4,555 research outputs found
Do we need a zero pure time preference or the risk of climate catastrophes to justify a 2C global warming target ?
This paper confronts the wide political support for the 2C objective of global increase in temperature, reaffirmed in Copenhagen, with the consistent set of hypotheses on which it relies. It explains why neither an almost zero pure time preference nor concerns about catastrophic damages in case of uncontrolled global warming are prerequisites for policy decisions preserving the possibility of meeting a 2C target. It rests on an optimal stochastic control model balancing the costs and benefits of climate policies resolved sequentially in order to account for the arrival of new information (the RESPONSE model). This model describes the optimal abatement pathways for 2,304 worldviews, combining hypotheses about growth rates, baseline emissions, abatement costs, pure time preference, damages, and climate sensitivity. It shows that 26 percent of the worldviews selecting the 2C target are not characterized by one of the extreme assumptions about pure time preference or climate change damages.Climate Change Mitigation and Green House Gases,Climate Change Economics,Science of Climate Change,Global Environment Facility,Environment and Energy Efficiency
Compositional characterisation of the Themis family
Context. It has recently been proposed that the surface composition of icy
main-belt asteroids (B-,C-,Cb-,Cg-,P-,and D-types) may be consistent with that
of chondritic porous interplanetary dust particles (CPIDPs). Aims. In the light
of this new association, we re-examine the surface composition of a sample of
asteroids belonging to the Themis family in order to place new constraints on
the formation and evolution of its parent body. Methods. We acquired NIR
spectral data for 15 members of the Themis family and complemented this dataset
with existing spectra in the visible and mid-infrared ranges to perform a
thorough analysis of the composition of the family. Assuming end-member
minerals and particle sizes (<2\mum) similar to those found in CPIDPs, we used
a radiative transfer code adapted for light scattering by small particles to
model the spectral properties of these asteroids. Results. Our best-matching
models indicate that most objects in our sample possess a surface composition
that is consistent with the composition of CP IDPs.We find ultra-fine grained
Fe-bearing olivine glasses to be among the dominant constituents. We further
detect the presence of minor fractions of Mg-rich crystalline silicates. The
few unsuccessfully matched asteroids may indicate the presence of interlopers
in the family or objects sampling a distinct compositional layer of the parent
body. Conclusions. The composition inferred for the Themis family members
suggests that the parent body accreted from a mixture of ice and anhydrous
silicates (mainly amorphous) and subsequently underwent limited heating. By
comparison with existing thermal models that assume a 400km diameter
progenitor, the accretion process of the Themis parent body must have occurred
relatively late (>4Myr after CAIs) so that only moderate internal heating
occurred in its interior, preventing aqueous alteration of the outer shell.Comment: 9 pages, 5 figures, accepted for publication in A&
Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system
The transneptunian region of the solar system is populated by a wide variety
of icy bodies showing great diversity. The dwarf planet (136108) Haumea is
among the largest TNOs and displays a highly elongated shape and hosts two
moons, covered with crystalline water ice like Hamuea. Haumea is also the
largest member of the sole TNO family known to date. A catastrophic collision
is likely responsible for its unique characteristics. We report here on the
analysis of a new set of observations of Haumea obtained with SINFONI at the
ESO VLT. Combined with previous data, and using light-curve measurements in the
optical and far infrared, we carry out a rotationally resolved spectroscopic
study of the surface of Haumea. We describe the physical characteristics of the
crystalline water ice present on the surface of Haumea for both regions, in and
out of the Dark Red Spot (DRS), and analyze the differences obtained for each
individual spectrum. The presence of crystalline water ice is confirmed over
more than half of the surface of Haumea. Our measurements of the average
spectral slope confirm the redder characteristic of the spot region. Detailed
analysis of the crystalline water-ice absorption bands do not show significant
differences between the DRS and the remaining part of the surface. We also
present the results of applying Hapke modeling to our data set. The best
spectral fit is obtained with a mixture of crystalline water ice (grain sizes
smaller than 60 micron) with a few percent of amorphous carbon. Improvements to
the fit are obtained by adding ~10% of amorphous water ice. Additionally, we
used the IFU-reconstructed images to measure the relative astrometric position
of the largest satellite Hi`iaka and determine its orbital elements. An orbital
solution was computed with our genetic-based algorithm GENOID and our results
are in full agreement with recent results.Comment: Accepted for publication in A&
Flexible Wedge Phased Array Transducers for Inspecting Variable-Geometry or Complex Components
The transmission of ultrasound from the transducer into the inspected component is a determining factor in the performance of ultrasound inspections.
Various coupling solutions exist to ensure this transmission. The most frequently used are:• Immersion of the component in water tank: This coupling presents the best acoustic performance (low attenuation, coupling homogeneity, no intermediate interface). However, the inspected parts need to be fully immersed and thus complex control systems are required.• Coupling by direct contact with a liquid couplant, or via a rigid wedge or a delay line with liquid couplant at the interfaces: This coupling requires simpler control systems for the inspection, but the homogeneity of the couplant film and attenuation in the wedges deteriorate the signal.
