20,020 research outputs found
Variable pitch fan system for NASA/Navy research and technology aircraft
Preliminary design of a shaft driven, variable-pitch lift fan and lift-cruise fan was conducted for a V/STOL Research and Technology Aircraft. The lift fan and lift-cruise fan employed a common rotor of 157.5 cm diameter, 1.18 pressure ratio variable-pitch fan designed to operate at a rotor-tip speed of 284 mps. Fan performance maps were prepared and detailed aerodynamic characteristics were established. Cost/weight/risk trade studies were conducted for the blade and fan case. Structural sizing was conducted for major components and weights determined for both the lift and lift-cruise fans
Mass return to the interstellar medium from highly-evolved carbon stars
Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated
Spinning compact binary inspiral II: Conservative angular dynamics
We establish the evolution equations of the set of independent variables
characterizing the 2PN rigorous conservative dynamics of a spinning compact
binary, with the inclusion of the leading order spin-orbit, spin-spin and mass
quadrupole - mass monopole effects, for generic (noncircular, nonspherical)
orbits. More specifically, we give a closed system of first order ordinary
differential equations for the orbital elements of the osculating ellipse and
for the angles characterizing the spin orientations with respect to the
osculating orbit. We also prove that (i) the relative angle of the spins stays
constant for equal mass black holes, irrespective of their orientation, and
(ii) the special configuration of equal mass black holes with equal, but
antialigned spins, both laying in the plane of motion (leading to the largest
recoil found in numerical simulations) is preserved at 2PN level of accuracy,
with leading order spin-orbit, spin-spin and mass quadrupolar contributions
included.Comment: v2: 19 pages, extended, improved, published versio
Low- and high-frequency noise from coherent two-level systems
Recent experiments indicate a connection between the low- and high-frequency
noise affecting superconducting quantum systems. We explore the possibilities
that both noises can be produced by one ensemble of microscopic modes, made up,
e.g., by sufficiently coherent two-level systems (TLS). This implies a relation
between the noise power in different frequency domains, which depends on the
distribution of the parameters of the TLSs. We show that a distribution,
natural for tunneling TLSs, with a log-uniform distribution in the tunnel
splitting and linear distribution in the bias, accounts for experimental
observations.Comment: minor corrections, references adde
Dynamic scaling approach to study time series fluctuations
We propose a new approach for properly analyzing stochastic time series by
mapping the dynamics of time series fluctuations onto a suitable nonequilibrium
surface-growth problem. In this framework, the fluctuation sampling time
interval plays the role of time variable, whereas the physical time is treated
as the analog of spatial variable. In this way we found that the fluctuations
of many real-world time series satisfy the analog of the Family-Viscek dynamic
scaling ansatz. This finding permits to use the powerful tools of kinetic
roughening theory to classify, model, and forecast the fluctuations of
real-world time series.Comment: 25 pages, 7 figures, 1 tabl
Nonlinear acoustic and microwave absorption in glasses
A theory of weakly-nonlinear low-temperature relaxational absorption of
acoustic and electromagnetic waves in dielectric and metallic glasses is
developed. Basing upon the model of two-level tunneling systems we show that
the nonlinear contribution to the absorption can be anomalously large. This is
the case at low enough frequencies, where freqeuency times the minimal
relaxation time for the two-level system are much less than one. In dielectric
glasses, the lowest-order nonlinear contribution is proportional to the wave's
intensity. It is negative and exhibits anomalous frequency and temperature
dependencies. In metallic glasses, the nonlinear contribution is also negative,
and it is proportional to the square root of the wave's intensity and to the
frequency. Numerical estimates show that the predicted nonlinear contribution
can be measured experimentally
Universal conductance fluctuations in three dimensional metallic single crystals of Si
In this paper we report the measurement of conductance fluctuations in single
crystals of Si made metallic by heavy doping (n \approx 2-2.5n_c, n_c being
critical composition at Metal-Insulator transition). Since all dimensions (L)
of the samples are much larger than the electron phase coherent length L_\phi
(L/L_\phi \sim 10^3), our system is truly three dimensional. Temperature and
magnetic field dependence of noise strongly indicate the universal conductance
fluctuations (UCF) as predominant source of the observed magnitude of noise.
Conductance fluctuations within a single phase coherent region of L_\phi^3 was
found to be saturated at \approx (e^2/h)^2. An accurate
knowledge of the level of disorder, enables us to calculate the change in
conductance \delta G_1 due to movement of a single scatterer as \delta G_1 \sim
e^2/h, which is \sim 2 orders of magnitude higher than its theoretically
expected value in 3D systems.Comment: Text revised version. 4 eps figs unchange
Precision neutron interferometric measurement of the nd coherent neutron scattering length and consequences for models of three-nucleon forces
We have performed the first high precision measurement of the coherent
neutron scattering length of deuterium in a pure sample using neutron
interferometry. We find b_nd = (6.665 +/- 0.004) fm in agreement with the world
average of previous measurements using different techniques, b_nd = (6.6730 +/-
0.0045) fm. We compare the new world average for the nd coherent scattering
length b_nd = (6.669 +/- 0.003) fm to calculations of the doublet and quartet
scattering lengths from several modern nucleon-nucleon potential models with
three-nucleon force (3NF) additions and show that almost all theories are in
serious disagreement with experiment. This comparison is a more stringent test
of the models than past comparisons with the less precisely-determined nuclear
doublet scattering length of a_nd = (0.65 +/- 0.04) fm.Comment: 4 pages, 4 figure
Exact correlation functions of the BCS model in the canonical ensemble
We evaluate correlation functions of the BCS model for finite number of
particles. The integrability of the Hamiltonian relates it with the Gaudin
algebra . Therefore, a theorem that Sklyanin proved for the
Gaudin model, can be applied. Several diagonal and off-diagonal correlators are
calculated. The finite size scaling behavior of the pairing correlation
function is studied.Comment: 4 pages revtex; 2 figures .eps. Revised version to be published in
Phys. Rev. Let
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