23,679 research outputs found
Airship economics
Projected operating and manufacturing costs of a large airship design which are considered practical with today's technology and environment are discussed. Data and information developed during an 18-month study on the question of feasibility, engineering, economics and production problems related to a large metalclad type airship are considered. An overview of other classic airship designs are provided, and why metalclad was selected as the most prudent and most economic design to be considered in the 1970-80 era is explained. Crew operation, ATC and enroute requirements are covered along with the question of handling, maintenance and application of systems to the large airship
Multiple jumps and vacancy diffusion in a face-centered cubic metal
The diffusion of monovacancies in gold has been studied by computer
simulation. Multiple jumps have been found to play a central role in the atomic
dynamics at high temperature, and have been shown to be responsible for an
upward curvature in the Arrhenius plot of the diffusion coefficient.
Appropriate saddle points on the potential energy surface have been found,
supporting the interpretation of vacancy multiple jumps as distinct migration
mechanisms.Comment: 16 page
Discrete Self-Similarity in Type-II Strong Explosions
We present new solutions to the strong explosion problem in a non-power law
density profile. The unperturbed self-similar solutions discovered by Waxman &
Shvarts describe strong Newtonian shocks propagating into a cold gas with a
density profile falling off as , where (Type-II
solutions). The perturbations we consider are spherically symmetric and
log-periodic with respect to the radius. While the unperturbed solutions are
continuously self-similar, the log-periodicity of the density perturbations
leads to a discrete self-similarity of the perturbations, i.e. the solution
repeats itself up to a scaling at discrete time intervals. We discuss these
solutions and verify them against numerical integrations of the time dependent
hydrodynamic equations. Finally we show that this method can be generalized to
treat any small, spherically symmetric density perturbation by employing
Fourier decomposition
Optimal Covariant Measurement of Momentum on a Half Line in Quantum Mechanics
We cannot perform the projective measurement of a momentum on a half line
since it is not an observable. Nevertheless, we would like to obtain some
physical information of the momentum on a half line. We define an optimality
for measurement as minimizing the variance between an inferred outcome of the
measured system before a measuring process and a measurement outcome of the
probe system after the measuring process, restricting our attention to the
covariant measurement studied by Holevo. Extending the domain of the momentum
operator on a half line by introducing a two dimensional Hilbert space to be
tensored, we make it self-adjoint and explicitly construct a model Hamiltonian
for the measured and probe systems. By taking the partial trace over the newly
introduced Hilbert space, the optimal covariant positive operator valued
measure (POVM) of a momentum on a half line is reproduced. We physically
describe the measuring process to optimally evaluate the momentum of a particle
on a half line.Comment: 12 pages, 3 figure
Measurement of the proton light response of various LAB based scintillators and its implication for supernova neutrino detection via neutrino-proton scattering
The proton light output function in electron-equivalent energy of various
scintillators based on linear alkylbenzene (LAB) has been measured in the
energy range from 1 MeV to 17.15 MeV for the first time. The measurement was
performed at the Physikalisch-Technische Bundesanstalt (PTB) using a neutron
beam with continuous energy distribution. The proton light output data is
extracted from proton recoil spectra originating from neutron-proton scattering
in the scintillator. The functional behavior of the proton light output is
described succesfully by Birks' law with a Birks constant kB between (0.0094
+/- 0.0002) cm/MeV and (0.0098 +/- 0.0003) cm/MeV for the different LAB
solutions. The constant C, parameterizing the quadratic term in the generalized
Birks law, is consistent with zero for all investigated scintillators with an
upper limit (95% CL) of about 10^{-7} cm^2/MeV^2. The resulting quenching
factors are especially important for future planned supernova neutrino
detection based on the elastic scattering of neutrinos on protons. The impact
of proton quenching on the supernova event yield from neutrino-proton
scattering is discussed.Comment: 12 pages, 17 figures, 4 tables, updated version for publication in
Eur.Phys.J.
An analytical and experimental comparison of the flow field of an advanced swept turboprop
An argon ion laser velocimeter with four beams was used to measure the detailed flow-field of an advanced eight blade propeller with 45% of tip sweep in an 8x6 foot supersonic wind tunnel. Data were obtained at a free stream Mach number of 0.8, the design advance ratio of 3.06 and a power coefficient of 1.8. Data are presented for inlet flow, exit flow, flow within the blades and flow slightly outside the blade tips. The data are compared to a lifting line theory. In general, the results of the comparison are considered favorable
An analytical and experimental study of a short s-shaped subsonic diffuser of a supersonic inlet
A subscale HiMAT forebody and inlet was investigated over a range of Mach numbers to 1.4. The inlet exhibited a transitory separation within the diffuser but steady state data indicated reattachment at the diffuser exit. A finite difference procedure for turbulent compressible flow in axisymmetric ducts was used to successfully model the HiMAT duct flow. The analysis technique was further used to estimate the initiation of separation and delineate the steady and unsteady flow regimes in similar S-shaped ducts
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