77,294 research outputs found
Change-point model on nonhomogeneous Poisson processes with application in copy number profiling by next-generation DNA sequencing
We propose a flexible change-point model for inhomogeneous Poisson Processes,
which arise naturally from next-generation DNA sequencing, and derive score and
generalized likelihood statistics for shifts in intensity functions. We
construct a modified Bayesian information criterion (mBIC) to guide model
selection, and point-wise approximate Bayesian confidence intervals for
assessing the confidence in the segmentation. The model is applied to DNA Copy
Number profiling with sequencing data and evaluated on simulated spike-in and
real data sets.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS517 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Spin current swapping and Hanle spin Hall effect in the two dimensional electron gas
We analyze the effect known as "spin current swapping" (SCS) due to
electron-impurity scattering in a uniform spin-polarized two-dimensional
electron gas. In this effect a primary spin current (lower index for
spatial direction, upper index for spin direction) generates a secondary spin
current if , or , with , if . Contrary
to naive expectation, the homogeneous spin current associated with the uniform
drift of the spin polarization in the electron gas does not generate a swapped
spin current by the SCS mechanism. Nevertheless, a swapped spin current will be
generated, if a magnetic field is present, by a completely different mechanism,
namely, the precession of the spin Hall spin current in the magnetic field. We
refer to this second mechanism as Hanle spin Hall effect, and we notice that it
can be observed in an experiment in which a homogeneous drift current is passed
through a uniformly magnetized electron gas. In contrast to this, we show that
an unambiguous observation of SCS requires inhomogeneous spin currents, such as
those that are associated with spin diffusion in a metal, and no magnetic
field. An experimental setup for the observation of the SCS is therefore
proposed.Comment: 8 pages, 5 figure
A new view of nonlinear water waves: the Hilbert spectrum
We survey the newly developed Hilbert spectral analysis method and its applications to Stokes waves, nonlinear wave evolution processes, the spectral form of the random wave field, and turbulence. Our emphasis is on the inadequacy of presently available methods in nonlinear and nonstationary data analysis. Hilbert spectral analysis is here proposed as an alternative. This new method provides not only a more precise definition of particular events in time-frequency space than wavelet analysis, but also more physically meaningful interpretations of the underlying dynamic processes
A method for monitoring the variability in nuclear absorption characteristics of aviation fuels
A technique for monitoring variability in the nuclear absorption characteristics of aviation fuels has been developed. It is based on a highly collimated low energy gamma radiation source and a sodium iodide counter. The source and the counter assembly are separated by a geometrically well-defined test fuel cell. A computer program for determining the mass attenuation coefficient of the test fuel sample, based on the data acquired for a preset counting period, has been developed and tested on several types of aviation fuel
On the average Gamma-Ray Burst X-ray flaring activity
Gamma-ray burst X-ray flares are believed to mark the late time activity of
the central engine. We compute the temporal evolution of the average flare
luminosity in the common rest frame energy band of 44 GRBs taken from
the large \emph{Swift} 5-years data base. Our work highlights the importance of
a proper consideration of the threshold of detection of flares against the
contemporaneous continuous X-ray emission. In the time interval ; this implies
that the flare isotropic energy scaling is . The decay of the continuum underlying the flare emission closely
tracks the average flare luminosity evolution, with a typical flare to
steep-decay luminosity ratio which is : this
suggests that flares and continuum emission are deeply related to one another.
We infer on the progenitor properties considering different models. According
to the hyper-accreting black hole scenario, the average flare luminosity
scaling can be obtained in the case of rapid accretion () or
when the last \sim 0.5 M_{\sun} of the original 14 M_{\sun} progenitor star
are accreted. Alternatively, the steep behaviour could be
triggered by a rapid outward expansion of an accretion shock in the material
feeding a convective disk. If instead we assume the engine to be a rapidly
spinning magnetar, then its rotational energy can be extracted to power a jet
whose luminosity is likely to be between the monopole () and
dipole () cases. In both scenarios we suggest the variability,
which is the main signature of the flaring activity, to be established as a
consequence of different kinds of instabilities.Comment: MNRAS accepte
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