9,499 research outputs found
Stochastic models for quality of service of component connectors
The intensifying need for scalable software has motivated modular development and using systems distributed over networks to implement large-scale applications. In Service-oriented Computing, distributed services are composed to provide large-scale services with a specific functionality. In this way, reusability of existing services can be increased. However, due to the heterogeneity of distributed software systems, software composition is not easy and requires additional mechanisms to impose some form of a coordination on a distributed software system. Besides functional correctness, a composed service must satisfy various quantitative requirements for its clients, which are generically called its quality of service (QoS). Particularly, it is tricky to obtain the overall QoS of a composed service even if the QoS information of its constituent distributed services is given. In this thesis, we propose Stochastic Reo to specify software composition with QoS aspects and its compositional semantic models. They are also used as intermediate models to generate their corresponding stochastic models for practical analysis. Based on this, we have implemented the tool Reo2MC. Using Reo2MC, we have modeled and analyzed an industrial software, the ASK system. Its analysis results provided the best cost-effective resource utilization and some suggestions to improve the performance of the system.UBL - phd migration 201
Simple scheme for expanding a polarization-entangled W state by adding one photon
We propose a simple scheme for expanding a polarization-entangled W state. By
mixing a single photon and one of the photons in an n-photon W state at a
polarization-dependent beam splitter (PDBS), we can obtain an (n+1)-photon W
state after post-selection. Our scheme also opens the door for generating
n-photon W states using single photons and linear optics.Comment: 3 pages, 2 figure
Generation of Three-Qubit Entangled W-State by Nonlinear Optical State Truncation
We propose an alternative scheme to generate W state via optical state
truncation using quantum scissors. In particular, these states may be generated
through three-mode optical state truncation in a Kerr nonlinear coupler. The
more general three-qubit state may be also produced if the system is driven by
external classical fields.Comment: 7 pages, 2 figur
The states of W-class as shared resources for perfect teleportation and superdense coding
As we know, the states of triqubit systems have two important classes:
GHZ-class and W-class.
In this paper, the states of W-class are considered for teleportation and
superdense coding, and are generalized to multi-particle systems. First we
describe two transformations of the shared resources for teleportation and
superdense coding, which allow many new protocols from some known ones for
that. As an application of these transformations, we obtain a sufficient and
necessary condition for a state of W-class being suitable for perfect
teleportation and superdense coding. As another application, we find that state
can be used to
transmit three classical bits by sending two qubits, which was considered to be
impossible by P. Agrawal and A. Pati [Phys. Rev. A to be published]. We
generalize the states of W-class to multi-qubit systems and multi-particle
systems with higher dimension. We propose two protocols for teleportation and
superdense coding by using W-states of multi-qubit systems that generalize the
protocols by using proposed by P. Agrawal and A. Pati. We obtain an
optimal way to partition some W-states of multi-qubit systems into two
subsystems, such that the entanglement between them achieves maximum value.Comment: 10 pages, critical comments and suggestions are welcom
Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures
We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.Comment: 4 pages, 5 figures, to be published in Phys. Rev. Let
Multiple Stellar Populations in the Globular Cluster omega Centauri as Tracers of a Merger Event
The discovery of the Sagittarius dwarf galaxy, which is being tidally
disrupted by and merging with the Milky Way, supports the view that the halo of
the Galaxy has been built up at least partially by the accretion of similar
dwarf systems. The Sagittarius dwarf contains several distinct populations of
stars, and includes M54 as its nucleus, which is the second most massive
globular cluster associated with the Milky Way. The most massive globular
cluster is omega Centauri, and here we report that omega Centauri also has
several distinct stellar populations, as traced by red-giant-branch stars. The
most metal-rich red-giant-branch stars are about 2 Gyr younger than the
dominant metal-poor component, indicating that omega Centauri was enriched over
this timescale. The presence of more than one epoch of star formation in a
globular cluster is quite surprising, and suggests that omega Centauri was once
part of a more massive system that merged with the Milky Way, as the
Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were
much more frequent in the early history of the Galaxy and omega Centauri
appears to be a relict of this era.Comment: 7 pages, 3 figures, Latex+nature.sty (included), To appear in
November 4th issue of Natur
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