3,563 research outputs found
Matrix Elements of Random Operators and Discrete Symmetry Breaking in Nuclei
It is shown that several effects are responsible for deviations of the
intensity distributions from the Porter-Thomas law. Among these are genuine
symmetry breaking, such as isospin; the nature of the transition operator;
truncation of the Hilbert space in shell model calculations and missing
transitionsComment: 8 pages, 3 figure
Role of virtual break-up of projectile in astrophysical fusion reactions
We study the effect of virtual Coulomb break-up, commonly known as the dipole
polarizability, of the deuteron projectile on the astrophysical fusion reaction
3He(d,p)4He. We use the adiabatic approximation to estimate the potential shift
due to the E1 transition to the continuum states in the deuteron, and compute
the barrier penetrability in the WKB approximation. We find that the
enhancement of the penetrability due to the deuteron break-up is too small to
resolve the longstanding puzzle observed in laboratory measurements that the
electron screening effect is surprisingly larger than theoretical prediction
based on an atomic physics model. The effect of the 3He break-up in the
3He(d,p)4He reaction, as well as the 7Li break-up in the 7Li(p,alpha)4He
reaction is also discussed.Comment: 9 pages, 2 eps figure
The Coulomb phase shift revisited
We investigate the Coulomb phase shift, and derive and analyze new and more
precise analytical formulae. We consider next to leading order terms to the
Stirling approximation, and show that they are important at small values of the
angular momentum and other regimes. We employ the uniform approximation.
The use of our expressions in low energy scattering of charged particles is
discussed and some comparisons are made with other approximation methods.Comment: 13 pages, 5 figures, 1 tabl
Deformed Gaussian Orthogonal Ensemble Analysis of the Interacting Boson Model
A Deformed Gaussian Orthogonal Ensemble (DGOE) which interpolates between the
Gaussian Orthogonal Ensemble and a Poissonian Ensemble is constructed. This new
ensemble is then applied to the analysis of the chaotic properties of the low
lying collective states of nuclei described by the Interacting Boson Model
(IBM). This model undergoes a transition order-chaos-order from the
limit to the limit. Our analysis shows that the quantum fluctuations of
the IBM Hamiltonian, both of the spectrum and the eigenvectors, follow the
expected behaviour predicted by the DGOE when one goes from one limit to the
other.Comment: 10 pages, 4 figures (avaiable upon request), IFUSP/P-1086 Replaced
version: in the previous version the name of one of the authors was omitte
Theory of Multiphonon Excitation in Heavy-Ion Collisions
We study the effects of channel coupling in the excitation dynamics of giant
resonances in relativistic heavy ions collisions. For this purpose, we use a
semiclassical approximation to the Coupled-Channels problem and separate the
Coulomb and the nuclear parts of the coupling into their main multipole
components. In order to assess the importance of multi-step processes, we
neglect the resonance widths and solve the set of coupled equations exactly.
Finite widths are then considered. In this case, we handle the coupling of the
ground state with the dominant Giant Dipole Resonance exactly and study the
excitation of the remaining resonances within the Coupled-Channels Born
Approximation. A comparison with recent experimental data is made.Comment: 29 pages, 7 Postscript figures available upon reques
Inertial amplification of continuous structures: Large band gaps from small masses
Wave motion in a continuous elastic rod with a periodically attached
inertial-amplification mechanism is investigated. The mechanism has properties
similar to an "inerter" typically used in vehicle suspensions, however here it
is constructed and utilized in a manner that alters the intrinsic properties of
a continuous structure. The elastodynamic band structure of the hybrid
rod-mechanism structure yields band gaps that are exceedingly wide and deep
when compared to what can be obtained using standard local resonators, while
still being low in frequency. With this concept, a large band gap may be
realized with as much as twenty times less added mass compared to what is
needed in a standard local resonator configuration. The emerging inertially
enhanced continuous structure also exhibits unique qualitative features in its
dispersion curves. These include the existence of a characteristic double-peak
in the attenuation constant profile within gaps and the possibility of
coalescence of two neighbouring gaps creating a large contiguous gap.Comment: Manuscript is under review for journal publicatio
Advanced lightweight 316L stainless steel cellular lattice structures fabricated via selective laser melting
PublishedJournal ArticleThis paper investigates the manufacturability and performance of advanced and lightweight stainless steel cellular lattice structures fabricated via selective laser melting (SLM). A unique cell type called gyroid is designed to construct periodic lattice structures and utilise its curved cell surface as a self-supported feature which avoids the building of support structures and reduces material waste and production time. The gyroid cellular lattice structures with a wide range of volume fraction were made at different orientations, showing it can reduce the constraints in design for the SLM and provide flexibility in selecting optimal manufacturing parameters. The lattice structures with different volume fraction were well manufactured by the SLM process to exhibit a good geometric agreement with the original CAD models. The strut of the SLM-manufactured lattice structures represents a rough surface and its size is slightly higher than the designed value. When the lattice structure was positioned with half of its struts at an angle of 0° with respect to the building plane, which is considered as the worst building orientation for SLM, it was manufactured with well-defined struts and no defects or broken cells. The compression strength and modulus of the lattice structures increase with the increase in the volume fraction, and two equations based on Gibson-Ashby model have been established to predict their compression properties. © 2013 Elsevier Ltd.This work has been supported by the TSB funded project is entitled âSAVING â Sustainable product development via design optimisation and AdditiVe manufacturINGâ and is a collaboration between the Simpleware Ltd., Delcam PLC, University of Exeter, 3T RPD, Crucible Industrial Design Ltd., EOS Electro Optical Systems Ltd. and Plunkett Associates Ltd. The characterization experiments in this study were supported by the founds of State Key Laboratory of Material Processing and Die & Mould Technology in Huazhong University of Science and Technology, China (Grant Nos. 2012-P02 and 2013-09). The authors thank Dr. Chang Hong and Dr. Wear Lesley for assistance with Micro-CT, SEM and optical microscope measurements
Level density for deformations of the Gaussian orthogonal ensemble
Formulas are derived for the average level density of deformed, or
transition, Gaussian orthogonal random matrix ensembles. After some general
considerations about Gaussian ensembles we derive formulas for the average
level density for (i) the transition from the Gaussian orthogonal ensemble
(GOE) to the Poisson ensemble and (ii) the transition from the GOE to GOEs.Comment: 7 pages revtex4, 5 eps figures, submitted to Phys. Rev.
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