732 research outputs found
Matrix exponential via Clifford algebras
We use isomorphism between matrix algebras and simple orthogonal
Clifford algebras \cl(Q) to compute matrix exponential of a real,
complex, and quaternionic matrix A. The isomorphic image in
\cl(Q), where the quadratic form has a suitable signature is
exponentiated modulo a minimal polynomial of using Clifford exponential.
Elements of \cl(Q) are treated as symbolic multivariate polynomials in
Grassmann monomials. Computations in \cl(Q) are performed with a Maple
package `CLIFFORD'. Three examples of matrix exponentiation are given
Classification of Low Dimensional Lie Super-Bialgebras
A thorough analysis of Lie super-bialgebra structures on Lie super-algebras
osp(1|2) and super-e(2) is presented. Combined technique of computer algebraic
computations and a subsequent identification of equivalent structures is
applied. In all the cases Poisson-Lie brackets on supergroups are found.
Possibility of quantizing them in order to obtain quantum groups is discussed.
It turns out to be straightforward for all but one structures for super-E(2)
group.Comment: 15 pages, LaTe
Spectral functions for medium-sized nuclei
The spectral functions for calcium and argon are constructed. It is verified
that their predictions for the quasielastic electron-nucleus cross sections in
the energy range ~1 GeV agree with the data. The argon spectral function is
then used to obtain the quasielastic neutrino-nucleus cross section.Comment: 3 pages, 3 figures, presented at 5th International Workshop on
Neutrino-Nucleus Interactions in the Few-GeV Region (NuInt07), Fermilab, USA,
30.05-3.06.200
Spectral function for He using the Chebyshev expansion in coupled-cluster theory
We compute spectral function for He by combining coupled-cluster theory
with an expansion of integral transforms into Chebyshev polynomials. Our method
allows to estimate the uncertainty of spectral reconstruction. The properties
of the Chebyshev polynomials make the procedure numerically stable and
considerably lower in memory usage than the typically employed Lanczos
algorithm. We benchmark our predictions with other calculations in the
literature and with electron scattering data in the quasi-elastic peak. The
spectral function formalism allows one to extend ab-initio lepton-nucleus cross
sections into the relativistic regime. This makes it a promising tool for
modeling this process at higher energy transfers. The results we present open
the door for studies of heavier nuclei, important for the neutrino oscillation
programs.Comment: 12 pages, 5 figure
Truss-like Discrete Element Method Applied to Damage Process Simulation in Quasi-Brittle Materials
This paper discusses the combined application of the lattice discrete element method (LDEM) and the acoustic emission (AE) technique to analyze damage in quasi-brittle materials. These methods were used to study the damage in a concrete slab under pure-shear stress and a pre-fissured sandstone beam subjected to three-point bending. The first test was restricted to simulation results, whereas the second included experimental data. The discrete element method was used to perform the simulations for both tests, whereas the corresponding results and the information from the experiments were assessed using AE analysis tools. It was shown that the synergistic use of these two methods led to a comprehensive understanding of the two analyzed cases and offered an effective, generalizable approach for assessing damage processes in quasi-brittle materials
Damage Evolution in Quasi-Brittle Materials: Experimental Analysis by AE and Numerical Simulation
This work investigates the extension of a total-collapse prediction method to include local failures in quasi-brittle materials as they undergo damage processes. The analysis is experimentally conducted with acoustic emission data from a basalt specimen under a prescribed displacement loading test. The proposed failure index is compared with the well-established b-value to evaluate its usefulness; the simulation results are also used to further investigations. In particular, the simulations show that the parameter calculation can be carried out by indirectly estimating the elastic energy released within the system throughout the damage process, which cannot be measured directly. It is concluded that the proposed method is valid, consistently outperforming the b-value as a failure precursor throughout the experimental studies
Final State Interactions Effects in Neutrino-Nucleus Interactions
Final State Interactions effects are discussed in the context of Monte Carlo
simulations of neutrino-nucleus interactions. A role of Formation Time is
explained and several models describing this effect are compared. Various
observables which are sensitive to FSI effects are reviewed including
pion-nucleus interaction and hadron yields in backward hemisphere. NuWro Monte
Carlo neutrino event generator is described and its ability to understand
neutral current production data in GeV neutrino flux
experiments is demonstrated.Comment: 13 pages, 16 figure
Quantum E(2) groups and Lie bialgebra structures
Lie bialgebra structures on are classified. For two Lie bialgebra
structures which are not coboundaries (i.e. which are not determined by a
classical -matrix) we solve the cocycle condition, find the Lie-Poisson
brackets and obtain quantum group relations. There is one to one correspondence
between Lie bialgebra structures on and possible quantum deformations of
and .Comment: 8 pages, plain TEX, harvmac, to appear in J. Phys.
Analysis of Acoustic Emission Activity during Progressive Failure in Heterogeneous Materials: Experimental and Numerical Investigation
This work focuses on an experimental and numerical investigation into monitoring damage in a cube-shaped concrete specimen under compression. Experimental monitoring uses acoustic emission (AE) signals acquired by two independent measurement apparatuses, and the same damage process is numerically simulated with the lattice discrete element method (LDEM). The results from the experiment and simulation are then compared in terms of their failure load, final configurations, and the evolution of global parameters based on AE signals, such as the b-value coefficient and the natural time approach. It is concluded that the results from the AE analysis present a significant sensitivity to the characteristics of the acquisition systems. However, natural time methods are more robust for determining such differences, indicating the same general tendency for all three data sets
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