23,237 research outputs found
Study and development of acoustic treatment for jet engine tailpipes
A study and development program was accomplished to attenuate turbine noise generated in the JT3D turbofan engine. Analytical studies were used to design an acoustic liner for the tailpipe. Engine ground tests defined the tailpipe environmental factors and laboratory tests were used to support the analytical studies. Furnace-brazed, stainless steel, perforated sheet acoustic liners were designed, fabricated, installed, and ground tested in the tailpipe of a JT3D engine. Test results showed the turbine tones were suppressed below the level of the jet exhaust for most far field polar angles
Photometric, Spectroscopic and Orbital Period Study of Three Early Type Semi-detached Systems: XZ Aql, UX Her and AT Peg
In this paper we present a combined photometric, spectroscopic and orbital
period study of three early-type eclipsing binary systems: XZ Aql, UX Her, and
AT Peg. As a result, we have derived the absolute parameters of their
components and, on that basis, we discuss their evolutionary states.
Furthermore, we compare their parameters with those of other binary systems and
with the theoretical models. An analysis of all available up-to-date times of
minima indicated that all three systems studied here show cyclic orbital
changes, their origin is discussed in detail. Finally, we performed a frequency
analysis for possible pulsational behavior and as a result we suggest that XZ
Aql hosts a {\delta} Scuti component.Comment: 40 pages, 16 figure
Probabilistic computer model of optimal runway turnoffs
Landing delays are currently a problem at major air carrier airports and many forecasters agree that airport congestion will get worse by the end of the century. It is anticipated that some types of delays can be reduced by an efficient optimal runway exist system allowing increased approach volumes necessary at congested airports. A computerized Probabilistic Runway Turnoff Model which locates exits and defines path geometry for a selected maximum occupancy time appropriate for each TERPS aircraft category is defined. The model includes an algorithm for lateral ride comfort limits
Models of Ultraluminous X-Ray Sources with Intermediate-Mass Black Holes
We have computed models for ultraluminous X-ray sources ("ULXs") consisting
of a black-hole accretor of intermediate mass ("IMBH"; e.g., ~1000 Msun) and a
captured donor star. For each of four different sets of initial donor masses
and orbital separations, we computed 30,000 binary evolution models using a
full Henyey stellar evolution code. To our knowledge this is the first time
that a population of X-ray binaries this large has been carried out with other
than approximation methods, and it serves to demonstrate the feasibility of
this approach to large-scale population studies of mass-transfer binaries. In
the present study, we find that in order to have a plausible efficiency for
producing active ULX systems with IMBHs having luminosities > 10^{40} ergs/sec,
there are two basic requirements for the capture of companion/donor stars.
First, the donor stars should be massive, i.e., > 8 Msun. Second, the initial
orbital separations, after circularization, should be close, i.e., < 6-30 times
the radius of the donor star when on the main sequence. Even under these
optimistic conditions, we show that the production rate of IMBH-ULX systems may
fall short of the observed values by factors of 10-100.Comment: 5 pages, 2 figures, submitted to Ap
Vortex Pinning and Non-Hermitian Quantum Mechanics
A delocalization phenomenon is studied in a class of non-Hermitian random
quantum-mechanical problems. Delocalization arises in response to a
sufficiently large constant imaginary vector potential. The transition is
related to depinning of flux lines from extended defects in type-II
superconductors subject to a tilted external magnetic field. The physical
meaning of the complex eigenvalues and currents of the non-Hermitian system is
elucidated in terms of properties of tilted vortex lines. The singular behavior
of the penetration length describing stretched exponential screening of a
perpendicular magnetic field (transverse Meissner effect), the surface
transverse magnetization, and the trapping length are determined near the
flux-line depinning point.Comment: 2-column 27-pages RevTex file with 35 eps figure files embedded.
Minor errors amended. To be published in Phys. Rev.
Perturbation expansion for the diluted two-dimensional XY model
We study the quasi-long-range ordered phase of a 2D XY model with quenched
site-dilution using the spin-wave approximation and expansion in the parameter
which characterizes the deviation from completely homogeneous dilution. The
results, obtained by keeping the terms up to the third order in the expansion,
show good accordance with Monte Carlo data in a wide range of dilution
concentrations far enough from the percolation threshold. We discuss different
types of expansion.Comment: 8 pages, 1 eps figure, style file include
Deconfinement in the Two Dimensional XY Model
The unbinding of vortex-antivortex pairs for the classical two-dimensional XY
model in a magnetic field is studied. A single such pair is connected by a
string of overturned spins, leading to linear confinement. We show that this
system supports two phase transitions, one in which closed strings proliferate,
and a second in which vortices unbind. The transitions are shown to be dual to
one another, and are remarkably continuous. Possible consequences for a variety
of systems are discussed.Comment: 4 pages, 3 figures. Typos corrected, small but important change in
intro. Accepted for publication in Physical Review Letter
Electronic properties of disclinated flexible membrane beyond the inextensional limit: Application to graphene
Gauge-theory approach to describe Dirac fermions on a disclinated flexible
membrane beyond the inextensional limit is formulated. The elastic membrane is
considered as an embedding of 2D surface into R^3. The disclination is
incorporated through an SO(2) gauge vortex located at the origin, which results
in a metric with a conical singularity. A smoothing of the conical singularity
is accounted for by replacing a disclinated rigid plane membrane with a
hyperboloid of near-zero curvature pierced at the tip by the SO(2) vortex. The
embedding parameters are chosen to match the solution to the von Karman
equations. A homogeneous part of that solution is shown to stabilize the
theory. The modification of the Landau states and density of electronic states
of the graphene membrane due to elasticity is discussed.Comment: 15 pages, Journal of Physics:Condensed Matter in pres
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