44,871 research outputs found
Roles of the Bloom's syndrome helicase in the maintenance of genome stability
The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIalpha, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules
Topological dilaton black holes
In four-dimensional spacetime, when the two-sphere of black hole event
horizons is replaced by a two-dimensional hypersurface with zero or negative
constant curvature, the black hole is referred to as a topological black hole.
In this paper we present some exact topological black hole solutions in the
Einstein-Maxwell-dilaton theory with a Liouville-type dilaton potential.Comment: 8 pages, Revtex, no figure
C_8H_8: a density functional theory study of molecular geometries introducing the localised bond density
In this paper we use density functional theory with all the common exchange-correlation functionals to investigate the structures of three isomers of C_8H_8 found in F. A. Cotton's text, barrelene, cyclooctatetraene, tetramethylenecyclobutane and also ethane and ethene. All calculations were performed with TZ2P basis sets and large quadrature. The results are compared with experiment and those obtained with Hartree–Fock theory. Delocalisation in the three molecules is discussed. A localised bond density in introduced to explain the transferability of the trends in the predictions of the functionals between different molecules. Three-parameter adiabatic connection functionals are examined and their usefulness in geometry prediction questioned. Finally a physical picture of the correlation as modelled by density functional theory is presented and used to explain trends in the overestimation or underestimation of bond lengths
Rotating Dilaton Solutions in 2+1 Dimensions
We report a three parameter family of solutions for dilaton gravity in 2+1
dimensions with finite mass and finite angular momentum. These solutions are
obtained by a compactification of vacuum solutions in 3+1 dimensions with
cylindrical symmetry. One class of solutions corresponds to conical
singularities and the other leads to curvature singularities.Comment: Accepted to be published in Gen. Rel. Grav., added reference
Finding diamonds in the rough: Targeted Sub-threshold Search for Strongly-lensed Gravitational-wave Events
Strong gravitational lensing of gravitational waves can produce duplicate
signals separated in time with different amplitudes. We consider the case in
which strong lensing produces identifiable gravitational-wave events and weaker
sub-threshold signals hidden in the noise background. We present a search
method for the sub-threshold signals using reduced template banks targeting
specific confirmed gravitational-wave events. We apply the method to all events
from Advanced LIGO's first and second observing run O1/O2. Using GW150914 as an
example, we show that the method effectively reduces the noise background and
raises the significance of (near-) sub-threshold triggers. In the case of
GW150914, we can improve the sensitive distance by . Finally,
we present the top possible lensed candidates for O1/O2 gravitational-wave
events that passed our nominal significance threshold of False-Alarm-Rate days
α-pinene photooxidation under controlled chemical conditions – Part 2: SOA yield and composition in low- and high-NO_x environments
The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O_3 in the atmosphere followed by reactions with both HO_2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NO_x OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O_3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO_2) reacted primarily with either HO_2 under low-NO_x conditions or NO under high-NO_x conditions. SOA yield was suppressed under conditions of high-NO_x. SOA yield under high-NO_x conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NO_x conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NO_x products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NO_x conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols
Modifications of the BTZ black hole by a dilaton/scalar
We investigate some modifications of the static BTZ black hole solution due
to a chosen asymptotically constant dilaton/scalar. New classes of static black
hole solutions are obtained. One of the solutions contains the Martinez-Zanelli
conformal black hole solution as a special case. Using quasilocal formalism, we
calculate their mass for a finite spatial region that contains the black hole.
Their temperatures are also computed. Finally, using some of the curvature
singularities as examples, we investigate whether a quantum particle behaves
singularly or not.Comment: 18 pages, Latex, in press in Phys. Rev.
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