785 research outputs found
Taxonomy and biostratigraphy of new and emended species of Cenozoic deep-water agglutinated foraminifera from the Labrador and North Seas
Deep marine, fine grained sedimentary strata of Maastrichtian through Miocene age in the Labrador and North Sea sedimentary basins are rich in agglutinated benthic foraminifera. Six new taxa have been found in these regions, several of which also extend to other circum-Atlantic Paleogene localities. The new taxa are: Ammomarginulina aubertae, n. sp. (Maastrichtian to Eocene), Adercotryma agterbergi, n. sp. (middle Eocene to lower Oligocene), Reticulophragmoides jarvisi (Thalmann) emended herein (Paleocene to lower Oligocene), Reticulophragmoides sp. 5 (Oligocene to Miocene), and Spiroplectammina navarroana Cushman emended herein (Maastrichtian to lower middle Eocene). The last occurrences of these taxa are important elements in the high-resolution probabilistic biozonations for the Labrador and North Sea basins
Jurassic micropaleontology of the Grand Banks
Jurassic foraminifera in the marine deposits (up to 3km thick) of the Grand Banks of Newfoundland define eight biostratigraphic zones of Pliensbachian through Tithonian age. Jurassic marine deposition (~4cm/10k.y) kept pace with subsidence resulting in a relatively continuous, shallow marine sedimentation pattern. Central Grand Banks subsidence ceased in Late Jurassic time and the area became emergent with erosion taking place until Albian time.
Grand Banks Jurassic foraminiferal assemblages are of a distinctly Old World affinity reflecting the contracted early Atlantic paleogeography. Compositional differences with Portuguese Middle-Late Jurassic microfauna are probably related to differences in depositional history of the Portuguese and Grand Banks Basin
Mass mortality and extraterrestrial impacts
The discovery of iridium enrichment at the Cretaceous/Tertiary boundary resulted in formulation of hypothesis of a cometary or asteroid impact as the cause of the biological extinctions at this boundary. Subsequent discoveries of geochemical anomalies at major stratigraphic boundaries like the Precambrian/Cambrian, Permian/Triassic, Middle/Late Jurassic, resulted in the application of similar extraterrestrial impact theories to explain biological changes at these boundaries. Until recently the major physical evidence, as is the location of the impact crater site, to test the impact induced biological extinction was lacking. The diameter of such a crater would be in the range of 60 to 100 km. The recent discovery of the first impact crater in the ocean provide the first opportunity to test the above theory. The crater, named Montagnais and located on the outer shelf off Nova Scotia, Canada, has a minimum diameter of 42 km, with some evidence to a diameter of more than 60 km. At the Montagnais impact site, micropaleontological analysis of the uppermost 80 m of the fall-back breccia represented by a mixture of pre-impact sediments and basement rocks which fills the crater and of the basal 50 m of post-impact marine sediments which overly the impact deposits, revealed presence of diversified foraminiferal and nannoplankton assemblages. The sediments which are intercalated within the uppermost part of the fall-back breccia, had to be deposited before the meteorite impact. The post-impact deposits were laid down almost immediately after the impact as also supported by the micropaleontological data. In conclusion, micropaleontological studies of sediments from the first submarine impact crater site identified in the ocean did not reveal any mass extinction or significant biological changes at the impact site or in the proximal deep ocean basin
Decoherence of number states in phase-sensitive reservoirs
The non-unitary evolution of initial number states in general Gaussian
environments is solved analytically. Decoherence in the channels is quantified
by determining explicitly the purity of the state at any time. The influence of
the squeezing of the bath on decoherence is discussed. The behavior of coherent
superpositions of number states is addressed as well.Comment: 5 pages, 2 figures, minor changes, references adde
Vortex Plasma in a Superconducting Film with Magnetic Dots
We consider a superconducting film, placed upon a magnetic dot array.
