2,548 research outputs found
Confinement of Spin and Charge in High-Temperature Superconductors
By exploiting the internal gauge-invariance intrinsic to a spin-charge
separated electron, we show that such degrees of freedom must be confined in
two-dimensional superconductors experiencing strong inter-electron repulsion.
We also demonstrate that incipient confinement in the normal state can prevent
chiral spin-fluctuations from destroying the cross-over between strange and
psuedo-gap regimes in under-doped high-temperature superconductors. Last, we
suggest that the negative Hall anomaly observed in these materials is connected
with this confinement effect.Comment: 12 pages, 1 postscript figure, to appear in PRB (RC), May 199
Defective Vortex Lattices in Layered Superconductors with Point Pins at the Extreme Type-II Limit
The mixed phase of layered superconductors with no magnetic screening is
studied through a partial duality analysis of the corresponding frustrated XY
model in the presence of weak random point pins. Isolated layers exhibit a
defective vortex lattice at low temperature that is phase coherent.
Sufficiently weak Josephson coupling between adjacent layers results in an
entangled vortex solid that exhibits weak superconductivity across layers. The
corresponding vortex liquid state shows an inverted specific heat anomaly that
we propose accounts for that seen in YBCO. A three-dimensional vortex lattice
with dislocations occurs at stronger coupling. This crossover sheds light on
the apparent discrepancy concerning the observation of a vortex-glass phase in
recent Monte Carlo simulations of the same XY model.Comment: 4 pages, 1 figure. To appear in PRB, rapid communicatio
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Maximizing the Strength of Fused-Deposition ABS Plastic Parts
Fused-Deposition (FD) creates parts using robotic extrusion of set.D.i-liquid .polymer
fiber, which molecularly bonds with neighboring fibers via thermal-dlffuslo.n bonding. T~e
strength ofthe. part depends on the bulk polymer strength, themesostructure ~flber layout, vOid
geom~try, extent of fiber bonding), and thefiber-t~-fiber ~ond strength. The ~nfluence of these
factors on the mechanical strength of FD-ABS.plasttc parts IS reported.along with the.FD process
variable settingsfor maximum strength. Substantial increases in transverse strength are achieved
at the optirnal settings and additional increases can be achieved by post..fabrication annealing.
Keywords: Stratasys, fused-deposition, ABSplastic, functional parts, strength, mesostructure, polymer diffusion.Mechanical Engineerin
Theory for Decoupling in High-T_c Superconductors from an Analysis of the Layered XY Model with Frustration
The nature of decoupling in the mixed phase of extremely type-II layered
superconductors is studied theoretically through a duality transformation of
the layered XY model with frustration. In the limit of weak coupling, we
generally find that the Josephson effect is absent if and only if the phase
correlations within isolated layers are short range. In the case specific to
uniform frustration, we notably identify a decoupled pancake vortex liquid
phase that is bounded by first-order and second-order decoupling lines in the
magnetic field vs. temperature plane. These transitions potentially account for
the flux-lattice melting and for the flux-lattice depinning that is observed in
clean high-temperature superconductors.Comment: 11 pgs. of Plain TeX, 1 postscript fig., based on a talk given at the
VORTEX Euroconference held in Heraklion, Crete, Sept. 199
Genomic Evolution of Two Acinetobacter baumannii Clinical Strains from ST-2 Clones Isolated in 2000 and 2010 (ST-2_clon_2000 and ST-2_clon_2010)
Acinetobacter baumannii is a successful nosocomial pathogen due to its ability to persist in hospital environments by acquiring
mobile elements such as transposons, plasmids, and phages. In this study, we compared two genomes of A. baumannii clinical
strains isolated in 2000 (ST-2_clon_2000) and 2010 (ST-2_clon_2010) from GenBank project PRJNA308422
Low Temperature Measurements by Infrared Spectroscopy in CoFeO Ceramic
In this paper results of new far-infrared and middle-infrared measurements
(wavenumber range of 4000cm-1 - 100cm-1) in the range of the temperature from
300K to 8K of the CoFe2O4 ceramic are presented. The bands positions and their
shapes are the same in the wide temperature range. The quality of the sample
was investigated by X-ray, EDS and EPMA studies. The CoFe2O4 reveals the cubic
structure (Fd-3m) in the temperature range from 85K to 360 K without any traces
of distortion. On the current level of knowledge the polycrystalline CoFe2O4
does not exhibit phase transition in the temperature range from 8 K to 300 K.Comment: 10 pages, 6 figure
A lattice estimate of the g_{D^* D pi} coupling
We present the results of the first direct determination of the g_{D^* D pi}
coupling using lattice QCD. From our simulations in the quenched approximation,
we obtain g_{D^* D pi} = 18.8 +/- 2.3^{+1.1}_{-2.0} and hat(g) = 0.67 +/-
0.08^{+0.04}_{-0.06}. It is in agreement with a recent experimental result from
CLEO.Comment: Lattice2002(heavyquark), 3 pages, 3 figure
Quantized Skyrmion Fields in 2+1 Dimensions
A fully quantized field theory is developped for the skyrmion topological
excitations of the O(3) symmetric CP-Nonlinear Sigma Model in 2+1D. The
method allows for the obtainment of arbitrary correlation functions of quantum
skyrmion fields. The two-point function is evaluated in three different
situations: a) the pure theory; b) the case when it is coupled to fermions
which are otherwise non-interacting and c) the case when an electromagnetic
interaction among the fermions is introduced. The quantum skyrmion mass is
explicitly obtained in each case from the large distance behavior of the
two-point function and the skyrmion statistics is inferred from an analysis of
the phase of this function. The ratio between the quantum and classical
skyrmion masses is obtained, confirming the tendency, observed in semiclassical
calculations, that quantum effects will decrease the skyrmion mass. A brief
discussion of asymptotic skyrmion states, based on the short distance behavior
of the two-point function, is also presented.Comment: Accepted for Physical Review
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