4,184 research outputs found
Geometry of Keplerian disk systems and bounds on masses of their components
We investigate accreting disk systems with polytropic gas in Keplerian
motion. Numerical data and partial analytic results show that the
self-gravitation of the disk speeds up its rotation -- its rotational frequency
is larger than that given by the well known strictly Keplerian formula that
takes into account the central mass only. Thus determination of central mass in
systems with massive disks requires great care -- the strictly Keplerian
formula yields only an upper bound. The effect of self-gravity depends on
geometric aspects of disk configurations. Disk systems with a small (circa
) ratio of the innermost radius to the outermost disk radius have the
central mass close to the upper limit, but if this ratio is of the order of
unity then the central mass can be smaller by many orders of magnitude from
this bound.Comment: 20 pages, 10 figure
Enhanced time response of 1-in. LaBr3(Ce) crystals by leading edge and constant fraction techniques
We have characterized in depth the time response of three detectors equipped
with cylindrical LaBr (Ce) crystals with dimensions of 1-in. in height
and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and
10%. Measurements were performed at Co and Na {\gamma}-ray
energies against a fast BaF reference detector. The time resolution was
optimized by the choice of the photomultiplier bias voltage and the fine tuning
of the parameters of the constant fraction discriminator, namely the
zero-crossing and the external delay. We report here on the optimal time
resolution of the three crystals. It is observed that timing properties are
influenced by the amount of Ce doping and the crystal homogeneity. For the
crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays
in addition to the Hamamatsu R9779 PMT has made it possible to improve the
LaBr(Ce) time resolution from the best literature value at 60Co photon
energies to below 100 ps.Comment: Article submitted to Nuclear Instruments and Methods in Physics
Research Section A: Accelerators, Spectrometers, Detectors and Associated
Equipmen
Senior March : Bradford Academy
https://digitalcommons.library.umaine.edu/mmb-ps/1778/thumbnail.jp
On the Reproducibility of TCGA Ovarian Cancer MicroRNA Profiles
Dysregulated microRNA (miRNA) expression is a well-established feature of
human cancer. However, the role of specific miRNAs in determining cancer
outcomes remains unclear. Using Level 3 expression data from the Cancer Genome
Atlas (TCGA), we identified 61 miRNAs that are associated with overall survival
in 469 ovarian cancers profiled by microarray (p<0.01). We also identified 12
miRNAs that are associated with survival when miRNAs were profiled in the same
specimens using Next Generation Sequencing (miRNA-Seq) (p<0.01). Surprisingly,
only 1 miRNA transcript is associated with ovarian cancer survival in both
datasets. Our analyses indicate that this discrepancy is due to the fact that
miRNA levels reported by the two platforms correlate poorly, even after
correcting for potential issues inherent to signal detection algorithms.
Further investigation is warranted
On the difference between proton and neutron spin-orbit splittings in nuclei
The latest experimental data on nuclei at Sn permit us for the first
time to determine the spin-orbit splittings of neutrons and protons in
identical orbits in this neutron-rich doubly-magic region and compare the case
to that of Pb. Using the new results, which are now consistent for the
two neutron-rich doubly magic regions, a theoretical analysis defines the
isotopic dependence of the mean field spin-orbit potential and leads to a
simple explicit expression for the difference between the spin-orbit splittings
of neutrons and protons. The isotopic dependence is explained in the framework
of different theoretical approaches.Comment: 8 pages, revte
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