491 research outputs found
Structural Analysis and Matrix Interpetive System /SAMIS/ program Technical report, Feb. - Aug. 1966
Development of characteristic equations and error analysis for computer programs contained in structural analysis and matrix interpretive syste
Fabrication of Conducting Si Nanowire Arrays
The recent development of the superlattice nanowire pattern transfer (SNAP)
technique allows for the fabrication of arrays of nanowires at a diameter,
pitch, aspect ratio, and regularity beyond competing approaches. Here, we
report the fabrication of conducting Si nanowire arrays with wire widths and
pitches of 10-20 nm and 40-50 nm, respectively, and resistivity values
comparable to the bulk through the selection of appropriate
silicon-on-insulator substrates, careful reactive-ion etching, and spin-on
glass doping. These results promise the realization of interesting
nano-electronic circuits and devices, including chemical and biological
sensors, nano-scale mosaics for molecular electronics, and ultra-dense
field-effect transistor (FET) arrays.Comment: 10 pages, 3 figures, submitted to APL Mar '0
Cratering Experiments on the Self Armoring of Coarse-Grained Granular Targets
Recently published crater statistics on the small asteroids 25143 Itokawa and
433 Eros show a significant depletion of craters below approx. 100 m in
diameter. Possible mechanisms that were brought up to explain this lack of
craters were seismic crater erasure and self armoring of a coarse, boulder
covered asteroid surface. While seismic shaking has been studied in this
context, the concept of armoring lacks a deeper inspection and an experimental
ground truth. We therefore present cratering experiments of glass bead
projectiles impacting into granular glass bead targets, where the grain sizes
of projectile and target are in a similar range. The impact velocities are in
the range of 200 to 300 m/s. We find that craters become fainter and irregular
shaped as soon as the target grains are larger than the projectile sizes and
that granular craters rarely form when the size ratio between projectile and
target grain is around 1:10 or smaller. In that case, we observe a formation of
a strength determined crater in the first struck target grain instead. We
present a simple model based on the transfer of momentum from the projectile to
this first target grain, which is capable to explain our results with only a
single free parameter, which is moreover well determined by previous
experiments. Based on estimates of typical projectile size and boulder size on
Itokawa and Eros, given that our results are representative also for km/s
impact velocities, armoring should play an important role for their evolution.Comment: accepted for publication in Icaur
Remote visual detection of impacts on the lunar surface
We propose a novel method of remotely observing impacts on the airless Moon that may extend the present data base on meteoroids down to 1 m in diameter. Meteorites or comets of radius approximately 1-100 m are burnt away or dispersed in the atmospheres of the Earth and Venus. However, when such objects strike the Moon they deposit their energy in a small initial volume, forming a plasma plume whose visible and infrared radiation may be visible from the Earth. We consider impacts of model SiO2 projectiles on the surface of an SiO2 model Moon
Spin in relativistic quantum theory
We discuss the role of spin in Poincar\'e invariant formulations of quantum
mechanics.Comment: 54 page
Heavy quark supermultiplet excitations
Lorentz covariant wave functions for meson and baryon supermultiplets are
simply derived by boosting representations corresponding to
multiquark systems at rest.Comment: 12 pages (Revtex), UTAS-PHYS-93-4
Form factors of the exotic baryons with isospin I=5/2
The electromagnetic form factors of the exotic baryons are calculated in the
framework of the relativistic quark model at small and intermediate momentum
transfer. The charge radii of the E+++ baryons are determined.Comment: 12pages, 2 figure
Spin Structure of the Pion in a Light-Cone Representation
The spin structure of the pion is discussed by transforming the wave function
for the pion in the naive quark model into a light-cone representation. It is
shown that there are higher helicity () states in
the full light-cone wave function for the pion besides the ordinary helicity
() component wave functions as a consequence from
the Melosh rotation relating spin states in light-front dynamics and those in
instant-form dynamics. Some low energy properties of the pion, such as the
electromagnetic form factor, the charged mean square radius, and the weak decay
constant, could be interrelated in this representation with reasonable
parameters.Comment: 15 Latex pages, 2 figures upon reques
Dynamical Chiral Symmetry Breaking on the Light Front.II. The Nambu--Jona-Lasinio Model
An investigation of dynamical chiral symmetry breaking on the light front is
made in the Nambu--Jona-Lasinio model with one flavor and N colors. Analysis of
the model suffers from extraordinary complexity due to the existence of a
"fermionic constraint," i.e., a constraint equation for the bad spinor
component. However, to solve this constraint is of special importance. In
classical theory, we can exactly solve it and then explicitly check the
property of ``light-front chiral transformation.'' In quantum theory, we
introduce a bilocal formulation to solve the fermionic constraint by the 1/N
expansion. Systematic 1/N expansion of the fermion bilocal operator is realized
by the boson expansion method. The leading (bilocal) fermionic constraint
becomes a gap equation for a chiral condensate and thus if we choose a
nontrivial solution of the gap equation, we are in the broken phase. As a
result of the nonzero chiral condensate, we find unusual chiral transformation
of fields and nonvanishing of the light-front chiral charge. A leading order
eigenvalue equation for a single bosonic state is equivalent to a leading order
fermion-antifermion bound-state equation. We analytically solve it for scalar
and pseudoscalar mesons and obtain their light-cone wavefunctions and masses.
All of the results are entirely consistent with those of our previous analysis
on the chiral Yukawa model.Comment: 23 pages, REVTEX, the version to be published in Phys.Rev.D; Some
clarifications in discussion of the LC wavefunctions adde
Comparison among Hamiltonian light-front formalisms at q+ = 0 and q+ <> 0: space-like elastic form factors of pseudoscalar and vector mesons
The electromagnetic elastic form factors of pseudoscalar and vector mesons
are analyzed for space-like momentum transfers in terms of relativistic quark
models based on the Hamiltonian light-front formalism elaborated in different
reference frames (q+ 0 and q+ 0). As far as the one-body approximation for
the electromagnetic current operator is concerned, it is shown that the
predictions of the light-front approach at q+=0 should be preferred,
particularly in case of light hadrons, because of: i) the relevant role played
by the Z-graph at q+ 0, and ii) the appropriate elimination of spurious
effects, related to the orientation of the null hyperplane where the
light-front wave function is defined.Comment: version to appear in Phys. Rev. C. No change in the results and in
the conclusion
- …