66,462 research outputs found
Dynamic transition and Shapiro-step melting in a frustrated Josephson-junction array
We consider a two-dimensional fully frustrated Josephson-junction array
driven by combined direct and alternating currents. Interplay between the mode
locking phenomenon, manifested by giant Shapiro steps in the current-voltage
characteristics, and the dynamic phase transition is investigated at finite
temperatures. Melting of Shapiro steps due to thermal fluctuations is shown to
be accompanied by the dynamic phase transition, the universality class of which
is also discussed
Affine maps of density matrices
For quantum systems described by finite matrices, linear and affine maps of
matrices are shown to provide equivalent descriptions of evolution of density
matrices for a subsystem caused by unitary Hamiltonian evolution in a larger
system; an affine map can be replaced by a linear map, and a linear map can be
replaced by an affine map. There may be significant advantage in using an
affine map. The linear map is generally not completely positive, but the linear
part of an equivalent affine map can be chosen to be completely positive and
related in the simplest possible way to the unitary Hamiltonian evolution in
the larger system.Comment: 4 pages, title changed, sentence added, reference update
Capacitively coupled Josephson-junction chains: straight and slanted coupling
Two chains of ultrasmall Josephson junctions, coupled capacitively with each
other in the two different ways, straight and slanted coupling, are considered.
As the coupling capacitance increases, regardless of the coupling scheme, the
transport of particle-hole pairs in the system is found to drive the
quantum-phase transition at zero temperature, which is a
insulator-to-superfluid transition of the particle-hole pairs and belongs to
the Berezinskii-Kosterlitz-Thouless universal class. The different underlying
transport mechanisms for the two coupling schemes are reflected in the
difference between the transition points.Comment: REVTeX + 7 EPS figures, detailed version of cond-mat/980219
Cotunneling Transport and Quantum Phase Transitions in Coupled Josephson-Junction Chains with Charge Frustration
We investigate the quantum phase transitions in two capacitively coupled
chains of ultra-small Josephson-junctions, with emphasis on the external charge
effects. The particle-hole symmetry of the system is broken by the gate voltage
applied to each superconducting island, and the resulting induced charge
introduces frustration to the system. Near the maximal-frustration line, where
the system is transformed into a spin-1/2 Heisenberg antiferromagnetic chain,
cotunneling of the particles along the two chains is shown to play a major role
in the transport and to drive a quantum phase transition out of the
charge-density wave insulator, as the Josephson-coupling energy is increased.
We also argue briefly that slightly off the symmetry line, the universality
class of the transition remains the same as that right on the line, still being
driven by the particle-hole pairs.Comment: Final version accepted to Phys. Rev. Lett. (Longer version is
available from http://ctp.snu.ac.kr/~choims/
Classification of bi-qutrit positive partial transpose entangled edge states by their ranks
We construct PPT entangled edge states with maximal ranks, to
complete the classification of PPT entangled edge states by their
types. The ranks of the states and their partial transposes are 8 and 6,
respectively. These examples also disprove claims in the literature.Comment: correct the title to avoid an acronym, correct few text
Partial scaling transform of multiqubit states as a criterion of separability
The partial scaling transform of the density matrix for multiqubit states is
introduced to detect entanglement of quantum states. The transform contains
partial transposition as a special case. The scaling transform corresponds to
partial time scaling of subsystem (or partial Planck's constant scaling) which
was used to formulate recently separability criterion for continous variables.A
measure of entanglement which is a generalization of negativity measure is
introduced being based on tomographic probability description of spin states.Comment: 16 pages, 5 figures, submitted to J. Phys. A: Math. Ge
Intersecting Brane World from Type I Compactification
We elaborate that general intersecting brane models on orbifolds are obtained
from type I string compactifications and their T-duals. Symmetry breaking and
restoration occur via recombination and parallel separation of branes,
preserving supersymmetry. The Ramond-Ramond tadpole cancelation and the toron
quantization constrain the spectrum as a branching of the adjoints of SO(32),
up to orbifold projections. Since the recombination changes the gauge coupling,
the single gauge coupling of type I could give rise to different coupling below
the unification scale. This is due to the nonlocal properties of the
Dirac-Born-Infeld action. The weak mixing angle sin^2 theta_W = 3/8 is
naturally explained by embedding the quantum numbers to those of SO(10).Comment: 31 pages, 5 figure
Two-Electron Linear Intersubband Light Absorption in a Biased Quantum Well
We point out a novel manifestation of many-body correlations in the linear
optical response of electrons confined in a quantum well. Namely, we
demonstrate that along with conventional absorption peak at frequency close to
intersubband energy, there exists an additional peak at double frequency. This
new peak is solely due to electron-electron interactions, and can be understood
as excitation of two electrons by a single photon. The actual peak lineshape is
comprised of a sharp feature, due to excitation of pairs of intersubband
plasmons, on top of a broader band due to absorption by two single-particle
excitations. The two-plasmon contribution allows to infer intersubband plasmon
dispersion from linear absorption experiments.Comment: 4 pages, 3 figures; published versio
Dynamic model of fiber bundles
A realistic continuous-time dynamics for fiber bundles is introduced and
studied both analytically and numerically. The equation of motion reproduces
known stationary-state results in the deterministic limit while the system
under non-vanishing stress always breaks down in the presence of noise.
Revealed in particular is the characteristic time evolution that the system
tends to resist the stress for considerable time, followed by sudden complete
rupture. The critical stress beyond which the complete rupture emerges is also
obtained
Targeting kidney mesangium by nanoparticles of defined size
Nanoparticles are being investigated for numerous medical applications and are showing potential as an emerging class of carriers for drug delivery. Investigations on how the physicochemical properties (e.g., size, surface charge, shape, and density of targeting ligands) of nanoparticles enable their ability to overcome biological barriers and reach designated cellular destinations in sufficient amounts to elicit biological efficacy are of interest. Despite proven success in nanoparticle accumulation at cellular locations and occurrence of downstream therapeutic effects (e.g., target gene inhibition) in a selected few organs such as tumor and liver, reports on effective delivery of engineered nanoparticles to other organs still remain scarce. Here, we show that nanoparticles of ~75 ± 25-nm diameters target the mesangium of the kidney. These data show the effects of particle diameter on targeting the mesangium of the kidney. Because many diseases originate from this area of the kidney, our findings establish design criteria for constructing nanoparticle-based therapeutics for targeting diseases that involve the mesangium of the kidney
- …