209 research outputs found
Mobility of thorium ions in liquid xenon
We present a measurement of the Th ion mobility in LXe at 163.0 K and
0.9 bar. The result obtained, 0.2400.011 (stat) 0.011 (syst)
cm/(kV-s), is compared with a popular model of ion transport.Comment: 6.5 pages,
How spiking neurons give rise to a temporal-feature map
A temporal-feature map is a topographic neuronal representation of temporal attributes of phenomena or objects that occur in the outside world. We explain the evolution of such maps by means of a spike-based Hebbian learning rule in conjunction with a presynaptically unspecific contribution in that, if a synapse changes, then all other synapses connected to the same axon change by a small fraction as well. The learning equation is solved for the case of an array of Poisson neurons. We discuss the evolution of a temporal-feature map and the synchronization of the single cells’ synaptic structures, in dependence upon the strength of presynaptic unspecific learning. We also give an upper bound for the magnitude of the presynaptic interaction by estimating its impact on the noise level of synaptic growth. Finally, we compare the results with those obtained from a learning equation for nonlinear neurons and show that synaptic structure formation may profit
from the nonlinearity
Parity nonconserving cold neutron-parahydrogen interactions
Three pion dominated observables of the parity nonconserving interactions
between the cold neutrons and parahydrogen are calculated. The transversely
polarized neutron spin rotation, unpolarized neutron longitudinal polarization,
and photon-asymmetry of the radiative polarized neutron capture are considered.
For the numerical evaluation of the observables, the strong interactions are
taken into account by the Reid93 potential and the parity nonconserving
interactions by the DDH model along with the two-pion exchange.Comment: 17 pages, 2 figure
Electroweak Radiative Corrections to Parity-Violating Electroexcitation of the
We analyze the degree to which parity-violating (PV) electroexcitation of the
resonance may be used to extract the weak neutral axial vector
transition form factors. We find that the axial vector electroweak radiative
corrections are large and theoretically uncertain, thereby modifying the
nominal interpretation of the PV asymmetry in terms of the weak neutral form
factors. We also show that, in contrast to the situation for elastic electron
scattering, the axial PV asymmetry does not vanish at the photon
point as a consequence of a new term entering the radiative corrections. We
argue that an experimental determination of these radiative corrections would
be of interest for hadron structure theory, possibly shedding light on the
violation of Hara's theorem in weak, radiative hyperon decays.Comment: RevTex, 76 page
Partially Annealed Disorder and Collapse of Like-Charged Macroions
Charged systems with partially annealed charge disorder are investigated
using field-theoretic and replica methods. Charge disorder is assumed to be
confined to macroion surfaces surrounded by a cloud of mobile neutralizing
counterions in an aqueous solvent. A general formalism is developed by assuming
that the disorder is partially annealed (with purely annealed and purely
quenched disorder included as special cases), i.e., we assume in general that
the disorder undergoes a slow dynamics relative to fast-relaxing counterions
making it possible thus to study the stationary-state properties of the system
using methods similar to those available in equilibrium statistical mechanics.
By focusing on the specific case of two planar surfaces of equal mean surface
charge and disorder variance, it is shown that partial annealing of the
quenched disorder leads to renormalization of the mean surface charge density
and thus a reduction of the inter-plate repulsion on the mean-field or
weak-coupling level. In the strong-coupling limit, charge disorder induces a
long-range attraction resulting in a continuous disorder-driven collapse
transition for the two surfaces as the disorder variance exceeds a threshold
value. Disorder annealing further enhances the attraction and, in the limit of
low screening, leads to a global attractive instability in the system.Comment: 21 pages, 2 figure
Mutation of Ser172 in Yeast β Tubulin Induces Defects in Microtubule Dynamics and Cell Division
Ser172 of β tubulin is an important residue that is mutated in a human brain disease and phosphorylated by the cyclin-dependent kinase Cdk1 in mammalian cells. To examine the role of this residue, we used the yeast S. cerevisiae as a model and produced two different mutations (S172A and S172E) of the conserved Ser172 in the yeast β tubulin Tub2p. The two mutants showed impaired cell growth on benomyl-containing medium and at cold temperatures, altered microtubule (MT) dynamics, and altered nucleus positioning and segregation. When cytoplasmic MT effectors Dyn1p or Kar9p were deleted in S172A and S172E mutants, cells were viable but presented increased ploidy. Furthermore, the two β tubulin mutations exhibited synthetic lethal interactions with Bik1p, Bim1p or Kar3p, which are effectors of cytoplasmic and spindle MTs. In the absence of Mad2p-dependent spindle checkpoint, both mutations are deleterious. These findings show the importance of Ser172 for the correct function of both cytoplasmic and spindle MTs and for normal cell division
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Measurement of spin correlation in ttbar production using dilepton final states
We measure the correlation between the spin of the top quark and the spin of
the anti-top quark in (ttbar -> W+ W- b bbar -> l+ nu b l- nubar bbar) final
states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96
TeV, where l is an electron or muon. The data correspond to an integrated
luminosity of 5.4 fb-1 and were collected with the D0 detector at the Fermilab
Tevatron collider. The correlation is extracted from the angles of the two
leptons in the t and tbar rest frames, yielding a correlation strength C=
0.10^{+0.45}_{-0.45}, in agreement with the NLO QCD prediction within two
standard deviations, but also in agreement with the no correlation hypothesis.Comment: 10 pages, 3 figures, submitted to PL
Search for charged Higgs bosons in top quark decays
We present a search for charged Higgs bosons in top quark decays. We analyze
the \eplus, \muplus, , , , \etau and \mutau final states from
top quark pair production events, using data from about 1 of
integrated luminosity recorded by the \dzero experiment at the Fermilab
Tevatron Collider. We consider different scenarios of possible charged Higgs
boson decays, one where the charged Higgs boson decays purely hadronically into
a charm and a strange quark, another where it decays into a lepton and a
neutrino and a third one where both decays appear. We extract limits on
the branching ratio for all these models. We use two methods,
one where the production cross section is fixed, and one where the
cross section is fitted simultaneously with . Based on the
extracted limits, we exclude regions in the charged Higgs boson mass and parameter space for different scenarios of the minimal supersymmetric
standard model.Comment: 10 pages, 8 figures, submitted to PL
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
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