1,123 research outputs found
Low-Energy Shape Resonances of a Nucleobase in Water
When high-energy radiation passes through aqueous material, low-energy electrons are produced which cause DNA damage. Electronic states of anionic nucleobases have been suggested as an entrance channel to capture the electron. However, identifying these electronic resonances have been restricted to gas-phase electron-nucleobase studies and offer limited insight into the resonances available within the aqueous environment of DNA. Here, resonance and detachment energies of the micro-hydrated uracil pyrimidine nucleobase anion are determined by two-dimensional photoelectron spectroscopy and are shown to extrapolate linearly with cluster size. This extrapolation allows the corresponding resonance and detachment energies to be determined for uracil in aqueous solution as well as the reorganization energy associated with electron capture. Two shape resonances are clearly identified that can capture low-energy electrons and subsequently form the radical anion by solvent stabilization and internal conversion to the ground electronic state. The resonances and their dynamics probed here are the nucleobase-centered doorway states for low-energy electron capture and damage in DNA
Synchronous N-S and E-W extension at the Tibet-to-Himalaya transition in NW Bhutan
Despite ~50 Myr of continuous continent-continent collision, contractional structures in the Himalayan-Tibetan orogen are today limited to the northern and southern margins of the system, while extension dominates much of the interior. On the Tibetan Plateau, Cenozoic E-W extension has been accommodated by strike-slip faults and extensional grabens, while N-S extension at the Tibet-to-Himalaya transition has been accommodated by the South Tibetan fault system (STFS). The genetic relationship between N-S and E-W extension is disputed, although age constraints indicate temporal overlap of at least 7 Myr. In NW Bhutan the two intersect where the STFS basal detachment is cut by the Yadong cross structure (YCS), an extensional half graben that provides a rare opportunity to constrain relative timings. We report U-Pb zircon dates from four STFS footwall leucogranites consistent with episodic magmatism during the middle-late Miocene and in situ U(-Th)-Pb monazite and xenotime dates from three metasedimentary rocks ranging from late Oligocene to middle Miocene. We suggest that amphibolite facies footwall metamorphism was ongoing at the time the basal STFS detachment initiated as a ductile structure in the middle-late Miocene. Late-stage granitic intrusions may reflect footwall melting during extensional exhumation along the STFS, but post-metamorphic and post-intrusion fabrics suggest that most displacement occurred after emplacement of the youngest granites. Some of the oldest YCS-related fabrics are found in a deformed 14 Ma leucogranite, implying middle Miocene ductile deformation. This observation, along with evidence for subsequent brittle YCS deformation, suggests that N-S and E-W extensional structures in the area had protracted and overlapping deformation histories
Modeling Dynamic Channel-Allocation Algorithms in Multi-BS TDD Wireless Networks With Internet-Based Traffic
Signatures of Electronic Nematic Phase at Isotropic-Nematic Phase Transition
The electronic nematic phase occurs when the point-group symmetry of the
lattice structure is broken, due to electron-electron interactions. We study a
model for the nematic phase on a square lattice with emphasis on the phase
transition between isotropic and nematic phases within mean field theory. We
find the transition to be first order, with dramatic changes in the Fermi
surface topology accompanying the transition. Furthermore, we study the
conductivity tensor and Hall constant as probes of the nematic phase and its
transition. The relevance of our findings to Hall resistivity experiments in
the high- cuprates is discussed.Comment: 5 pages, 3 figure
Foam Diagram Summation at Finite Temperature
We show that large- theory is not trivial if one accepts the
presence of a tachyon with a truly huge mass, and that it allows exact
calculation. We use it to illustrate how to calculate the exact resummed
pressure at finite temperature and verify that it is infrared and ultraviolet
finite even in the zero-mass case. In 3 dimensions a residual effect of the
resummed infrared divergences is that at low temperature or strong coupling the
leading term in the interaction pressure becomes independent of the coupling
and is 4/5 of the free-field pressure. In 4 dimensions the pressure is
well-defined provided that the temperature is below the tachyon mass. We
examine how rapidly this expansion converges and use our analysis to suggest
how one might reorganise perturbation theory to improve the calculation of the
pressure for the QCD plasma.Comment: 18 pages plain tex, with 8 figures embedded with epsf. Equation
(2.15) has been corrected and the consequent changes made to the figures. A
further analytic result has been added to the 3-dimensional calculatio
New insulating phases of two-dimensional electrons in high Landau levels: observation of sharp thresholds to conduction
The intriguing re-entrant integer quantized Hall states recently discovered
