45,370 research outputs found
Supercorotating return flow from reconnection in Saturn's magnetotail
No full textDetecting plasma dynamics in Saturn's magnetosphere is essential for understanding energy flow through the system. It has been proposed that both the Dungey and Vasyliunas cycles operate at Saturn, and the competition between these cycles has been debated. We examine data taken by the Cassini spacecraft in Saturn's post-dawn magnetosphere, similar to 17.5 Saturn radii from the planet, and identify an example of return flow from magnetotail reconnection. The flow included water group ions and had elevated ion temperatures (of order 1 keV), consistent with Vasyliunas cycle return flow. The flow was also supercorotating (similar to 200 km s(-1), similar to 120% of corotation), which is highly atypical of Saturn's outer magnetosphere. Our results suggest that return flows are time-variable, and our results concerning Dungey cycle return flows are inconclusive. We propose that supercorotating flows in Saturn's dawn magnetosphere strongly influence the current system that is responsible for the planet's main auroral emission. Citation: Masters, A., M. F. Thomsen, S. V. Badman, C. S. Arridge, D. T. Young, A. J. Coates, and M. K. Dougherty (2011), Supercorotating return flow from reconnection in Saturn's magnetotail, Geophys. Res. Lett., 38, L03103, doi: 10.1029/2010GL046149
Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ ) and the directCP asymmetry inB 0→K∗0γ
No full textThe ratio of branching fractions of the radiative B decays B0→K⁎0γ and B0s→ϕγ has been measured using an integrated luminosity of 1.0 fb−1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of s√=7TeV. The value obtained is
B(B0→K⁎0γ)B(B0s→ϕγ)=1.23±0.06(stat.)±0.04(syst.)±0.10(fs/fd),
where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for B(B0→K⁎0γ), the branching fraction B(B0s→ϕγ) is measured to be (3.5±0.4)×10−5.
The direct CP asymmetry in B0→K⁎0γ decays has also been measured with the same data and found to be
ACP(B0→K⁎0γ)=(0.8±1.7(stat.)±0.9(syst.))%.
Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations
Topics in genomic image processing
No full textThe image processing methodologies that have been actively studied and developed
now play a very significant role in the flourishing biotechnology research. This work
studies, develops and implements several image processing techniques for M-FISH and
cDNA microarray images. In particular, we focus on three important areas: M-FISH
image compression, microarray image processing and expression-based classification.
Two schemes, embedded M-FISH image coding (EMIC) and Microarray BASICA:
Background Adjustment, Segmentation, Image Compression and Analysis, have been
introduced for M-FISH image compression and microarray image processing, respectively.
In the expression-based classification area, we investigate the relationship
between optimal number of features and sample size, either analytically or through
simulation, for various classifiers
Saturn’s Magnetic Field and Dynamo
No full textThe magnetometer measurements taken by Cassini have confirmed the unusual character of Saturn’s internal magnetic field known from previous flybys and have revealed additional properties that suggest a rather unique dynamo in this planet. Within measurement uncertainty, the internal magnetic field is completely symmetric with respect to Saturn’s spin axis. The upper limit on the tilt of the magnetic dipole could be reduced from 1 to 0.06 degree. Moreover, only axisymmetric quadrupole and octupole moments are needed to fit the data. The lack of non-axisymmetric field components prevents a reliable determination of the bulk rotation rate of Saturn’s deep interior. Using data from Cassini’s closest approach to Saturn during orbit insertion, the magnetic moments of degrees four and five have been determined. The spatial power spectrum shows a zig-zag pattern with high power in odd spherical harmonic degrees and low power in even degrees. Compared to a simple dipole field, this corresponds to a concentration of magnetic flux towards the rotation poles. The flux concentration becomes progressively more pronounced when the field is continued into the interior. Comparison of the Cassini field model with that based on the Pioneer 11 and Voyager 1 and 2 measurements taken roughly 30 years earlier suggests that the secular variation of Saturn’s field is at least one order of magnitude slower than that of the Earth. A viable explanation for most of the unusual field properties is that a stably stratified and electrically conducting layer, formed by a partial demixing of helium from metallic hydrogen, exists on top of a “standard” dynamo in Saturn’s deep interior. This dynamo, driven by thermal and compositional convection, generates a magnetic field that is moderately asymmetric and time dependent. Rapid time