1,565 research outputs found
Interactions of satellite-speed helium atoms with satellite surfaces. 3: Drag coefficients from spatial and energy distributions of reflected helium atoms
Spatial and energy distributions of helium atoms scattered from an anodized 1235-0 aluminum surface as well as the tangential and normal momentum accommodation coefficients calculated from these distributions are reported. A procedure for calculating drag coefficients from measured values of spatial and energy distributions is given. The drag coefficient calculated for a 6061 T-6 aluminum sphere is included
Interactions of satellite-speed helium atoms with satellite surfaces. 2: Energy distributions of reflected helium atoms
Energy transfer in collisions of satellite-speed (7,000 m/sec) helium atoms with a cleaned 6061-T6 satellite-type aluminum surface was investigated using the molecular-beam technique. The amount of energy transferred was determined from the measured energy of the molecular-beam and the measured spatial and energy distributions of the reflected atoms. Spatial distributions of helium atoms scattered from a 6061-T6 aluminum surface were measured. The scattering pattern exhibits a prominent backscattering, probably due to the gross surface roughness and/or the relative lattice softness of the aluminum surface. Energy distributions of reflected helium atoms from the same surface were measured for six different incidence angles. For each incidence angle, distributions were measured at approximately sixty scattering positions. At a given scattering position, the energy spectra of the reflected helium atoms and the background gas were obtained using the retarding-field energy analyzer
Researches on interactions of satellite-speed helium atoms with aluminum and quartz surfaces
Three major areas were experimentally studied: (1) energy transfer in collisions of satellite-speed (700 m/sec) helium atoms with a cleaned satellite-type aluminum surface was investigated using the molecular-beam technique. Spatial and energy distributions of reflected helium atoms were measured and analyzed, (2) The gross accommodation coefficient for a satellite-speed (7000 m/sec) helium beam entering a 2-inch-diameter aluminum spherical cavity was determined by measuring the exit velocity distribution of the leaving helium atoms using a metastable time-of-flight method. Results indicate that the 7000-m/sec satellite-speed helium atoms entering the cavity gain full accommodation with the room-temperature inner surface of the sphere through a large number of collisions before leaving the spherical cavity; and (3) the feasibility of producing a satellite-speed atomic hydrogen beam by arc-heating, for use in studies of interactions of satellite-surfaces with hydrogen atoms under laboratory conditions, was investigated. It was found that a stable arc-heated molecular hydrogen beam can be obtained using the arc-heater, and that a partially dissociated hydrogen beam can be produced. Photographs of laboratory equipment are shown
Automatic navigation of a long range rocket vehicle
The flight of a rocket vehicle in the equatorial plane of a rotating earth is considered with possible disturbances in the atmosphere due to changes in density, in temperature, and in wind speed. These atmospheric disturbances together with possible deviations in weight and in moment of inertia of the vehicle tend to change the flight path away from the normal flight path. The paper gives the condition for the proper cut-off time for the rocket power, and the proper corrections in the elevator angle so that the vehicle will land at the chosen destination in spite of such disturbances. A scheme of tracking and automatic navigation involving a high-speed computer and elevator servo is suggested for this purpose
Information-Based Physics: An Observer-Centric Foundation
It is generally believed that physical laws, reflecting an inherent order in
the universe, are ordained by nature. However, in modern physics the observer
plays a central role raising questions about how an observer-centric physics
can result in laws apparently worthy of a universal nature-centric physics.
Over the last decade, we have found that the consistent apt quantification of
algebraic and order-theoretic structures results in calculi that possess
constraint equations taking the form of what are often considered to be
physical laws. I review recent derivations of the formal relations among
relevant variables central to special relativity, probability theory and
quantum mechanics in this context by considering a problem where two observers
form consistent descriptions of and make optimal inferences about a free
particle that simply influences them. I show that this approach to describing
such a particle based only on available information leads to the mathematics of
relativistic quantum mechanics as well as a description of a free particle that
reproduces many of the basic properties of a fermion. The result is an approach
to foundational physics where laws derive from both consistent descriptions and
optimal information-based inferences made by embedded observers.Comment: To be published in Contemporary Physics. The manuscript consists of
43 pages and 9 Figure
A Formal Definition of SOL
This paper gives a formal definition of SOL, a general-purpose algorithmic language useful for describing and simulating complex systems. SOL is described using meta-linguistic formulas as used in the definition of ALGOL 60. The principal differences between SOL and problem-oriented languages such as ALGOL or FORTRAN is that SOL includes capabilities for expressing parallel computation, convenient notations for embedding random quantities within arithmetic expressions and automatic means for gathering statistics about the elements involved. SOL differs from other simulation languages such as SIMSCRIPT primarily in simplicity of use and in readability since it is capable of describing models without including computer-oriented characteristics
Molecular dynamics simulations of ballistic annihilation
Using event-driven molecular dynamics we study one- and two-dimensional
ballistic annihilation. We estimate exponents and that describe
the long-time decay of the number of particles () and of
their typical velocity (). To a good accuracy our results
confirm the scaling relation . In the two-dimensional case our
results are in a good agreement with those obtained from the Boltzmann kinetic
theory.Comment: 4 pages; some changes; Physical Review E (in press
The Mott insulator phase of the one dimensional Bose-Hubbard model: a high order perturbative study
The one dimensional Bose-Hubbard model at a unit filling factor is studied by
means of a very high order symbolic perturbative expansion. Analytical
expressions are derived for the ground state quantities such as energy per
site, variance of on-site occupation, and different correlation functions.
These findings are compared to numerics and good agreement is found in the Mott
insulator phase. Our results provide analytical approximations to important
observables in the Mott phase, and are also of direct relevance to future
experiments with ultra cold atomic gases placed in optical lattices. We also
discuss the symmetry of the Bose-Hubbard model associated with the sign change
of the tunneling coupling.Comment: 7 pages, 4 figures, 1 table. Significantly expanded version with
respect to former submission (to appear in Phys. Rev. A
SOL - A Symbolic Language for General-Purpose Systems Simulation
This paper illustrates the use of SOL, a general-purpose algorithmic language useful for describing and simulating complex systems. Such a system is described as a number of individual processes which simultaneously enact a program very much like a computer program. (Some features of the SOL language are directly applicable to programming languages for parallel computers, as well as for simulation.) Once a system has been described in the language, the program can be translated by the SOL compiler into an interpretive code, and the execution of this code produces statistical information about the model. A detailed example of a SOL model for a multiple on-line console system is exhibited, indicating the notational simplicity and intuitive nature of the language
Quantum computers can search arbitrarily large databases by a single query
This paper shows that a quantum mechanical algorithm that can query
information relating to multiple items of the database, can search a database
in a single query (a query is defined as any question to the database to which
the database has to return a (YES/NO) answer). A classical algorithm will be
limited to the information theoretic bound of at least O(log N) queries (which
it would achieve by using a binary search).Comment: Several enhancements to the original pape
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