21,048 research outputs found
Coefficients and terms of the liquid drop model and mass formula
The coefficients of different combinations of terms of the liquid drop model
have been determined by a least square fitting procedure to the experimental
atomic masses. The nuclear masses can also be reproduced using a Coulomb radius
taking into account the increase of the ratio with increasing
mass, the fitted surface energy coefficient remaining around 18 MeV
Liquid-Drop Model and Quantum Resistance Against Noncompact Nuclear Geometries
The importance of quantum effects for exotic nuclear shapes is demonstrated.
Based on the example of a sheet of nuclear matter of infinite lateral
dimensions but finite thickness, it is shown that the quantization of states in
momentum space, resulting from the confinement of the nucleonic motion in the
conjugate geometrical space, generates a strong resistance against such a
confinement and generates restoring forces driving the system towards compact
geometries. In the liquid-drop model, these quantum effects are implicitly
included in the surface energy term, via a choice of interaction parameters, an
approximation that has been found valid for compact shapes, but has not yet
been scrutinized for exotic shapes.Comment: 9 pages with 3 figure
Surface tension in a compressible liquid-drop model: Effects on nuclear density and neutron skin thickness
We examine whether or not the surface tension acts to increase the nucleon
density in the nuclear interior within a compressible liquid-drop model. We
find that it depends on the density dependence of the surface tension, which
may in turn be deduced from the neutron skin thickness of stable nuclei.Comment: 4 pages, 1 figure, to be published in Physical Review
Stability of bubble nuclei through Shell-Effects
We investigate the shell structure of bubble nuclei in simple
phenomenological shell models and study their binding energy as a function of
the radii and of the number of neutron and protons using Strutinsky's method.
Shell effects come about, on the one hand, by the high degeneracy of levels
with large angular momentum and, on the other, by the big energy gaps between
states with a different number of radial nodes. Shell energies down to -40 MeV
are shown to occur for certain magic nuclei. Estimates demonstrate that the
calculated shell effects for certain magic numbers of constituents are probably
large enough to produce stability against fission, alpha-, and beta-decay. No
bubble solutions are found for mass number A < 450.Comment: 9 pages and 9 figures in the eps format include
Lunar contour mapping system /lucom/ final report, 5 aug. 1964 - 18 mar. 1965
Radar sensor system for acquisition of lunar surface data - Lunar contour mapping syste
Assessing An Economics Programme: Hansen Proficiencies, ePortfolio, and Undergraduate Research
Numerous sources calling for more accountability in higher education are putting increased pressure on many economics departments to develop assessment plans. This paper discusses a set of principles for programmatic assessment gleaned from the assessment literature, while highlighting one US economic department's journey to develop an assessment of student learning outcomes based on Hansen's proficiencies. We explain the curriculum reforms that culminate with independent undergraduate research as suggested by the highest level of Hansen's proficiencies. We describe ePortfolios which showcase student abilities and integrate evidence of student learning across the curriculum. For departments without direct guidance from accreditation boards or other agencies, we put forth a process of forming programmatic assessment in economics.
Orbital maneuvering end effectors
This invention relates to an end effector device for grasping and maneuvering objects such as berthing handles of a space telescope. The device includes a V-shaped capture window defined as inclined surfaces in parallel face plates which converge toward a retainer recess in which the handle is retained. A pivotal finger (30) meshes with a pair of pivoted fingers which rotate in counterrotation. The fingers rotate to pull a handle within the capture window into recess where latches lock handle in the recess. To align the capture window, plates may be cocked plus or minus five degrees on base. Drive means is included in the form of a motor coupled with a harmonic drive speed reducer, which provides for slow movement of the fingers at a high torque so that large articles may be handled. Novelty of the invention is believed to reside in the combined intermeshing finger structure, drive means and the harmonic drive speed reducer, which features provide the required maneuverability and strength
Black Holes with a Generalized Gravitational Action
Microscopic black holes are sensitive to higher dimension operators in the
gravitational action. We compute the influence of these operators on the
Schwarzschild solution using perturbation theory. All (time reversal invariant)
operators of dimension six are included (dimension four operators don't alter
the Schwarzschild solution). Corrections to the relation between the Hawking
temperature and the black hole mass are found. The entropy is calculated using
the Gibbons-Hawking prescription for the Euclidean path integral and using
naive thermodynamic reasoning. These two methods agree, however, the entropy is
not equal to 1/4 the area of the horizon.Comment: plain tex(uses phyzzx.tex), 8 pages, CALT-68-185
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