19,663 research outputs found
NASA Developmental Biology Workshop: A summary
The Life Sciences Division of the National Aeronautics and Space Administration (NASA) as part of its continuing assessment of its research program, convened a workshop on Developmental Biology to determine whether there are important scientific studies in this area which warrant continued or expanded NASA support. The workshop consisted of six panels, each of which focused on a single major phylogenetic group. The objectives of each panel were to determine whether gravity plays a role in the ontogeny of their subject group, to determine whether the microgravity of spaceflight can be used to help understand fundamental problems in developmental biology, to develop the rationale and hypotheses for conducting NASA-relevant research in development biology both on the ground and in space, and to identify any unique equipment and facilities that would be required to support both ground-based and spaceflight experiments
Nuclear isotope thermometry
We discuss different aspects which could influence temperatures deduced from
experimental isotopic yields in the multifragmentation process. It is shown
that fluctuations due to the finite size of the system and distortions due to
the decay of hot primary fragments conspire to blur the temperature
determination in multifragmentation reactions. These facts suggest that caloric
curves obtained through isotope thermometers, which were taken as evidence for
a first-order phase transition in nuclear matter, should be investigated very
carefully.Comment: 9 pages, 7 figure
On possible violation of the CHSH Bell inequality in a classical context
It has been shown that there is a small possibility to experimentally violate
the CHSH Bell inequality in a 'classical' context. The probability of such a
violation has been estimated in the framework of a classical probabilistic
model in the language of a random-walk representation.Comment: 9 pages, 1 figur
Apparent horizons in the quasi-spherical Szekeres models
The notion of an apparent horizon (AH) in a collapsing object can be carried
over from the Lema\^{\i}tre -- Tolman (L--T) to the quasispherical Szekeres
models in three ways: 1. Literally by the definition -- the AH is the boundary
of the region, in which every bundle of null geodesics has negative expansion
scalar. 2. As the locus, at which null lines that are as nearly radial as
possible are turned toward decreasing areal radius . These lines are in
general nongeodesic. The name "absolute apparent horizon" (AAH) is proposed for
this locus. 3. As the boundary of a region, where null \textit{geodesics} are
turned toward decreasing . The name "light collapse region" (LCR) is
proposed for this region (which is 3-dimensional in every space of constant
); its boundary coincides with the AAH. The AH and AAH coincide in the L--T
models. In the quasispherical Szekeres models, the AH is different from (but
not disjoint with) the AAH. Properties of the AAH and LCR are investigated, and
the relations between the AAH and the AH are illustrated with diagrams using an
explicit example of a Szekeres metric. It turns out that an observer who is
already within the AH is, for some time, not yet within the AAH. Nevertheless,
no light signal can be sent through the AH from the inside. The analogue of the
AAH for massive particles is also considered.Comment: 14 pages, 9 figures, includes little extensions and style corrections
made after referee's comments, the text matches the published versio
Geometry of the quasi-hyperbolic Szekeres models
Geometric properties of the quasi-hyperbolic Szekeres models are discussed
and related to the quasi-spherical Szekeres models. Typical examples of shapes
of various classes of 2-dimensional coordinate surfaces are shown in graphs;
for the hyperbolically symmetric subcase and for the general quasi-hyperbolic
case. An analysis of the mass function is carried out in parallel to an
analogous analysis for the quasi-spherical models. This leads to the conclusion
that determines the density of rest mass averaged over the whole space
of constant time.Comment: 19 pages, 13 figures. This version matches the published tex
Spectral, mineralogical, and geochemical variations across Home Plate, Gusev Crater, Mars indicate high and low temperature alteration
Over the last ~ 3 years in Gusev Crater, Mars, the Spirit rover observed coherent variations in color, mineralogy, and geochemistry across Home Plate, an ~ 80 m-diameter outcrop of basaltic tephra. Observations of Home Plate from orbit and from the summit of Husband Hill reveal clear differences in visible/near-infrared (VNIR) colors between its eastern and western regions that are consistent with mineralogical compositions indicated by Mössbauer spectrometer (MB) and by Miniature Thermal Emission Spectrometer (Mini-TES). Pyroxene and magnetite dominate the east side, while olivine, nanophase Fe oxide (npOx) and glass are more abundant on the western side. Alpha Particle X-Ray Spectrometer (APXS) observations reveal that eastern Home Plate has higher Si/Mg, Al, Zn, Ni, and K, while Cl and Br are higher in the west. We propose that these variations are the result of two distinct alteration regimes that may or may not be temporally related: a localized, higher temperature recrystallization and alteration of the east side of Home Plate and lower temperature alteration of the western side that produced npOx
Orbital Magnetic Dipole Mode in Deformed Clusters: A Fully Microscopic Analysis
The orbital M1 collective mode predicted for deformed clusters in a schematic
model is studied in a self-consistent random-phase-approximation approach which
fully exploits the shell structure of the clusters. The microscopic mechanism
of the excitation is clarified and the close correlation with E2 mode
established. The study shows that the M1 strength of the mode is fragmented
over a large energy interval. In spite of that, the fraction remaining at low
energy, well below the overwhelming dipole plasmon resonance, is comparable to
the strength predicted in the schematic model. The importance of this result in
view of future experiments is stressed.Comment: 10 pages, 3 Postscript figures, uses revte
Atributos quĂmicos e fĂsicos de Terras Pretas de ĂŤndio (TPI) de várzea e terra firme na calha do rio Solimões/Amazonas.
O objetivo desse trabalho foi comparar perfis de TPI encontrados na várzea do Solimões com TPI de Terras Firme associados ao mesmo rio
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