2,495 research outputs found
Lightcone fluctuations in quantum gravity and extra dimensions
We discuss how compactified extra dimensions may have potentially observable
effects which grow as the compactification scale decreases. This arises because
of lightcone fluctuations in the uncompactified dimensions which can result in
the broadening of the spectral lines from distant sources. We analyze this
effect in a five dimensional model, and argue that data from gamma ray burst
sources require the compactification length to be greater than about cm
in this model.Comment: Two additional references adde
Testing MONDian Dark Matter with Galactic Rotation Curves
MONDian dark matter (MDM) is a new form of dark matter quantum that naturally
accounts for Milgrom's scaling, usually associated with modified Newtonian
dynamics (MOND), and theoretically behaves like cold dark matter (CDM) at
cluster and cosmic scales. In this paper, we provide the first observational
test of MDM by fitting rotation curves to a sample of 30 local spiral galaxies
(z approximately 0.003). For comparison, we also fit the galactic rotation
curves using MOND, and CDM. We find that all three models fit the data well.
The rotation curves predicted by MDM and MOND are virtually indistinguishable
over the range of observed radii (~1 to 30 kpc). The best-fit MDM and CDM
density profiles are compared. We also compare with MDM the dark matter density
profiles arising from MOND if Milgrom's formula is interpreted as Newtonian
gravity with an extra source term instead of as a modification of inertia. We
find that discrepancies between MDM and MOND will occur near the center of a
typical spiral galaxy. In these regions, instead of continuing to rise sharply,
the MDM mass density turns over and drops as we approach the center of the
galaxy. Our results show that MDM, which restricts the nature of the dark
matter quantum by accounting for Milgrom's scaling, accurately reproduces
observed rotation curves.Comment: Preprint number IPMU13-0147. Accepted for publication in Ap
Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators
The largest Lyapunov exponent of a system composed by a heavy impurity
embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators
is numerically computed for various values of the impurity mass . A
crossover between weak and strong chaos is obtained at the same value
of the energy density (energy per degree of freedom)
for all the considered values of the impurity mass . The threshold \epsi
lon_{_T} coincides with the value of the energy density at which a
change of scaling of the relaxation time of the momentum autocorrelation
function of the impurity ocurrs and that was obtained in a previous work ~[M.
Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete
Lyapunov spectrum does not depend significantly on the impurity mass . These
results suggest that the impurity does not contribute significantly to the
dynamical instability (chaos) of the chain and can be considered as a probe for
the dynamics of the system to which the impurity is coupled. Finally, it is
shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak
to strong chaos at the same value of the energy density that the crossover
value of largest Lyapunov exponent. Implications of this result
are discussed.Comment: 6 pages, 5 figures, revtex4 styl
New observations of the NGC 1275 phenomenon
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Patient-reported outcomes following treatment with the human GLP-1 analogue liraglutide or glimepiride in monotherapy: results from a randomized controlled trial in patients with type 2 diabetes
Aim: As weight gain and hypoglycaemia associated with glimepiride therapy can negatively impact weight perceptions, psychological well-being and overall quality of life in type 2 diabetes, we investigated whether liraglutide treatment could improve these factors
Blasts and shocks in the disc of NGC 4258
We present integral field spectroscopic observations of the central region of
the active galaxy NGC 4258 obtained with the fibre IFU system INTEGRAL. We have
been able to detect cold neutral gas by means of the interstellar NaD doublet
absorption and to trace its distribution and kinematics with respect to the
underlying disc. The neutral gas is blue-shifted with projected velocities in
the 120--370 km/s range. We have also detected peculiar kinematics in part of
the ionized gas in this region by means of a careful kinematic decomposition.
