874 research outputs found
Investigation of the Stock Structure of Atlantic Walrus (Odobenus rosmarus rosmarus) in Canada and Greenland Using Dental Pb Isotopes Derived from Local Geochemical Environments
The chemical composition of animal tissues such as teeth appears to reflect an individual's exposure to its geochemical environment. In this study, the lead (Pb) isotope composition of dental cementum was used to investigate the stock structure of Atlantic walrus (Odobenus rosmarus rosmarus) in the Canadian Arctic and Greenland. The 12 communities providing walrus samples for this study represent most of the Canadian and Greenlandic villages where walrus still form an important part of the traditional Inuit diet. Significant differences between locations in mean Pb isotope ratios and the limited overlap of the ranges of values indicate that each village harvested walrus herds that exploited substantially different geological/geographical habitats. This geographic segregation based on isotopic signatures suggests that most walrus stocks (i.e., the groups of walrus that interact with hunters at each community) are more localized in their range than previously thought. 208Pb/207Pb and 208Pb/204Pb were the most important stock discriminators, reflecting the influence of local geological Th/U composition (i.e., 208Pb) on Pb isotope composition in walrus teeth. 204Pb-based isotope ratios in walrus were consistently higher (more radiogenic) and more homogeneous than those in regional terrestrial bedrock, a difference probably due to selective leaching of radiogenic Pb from mineral phases into seawater and mixing during weathering and transport. Dental Pb isotope signatures may have widespread application to stock discrimination of other coastal marine mammal species.La composition chimique de tissus animaux tels que les dents semble refléter l'exposition d'un individu à son milieu géochimique. Pour la présente étude, on a utilisé la composition isotopique du plomb (Pb) contenu dans le cément pour examiner la structure du stock du morse de l'Atlantique (Odobenus rosmarus rosmarus) dans l'Arctique canadien et le Groenland. Les 12 communautés qui ont fourni les échantillons de morse pour ce projet représentent la majorité des villages canadiens et groenlandais où le morse constitue toujours une grande partie du régime alimentaire traditionnel des Inuits. Des différences marquées entre les sites dans la moyenne des rapports isotopiques du Pb et le faible recoupement des gammes de valeurs révèlent que chaque village prélevait des morses au sein de troupeaux qui exploitaient des habitats géologiques/géographiques bien distincts. Cette ségrégation géographique fondée sur des signatures isotopiques suggère que la plupart des stocks de morses (c.-à-d. le groupe de morses qui interagit avec les chasseurs dans chaque communauté) sont plus localisés dans leur territoire qu'on ne le pensait auparavant. 208Pb/207Pb et 208Pb/204Pb étaient les grands caractères discriminants des stocks, reflétant l'influence de la composition géologique locale Th/U (c-à-d. 208Pb) sur la composition isotopique du Pb dans les dents du morse. Les rapports isotopiques fondés sur 204Pb étaient constamment plus élevés (plus radiogéniques) et plus homogènes que ceux du substratum terrestre, la différence étant probablement due à la lixiviation sélective du Pb radiogénique passant des phases minérales dans l'eau de mer et à son mélange durant la météorisation et le transport. Les signatures isotopiques du plomb dentaire peuvent avoir de vastes applications dans la discrimination des stocks d'autres espèces de mammifères marins côtiers
Correlation of structural and spectroscopic properties of a photosynthetic reaction center
Polarized spectra of absorption and light-induced absorbance changes are presented for the crystallized reaction centers of Rhodopseudomonas viridis. We find that a model based on extended dipole interaction between all six pigments is capable of interpreting detailed features such as the contributions from the individual pigments to the various absorption peaks. Even though the pigments are arranged in approximate C2 symmetry, the optical spectra together with the calculations reflect deviations from this symmetry, which may be important in understanding the electron pathway
Supersymmetry and Gauge Invariance Constraints in a U(1)U(1)-Higgs Superconducting Cosmic String Model
A supersymmetric extension of the -Higgs bosonic
superconducting cosmic string model is considered,and the constraints imposed
upon such a model due to renormalizability, supersymmetry, and gauge invariance
are examined. For a simple model with a single chiral superfield and a
single chiral superfield, the Witten mechanism for bosonic
superconductivity (giving rise to long range gauge fields outside of the
string) does not exist. The simplest model that can accommodate the requisite
interactions requires five chiral supermultiplets. This superconducting cosmic
string solution is investigated.Comment: 17 pages, revtex, no figures; to appear in Phys. Rev.
