6,164 research outputs found
Picking out polymorphs: H-bond prediction and crystal structure stability
A methodology has been developed to predict the propensity for hydrogen bonds to form in crystal structures, treating each potential H-bond as a binary response variable, and modelling its likelihood using a set of relevant chemical descriptors [1]. Modelling is tailored to a target using chemically similar known structures, from e.g. the Cambridge Structural Database [2], making it accessible to the complete spectrum of organic structures, including solvates, hydrates and cocrystals. Recent work has developed the approach to predicting interand intramolecular H-bonds when either type can occur. By way of a comparison between possible and observed H-bonds, the method has been applied to assess structural stability, which shows much promise in the domain of polymorph screening in the pharmaceutical industry. We will introduce the methodology and illustrate its application using a selection of pharmaceutical compounds, one of which will be Abbott’s wellpublicised anti-HIV medication ritonavir (Norvir™). Owing to a hidden, more stable form II with much lower bioavailability, ritonavir was temporarily withdrawn from the market with significant financial impact [3]. Our method quickly suggests a real threat of polymorphism in this compound, and strongly supports the relative stability of form II over form I. For all examples, the high predictivity of the method is emphasised
Compositionality for Quantitative Specifications
We provide a framework for compositional and iterative design and verification of systems with quantitative information, such as rewards, time or energy. It is based on disjunctive modal transition systems where we allow actions to bear various types of quantitative information. Throughout the design process the actions can be further refined and the information made more precise. We show how to compute the results of standard operations on the systems, including the quotient (residual), which has not been previously considered for quantitative non-deterministic systems. Our quantitative framework has close connections to the modal nu-calculus and is compositional with respect to general notions of distances between systems and the standard operations
Methyl (2′S,3′S)-3,4-O-(2′,3′-dimethoxybutane-2′,3′-diyl)-α-l-rhamnopyranoside: a glycosyl acceptor
The title compound, C13H24O7, is the product of the ketalization of methyl l-(+)-rhamnopyranoside with 2,3-butanedione. It crystallizes with two molecules in the asymmetric unit, which are connected by O—H⋯O hydrogen bonds. The C-3,4 diequatorial hydroxy groups of the methyl l-(+)-rhamnopyranoside were protected, leaving the C-2 hydroxy group free. The l-(+)-rhamnopyranoside and 2′,3′-dimethoxybutane-2′,3′-diyl rings adopt chair conformations and all methoxy groups are in axial positions. The absolute configuration was assumed from the synthesis
and meson exclusive decay in QCD factorization
Belle has observed surprisingly copious production of in
meson decay , of which the rate is comparable to that of
. We study this puzzling process in the QCD factorization
approach with the effect of S-D mixing considered. We find that the soft
scattering effects in the spectator interactions play an essential role. With a
proper parametrization for the higher twist soft end-point singularities
associated with kaon, and with the S-D mixing angle , the
calculated decay rates can be close to the data. Implications of these soft
spectator effects to other charmonium production in exclusive decays are
also emphasized.Comment: journal versio
Yang-Mills instantons and dyons on homogeneous G_2-manifolds
We consider Lie G-valued Yang-Mills fields on the space R x G/H, where G/H is
a compact nearly K"ahler six-dimensional homogeneous space, and the manifold R
x G/H carries a G_2-structure. After imposing a general G-invariance condition,
Yang-Mills theory with torsion on R x G/H is reduced to Newtonian mechanics of
a particle moving in R^6, R^4 or R^2 under the influence of an inverted
double-well-type potential for the cases G/H = SU(3)/U(1)xU(1),
Sp(2)/Sp(1)xU(1) or G_2/SU(3), respectively. We analyze all critical points and
present analytical and numerical kink- and bounce-type solutions, which yield
G-invariant instanton configurations on those cosets. Periodic solutions on S^1
x G/H and dyons on iR x G/H are also given.Comment: 1+26 pages, 14 figures, 6 miniplot
Parallelization of Kinetic Theory Simulations
Numerical studies of shock waves in large scale systems via kinetic
simulations with millions of particles are too computationally demanding to be
processed in serial. In this work we focus on optimizing the parallel
performance of a kinetic Monte Carlo code for astrophysical simulations such as
core-collapse supernovae. Our goal is to attain a flexible program that scales
well with the architecture of modern supercomputers. This approach requires a
hybrid model of programming that combines a message passing interface (MPI)
with a multithreading model (OpenMP) in C++. We report on our approach to
implement the hybrid design into the kinetic code and show first results which
demonstrate a significant gain in performance when many processors are applied.Comment: 10 pages, 3 figures, conference proceeding
Contact Manifolds, Contact Instantons, and Twistor Geometry
Recently, Kallen and Zabzine computed the partition function of a twisted
supersymmetric Yang-Mills theory on the five-dimensional sphere using
localisation techniques. Key to their construction is a five-dimensional
generalisation of the instanton equation to which they refer as the contact
instanton equation. Subject of this article is the twistor construction of this
equation when formulated on K-contact manifolds and the discussion of its
integrability properties. We also present certain extensions to higher
dimensions and supersymmetric generalisations.Comment: v3: 28 pages, clarifications and references added, version to appear
in JHE
Preliminary Limits on the WIMP-Nucleon Cross Section from the Cryogenic Dark Matter Search (CDMS)
We are conducting an experiment to search for WIMPs, or weakly-interacting
massive particles, in the galactic halo using terrestrial detectors. This
generic class of hypothetical particles, whose properties are similar to those
predicted by extensions of the standard model of particle physics, could
comprise the cold component of non-baryonic dark matter. We describe our
experiment, which is based on cooled germanium and silicon detectors in a
shielded low-background cryostat. The detectors achieve a high degree of
background rejection through the simultaneous measurement of the energy in
phonons and ionization. Using exposures on the order of one kilogram-day from
initial runs of our experiment, we have achieved (preliminary) upper limits on
the WIMP-nucleon cross section that are comparable to much longer runs of other
experiments.Comment: 5 LaTex pages, 5 eps figs, epsf.sty, espcrc2dsa2.sty. Proceedings of
TAUP97, Gran Sasso, Italy, 7-11 Sep 1997, Nucl. Phys. Suppl., A. Bottino, A.
di Credico and P. Monacelli (eds.). See also http://cfpa.berkeley.ed
LNCS
We introduce the monitoring of trace properties under assumptions. An assumption limits the space of possible traces that the monitor may encounter. An assumption may result from knowledge about the system that is being monitored, about the environment, or about another, connected monitor. We define monitorability under assumptions and study its theoretical properties. In particular, we show that for every assumption A, the boolean combinations of properties that are safe or co-safe relative to A are monitorable under A. We give several examples and constructions on how an assumption can make a non-monitorable property monitorable, and how an assumption can make a monitorable property monitorable with fewer resources, such as integer registers
Cross modal perception of body size in domestic dogs (Canis familiaris)
While the perception of size-related acoustic variation in animal vocalisations is well documented, little attention has been given to how this information might be integrated with corresponding visual information. Using a cross-modal design, we tested the ability of domestic dogs to match growls resynthesised to be typical of either a large or a small dog to size- matched models. Subjects looked at the size-matched model significantly more often and for a significantly longer duration than at the incorrect model, showing that they have the ability to relate information about body size from the acoustic domain to the appropriate visual category. Our study suggests that the perceptual and cognitive mechanisms at the basis of size assessment in mammals have a multisensory nature, and calls for further investigations of the multimodal processing of size information across animal species
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