4,632 research outputs found
Physical Acoustics
Contains reports on four research projects.United States Navy, Office of Naval Research (Contract Nonr-1841(42)
Aircraft and avionic related research required to develop an effective high-speed runway exit system
Research was conducted to increase airport capacity by studying the feasibility of the longitudinal separation between aircraft sequences on final approach. The multidisciplinary factors which include the utility of high speed exits for efficient runway operations were described along with recommendations and highlights of these studies
Note and Comment
Necessity of Valid Contract to Support Escrow - In Foulkes V. Sengstqcken, (Ore. 1917) 163 Pac. 311, it is said that A pure escrow presupposes the existence of a valid contract with sufficient parties, a proper subject matter, and a consideration. There must be an actual contract of sale on the one side and of purchase on the other, afid until there is such a contract, the instrument executed by the supposed grantor, though in form a deed, is neither a deed nor an escrow. Accordingly it was held that performance of conditions by a grantee after the grantor had withdrawn the instrument from the custodian was ineffective to accomplish a conveyance. In its decision the court follows Davis v. Brigham, 56 Ore. 41, io7 Pac. 961, Ann. Cas. 1912B 1340, where the same doctrine, though probably not necessary to the decision, was laid down
Short Wavelength Analysis of the Evolution of Perturbations in a Two-component Cosmological Fluid
The equations describing a two-component cosmological fluid with linearized
density perturbations are investigated in the small wavelength or large
limit. The equations are formulated to include a baryonic component, as well as
either a hot dark matter (HDM) or cold dark matter (CDM) component. Previous
work done on such a system in static spacetime is extended to reveal some
interesting physical properties, such as the Jeans wavenumber of the mixture,
and resonant mode amplitudes. A WKB technique is then developed to study the
expanding universe equations in detail, and to see whether such physical
properties are also of relevance in this more realistic scenario. The Jeans
wavenumber of the mixture is re-interpreted for the case of an expanding
background spacetime. The various modes are obtained to leading order, and the
amplitudes of the modes are examined in detail to compare to the resonances
observed in the static spacetime results. It is found that some conclusions
made in the literature about static spacetime results cannot be carried over to
an expanding cosmology.Comment: 42 pages, 12 figure
Geometric Parameterization of Absorption in Heavy Ion Collisions
We calculate the survival probability of particles in various
colliding systems using a Glauber model. An analysis of recent data has
reported a -nucleon breakup cross section of 6.20.7 mb derived
from an exponential fit to the ratio of to Drell-Yan yields as a
function of a simple, linearly-averaged mean path length through the nuclear
medium. Our calculations indicate that, due to the nature of the calculation,
this approach yields an apparent breakup cross section which is systematically
lower than the actual value.Comment: LaTex, 7 pages, 2 figure
Geometry of the energy landscape of the self-gravitating ring
We study the global geometry of the energy landscape of a simple model of a
self-gravitating system, the self-gravitating ring (SGR). This is done by
endowing the configuration space with a metric such that the dynamical
trajectories are identified with geodesics. The average curvature and curvature
fluctuations of the energy landscape are computed by means of Monte Carlo
simulations and, when possible, of a mean-field method, showing that these
global geometric quantities provide a clear geometric characterization of the
collapse phase transition occurring in the SGR as the transition from a flat
landscape at high energies to a landscape with mainly positive but fluctuating
curvature in the collapsed phase. Moreover, curvature fluctuations show a
maximum in correspondence with the energy of a possible further transition,
occurring at lower energies than the collapse one, whose existence had been
previously conjectured on the basis of a local analysis of the energy landscape
and whose effect on the usual thermodynamic quantities, if any, is extremely
weak. We also estimate the largest Lyapunov exponent of the SGR using
the geometric observables. The geometric estimate always gives the correct
order of magnitude of and is also quantitatively correct at small
energy densities and, in the limit , in the whole homogeneous
phase.Comment: 20 pages, 12 figure
Balancing torques in membrane-mediated interactions: Exact results and numerical illustrations
Torques on interfaces can be described by a divergence-free tensor which is
fully encoded in the geometry. This tensor consists of two terms, one
originating in the couple of the stress, the other capturing an intrinsic
contribution due to curvature. In analogy to the description of forces in terms
of a stress tensor, the torque on a particle can be expressed as a line
integral along any contour surrounding the particle. Interactions between
particles mediated by a fluid membrane are studied within this framework. In
particular, torque balance places a strong constraint on the shape of the
membrane. Symmetric two-particle configurations admit simple analytical
expressions which are valid in the fully nonlinear regime; in particular, the
problem may be solved exactly in the case of two membrane-bound parallel
cylinders. This apparently simple system provides some flavor of the remarkably
subtle nonlinear behavior associated with membrane-mediated interactions.Comment: 16 pages, 10 figures, REVTeX4 style. The Gaussian curvature term was
included in the membrane Hamiltonian; section II.B was rephrased to smoothen
the flow of presentatio
Genetic diversity of the rain tree (Albizia saman) in Colombian seasonally dry tropical forest for informing conservation and restoration interventions
Albizia saman is a multipurpose tree species of seasonally dry tropical forests (SDTFs) of Mesoamerica and northern South America typically cultivated in silvopastoral and other agroforestry systems around the world, a trend that is bound to increase in light of multimillion hectare commitments for forest and landscape restoration. The effective conservation and sustainable use of A. saman requires detailed knowledge of its genetic diversity across its native distribution range of which surprisingly little is known to date. We assessed the genetic diversity and structure of A.saman across twelve representative locations of SDTF in Colombia, and how they may have been shaped by past climatic changes and human influence. We found four different genetic groups which may be the result of differentiation due to isolation of populations in preglacial times. The current distribution and mixture of genetic groups across STDF fragments we observed might be the result of range expansion of SDTFs during the last glacial period followed by range contraction during the Holocene and humanâinfluenced movement of germplasm associated with cattle ranching. Despite the fragmented state of the presumed natural A. saman stands we sampled, we did not find any signs of inbreeding, suggesting that gene flow is not jeopardized in humanized landscapes. However, further research is needed to assess potential deleterious effects of fragmentation on progeny. Climate change is not expected to seriously threaten the in situ persistence of A. saman populations and might present opportunities for future range expansion. However, the sourcing of germplasm for tree planting activities needs to be aligned with the genetic affinity of reference populations across the distribution of Colombian SDTFs. We identify priority source populations for in situ conservation based on their high genetic diversity, lack or limited signs of admixture, and/or genetic uniqueness
Monte Carlo study of the magnetic critical properties of the two-dimensional Ising fluid
A two-dimensional fluid of hard spheres each having a spin and
interacting via short-range Ising-like interaction is studied near the second
order phase transition from the paramagnetic gas to the ferromagnetic gas
phase. Monte Carlo simulation technique and the multiple histogram data
analysis were used. By measuring the finite-size behaviour of several different
thermodynamic quantities,we were able to locate the transition and estimate
values of various static critical exponents. The values of exponents
and are close to the ones for the two-dimensional
lattice Ising model. However, our result for the exponent is very
different from the one for the Ising universality class.Comment: 6 pages, 8 figures. To appear in Phys. Rev.
Moving frames applied to shell elasticity
Exterior calculus and moving frames are used to describe curved elastic
shells. The kinematics follow from the Lie-derivative on forms whereas the
dynamics via stress-forms.Comment: 20 pages, 1 figur
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