265 research outputs found
Palaeoenvironmental analysis of the Miocene barnacle facies: case studies from Europe and South America
Acorn barnacles are sessile crustaceans common in shallow-water settings, both in modern oceans and in the Miocene geological record. Barnacle-rich facies occur from polar to equatorial latitudes, generally associated with shallow-water, high-energy, hard substrates. The aim of this work is to investigate this type of facies by analysing, from the palaeontological, sedimentological and petrographical points of view, early Miocene examples from Northern Italy, Southern France and South-western Peru. Our results are then compared with the existing information on both modern and fossil barnacle-rich deposits. The studied facies can be divided into two groups. The first one consists of very shallow, nearshore assemblages where barnacles are associated with an abundant hard-substrate biota (e.g., barnamol). The second one includes a barnacle-coralline algae association, here named “barnalgal” (= barnacle / red algal dominated), related to a deeper setting. The same pattern occurs in the distribution of both fossil and recent barnacle facies. The majority of them are related to very shallow, high-energy, hard-substrate, a setting that represents the environmental optimum for the development of barnacle facies, but exceptions do occur. These atypical facies can be identified through a complete analysis of both the skeletal assemblage and the barnacle association, showing that barnacle palaeontology can be a powerful tool for palaeoenvironmental reconstruction
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Functional MRI using robotic MRI compatible devices for monitoring rehabilitation from chronic stroke in the molecular medicine era (Review)
The number of individuals suffering from stroke is increasing daily, and its consequences are a major contributor to invalidity in today’s society. Stroke rehabilitation is relatively new, having been hampered from the longstanding view that lost functions were not recoverable. Nowadays, robotic devices, which aid by stimulating brain plasticity, can assist in restoring movement compromised by stroke-induced pathological changes in the brain which can be monitored by MRI. Multiparametric magnetic resonance imaging (MRI) of stroke patients participating in a training program with a novel Magnetic Resonance Compatible Hand-Induced Robotic Device (MR_CHIROD) could yield a promising biomarker that, ultimately, will enhance our ability to advance hand motor recovery following chronic stroke. Using state-of-the art MRI in conjunction with MR_CHIROD-assisted therapy can provide novel biomarkers for stroke patient rehabilitation extracted by a meta-analysis of data. Successful completion of such studies may provide a ground breaking method for the future evaluation of stroke rehabilitation therapies. Their results will attest to the effectiveness of using MR-compatible hand devices with MRI to provide accurate monitoring during rehabilitative therapy. Furthermore, such results may identify biomarkers of brain plasticity that can be monitored during stroke patient rehabilitation. The potential benefit for chronic stroke patients is that rehabilitation may become possible for a longer period of time after stroke than previously thought, unveiling motor skill improvements possible even after six months due to retained brain plasticity
Shell model calculations of stellar weak interaction rates: I. Gamow-Teller distributions and spectra of nuclei in the mass range A=45-65
Electron capture and beta-decay rates on nuclei in the mass range A=45-65
play an important role in many astrophysical environments. The determination of
these rates by large-scale shell model calculations is desirable, but it
requires to reproduce the Gamow-Teller strength distributions and spectra of
the pf shell nuclei. We show in this paper that large-scale shell model
calculations, employing a slightly monopole-corrected version of the wellknown
KB3 interaction, fulfill these necessary requirements. In particular, our
calculations reproduce the experimentally available GT+ and GT- strength
distributions and the nuclear halflives, and describe the nuclear spectra
appropriately.Comment: 11 pages, 5 figure
Effect of atomic ordering on the magnetic anisotropy of single crystal Ni80Fe20
We investigate the effect of atomic ordering on the magnetic anisotropy of
Ni80Fe20 at.% (Py). To this end, Py films were grown epitaxially on MgO (001)
using dc magnetron sputtering (dcMS) and high power impulse magnetron
sputtering (HiPIMS). Aside from twin boundaries observed in the latter case,
both methods present high quality single crystals with cube-on-cube epitaxial
relationship as verified by the polar mapping of important crystal planes.
However, X-ray diffraction results indicate higher order for the dcMS deposited
film towards L12 Ni3Fe superlattice. This difference can be understood by the
very high deposition rate of HiPIMS during each pulse which suppresses adatom
mobility and ordering. We show that the dcMS deposited film presents biaxial
anisotropy while HiPIMS deposition gives well defined uniaxial anisotropy.
