817 research outputs found
Nucleon-nucleon resonances at intermediate energies using a complex energy formalism
We apply our method of complex scaling, valid for a general class of
potentials, in a search for nucleon-nucleon S-matrix poles up to 2 GeV
laboratory kinetic energy. We find that the realistic potentials JISP16,
constructed from inverse scattering, and chiral field theory potentials NLO
and NLO support resonances in energy regions well above their fit
regions. In some cases these resonances have widths that are narrow when
compared with the real part of the S-matrix pole.Comment: 7 pages, 5 figures, 2 Table
Use of an ultrasonic-acoustic technique for nondestructive evaluation of fiber composite strength
Details of the method used to measure the stress wave factor are described. Frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor was measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. The technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels, and results obtained are compared with through transmission immersion ultrasonic scans
NDE of structural ceramics
Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed
Boundary between Hadron and Quark/Gluon Structure of Nuclei
We show that the boundary between quark-dominated and hadron-dominated
regions of nuclear structure may be blurred by multi-nucleon quark clusters
arising from color percolation. Recent experiments supporting partial
percolation in cold nuclei and full percolation in hot/dense nuclear matter
include: deep inelastic lepton-nucleus scattering, relativistic heavy-ion
collisions and the binding energy in .Comment: 10 pages, 4 figures; added references; improved figures; fixed a typo
(wrong sign in Eqn 6); Fixed typos in Equation 2; updated reference
Nondestructive techniques for characterizing mechanical properties of structural materials: An overview
An overview of nondestructive evaluation (NDE) is presented to indicate the availability and application potentials of techniques for quantitative characterization of the mechanical properties of structural materials. The purpose is to review NDE techniques that go beyond the usual emphasis on flaw detection and characterization. Discussed are current and emerging NDE techniques that can verify and monitor entrinsic properties (e.g., tensile, shear, and yield strengths; fracture toughness, hardness, ductility; elastic moduli) and underlying microstructural and morphological factors. Most of the techniques described are, at present, neither widely applied nor widely accepted in commerce and industry because they are still emerging from the laboratory. The limitations of the techniques may be overcome by advances in applications research and instrumentation technology and perhaps by accommodations for their use in the design of structural parts
No-core shell model for 48-Ca, 48-Sc and 48-Ti
We report the first no-core shell model results for , and
with derived and modified two-body Hamiltonians. We use an oscillator
basis with a limited range around and a limited model space up to . No single-particle
energies are used. We find that the charge dependence of the bulk binding
energy of eight A=48 nuclei is reasonably described with an effective
Hamiltonian derived from the CD-Bonn interaction while there is an overall
underbinding by about 0.4 MeV/nucleon. However, the resulting spectra exhibit
deficiencies that are anticipated due to: (1) basis space limitations and/or
the absence of effective many-body interactions; and, (2) the absence of
genuine three-nucleon interactions. We then introduce additive
isospin-dependent central terms plus a tensor force to our Hamiltonian and
achieve accurate binding energies and reasonable spectra for all three nuclei.
The resulting no-core shell model opens a path for applications to the
double-beta () decay process.Comment: Revised content and added reference
Ultrasonic evaluation of the strength of unidirectional graphite-polyimide composites
An acoustic-ultrasonic method is described that was successful in ranking unidirectional graphite-polyimide composite specimens according to variations in interlaminar shear strength. Using this method, a quantity termed the stress wave factor was determined. It was found that this factor increases directly with interlaminar shear strength. The key variables in this investigation were composite density, fiber weight fraction, and void content. The stress wave factor and other ultrasonic factors that were studied were found to provide a powerful means for nondestructive evaluation of mechanical strength properties
Application of scanning acoustic microscopy to advanced structural ceramics
A review is presentod of research investigations of several acoustic microscopy techniques for application to structural ceramics for advanced heat engines. Results obtained with scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM) are compared. The techniques were evaluated on research samples of green and sintered monolithic silicon nitrides and silicon carbides in the form of modulus-of-rupture bars containing deliberately introduced flaws. Strengths and limitations of the techniques are described with emphasis on statistics of detectability of flaws that constitute potential fracture origins
Dynamical Symmetries Reflected in Realistic Interactions
Realistic nucleon-nucleon (NN) interactions, derived within the framework of
meson theory or more recently in terms of chiral effective field theory, yield
new possibilities for achieving a unified microscopic description of atomic
nuclei. Based on spectral distribution methods, a comparison of these
interactions to a most general Sp(4) dynamically symmetric interaction, which
previously we found to reproduce well that part of the interaction that is
responsible for shaping pairing-governed isobaric analog 0+ states, can
determine the extent to which this significantly simpler model Hamiltonian can
be used to obtain an approximate, yet very good description of low-lying
nuclear structure. And furthermore, one can apply this model in situations that
would otherwise be prohibitive because of the size of the model space. In
addition, we introduce a Sp(4) symmetry breaking term by including the
quadrupole-quadrupole interaction in the analysis and examining the capacity of
this extended model interaction to imitate realistic interactions. This
provides a further step towards gaining a better understanding of the
underlying foundation of realistic interactions and their ability to reproduce
striking features of nuclei such as strong pairing correlations or collective
rotational motion.Comment: 10 pages, 4 figures, Proceedings of the XXV International Workshop on
Nuclear Theory, June 26-July 1, 2006, Rila Mountains, Bulgari
- …