14,704 research outputs found
Studies of the major planet satellite systems
A summary is presented of the available data on the satellites of the major planets, including the currently most plausible models for several observed phenomena, for the planning of spacecraft missions to these objects. Some of the important questions likely to be solved by flyby and/or orbital missions to the giant planets are detailed, the importance of these studies to our understanding of the solar system as a whole is indicated
Comparative planetology: Significance for terrestrial geology
The crustal evolution of the terrestrial planets increase in complexity and duration with increasing size and mass of the planet. The lunar and mercurian surfaces are largely the result of intense, post-differentiation impact bombardment and subsequent volcanic filling of major impact basins. Mars, being larger, has evolved further: crustal uplifts, rifting, and shield volcanoes have begun to modify its largely Moon-like surface. The Earth is the large end-number of this sequence, where modern plate tectonic processes have erased the earlier lunar and martian type of surfaces. Fundamental problems of the origin of terrestrial continents, ocean basins, and plate tectonics are now addressed within the context of the evolutionary pattern of the terrestrial planets
Proposed satellite laser ranging and very long baseline interferometry sites for crustal dynamics investigations
Recommendations are presented for a global network of 125 sites for geodetic measurements by satellite laser ranging and very long baseline interferometry. The sites were proposed on the basis of existing facilities and scientific value for investigation of crustal dynamics as related to earthquake hazards. Tectonic problems are discussed for North America peripheral regions and for the world. The sites are presented in tables and maps, with bibliographic references
Statics and Dynamics of the Wormlike Bundle Model
Bundles of filamentous polymers are primary structural components of a broad
range of cytoskeletal structures, and their mechanical properties play key
roles in cellular functions ranging from locomotion to mechanotransduction and
fertilization. We give a detailed derivation of a wormlike bundle model as a
generic description for the statics and dynamics of polymer bundles consisting
of semiflexible polymers interconnected by crosslinking agents. The elastic
degrees of freedom include bending as well as twist deformations of the
filaments and shear deformation of the crosslinks. We show that a competition
between the elastic properties of the filaments and those of the crosslinks
leads to renormalized effective bend and twist rigidities that become
mode-number dependent. The strength and character of this dependence is found
to vary with bundle architecture, such as the arrangement of filaments in the
cross section and pretwist. We discuss two paradigmatic cases of bundle
architecture, a uniform arrangement of filaments as found in F-actin bundles
and a shell-like architecture as characteristic for microtubules. Each
architecture is found to have its own universal ratio of maximal to minimal
bending rigidity, independent of the specific type of crosslink induced
filament coupling; our predictions are in reasonable agreement with available
experimental data for microtubules. Moreover, we analyze the predictions of the
wormlike bundle model for experimental observables such as the tangent-tangent
correlation function and dynamic response and correlation functions. Finally,
we analyze the effect of pretwist (helicity) on the mechanical properties of
bundles. We predict that microtubules with different number of protofilaments
should have distinct variations in their effective bending rigidity
The use of happiness research for public policy
Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator
Overdamped Stress Relaxation in Buckled Rods
We present a comprehensive theoretical analysis of the stress relaxation in a
multiply but weakly buckled incompressible rod in a viscous solvent. In the
bulk two interesting regimes of generic self--similar intermediate asymptotics
are distinguished, which give rise to two classes of approximate and exact
power--law solutions, respectively. For the case of open boundary conditions
the corresponding non--trivial boundary--layer scenarios are derived by a
multiple--scale perturbation (``adiabatic'') method. Our results compare well
with -- and provide the theoretical explanation for -- previous results from
numerical simulations, and they suggest new directions for further fruitful
numerical and experimental investigations.Comment: 20 pages, 12 figure
Canonical phase space approach to the noisy Burgers equation
Presenting a general phase approach to stochastic processes we analyze in
particular the Fokker-Planck equation for the noisy Burgers equation and
discuss the time dependent and stationary probability distributions. In one
dimension we derive the long-time skew distribution approaching the symmetric
stationary Gaussian distribution. In the short time regime we discuss
heuristically the nonlinear soliton contributions and derive an expression for
the distribution in accordance with the directed polymer-replica model and
asymmetric exclusion model results.Comment: 4 pages, Revtex file, submitted to Phys. Rev. Lett. a reference has
been added and a few typos correcte
Manual for 70 mm hand-held photography from Skylab
A manual and atlas used on the Skylab mission for hand-held photography are presented. The manual covers terrain, environmental, meteorological, and dim light photography while the atlas covers sections from the Army Map Service 1:40.000,000 world map, a glossary of geologic terms, geologic maps, and recommended exposure times
Dual-Frequency VSOP Observations of AO 0235+164
AO 0235+164 is a very compact, flat spectrum radio source identified as a BL
Lac object at a redshift of z=0.94. It is one of the most violently variable
extragalactic objects at both optical and radio wavelengths. The radio
structure of the source revealed by various ground-based VLBI observations is
dominated by a nearly unresolved compact component at almost all available
frequencies.
Dual-frequency space VLBI observations of AO 0235+164 were made with the VSOP
mission in January-February 1999. The array of the Japanese HALCA satellite and
co-observing ground radio telescopes in Australia, Japan, China and South
Africa allowed us to study AO 0235+164 with an unprecedented angular resolution
at frequencies of 1.6 and 5 GHz. We report on the sub-milliarcsecond structural
properties of the source. The 5-GHz observations led to an estimate of T_B >
5.8 x 10^{13} K for the rest-frame brightness temperature of the core, which is
the highest value measured with VSOP to date.Comment: 8 pages, 8 figures, to appear in Publ. Astron. Soc. Japa
The Universal Kaehler Modulus in Warped Compactifications
We construct the effective theory of the universal Kaehler modulus in warped
compactifications using the Hamiltonian formulation of general relativity. The
spacetime dependent 10d solution is constructed at the linear level for both
the volume modulus and its axionic partner, and nontrivial cancellations of
warping effects are found in the dimensional reduction. Our main result is that
the Kaehler potential is not corrected by warping, up to an overall shift in
the background value of the volume modulus. We extend the analysis beyond the
linearized approximation by computing the fully backreacted 10d metric
corresponding to a finite volume modulus fluctuation. Also, we discuss the
behavior of the modulus in strongly warped regions and show that there are no
mixings with light Kaluza-Klein modes. These results are important for the
phenomenology and cosmology of flux compactifications.Comment: 28 pages, 1 figure; v2. corrected typos, added refs & minor
clarification
- …