Reconciling inflation with openness
It is already understood that the increasing observational evidence for an
open Universe can be reconciled with inflation if our horizon is contained
inside one single huge bubble nucleated during the inflationary phase
transition. In this frame of ideas, we show here that the probability of living
in a bubble with the right (now the observations require ) can be comparable with unity, rather than infinitesimally small.
For this purpose we modify both quantitatively and qualitatively an intuitive
toy model based upon fourth order gravity. As this scheme can be implemented in
canonical General Relativity as well (although then the inflation driving
potential must be designed entirely ad hoc), inferring from the observations
that not only does not conflict with the inflationary paradigm,
but rather supports therein the occurrence of a primordial phase transition.Comment: 4 pages, one postscript figure, to be published on Physical Review D
PACS: 98.80. C
Quantum Limits of Stochastic Cooling of a Bosonic Gas
The quantum limits of stochastic cooling of trapped atoms are studied. The
energy subtraction due to the applied feedback is shown to contain an
additional noise term due to atom-number fluctuations in the feedback region.
This novel effect is shown to dominate the cooling efficiency near the
condensation point. Furthermore, we show first results that indicate that
Bose--Einstein condensation could be reached via stochastic cooling.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Kerr black hole quasinormal frequencies
Black-hole quasinormal modes (QNM) have been the subject of much recent
attention, with the hope that these oscillation frequencies may shed some light
on the elusive theory of quantum gravity. We compare numerical results for the
QNM spectrum of the (rotating) Kerr black hole with an {\it exact} formula
Re, which is based on Bohr's correspondence
principle. We find a close agreement between the two. Possible implications of
this result to the area spectrum of quantum black holes are discussed.Comment: 3 pages, 2 figure
Dark Energy and Extending the Geodesic Equations of Motion: Connecting the Galactic and Cosmological Length Scales
Recently, an extension of the geodesic equations of motion using the Dark
Energy length scale was proposed. Here, we apply this extension to the
analyzing the motion of test particles at the galactic scale and longer. A
cosmological check of the extension is made using the observed rotational
velocity curves and core sizes of 1393 spiral galaxies. We derive the density
profile of a model galaxy using this extension, and with it, we calculate
to be ; this is within experimental error of the
WMAP value of . We then calculate to be
kpc, which is in reasonable agreement with observations.Comment: 25 pages. Accepted for publication in General Relativity and
Gravitation. Paper contains the published version of the second half of
arXiv:0711.3124v2 with corrections include
Testing quantum correlations in a confined atomic cloud by scattering fast atoms
We suggest measuring one-particle density matrix of a trapped ultracold
atomic cloud by scattering fast atoms in a pure momentum state off the cloud.
The lowest-order probability of the inelastic process, resulting in a pair of
outcoming fast atoms for each incoming one, turns out to be given by a Fourier
transform of the density matrix. Accordingly, important information about
quantum correlations can be deduced directly from the differential scattering
cross-section. A possible design of the atomic detector is also discussed.Comment: 5 RevTex pages, no figures, submitted to PR
Raman coupler for a trapped two-component quantum-degenerate Fermi gas
We investigate theoretically the Raman coupling between two internal states
of a trapped low-density quantum-degenerate Fermi gas. In general, the trap
frequencies associated with the two internal states can be different, leading
to the onset of collapses and revivals in the population difference of the two
internal states. This behavior can be changed drastically by two-body
collisions. In particular, we show that under appropriate conditions they can
suppress the dephasing leading to the collapse of the population difference,
and restore almost full Rabi oscillations between the two internal states.
These results are compared and contrasted to those for a quantum-degenerate
bosonic gas.Comment: 7 pages incl. 7 PostScript figures (.eps), LaTeX using RevTeX4,
submitted to Phys. Rev. A, modified versio
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