36,439 research outputs found
K Means Segmentation of Alzheimers Disease in PET scan datasets: An implementation
The Positron Emission Tomography (PET) scan image requires expertise in the
segmentation where clustering algorithm plays an important role in the
automation process. The algorithm optimization is concluded based on the
performance, quality and number of clusters extracted. This paper is proposed
to study the commonly used K Means clustering algorithm and to discuss a brief
list of toolboxes for reproducing and extending works presented in medical
image analysis. This work is compiled using AForge .NET framework in windows
environment and MATrix LABoratory (MATLAB 7.0.1)Comment: International Joint Conference on Advances in Signal Processing and
Information Technology, SPIT201
Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare
We analyzed high-cadence sit-and-stare observations acquired with the
Hinode/EIS spectrometer and HXR measurements acquired with RHESSI during an
M-class flare. During the flare impulsive phase, we observe no significant
flows in the cooler Fe XIII line but strong upflows, up to 80-150 km/s, in the
hotter Fe XVI line. The largest Doppler shifts observed in the Fe XVI line were
co-temporal with the sharp intensity peak. The electron density obtained from a
Fe XIII line pair ratio exhibited fast increase (within two minutes) from the
pre-flare level of 5.01x10^(9) cm^(-3) to 3.16x10^(10) cm^(-3) during the flare
peak. The nonthermal energy flux density deposited from the coronal
acceleration site to the lower atmospheric layers during the flare peak was
found to be 1.34x10^(10) erg/s/cm^(2) for a low-energy cut-off that was
estimated to be 16 keV. During the decline flare phase, we found a secondary
intensity and density peak of lower amplitude that was preceded by upflows of
15 km/s that were detected in both lines. The flare was also accompanied by a
filament eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km/s for the upflowing filament material.The
spectroscopic results for the flare peak are consistent with the scenario of
explosive chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the flare. This
outcome is discussed in the context of recent hydrodynamic simulations. It
provides observational evidence that the response of the atmospheric plasma
strongly depends on the properties of the electron beams responsible for the
heating, in particular the steepness of the energy distribution.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
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Dynamic Behavior of Precast Concrete Beam-Column Sub-Assemblages with High Performance Connections Subjected to Sudden Column Removal Scenario
Unbonded posttensioned precast concrete (UPPC) structure has shown its excellent aseismic performance in laboratory tests and earthquake investigation. However, the progressive collapse behavior of UPPC subjected to column removal scenario is still unclear. To fill this knowledge gap, two 1/2 scaled UPPC beam-column sub-assemblages were tested under a penultimate column removal scenario. The dynamic test results indicated that UPPC sub-assemblages have desirable load redistribution capacity to mitigate progressive collapse. The failure modes of the sub-assemblages observed in dynamic test were quite similar to that in static counterparts
Isotopic difference in the heteronuclear loss rate in a two-species surface trap
We have realized a two-species mirror-magneto-optical trap containing a
mixture of Rb (Rb) and Cs atoms. Using this trap, we have
measured the heteronuclear collisional loss rate due to
intra-species cold collisions. We find a distinct difference in the magnitude
and intensity dependence of for the two isotopes Rb and
Rb which we attribute to the different ground-state hyperfine splitting
energies of the two isotopes.Comment: 4 pages, 2 figure
Dirac Cosmology and the Acceleration of the Contemporary Universe
A model is suggested to unify the Einstein GR and Dirac Cosmology. There is
one adjusted parameter in our model. After adjusting the parameter
in the model by using the supernova data, we have calculated the gravitational
constant and the physical quantities of , and by using the present day quantities as the initial conditions and
found that the equation of state parameter equals to -0.83, the
ratio of the density of the addition creation and the
ratio of the density of the matter including multiplication creation, radiation
and normal matter at present. The results are self-consistent
and in good agreement with present knowledge in cosmology. These results
suggest that the addition creation and multiplication creation in Dirac
cosmology play the role of the dark energy and dark matter.Comment: 13 pages, 8 figure
A sequential regularization method for time-dependent incompressible Navier--Stokes equations
The objective of the paper is to present a method, called sequential regularization method (SRM), for the nonstationary incompressible Navier-Stokes equations from the viewpoint of regularization of differential-algebraic equations (DAEs) , and to provide a way to apply a DAE method to partial differential-algebraic equations (PDAEs). The SRM is a functional iterative procedure. It is proved that its convergence rate is O(ffl m ), where m is the number of the SRM iterations and ffl is the regularization parameter. The discretization and implementation issues of the method are considered. In particular, a simple explicit difference scheme is analyzed and its stability is proved under the usual step size condition of explicit schemes. It appears that the SRM formulation is new in the Navier-Stokes context. Unlike other regularizations or pseudo-compressibility methods in the Navier-Stokes context, the regularization parameter ffl in the SRM need not be very small, and the regularized..
Highlights of the SLD Physics Program at the SLAC Linear Collider
Starting in 1989, and continuing through the 1990s, high-energy physics
witnessed a flowering of precision measurements in general and tests of the
standard model in particular, led by e+e- collider experiments operating at the
Z0 resonance. Key contributions to this work came from the SLD collaboration at
the SLAC Linear Collider. By exploiting the unique capabilities of this
pioneering accelerator and the SLD detector, including a polarized electron
beam, exceptionally small beam dimensions, and a CCD pixel vertex detector, SLD
produced a broad array of electroweak, heavy-flavor, and QCD measurements. Many
of these results are one of a kind or represent the world's standard in
precision. This article reviews the highlights of the SLD physics program, with
an eye toward associated advances in experimental technique, and the
contribution of these measurements to our dramatically improved present
understanding of the standard model and its possible extensions.Comment: To appear in 2001 Annual Review of Nuclear and Particle Science; 78
pages, 31 figures; A version with higher resolution figures can be seen at
http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8985.html; Second
version incorporates minor changes to the tex
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