9,102 research outputs found
Visible-Light-Induced, Copper-Catalyzed Three-Component Coupling of Alkyl Halides, Olefins, and Trifluoromethylthiolate to Generate Trifluoromethyl Thioethers
Photoinduced, copper-catalyzed coupling reactions are emerging as a powerful method for generating Csp^3âY (Y = C or heteroatom) bonds from alkyl electrophiles and nucleophiles. Corresponding three-component couplings of alkyl electrophiles, olefins, and nucleophiles have the potential to generate an additional Csp3âY bond and to efficiently add functional groups to both carbons of an olefin, which serves as a readily available linchpin. In this report, we establish that a variety of electrophiles and a trifluoromethylthiolate nucleophile can add across an array of olefins (including styrenes and electron-poor olefins) in the presence of CuI/binap and blue-LED irradiation, thereby generating trifluoromethyl thioethers in good yield. The process tolerates a wide range of functional groups, and an initial survey of other nucleophiles (i.e., bromide, cyanide, and azide) suggests that this three-component coupling strategy is versatile. Mechanistic studies are consistent with a photoexcited Cu(I)/binap/SCF_3 complex serving as a reductant to generate an alkyl radical from the electrophile, which likely reacts in turn with the olefin and a Cu(II)/SCF_3 complex to afford the coupling product
Two Optimal Strategies for Active Learning of Causal Models from Interventional Data
From observational data alone, a causal DAG is only identifiable up to Markov
equivalence. Interventional data generally improves identifiability; however,
the gain of an intervention strongly depends on the intervention target, that
is, the intervened variables. We present active learning (that is, optimal
experimental design) strategies calculating optimal interventions for two
different learning goals. The first one is a greedy approach using
single-vertex interventions that maximizes the number of edges that can be
oriented after each intervention. The second one yields in polynomial time a
minimum set of targets of arbitrary size that guarantees full identifiability.
This second approach proves a conjecture of Eberhardt (2008) indicating the
number of unbounded intervention targets which is sufficient and in the worst
case necessary for full identifiability. In a simulation study, we compare our
two active learning approaches to random interventions and an existing
approach, and analyze the influence of estimation errors on the overall
performance of active learning
VO: Vaccine Ontology
Vaccine research, as well as the development, testing, clinical trials, and commercial uses of vaccines involve complex processes with various biological data that include gene and protein expression, analysis of molecular and cellular interactions, study of tissue and whole body responses, and extensive epidemiological modeling. Although many data resources are available to meet different aspects of vaccine needs, it remains a challenge how we are to standardize vaccine annotation, integrate data about varied vaccine types and resources, and support advanced vaccine data analysis and inference. To address these problems, the community-based Vaccine Ontology (VO, "http://www.violinet.org/vaccineontology":http://www.violinet.org/vaccineontology) has been developed through collaboration with vaccine researchers and many national and international centers and programs, including the National Center for Biomedical Ontology (NCBO), the Infectious Disease Ontology (IDO) Initiative, and the Ontology for Biomedical Investigations (OBI). VO utilizes the Basic Formal Ontology (BFO) as the top ontology and the Relation Ontology (RO) for definition of term relationships. VO is represented in the Web Ontology Language (OWL) and edited using the Protégé-OWL. Currently VO contains more than 2000 terms and relationships. VO emphasizes on classification of vaccines and vaccine components, vaccine quality and phenotypes, and host immune response to vaccines. These reflect different aspects of vaccine composition and biology and can thus be used to model individual vaccines. More than 200 licensed vaccines and many vaccine candidates in research or clinical trials have been modeled in VO. VO is being used for vaccine literature mining through collaboration with the National Center for Integrative Biomedical Informatics (NCIBI). Multiple VO applications will be presented.

