11,947 research outputs found
Modifying and Accelerating the Method of Moments Calculation
This manuscript deals with optimizing the numerical method called the method of moments (MoM). This method is widely utilized for field computation of 3D structures. MoM is exploited in hydraulics as well as in the electromagnetic field theory. Emphasis is put on minimizing calculations necessary for constructing a system of linear equations exploiting symmetry or similarity of elements of geometric structure. The manuscript also contains a comparison of computing times using standard MoM and a proposed modified MoM keeping the same structure of the solved construction
Modeling the Phase-Space Distribution around Massive Halos
The comparison between dynamical mass and lensing mass provides a targeted
test for a wide range of modified gravity models. In our previous paper we
showed, through numerical simulations, that the measurement of the
line-of-sight velocity dispersion around stacked massive clusters whose lensing
masses are known allows for stringent constraints on modified gravity on scales
of 2 - 15 Mpc/h. In this work we develop a semi-analytical approach based on
the halo model to describe the phase-space distribution and the line-of-sight
velocity dispersion for different tracers. The model distinguishes
contributions from the halo pairwise velocity and the virial velocity within
halos. We also discuss observational complications, in particular the
contribution from Hubble flow, and show how our model can incorporate these
complications. We then incorporate the effects of modified gravity
(specifically, f(R) and braneworld models), and show that the model predictions
are in excellent agreement with modified gravity simulations. More broadly, the
phase-space distribution provides a sensitive test of our understanding of
hierarchical structure formation when confronted with observations via this
model.Comment: 27 pages, 18 figures. To be submitte
Likelihood-Based Inference for Discretely Observed Birth-Death-Shift Processes, with Applications to Evolution of Mobile Genetic Elements
Continuous-time birth-death-shift (BDS) processes are frequently used in
stochastic modeling, with many applications in ecology and epidemiology. In
particular, such processes can model evolutionary dynamics of transposable
elements - important genetic markers in molecular epidemiology. Estimation of
the effects of individual covariates on the birth, death, and shift rates of
the process can be accomplished by analyzing patient data, but inferring these
rates in a discretely and unevenly observed setting presents computational
challenges. We propose a mutli-type branching process approximation to BDS
processes and develop a corresponding expectation maximization (EM) algorithm,
where we use spectral techniques to reduce calculation of expected sufficient
statistics to low dimensional integration. These techniques yield an efficient
and robust optimization routine for inferring the rates of the BDS process, and
apply more broadly to multi-type branching processes where rates can depend on
many covariates. After rigorously testing our methodology in simulation
studies, we apply our method to study intrapatient time evolution of IS6110
transposable element, a frequently used element during estimation of
epidemiological clusters of Mycobacterium tuberculosis infections.Comment: 31 pages, 7 figures, 1 tabl
Measurement of electric fields in the ionosphere. Volume 1 - Technical summary report Final report, Aug. 1966 - Sep. 1967
Design and performance of electron beam electric field meter for ionospheric measurements near spacecraf
New approach to the resummation of logarithms in Higgs-boson decays to a vector quarkonium plus a photon
We present a calculation of the rates for Higgs-boson decays to a vector
heavy-quarkonium state plus a photon, where the heavy quarkonium states are the
J/psi and the Upsilon(nS) states, with n=1, 2, or 3. The calculation is carried
out in the light-cone formalism, combined with nonrelativistic QCD
factorization, and is accurate at leading order in m_Q^2/m_H^2, where m_Q is
the heavy-quark mass and m_H is the Higgs-boson mass. The calculation contains
corrections through next-to-leading order in the strong-coupling constant
alpha_s and the square of the heavy-quark velocity v, and includes a
resummation of logarithms of m_H^2/m_Q^2 at next-to-leading logarithmic
accuracy. We have developed a new method, which makes use of Abel summation,
accelerated through the use of Pade approximants, to deal with divergences in
the resummed expressions for the quarkonium light-cone distribution amplitudes.
This approach allows us to make definitive calculations of the resummation
effects. Contributions from the order-alpha_s and order-v^2 corrections to the
light-cone distribution amplitudes that we obtain with this new method differ
substantially from the corresponding contributions that one obtains from a
model light-cone distribution amplitude [M. Koenig and M. Neubert, J. High
Energy Phys. 08 (2015) 012]. Our results for the real parts of the
direct-process amplitudes are considerably smaller than those from one earlier
calculation [G. T. Bodwin, H. S. Chung, J.-H. Ee, J. Lee, and F. Petriello,
Phys. Rev. D 90, 113010 (2014)], reducing the sensitivity to the
Higgs-boson--heavy-quark couplings, and are somewhat smaller than those from
another earlier calculation [M. Koenig and M. Neubert, J. High Energy Phys. 08
(2015) 012]. However, our results for the standard-model Higgs-boson branching
fractions are in good agreement with those in M. Koenig and M. Neubert, J. High
Energy Phys. 08 (2015) 012.Comment: 40 pages, improved discussion of the convergence of the
nonrelativistic expansion, minor corrections and changes in nomenclature,
version published in Phys. Rev.
Three-component modeling of C-rich AGB star winds I. Method and first results
Radiative acceleration of newly-formed dust grains and transfer of momentum
from the dust to the gas plays an important role for driving winds of AGB
stars. Therefore a detailed description of the interaction of gas and dust is a
prerequisite for realistic models of such winds. In this paper we present the
method and first results of a three-component time-dependent model of
dust-driven AGB star winds. With the model we plan to study the role and
effects of the gas-dust interaction on the mass loss and wind formation. The
wind model includes separate conservation laws for each of the three components
of gas, dust and the radiation field and is developed from an existing model
which assumes position coupling between the gas and the dust. As a new feature
we introduce a separate equation of motion for the dust component in order to
fully separate the dust phase from the gas phase. The transfer of mass, energy
and momentum between the phases is treated by interaction terms. We also carry
out a detailed study of the physical form and influence of the momentum
transfer term (the drag force) and three approximations to it. In the present
study we are interested mainly in the effect of the new treatment of the dust
velocity on dust-induced instabilities in the wind. As we want to study the
consequences of the additional freedom of the dust velocity on the model we
calculate winds both with and without the separate dust equation of motion. The
wind models are calculated for several sets of stellar parameters. We find that
there is a higher threshold in the carbon/oxygen abundance ratio at which winds
form in the new model. The winds of the new models, which include drift, differ
from the previously stationary winds, and the winds with the lowest mass loss
rates no longer form.Comment: 15 pages, 5 figures, accepted by A&
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