2,837 research outputs found
On complex singularities of the 2D Euler equation at short times
We present a study of complex singularities of a two-parameter family of
solutions for the two-dimensional Euler equation with periodic boundary
conditions and initial conditions F(p) cos p z + F(q) cos q z in the short-time
asymptotic regime. As has been shown numerically in W. Pauls et al., Physica D
219, 40-59 (2006), the type of the singularities depends on the angle between
the modes p and q. Here we show for the two particular cases of the angle going
to zero and to pi that the type of the singularities can be determined very
accurately, being characterised by the values 5/2 and 3 respectively. In these
two cases we are also able to determine the subdominant corrections.
Furthermore, we find that the geometry of the singularities in these two cases
is completely different, the singular manifold being located "over" different
points in the real domain.Comment: 12 pages, 7 figure
A Data Exchange Standard for Optical (Visible/IR) Interferometry
This paper describes the OI Exchange Format, a standard for exchanging
calibrated data from optical (visible/infrared) stellar interferometers. The
standard is based on the Flexible Image Transport System (FITS), and supports
storage of the optical interferometric observables including squared visibility
and closure phase -- data products not included in radio interferometry
standards such as UV-FITS. The format has already gained the support of most
currently-operating optical interferometer projects, including COAST, NPOI,
IOTA, CHARA, VLTI, PTI, and the Keck Interferometer, and is endorsed by the IAU
Working Group on Optical Interferometry. Software is available for reading,
writing and merging OI Exchange Format files.Comment: 26 pages, 1 figur
Reading Teachers Are Asked What is Relevant In the Classroom?
One of the most crucial problems facing teacher education today is one of relevancy. This cry for relevance suggests that what we in higher education do as we prepare students to become teachers is not compatible with the real world of the classroom. Backman tells us that as teacher educators we are perceived as (1) delivering preparation programs which have little real influence on the way in which our graduates actually teach; and (2) being completely out of touch with the actual teaching conditions in contemporary schools (1984)
Computerized Searches on Articles Reporting Reading Research: A Closer Look
This article, which draws on examples supplied by previous studies involving fifty articles in the psycholinguistic literature [ 4], [5], [6], explores how the choice of terminology used in database records and in searches may actually impede retrieval, and it suggests compensatory measures
Entire solutions of hydrodynamical equations with exponential dissipation
We consider a modification of the three-dimensional Navier--Stokes equations
and other hydrodynamical evolution equations with space-periodic initial
conditions in which the usual Laplacian of the dissipation operator is replaced
by an operator whose Fourier symbol grows exponentially as \ue ^{|k|/\kd} at
high wavenumbers . Using estimates in suitable classes of analytic
functions, we show that the solutions with initially finite energy become
immediately entire in the space variables and that the Fourier coefficients
decay faster than \ue ^{-C(k/\kd) \ln (|k|/\kd)} for any . The
same result holds for the one-dimensional Burgers equation with exponential
dissipation but can be improved: heuristic arguments and very precise
simulations, analyzed by the method of asymptotic extrapolation of van der
Hoeven, indicate that the leading-order asymptotics is precisely of the above
form with . The same behavior with a universal constant
is conjectured for the Navier--Stokes equations with exponential
dissipation in any space dimension. This universality prevents the strong
growth of intermittency in the far dissipation range which is obtained for
ordinary Navier--Stokes turbulence. Possible applications to improved spectral
simulations are briefly discussed.Comment: 29 pages, 3 figures, Comm. Math. Phys., in pres
Nature of complex singularities for the 2D Euler equation
A detailed study of complex-space singularities of the two-dimensional
incompressible Euler equation is performed in the short-time asymptotic
r\'egime when such singularities are very far from the real domain; this allows
an exact recursive determination of arbitrarily many spatial Fourier
coefficients. Using high-precision arithmetic we find that the Fourier
coefficients of the stream function are given over more than two decades of
wavenumbers by \hat F(\k) = C(\theta) k^{-\alpha} \ue ^ {-k \delta(\theta)},
where \k = k(\cos \theta, \sin \theta). The prefactor exponent ,
typically between 5/2 and 8/3, is determined with an accuracy better than 0.01.