variations and non-axisymmetric field components are filtered out in the stable layer by a skin effect. This model also implies that the top of the active dynamo may be located rather deep in Saturn’s interior and the geometric drop-off of the dipole strength with the radius cubed could explain the unexpectedly low field strength at Saturn’s surface. The stable layer model does not provide an explanation for the magnetic flux concentration towards the poles. Strong differential rotation in the dynamo region can have this effect, but a physical mechanism for such a flow state remains to be explored. From magnetic measurements to be taken during the very close approaches in the Grand Finale of the Cassini mission, we can expect to characterize Saturn’s magnetic field up to at least spherical harmonic degree nine and possibly to detect weak non-axisymmetric field components, which would enable an accurate determination of Saturn’s rotation period
Cassini encounters with hot flow anomaly-like phenomena at Saturn's bow shock
No full textThe first observations of the kronian equivalent of hot flow anomalies (HFAs) are presented. Using magnetic field and plasma data we discuss two events that were observed upstream of Saturn's bow shock during the first two orbits of the Cassini spacecraft. We suggest that these events result from the interaction between interplanetary current sheets and the shock surface. This same interaction is responsible for HFAs at the terrestrial bow shock. Calculations of electron temperature reveal an increase by a factor of approximately two for the first event, which is less than for terrestrial HFAs where the increase is by approximately an order of magnitude. In contrast to terrestrial HFAs we find that these events are associated with density enhancement rather than reduction. Estimates of the total pressure for the first event imply that the central region is expanding
∑_(l+m=k,l,m≥0) ((α+l-1)¦l) ((β+m-1)¦m)=((α+β+k-1)¦k) and its application to negative binomial distribution
No full textWe prove here the following equation: ∑_(l+m=k,l,m≥0) ((α+l-1)¦l) ((β+m-1)¦m)=((α+β+k-1)¦k) and give its application to prove the reproductive property of the negative binomial distribution.
These finite sum equation involving binomial coefficients and proof of the reproductive property are not known as far as the author knows.論文(Article)departmental bulletin pape
Nonparametric Bayesian analysis of some clustering problems
No full textNonparametric Bayesian models have been researched extensively in the past 10 years
following the work of Escobar and West (1995) on sampling schemes for Dirichlet processes.
The infinite mixture representation of the Dirichlet process makes it useful
for clustering problems where the number of clusters is unknown. We develop nonparametric
Bayesian models for two different clustering problems, namely functional
and graphical clustering.
We propose a nonparametric Bayes wavelet model for clustering of functional or
longitudinal data. The wavelet modelling is aimed at the resolution of global and
local features during clustering. The model also allows the elicitation of prior belief
about the regularity of the functions and has the ability to adapt to a wide range
of functional regularity. Posterior inference is carried out by Gibbs sampling with
conjugate priors for fast computation. We use simulated as well as real datasets to
illustrate the suitability of the approach over other alternatives.
The functional clustering model is extended to analyze splice microarray data.
New microarray technologies probe consecutive segments along genes to observe alternative
splicing (AS) mechanisms that produce multiple proteins from a single gene.
Clues regarding the number of splice forms can be obtained by clustering the functional
expression profiles from different tissues. The analysis was carried out on the Rosetta dataset (Johnson et al., 2003) to obtain a splice variant by tissue distribution
for all the 10,000 genes. We were able to identify a number of splice forms that appear
to be unique to cancer.
We propose a Bayesian model for partitioning graphs depicting dependencies
in a collection of objects. After suitable transformations and modelling techniques,
the problem of graph cutting can be approached by nonparametric Bayes clustering.
We draw motivation from a recent work (Dhillon, 2001) showing the equivalence of
kernel k-means clustering and certain graph cutting algorithms. It is shown that
loss functions similar to the kernel k-means naturally arise in this model, and the
minimization of associated posterior risk comprises an effective graph cutting strategy.
We present here results from the analysis of two microarray datasets, namely the
melanoma dataset (Bittner et al., 2000) and the sarcoma dataset (Nykter et al.,
2006)
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