The geometry of the inspected part can make the coupling more difficult to setup, particularly if the surface is complex or varies from one point to another. The problem becomes critical when the dimensions of the transducer are large in comparison with the local curvature of the interface.
The use of transducers that are flexible, or that are fitted with a flexible wedge, improves the quality of the coupling for components with complex or variable geometry, and in some cases, makes it possible to do certain inspections that currently have no solution.
This article presents the recent developments and results obtained in the context of transducers with flexible wedges, in particular:
• Design options;
• Flexible membranes and mechanical interfaces development for PA transducers;
• Mechanical supports development for manual or automated use;
• Acoustic performance, and wear resistance tests;
These studies have demonstrated the contribution of flexible wedge transducers to various applications, with acoustic performances similar to that of immersion and easy implementation comparable to standard contact inspections, while remaining compatible with an industrial use.
The detailed results will be presented, as well as the possibilities for the future developments of transducers with flexible wedges
Improving the Acoustic Performance of Linear Multi-Element Transducers
The electro-acoustic performance of transducers has a direct impact on the performance of ultrasound inspections. The signal/noise ratio and the resolution (both axial and lateral) are key factors for detecting and/or proportioning the indications being sought. The signal/noise ratio partly depends on the sensitivity and the signal/noise ratio of the transducer itself. The axial resolution depends on the length of the signal and therefore, for a given maximum frequency, on the damping of the transducer.
Sensitivity and damping are often considered antagonistic, as damping traditionally reduces resonance and therefore sensitivity. Earlier studies have demonstrated the advantages gained through using piezocomposite technology to improve this compromise. These two parameters also depend on the acoustic adaptation to the coupling medium (water, plexiglass, rexolite, steel, etc.), and according to the design used, performance deteriorates more or less as one moves further from the nominal use.
In addition to sensitivity and the signal/noise ratio, other parameters such as the angular acceptance and resistance to abrasion are sometimes to be integrated in the expected performances.
This article presents the recent developments undertaken and tested in the context of improving the acoustic performance of multi-element probes:
- Identification of the components that influence performance;
- Simulations;
- Selection of the configurations that meet the needs of various applications;
- The experimental results obtained;
- Comparison with the simulations.
These studies have led to the development of a design expertise for responding to requests for custom-made, industrial, multi-element probes with improved performance, for production runs from a single item to dozens, even hundreds.
The detailed results will be presented, as well as the possibilities for future development
Type II and IV radio bursts in the active period October-November 2003
In this report we present the Type II and IV radio bursts observed and
analyzed by the radio spectrograph ARTEMIS IV1, in the 650-20MHz frequency
range, during the active period October-November 2003. These bursts exhibit
very rich fine structures such fibers, pulsations and zebra patterns which is
associated with certain characteristics of the associated solar flares and
CMEs.Comment: Recent Advances in Astronomy and Astrophysics: 7th International
Conference of the Hellenic Astronomical Society. AIP Conference Proceedings,
Volume 848, pp. 199-206 (2006
Ten Years of the Solar Radiospectrograph ARTEMIS-IV
The Solar Radiospectrograph of the University of Athens (ARTEMIS-IV) is in
operation at the Thermopylae Satellite Communication Station since 1996. The
observations extend from the base of the Solar Corona (650 MHz) to about 2
Solar Radii (20 MHz) with time resolution 1/10-1/100 sec. The instruments
recordings, being in the form of dynamic spectra, measure radio flux as a
function of height in the corona; our observations are combined with spatial
data from the Nancay Radioheliograph whenever the need for 3D positional
information arises. The ARTEMIS-IV contribution in the study of solar radio
bursts is two fold- Firstly, in investigating new spectral characteristics
since its high sampling rate facilitates the study of fine structures in radio
events. On the other hand it is used in studying the association of solar
bursts with interplanetary phenomena because of its extended frequency range
which is, furthermore, complementary to the range of the WIND/WAVES receivers
and the observations may be readily combined. This reports serves as a brief
account of this operation. Joint observations with STEREO/WAVES and LOFAR low
frequency receivers are envisaged in the future
Type II Shocks Characteristics: Comparison with associated CMEs and Flares
A number of metric (100-650 MHz) typeII bursts was recorded by the ARTEMIS-IV
radiospectrograph in the 1998-2000 period; the sample includes both CME driven
shocks and shocks originating from flare blasts. We study their characteristics
in comparison with characteristics of associated CMEs and flares.Comment: Recent Advances in Astronomy and Astrophysics: 7th International
Conference of the Hellenic Astronomical Society. AIP Conference Proceedings,
Volume 848, pp. 238-242 (2006
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