5,525 research outputs found
Apollo experience report: Communications used during recovery operations
Apollo program experience in recovery-support communications is reviewed, and the working relationships among NASA, the Department of Defense, and commercial communications facilities are discussed. The organization, facilities, philosophy, and funding of recovery-support communications are described. The relocation of two recovery control centers is discussed, as are the functions of primary and secondary recovery ships, aircraft, and relay satellities. The possibility of using ships of opportunity for recovery operations is considered. Finally, the means by which money, manpower, and resources have been saved and longlines leased are delineated
Remarks on NonHamiltonian Statistical Mechanics: Lyapunov Exponents and Phase-Space Dimensionality Loss
The dissipation associated with nonequilibrium flow processes is reflected by
the formation of strange attractor distributions in phase space. The
information dimension of these attractors is less than that of the equilibrium
phase space, corresponding to the extreme rarity of nonequilibrium states. Here
we take advantage of a simple model for heat conduction to demonstrate that the
nonequilibrium dimensionality loss can definitely exceed the number of
phase-space dimensions required to thermostat an otherwise Hamiltonian system.Comment: 5 pages, 2 figures, minor typos correcte
Parametric Relationships of Conventional Versus Repetitive Loading Triaxial Tests
This investigation was developed to examine response of a field-mixed asphalt-treated granular base material to 100,000 repetitions of a load whose magnitude was determined by a failure criterion proposed by Hoover (1970), and Fish and Hoover (1969). Axial strain and load at the point of maximum volume of a specimen during a conventional triaxial test appear to produce a proportional limit, indicating that failure may have started. Axial stress at this point was applied in the repetitive loading triaxial test at the same confining pressure, during which axial strain and pore pressure continuously increased and specimen volume decreased in each of three series of tests. Post repetitive specimen condition, determined by retesting in the conventional manner indicated that none of the specimens had failed during repetitive loading. Results of this series of tests indicate a further potential feasibility of the use of minimum volume failure criteria for thickness design of a granular base material
Irreversibility in a simple reversible model
This paper studies a parametrized family of familiar generalized baker maps,
viewed as simple models of time-reversible evolution. Mapping the unit square
onto itself, the maps are partly contracting and partly expanding, but they
preserve the global measure of the definition domain. They possess periodic
orbits of any period, and all maps of the set have attractors with well defined
structure. The explicit construction of the attractors is described and their
structure is studied in detail. There is a precise sense in which one can speak
about absolute age of a state, regardless of whether the latter is applied to a
single point, a set of points, or a distribution function. One can then view
the whole trajectory as a set of past, present and future states. This
viewpoint is then applied to show that it is impossible to define a priori
states with very large "negative age". Such states can be defined only a
posteriori. This gives precise sense to irreversibility -- or the "arrow of
time" -- in these time-reversible maps, and is suggested as an explanation of
the second law of thermodynamics also for some realistic physical systems.Comment: 15 pages, 12 Postscript figure
Comment on the calculation of forces for multibody interatomic potentials
The system of particles interacting via multibody interatomic potential of
general form is considered. Possible variants of partition of the total force
acting on a single particle into pair contributions are discussed. Two
definitions for the force acting between a pair of particles are compared. The
forces coincide only if the particles interact via pair or embedded-atom
potentials. However in literature both definitions are used in order to
determine Cauchy stress tensor. A simplest example of the linear pure shear of
perfect square lattice is analyzed. It is shown that, Hardy's definition for
the stress tensor gives different results depending on the radius of
localization function. The differences strongly depend on the way of the force
definition.Comment: 9 pages, 2 figure
THE EFFECTS OF BLOOD FLOW RESTRICTION ON MEASURES OF GROSS MOTOR COORDINATION DURING THE WINGATE ANAEROBIC TEST
To date little research has addressed the impact of blood flow restriction (BFR) training upon gross motor coordination measures (GMCM) during a wide variety of maximal activities. The purpose of this study was to assess the effects of BFR on GMCM exhibited during maximal cycling. The performance of 14 females between the ages of eighteen and thirty-five were analyzed during the Wingate Anaerobic Test (WAnT). The participants completed the test under two conditions, using BFR and without. Results showed statistically significant differences (p ≤ 0.05) between conditions for dependent variables assessed throughout this common 30 second test of maximal cycling. These findings suggest that BFR negatively influenced GMCM exhibited during the WAnT
Recommended from our members
Plastic dislocation motion via nonequilibrium molecular and continuum dynamics
The classical two-dimensional close-packed triangular lattice, with nearest-neighbor spring forces, is a convenient standard material for the investigation of dislocation motion and plastic flow. Two kinds of calculations, based on this standard material, are described here: (1) Molecular Dynamics simulations, incorporating adiabatic strains described with the help of Doll's Tensor, and (2) Continuum Dynamics simulations, incorporating periodic boundaries and dislocation interaction through stress-field superposition
BLOOD FLOW RESTRICTION DOES NOT AFFECT ACUTE MEASURES OF POWER AND FATIGUE DURING MAXIMAL CYCLING AMONG WOMEN
While it is known that blood flow restriction (BFR) can positively affect training and rehabilitation progression timelines, the physiological basis of this intervention is not fully understood. The purpose of this study was to determine the short-term impact of BFR upon power and fatigue performance measures during maximal cycling. In this study, maximal cycling was assessed using the Wingate Anaerobic Test (WAnT). Using a counterbalanced design, fourteen female participants completed standardized BFR and non-BFR protocols while completing the WAnT. No statistically-significant differences (p ≤ 0.05) were found between conditions for measures of peak power (PP), low power (LP) or fatigue index (FI). These findings suggest that BFR had no statistically-significant acute effect on these performance measures commonly assessed during the WAnT
Three-phase point in a binary hard-core lattice model?
Using Monte Carlo simulation, Van Duijneveldt and Lekkerkerker [Phys. Rev.
Lett. 71, 4264 (1993)] found gas-liquid-solid behaviour in a simple
two-dimensional lattice model with two types of hard particles. The same model
is studied here by means of numerical transfer matrix calculations, focusing on
the finite size scaling of the gaps between the largest few eigenvalues. No
evidence for a gas-liquid transition is found. We discuss the relation of the
model with a solvable RSOS model of which the states obey the same exclusion
rules. Finally, a detailed analysis of the relation with the dilute three-state
Potts model strongly supports the tricritical point rather than a three-phase
point.Comment: 17 pages, LaTeX2e, 13 EPS figure
- …