824 research outputs found
High voltage electrical insulation coating for refractory materials
Formula and process have been developed for coating refractory metal surfaces with high voltage electrical insulation for use at temperatures to 600 C. Coatings were specifically developed as an insulation for the surface of a perforated, molybdenum, ion-accelerator grid, but are not limited to this application
Method for fiberizing ceramic materials Patent
Process for fiberizing ceramic materials with high fusion temperatures and tensile strengt
Quantum dynamics, dissipation, and asymmetry effects in quantum dot arrays
We study the role of dissipation and structural defects on the time evolution
of quantum dot arrays with mobile charges under external driving fields. These
structures, proposed as quantum dot cellular automata, exhibit interesting
quantum dynamics which we describe in terms of equations of motion for the
density matrix. Using an open system approach, we study the role of asymmetries
and the microscopic electron-phonon interaction on the general dynamical
behavior of the charge distribution (polarization) of such systems. We find
that the system response to the driving field is improved at low temperatures
(and/or weak phonon coupling), before deteriorating as temperature and
asymmetry increase. In addition to the study of the time evolution of
polarization, we explore the linear entropy of the system in order to gain
further insights into the competition between coherent evolution and
dissipative processes.Comment: 11pages,9 figures(eps), submitted to PR
Bound States and Threshold Resonances in Quantum Wires with Circular Bends
We study the solutions to the wave equation in a two-dimensional tube of unit
width comprised of two straight regions connected by a region of constant
curvature. We introduce a numerical method which permits high accuracy at high
curvature. We determine the bound state energies as well as the transmission
and reflection matrices, and and focus on the nature of
the resonances which occur in the vicinity of channel thresholds. We explore
the dependence of these solutions on the curvature of the tube and angle of the
bend and discuss several limiting cases where our numerical results confirm
analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures
include
Two-Bit Gates are Universal for Quantum Computation
A proof is given, which relies on the commutator algebra of the unitary Lie
groups, that quantum gates operating on just two bits at a time are sufficient
to construct a general quantum circuit. The best previous result had shown the
universality of three-bit gates, by analogy to the universality of the Toffoli
three-bit gate of classical reversible computing. Two-bit quantum gates may be
implemented by magnetic resonance operations applied to a pair of electronic or
nuclear spins. A ``gearbox quantum computer'' proposed here, based on the
principles of atomic force microscopy, would permit the operation of such
two-bit gates in a physical system with very long phase breaking (i.e., quantum
phase coherence) times. Simpler versions of the gearbox computer could be used
to do experiments on Einstein-Podolsky-Rosen states and related entangled
quantum states.Comment: 21 pages, REVTeX 3.0, two .ps figures available from author upon
reques
Local IL-13 gene transfer prior to immune-complex arthritis inhibits chondrocyte death and matrix-metalloproteinase-mediated cartilage matrix degradation despite enhanced joint inflammation
During immune-complex-mediated arthritis (ICA), severe cartilage destruction is mediated by Fcγ receptors (FcγRs) (mainly FcγRI), cytokines (e.g. IL-1), and enzymes (matrix metalloproteinases (MMPs)). IL-13, a T helper 2 (Th2) cytokine abundantly found in synovial fluid of patients with rheumatoid arthritis, has been shown to reduce joint inflammation and bone destruction during experimental arthritis. However, the effect on severe cartilage destruction has not been studied in detail. We have now investigated the role of IL-13 in chondrocyte death and MMP-mediated cartilage damage during ICA. IL-13 was locally overexpressed in knee joints after injection of an adenovirus encoding IL-13 (AxCAhIL-13), 1 day before the onset of arthritis; injection of AxCANI (an empty adenoviral construct) was used as a control. IL-13 significantly increased the amount of inflammatory cells in the synovial lining and the joint cavity, by 30% to 60% at day 3 after the onset of ICA. Despite the enhanced inflammatory response, chondrocyte death was diminished by two-thirds at days 3 and 7. The mRNA level of FcγRI, a receptor shown to be crucial in the induction of chondrocyte death, was significantly down-regulated in synovium. Furthermore, MMP-mediated cartilage damage, measured as neoepitope (VDIPEN) expression using immunolocalization, was halved. In contrast, mRNA levels of MMP-3, -9, -12, and -13 were significantly higher and IL-1 protein, which induces production of latent MMPs, was increased fivefold by IL-13. This study demonstrates that IL-13 overexpression during ICA diminished both chondrocyte death and MMP-mediated VDIPEN expression, even though joint inflammation was enhanced
Bias-voltage dependence of the magneto-resistance in ballistic vacuum tunneling: Theory and application to planar Co(0001) junctions
Motivated by first-principles results for jellium and by surface-barrier
shapes that are typically used in electron spectroscopies, the bias voltage in
ballistic vacuum tunneling is treated in a heuristic manner. The presented
approach leads in particular to a parameterization of the tunnel-barrier shape,
while retaining a first-principles description of the electrodes. The proposed
tunnel barriers are applied to Co(0001) planar tunnel junctions. Besides
discussing main aspects of the present scheme, we focus in particular on the
absence of the zero-bias anomaly in vacuum tunneling.Comment: 19 pages with 8 figure
Two-electron quantum dots as scalable qubits
We show that two electrons confined in a square semiconductor quantum dot
have two isolated low-lying energy eigenstates, which have the potential to
form the basis of scalable computing elements (qubits). Initialisation,
one-qubit and two-qubit universal gates, and readout are performed using
electrostatic gates and magnetic fields. Two-qubit transformations are
performed via the Coulomb interaction between electrons on adjacent dots.
Choice of initial states and subsequent asymmetric tuning of the tunnelling
energy parameters on adjacent dots control the effect of this interaction.Comment: Revised version, accepted by PR
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