5,871 research outputs found
The Variable-Atmosphere Wave Tank
A facility was constructed for the study of water-entry,
water-exit, and underwater trajectory behavior of
small momentum-propelled missiles for varied trajectory
launching angles, missile accelerations and velocities,
wave fields and conditions of cavitation. A unique feature
is the electromagnetic missile propulsion system.
The facility is made principally of non-magnetic and
electrically non-conducting materials to permit the determination of missile accelerating force from the reactive force on the launching coil
Fluid Free Surface Proximity Effect on a Sphere Vertically Accelerated from Rest
Theory is developed to estimate the effect of free
surface proximity on the initial added mass of a sphere
accelerated vertically upward from rest in an ideal fluid.
It is assumed that the acceleration regime is sufficiently
brief that inertial forces predominate and gravitational
effects may be neglected. Results of tests in water indicate
that while there are slight viscous and gravitational effects
over the acceleration regime, the agreement between theory
and experiment is good. It is concluded that over briefer
acceleration regimes these effects would decrease and the
agreement would improve
Consistent thermodynamics for spin echoes
Spin-echo experiments are often said to constitute an instant of
anti-thermodynamic behavior in a concrete physical system that violates the
second law of thermodynamics. We argue that a proper thermodynamic treatment of
the effect should take into account the correlations between the spin and
translational degrees of freedom of the molecules. To this end, we construct an
entropy functional using Boltzmann macrostates that incorporates both spin and
translational degrees of freedom. With this definition there is nothing special
in the thermodynamics of spin echoes: dephasing corresponds to Hamiltonian
evolution and leaves the entropy unchanged; dissipation increases the entropy.
In particular, there is no phase of entropy decrease in the echo. We also
discuss the definition of macrostates from the underlying quantum theory and we
show that the decay of net magnetization provides a faithful measure of entropy
change.Comment: 15 pages, 2 figs. Changed figures, version to appear in PR
Real Fluid Effects on an Accelerated Sphere Before Boundary-Layer Separation
Studies were made on the apparent increase in mass on acceleration (added mass) of a sphere accelerated from rest and before boundary-layer separation, in cylinders
of various diameters filled with water or oil. From a comparison of theoretical and experimentally obtained added masses, the following conclusions were drawn: In the
absence of wall effects on the boundary layer, the wall shear stress over elements of the sphere can be approximated by the solution for the flat plate moving parallel to itself and the potential flow over the elements outside the boundary layer. The impulse on the elements is obtained by integration with respect to time, and the wall
drag and drag impulse on the sphere by integration over the sphere surface. Good theoretical and experimental agreement obtains under the assumption that a mass of fluid, estimated from the wall drag impulse, is carried in the boundary layer and may be university distributed over the sphere
Refractory composite materials for spacecraft thrust chambers Final report, 23 Jul. 1968 - 22 Feb. 1970
Hot firing tests with FLOX/methane propellants for evaluating pyrolytic refractory composite materials for thrust chamber
Strong Tunneling in Double-Island Structures
We study the electron transport through a system of two low-capacitance metal
islands connected in series between two electrodes. The work is motivated in
part by experiments on semiconducting double-dots, which show intriguing
effects arising from coherent tunneling of electrons and mixing of the
single-electron states across tunneling barriers. In this article, we show how
coherent tunneling affects metallic systems and leads to a mixing of the
macroscopic charge states across the barriers. We apply a recently formulated
RG approach to examine the linear response of the system with high tunnel
conductances (up to 8e^2/h). In addition we calculate the (second order)
cotunneling contributions to the non-linear conductance. Our main results are
that the peaks in the linear and nonlinear conductance as a function of the
gate voltage are reduced and broadened in an asymmetric way, as well as shifted
in their positions. In the limit where the two islands are coupled weakly to
the electrodes, we compare to theoretical results obtained by Golden and
Halperin and Matveev et al. In the opposite case when the two islands are
coupled more strongly to the leads than to each other, the peaks are found to
shift, in qualitative agreement with the recent prediction of Andrei et al. for
a similar double-dot system which exhibits a phase transition.Comment: 12 page
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