56,776 research outputs found
Elastic ice shells of synchronous moons: Implications for cracks on Europa and non-synchronous rotation of Titan
A number of synchronous moons are thought to harbor water oceans beneath
their outer ice shells. A subsurface ocean frictionally decouples the shell
from the interior. This has led to proposals that a weak tidal or atmospheric
torque might cause the shell to rotate differentially with respect to the
synchronously rotating interior. As a result of centrifugal and tidal forces,
the ocean would assume an ellipsoidal shape with its long axis aligned toward
the parent planet. Any displacement of the shell away from its equilibrium
position would induce strains thereby increasing its elastic energy and giving
rise to an elastic restoring torque. We compare the elastic torque with the
tidal torque acting on Europa and the atmospheric torque acting on Titan. For
Europa, the tidal torque is far too weak to produce stresses that could
fracture the ice shell, thus refuting a widely advocated idea. Instead, we
suggest that cracks arise from time-dependent stresses due to non-hydrostatic
gravity anomalies from tidally driven, episodic convection in the interior. Two
years of Cassini RADAR observations of Titan's surface are interpreted as
implying an angular displacement of ~0.24 degrees relative to synchroneity.
Compatibility of the amplitude and phase of the observed non-synchronous
rotation with estimates of the atmospheric torque requires that Titan's shell
be decoupled from its interior. We find that the elastic torque balances the
atmospheric torque at an angular displacement <0.05 degrees, thus coupling the
shell to the interior. Moreover, if Titan's surface were spinning faster than
synchronous, the tidal torque tending to restore synchronous rotation would
certainly be larger than the atmospheric torque. There must either be a problem
with the interpretation of the radar observations, or with our understanding of
Titan's atmosphere and/or interior.Comment: Icarus, in pres
Herding Cats: Improving Law School Teaching
What makes a good law teacher? Is excellence in teaching largely a matter of intellectual brilliance, of superior organization and delivery of material, of friendliness and fairness to one\u27s students? Or does it have more to do with style, with stage presence, with the ability to engage an audience in the act of reflective and spontaneous thinking?
While the question of how to define and evaluate teaching necessarily bedevils deans and tenure committees who must make personnel decisions, the focus on defining the competent teacher has obscured from faculty attention the more fundamental question: how can we implement a system to improve faculty performance across the board? It is this question that law schools around the country have not adequately addressed.
Three years ago, the faculty of Franklin Pierce Law Center adopted a program to improve our classroom teaching. This article describes and evaluates that program, in which all three authors played a role
Thermodynamics of Solitonic Matter Waves in a Toroidal Trap
We investigate the thermodynamic properties of a Bose-Einstein condensate
with negative scattering length confined in a toroidal trapping potential. By
numerically solving the coupled Gross-Pitaevskii and Bogoliubov-de Gennes
equations, we study the phase transition from the uniform state to the
symmetry-breaking state characterized by a bright-soliton condensate and a
localized thermal cloud. In the localized regime three states with a finite
condensate fraction are present: the thermodynamically stable localized state,
a metastable localized state and also a metastable uniform state. Remarkably,
the presence of the stable localized state strongly increases the critical
temperature of Bose-Einstein condensation.Comment: 4 pages, 4 figures, to be published in Physical Review A as a Rapid
Communication. Related papers can be found at
http://www.padova.infm.it/salasnich/tdqg.htm
Human Factors Considerations in System Design
Human factors considerations in systems design was examined. Human factors in automated command and control, in the efficiency of the human computer interface and system effectiveness are outlined. The following topics are discussed: human factors aspects of control room design; design of interactive systems; human computer dialogue, interaction tasks and techniques; guidelines on ergonomic aspects of control rooms and highly automated environments; system engineering for control by humans; conceptual models of information processing; information display and interaction in real time environments
Concepts for 18/30 GHz satellite communication system study. Executive summary
An examination of a multiplicity of interconnected parameters ranging from specific technology details to total system economic costs for satellite communication systems at the 18/30 GHz transmission bands are presented. It was determined that K sub A band systems can incur a small communications outage during very heavy rainfall periods and that reducing the outage to zero would lead to prohibitive system costs. On the other hand, the economics of scale, ie, one spacecraft accommodating 2.5 GHz of bandwidth coupled with multiple beam frequency reuse, leads to very low costs for those users who can tolerate the 5 to 50 hours per year of downtime. A multiple frequency band satellite network can provide the ultimate optimized match to the consumer performance/economics demands
OH(A-X) fluorescence from photodissociative excitation of HO2 at 157.5 nm
The OH(A-X) fluorescence from photodissociative excitation of HO2 by F2 laser photons (157.5 nm) was observed and compared with the OH fluorescence spectra of H2O2 and the O2+CH3OH mixture. The rotational population distributions of OH(A) were obtained from the fluorescence spectra. The most populated levels are J = 4 for photodissociative excitation of HO2, J = 20 for H2O2, and J = 21 for the O2+CH3OH mixture. The fluorescence from the gas mixture is attributed to the O + H recombination for which the atoms are produced from photodissociation of parent molecules
Human factors analysis of workstation design: Earth Radiation Budget Satellite Mission Operations Room
A human factors analysis addressed three related yet distinct issues within the area of workstation design for the Earth Radiation Budget Satellite (ERBS) mission operation room (MOR). The first issue, physical layout of the MOR, received the most intensive effort. It involved the positioning of clusters of equipment within the physical dimensions of the ERBS MOR. The second issue for analysis was comprised of several environmental concerns, such as lighting, furniture, and heating and ventilation systems. The third issue was component arrangement, involving the physical arrangement of individual components within clusters of consoles, e.g., a communications panel
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