The bipolar spatial distribution of the broader component is roughly coincident
with the morphology of the X-ray diffuse emission. The kinematics of this gas
can be explained in terms of expansion at very high (projected) velocities of
up to 300 km/s. The observations also reveal the existence of a strip of
neutral gas, parallel to the major kinematic axis, that is nearly coincident
with a region of very high [SII]/H ratio tracing the shocked gas. Our
observations are consistent with the jet model presented by \cite{wilsonetal01}
in which a cocoon originating from the nuclear jet is shocking the gas in the
galaxy disc. Alternatively, our observations are also consistent with the
bipolar hypershell model of \cite{Sofue80} and \cite{SofueandVogler01}. On
balance, we prefer the latter model as the most likely explanation for the
puzzling features of this peculiar object.Comment: 7 pages, 10 colour figures. Accepted for publication in MNRAS
Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4 spiral
galaxies which are characterized by a zero-velocity plateau along the major
axis and a velocity gradient along the minor axis, respectively. By combining
these new kinematical data with those available in the literature for the
ionized-gas component of the S0s and spirals listed in the Revised Shapley-Ames
Catalog of Bright Galaxies we realized that about 50% of unbarred galaxies show
a remarkable gas velocity gradient along the optical minor axis. This fraction
rises to about 60% if we include unbarred galaxies with an irregular velocity
profile along the minor axis. This phenomenon is observed all along the Hubble
sequence of disk galaxies, and it is particularly frequent in early-type
spirals. Since minor-axis velocity gradients are unexpected if the gas is
moving onto circular orbits in a disk coplanar to the stellar one, we conclude
that non-circular and off-plane gas motions are not rare in the inner regions
of disk galaxies.Comment: 12 pages, 4 postscript figures. Accepted for publication in A&
A Review of Hot Deck Imputation for Survey Non-response
L'imputation hot deck est une méthode de gestion des données manquantes dans laquelle chaque valeur manquante est remplacée par une réponse observée à partir d'une unité“similaire.” Bien qu'elle soit largement utilisée en pratique, sa théorie n'est pas aussi développée que celle des autres méthodes d'imputation. Nous avons constaté qu'il n'existe aucun consensus quant à la meilleure faon d'appliquer les hot deck et obtenir des inférences à partir de la série de données complète. Ici, nous passons en revue les différentes formes de hot deck et les recherches existantes sur ses propriétés statistiques. Nous décrivons les applications du hot deck actuellement utilisées, y compris le hot deck du Bureau US du recensement pour la Current Population Survey (CPS). Nous proposons aussi des exemples nombreux de variations du hot deck à la troisième National Health and Nutrition Examination Survey (NHANES III). Certains domaines possibles de recherches futures sont mises en évidence.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78729/1/j.1751-5823.2010.00103.x.pd
The rotation curves shapes of late-type dwarf galaxies
We present rotation curves derived for a sample of 62 late-type dwarf
galaxies that have been observed as part of the Westerbork HI Survey of Spiral
and Irregular Galaxies (WHISP) project. The rotation curves were derived by
interactively fitting model data cubes to the observed cubes, taking rotation
curve shape, HI distribution, inclination, and the size of the beam into
account. This makes it possible to correct for the effects of beam smearing.
The dwarf galaxies in our sample have rotation-curve shapes that are similar to
those of late-type spiral galaxies, in the sense that their rotation curves,
when expressed in units of disk scale lengths, rise as steeply in the inner
parts and start to flatten at two disk scale lengths. None of the galaxies in
our sample have solid-body rotation curves that extend beyond three scale
lengths. The logarithmic outer rotation curve slopes are similar between
late-type dwarf and spiral galaxies. Thus, whether the flat part of the
rotation curve is reached seems to depend more on the extent of the rotation
curve than on its amplitude. We also find that the outer rotation curve shape
does not strongly depend on luminosity, at least for galaxies fainter than
M_R~-19. We find that in spiral galaxies and in the central regions of
late-type dwarf galaxies, the shape of the central distribution of light and
the inner rise of the rotation curve are related. This implies that galaxies
with stronger central concentrations of light also have higher central mass
densities, and it suggests that the luminous mass dominates the gravitational
potential in the central regions, even in low surface brightness dwarf
galaxies.Comment: 22 pages, 2009 A&A 493, 87
A review for clinical outcomes research: hypothesis generation, data strategy, and hypothesis-driven statistical analysis
In recent years, more and more large, population-level databases have become available for clinical research. The size and complexity of these databases often present a methodological challenge for investigators. We propose that a “protocol” may facilitate the research process using these databases. In addition, much like the structured History and Physical (H&P) helps the audience appreciate the details of a patient case more systematically, a formal outcomes research protocol can also help in the systematic evaluation of an outcomes research manuscript
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