7,259 research outputs found
Threshold behavior of bosonic two-dimensional few-body systems
Bosonic two-dimensional self-bound clusters consisting of atoms
interacting through additive van der Waals potentials become unbound at a
critical mass m*(N); m*(N) has been predicted to be independent of the size of
the system. Furthermore, it has been predicted that the ground state energy
E(N) of the N-atom system varies exponentially as the atomic mass approaches
m*. This paper reports accurate numerical many-body calculations that allow
these predictions to be tested. We confirm the existence of a universal
critical mass m*, and show that the near-threshold behavior can only be
described properly if a previously neglected term is included. We comment on
the universality of the energy ratio E(N+1)/E(N) near threshold.Comment: 6 pages, 3 figure
Equilibrium concepts for social interaction models
equilibrium analysis;public choice
Attention to attributes and objects in working memory
It has been debated on the basis of change-detection procedures whether visual working memory is limited by the number of objects, task-relevant attributes within those objects, or bindings between attributes. This debate, however, has been hampered by several limitations, including the use of conditions that vary between studies and the absence of appropriate mathematical models to estimate the number of items in working memory in different stimulus conditions. We re-examined working memory limits in two experiments with a wide array of conditions involving color and shape attributes, relying on a set of new models to fit various stimulus situations. In Experiment 2, a new procedure allowed identical retrieval conditions across different conditions of attention at encoding. The results show that multiple attributes compete for attention, but that retaining the binding between attributes is accomplished only by retaining the attributes themselves. We propose a theoretical account in which a fixed object capacity limit contains within it the possibility of the incomplete retention of object attributes, depending on the direction of attention
A study of real-time computer graphic display technology for aeronautical applications
Hardware, algorithms and software for real-time raster graphics were designed and implemented
Pseudo-potential treatment of two aligned dipoles under external harmonic confinement
Dipolar Bose and Fermi gases, which are currently being studied extensively
experimentally and theoretically, interact through anisotropic, long-range
potentials. Here, we replace the long-range potential by a zero-range
pseudo-potential that simplifies the theoretical treatment of two dipolar
particles in a harmonic trap. Our zero-range pseudo-potential description
reproduces the energy spectrum of two dipoles interacting through a
shape-dependent potential under external confinement very well, provided that
sufficiently many partial waves are included, and readily leads to a
classification scheme of the energy spectrum in terms of approximate angular
momentum quantum numbers. The results may be directly relevant to the physics
of dipolar gases loaded into optical lattices.Comment: 9 pages, 4 figure
Application of a Modified Universal Design Survey for Evaluation of Ares 1 Ground Crew Worksites
Operability is a driving requirement for NASA's Ares 1 launch vehicle. Launch site ground operations include several operator tasks to prepare the vehicle for launch or to perform maintenance. Ensuring that components requiring operator interaction at the launch site are designed for optimal human use is a high priority for operability. To support design evaluation, the Ares 1 Upper Stage (US) element Human Factors Engineering (HFE) group developed a survey based on the Universal Design approach. Universal Design is a process to create products that can be used effectively by as many people as possible. Universal Design per se is not a priority for Ares 1 because launch vehicle processing is a specialized skill and not akin to a consumer product that should be used by all people of all abilities. However, applying principles of Universal Design will increase the probability of an error free and efficient design which is a priority for Ares 1. The Design Quality Evaluation Survey centers on the following seven principles: (1) Equitable use, (2) Flexibility in use, (3) Simple and intuitive use, (4) Perceptible information, (5) Tolerance for error, (6) Low physical effort, (7) Size and space for approach and use. Each principle is associated with multiple evaluation criteria which were rated with the degree to which the statement is true. All statements are phrased in the utmost positive, or the design goal so that the degree to which judgments tend toward "completely agree" directly reflects the degree to which the design is good. The Design Quality Evaluation Survey was employed for several US analyses. The tool was found to be most useful for comparative judgments as opposed to an assessment of a single design option. It provided a useful piece of additional data when assessing possible operator interfaces or worksites for operabilit
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