912 research outputs found
Transparent yttrium hydride thin films prepared by reactive sputtering
Metal hydrides have earlier been suggested for utilization in solar cells.
With this as a motivation we have prepared thin films of yttrium hydride by
reactive magnetron sputter deposition. The resulting films are metallic for low
partial pressure of hydrogen during the deposition, and black or
yellow-transparent for higher partial pressure of hydrogen. Both metallic and
semiconducting transparent YHx films have been prepared directly in-situ
without the need of capping layers and post-deposition hydrogenation. Optically
the films are similar to what is found for YHx films prepared by other
techniques, but the crystal structure of the transparent films differ from the
well-known YH3 phase, as they have an fcc lattice instead of hcp
Speeding up Cylindrical Algebraic Decomposition by Gr\"obner Bases
Gr\"obner Bases and Cylindrical Algebraic Decomposition are generally thought
of as two, rather different, methods of looking at systems of equations and, in
the case of Cylindrical Algebraic Decomposition, inequalities. However, even
for a mixed system of equalities and inequalities, it is possible to apply
Gr\"obner bases to the (conjoined) equalities before invoking CAD. We see that
this is, quite often but not always, a beneficial preconditioning of the CAD
problem.
It is also possible to precondition the (conjoined) inequalities with respect
to the equalities, and this can also be useful in many cases.Comment: To appear in Proc. CICM 2012, LNCS 736
Improving resilience to climate impacts in West Africa through improved availability, access and use of climate information: dialog with users
The stakeholder workshop on âImproving Resilience to Climate Impacts in West Africa
Through Improved Availability, Access and Use of Climate Information: Dialogue With
Usersâ was convened by the Centre Regional de Formation et d'Application en
Agrométéorologie et Hydrologie Opérationnelle (AGRHYMET) in collaboration with the
International Research Institute for Climate and Society (IRI) with funding and technical
support from the United States Agency for International Development (USAID), the CGIAR
Research Program on Climate Change, Agriculture and Food Security (CCAFS) and the
United Nations Development Program (UNDP). Stakeholders from six Permanent Inter-state
Committee for Drought Control in the Sahel (CILSS) countries were invited, in addition to
representatives of five river basin organizations and the African Center of Meteorological
Application for Development (ACMAD). The three-day meeting in Niamey, Niger (January
21-23, 2014) was attended by 40 participants and facilitators. It consisted of five components:
âą Introduction to AGRHYMETâs latest climate data, tools, and information products;
âą Training on the use of the tools for data analysis and visualization;
âą Engagement on the concept of climate risk management in the different sectors;
âą Soliciting feedback and needs from participants, to assess the value of the available tools
and products to users, and inform improvements that are most relevant to stakeholders;
and
âą Exploration of an Advisory Group for improving Climate Services provided by the
AGRHYMET Center.
The workshop introduced and solicited feedback on data, products and decision-support tools
launched to support improved resilience to climate impacts, across sectors, initially targeting
the agriculture, water and disaster risk management communities
Ascaroside Signaling Is Widely Conserved among Nematodes
Background: Nematodes are among the most successful animals on earth and include important human pathogens, yet little is known about nematode pheromone systems. A group of small molecules called ascarosides has been found to mediate mate finding, aggregation, and developmental diapause in Caenorhabditis elegans, but it is unknown whether ascaroside signaling exists outside of the genus Caenorhabditis.
Results: To determine whether ascarosides are used as signaling molecules by other nematode species, we performed a mass spectrometry-based screen for ascarosides in secretions from a variety of both free-living and parasitic (plant, insect, and animal) nematodes. We found that most of the species analyzed, including nematodes from several different clades, produce species-specific ascaroside mixtures. In some cases, ascaroside biosynthesis patterns appear to correlate with phylogeny, whereas in other cases, biosynthesis seems to correlate with lifestyle and ecological niche. We further show that ascarosides mediate distinct nematode behaviors, such as retention, avoidance, and long-range attraction, and that different nematode species respond to distinct, but overlapping, sets of ascarosides.
Conclusions: Our findings indicate that nematodes utilize a conserved family of signaling molecules despite having evolved to occupy diverse ecologies. Their structural features and level of conservation are evocative of bacterial quorum sensing, where acyl homoserine lactones (AHLs) are both produced and sensed by many species of gram-negative bacteria. The identification of species-specific ascaroside profiles may enable pheromone-based approaches to interfere with reproduction and survival of parasitic nematodes, which are responsible for significant agricultural losses and many human diseases worldwide
NLO QCD corrections to processes with multiple electroweak bosons
The VBFNLO program package is a collection of Monte Carlo programs for the
calculation of NLO QCD corrections to vector boson fusion cross sections,
double and triple vector boson production, or the production of two electroweak
bosons in association with an additional jet. An overview is given of the
processes and features implemented in VBFNLO. WWgamma and Wgamma jet production
are discussed as examples.Comment: 6 pages, 3 figures; talk given at RADCOR 2009 - 9th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25 - 30 2009, Ascona, Switzerlan
Towards Physical Hybrid Systems
Some hybrid systems models are unsafe for mathematically correct but
physically unrealistic reasons. For example, mathematical models can classify a
system as being unsafe on a set that is too small to have physical importance.
