12,599 research outputs found
Translation of Time-Reversal Violation in the Neutral K-Meson System into a Table-Top Mechanical System
Weak interactions break time-reversal (T) symmetry in the two-state system of
neutral K mesons. We present and discuss a two-state mechanical system, a
Foucault-type pendulum on a rotating table, for a full representation of K0
K0bar transitions by the pendulum motions including T violation. The pendulum
moves with two different oscillation frequencies and two different magnetic
dampings. Its equation of motion is identical with the differential equation
for the real part of the CPT-symmetric K-meson wave function. The pendulum is
able to represent microscopic CP and T violation with CPT symmetry owing to the
macroscopic Coriolis force which breaks the symmetry under reversal-of-motion.
Video clips of the pendulum motions are shown as supplementary material.Comment: 11 pages, 5 figures, 1 external url with video clip
Enhanced imaging of microcalcifications in digital breast tomosynthesis through improved image-reconstruction algorithms
PURPOSE: We develop a practical, iterative algorithm for image-reconstruction
in under-sampled tomographic systems, such as digital breast tomosynthesis
(DBT).
METHOD: The algorithm controls image regularity by minimizing the image total
-variation (TpV), a function that reduces to the total variation when
or the image roughness when . Constraints on the image, such as
image positivity and estimated projection-data tolerance, are enforced by
projection onto convex sets (POCS). The fact that the tomographic system is
under-sampled translates to the mathematical property that many widely varied
resultant volumes may correspond to a given data tolerance. Thus the
application of image regularity serves two purposes: (1) reduction of the
number of resultant volumes out of those allowed by fixing the data tolerance,
finding the minimum image TpV for fixed data tolerance, and (2) traditional
regularization, sacrificing data fidelity for higher image regularity. The
present algorithm allows for this dual role of image regularity in
under-sampled tomography.
RESULTS: The proposed image-reconstruction algorithm is applied to three
clinical DBT data sets. The DBT cases include one with microcalcifications and
two with masses.
CONCLUSION: Results indicate that there may be a substantial advantage in
using the present image-reconstruction algorithm for microcalcification
imaging.Comment: Submitted to Medical Physic
Molecular Dynamics Simulations of Field Emission From a Prolate Spheroidal Tip
High resolution molecular dynamics simulations with full Coulomb interactions
of electrons are used to investigate field emission from a prolate spheroidal
tip. The space charge limited current is several times lower than the current
calculated with the Fowler-Nordheim formula. The image-charge is taken into
account with a spherical approximation, which is good around the top of the
tip, i.e. region where the current is generated.Comment: 6 pages, 8 figure
Imaging of Hepatocellular Carcinoma by Computed Tomography and Magnetic Resonance Imaging: State of the Art
Hepatocellular carcinoma (HCC) is a very frequent tumor worldwide. Its incidence is linked to the distribution of liver cirrhosis and viral hepatitis, which are the main risk factors for the development of HCC. For the evaluation of the cirrhotic liver and for the diagnosis of HCC, multidetector computed tomography (MDCT) proved to be a robust and reliable tool. In MDCT the diagnosis of HCC can be made based on neovascularization with increased arterial and decreased portal venous supply. With modern magnetic resonance imaging (MRI), spatial resolution and robustness increased dramatically. Beside the evaluation of neovascularization by means of gadolinium-enhanced early dynamic MRI, the main advantages of MRI are additional information on tissue composition and liver-specific function. With diffusion-weighted imaging or plain T(1)- and T(2)-weighted sequences, different tissue elements like fat, hemorrhage, glycogen, edema and cellular density can be evaluated. Liver-specific contrast agents give insight into the Kupffer cell density or the hepatocellular function. The integration of all these parts into the MR examination allows for a very high detection rate for overt HCC nowadays, although very small HCCs are still a challenge. Moreover, insight into the different stages of hepatocarcinogenesis can be possible with MRI. Despite its limited availability in some countries, it has to be rendered to be the modality of choice for the distinct evaluation of the cirrhotic liver. Copyright (C) 2009 S. Karger AG, Base
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