7,164 research outputs found
On Distance-Regular Graphs with Smallest Eigenvalue at Least
A non-complete geometric distance-regular graph is the point graph of a
partial geometry in which the set of lines is a set of Delsarte cliques. In
this paper, we prove that for fixed integer , there are only finitely
many non-geometric distance-regular graphs with smallest eigenvalue at least
, diameter at least three and intersection number
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
On the best compact approximation problem for operators between Lp-spaces
AbstractWe construct (for 1 < p < 2) an operator from lp into Lp which has no nearest compact operator. We also give a sufficient condition for an operator from Lp into Lp (2 < p < ∞) to have a best compact approximant
A Generalized Second Order Compensator Design for Vibration Control of Flexible Structures
The article of record as published may be found at http://dx.doi.org/10.2514/6.1994-1626In this paper, a modified positive position feedback compensator design is presented for vibration control of flexible structures. The new method provides extended capability of controlling structural natural frequencies and damping. A similar compensator design where only rate sensors are available is also discussed. Ahalytical and experimental results are presented to verify the proposed method
Superconductivity-induced Phonon Renormalization on NaFeCoAs
We report a study of the lattice dynamics in superconducting NaFeAs (Tc = 8
K) and doped NaFe0.97Co0.03As (Tc = 20 K) using Raman light scattering. Five of
the six phonon modes expected from group theory are observed. In contrast with
results obtained on iso-structural and iso-electronic LiFeAs, anomalous
broadening of Eg(As) and A1g(Na) modes upon cooling is observed in both
samples. In addition, in the Co-doped sample, a superconductivity-induced
renormalization of the frequency and linewidth of the B1g(Fe) vibration is
observed. This renormalization can not be understood within a single band and
simple multi-band approaches. A theoretical model that includes the effects of
SDW correlations along with sign-changing s-wave pairing state and interband
scattering has been developed to explain the observed behavior of the B1g(Fe)
mode.Comment: 10 pages; 6 figure
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Development of Nanocomposite Powders for the SLS Process to Enhance Mechanical Properties
In an effort to fabricate prototypes with improved mechanical properties in the dual laser
sintering process, functionalized graphite nanoplatelets were added to the PA-12 powder to
produce a nanocomposite powder. The PA-12 powder was chosen as the matrix polymer
because it has features conducive to laser sintering such as relatively low melting temperature
and high mechanical properties. The GNPs were oxidized through a nitric acid treatment to
improve the interfacial bonding. The resulting nanocomposite powder was layered and sintered
by laser without any sign of agglomeration. Although the result is preliminary, it nevertheless
shows the suitability of the nanocomposite powder for the laser sintering process.Mechanical Engineerin
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Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser
The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6x10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed. DOI: 10.1103/PhysRevE.87.023106Glenn Focht Memorial FellowshipNNSA DE-FC52-08NA28512DOE Office of Basic Energy SciencesPhysic
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