In particular, differences in measure zero sets in models of cyber-physical
systems (CPS) have significant mathematical impact on the mathematical safety
of these models even though differences on measure zero sets have no tangible
physical effect in a real system. We develop the concept of "physical hybrid
systems" (PHS) to help reunite mathematical models with physical reality. We
modify a hybrid systems logic (differential temporal dynamic logic) by adding a
first-class operator to elide distinctions on measure zero sets of time within
CPS models. This approach facilitates modeling since it admits the verification
of a wider class of models, including some physically realistic models that
would otherwise be classified as mathematically unsafe. We also develop a proof
calculus to help with the verification of PHS.Comment: CADE 201
Constructive Hybrid Games
Hybrid games are models which combine discrete, continuous, and adversarial
dynamics. Game logic enables proving (classical) existence of winning
strategies. We introduce constructive differential game logic (CdGL) for hybrid
games, where proofs that a player can win the game correspond to computable
winning strategies. This is the logical foundation for synthesis of correct
control and monitoring code for safety-critical cyber-physical systems. Our
contributions include novel static and dynamic semantics as well as soundness
and consistency.Comment: 60 pages, preprint, under revie
Panchromatic light harvesting and stabilizing charge-separated states in corroleâphthalocyanine conjugates through coordinating a subphthalocyanine
Owing to the electron-donating and -accepting nature of corroles (Corr) and phthalocyanines (Pc), respectively, we designed and developed two novel covalently linked Corr-Pc conjugates. The synthetic route allows the preparation of the target conjugates in satisfying yields. Comprehensive steady-state absorption, fluorescence, and electrochemical assays enabled insights into energy and electron-transfer processes upon photoexcitation. Coordinating a pyridine-appended subphthalocyanine (SubPc) to the Pc of the conjugate sets up the ways and means to realize the first example of an array composed by three different porphyrinoids, which drives a cascade of energy and charge-transfer processes. Importantly, the SubPc assists in stabilizing the charge-separated state, that is, one-electron oxidized Corr and the one electron-reduced Pc, upon photoexcitation by means of a reductive charge transfer to the SubPc. To the best of our knowledge, this is the first case of an intramolecular oxidation of a Corr within electron-donorâacceptor conjugates by means of just photoexcitation. Moreover, the combination of Corr, Pc, and SubPc guarantees panchromatic absorption across the visible range of the solar spectrum, with the SubPc covering the âgreen gapâ that usually affects porphyrinoids
Controlling electronic events through rational structural design in subphthalocyanineâcorrole dyads: synthesis, characterization, and photophysical properties
Porphyrinoids are considered perfect candidates for their incorporation into electron donorâacceptor (DâA) arrays due to their remarkable optoelectronic properties and low reorganization energies. For the first time, a series of subphthalocyanine (SubPc) and corrole (Cor) were covalently connected through a short-range linkage. SubPc axial substitution strategies were employed, which allowed the synthesis of the target molecules in decent yields. In this context, a qualitative synthetic approach was performed to reverse the expected direction of the different electronic events. Consequently, in-depth absorption, fluorescence, and electrochemical assays enabled the study of electronic and photophysical properties. Charge separation was observed in cases of electron-donating Cors, whereas a quantitative energy transfer from the Cor to the SubPc was detected in the case of electron accepting Cors
A Method for Invariant Generation for Polynomial Continuous Systems
International audienceThis paper presents a method for generating semi-algebraic invariants for systems governed by non-linear polynomial ordinary differential equations under semi-algebraic evolution constraints. Based on the notion of discrete abstraction , our method eliminates unsoundness and unnecessary coarseness found in existing approaches for computing abstractions for non-linear continuous systems and is able to construct invariants with intricate boolean structure, in contrast to invariants typically generated using template-based methods. In order to tackle the state explosion problem associated with discrete abstraction, we present invariant generation algorithms that exploit sound proof rules for safety verification , such as differential cut (DC), and a new proof rule that we call differential divide-and-conquer (DDC), which splits the verification problem into smaller sub-problems. The resulting invariant generation method is observed to be much more scalable and efficient than the našıvenašıve approach, exhibiting orders of magnitude performance improvement on many of the problems
- âŠ