151,645 research outputs found
Nature of the Quantum Phase Transition in Quantum Compass Model
In this work, we show that the quantum compass model on an square lattice can
be mapped to a fermionic model with local density interaction. We introduce a
mean-field approximation where the most important fluctuations, those
perpendicular to the ordering direction, are taken into account exactly. It is
found that the quantum phase transition point at marks a first order
phase transition. We also show that the mean field result is robust against the
remaining fluctuation corrections up to the second order.Comment: 7 pages, 10 fig
A cost-effective intelligent robotic system with dual-arm dexterous coordination and real-time vision
Dexterous coordination of manipulators based on the use of redundant degrees of freedom, multiple sensors, and built-in robot intelligence represents a critical breakthrough in development of advanced manufacturing technology. A cost-effective approach for achieving this new generation of robotics has been made possible by the unprecedented growth of the latest microcomputer and network systems. The resulting flexible automation offers the opportunity to improve the product quality, increase the reliability of the manufacturing process, and augment the production procedures for optimizing the utilization of the robotic system. Moreover, the Advanced Robotic System (ARS) is modular in design and can be upgraded by closely following technological advancements as they occur in various fields. This approach to manufacturing automation enhances the financial justification and ensures the long-term profitability and most efficient implementation of robotic technology. The new system also addresses a broad spectrum of manufacturing demand and has the potential to address both complex jobs as well as highly labor-intensive tasks. The ARS prototype employs the decomposed optimization technique in spatial planning. This technique is implemented to the framework of the sensor-actuator network to establish the general-purpose geometric reasoning system. The development computer system is a multiple microcomputer network system, which provides the architecture for executing the modular network computing algorithms. The knowledge-based approach used in both the robot vision subsystem and the manipulation control subsystems results in the real-time image processing vision-based capability. The vision-based task environment analysis capability and the responsive motion capability are under the command of the local intelligence centers. An array of ultrasonic, proximity, and optoelectronic sensors is used for path planning. The ARS currently has 18 degrees of freedom made up by two articulated arms, one movable robot head, and two charged coupled device (CCD) cameras for producing the stereoscopic views, and articulated cylindrical-type lower body, and an optional mobile base. A functional prototype is demonstrated
A Note on Doubly Warped Product Contact CR-Submanifolds in trans-Sasakian Manifolds
Warped product CR-submanifolds in Kaehlerian manifolds were intensively
studied only since 2001 after the impulse given by B.Y. Chen. Immediately
after, another line of research, similar to that concerning Sasakian geometry
as the odd dimensional version of Kaehlerian geometry, was developed, namely
warped product contact CR-submanifolds in Sasakian manifolds. In this note we
proved that there exists no proper doubly warped product contact
CR-submanifolds in trans-Sasakian manifolds.Comment: 5 Latex page
Radio Frequency Spectroscopy of Trapped Fermi Gases with Population Imbalance
Motivated by recent experiments, we address, in a fully self consistent
fashion, the behavior and evolution of radio frequency (RF) spectra as
temperature and polarization are varied in population imbalanced Fermi gases.
We discuss a series of scenarios for the experimentally observed zero
temperature pseudogap phase and show how present and future RF experiments may
help in its elucidation. We conclude that the MIT experiments at the lowest
may well reflect ground state properties, but take issue with their claim that
the pairing gap survives up to temperatures of the order of the degeneracy
temperature at unitarity.Comment: 4 page, 3 figures, submitted to PRA Rapi
Population-only decay map for n-qubit n-partite inseparability detection
We introduce a new positive linear map for a single qubit. This map is a
decay only in populations of a single-qubit density operator. It is shown that
an n-fold product of this map may be used for a detection of n-partite
inseparability of an n-qubit density operator (i.e., detection of impossibility
of representing a density operator in the form of a convex combination of
products of density operators of individual qubits). This product map is also
investigated in relation to a variant of the entanglement detection method
mentioned by Laskowski and Zukowski.Comment: 5 pages, 1 figure, RevTex4, v2 minor grammatical changes, typos
correcte
Constructing entanglement witnesses for infinite-dimensional systems
It is shown that, every entangled state in an infinite-dimensional composite
system has a simple entanglement witness of the form with
a nonnegative number and a finite rank self-adjoint operator. We also
provide two methods of constructing entanglement witness and apply them to
obtain some entangled states that cannot be detected by the PPT criterion and
the realignment criterion.Comment: 15 page
Stress-Energy Tensor Induced by Bulk Dirac Spinor in Randall-Sundrum Model
Motivated by the possible extension into a supersymmetric Randall-Sundrum
(RS) model, we investigate the properties of the vacuum expectation value (VEV)
of the stress-energy tensor for a quantized bulk Dirac spinor field in the RS
geometry and compare it with that for a real scalar field. This is carried out
via the Green function method based on first principles without invoking the
degeneracy factor, whose validity in a warp geometry is a priori unassured. In
addition, we investigate the local behavior of the Casimir energy near the two
branes. One salient feature we found is that the surface divergences near the
two branes have opposite signs. We argue that this is a generic feature of the
fermionic Casimir energy density due to its parity transformation in the fifth
dimension. Furthermore, we investigate the self-consistency of the RS metric
under the quantum correction due to the stress-energy tensor. It is shown that
the VEV of the stress-energy tensor and the classical one become comparable
near the visible brane if k ~ M ~ M_Pl (the requirement of no hierarchy
problem), where k is the curvature of the RS warped geometry and M the
5-dimensional Planck mass. In that case the self-consistency of RS model that
includes bulk fields is in doubt. If, however, k <~ M, then an approximate
self-consistency of the RS-type metric may still be satisfied.Comment: 7 pages with 2 figure
- …