804 research outputs found
Cosmic neutrinos at IceCube: , and initial flavor composition
We discuss the prospect of extracting the values of the mixing parameters
and through the detection of cosmic neutrinos in the
planned and forthcoming neutrino telescopes. We take the ratio of the
muon-track to shower-like events, R, as the realistic quantity that can be
measured in the neutrino telescopes. We take into account several sources of
uncertainties that enter the analysis. We then examine to what extent the
deviation of the initial flavor composition from w_e:w_\mu:w_\tau=1:2:0 can be
tested.Comment: 3 pages, 2 figures, Talk given at the TAUP 2009 conference, Rome,
Italy; J. Phys. Conf. Series to appea
Image reconstruction in fluorescence molecular tomography with sparsity-initialized maximum-likelihood expectation maximization
We present a reconstruction method involving maximum-likelihood expectation
maximization (MLEM) to model Poisson noise as applied to fluorescence molecular
tomography (FMT). MLEM is initialized with the output from a sparse
reconstruction-based approach, which performs truncated singular value
decomposition-based preconditioning followed by fast iterative
shrinkage-thresholding algorithm (FISTA) to enforce sparsity. The motivation
for this approach is that sparsity information could be accounted for within
the initialization, while MLEM would accurately model Poisson noise in the FMT
system. Simulation experiments show the proposed method significantly improves
images qualitatively and quantitatively. The method results in over 20 times
faster convergence compared to uniformly initialized MLEM and improves
robustness to noise compared to pure sparse reconstruction. We also
theoretically justify the ability of the proposed approach to reduce noise in
the background region compared to pure sparse reconstruction. Overall, these
results provide strong evidence to model Poisson noise in FMT reconstruction
and for application of the proposed reconstruction framework to FMT imaging
Primordial features and Planck polarization
With the Planck 2015 Cosmic Microwave Background (CMB) temperature and
polarization data, we search for possible features in the primordial power
spectrum (PPS). We revisit the Wiggly Whipped Inflation (WWI) framework and
demonstrate how generation of some particular primordial features can improve
the fit to Planck data. WWI potential allows the scalar field to transit from a
steeper potential to a nearly flat potential through a discontinuity either in
potential or in its derivatives. WWI offers the inflaton potential
parametrizations that generate a wide variety of features in the primordial
power spectra incorporating most of the localized and non-local inflationary
features that are obtained upon reconstruction from temperature and
polarization angular power spectrum. At the same time, in a single framework it
allows us to have a background parameter estimation with a nearly free-form
primordial spectrum. Using Planck 2015 data, we constrain the primordial
features in the context of Wiggly Whipped Inflation and present the features
that are supported both by temperature and polarization. WWI model provides
more than improvement in fit to the data with respect to the best
fit power law model considering combined temperature and polarization data from
Planck and B-mode polarization data from BICEP and Planck dust map. We use 2-4
extra parameters in the WWI model compared to the featureless strict slow roll
inflaton potential. We find that the differences between the temperature and
polarization data in constraining background cosmological parameters such as
baryon density, cold dark matter density are reduced to a good extent if we use
primordial power spectra from WWI. We also discuss the extent of bispectra
obtained from the best potentials in arbitrary triangular configurations using
the BI-spectra and Non-Gaussianity Operator (BINGO).Comment: v1: 22 pages, 7 figures and 1 table; v2: 23 pages, 7 figures and 1
table, minor changes, references added, matches published version in JCA
Incorporating reflection boundary conditions in the Neumann series radiative transport equation: Application to photon propagation and reconstruction in diffuse optical imaging
We propose a formalism to incorporate boundary conditions in a Neumann-series-based radiative transport equation. The formalism accurately models the reflection of photons at the tissue-external medium interface using Fresnel’s equations. The formalism was used to develop a gradient descent-based image reconstruction technique. The proposed methods were implemented for 3D diffuse optical imaging. In computational studies, it was observed that the average root-mean-square error (RMSE) for the output images and the estimated absorption coefficients reduced by 38% and 84%, respectively, when the reflection boundary conditions were incorporated. These results demonstrate the importance of incorporating boundary conditions that model the reflection of photons at the tissue-external medium interface
Measurement of spray combustion processes
A free jet configuration was chosen for measuring noncombusting spray fields and hydrocarbon-air spray flames in an effort to develop computational models of the dynamic interaction between droplets and the gas phase and to verify and refine numerical models of the entire spray combustion process. The development of a spray combustion facility is described including techniques for laser measurements in spray combustion environments and methods for data acquisition, processing, displaying, and interpretation
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