Observation of J/psi-->3gamma

We report the first observation of the decay J/psi-->3gamma. The signal has a statistical significance of 6sigma and corresponds to a branching fraction of B(J/psi-->3gamma)=(1.2+/-0.3+/-0.2)x10;{-5}, in which the errors are statistical and systematic, respectively. The measurement uses psi(2S)-->pi;{+}pi;{-}J/psi events acquired with the CLEO-c detector operating at the CESR e;{+}e;{-} collider.     

Rapid self-assembly of core-shell organosilicon microcapsules within a microfluidic device

The preparation of hierarchically structured organosilicon microcapsules from commercially available starting materials is described. Using a microfluidic device, an emulsion of dichlorodiphenylsilane is formed in a continuous phase of aqueous glycerol. The silane droplets undergo hydrolysis, condensation, and crystallization within minutes to form self-assembled, core-shell microcapsules. The microparticles have been characterized with light and electron microscopy, nuclear magnetic resonance spectroscopy (NMR), diffusion-ordered NMR spectroscopy (DOSY), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). The characterization data show that the microcapsule walls consist of amorphous, oligomeric poly(diphenylsiloxane) surrounded by a spiny layer of crystalline diphenylsilanediol. Glycerol is occluded within the wall material but is not covalently bound to the silicon components. Glycerol is a crucial element for producing low-dispersity microcapsules with well-ordered surface spines, as the use of methyl cellulose as viscomodifier yields amorphous surfaces.     

Network Forming Fluids: Yukawa Square-Well <Emphasis Type="Italic">m</Emphasis>-Point Model

Thermal and connectivity properties of the Yukawa square-well m-point (YSWmP) model of the network forming fluid are studied using solution of the multidensity Ornstein-Zernike and connectedness Ornstein-Zernike equations supplemented by the associative mean spherical approximation (AMSA). The model is represented by the multicomponent mixture of Yukawa hard spheres with m_s^am_{s}^{a} square-well sites, located on the surface of each hard sphere. To validate the accuracy of the theory, computer simulation is used to calculate the structure, thermodynamic and connectivity properties of the one-component YSW4P version of the model which is compared against corresponding theoretical data. In addition, connectivity properties of the model were studied using Flory-Stockmayer (FS) theory. Predictions of the AMSA for the thermal properties of the model (radial distribution functions (RDF), internal energy, pressure, fractions of the particles in different bonding states) are in good agreement with computer simulation predictions. Similarly, good agreement was found for the connectedness RDF (CRDF), except for the statepoints located close to the percolation threshold, where the theory fails to reproduce the long-range behavior of the CRDF. Results of both theories (AMSA and FS) for the mean cluster size are reasonably accurate only at low degrees of association. Predictions of the FS theory for the percolation lines are in a good agreement with computer simulation predictions. AMSA predictions of percolation are much less accurate, where corresponding percolation lines are located at a temperatures approximately 25% lower then those calculated using computer simulation.     

Tuning percolation speed in layer-by-layer assembled polyaniline�Cnanocellulose composite films

Polyaniline of low molecular weight (ca. 10?kDa) is combined with cellulose nanofibrils (sisal, 4?C5?nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4?nm per layer. Stable and strongly adhering films are formed with thickness-dependent coloration. Electrochemical measurements in aqueous H₂SO₄ confirm the presence of two prominent redox waves consistent with polaron and bipolaron formation processes in the polyaniline?Cnanocellulose composite. Measurements with a polyaniline?Cnanocellulose film applied across an ITO junction (a 700?nm gap produced by ion beam milling) suggest a jump in electrical conductivity at ca. 0.2?V vs. SCE and a propagation rate (or percolation speed) two orders of magnitude slower compared to that observed in pure polyaniline This effect allows tuning of the propagation rate based on the nanostructure architecture. Film thickness-dependent electrocatalysis is observed for the oxidation of hydroquinone.     

PREPARATION,DERIVATIZATION WITH TRIMETHYLSILYLDIAZOMETHANE,AND GC/MS ANALYSIS OF A “POOL” OF ALKYL METHYLPHOSPHONIC ACIDS FOR USE AS QUALITATIVE STANDARDS IN SUPPORT OF COUNTERTERRORISM AND THE CHEMICAL WEAPONS CONVENTION

There are hundreds of nerve agents in the class of alkyl methylphosphonofluoridates covered by Schedule 1 of the CWC (Chemical Weapons Convention). Hydrolysis of these sarin-like nerve agents results in an equal number of alkyl methylphosphonic acids. These alkyl methylphosphonic acids are persistent and provide good evidence of specific agent production or use. In order to support the CWC and counterterrorism activities, it is desirable to have ready access to each of these hydrolysis products for use as qualitative standards. A means for simultaneously producing multiple alkyl methylphosphonates from methylphosphonic acid and the corresponding alcohols was developed. Derivatization of these alkyl methylphosphonic acids with trimethylsilyldiazomethane yields the corresponding methyl esters which are suitable for GC/MS analysis.     

