8,517 research outputs found
A quantum central limit theorem for non-equilibrium systems: Exact local relaxation of correlated states
We prove that quantum many-body systems on a one-dimensional lattice locally
relax to Gaussian states under non-equilibrium dynamics generated by a bosonic
quadratic Hamiltonian. This is true for a large class of initial states - pure
or mixed - which have to satisfy merely weak conditions concerning the decay of
correlations. The considered setting is a proven instance of a situation where
dynamically evolving closed quantum systems locally appear as if they had truly
relaxed, to maximum entropy states for fixed second moments. This furthers the
understanding of relaxation in suddenly quenched quantum many-body systems. The
proof features a non-commutative central limit theorem for non-i.i.d. random
variables, showing convergence to Gaussian characteristic functions, giving
rise to trace-norm closeness. We briefly relate our findings to ideas of
typicality and concentration of measure.Comment: 27 pages, final versio
Unsteady Crack Motion and Branching in a Phase-Field Model of Brittle Fracture
Crack propagation is studied numerically using a continuum phase-field
approach to mode III brittle fracture. The results shed light on the physics
that controls the speed of accelerating cracks and the characteristic branching
instability at a fraction of the wave speed.Comment: 11 pages, 4 figure
Geometrical Expression for the Angular Resolution of a Network of Gravitational-Wave Detectors
We report for the first time general geometrical expressions for the angular
resolution of an arbitrary network of interferometric gravitational-wave (GW)
detectors when the arrival-time of a GW is unknown. We show explicitly elements
that decide the angular resolution of a GW detector network. In particular, we
show the dependence of the angular resolution on areas formed by projections of
pairs of detectors and how they are weighted by sensitivities of individual
detectors. Numerical simulations are used to demonstrate the capabilities of
the current GW detector network. We confirm that the angular resolution is poor
along the plane formed by current LIGO-Virgo detectors. A factor of a few to
more than ten fold improvement of the angular resolution can be achieved if the
proposed new GW detectors LCGT or AIGO are added to the network. We also
discuss the implications of our results for the design of a GW detector
network, optimal localization methods for a given network, and electromagnetic
follow-up observations.Comment: 13 pages, for Phys. Rev.
Integrative oncology: Best of both worlds - Theoretical, practical, and research issues
More and more cancer patients use complementary therapies. As the majority of patients do not disclose their use of complementary therapies to their oncologists, they expose themselves to possible detrimental effects from the therapies due to drug interactions. To meet the needs of patients and health care professionals on valid information on complementary therapies, the collaborative research project "Competence Network Complementary Medicine in Oncology - KOKON", an interdisciplinary network for complementary medicine research in oncology, was established. Moreover, Integrative Oncology, a combination of conventional and evidenced-based complementary therapies delivered using a comprehensive approach, is now increasingly used in the United States and Europe. A variety of different Integrative Oncology models have been established worldwide including an expert-based model at the Kliniken Essen-Mitte, Essen, Germany and a patient-centered, evidenced-based approach at The University of Texas MD Anderson Cancer Center. Both models are briefly reviewed. More research is needed and Comparative Effectiveness Research that places strong emphasis on the comparison of different treatment options in usual care settings by including more heterogeneous patients, using less standardized treatment protocols, and measuring patient-centered outcomes would provide useful information for decision-making. To improve the quality of care and research in Integrative Oncology, sustainable financial models for Integrative Oncology and more funding for research are needed. © 2013 Holger Cramer et al
Biased tomography schemes: an objective approach
We report on an intrinsic relationship between the maximum-likelihood
quantum-state estimation and the representation of the signal. A quantum
analogy of the transfer function determines the space where the reconstruction
should be done without the need for any ad hoc truncations of the Hilbert
space. An illustration of this method is provided by a simple yet practically
important tomography of an optical signal registered by realistic binary
detectors.Comment: 4 pages, 3 figures, accepted in PR
Tip‐induced lifting of the Au{100} (hex)‐phase reconstruction in a low temperature ultrahigh vacuum scanning tunneling microscope
The clean Au{100} surface is known to be reconstructed, forming a pseudohexagonal (5×27) outermost layer. This structure is observed both in ultrahigh vacuum (UHV) and in the electrochemical environment at potentials corresponding to small negative surface electronic charges. Using a UHV scanning tunneling microscope (STM) at 77 K we have observed that the reconstruction can be lifted at large positive sample biases. The 20% less dense bulk‐terminated surface is produced and the excess material appears as irregularly shaped gold clusters. Over a period of a few minutes, however, the surface relaxes back to the pseudo‐hexagonal phase, a process that can also be followed with the STM
