Ordering arc-reversal operations when eliminating variables in lazy AR propagation

This paper considers the problem of ordering arc-reversal operations and breaking ties in cost measures when eliminating variables in Lazy AR Propagation (LPAR). In particular, the paper presents the BreakTies algorithm for breaking ties in cost measures when selecting the next arc to reverse in a variable elimination operation. BreakTies is based upon using a sequence of cost measures instead of randomly selecting an arc to reverse when multiple arcs share the same cost. The paper reports on an experimental evaluation of LPAR for belief update in Bayesian networks considering six sequences of five cost measures for breaking ties using BreakTies. The experimental results show that using BreakTies to select the next arc to reverse in a variable elimination operation can improve performance of LPAR.     

Magnetic polyvinylamine nanoparticles by in situ precipitation reaction

Magnetic nanoparticles represent emerging tools in biomedical and pharmaceutical research. Because in most cases, the surfaces of these nanoparticles are hydrophobic, surface modifiers are usually applied to stabilize the colloidal suspension in an aqueous media. This investigation reports a simple technique for the preparation of MnFe₂O₄ synthesized within polyvinylamine (PVAm) nanoparticle reactors. Magnetite nanoparticles were previously synthesized using a similar scheme; however, substituting MnFe₂O₄ for Fe₃O₄ improved nanoparticle magnetization properties and further established the synthetic approach. PVAm nanoparticles exhibited more than 18% manganese ferrite loading by weight, a saturation magnetization of ～ 40 emu/g of MnFe₂O₄, excellent colloidal stability, and reactive primary amines for possible drug conjugation or surface modification. Transmission electron micrographs revealed that the dispersions contained ～ 50 nm PVAm nanoparticles incorporating manganese ferrite particles with a size less than ～ 7 nm. This reaction scheme further justifies a unique synthetic methodology for magnetic nanoparticles offering potential use in contrast‐enhanced magnetic resonance imaging or drug delivery. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 991–996, 2010     

Chromatography in a single metal-organic framework (MOF) crystal

Millimeter-sized single MOF-5 crystals are used as "chromatographic columns" to effectively separate mixtures of organic dyes. Remarkably, owing to the nanoscopic pore dimensions and the molecular-level interactions between the migrating molecules and the MOF scaffold, the separations occur over a distance of only a few hundred micrometers which is unambiguously confirmed by fluorescence confocal microscopy.     

Chemical perturbation of secondary metabolism demonstrates important links to primary metabolism

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Highlights? A chemical screen recapitulates all genetic phenotypes in S. coelicolor ? 19 compounds remodel secondary metabolism in Streptomyces coelicolor ? Partial inhibition of fatty acid synthesis remodels secondary metabolite production     

Parallel information transfer in a multinode quantum information processor

We describe a method for coupling disjoint quantum bits (qubits) in different local processing nodes of a distributed node quantum information processor. An effective channel for information transfer between nodes is obtained by moving the system into an interaction frame where all pairs of cross-node qubits are effectively coupled via an exchange interaction between actuator elements of each node. All control is achieved via actuator-only modulation, leading to fast implementations of a universal set of internode quantum gates. The method is expected to be nearly independent of actuator decoherence and may be made insensitive to experimental variations of system parameters by appropriate design of control sequences. We show, in particular, how the induced cross-node coupling channel may be used to swap the complete quantum states of the local processors in parallel.     

Simulating radiative transfer with filtered spherical harmonics

This Letter presents a novel application of filters to the spherical harmonics (PN) expansion for radiative transfer problems in the high-energy-density regime. The filter, which is based on non-oscillatory spherical splines, preserves both the equilibrium diffusion limit and formal convergence properties of the unfiltered expansion. While the method requires further mathematical justification and computational studies, preliminary results demonstrate that solutions to the filtered PN equations are (1) more robust and less oscillatory than standard PN solutions and (2) more accurate than discrete ordinates solutions of comparable order. The filtered P₇ solution demonstrates comparable accuracy to an implicit Monte Carlo solution for a benchmark hohlraum problem. Given the benefits of this method we believe it will enable more routine use of high-fidelity radiation-hydrodynamics calculations in the simulation of physical systems.     

In situ data collection and structure refinement from microcapillary protein crystallization

In situ X-ray data collection has the potential to eliminate the challenging task of mounting and cryocooling often fragile protein crystals, reducing a major bottleneck in the structure determination process. An apparatus used to grow protein crystals in capillaries and to compare the background X-ray scattering of the components, including thin-walled glass capillaries against Teflon, and various fluorocarbon oils against each other, is described. Using thaumatin as a test case at 1.8 ? resolution, this study demonstrates that high-resolution electron density maps and refined models can be obtained from in situ diffraction of crystals grown in microcapillaries.     

CATALYTIC DEHYDROCOUPLING OF AMINE-BORANE ADDUCTS TO FORM AMINOBORANES AND BORAZINES

A mild, catalytic dehydrocoupling route to aminoboranes and borazine derivatives from either primary or secondary amine-borane adducts has been developed using late transition metal complexes as precatalysts. The dehydrocoupling of Me ₂ NH·BH ₃ was found to be catalyzed by 0.5 mol% [Rh(1,5-cod)(μ-Cl)] ₂ in solution at 25°C to give [Me ₂ N─BH ₂ ] ₂ (1) quantitatively after ca. 8 h. This new catalytic method was extended to other secondary adducts RR ′NH·BH ₃ which afforded the dimeric [(1,4-C ₄ H ₈ )N─BH ₂ ] ₂ (2) and [PhCH ₂ (Me)N─BH ₂ ] ₂ (3) or the monomeric aminoborane ⁱ Pr ₂ N═BH ₂ (4) under mild conditions. The catalytic dehydrocoupling of NH ₃ ·BH ₃ , MeNH ₂ ·BH ₃ , and PhNH ₂ ·BH ₃ at 45°C affords the borazine derivatives [RN─BH] ₃ (5: R = H; 6: R = Me; 7:R = Ph). TEM analysis of the contents of the reaction solution for the [Rh(1,5-cod)(μ-Cl)] ₂ catalyzed dehydrocoupling of Me ₂ NH·BH ₃ together with Hg poisoning experiments suggested a soluble heterogeneous catalyst involving Rh(0) nanoclusters.