in high Landau levels of high-mobility 2D electron systems are found to exhibit
extremely non-linear transport. At small currents these states reflect
insulating behavior of the electrons in the uppermost Landau level. At larger
currents, however, a discontinuous and hysteretic transition to a conducting
state is observed. These phenomena, found only in very narrow magnetic field
ranges, are suggestive of the depinning of a charge density wave state, but
other explanations can also be constructed.Comment: 5 pages, 5 figure
Quantum Hall ferromagnets, cooperative transport anisotropy, and the random field Ising model
We discuss the behaviour of a quantum Hall system when two Landau levels with
opposite spin and combined filling factor near unity are brought into energetic
coincidence using an in-plane component of magnetic field. We focus on the
interpretation of recent experiments under these conditions [Zeitler et al,
Phys. Rev. Lett. 86, 866 (2001); Pan et al, Phys. Rev. B 64, 121305 (2001)], in
which a large resistance anisotropy develops at low temperatures. Modelling the
systems involved as Ising quantum Hall ferromagnets, we suggest that this
transport anisotropy reflects domain formation induced by a random field
arising from isotropic sample surface roughness.Comment: 4 pages, submitted to Physical Review
Healthcare-associated outbreak of meticillin-resistant Staphylococcus aureus bacteraemia: role of a cryptic variant of an epidemic clone
BACKGROUND
New strains of meticillin-resistant Staphylococcus aureus (MRSA) may be associated with changes in rates of disease or clinical presentation. Conventional typing techniques may not detect new clonal variants that underlie changes in epidemiology or clinical phenotype.
AIM
To investigate the role of clonal variants of MRSA in an outbreak of MRSA bacteraemia at a hospital in England.
METHODS
Bacteraemia isolates of the major UK lineages (EMRSA-15 and -16) from before and after the outbreak were analysed by whole-genome sequencing in the context of epidemiological and clinical data. For comparison, EMRSA-15 and -16 isolates from another hospital in England were sequenced. A clonal variant of EMRSA-16 was identified at the outbreak hospital and a molecular signature test designed to distinguish variant isolates among further EMRSA-16 strains.
FINDINGS
By whole-genome sequencing, EMRSA-16 isolates during the outbreak showed strikingly low genetic diversity (P < 1 × 10(-6), Monte Carlo test), compared with EMRSA-15 and EMRSA-16 isolates from before the outbreak or the comparator hospital, demonstrating the emergence of a clonal variant. The variant was indistinguishable from the ancestral strain by conventional typing. This clonal variant accounted for 64/72 (89%) of EMRSA-16 bacteraemia isolates at the outbreak hospital from 2006.
CONCLUSIONS
Evolutionary changes in epidemic MRSA strains not detected by conventional typing may be associated with changes in disease epidemiology. Rapid and affordable technologies for whole-genome sequencing are becoming available with the potential to identify and track the emergence of variants of highly clonal organisms
The effect of memory on relaxation in a scalar field theory
We derive a kinetic equation with a non-Markovian collision term which
includes a memory effect, from Kadanoff-Baym equations in theory
within the three-loop level for the two-particle irreducible (2PI) effective
action. The memory effect is incorporated into the kinetic equation by a
generalized Kadanoff-Baym ansatz.Based on the kinetic equations with and
without the memory effect, we investigate an influence of this effect on decay
of a single particle excitation with zero momentum in 3+1 dimensions and the
spatially homogeneous case. Numerical results show that, while the time
evolution of the zero mode is completely unaffected by the memory effect due to
a separation of scales in the weak coupling regime, this effect leads first to
faster relaxation than the case without it and then to slower relaxation as the
coupling constant increases.Comment: 12 pages, 6 eps figure
Anisotropic transport in unidirectional lateral superlattice around half-filling of the second Landau level
We have observed marked transport anisotropy in short period (a=92 nm)
unidirectional lateral superlattices around filling factors nu=5/2 and 7/2:
magnetoresistance shows a sharp peak for current along the modulation grating
while a dip appears for current across the grating. By altering the ratio a/l
(with l=sqrt{hbar/eB_perp} the magnetic length) via changing the electron
density n_e, it is shown that the nu=5/2 anisotropic features appear in the
range 6.6 alt a/l alt 7.2 varying their intensities, becoming most conspicuous
at a/l simeq 6.7. The peak/dip broadens with temperature roughly preserving its
height/depth up to 250 mK. Tilt experiments reveal that the structures are
slightly enhanced by an in-plane magnetic field B_| perpendicular to the
grating but are almost completely destroyed by B_| parallel to the grating. The
observations suggest the stabilization of a unidirectional charge-density-wave
or stripe phase by weak external periodic modulation at the second Landau
level.Comment: REVTeX, 5 pages, 3 figures, Some minor revisions, Added notes and
reference
- …