15,292 research outputs found
Ultrafast absorption kinetics of NADH in folded and unfolded conformations
The non-radiative energy transfer is shown to occur on a ~3ps time scale for NADH in the folded form in H2O. Addition of methanol thermodynamically favours the open form, for which energy transfer does not occur
Critical Collapse in Einstein-Gauss-Bonnet Gravity in Five and Six Dimensions
Einstein-Gauss-Bonnet gravity (EGB) provides a natural higher dimensional and
higher order curvature generalization of Einstein gravity. It contains a new,
presumably microscopic, length scale that should affect short distance
properties of the dynamics, such as Choptuik scaling. We present the results of
a numerical analysis in generalized flat slice co-ordinates of self-gravitating
massless scalar spherical collapse in five and six dimensional EGB gravity near
the threshold of black hole formation. Remarkably, the behaviour is universal
(i.e. independent of initial data) but qualitatively different in five and six
dimensions. In five dimensions there is a minimum horizon radius, suggestive of
a first order transition between black hole and dispersive initial data. In six
dimensions no radius gap is evident. Instead, below the GB scale there is a
change in the critical exponent and echoing period.Comment: 21 pages, 39 figures, a couple of references and two new figures
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Gedanken Experiments involving Black Holes
Analysis of several gedanken experiments indicates that black hole
complementarity cannot be ruled out on the basis of known physical principles.
Experiments designed by outside observers to disprove the existence of a
quantum-mechanical stretched horizon require knowledge of Planck-scale effects
for their analysis. Observers who fall through the event horizon after sampling
the Hawking radiation cannot discover duplicate information inside the black
hole before hitting the singularity. Experiments by outside observers to detect
baryon number violation will yield significant effects well outside the
stretched horizon.Comment: 22 pages (including 7 figures), SU-ITP-93-1
Dynamics and pattern formation in invasive tumor growth
In this work, we study the in-vitro dynamics of the most malignant form of
the primary brain tumor: Glioblastoma Multiforme. Typically, the growing tumor
consists of the inner dense proliferating zone and the outer less dense
invasive region. Experiments with different types of cells show qualitatively
different behavior. Wild-type cells invade a spherically symmetric manner, but
mutant cells are organized in tenuous branches. We formulate a model for this
sort of growth using two coupled reaction-diffusion equations for the cell and
nutrient concentrations. When the ratio of the nutrient and cell diffusion
coefficients exceeds some critical value, the plane propagating front becomes
unstable with respect to transversal perturbations. The instability threshold
and the full phase-plane diagram in the parameter space are determined. The
results are in a good agreement with experimental findings for the two types of
cells.Comment: 4 pages, 4 figure
Orthogonality catastrophe in a composite fermion liquid
We discuss the emergence of an orthogonality catastrophe in the response of a
composite fermion liquid as the filling factor \nu approaches 1/2m, where
m=1,2,3.... A tunneling experiment is proposed in which dramatic changes in the
I-V characteristic should be observable as \nu is varied. Explicit I-V
characteristics calculated within the so-called Modified Random Phase
Approximation, are provided for \nu=1/3 -> \nu=1/2.Comment: Latex two-column 6 pages including 5 figure
The Number of States of Two Dimensional Critical String Theory
We discuss string theory vacua which have the wrong number of spacetime
dimensions, and give a crude argument that vacua with more than four large
dimensions are improbable. We then turn to two dimensional vacua, which naively
appear to violate Bekenstein's entropy principle. A classical analysis shows
that the naive perturbative counting of states is unjustified. All excited
states of the system have strong coupling singularities which prevent us from
concluding that they really exist. A speculative interpretation of the
classical solutions suggests only a finite number of states will be found in
regions bounded by a finite area. We also argue that the vacuum degeneracy of
two dimensional classical string theory is removed in quantum mechanics. The
system appears to be in a Kosterlitz-Thouless phase. This leads to the
conclusion that it is also improbable to have only two large spacetime
dimensions in string theory. However, we note that, unlike our argument for
high dimensions, our conclusions about the ground state have neglected two
dimensional quantum gravitational effects, and are at best incomplete.Comment: 12 pages, harvma
Black Hole Evaporation in 1+1 Dimensions
The formation and quantum mechanical evaporation of black holes in two
spacetime dimensions can be studied using effective classical field equations,
recently introduced by Callan {\it et al.} We find that gravitational collapse
always leads to a curvature singularity, according to these equations, and that
the region where the quantum corrections introduced by Callan {\it et al.}
could be expected to dominate is on the unphysical side of the singularity. The
model can be successfully applied to study the back-reaction of Hawking
radiation on the geometry of large mass black holes, but the description breaks
down before the evaporation is complete.Comment: 10 page
Neural mechanisms of resistance to peer influence in early adolescence
During the shift from a parent-dependent child to a fully autonomous adult, peers take on a significant role in shaping the adolescent’s behaviour. Peer-derived influences are not always positive, however. Here we explore neural correlates of inter-individual differences in the probability of resisting peer influence in early adolescence. Using functional magnetic-resonance imaging (fMRI), we found striking differences between 10-year old children with high and low resistance to peer influence in their brain activity during observation of angry hand-movements and angry facial expressions: compared with subjects with low resistance to peer influence, individuals with high resistance showed a highly coordinated brain activity in neural systems underlying perception of action and decision making. These findings suggest that the probability of resisting peer influence depends on neural interactions during observation of emotion-laden actions
Season of the year influences infection rates following total hip arthroplasty
To research the influence of season of the year on periprosthetic joint infections. METHODS We conducted a retrospective review of the entire Medicare files from 2005 to 2014. Seasons were classified as spring, summer, fall or winter. Regional variations were accounted for by dividing patients into four geographic regions as per the United States Census Bureau (Northeast, Midwest, West and South). Acute postoperative infection and deep periprosthetic infections within 90 d after surgery were tracked. RESULTS In all regions, winter had the highest incidence of periprosthetic infections (mean 0.98%, SD 0.1%) and was significantly higher than other seasons in the Midwest, South and West (P \u3c 0.05 for all) but not the Northeast (P = 0.358). Acute postoperative infection rates were more frequent in the summer and were significantly affected by season of the year in the West. CONCLUSION Season of the year is a risk factor for periprosthetic joint infection following total hip arthroplasty (THA). Understanding the influence of season on outcomes following THA is essential when risk-stratifying patients to optimize outcomes and reduce episode of care costs. © The Author(s) 2017
Asymptotic level density in heterotic string theory and rotating black holes
We calculate the density of states with given mass and spin in string theory
and obtain asymptotic formulas. We also compute the tree-level gyromagnetic
couplings for arbitrary physical states in the heterotic string theory. These
results are then applied to study whether fundamental strings can consistently
describe the microphysics of the black hole horizon in the case of a general
classical solution characterized by mass, charge and angular momentum.Comment: 15 pages, UTTG-9-9
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