Dimension and bases for geometrically continuous splines on surfaces of arbitrary topology
We analyze the space of geometrically continuous piecewise polynomial functions, or splines, for rectangular and triangular patches with arbitrary topology and general rational transition maps. To define these spaces of G 1 spline functions, we introduce the concept of topological surface with gluing data attached to the edges shared by faces. The framework does not require manifold constructions and is general enough to allow non-orientable surfaces. We describe compatibility conditions on the transition maps so that the space of differentiable functions is ample and show that these conditions are necessary and sufficient to construct ample spline spaces. We determine the dimension of the space of G1 spline functions which are of degree less than or equal to k on triangular pieces and of bi-degree less than or equal to (k, k) on rectangular pieces, for k big enough. A separability property on the edges is involved to obtain the dimension formula. An explicit construction of basis functions attached resspectively to vertices, edges and faces is proposed; examples of bases of G1 splines of small degree for topological surfaces with boundary and without boundary are detailed
Photografted methacrylate-based monolithic columns coated with cellulose tris(3,5-dimethylphenylcarbamate) for chiral separation in CEC
A chiral capillary monolithic column for enantiomer separation in capillary electrochromatography was prepared by coating cellulose tris(3,5-dimethylphenylcarbamate) on porous glycidyl methacrylate-co-ethylene dimethacrylate monolith in capillary format grafted with chains of [2(methacryloyloxy)ethyl] trimethylammonium chloride. The surface modification of the monolith by the photografting of [2(methacryloyloxy)ethyl] trimethylammonium chloride monomer as well as the coating conditions of cellulose tris(3,5-dimethylphenylcarbamate) onto the grafted monolithic scaffold were optimized to obtain a stable and reproducible chiral stationary phase for capillary electrochromatography. The effect of organic modifier (acetonitrile) in aqueous mobile phase for the enantiomer separation by capillary electrochromatography was also investigated. Several pairs of enantiomers including acidic, neutral, and basic analytes were tested and most of them were partially or completely resolved under aqueous mobile phases. The prepared monolithic chiral stationary phases exhibited a good stability, repeatability, and column-to-column reproducibility, with relative standard deviations below 11% in the studied electrochromatographic parameters.Fil: Echevarria, Romina Noel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; ArgentinaFil: Carrasco Correa, Enrique Javier. Universidad de Valencia; EspañaFil: Keunchkarian, Sonia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; ArgentinaFil: Reta, Mario Roberto. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Herrero Martinez, JosĂ© Manuel. Universidad de Valencia; Españ
Techno-economic model of a second-life energy storage system for utility-scale solar power considering li-ion calendar and cycle aging
While the use of energy storage combined with grid-scale photovoltaic power
plants continues to grow, given current lithium-ion battery prices, there
remains uncertainty about the profitability of these solar-plus-storage
projects. At the same time, the rapid proliferation of electric vehicles is
creating a fleet of millions of lithium-ion batteries that will be deemed
unsuitable for the transportation industry once they reach 80 percent of their
original capacity. The repurposing and deployment of these batteries as
stationary energy storage provides an opportunity to reduce the cost of
solar-plus-storage systems, if the economics can be proven. We present a
techno-economic model of a solar-plus-second-life energy storage project in
California, including a data-based model of lithium nickel manganese cobalt
oxide battery degradation, to predict its capacity fade over time, and compare
it to a project that uses a new lithium-ion battery. By setting certain control
policy limits, to minimize cycle aging, we show that a system with SOC limits
in a 65 to 15 percent range, extends the project life to over 16 years,
assuming a battery reaches its end-of-life at 60 percent of its original
capacity. Under these conditions, a second-life project is more economically
favorable than a project that uses a new battery and 85 to 20 percent SOC
limits, for second-life battery costs that are less than 80 percent of the new
battery. The same system reaches break-even and profitability for second-life
battery costs that are less than 60 percent of the new battery. Our model shows
that using current benchmarked data for the capital and O&M costs of
solar-plus-storage systems, and a semi-empirical data-based degradation model,
it is possible for EV manufacturers to sell second-life batteries for less than