Thus, higher order achieved in the dcMS deposition behaves as predicted by
magnetocrystalline anisotropy i.e. easy axis along the [111] direction that
forced in the plane along the [110] direction due to shape anisotropy. The
uniaxial behaviour in HiPIMS deposited film then can be explained by pair
ordering or more recent localized composition non-uniformity theories. Further,
we studied magnetoresistance of the films along the [100] directions using an
extended van der Pauw method. We find that the electrical resistivities of the
dcMS deposited film are lower than in their HiPIMS counterparts verifying the
higher order in the dcMS case.Comment: 8 page
Palaeoenvironmental analysis of the Miocene barnacle facies: Case studies from Europe and South America
Acorn barnacles are sessile crustaceans common in shallow-water settings, both in modern oceans and in the Miocene geological record. Barnacle-rich facies occur from polar to equatorial latitudes, generally associated with shallow-water, high-energy, hard substrates. The aim of this work is to investigate this type of facies by analysing, from the palaeontological, sedimentological and petrographical points of view, early Miocene examples from Northern Italy, Southern France and South-western Peru. Our results are then compared with the existing information on both modern and fossil barnacle-rich deposits. The studied facies can be divided into two groups. The first one consists of very shallow, nearshore assemblages where barnacles are associated with an abundant hard-substrate biota (e.g., barnamol). The second one includes a barnacle-coralline algae association, here named "barnalgal" (=barnacle/red algal dominated), related to a deeper setting. The same pattern occurs in the distribution of both fossil and recent barnacle facies. The majority of them are related to very shallow, high-energy, hard-substrate, a setting that represents the environmental optimum for the development of barnacle facies, but exceptions do occur. These atypical facies can be identified through a complete analysis of both the skeletal assemblage and the barnacle association, showing that barnacle palaeontology can be a powerful tool for palaeoenvironmental reconstruction
Gamow-Teller strength distributions for nuclei in pre-supernova stellar cores
Electron-capture and -decay of nuclei in the core of massive stars
play an important role in the stages leading to a type II supernova explosion.
Nuclei in the f-p shell are particularly important for these reactions in the
post Silicon-burning stage of a presupernova star. In this paper, we
characterise the energy distribution of the Gamow-Teller Giant Resonance (GTGR)
for mid-fp-shell nuclei in terms of a few shape parameters, using data obtained
from high energy, forward scattering (p,n) and (n,p) reactions. The energy of
the GTGR centroid is further generalised as function of nuclear
properties like mass number, isospin and other shell model properties of the
nucleus. Since a large fraction of the GT strength lies in the GTGR region, and
the GTGR is accessible for weak transitions taking place at energies relevant
to the cores of presupernova and collapsing stars, our results are relevant to
the study of important -capture and -decay rates of arbitrary,
neutron-rich, f-p shell nuclei in stellar cores. Using the observed GTGR and
Isobaric Analog States (IAS) energy systematics we compare the coupling
coefficients in the Bohr-Mottelson two particle interaction Hamiltonian for
different regions of the Isotope Table.Comment: Revtex, 28 pages +7 figures (PostScript Figures, uuencoded, filename:
Sutfigs.uu). If you have difficulty printing the figures, please contact
[email protected]. Accepted for publication in Phys. Rev. C, Nov 01,
199
Gamow-Teller strength in 54Fe and 56Fe
Through a sequence of large scale shell model calculations, total
Gamow-Teller strengths ( and ) in Fe and Fe are
obtained. They reproduce the experimental values once the operator
is quenched by the standard factor of . Comparisons are made with recent
Shell Model Monte Carlo calculations. Results are shown to depend critically on
the interaction. From an analysis of the GT+ and GT strength functions it is
concluded that experimental evidence is consistent with the sum rule.Comment: 6 pages, RevTeX 3.0 using psfig, 7 Postscript figures included using
uufile
Electron capture on iron group nuclei
We present Gamow-Teller strength distributions from shell model Monte Carlo
studies of fp-shell nuclei that may play an important role in the pre-collapse
evolution of supernovae. We then use these strength distributions to calculate
the electron-capture cross sections and rates in the zero-momentum transfer
limit. We also discuss the thermal behavior of the cross sections. We find
large differences in these cross sections and rates when compared to the naive
single-particle estimates. These differences need to be taken into account for
improved modeling of the early stages of type II supernova evolution
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