Adsorbate site determination with the scanning tunneling microscope: C<sub>2</sub>H<sub>4</sub> on Cu{110}
Scanning tunneling microscopy at T=4 K has been used to determine directly the binding site of a molecule chemisorbed on a metal surface, namely, ethene on Cu〈110〉, by simultaneous imaging of the adsorbate and the underlying lattice. The molecule is found to bond in the short bridge site on the close-packed rows with its C-C axis oriented in the 〈110〉 direction
An assistive tabletop keyboard for stroke rehabilitation
We propose a tabletop keyboard that assists stroke patients in using computers. Using computers for purposes such as paying bills, managing bank accounts, sending emails, etc., which all include typing, is part of Activities of Daily Living (ADL) that stroke patients wish to recover. To date, stroke rehabilitation research has greatly focused on using computer-assisted technology for rehabilitation. However, working with computers as a skill that patients need to recover has been neglected. The conventional human computer interfaces are mouse and keyboard. Using keyboard stays the main challenge for hemiplegic stroke patients because typing is usually a bimanual task. Therefore, we propose an assistive tabletop keyboard which is not only a novel computer interface that is specially designed to facilitate patient-computer interaction but also a rehab medium through which patients practice the desired arm/hand functions. © 2013 Authors
Qubit metrology and decoherence
Quantum properties of the probes used to estimate a classical parameter can
be used to attain accuracies that beat the standard quantum limit. When qubits
are used to construct a quantum probe, it is known that initializing qubits
in an entangled "cat state," rather than in a separable state, can improve the
measurement uncertainty by a factor of . We investigate how the
measurement uncertainty is affected when the individual qubits in a probe are
subjected to decoherence. In the face of such decoherence, we regard the rate
at which qubits can be generated and the total duration of a
measurement as fixed resources, and we determine the optimal use of
entanglement among the qubits and the resulting optimal measurement uncertainty
as functions of and .Comment: 24 Pages, 3 Figure
Platelet-activating factor and hyperacute rejection: The effect of a platelet-activating factor antagonist, sri 63-441, on rejection of xenografts and allografts in sensitized hosts
The pathogenesis of hyperacute transplantation reactions includes the activation of a cascade of nonspecific inflammatory reactions that precipitates the destruction of the target organ. Platelet-activating factor (PAF) represents an important component of these inflammatory cascades, and we have examined the influence of a specific PAF receptor antagonist (SRI 63-441) on the inhibition of hyperacute rejection in two experimental models, the rejection of rat cardiac allografts by presensitized recipients and guinea pig-to-rat and mouse-to- rat cardiac xenografts. Our results demonstrate that inhibition of PAF function by SRI 63-441 has a variable effect on the survival of cardiac allografts in presensitized rat recipients. In the ACI to sensitized BN cardiac allograft model, the use of SRI 63-441 alone, or in combination with CsA, FK506, or prostaglandin E2(PGE2), does not prolong graft survival. As we have previously reported, SRI 63-441 does act as a single agent to prolong the survival of ACI to sensitized LEW grafts, and this survival effect is synergistic when combined with CsA. Here we extend these results to demonstrate that this survival is also extended when FK506 is used in the ACI-to-LEW model. Concordant mouse-to- rat cardiac xenografts are also relatively resistant to prolongation of graft survival following treatment with SRI 63-441 alone or in combination with CsA or FK506. Discordant xenografts appear to be more susceptible to inhibition of the rejection reaction with SRI 63-441. When either donor or recipient animals were treated with SRI 63-441 alone, or in combination with CsA or FK506, there was significant prolongation of guinea pig-to-rat cardiac xenograft survival. These results are consistent with our earlier description of the effectiveness of SRI 63-441 in preventing the rejection of cat- to-rabbit kidney xenografts. We believe that these resuits demonstrate that the use of the SRI 63-441 to specifically interfere with the function of PAF has the effect of prolonging graft survival in those systems in which preformed antibody and/or complement activation are important components of the hyperacute reaction. This synthetic drug is representative of a family of compounds whose structure can be modified to balance their therapeutic and toxicity activities, and may prove to be important components of a polytherapeutic approach to the control of graft rejection in sensitized patients or following discordant xenografting. © 1990 by Williams and Wilkins
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