7,183 research outputs found
Precise determination of lattice phase shifts and mixing angles
We introduce a general and accurate method for determining lattice phase
shifts and mixing angles, which is applicable to arbitrary, non-cubic lattices.
Our method combines angular momentum projection, spherical wall boundaries and
an adjustable auxiliary potential. This allows us to construct radial lattice
wave functions and to determine phase shifts at arbitrary energies. For coupled
partial waves, we use a complex-valued auxiliary potential that breaks
time-reversal invariance. We benchmark our method using a system of two
spin-1/2 particles interacting through a finite-range potential with a strong
tensor component. We are able to extract phase shifts and mixing angles for all
angular momenta and energies, with precision greater than that of extant
methods. We discuss a wide range of applications from nuclear lattice
simulations to optical lattice experiments.Comment: 7 pp, 4 figs, 1 tabl
Breaking and restoration of rotational symmetry for irreducible tensor operators on the lattice
We study the breaking of rotational symmetry on the lattice for irreducible
tensor operators and practical methods for suppressing this breaking. We
illustrate the features of the general problem using an cluster model
for Be. We focus on the lowest states with non-zero angular momentum and
examine the matrix elements of multipole moment operators. We show that the
physical reduced matrix element is well reproduced by averaging over all
possible orientations of the quantum state, and this is expressed as a sum of
matrix elements weighted by the corresponding Clebsch-Gordan coefficients. For
our cluster model we find that the effects of rotational symmetry
breaking can be largely eliminated for lattice spacings of fm, and
we expect similar improvement for actual lattice Monte Carlo calculations.Comment: 8 pages, 4 figure
Chronically Depressed Suicidal
Collagen is a protein that makes up the fibres, which are part of the connective tissue, along with elastic fibers and hyaluronic acid. Collagen is a natural protein found in bone, cartilage, skin, and tendons; there are 27 different types of naturally occurring collagens in the body. Collagen is used in cosmetics to remove wrinkles on the face, smooth skin in the nasolabial folds, the eyes and mouth corners. Previously, collagen fillers were very popular, but with the development of other, newer materials for bio gels, its use decreased. As already mentioned, collagen is a basic type of fiber is present in the connective tissue
Viability of carbon-based life as a function of the light quark mass
The Hoyle state plays a crucial role in the helium burning of stars that have
reached the red giant stage. The close proximity of this state to the
triple-alpha threshold is needed for the production of carbon, oxygen, and
other elements necessary for life. We investigate whether this life-essential
condition is robust or delicately fine-tuned by measuring its dependence on the
fundamental constants of nature, specifically the light quark mass and the
strength of the electromagnetic interaction. We show that there exist strong
correlations between the alpha-particle binding energy and the various energies
relevant to the triple-alpha process. We derive limits on the variation of
these fundamental parameters from the requirement that sufficient amounts of
carbon and oxygen be generated in stars. We also discuss the implications of
these results for an anthropic view of the universe.Comment: 4 pages, 2 figures, version published in Phys. Rev. Lett., title
changed in journa
Dynamic Matrix Factorization with Priors on Unknown Values
Advanced and effective collaborative filtering methods based on explicit
feedback assume that unknown ratings do not follow the same model as the
observed ones (\emph{not missing at random}). In this work, we build on this
assumption, and introduce a novel dynamic matrix factorization framework that
allows to set an explicit prior on unknown values. When new ratings, users, or
items enter the system, we can update the factorization in time independent of
the size of data (number of users, items and ratings). Hence, we can quickly
recommend items even to very recent users. We test our methods on three large
datasets, including two very sparse ones, in static and dynamic conditions. In
each case, we outrank state-of-the-art matrix factorization methods that do not
use a prior on unknown ratings.Comment: in the Proceedings of 21st ACM SIGKDD Conference on Knowledge
Discovery and Data Mining 201
A non-perturbative analysis of symmetry breaking in two-dimensional phi^4 theory using periodic field methods
We describe the generalization of spherical field theory to other modal
expansion methods. The main approach remains the same, to reduce a
d-dimensional field theory into a set of coupled one-dimensional systems. The
method we discuss here uses an expansion with respect to periodic-box modes. We
apply the method to phi^4 theory in two dimensions and compute the critical
coupling and critical exponents. We compare with lattice results and
predictions via universality and the two-dimensional Ising model.Comment: 12 pages, 4 figures, version to appear in Physics Letters
Ab initio calculation of the spectrum and structure of O
We present ab initio lattice calculations of the low-energy even-parity
states of O using chiral nuclear effective field theory. We find good
agreement with the empirical energy spectrum, and with the electromagnetic
properties and transition rates. For the ground state, we find that the
nucleons are arranged in a tetrahedral configuration of alpha clusters. For the
first excited spin-0 state, we find that the predominant structure is a square
configuration of alpha clusters, with rotational excitations that include the
first spin-2 state.Comment: 4 pages, 4 figures, final version to appear in Phys. Rev. Let
The Hoyle state in Nuclear Lattice EFT
We review the calculation of the Hoyle state of C in Nuclear Lattice
Effective Field Theory (NLEFT) and its anthropic implications for the
nucleosynthesis of C and O in red giant stars. We also review the
extension of NLEFT to the regime of medium-mass nuclei, with emphasis on the
determination of the ground-state energies of the alpha nuclei O,
Ne, Mg and Si by means of Euclidean time projection.
Finally, we review recent NLEFT results for the spectrum, electromagnetic
properties, and alpha-cluster structure of O.Comment: 9 pages, 1 figure, 5 tables, invited talk at the DAE symposium on
nuclear physics, December 2-6 2013, Anushakti Nagar, Mumbai, India. To appear
in Pramana - Journal of Physic
Lattice Effective Field Theory for Medium-Mass Nuclei
We extend Nuclear Lattice Effective Field Theory (NLEFT) to medium-mass
nuclei, and present results for the ground states of alpha nuclei from He
to Si, calculated up to next-to-next-to-leading order (NNLO) in the EFT
expansion. This computational advance is made possible by extrapolations of
lattice data using multiple initial and final states. For our soft two-nucleon
interaction, we find that the overall contribution from multi-nucleon forces
must change sign from attractive to repulsive with increasing nucleon number.
This effect is not produced by three-nucleon forces at NNLO, but it can be
approximated by an effective four-nucleon interaction. We discuss the
convergence of the EFT expansion and the broad significance of our findings for
future ab initio calculations.Comment: 10 pages, 3 figures, 1 table, to appear in Physics Letters
Lattice effective field theory for nuclei from A = 4 to A = 28
We present an overview of the extension of Nuclear Lattice Effective Field
Theory simulations to the regime of medium-mass nuclei. We focus on the
determination of the ground-state energies of the alpha nuclei O,
Ne, Mg and Si by means of Euclidean time projection.Comment: 7 pages, 4 figures, presented at the 31st International Symposium on
Lattice Field Theory (LATTICE 2013), July 29 - August 3, 2013, Mainz, German
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