60 percent of their original price to developers of profitable
solar-plus-storage projects.Comment: 19 pages, 6 figure
CYP72A enzymes catalyse 13-hydrolyzation of gibberellins
Bioactive gibberellins (GAs, diterpenes) are essential hormones in land plants, controlling many aspects of plant growth and developments. In flowering plants, 13-OH (low bioactivity; such as GA1) and 13-H GAs (high bioactivity; such as GA4) frequently coexist. However, the bona fide GA 13-hydroxylase and its physiological functions in Arabidopsis remain unknown. Here, we report that novel cytochrome P450 genes (CYP72A9 and its homologs) encode active GA 13- hydroxylases in Brassicaceae plants. CYP72A9-overexpressing plants exhibited semi-dwarfism, which was caused by significant reduction in GA4 levels. Biochemical assays revealed that recombinant CYP72A9 protein catalyzed the conversion from 13-H GAs to the corresponding 13-OH GAs. CYP72A9 was expressed predominantly in developing seeds in Arabidopsis. Freshly harvested seeds of cyp72a9 mutants germinated more quickly than wild-type, while long-term storage and stratification-treated seeds did not. The evolutionary origin of GA 13- oxidases from the CYP72A subfamily also was investigated and discussed here
High-Precision Extraction of Emerging Concepts from Scientific Literature
Identification of new concepts in scientific literature can help power
faceted search, scientific trend analysis, knowledge-base construction, and
more, but current methods are lacking. Manual identification cannot keep up
with the torrent of new publications, while the precision of existing automatic
techniques is too low for many applications. We present an unsupervised concept
extraction method for scientific literature that achieves much higher precision
than previous work. Our approach relies on a simple but novel intuition: each
scientific concept is likely to be introduced or popularized by a single paper
that is disproportionately cited by subsequent papers mentioning the concept.
From a corpus of computer science papers on arXiv, we find that our method
achieves a Precision@1000 of 99%, compared to 86% for prior work, and a
substantially better precision-yield trade-off across the top 15,000
extractions. To stimulate research in this area, we release our code and data
(https://github.com/allenai/ForeCite).Comment: Accepted to SIGIR 202
Interaction of anticancer reduced Schiff base coumarin derivatives with human serum albumin investigated by fluorescence quenching and molecular modeling
The specific binding of five reduced Schiff base derived 7-amino-coumarin compounds with
antitumor activity to human serum albumin, the principal binding protein of blood, was
studied by fluorescence spectroscopy. Their conditional binding constants were computed and
the reversible binding at the Sudlowâs site I was found to be strong (KD ~ 0.03-2.09 M).
Based on the data albumin can provide a depot for the compounds and is responsible for their
biodistribution and transport processes. The experimental data is complemented by proteinâ
ligand docking calculations for two representatives which support the observations. The
proton dissociation constants of the compounds were also determined by UV-Vis
spectrophotometric and fluorometric titrations to obtain the actual charges and distribution of
the species in the various protonation states at physiological pH
Wall Orientation and Shear Stress in the Lattice Boltzmann Model
The wall shear stress is a quantity of profound importance for clinical
diagnosis of artery diseases. The lattice Boltzmann is an easily parallelizable
numerical method of solving the flow problems, but it suffers from errors of
the velocity field near the boundaries which leads to errors in the wall shear
stress and normal vectors computed from the velocity. In this work we present a
simple formula to calculate the wall shear stress in the lattice Boltzmann
model and propose to compute wall normals, which are necessary to compute the
wall shear stress, by taking the weighted mean over boundary facets lying in a
vicinity of a wall element. We carry out several tests and observe an increase
of accuracy of computed normal vectors over other methods in two and three
dimensions. Using the scheme we compute the wall shear stress in an inclined
and bent channel fluid flow and show a minor influence of the normal on the
numerical error, implying that that the main error arises due to a corrupted
velocity field near the staircase boundary. Finally, we calculate the wall
shear stress in the human abdominal aorta in steady conditions using our method
and compare the results with a standard finite volume solver and experimental
data available in the literature. Applications of our ideas in a simplified
protocol for data preprocessing in medical applications are discussed.Comment: 9 pages, 11 figure
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