344 research outputs found
Entanglement in a Time-Dependent Coupled XY Spin Chain in an External Magnetic Field
We consider an infinite one dimensional anisotropic XY spin chain with a
nearest neighbor time-dependent Heisenberg coupling J(t) between the spins in
presence of a time-dependent magnetic field h(t). We discuss a general solution
for the system and present an exact solution for particular choice of J and h
of practical interest. We investigate the dynamics of entanglement for
different degrees of anisotropy of the system and at both zero and finite
temperatures. We find that the time evolution of entanglement in the system
show non-ergodic and critical behavior at zero and finite temperatures and
different degrees of anisotropy. The asymptotic behavior of entanglement at the
infinite time limit at zero temperature and constant J and h depends only the
parameter lambda=J/h rather than the individual values of J and h for all
degrees of anisotropy but changes for nonzero temperature. Furthermore, the
asymptotic behavior is very sensitive to the initial values of J and h and for
particular choices we may create finite asymptotic entanglement regardless of
the final values of J and h. The persistence of quantum effects in the system
as it evolves and as the temperature is raised is studied by monitoring the
entanglement. We find that the quantum effects dominates within certain regions
of the kT-lambda space that vary significantly depending on the degree of the
anisotropy of the system. Particularly, the quantum effects in the Ising model
case persists in the vicinity of both its critical phase transition point and
zero temperature as it evolves in time. Moreover, the interplay between the
different system parameters to tune and control the entanglement evolution is
explored.Comment: 33 pages, 17 figures; v3: Grammar errors and typos corrected, Figure
17(b) update
Bottle atom trapping configuration by optical dipole forces
AbstractThe bottle beam configuration is a light field created by the interference of a pair of Laguerre–Gauss light beams with zero orbital angular momentum. In this work we show the theoretical study of the bottle beam as well as the use of this beam for the creation of a novel atom optical dipole trap namely the bottle atom trap. In such a trap the resulting dark trapping region is three-dimensional and has a cylindrical symmetry. These promising results show that this trap is a nice candidate for trapping Bose–Einstein condensates and may serve as an optical tweezer mechanism potentially useful for trapping micron-sized dielectric particles
Nuclear-induced time evolution of entanglement of two-electron spins in anisotropically coupled quantum dot
We study the time evolution of entanglement of two spins in anisotropically
coupled quantum dot interacting with the unpolarized nuclear spins environment.
We assume that the exchange coupling strength in the z-direction is
different from the lateral one . We observe that the entanglement decays
as a result of the coupling to the nuclear environment and reaches a saturation
value, which depends on the value of the exchange interaction difference between the two spins and the strength of the applied external
magnetic field. We find that the entanglement exhibits a critical behavior
controlled by the competition between the exchange interaction and the
external magnetic field. The entanglement shows a quasi-symmetric behavior
above and below a critical value of the exchange interaction. It becomes more
symmetric as the external magnetic field increases. The entanglement reaches a
large saturation value, close to unity, when the exchange interaction is far
above or below its critical value and a small one as it closely approaches the
critical value. Furthermore, we find that the decay rate profile of
entanglement is linear when the exchange interaction is much higher or lower
than the critical value but converts to a power law and finally to a Gaussian
as the critical value is approached from both directions. The dynamics of
entanglement is found to be independent of the exchange interaction for
isotropically coupled quantum dot.Comment: 24 pages and 7 figures. v3: major change
De-interleaving of Radar Pulses for EW Receivers with an ELINT Application
De-interleaving is a critical function in Electronic Warfare (EW) that has not received much attention in the literature regarding on-line Electronic Intelligence (ELINT) application. In ELINT, on-line analysis is important in order to allow for efficient data collection and for support of operational decisions. This dissertation proposed a de-interleaving solution for use with ELINT/Electronic-Support-Measures (ESM) receivers for purposes of ELINT with on-line application. The proposed solution does not require complex integration with existing EW systems or modifications to their sub-systems. Before proposing the solution, on-line de-interleaving algorithms were surveyed. Density-based spatial clustering of applications with noise (DBSCAN) is a clustering algorithm that has not been used before in de-interleaving; in this dissertation, it has proved to be effective. DBSCAN was thus selected as a component of the proposed de-interleaving solution due to its advantages over other surveyed algorithms. The proposed solution relies primarily on the parameters of Angle of Arrival (AOA), Radio Frequency (RF), and Time of Arrival (TOA). The time parameter was utilized in resolving RF agility. The solution is a system that is composed of different building blocks. The solution handles complex radar environments that include agility in RF, Pulse Width (PW), and Pulse Repetition Interval (PRI)
Numerical Analyses of Heat Transfer and Fluid Flow in a Corrugated Duct
Steady laminar two-dimensional and forced convection in a corrugated duct with different configurations and flow conditions were investigated numerically. The full Naiver-Stokes and energy equation were considered. These equations have been solved using the finite element method. Flow-fields were obtained for various flow conditions. The flow patterns and reattachment indicate a firm agreement with those in the literature. It has been noticed that the maximum value of the local Nusselt number occurs near the reattachment point. The 45-to-50-degree corrugation angle provides the heights Nusselt number by 1 to 2 percent and the lowest pressure drop compared to larger or smaller angles. The influence of the Prandtl number on the thermal performance was considered, as the Prandtl number increases the average Nusselt number grows. The enhancing performance of heat transfer rate is more effective for P
Revisiting Major Discoveries in Linguistic Geometry with Mosaic Reasoning
AbstractIn discovering the nature of the Primary Language of the human brain introduced by J. von Neumann, two components have been investigated. The first component is Linguistic Geometry (LG), the algorithm of optimizing war-fighting strategies. LG's universal applicability in various domains and its power in generating human-like strategies suggested that LG should be a component of the Primary Language. The second component is the algorithm of inventing new algorithms. This paper researches the role of mosaic reasoning, a component of the Algorithm of Discovery, in obtaining the key results in LG such as the algorithms for generating trajectories and zones
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