610,955 research outputs found
Fast Fits for Lattice QCD Correlators
We illustrate a technique for fitting lattice QCD correlators to sums of
exponentials that is significantly faster than traditional fitting methods ---
10--40 times faster for the realistic examples we present. Our examples are
drawn from a recent analysis of the Upsilon spectrum, and another recent
analysis of the D -> pi semileptonic form factor. For single correlators, we
show how to simplify traditional effective-mass analyses.Comment: 5 pages, 4 figure
tmfast fits topic models fast
tmfast is an R package for fitting topic models using a fast algorithm based
on partial PCA and the varimax rotation. After providing mathematical
background to the method, we present two examples, using a simulated corpus and
aggregated works of a selection of authors from the long nineteenth century,
and compare the quality of the fitted models to a standard topic modeling
package
Analysis of a HMM time-discretization scheme for a system of Stochastic PDE's
We consider the discretization in time of a system of parabolic stochastic
partial differential equations with slow and fast components; the fast equation
is driven by an additive space-time white noise. The numerical method is
inspired by the Averaging Principle satisfied by this system, and fits to the
framework of Heterogeneous Multiscale Methods.The slow and the fast components
are approximated with two coupled numerical semi-implicit Euler schemes
depending on two different timestep sizes. We derive bounds of the
approximation error on the slow component in the strong sense - approximation
of trajectories - and in the weak sense - approximation of the laws. The
estimates generalize the results of \cite{E-L-V} in the case of infinite
dimensional processes
aMCfast: automation of fast NLO computations for PDF fits
We present the interface between MadGraph5 aMC@NLO, a self-contained program that calculates cross sections up to next-to-leading order accuracy in an automated manner, and APPLgrid, a code that parametrises such cross sections in the form of look-up tables which can be used for the fast computations needed in the context of PDF fits. The main characteristic of this interface, which we dub aMCfast, is its being fully automated as well, which removes the need to extract manually the process-specific information for additional physics processes, as is the case with other matrix-element calculators, and renders it straightforward to include any new process in the PDF fits. We demonstrate this by studying several cases which are easily measured at the LHC, have a good constraining power on PDFs, and some of which were previously unavailable in the form of a fast interface
Fast TeV variability from misaligned minijets in the jet of M87
The jet of the radio galaxy M87 is misaligned, resulting in a Doppler factor
delta~1 for emission of plasma moving parallel to the jet. This makes the
observed fast TeV flares on timescales of t_v~5R_g/c harder to understand as
emission from the jet. In previous work, we have proposed a jets-in-a-jet model
for the ultra-fast TeV flares with t_v<<R_g/c seen in Mrk 501 and PKS 2155-304.
Here, we show that about half of the minijets beam their emission outside the
jet cone. Minijets emitting off the jet axis result in rapidly evolving TeV
(and maybe lower energy) flares that can be observed in nearby radio galaxies.
The TeV flaring from M87 fits well into this picture, if M87 is a misaligned
blazar.Comment: 9 pages, 5 figures, minor changes, MNRAS, accepte
Nanoscale surface relaxation of a membrane stack
Recent measurements of the short-wavelength (~ 1--100 nm) fluctuations in
stacks of lipid membranes have revealed two distinct relaxations: a fast one
(decay rate of ~ 0.1 ns^{-1}), which fits the known baroclinic mode of bulk
lamellar phases, and a slower one (~ 1--10 \mu s^{-1}) of unknown origin. We
show that the latter is accounted for by an overdamped capillary mode,
depending on the surface tension of the stack and its anisotropic viscosity. We
thereby demonstrate how the dynamic surface tension of membrane stacks could be
extracted from such measurements.Comment: 4 page
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