It depends on the initial condition but not on . The vorticity diverges
as , where and is the distance to the
(complex) singular manifold. This new type of non-universal singularity is
permitted by the strong reduction of nonlinearity (depletion) which is
associated to incompressibility. Spectral calculations show that the scaling
reported above persists well beyond the time of validity of the short-time
asymptotics. A simple model in which the vorticity is treated as a passive
scalar is shown analytically to have universal singularities with exponent
.Comment: 22 pages, 24 figures, published version; a version of the paper with
higher-quality figures is available at http://www.obs-nice.fr/etc7/euler.pd
Influence of temperature and viscosity on anthracene rotational diffusion in organic solvents: Molecular dynamics simulations and fluorescence anisotropy study
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/107/21/10.1063/1.475172.Molecular dynamics simulations and fluorescenceanisotropy decay measurements are used to investigate the rotational diffusion of anthracene in two organic solvents—cyclohexane and 2-propanol—at several temperatures. Molecular dynamics simulations of 1 ns length were performed for anthracene in cyclohexane (at 280, 296, and 310 K) and in 2-propanol (at 296 K). The calculated time constants for reorientation of the short in-plane axis were 7–9 and 11–16 ps at 296 K in cyclohexane and 2-propanol, respectively, in excellent agreement with corresponding fluorescence depolarization measurements of 8 and 14 ps. The measured rotational reorientation times and the calculated average rotational diffusion coefficients varied in accord with Debye–Stokes–Einstein theory. Their magnitudes were close to values predicted for an ellipsoid of shape and size equivalent to an anthracene molecule, and exhibited predictable variation with external conditions—increasing with temperature and decreasing with solventviscosity. However, analysis of the calculated rotational diffusion coefficients for the individual molecular axes gave a more complex picture. The diffusion was highly anisotropic and changes in temperature and solvent type led to nonuniform variation of the diffusion coefficients. The nature of these changes was rationalized based on analysis of variation of solvation patterns with temperature and solvent
A measure of centrality based on the spectrum of the Laplacian
We introduce a family of new centralities, the k-spectral centralities.
k-Spectral centrality is a measurement of importance with respect to the
deformation of the graph Laplacian associated with the graph. Due to this
connection, k-spectral centralities have various interpretations in terms of
spectrally determined information.
We explore this centrality in the context of several examples. While for
sparse unweighted networks 1-spectral centrality behaves similarly to other
standard centralities, for dense weighted networks they show different
properties. In summary, the k-spectral centralities provide a novel and useful
measurement of relevance (for single network elements as well as whole
subnetworks) distinct from other known measures.Comment: 12 pages, 6 figures, 2 table
Radio Observations and Spectrum of the SNR G127.1+0.5 and its Central Source 0125+628
We present new images of the Supernova Remnant (SNR) G127.1+0.5 (R5), based
on the 408 MHz and 1420 MHz continuum emission and the HI-line emission data of
the Canadian Galactic Plane Survey (CGPS). The radio spectrum of the central
compact source (0125+628) is analyzed in the range 178 MHz - 8.7 GHz,
indicating a flat spectrum with synchrotron self-absorption below 800 MHz. The
SNR's flux density at 408 MHz is 17.11.7 Jy and at 1420 MHz is
10.00.8 Jy, corrected for flux densities from compact sources within the
SNR. The SNR's integrated flux density based spectral index
(S) is 0.430.10. The respective T-T plot
spectral index (derived from the relative size of brightness temperature
variations between two frequencies, see text for details) is 0.460.01.
There is no evidence at 1 for spatial variations in spectral index
within G127.1+0.5. In particular, we compared the northern shell, southern
shell and central diffuse region. HI observations show structures associated
with the SNR in the radial velocity range of -12 to -16 kms, suggesting
G127.1+0.5's distance is 1.15 kpc. The estimated Sedov age is 2 - 3
yr.Comment: 13 pages, 5 figures, 5 tables, accepted by A&
Perekonomian Indonesia dalam Menghadapi Sistem Globalisasi
Globalisation is a part of human being. Until now, there aren´t succes for a nation without relation and assosiation to other countries. Indonesia hope, that globalisation can continue the national economic market system to the international level. What is our attitude to face it? what is the agenda need to be prepared? Preparing non market institution is a key toface globalisation and executing more effective diplomacy. Keywords:Globalisation, Economic market system
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