1,669 research outputs found
Third minima in actinides - do they exist?
We study the existence of third, hyperdeformed minima in a number of
even-even Th, U and Pu nuclei using the Woods-Saxon microscopic-macroscopic
model that very well reproduces first and second minima and fission barriers in
actinides. Deep ( MeV) minima found previously by \'Cwiok et al. are
found spurious after sufficiently general shapes are included. Shallow third
wells may exist in Th, with IIIrd barriers 200 and 330 keV
(respectively). Thus, a problem of qualitative discrepancy between
microscopic-macroscopic and selfconsistent predictions is resolved. Now, an
understanding of experimental results on the apparent third minima in uranium
becomes an issue.Comment: 5 pages, 3 figures, 02. 03. 2012 - submitted to PR
Subunit interactions influence the biochemical and biological properties of Hsp104
Point mutations in either of the two nucleotide-binding domains (NBD) of Hsp104 (NBD1 and NBD2) eliminate its thermotolerance function in vivo. In vitro, NBD1 mutations virtually eliminate ATP hydrolysis with little effect on hexamerization; analogous NBD2 mutations reduce ATPase activity and severely impair hexamerization. We report that high protein concentrations overcome the assembly defects of NBD2 mutants and increase ATP hydrolysis severalfold, changing V(max) with little effect on K(m). In a complementary fashion, the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate inhibits hexamerization of wild-type (WT) Hsp104, lowering V(max) with little effect on K(m). ATP hydrolysis exhibits a Hill coefficient between 1.5 and 2, indicating that it is influenced by cooperative subunit interactions. To further analyze the effects of subunit interactions on Hsp104, we assessed the effects of mutant Hsp104 proteins on WT Hsp104 activities. An NBD1 mutant that hexamerizes but does not hydrolyze ATP reduces the ATPase activity of WT Hsp104 in vitro. In vivo, this mutant is not toxic but specifically inhibits the thermotolerance function of WT Hsp104. Thus, interactions between subunits influence the ATPase activity of Hsp104, play a vital role in its biological functions, and provide a mechanism for conditionally inactivating Hsp104 function in vivo
VІ Міжнародна науково-практична конференція «Чиста вода. Фундаментальні, прикладні та промислові аспекти»
Magnetic Field Effects near the launching region of Astrophysical Jets
One of the fundamental properties of astrophysical magnetic fields is their
ability to change topology through reconnection and in doing so, to release
magnetic energy, sometimes violently. In this work, we review recent results on
the role of magnetic reconnection and associated heating and particle
acceleration in jet/accretion disk systems, namely young stellar objects
(YSOs), microquasars, and active galactic nuclei (AGNs).Comment: 9 pages, 3 figures, invited paper for the Procs. of the Conference on
High Energy Phenomena in Relativistic Outflows II, Buenos Aires, October
2009. Submitted to International Journal of Modern Physics
Percolation with excluded small clusters and Coulomb blockade in a granular system
We consider dc-conductivity of a mixture of small conducting and
insulating grains slightly below the percolation threshold, where finite
clusters of conducting grains are characterized by a wide spectrum of sizes.
The charge transport is controlled by tunneling of carriers between neighboring
conducting clusters via short ``links'' consisting of one insulating grain.
Upon lowering temperature small clusters (up to some -dependent size) become
Coulomb blockaded, and are avoided, if possible, by relevant hopping paths. We
introduce a relevant percolational problem of next-nearest-neighbors (NNN)
conductivity with excluded small clusters and demonstrate (both numerically and
analytically) that decreases as power law of the size of excluded
clusters. As a physical consequence, the conductivity is a power-law function
of temperature in a wide intermediate temperature range. We express the
corresponding index through known critical indices of the percolation theory
and confirm this relation numerically.Comment: 7 pages, 6 figure
Can jets make the radioactively powered emission from neutron star mergers bluer?
Neutron star mergers eject neutron-rich matter in which heavy elements are synthesized. The decay of these freshly synthesized elements powers electromagnetic transients ('macronovae' or 'kilonovae') whose luminosity and colour strongly depend on their nuclear composition. If the ejecta are very neutron-rich (electron fraction Ye < 0.25), they contain fair amounts of lanthanides and actinides that have large opacities and therefore efficiently trap the radiation inside the ejecta so that the emission peaks in the red part of the spectrum. Even small amounts of this high-opacity material can obscure emission from lower lying material and therefore act as a 'lanthanide curtain'. Here, we investigate how a relativistic jet that punches through the ejecta can potentially push away a significant fraction of the high opacity material before the macronova begins to shine. We use the results of detailed neutrino-driven wind studies as initial conditions and explore with 3D special relativistic hydrodynamic simulations how jets are propagating through these winds. Subsequently, we perform Monte Carlo radiative transfer calculations to explore the resulting macronova emission. We find that the hole punched by the jet makes the macronova brighter and bluer for on-axis observers during the first few days of emission, and that more powerful jets have larger impacts on the macronova
System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector
Reconstruction of the image in Positron Emission Tomographs (PET) requires
the knowledge of the system response kernel which describes the contribution of
each pixel (voxel) to each tube of response (TOR). This is especially important
in list-mode reconstruction systems, where an efficient analytical
approximation of such function is required. In this contribution, we present a
derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear
physics and innovative technologies, Cracow, 03-06 June 201
Novel method for hit-position reconstruction using voltage signals in plastic scintillators and its application to Positron Emission Tomography
Currently inorganic scintillator detectors are used in all commercial Time of
Flight Positron Emission Tomograph (TOF-PET) devices. The J-PET collaboration
investigates a possibility of construction of a PET scanner from plastic
scintillators which would allow for single bed imaging of the whole human body.
This paper describes a novel method of hit-position reconstruction based on
sampled signals and an example of an application of the method for a single
module with a 30 cm long plastic strip, read out on both ends by Hamamatsu
R4998 photomultipliers. The sampling scheme to generate a vector with samples
of a PET event waveform with respect to four user-defined amplitudes is
introduced. The experimental setup provides irradiation of a chosen position in
the plastic scintillator strip with an annihilation gamma quanta of energy
511~keV. The statistical test for a multivariate normal (MVN) distribution of
measured vectors at a given position is developed, and it is shown that signals
sampled at four thresholds in a voltage domain are approximately normally
distributed variables. With the presented method of a vector analysis made out
of waveform samples acquired with four thresholds, we obtain a spatial
resolution of about 1 cm and a timing resolution of about 80 p
Application of Compressive Sensing Theory for the Reconstruction of Signals in Plastic Scintillators
Compressive Sensing theory says that it is possible to reconstruct a measured
signal if an enough sparse representation of this signal exists in comparison
to the number of random measurements. This theory was applied to reconstruct
signals from measurements of plastic scintillators. Sparse representation of
obtained signals was found using SVD transform.Comment: 7 pages, 3 figures; Presented at Symposium on applied nuclear physics
and innovative technologies, Cracow, 03-06 June 201
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