4,029 research outputs found
Lasing characteristics of gas mixtures involving UFG: Application to nuclear pumping of lasers
Intense blue-green fluorescence from a structured band centered at lambda approximately 484 nm was observed from Ar, CF3I and NF3 gas mixtures excited by an electron beam. This emission was tentatively assigned to the E yields A transition of the iodine monofluoride (IF) molecule. The fluorescence efficiency of the IF(E yields A) band and the IF (E) state radiative lifetime were estimated to be approximately 6% and 15 ns, respectively. The emission band structure, the short IF(E) radiative lifetime and the Franck-Condon shift between the E and A states suggest that IF is an attractive candidate for a blue-green laser
Examining Tensions in the Past and Present Uses of Concepts (preprint)
Examining tensions between the past and present uses of scientific concepts can help clarify their contributions as tools in experimental practices. This point can be illustrated by considering the concepts of mental imagery and hallucinations: despite debates over their respective referential reliabilities remaining unresolved within their interdependent histories, both are used as independently stable concepts in neuroimaging experiments. Building on an account of how these concepts function as tools structured for pursuit of diverging goals in experiments, this paper explores this tension by re-examining the continued reliance of each concept on inverse characterisations inherited from the nominally-discarded âmediator-viewâ of sensory-like mental phenomena (SLMP). In doing so, I seek to demonstrate how examining unresolved tensions can help highlight that entrenched associations can remain both integral to, and obscured by, the uses of concepts as goal-directed tools within experimental practices
Partial non-renormalisation of the stress-tensor four-point function in N=4 SYM and AdS/CFT
We show that, although the correlator of four stress-tensor multiplets in N=4
SYM is known to have radiative corrections, certain linear combinations of its
components are protected from perturbative renormalisation and remain at their
free-field values. This result is valid for weak as well as for strong coupling
and for any gauge group. Our argument uses Intriligator's insertion formula,
and includes a proof that the possible contact term contributions cannot change
the form of the amplitudes. Combining this new non-renormalisation theorem with
Maldacena's conjecture allows us to make a prediction for the structure of the
corresponding correlator in AdS supergravity. This is verified by first
considerably simplifying the strong coupling expression obtained by recent
supergravity calculations, and then showing that it does indeed exhibit the
expected structure.Comment: 21 pages, no figure
On Approximating the Number of -cliques in Sublinear Time
We study the problem of approximating the number of -cliques in a graph
when given query access to the graph.
We consider the standard query model for general graphs via (1) degree
queries, (2) neighbor queries and (3) pair queries. Let denote the number
of vertices in the graph, the number of edges, and the number of
-cliques. We design an algorithm that outputs a
-approximation (with high probability) for , whose
expected query complexity and running time are
O\left(\frac{n}{C_k^{1/k}}+\frac{m^{k/2}}{C_k}\right)\poly(\log
n,1/\varepsilon,k).
Hence, the complexity of the algorithm is sublinear in the size of the graph
for . Furthermore, we prove a lower bound showing that
the query complexity of our algorithm is essentially optimal (up to the
dependence on , and ).
The previous results in this vein are by Feige (SICOMP 06) and by Goldreich
and Ron (RSA 08) for edge counting () and by Eden et al. (FOCS 2015) for
triangle counting (). Our result matches the complexities of these
results.
The previous result by Eden et al. hinges on a certain amortization technique
that works only for triangle counting, and does not generalize for larger
cliques. We obtain a general algorithm that works for any by
designing a procedure that samples each -clique incident to a given set
of vertices with approximately equal probability. The primary difficulty is in
finding cliques incident to purely high-degree vertices, since random sampling
within neighbors has a low success probability. This is achieved by an
algorithm that samples uniform random high degree vertices and a careful
tradeoff between estimating cliques incident purely to high-degree vertices and
those that include a low-degree vertex
Nonlinear field theories during homogeneous spatial dilation
The effect of a uniform dilation of space on stochastically driven nonlinear
field theories is examined. This theoretical question serves as a model problem
for examining the properties of nonlinear field theories embedded in expanding
Euclidean Friedmann-Lema\^{\i}tre-Robertson-Walker metrics in the context of
cosmology, as well as different systems in the disciplines of statistical
mechanics and condensed matter physics. Field theories are characterized by the
speed at which they propagate correlations within themselves. We show that for
linear field theories correlations stop propagating if and only if the speed at
which the space dilates is higher than the speed at which correlations
propagate. The situation is in general different for nonlinear field theories.
In this case correlations might stop propagating even if the velocity at which
space dilates is lower than the velocity at which correlations propagate. In
particular, these results imply that it is not possible to characterize the
dynamics of a nonlinear field theory during homogeneous spatial dilation {\it a
priori}. We illustrate our findings with the nonlinear Kardar-Parisi-Zhang
equation
Timing matters: impact of anticonvulsant drug treatment and spikes on seizure risk in benign epilepsy with centrotemporal spikes
OBJECTIVE: Benign epilepsy with centrotemporal spikes (BECTS) is a common, self-limited epilepsy syndrome affecting school-age children. Classic interictal epileptiform discharges (IEDs) confirm diagnosis, and BECTS is presumed to be pharmacoresponsive. As seizure risk decreases in time with this disease, we hypothesize that the impact of IEDs and anticonvulsive drug (ACD) treatment on the risk of subsequent seizure will differ based on disease duration. METHODS: We calculate subsequent seizure risk following diagnosis in a large retrospective cohort of children with BECTS (n = 130), evaluating the impact of IEDs and ACD treatment in the first, second, third, and fourth years of disease. We use a Kaplan-Meier survival analysis and logistic regression models. Patients were censored if they were lost to follow-up or if they changed group status. RESULTS: Two-thirds of children had a subsequent seizure within 2 years of diagnosis. The majority of children had a subsequent seizure within 3 years despite treatment. The presence of IEDs on electroencephalography (EEG) did not impact subsequent seizure risk early in the disease. By the fourth year of disease, all children without IEDs remained seizure free, whereas one-third of children with IEDs at this stage had a subsequent seizure. Conversely, ACD treatment corresponded with lower risk of seizure early in the disease but did not impact seizure risk in later years. SIGNIFICANCE: In this cohort, the majority of children with BECTS had a subsequent seizure despite treatment. In addition, ACD treatment and IEDs predicted seizure risk at specific points of disease duration. Future prospective studies are needed to validate these exploratory findings.Published versio
b anti-b Higgs production at the LHC: Yukawa corrections and the leading Landau singularity
At tree-level Higgs production in association with a b-quark pair proceeds
through the small Yukawa bottom coupling in the Standard Model. Even in the
limit where this coupling vanishes, electroweak one-loop effects, through the
top-Higgs Yukawa coupling in particular, can still trigger this reaction. This
contribution is small for Higgs masses around 120GeV but it quickly picks up
for higher Higgs masses especially because the one-loop amplitude develops a
leading Landau singularity and new thresholds open up. These effects can be
viewed as the production of a pair of top quarks which rescatter to give rise
to Higgs production through WW fusion. We study the leading Landau singularity
in detail. Since this singularity is not integrable when the one-loop amplitude
is squared, we regulate the cross section by taking into account the width of
the internal top and W particles. This requires that we extend the usual box
one-loop function to the case of imaginary masses. We show how this can be
implemented analytically in our case. We study in some detail the cross section
at the LHC as a function of the Higgs mass and show how some distributions can
be drastically affected compared to the tree-level result.Comment: 48 pages, 20 figures. Phys.Rev.D accepted version. Conclusions
unchanged, minor changes and references adde
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