Synthesis and Characterization of Poly(Aryl Ether-Bissulfone)s

A series of poly(aryl ether-bissulfone)s were synthesized from bis-phenols, 4,4′-bis(4-chlorophenylsulfonyl)biphenyl, and 4,4′-bis(4-fluorophenylsulfonyl)biphenyl. The bishalide monomers were synthesized by reaction of 4,4′-bis(chlorosulfonyl)biphenyl with a suitable aryl halide. Potassium carbonate mediated reaction in di-methylacetamide gave high molecular weight polymers in excellent yield. The polymers are soluble in dipolar aprotic solvents. Unlike the corresponding monosulfone analogues, the poly(aryl ether-bissulfone)s exhibited poor solubility in chlorinated hydrocarbons. The glass transition temperatures of the polymers are among the highest known for poly(aryl ether)s (241-271 °C). In addition, the polymers exhibit excellent thermal stability and they produce clear, colorless tough films by solution casting or compression molding.     

Manager-worker-based model for the parallelization of quantum Monte Carlo on heterogeneous and homogeneous networks

A manager-worker-based parallelization algorithm for Quantum Monte Carlo (QMC-MW) is presented and compared with the pure iterative parallelization algorithm, which is in common use. The new manager-worker algorithm performs automatic load balancing, allowing it to perform near the theoretical maximal speed even on heterogeneous parallel computers. Furthermore, the new algorithm performs as well as the pure iterative algorithm on homogeneous parallel computers. When combined with the dynamic distributable decorrelation algorithm (DDDA) [Feldmann et al., J Comput Chem 28, 2309 (2007)], the new manager-worker algorithm allows QMC calculations to be terminated at a prespecified level of convergence rather than upon a prespecified number of steps (the common practice). This allows a guaranteed level of precision at the least cost. Additionally, we show (by both analytic derivation and experimental verification) that standard QMC implementations are not "perfectly parallel" as is often claimed.     

Carboxylation and esterification of functionalized arylcopper reagents

Functionalized arylcopper reagents have been produced in good yields at 25 degrees C from activated copper and the corresponding functionalized aryl iodides without the need of traditional organolithium or Grignard precursors. These organocopper compounds will undergo carboxylation with CO(2) to form the corresponding copper benzoates. In turn, these salts can be acidified to produce the functionalized aryl acids or treated with appropriate alkyl halides in the presence of a dipolar aprotic solvent to generate the corresponding aryl esters. This methodology permits the formation of functionalized organic acids and esters that could not be generated by the carboxylation of organomagnesium compounds.     

Identity crises and strong compactness

From a proper class of supercompact cardinals, we force and obtain a model in which the proper classes of strongly compact and strong cardinals precisely coincide. In this model, it is the case that no strongly compact cardinal is supercompact. Received: 16 December 1998 / Revised version: 29 March 1999     

Test sets for generalized matrix functions

Let G = (V,E) be a biconnected graph and let C be a cycle in G. The subgraphs of G identified with the biconnected components of the contraction of C in G are called the bridges of C. Associated with the set of bridges of a cycle C is an auxilliary graphical structure G_C called a bridge graph or an overlap graph. Such auxilliary graphs have provided important insights in classical graph theory, algorithmic graph theory, and complexity theory. In this paper, we use techniques from algorithmic combinatorics and complexity theory to derive canonical forms for cycles in bridge graphs. These canonical forms clarify the relationship between cycles in bridge graphs, the structure of the underlying graph G, and lexicographic order relations on the vertices of attachment of bridges of a cycle. The first canonical form deals with the structure of induced bridge graph cycles of length greater than three. Cycles of length three in bridge graphs are studied from a different point of view, namely that of the characterization of minimal elements in certain related posets: ordered bridge three-cycles (10 minimal elements), bridge three-cycles (5 minimal elements), bridge deletion three-cycles (infinite number, 7 classes), minor order (K ₅ K _3,3), chordal bridge three-cycles (13 minimal elements), contraction poset (5 minimal elements), cycle-minor poset (infinite number, 14 classes). These results, each giving a different insight into the structure of bridge three-cycles, follow as corollaries from the characterization of the 10 minimal elements of the ordered bridge three-cycle poset. This characterization is constructive and may be regarded as an extension of the classical Kuratowski's Theorem which follows as a corollary. Algorithms are described for constructing these various minimal elements in time O(∣E∣) or O(∣V∣) depending on the case. The first canonical form gives a constructive proof of the result that a graph is nonplanar if and only if it has a cycle C whose bridge graph G_C (alternatively, skew bridge graph) has a three-cycle. An algorithm is described that constructs this three-cycle in time O(∣E∣). This is best possible.