpass filters with constant group delay in the pass band and 60 dB minimum attenuation in the stop band. The desired 3 dB frequencies are (in Hertz) 2.5, 5, 10, 20, 40, 80, 160, and 320. A filter class that satisfies the constant delay (linear phase) requirement while providing quite a narrow transition band is the Bessel-Chebyshev filters. It was found that the 7th order Bessel-Chebyshev response satisfied the requirement of the filter
Quantum Holography
We propose to make use of quantum entanglement for extracting holographic
information about a remote 3-D object in a confined space which light enters,
but from which it cannot escape. Light scattered from the object is detected in
this confined space entirely without the benefit of spatial resolution. Quantum
holography offers this possibility by virtue of the fourth-order quantum
coherence inherent in entangled beams.Comment: 7 pages, submitted to Optics Expres
Reexamining the Racial Record of Abraham Lincoln
Since his death in 1865 Abraham Lincoln has been universally honored in black America. In many black homes and businesses, his photograph often hangs in honor next to the one of Martin Luther King Jr. But a new book by Ebony editor Lerone Bennett Jr. contends that Lincoln was a crude bigot who told demeaning darky jokes, had an unquenchable thirst for minstrel shows, consistently used the word nigger, and supported efforts to ship Negroes back to Africa.
As Jack E. White pointed out in a recent Time magazine article, this book largely has been ignored by the mainstream press. The book was not reviewed in The Washington Post, The New Yorker, The Chicago Tribune, or USA Today.
JBHE [Journal of Blacks in Higher Education] asked a group of leading Lincoln scholars for their opinions of the Bennett book and the controversy surrounding its publication. Here are the replies
Spectrum of stochastic evolution operators: Local matrix representation approach
A matrix representation of the evolution operator associated with a nonlinear
stochastic flow with additive noise is used to compute its spectrum. In the
weak noise limit a perturbative expansion for the spectrum is formulated in
terms of local matrix representations of the evolution operator centered on
classical periodic orbits. The evaluation of perturbative corrections is easier
to implement in this framework than in the standard Feynman diagram
perturbation theory. The result are perturbative corrections to a stochastic
analog of the Gutzwiller semiclassical spectral determinant computed to several
orders beyond what has so far been attainable in stochastic and
quantum-mechanical applications.Comment: 7 pages, 2 figures, Third approach to a problem we considered in
chao-dyn/9807034 and chao-dyn/981100
Major loop reconstruction from switching of individual particles
Major hysteresis loops of groups of isolated 60 mm square garnet particles of a regular
two-dimensional array, have been measured magnetooptically. Individual loops for each particle
were measured, and the statistics of the distribution of coercivities and interaction fields was
determined. It is shown that from the measured coercivity distribution and calculated magnetostatic
interaction fields the major hysteresis loop can be reconstructed. The switching sequence, and the
major loop of an assembly of 535 particles were calculated numerically for two cases: first, when
calculating the magnetostatic interaction, the 25 particles were assumed to be isolated; second, the
major loop of the same 25 particles, embedded into a 939 square, was reconstructed taking into
account the interactions among all 81 particles. The numerically simulated major hysteresis loops
agree very well with the measured loops, demonstrating the reliability of numerical modeling
Role of Astrocytes in Neurovascular Coupling
Neural activity is intimately tied to blood flow in the brain. This coupling is specific enough in space and time that modern imaging methods use local hemodynamics as a measure of brain activity. In this review, we discuss recent evidence indicating that neuronal activity is coupled to local blood flow changes through an intermediary, the astrocyte. We highlight unresolved issues regarding the role of astrocytes and propose ways to address them using novel techniques. Our focus is on cellular level analysis in vivo, but we also relate mechanistic insights gained from ex vivo experiments to native tissue. We also review some strategies to harness advances in optical and genetic methods to study neurovascular coupling in the intact brain
HARM: A Numerical Scheme for General Relativistic Magnetohydrodynamics
We describe a conservative, shock-capturing scheme for evolving the equations
of general relativistic magnetohydrodynamics. The fluxes are calculated using
the Harten, Lax, and van Leer scheme. A variant of constrained transport,
proposed earlier by T\'oth, is used to maintain a divergence free magnetic
field. Only the covariant form of the metric in a coordinate basis is required
to specify the geometry. We describe code performance on a full suite of test
problems in both special and general relativity. On smooth flows we show that
it converges at second order. We conclude by showing some results from the
evolution of a magnetized torus near a rotating black hole.Comment: 38 pages, 18 figures, submitted to Ap
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