99,777 research outputs found
The Schrodinger-like Equation for a Nonrelativistic Electron in a Photon Field of Arbitrary Intensity
The ordinary Schrodinger equation with minimal coupling for a nonrelativistic
electron interacting with a single-mode photon field is not satisfied by the
nonrelativistic limit of the exact solutions to the corresponding Dirac
equation. A Schrodinger-like equation valid for arbitrary photon intensity is
derived from the Dirac equation without the weak-field assumption. The
"eigenvalue" in the new equation is an operator in a Cartan subalgebra. An
approximation consistent with the nonrelativistic energy level derived from its
relativistic value replaces the "eigenvalue" operator by an ordinary number,
recovering the ordinary Schrodinger eigenvalue equation used in the formal
scattering formalism. The Schrodinger-like equation for the multimode case is
also presented.Comment: Tex file, 13 pages, no figur
AGN Feedback and Bimodality in Cluster Core Entropy
We investigate a series of steady-state models of galaxy clusters, in which
the hot intracluster gas is efficiently heated by active galactic nucleus (AGN)
feedback and thermal conduction, and in which the mass accretion rates are
highly reduced compared to those predicted by the standard cooling flow models.
We perform a global Lagrangian stability analysis. We show for the first time
that the global radial instability in cool core clusters can be suppressed by
the AGN feedback mechanism, provided that the feedback efficiency exceeds a
critical lower limit. Furthermore, our analysis naturally shows that the
clusters can exist in two distinct forms. Globally stable clusters are expected
to have either: 1) cool cores stabilized by both AGN feedback and conduction,
or 2) non-cool cores stabilized primarily by conduction. Intermediate central
temperatures typically lead to globally unstable solutions. This bimodality is
consistent with the recently observed anticorrelation between the flatness of
the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the
observation by Rafferty et al. (2008) that the shorter central cooling times
tend to correspond to significantly younger AGN X-ray cavities.Comment: 4 pages, to appear in the proceedings of "The Monster's Fiery Breath:
Feedback in Galaxies, Groups, and Clusters", Eds. Sebastian Heinz, Eric
Wilcots (AIP conference series
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Performance of bolted steel-beam to CFST-column joints using stiffened angles in column-removal scenario
This paper presents three experimental investigations on the performance of steel-beam to CFST-column joints using stiffened angle, long bolts and fin plate under a middle column removal scenario. Three specimens were designed and tested. The failure modes and catenary action are investigated in detail. The test results show that increasing the angle plate thickness at the joint could not only improve its performance significantly, but also trigger an early formation of catenary action. Increasing the length of short-limb had influence on the deformation ability of the proposed joint, rather than the load capacity. The buckling of stiffeners could prevent the brittle failure of the joints. With the contribution of catenary action, the joint shows much higher rotation capacities than that required in DoD design guidance. The initial stiffness of the joint was calculated using an analytical model with consideration of bolt pretension. Good agreement to the test results is achieved. A numerical analysis is also carried out, whose results show that adding additional row of bolts would improve the redundancy of the joint under column loss. An equivalent dynamic response evaluation of the joints was also performed. The results show that dynamic amplification coefficient should be worked out considering catenary action under large deformation
Theoretic Limits on the Equation of State Parameter of Quintessence
The value of scalar field coupled to gravity should be less than the Planck
scale in the consistent theory of quantum gravity. It provides a theoretic
constraint on the equation of state parameter for the quintessence. In some
cases our theoretic constraints are more stringent than the constraints from
the present experiments.Comment: 4 pages, 2 figures; minor corrections and refs adde
\Lambda_b \to \Lambda_c P(V) Nonleptonic Weak Decays
The two-body nonleptonic weak decays of \Lambda_b \to \Lambda_c P(V) (P and V
represent pseudoscalar and vector mesons respectively) are analyzed in two
models, one is the Bethe-Salpeter (B-S) model and the other is the hadronic
wave function model. The calculations are carried out in the factorization
approach. The obtained results are compared with other model calculations.Comment: 18 pages, Late
Statistical physics-based reconstruction in compressed sensing
Compressed sensing is triggering a major evolution in signal acquisition. It
consists in sampling a sparse signal at low rate and later using computational
power for its exact reconstruction, so that only the necessary information is
measured. Currently used reconstruction techniques are, however, limited to
acquisition rates larger than the true density of the signal. We design a new
procedure which is able to reconstruct exactly the signal with a number of
measurements that approaches the theoretical limit in the limit of large
systems. It is based on the joint use of three essential ingredients: a
probabilistic approach to signal reconstruction, a message-passing algorithm
adapted from belief propagation, and a careful design of the measurement matrix
inspired from the theory of crystal nucleation. The performance of this new
algorithm is analyzed by statistical physics methods. The obtained improvement
is confirmed by numerical studies of several cases.Comment: 20 pages, 8 figures, 3 tables. Related codes and data are available
at http://aspics.krzakala.or
Optimal design of an aeroelastic wing structure with seamless control surfaces
This article presents an investigation into the concept and optimal design of a lightweight seamless aeroelastic wing (SAW) structure for small air vehicles. Attention has been first focused on the design of a hingeless flexible trailing edge (TE) control surface. Two innovative design features have been created in the SAW TE section: an open sliding TE and a curved beam and disc actuation mechanism. This type of actuated TE section allows for the SAW having a camber change in a desirable shape and minimum control power demand. This design concept has been simulated numerically and demonstrated by a test model. For a small air vehicle of large sweep back wing, it is noted that significant structural weight saving can be achieved. However, further weight saving is mainly restricted by the aeroelastic stability and minimum number of carbon/epoxy plies in a symmetric layup rather than the structural strength. Therefore, subsequent effort was made to optimize the primary wing box structure. The results show that an initial structural weight can be reduced significantly under the strength criterion. The resulting reduction of the wing box stiffness and aeroelastic stability and control effectiveness can be improved by applying the aeroelastic tailoring. Because of the large swept angle and resulting lightweight and highly flexible SAW, geometrical non-linearity and large bending-torsion aeroelastic coupling have been considered in the analysis
Entanglement changing power of two-qubit unitary operations
We consider a two-qubit unitary operation along with arbitrary local unitary
operations acts on a two-qubit pure state, whose entanglement is C_0. We give
the conditions that the final state can be maximally entangled and be
non-entangled. When the final state can not be maximally entangled, we give the
maximal entanglement C_max it can reach. When the final state can not be
non-entangled, we give the minimal entanglement C_min it can reach. We think
C_max and C_min represent the entanglement changing power of two-qubit unitary
operations. According to this power we define an order of gates.Comment: 11 page
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