5,911 research outputs found
Protecting Two-Qubit Quantum States by -Phase Pulses
We study the state decay of two qubits interacted with a common harmonic
oscillator reservoir. There are both decoherence error and the error caused by
the amplitude change of the superradiant state. We show that frequent
-phase pulses can eliminate both typpes of errors therefore protect a
two-qubit odd-parity state more effectively than the frequent measurement
method. This shows that the the methods using dynamical decoupling and the
quantum Zeno effects actually can give rather {\em different} results when the
operation frequency is finite
Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFeSe and AFeSe (A=K, Rb, or Cs)
By the first-principles electronic structure calculations, we find that the
ground state of the Fe-vacancies ordered TlFeSe is a
quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy
gap of 94 meV, in agreement with experimental measurements. This
antiferromagnetic order is driven by the Se-bridged antiferromagnetic
superexchange interactions between Fe moments. Similarly, we find that crystals
AFeSe (A=K, Rb, or Cs) are also antiferromagnetic semiconductors
but with a zero-gap semiconducting state or semimetallic state nearly
degenerated with the ground states. Thus rich physical properties and phase
diagrams are expected.Comment: Add results about AFeSe (A=K, Rb, or Cs);4 pages and 7
figure
Dynamics of neutrino-driven winds: inclusion of accurate weak interaction rates in strong magnetic fields
Solving Newtonian steady-state wind equations with accurate weak interaction
rates and magnetic fields (MFs) of young neutron stars considered, we study the
dynamics and nucleosynthesis of neutrino-driven winds (NDWs) from proto neutron
stars (PNSs). For a typical 1.4 M PNS model, we find the
nucleosynthesis products are closely related to the luminosity of neutrinos and
anti-neutrinos. The lower the luminosity is, the larger effect to the NDWs
caused by weak interactions and MFs is. At a high anti-neutrino luminosity of
typically erg s, neutrinos and anti-neutrinos dominate
the processes in a NDW and the MFs hardly change the wind's properties. While
at a low anti-neutrino luminosity of erg s at the late stage
of a NDW, the mass of product and nucleosynthesis are changed significantly in
the strong MFs, they are less important than those in the early stage when the
anti-neutrino luminosity is high. Therefore for the most models considered for
the NDWs from PNSs, based on our calculations the influences of MFs and the net
weak interactions on the nucleosynthesis is not significant.Comment: 8 pages, 3 figures, accepted for publication in RA
Case Study – Ground Failures and Ruptures in Xian City
Xian city, the most well known ancient city of China for her incredible Terra Cotta Warriers and so forth, has been suffered from ground fracture for years. Surface ruptures and faultings encountered in strips all over the city. Hundreds of buildings were severely destroyed and many of them even have been demolished. Ground failures wide-spread and enlarged from time to time, especially right from Tangshan earthquake of July 28, 1976. Therefore serious concerns and suspicious of being associated with major earthquakes have arosed. Thus it has been a problem of both engineering and social influence. Like many other cities in China and even in the world such as Houston, Texas, USA, surface faulting or surface rupture often caused many guess-works and arguments among different engineers, geologists and seismologists. In turn, many projects either underway or co be undertaken will be seriously lagged out due to discrepancies of different assessment and measures of mitigation. The authors have been deeply involved in surface faulting and ruptures as a background for exploring the mechanism and predicting its possible effects from the engineering point of view. In this paper, the authors introduce their systematic ease study on Xian ground failures towards this end, including site investigations, typical damages assessment, numerical analysis on fracture mechanism, model tests in laboratory and comprehensive evaluations etc. Conclusions were drawn not only for this particular ancient city but also provided a referential real ease for the like in the world
Mechanism of Dynamic Consolidation and Its Environmental Effect
This paper is contributed as case histories in ground soil improvement with particular emphasis of dynamic consolidation. The authors try to present as much as they got from the field testings and observations including vibrational parameters, pore pressures, stereoscopic photogrammetry, etc. in order to trace the real behaviour of ground movement during tamping. It is believed that all the data got from the field work are rather informative and illustrative than that from theoretical modelling in the laboratory. Thus, some highlights relating effective thickness of compaction, maximum spacing between compaction points, number of blows for optimum tamping and seismic attenuation for environmental consideration are given
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