Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis

The structure of ruthenium-based olefin metathesis catalyst 3 and model π-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 toward sterically demanding substrates. Due to this tilt, the more sterically accessible face bears the two methyl substituents of the N-aryl rings. These experimental studies are supported by computational studies of these complexes by DFT. The experimental data provides a means to validate the accuracy of the B3LYP and M06 functionals. B3LYP provides geometries that match X-ray crystal structural data more closely, though it leads to slightly less (0.5 kcal mol^(−1)) accuracy than M06 most likely because it underestimates attractive noncovalent interactions

Uniqueness of Flat Spherically Symmetric Spacelike Hypersurfaces Admitted by Spherically Symmetric Static Spactimes

It is known that spherically symmetric static spacetimes admit a foliation by {\deg}at hypersurfaces. Such foliations have explicitly been constructed for some spacetimes, using different approaches, but none of them have proved or even discussed the uniqueness of these foliations. The issue of uniqueness becomes more important due to suitability of {\deg}at foliations for studying black hole physics. Here {\deg}at spherically symmetric spacelike hy- persurfaces are obtained by a direct method. It is found that spherically symmetric static spacetimes admit {\deg}at spherically symmetric hypersurfaces, and that these hypersurfaces are unique up to translation under the time- like Killing vector. This result guarantees the uniqueness of {\deg}at spherically symmetric foliations for such spacetimes.Comment: 10 page

Applying the extended molecule approach to correlated electron transport: important insight from model calculations

Theoretical approaches of electronic transport in correlated molecules usually consider an extended molecule, which includes, in addition to the molecule itself, parts of electrodes. In the case where electron correlations remain confined within the molecule, and the extended molecule is sufficiently large, the current can be expressed by means of Laudauer-type formulae. Electron correlations are embodied into the retarded Green function of a sufficiently large but isolated extended molecule, which represents the key quantity that can be accurately determined by means of ab initio quantum chemical calculations. To exemplify these ideas, we present and analyze numerical results obtained within full CI calculations for an extended molecule described by the interacting resonant level model. Based on them, we argue that for organic electrodes the transport properties can be reliably computed, because the extended molecule can be chosen sufficiently small to be tackled within accurate ab initio methods. For metallic electrodes, larger extended molecules have to be considered in general, but a (semi-)quantitative description of the transport should still be possible particularly in the typical cases where electron transport proceeds by off-resonant tunneling. Our numerical results also demonstrate that, contrary to the usual claim, the ratio between the characteristic Coulomb strength and the level width due to molecule-electrode coupling is not the only quantity needed to assess whether electron correlation effects are strong or weak

Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets

The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS.IR6 collimator forms part of the TCDQ system. The requirement to place the jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed

Note and Comment

The Effect of the Carmack Amendment to the Hepburn Act Upon Limitation by Common Carrier of the Amount of their Liability - Two cases, decided by the Supreme Court of the United States on March 10, 1913, may be considered together. They are developments of the cases reviewed in II MICH. L. Rev. 460. Plaintiff shipped two boxes and a barrel of \u27household goods under an agreement that the goods, in case of loss, should be valued at $5 per hundred-weight. One box, weighing not over 200 pounds and actually worth$75, was lost. The Supreme Court of Arkansas affirmed a judgment against the carrier for the full value. On error the Supreme Court of the United States reversed and remanded the case for further proceedings. In the other oase the plaintiff shipped four bulls and thirteen cows, show cattle, worth $10,640. The finding of the Texas Court of Civil Appeals, was reversed on the ground that the recovery should have been limited to$30 for each bull and $20 for each cow

Hypervelocity Impact Effect of Molecules from Enceladus’ Plume and Titan’s Upper Atmosphere on NASA’s Cassini Spectrometer from Reactive Dynamics Simulation

The NASA/ESA Cassini probe of Saturn analyzed the molecular composition of plumes emanating from one of its moons, Enceladus, and the upper atmosphere of another, Titan. However, interpretation of this data is complicated by the hypervelocity (HV) flybys of up to ∼18  km/sec that cause substantial molecular fragmentation. To interpret this data we use quantum mechanical based reactive force fields to simulate the HV impact of various molecular species and ice clathrates on oxidized titanium surfaces mimicking those in Cassini’s neutral and ion mass spectrometer (INMS). The predicted velocity dependent fragmentation patterns and composition mixing ratios agree with INMS data providing the means for identifying the molecules in the plume. We used our simulations to predict the surface damage from the HV impacts on the INMS interior walls, which we suggest acts as a titanium sublimation pump that could alter the instrument’s readings. These results show how the theory can identify chemical events from hypervelocity impacts in space plumes and atmospheres, providing in turn clues to the internal structure of the corresponding sources (e.g., Enceladus). This may be valuable in steering modifications in future missions

