31,738 research outputs found
Dynamical stability of entanglement between spin ensembles
We study the dynamical stability of the entanglement between the two spin
ensembles in the presence of an environment. For a comparative study, we
consider the two cases: a single spin ensemble, and two ensembles linearly
coupled to a bath, respectively. In both circumstances, we assume the validity
of the Markovian approximation for the bath. We examine the robustness of the
state by means of the growth of the linear entropy which gives a measure of the
purity of the system. We find out macroscopic entangled states of two spin
ensembles can stably exist in a common bath. This result may be very useful to
generate and detect macroscopic entanglement in a common noisy environment and
even a stable macroscopic memory.Comment: 4 pages, 1 figur
Opaque Service Virtualisation: A Practical Tool for Emulating Endpoint Systems
Large enterprise software systems make many complex interactions with other
services in their environment. Developing and testing for production-like
conditions is therefore a very challenging task. Current approaches include
emulation of dependent services using either explicit modelling or
record-and-replay approaches. Models require deep knowledge of the target
services while record-and-replay is limited in accuracy. Both face
developmental and scaling issues. We present a new technique that improves the
accuracy of record-and-replay approaches, without requiring prior knowledge of
the service protocols. The approach uses Multiple Sequence Alignment to derive
message prototypes from recorded system interactions and a scheme to match
incoming request messages against prototypes to generate response messages. We
use a modified Needleman-Wunsch algorithm for distance calculation during
message matching. Our approach has shown greater than 99% accuracy for four
evaluated enterprise system messaging protocols. The approach has been
successfully integrated into the CA Service Virtualization commercial product
to complement its existing techniques.Comment: In Proceedings of the 38th International Conference on Software
Engineering Companion (pp. 202-211). arXiv admin note: text overlap with
arXiv:1510.0142
Determination of the Sign of g factors for Conduction Electrons Using Time-resolved Kerr Rotation
The knowledge of electron g factor is essential for spin manipulation in the
field of spintronics and quantum computing. While there exist technical
difficulties in determining the sign of g factor in semiconductors by the
established magneto-optical spectroscopic methods. We develop a time resolved
Kerr rotation technique to precisely measure the sign and the amplitude of
electron g factor in semiconductors
Characterizing time series : when Granger causality triggers complex networks
In this paper, we propose a new approach to characterize time series with noise perturbations in both the time and frequency domains by combining Granger causality and complex networks. We construct directed and weighted complex networks from time series and use representative network measures to describe their physical and topological properties. Through analyzing the typical dynamical behaviors of some physical models and the MIT-BIH* human electrocardiogram data sets, we show that the proposed approach is able to capture and characterize various dynamics and has much potential for analyzing real-world time series of rather short length
Coulomb drag in double quantum wells with a perpendicular magnetic field
Momentum transfer due to electron-electron interaction (Coulomb drag) between
two quantum wells, separated by a distance , in the presence of a
perpendicular magnetic field, is studied at low temperatures. We find besides
the well known Shubnikov-de Haas oscillations, which also appear in the drag
effect, the momentum transfer is markedly enhanced by the magnetic field.Comment: 8 pages, Revtex, 4 Postscript figures are available upon request,
Accepted by Mod. Phys. Lett.
Monetary–fiscal interactions with endogenous liquidity frictions
I develop a tractable macro model with endogenous asset liquidity to understand monetary–fiscal interactions with liquidity frictions. Agents face idiosyncratic investment risks and meet financial intermediaries in competitive search markets. Asset liquidity is determined by the search friction and the cost of operating the financial intermediaries, and it drives the financing constraints of entrepreneurs (those who have investment projects) and their ability to invest. In contrast to private assets, government bonds are fully liquid and can be accumulated in anticipation of future opportunities to invest. A higher level of real government debt enhances the liquidity of entrepreneurs׳ portfolios and raises investment. However, the issuance of debt also raises the cost of financing government expenditures: a higher level of distortionary taxation and/or a higher real interest rate. A long-run optimal supply of government debt emerges. I also show that a proper mix of monetary and fiscal policies can avoid a deep financial recession
Macroeconomics of Delayed Capital Liquidation
This paper studies the macroeconomic effects of capital reallocation with financial shocks. I develop a model in which firms face borrowing constraints, idiosyncratic productivity shocks, and idiosyncratic liquidation costs. The idiosyncratic risks of productivity and liquidation costs generate an option value of staying in business and a liquidation delay for unproductive firms. A new feature arises from the delay. Unproductive firms that are not liquidated increase their leverage over time, pushing them to hit the borrowing limit. I show that adverse financial shocks that tighten borrowing constraints can raise the option value, and equilibrium effects can further delay capital liquidation and reallocation. Capital is thus persistently misallocated, leading to long-lasting economic contractions
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