1,480 research outputs found
An algebraic approach to problems with polynomial Hamiltonians on Euclidean spaces
Explicit expressions are given for the actions and radial matrix elements of
basic radial observables on multi-dimensional spaces in a continuous sequence
of orthonormal bases for unitary SU(1,1) irreps. Explicit expressions are also
given for SO(N)-reduced matrix elements of basic orbital observables. These
developments make it possible to determine the matrix elements of polynomial
and a other Hamiltonians analytically, to within SO(N) Clebsch-Gordan
coefficients, and to select an optimal basis for a particular problem such that
the expansion of eigenfunctions is most rapidly convergent.Comment: 19 pages, 8 figure
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Conceptual learning : the priority for higher education
The common sense notion of learning as the all-pervasive acquisition of new behaviour and knowledge, made vivid by experience, is an incomplete characterisation, because it assumes that the learning of behaviour and the learning of knowledge are indistinguishable, and that acquisition constitutes learning without reference to transfer. A psychological level of analysis is used to argue that conceptual learning should have priority in higher education
Diffusing-wave spectroscopy of nonergodic media
We introduce an elegant method which allows the application of diffusing-wave
spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on
the idea that light transmitted through a sandwich of two turbid cells can be
considered ergodic even though only the second cell is ergodic. If absorption
and/or leakage of light take place at the interface between the cells, we
establish a so-called "multiplication rule", which relates the intensity
autocorrelation function of light transmitted through the double-cell sandwich
to the autocorrelation functions of individual cells by a simple
multiplication. To test the proposed method, we perform a series of DWS
experiments using colloidal gels as model nonergodic media. Our experimental
data are consistent with the theoretical predictions, allowing quantitative
characterization of nonergodic media and demonstrating the validity of the
proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.
Dynamical mean-field theory of spiking neuron ensembles: response to a single spike with independent noises
Dynamics of an ensemble of -unit FitzHugh-Nagumo (FN) neurons subject to
white noises has been studied by using a semi-analytical dynamical mean-field
(DMF) theory in which the original -dimensional {\it stochastic}
differential equations are replaced by 8-dimensional {\it deterministic}
differential equations expressed in terms of moments of local and global
variables. Our DMF theory, which assumes weak noises and the Gaussian
distribution of state variables, goes beyond weak couplings among constituent
neurons. By using the expression for the firing probability due to an applied
single spike, we have discussed effects of noises, synaptic couplings and the
size of the ensemble on the spike timing precision, which is shown to be
improved by increasing the size of the neuron ensemble, even when there are no
couplings among neurons. When the coupling is introduced, neurons in ensembles
respond to an input spike with a partial synchronization. DMF theory is
extended to a large cluster which can be divided into multiple sub-clusters
according to their functions. A model calculation has shown that when the noise
intensity is moderate, the spike propagation with a fairly precise timing is
possible among noisy sub-clusters with feed-forward couplings, as in the
synfire chain. Results calculated by our DMF theory are nicely compared to
those obtained by direct simulations. A comparison of DMF theory with the
conventional moment method is also discussed.Comment: 29 pages, 2 figures; augmented the text and added Appendice
Tea drinking and cognitive function in oldest-old Chinese
10.1007/s12603-012-0077-1The Journal of Nutrition, Health & Aging169754-75
Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1−xN∕GaN blue light emitting diodes fabricated on freestanding GaN substrates
Prospective equivalent internal quantum efficiency (eta(int)) of approximately 34% at 300 K was demonstrated for the blue emission peak of nonpolar m-plane (1 (1) over bar 00) InxGa1-xN/GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the eta(int) value is yet lower than that of conventional c-plane blue LEDs (> 70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300 K. (c) 2006 American Institute of Physics
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
The bright end of the infrared luminosity functions and the abundance of hyperluminous infrared galaxies
16 pages, 11 figures, accepted for publication in A&A as part of the LOFAR Deep Fields Paper Splash. © 2020 The European Southern Observatory (ESO)We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities > 10^13 L_solar, thanks to the combination of the high sensitivity, angular resolution, and large area of the LOFAR Deep Fields, which probes an unprecedented dynamic range of luminosity and volume. We cross-match Herschel sources and LOFAR sources in Bootes (8.63 deg^2), Lockman Hole (10.28 deg^2), and ELAIS-N1 (6.74 deg^2) with rms sensitivities of around 32, 22, and 20 mJy per beam, respectively. We divide the matched samples into unique and multiple categories. For the multiple matches, we de-blend the Herschel fluxes using the LOFAR positions and the 150-MHz flux densities as priors. We perform spectral energy distribution (SED) fitting, combined with multi-wavelength counterpart identifications and photometric redshift estimates, to derive IR luminosities. The depth of the LOFAR data allows us to identify highly complete (around 92% completeness) samples of bright Herschel sources with a simple selection based on the 250 micron flux density (45, 40, and 35 mJy in Bootes, Lockman Hole, and ELAIS-N1, respectively). Most of the bright Herschel sources fall into the unique category (i.e. a single LOFAR counterpart). For the multiple matches, there is excellent correspondence between the radio emission and the far-IR emission. We find a good agreement in the IR LFs with a previous study out to z around 6 which used de-blended Herschel data. Our sample gives the strongest and cleanest indication to date that the population of HLIRGs has surface densities of around 5 to 18 / deg^2 (with variations due to a combination of the applied flux limit and cosmic variance) and an uncertainty of a factor of 2. In comparison, the GALFORM semi-analytic model significantly under-predicts the abundance of HLIRGs.Peer reviewe
- …