4,034 research outputs found
Elements of Design for Containers and Solutions in the LinBox Library
We describe in this paper new design techniques used in the \cpp exact linear
algebra library \linbox, intended to make the library safer and easier to use,
while keeping it generic and efficient. First, we review the new simplified
structure for containers, based on our \emph{founding scope allocation} model.
We explain design choices and their impact on coding: unification of our matrix
classes, clearer model for matrices and submatrices, \etc Then we present a
variation of the \emph{strategy} design pattern that is comprised of a
controller--plugin system: the controller (solution) chooses among plug-ins
(algorithms) that always call back the controllers for subtasks. We give
examples using the solution \mul. Finally we present a benchmark architecture
that serves two purposes: Providing the user with easier ways to produce
graphs; Creating a framework for automatically tuning the library and
supporting regression testing.Comment: 8 pages, 4th International Congress on Mathematical Software, Seoul :
Korea, Republic Of (2014
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
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&
The Resolved Asteroid Program - Size, shape, and pole of (52) Europa
With the adaptive optics (AO) system on the 10 m Keck-II telescope, we
acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa
on 2005 January 20. The epochs covered its rotation period and, by following
its changing shape and orientation on the plane of sky, we obtained its
triaxial ellipsoid dimensions and spin pole location. An independent
determination from images at three epochs obtained in 2007 is in good agreement
with these results. By combining these two data sets, along with a single epoch
data set obtained in 2003, we have derived a global fit for (52) Europa of
diameters (379x330x249) +/- (16x8x10) km, yielding a volume-equivalent
spherical-diameter of 315 +/- 7 km, and a rotational pole within 7 deg of [RA;
Dec] = [257,+12] in an Equatorial J2000 reference frame (ECJ2000: 255,+35).
Using the average of all mass determinations available forEuropa, we derive a
density of 1.5 +/- 0.4, typical of C-type asteroids. Comparing our images with
the shape model of Michalowski et al. (A&A 416, 2004), derived from optical
lightcurves, illustrates excellent agreement, although several edge features
visible in the images are not rendered by the model. We therefore derived a
complete 3-D description of Europa's shape using the KOALA algorithm by
combining our imaging epochs with 4 stellar occultations and 49 lightcurves. We
use this 3-D shape model to assess these departures from ellipsoidal shape.
Flat facets (possible giant craters) appear to be less distinct on (52) Europa
than on other C-types that have been imaged in detail. We show that fewer giant
craters, or smaller craters, is consistent with its expected impact history.
Overall, asteroid (52) Europa is still well modeled as a smooth triaxial
ellipsoid with dimensions constrained by observations obtained over several
apparitions.Comment: Accepted for publication in Icaru
RpfC (Rv1884) atomic structure shows high structural conservation within the resuscitation promoting factor catalytic domain
We report the first structure of the catalytic domain of RpfC (Rv1884), one of theresuscitation-promoting factors (RPFs) from Mycobacterium tuberculosis. The structure was solved using molecular replacement, once the space group had been correctly identified as twinned P21 rather than the apparent C2221 by searching for anomalous scattering sites in P1. The structure displays a very high degree of structural conservation with the structures of the catalytic domains of RpfB (Rv1009) and RpfE (Rv2450) already published. This structural conservation highlights the importance of the versatile domain composition of the RPF family
Early Chromosome Condensation By XIST Builds A-Repeat RNA Density That Facilitates Gene Silencing
XIST RNA triggers chromosome-wide gene silencing and condenses an active chromosome into a Barr body. Here, we use inducible human XIST to examine early steps in the process, showing that XIST modifies cytoarchitecture before widespread gene silencing. In just 2–4 h, barely visible transcripts populate the large “sparse zone” surrounding the smaller “dense zone”; importantly, density zones exhibit different chromatin impacts. Sparse transcripts immediately trigger immunofluorescence for H2AK119ub and CIZ1, a matrix protein. H3K27me3 appears hours later in the dense zone, which enlarges with chromosome condensation. Genes examined are silenced after compaction of the RNA/DNA territory. Insights into this come from the findings that the A-repeat alone can silence genes and rapidly, but only where dense RNA supports sustained histone deacetylation. We propose that sparse XIST RNA quickly impacts architectural elements to condense the largely non-coding chromosome, coalescing RNA density that facilitates an unstable, A-repeat-dependent step required for gene silencing
Deep imaging survey of young, nearby austral stars: VLT/NACO near-infrared Lyot-coronographic observations
Context. High contrast and high angular resolution imaging is the optimal search technique for substellar companions to nearby stars at physical separations larger than typically 10 AU. Two distinct populations of substellar companions, brown dwarfs and planets, can be probed and characterized. As a result, fossile traces of processes of formation and evolution can be revealed by physical and orbital properties, both for individual systems and as an ensemble.
Aims. Since November 2002, we have conducted a large, deep imaging, survey of young, nearby associations of the southern hemisphere. Our goal is detection and characterization of substellar companions with projected separations in the range 10–500 AU. We have observed a sample of 88 stars, primarily G to M dwarfs, younger than 100 Myr, and within 100 pc of Earth.
Methods. The VLT/NACO adaptive optics instrument of the ESO Paranal Observatory was used to explore the faint circumstellar environment between typically 0.1 and 10". Diffraction-limited observations in H and K_s-band combined with Lyot-coronagraphy enabled us to reach primary star-companion brightness ratios as small as 10^(-6). The existence of planetary mass companions could therefore be probed. We used a standardized observing sequence to precisely measure the position and flux of all detected sources relative to their visual primary star. Repeated observations at several epochs enabled us to discriminate comoving companions from background objects.
Results. We report the discovery of 17 new close (0.1–5.0") multiple systems. HIP 108195 AB and C (F1 III-M6), HIP 84642 AB (a~14 AU, K0-M5) and TWA22 AB (a~1.8 AU; M6-M6) are confirmed comoving systems. TWA22 AB is likely to be a rare astrometric calibrator that can be used to test evolutionary model predictions. Among our complete sample, a total of 65 targets were observed with deep coronagraphic imaging. About 240 faint companion candidates were detected around 36 stars. Follow-up observations with VLT or HST for 83% of these stars enabled us to identify a large fraction of background contaminants. Our latest results that pertain to the substellar companions to GSC 08047-00232, AB Pic and 2M1207 (confirmed during this survey and published earlier), are reviewed. Finally, a statistical analysis of our complete set of coronagraphic detection limits enables us to place constraints on the physical and orbital properties of giant planets between typically 20 and 150 AU
From Bloch model to the rate equations II: the case of almost degenerate energy levels
Bloch equations give a quantum description of the coupling between an atom
and a driving electric force. In this article, we address the asymptotics of
these equations for high frequency electric fields, in a weakly coupled regime.
We prove the convergence towards rate equations (i.e. linear Boltzmann
equations, describing the transitions between energy levels of the atom). We
give an explicit form for the transition rates. This has already been performed
in [BFCD03] in the case when the energy levels are fixed, and for different
classes of electric fields: quasi or almost periodic, KBM, or with continuous
spectrum. Here, we extend the study to the case when energy levels are possibly
almost degenerate. However, we need to restrict to quasiperiodic forcings. The
techniques used stem from manipulations on the density matrix and the averaging
theory for ordinary differential equations. Possibly perturbed small divisor
estimates play a key role in the analysis. In the case of a finite number of
energy levels, we also precisely analyze the initial time-layer in the rate
aquation, as well as the long-time convergence towards equilibrium. We give
hints and counterexamples in the infinite dimensional case
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