1,038 research outputs found
Pressure and heat flux results from the space shuttle/external fuel tank interaction test at Mach numbers 16 and 19
Heat transfer rates and pressures were measured on a 0.0175-scale model of the space shuttle external tank (ET), model MCR0200. Tests were conducted with the ET model separately and while mated with a 0.0175-scale model of the orbiter, model 21-OT (Grumman). The tests were conducted in the AEDC-VKF Hypervelocity Wind Tunnel (F) at Mach numbers 16 and 19. The primary data consisted of the interaction heating rates experienced by the ET while mated with the orbiter in the flight configuration. Data were taken for a range of Reynolds numbers from 50,000 to 65,000 under laminar flow conditions
Improved Semiclassical Approximation for Bose-Einstein Condensates: Application to a BEC in an Optical Potential
We present semiclassical descriptions of Bose-Einstein condensates for
configurations with spatial symmetry, e.g., cylindrical symmetry, and without
any symmetry. The description of the cylindrical case is quasi-one-dimensional
(Q1D), in the sense that one only needs to solve an effective 1D nonlinear
Schrodinger equation, but the solution incorporates correct 3D aspects of the
problem. The solution in classically allowed regions is matched onto that in
classically forbidden regions by a connection formula that properly accounts
for the nonlinear mean-field interaction. Special cases for vortex solutions
are treated too. Comparisons of the Q1D solution with full 3D and Thomas-Fermi
ones are presented.Comment: 14 pages, 5 figure
The Current Density Distribution in a Segmented-in-Series SOFC,”
A common tubular solid oxide fuel cell (SOFC) design consists of segmented-in-serie
Vector-soliton collision dynamics in nonlinear optical fibers
We consider the interactions of two identical, orthogonally polarized vector
solitons in a nonlinear optical fiber with two polarization directions,
described by a coupled pair of nonlinear Schroedinger equations. We study a
low-dimensional model system of Hamiltonian ODE derived by Ueda and Kath and
also studied by Tan and Yang. We derive a further simplified model which has
similar dynamics but is more amenable to analysis. Sufficiently fast solitons
move by each other without much interaction, but below a critical velocity the
solitons may be captured. In certain bands of initial velocities the solitons
are initially captured, but separate after passing each other twice, a
phenomenon known as the two-bounce or two-pass resonance. We derive an analytic
formula for the critical velocity. Using matched asymptotic expansions for
separatrix crossing, we determine the location of these "resonance windows."
Numerical simulations of the ODE models show they compare quite well with the
asymptotic theory.Comment: 32 pages, submitted to Physical Review
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The slowdown in mortality improvement rates 2011–2017: a multi-country analysis
Mortality rates have been falling or ‘improving’ in many demographically developed countries since the 1950s. However, there has been a slowdown since 2010 in the speed of improvement and this phenomenon has been particularly marked at ages over 50. To understand better this mortality slowdown, we have analysed long-run mortality trends of a group of developed countries using data up to 2017 from the Human Mortality Database. Specifically, we have used statistical models to parametrise the historical mortality trends of 21 countries between 1965 and 2010 and then forecast trends beyond 2011. We find that many countries have experienced lower mortality improvement rates in 2011–2017 than in the previous decade and also experienced lower improvement rates in 2011–2017 than would have been forecast based on the models fitted to data prior to 2011. Some of the Scandinavian populations have bucked the stalling mortality improvement trend, experiencing higher mortality improvement rates than the forecasts. We conclude that part of the slowdown in mortality improvement rates of the over 1950s since 2011 would have been expected from historical trends in many countries, especially among men. However, there has been a notable slowdown since 2011, compared with the model forecasts, in many countries especially among women. A few countries had higher mortality improvement rates than forecast. A better understanding of the drivers behind these complex trends would help decision makers in insurance companies and pension funds and also inform public policy
Hard loss of stability in Painlev\'e-2 equation
A special asymptotic solution of the Painlev\'e-2 equation with small
parameter is studied. This solution has a critical point corresponding to
a bifurcation phenomenon. When the constructed solution varies slowly
and when the solution oscillates very fast. We investigate the
transitional layer in detail and obtain a smooth asymptotic solution, using a
sequence of scaling and matching procedures
Theoretical approach to two-dimensional traffic flow models
In this paper we present a theoretical analysis of a recently proposed
two-dimensional Cellular Automata model for traffic flow in cities with the
novel ingredient of turning capability. Numerical simulations of this model
show that there is a transition between a freely moving phase with high
velocity to a jammed state with low velocity. We study the dynamics of such a
model starting with the microscopic evolution equation, which will serve as a
basis for further analysis. It is shown that a kinetic approach, based on the
Boltzmann assumption, is able to provide a reasonably good description of the
jamming transition. We further introduce a space-time continuous
phenomenological model leading to a couple of partial differential equations
whose preliminary results agree rather well with the numerical simulations.Comment: 15 pages, REVTeX 3.0, 7 uuencoded figures upon request to
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