52,213 research outputs found
Measure Factors, Tension, and Correlations of Fluid Membranes
We study two geometrical factors needed for the correct construction of
statistical ensembles of surfaces. Such ensembles appear in the study of fluid
bilayer membranes, though our results are more generally applicable. The naive
functional measure over height fluctuations must be corrected by these factors
in order to give correct, self-consistent formulas for the free energy and
correlation functions of the height. While one of these corrections -- the
Faddeev-Popov determinant -- has been studied extensively, our derivation
proceeds from very simple geometrical ideas, which we hope removes some of its
mystery. The other factor is similar to the Liouville correction in string
theory. Since our formulas differ from those of previous authors, we include
some explicit calculations of the effective frame tension and two-point
function to show that our version indeed secures coordinate-invariance and
consistency to lowest nontrivial order in a temperature expansion.Comment: 24 pp; plain Te
Comparison of Hirs' equation of Moody's equation for determining rotordynamic coefficients of annular pressure seals
The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs' equation, assumes the friction factor is a function of Reynolds number only. The second, Moody's equation, approximates Moody's diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs' constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals (e/2 H sub 0 = 0.05) Moody's equation predicts 44% greater direct stiffness, 35% greater cross-coupled stiffness, 19% smaller cross-coupled damping, 59% smaller cross-coupled inertia, and nominally the same direct damping and direct inertia
Alumina fiber strength improvement
The effective fiber strength of alumina fibers in an aluminum composite was increased to 173,000 psi. A high temperature heat treatment, combined with a glassy carbon surface coating, was used to prevent degradation and improve fiber tensile strength. Attempts to achieve chemical strengthening of the alumina fiber by chromium oxide and boron oxide coatings proved unsuccessful. A major problem encountered on the program was the low and inconsistent strength of the Dupont Fiber FP used for the investigation
SNS Timing System
This poster describes the timing system being designed for Spallation Neutron
Source being built at Oak Ridge National lab
Environmental modeling and recognition for an autonomous land vehicle
An architecture for object modeling and recognition for an autonomous land vehicle is presented. Examples of objects of interest include terrain features, fields, roads, horizon features, trees, etc. The architecture is organized around a set of data bases for generic object models and perceptual structures, temporary memory for the instantiation of object and relational hypotheses, and a long term memory for storing stable hypotheses that are affixed to the terrain representation. Multiple inference processes operate over these databases. Researchers describe these particular components: the perceptual structure database, the grouping processes that operate over this, schemas, and the long term terrain database. A processing example that matches predictions from the long term terrain model to imagery, extracts significant perceptual structures for consideration as potential landmarks, and extracts a relational structure to update the long term terrain database is given
Elasticity Theory of a Twisted Stack of Plates
We present an elastic model of B-form DNA as a stack of thin, rigid plates or
base pairs that are not permitted to deform. The symmetry of DNA and the
constraint of plate rigidity limit the number of bulk elastic constants
contributing to a macroscopic elasticity theory of DNA to four. We derive an
effective twist-stretch energy in terms of the macroscopic stretch epsilon
along and relative excess twist sigma about the DNA molecular axis. In addition
to the bulk stretch and twist moduli found previously, we obtain a
twist-stretch modulus with the following remarkable properties: 1) it vanishes
when the radius of the helical curve following the geometric center of each
plate is zero, 2) it vanishes with the elastic constant K_{23} that couples
compression normal to the plates to a shear strain, if the plates are
perpendicular to the molecular axis, and 3) it is nonzero if the plates are
tilted relative to the molecular axis. This implies that a laminated helical
structure carved out of an isotropic elastic medium will not twist in response
to a stretching force, but an isotropic material will twist if it is bent into
the shape of a helix.Comment: 19 pages, plain LaTeX, 1 included eps figur
Three Numerical Puzzles and the Top Quark's Chiral Weak-Moment
Versus the standard model's t --> W b decay helicity amplitudes, three
numerical puzzles occur at the 0.1 % level when one considers the amplitudes in
the case of an additional (f_M + f_E) coupling of relative strength 53 GeV. The
puzzles are theoretical ones which involve the t --> W b decay helicity
amplitudes in the two cases, the relative strength of this additional coupling,
and the observed masses of these three particles. A deeper analytic realization
is obtained for two of them. Equivalent realizations are given for the
remaining one. An empirical consequence of these analytic realizations is that
it is important to search for effects of a large chiral weak-moment of the
top-quark, the effective mass-scale is about 53 GeV. A full theoretical
resolution would include relating the origin of such a chiral weak-moment and
the mass generation of the top-quark, the W-boson, and probably the b-quark.Comment: 18 pages, 1 postscript table (revised to better explain notation,
model #1, add a little material...
Localization transitions in non-Hermitian quantum mechanics
We study the localization transitions which arise in both one and two
dimensions when quantum mechanical particles described by a random
Schr\"odinger equation are subjected to a constant imaginary vector potential.
A path-integral formulation relates the transition to flux lines depinned from
columnar defects by a transverse magnetic field in superconductors. The theory
predicts that the transverse Meissner effect is accompanied by stretched
exponential relaxation of the field into the bulk and a diverging penetration
depth at the transition.Comment: 4 pages (latex) with 3 figures (epsf) embedded in the text using the
style file epsf.st
A high-Reynolds-number seal test facility: Facility description and preliminary test data
A facility has been developed for testing the leakage and rotordynamic characteristics of interstage-seal configurations for the HPFTP (High Pressure Fuel Turbopump) of the SSME (Space Shuttle Main Engine). Axial Reynolds numbers on the order of 400,000 are realized in the test facility by using a Dupont freon fluid called Halon (CBrF3). The kinematic viscosity of Halon is of the same order as the liquid hydrogen used in the HPFTP. Initial testing has focused on the current flight configurations (a three-segment, stepped unit) and a convergent-taper candidate
- …