Self-assembly of carbon nanotubes into two-dimensional geometries using DNA origami templates

A central challenge in nanotechnology is the parallel fabrication of complex geometries for nanodevices. Here we report a general method for arranging single-walled carbon nanotubes in two dimensions using DNA origami—a technique in which a long single strand of DNA is folded into a predetermined shape. We synthesize rectangular origami templates (~75 nm × 95 nm) that display two lines of single-stranded DNA ‘hooks’ in a cross pattern with ~6 nm resolution. The perpendicular lines of hooks serve as sequence-specific binding sites for two types of nanotubes, each functionalized non-covalently with a distinct DNA linker molecule. The hook-binding domain of each linker is protected to ensure efficient hybridization. When origami templates and DNA-functionalized nanotubes are mixed, strand displacement-mediated deprotection and binding aligns the nanotubes into cross-junctions. Of several cross-junctions synthesized by this method, one demonstrated stable field-effect transistor-like behaviour. In such organizations of electronic components, DNA origami serves as a programmable nanobreadboard; thus, DNA origami may allow the rapid prototyping of complex nanotube-based structures

The digital divide and ICT learning in rural communities:examples of good practice service delivery

This article aims to gain a greater understanding of relevant and successful methods of stimulating an ICT culture and skills development in rural areas. The paper distils good practice activities, utilizing criteria derived from a review of the rural dimensions of ICT learning, from a range of relevant initiatives and programmes. These good practice activities cover: community resource centres providing opportunities for ‘tasting’ ICTs; video games and Internet Cafe´s as tools removing ‘entry barriers’; emphasis on ‘user management’ as a means of creating ownership; service delivery beyond fixed locations; use of ICT capacities in the delivery of general services; and selected use of financial support

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO_2, CO, and H^+

The preparation and characterization of a series of isostructural cobalt complexes Co(t-Bu)_2(P^EPy^EP)(t-Bu)_2(CH_3CN)_2]-[BF_4]_2 (Py = pyridine, E = CH_2, NH, O, and X = BF_4 (1a-c)) and the corresponding one-electron reduced analogues Co(t-Bu)_2P^EPy^EP(t-Bu)_2(CH_3CN)_2][BF_4]_2 (2a-c) are reported. The reactivity of the reduced cobalt complexes with CO_2, CO, and H^+ to generate intermediates in a CO_2 to CO and H_2O reduction cycle are described. The reduction of 1a-c and subsequent reactivity with CO_2 was investigated by cyclic voltammetry, and for 1a also by infrared spectroelectrochemistry. The corresponding CO complexes of (2a-c) were prepared, and the Co-CO bond strengths were characterized by IR spectroscopy. Quantum mechanical methods (B3LYP-d3 with solvation) were used to characterize the competitive reactivity of the reduced cobalt centers with H^+ versus CO_2. By investigating a series of isostructural complexes, correlations in reactivity with ligand electron withdrawing effects are made

A method to detect single-nucleotide polymorphisms accounting for a linkage signal using covariate-based affected relative pair linkage analysis

We evaluate an approach to detect single-nucleotide polymorphisms (SNPs) that account for a linkage signal with covariate-based affected relative pair linkage analysis in a conditional-logistic model framework using all 200 replicates of the Genetic Analysis Workshop 17 family data set. We begin by combining the multiple known covariate values into a single variable, a propensity score. We also use each SNP as a covariate, using an additive coding based on the number of minor alleles. We evaluate the distribution of the difference between LOD scores with the propensity score covariate only and LOD scores with the propensity score covariate and a SNP covariate. The inclusion of causal SNPs in causal genes increases LOD scores more than the inclusion of noncausal SNPs either within causal genes or outside causal genes. We compare the results from this method to results from a family-based association analysis and conclude that it is possible to identify SNPs that account for the linkage signals from genes using a SNP-covariate-based affected relative pair linkage approach