173 research outputs found
Prospectus, January 13, 1997
https://spark.parkland.edu/prospectus_1997/1000/thumbnail.jp
On the Stereochemistry of the Cations in the Doping Block of Superconducting Copper-Oxides
Metal-oxygen complexes containing Cu,- Tl-, Hg-, Bi- and Pb-cations are
electronically active in superconducting copper-oxides by stabilizing single
phases with enhanced , whereas other metal-oxygen complexes deteriorate
copper-oxide superconductivity. Cu, Tl, Hg, Bi, Pb in their actual oxidation
states are closed shell or inert pair ions. Their electronic
configurations have a strong tendency to polarize the oxygen environment. The
closed shell ions with low lying
excitations form linear complexes through hybridization polarizing
the apical oxygens. Comparatively low excitation energies
distinguish from other closed shell
ions deteriorating copper-oxide superconductivity, {\it e.g.} .Comment: 5 pages, uses REVTEX. To be published in: J. Superconductivity, Proc.
Int. Workshop on "Phase Separation, Electronic Inhomogenities and Related
Mechanisms for High T_c Superconductors", Erice (Sicily) 9-15 July 199
Band Gaps for Atoms in Light based Waveguides
The energy spectrum for a system of atoms in a periodic potential can exhibit
a gap in the band structure. We describe a system in which a laser is used to
produce a mechanical potential for the atoms, and a standing wave light field
is used to shift the atomic levels using the Autler-Townes effect, which
produces a periodic potential. The band structure for atoms guided by a hollow
optical fiber waveguide is calculated in three dimensions with quantised
external motion. The size of the band gap is controlled by the light guided by
the fiber. This variable band structure may allow the construction of devices
which can cool atoms. The major limitation on this device would be the
spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through
http://online.anu.edu.au/Physics/papers/atom.htm
L-type calcium channel blockers and substance P induce angiogenesis of cortical vessels associated with beta-amyloid plaques in an Alzheimer mouse model
AbstractIt is well established that L-type calcium channels (LTCCs) are expressed in astroglia. However, their functional role is still speculative, especially under pathologic conditions. We recently showed that the α1 subunit-like immunoreactivity of the CaV1.2 channel is strongly expressed in reactive astrocytes around beta-amyloid plaques in 11-month-old Alzheimer transgenic (tg) mice with the amyloid precursor protein London and Swedish mutations. The aim of the present study was to examine the cellular expression of all LTCC subunits around beta-amyloid plaques by in situ hybridization using 35S-labeled oligonucleotides. Our data show that messenger RNAs (mRNAs) of the LTCC CaV1.2 α1 subunit as well as all auxiliary β and α2δ subunits, except α2δ-4, were expressed in the hippocampus of age-matched wild-type mice. It was unexpected to see, that cells directly located in the plaque core in the cortex expressed mRNAs for CaV1.2 α1, β2, β4, and α2δ-1, whereas no expression was detected in the halo. Furthermore, cells in the plaque core also expressed preprotachykinin-A mRNA, the precursor for substance P. By means of confocal microscopy, we demonstrated that collagen-IV-stained brain vessels in the cortex were associated with the plaque core and were immunoreactive for substance P. In cortical organotypic brain slices of adult Alzheimer mice, we could demonstrate that LTCC blockers increased angiogenesis, which was further potentiated by substance P. In conclusion, our data show that brain vessels associated with beta-amyloid plaques express substance P and an LTCC and may play a role in angiogenesis
Extraction of lateral eigenmode properties in thin film bulk acoustic wave resonator from interferometric measurements
A heterodyne laser interferometer is used to study acoustic wave fields excited in a 1.8 GHz AlN thin film bulk acoustic waveresonator. The electrical response of the resonator exhibits a strong thickness resonance onto which spurious modes, caused by lateral standing plate waves, are superposed. Optical interferometermeasurements are used to extract dispersion curves of the laterally propagating waves responsible for the spurious responses. A discrete eigenmode spectrum due to the finite lateral dimensions of the resonator is observed. An equivalent circuit model for a multimode resonator is fitted to the mechanical resonator response extracted along a single curve in the dispersion diagram, and is used to determine properties, such as Q-values, of the individual lateral eigenmodes.Measuredwave field images, extracted dispersion curves, and the eigenmode spectrum with the model fitting results are presented.Peer reviewe
An Atom Laser Based on Raman Transitions
In this paper we present an atom laser scheme using a Raman transition for
the output coupling of atoms. A beam of thermal atoms (bosons) in a metastable
atomic state are pumped into a multimode atomic cavity. This cavity is
coupled through spontaneous emission to a single mode of another cavity for the
ground atomic state, . Above a certain threshold pumping rate a large
number of atoms, , builds up in this single quantum state and transitions
to the ground state of the cavity become enhanced by a factor .
Atoms in this state are then coupled to the outside of the cavity with a Raman
transition. This changes the internal state of the atom and imparts a momentum
kick, allowing the atoms to leave the system.Comment: 8 pages, 4 postscript figures, uses RevTex, home page at
http://online.anu.edu.au/Physics/Welcome.html (Some aspects of the exact
physical model have changed from original version. Other general improvements
included
Anomalous diffusion and Tsallis statistics in an optical lattice
We point out a connection between anomalous quantum transport in an optical
lattice and Tsallis' generalized thermostatistics. Specifically, we show that
the momentum equation for the semiclassical Wigner function that describes
atomic motion in the optical potential, belongs to a class of transport
equations recently studied by Borland [PLA 245, 67 (1998)]. The important
property of these ordinary linear Fokker--Planck equations is that their
stationary solutions are exactly given by Tsallis distributions. Dissipative
optical lattices are therefore new systems in which Tsallis statistics can be
experimentally studied.Comment: 4 pages, 1 figur
Cooling of a single atom in an optical trap inside a resonator
We present detailed discussions of cooling and trapping mechanisms for an
atom in an optical trap inside an optical cavity, as relevant to recent
experiments. The interference pattern of cavity QED and trapping fields in
space makes the trapping wells distinguishable from one another. This adds
considerable flexibility to creating effective trapping and cooling conditions
and to detection possibilities. Friction and diffusion coefficients are
calculated in and beyond the low excitation limit and full 3-D simulations of
the quasiclassical motion of a Cs atom are performed.Comment: One more figure and one more autho
Guiding Neutral Atoms with a Wire
We demonstrate guiding of cold neutral atoms along a current carrying wire.
Atoms either move in Kepler-like orbits around the wire or are guided in a
potential tube on the side of the wire which is created by applying an
additional homogeneous bias field. These atom guides are very versatile and
promising for applications in atom optics.Comment: 4 pages, 6 figures, submitted to PR
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