Magnetic moments of the dots are normal to the film and randomly oriented. We
determine how the concentration of the vortices in the film depends on the
magnetic moment of a dot at low temperatures. The concentration of the
vortices, bound to the dots, is proportional to the density of the dots and
depends on the magnetization of a dot in a step-like way. The concentration of
the unbound vortices oscillates about a value, proportional to the magnetic
moment of the dots. The period of the oscillations is equal to the width of a
step in the concentration of the bound vortices.Comment: RevTeX, 4 page
Characterization of tomographically faithful states in terms of their Wigner function
A bipartite quantum state is tomographically faithful when it can be used as
an input of a quantum operation acting on one of the two quantum systems, such
that the joint output state carries a complete information about the operation
itself. Tomographically faithful states are a necessary ingredient for
tomography of quantum operations and for complete quantum calibration of
measuring apparatuses. In this paper we provide a complete classification of
such states for continuous variables in terms of the Wigner function of the
state. For two-mode Gaussian states faithfulness simply resorts to correlation
between the modes.Comment: 9 pages. IOPAMS style. Some improvement
Meromorphic Solutions to a Differential--Difference Equation Describing Certain Self-Similar Potentials
In this paper we prove the existence of meromorphic solutions to a nonlinear
differential difference equation that describe certain self-similar potentials
for the Schroedinger operator.Comment: 10 pages, LaTeX, uses additional package
Plate reorganization: a cause of rapid late Neogene subsidence and sedimentation around the North Atlantic?
Spin relaxation at the singlet-triplet crossing in a quantum dot
We study spin relaxation in a two-electron quantum dot in the vicinity of the
singlet-triplet crossing. The spin relaxation occurs due to a combined effect
of the spin-orbit, Zeeman, and electron-phonon interactions. The
singlet-triplet relaxation rates exhibit strong variations as a function of the
singlet-triplet splitting. We show that the Coulomb interaction between the
electrons has two competing effects on the singlet-triplet spin relaxation. One
effect is to enhance the relative strength of spin-orbit coupling in the
quantum dot, resulting in larger spin-orbit splittings and thus in a stronger
coupling of spin to charge. The other effect is to make the charge density
profiles of the singlet and triplet look similar to each other, thus
diminishing the ability of charge environments to discriminate between singlet
and triplet states. We thus find essentially different channels of
singlet-triplet relaxation for the case of strong and weak Coulomb interaction.
Finally, for the linear in momentum Dresselhaus and Rashba spin-orbit
interactions, we calculate the singlet-triplet relaxation rates to leading
order in the spin-orbit interaction, and find that they are proportional to the
second power of the Zeeman energy, in agreement with recent experiments on
triplet-to-singlet relaxation in quantum dots.Comment: 29 pages, 14 figures, 1 tabl
Nonlinear Screening and Effective Electrostatic Interactions in Charge-Stabilized Colloidal Suspensions
A nonlinear response theory is developed and applied to electrostatic
interactions between spherical macroions, screened by surrounding microions, in
charge-stabilized colloidal suspensions. The theory describes leading-order
nonlinear response of the microions (counterions, salt ions) to the
electrostatic potential of the macroions and predicts microion-induced
effective many-body interactions between macroions. A linear response
approximation [Phys. Rev. E 62, 3855 (2000)] yields an effective pair potential
of screened-Coulomb (Yukawa) form, as well as a one-body volume energy, which
contributes to the free energy. Nonlinear response generates effective
many-body interactions and essential corrections to both the effective pair
potential and the volume energy. By adopting a random-phase approximation (RPA)
for the response functions, and thus neglecting microion correlations,
practical expressions are derived for the effective pair and triplet potentials
and for the volume energy. Nonlinear screening is found to weaken repulsive
pair interactions, induce attractive triplet interactions, and modify the
volume energy. Numerical results for monovalent microions are in good agreement
with available ab initio simulation data and demonstrate that nonlinear effects
grow with increasing macroion charge and concentration and with decreasing salt
concentration. In the dilute limit of zero macroion concentration,
leading-order nonlinear corrections vanish. Finally, it is shown that nonlinear
response theory, when combined with the RPA, is formally equivalent to the
mean-field Poisson-Boltzmann theory and that the linear response approximation
corresponds, within integral-equation theory, to a linearized hypernetted-chain
closure.Comment: 30 pages, 8 figures, Phys. Rev. E (in press
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