1,231 research outputs found
Ocean acidification impacts on the physiology and adhesive properties of the starfish <i>Asterias rubens</i>
Life-cycle of the Mediterranean calcareous sponge <i>Petrobiona massiliana</i>: histological variations of a potential climate changes recorder
Climate reconstruction based on archaeological bivalve shells
Several years of biogeochemical research on bivalve shells yielded in clear proxyrecords carrying potential for reconstruction of paleoseasonal trends in coastal environments. However, the interpretation of the proxy signals is still often problematic. Proxy concentrations can be influenced by several environmental parameters and by physiological processes. With more complex models these problems can be tackled. Two strategies are followed; (1) a statistical black-box model is being developed in parallel with (2) a physiological white-box model.The statistical black-box model can be described as a non-linear multi-proxy model. It is based on chemical measurements in modern bivalve shells and consists of the construction of a curve in a multi-dimensional space. The model describes the variations in the chemical signature of the shell during a full year cycle. The shortest distance from any other data point (e.g. a fossil shell) to the model will give a time point estimation in the annual cycle, which can further be linked to environmental parameters. At present our model approach achieves quite accurate SST reconstructions.A white box model is crucial for understanding the physiological processes and for an unambiguous interpretation of the proxy records. We investigated, in a first phase, in situ the influences of environmental parameters and physiology on the incorporation of proxies in Mytilus edulis at a well documented wave breaker site. In a second phase, in vitro culturing experiments under controlled laboratory conditions were carried out. Experiments were carried out at 8°C and 16°C and at salinities of 18‰ and 28‰. During these experiments mussels were fed under high and low supply regimes. By combining these in situ and in vitro approaches a white box multi-proxy model is generated for the reconstruction of SST and SSS
Formation of a stable deacagonal quasicrystalline Al-Pd-Mn surface layer
We report the in situ formation of an ordered equilibrium decagonal Al-Pd-Mn
quasicrystal overlayer on the 5-fold symmetric surface of an icosahedral
Al-Pd-Mn monograin. The decagonal structure of the epilayer is evidenced by
x-ray photoelectron diffraction, low-energy electron diffraction and electron
backscatter diffraction. This overlayer is also characterized by a reduced
density of states near the Fermi edge as expected for quasicrystals. This is
the first time that a millimeter-size surface of the stable decagonal Al-Pd-Mn
is obtained, studied and compared to its icosahedral counterpart.Comment: Submitted to Phys. Ref. Lett. (18 July 2001
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium
Future cosmology space missions will concentrate on measuring the
polarization of the Cosmic Microwave Background, which potentially carries
invaluable information about the earliest phases of the evolution of our
universe. Such ambitious projects will ultimately be limited by the sensitivity
of the instrument and by the accuracy at which polarized foreground emission
from our own Galaxy can be subtracted out. We present the PILOT balloon project
which will aim at characterizing one of these foreground sources, the
polarization of the dust continuum emission in the diffuse interstellar medium.
The PILOT experiment will also constitute a test-bed for using multiplexed
bolometer arrays for polarization measurements. We present the results of
ground tests obtained just before the first flight of the instrument.Comment: 17 pages, 13 figures. Presented at SPIE, Millimeter, Submillimeter,
and Far-Infrared Detectors and Instrumentation for Astronomy VII. To be
published in Proc. SPIE volume 915
Evaluating higher education teaching performance using combined analytic hierarchy process and data envelopment analysis
Evaluating higher education teaching performance is complex as it involves consideration of both objective and subjective criteria. The student evaluation of teaching (SET) is used to improve higher education quality. However, the traditional approaches to considering students’ responses to SET questionnaires for improving teaching quality have several shortcomings. This study proposes an integrated approach to higher education teaching evaluation that combines the analytical hierarchy process (AHP) and data envelopment analysis (DEA). The AHP allows consideration of the varying importance of each criterion of teaching performance, while DEA enables the comparison of tutors on teaching as perceived by students with a view to identifying the scope for improvement by each tutor. The proposed teaching evaluation method is illustrated using data from a higher education institution in Greece
Currents and Superpotentials in classical gauge invariant theories I. Local results with applications to Perfect Fluids and General Relativity
E. Noether's general analysis of conservation laws has to be completed in a
Lagrangian theory with local gauge invariance. Bulk charges are replaced by
fluxes of superpotentials. Gauge invariant bulk charges may subsist when
distinguished one-dimensional subgroups are present. As a first illustration we
propose a new {\it Affine action} that reduces to General Relativity upon gauge
fixing the dilatation (Weyl 1918 like) part of the connection and elimination
of auxiliary fields. It allows a comparison of most gravity superpotentials and
we discuss their selection by the choice of boundary conditions. A second and
independent application is a geometrical reinterpretation of the convection of
vorticity in barotropic nonviscous fluids. We identify the one-dimensional
subgroups responsible for the bulk charges and thus propose an impulsive
forcing for creating or destroying selectively helicity. This is an example of
a new and general Forcing Rule.Comment: 64 pages, LaTeX. Version 2 has two more references and one misprint
corrected. Accepted in Classical and Quantum Gravit
Bose-Einstein condensation of correlated atoms in a trap
The Bose-Einstein condensation of correlated atoms in a trap is studied by
examining the effect of inter-particle correlations to one-body properties of
atomic systems at zero temperature using a simplified formula for the
correlated two body density distribution. Analytical expressions for the
density distribution and rms radius of the atomic systems are derived using
four different expressions of Jastrow type correlation function. In one case,
in addition, the one-body density matrix, momentum distribution and kinetic
energy are calculated analytically, while the natural orbitals and natural
occupation numbers are also predicted in this case. Simple approximate
expressions for the mean square radius and kinetic energy are also given.Comment: 14 pages, 19 figures, 1 Table, RevTe
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