Convenient synthesis of Cu3(BTC)2 encapsulated Keggin heteropolyacid nanomaterial for application in catalysis

Nanomaterial of Cu(3)(BTC)(2) (BTC = benzene tricarboxylic acid) incorporating Keggin heteropolyacid conveniently prepared at room temperature and recovered by freeze drying outperforms ultrastable Y zeolite in acid catalysed esterification reaction.     

Synthesis and Self‐Aggregation of Enantiopure and Racemic Molecular Tweezers Based on the Bicyclo[3.3.1]nonane Framework

A pair of molecular tweezers (syn‐ 4 ) that consists of quinoline and pyrazine units fused to a bicyclic framework is presented. The tweezers were synthesised both as a racemic mixture (rac‐ 4 ) and an enantiomerically pure form ((R,R,R,R)‐ 4 ) starting from either racemic or enantiomerically pure bicyclo[3.3.1]nonane‐2,6‐dione ( 3 ). Homochiral dimers were observed in the solid state for rac‐ 4 . The self‐association of both rac‐ 4 and (R,R,R,R)‐ 4 was studied in solution. A weak self‐association constant in CDCl₃ was estimated by ¹H NMR spectroscopic dilution titration experiments in both cases, following several proton resonances. For this purpose, a general normalisation model for the accurate determination of association constants from multiple datasets was developed. In contrast to the solid state, no diastereomeric discrimination was observed for rac‐ 4 in solution.     

Topological solitons in three-band superconductors with broken time reversal symmetry

We show that three-band superconductors with broken time reversal symmetry allow magnetic flux-carrying stable topological solitons. They can be induced by fluctuations or quenching the system through a phase transition. It can provide an experimental signature of the time reversal symmetry breakdown.     

Vocal Fold Vibration and Phonation Start in Aspirated, Unaspirated, and Staccato Onset

Objectives/Hypotheses

Singers learn to produce well-controlled tone onsets by accurate synchronization of glottal adduction and buildup of subglottal pressure. Spectrographic analyses have shown that the higher spectrum partials are present also at the vowel onset in classically trained singers’ performances. Such partials are produced by a sharp discontinuity in the waveform of the transglottal airflow, presumably produced by vocal fold collision.

Study Design

After hearing a prompt series of a triad pattern, six singer subjects sang the same triad pattern on the vowel /i/ (1) preceded by an aspirated /p/, (2) preceded by an unaspirated /p/, and (3) without any preceding consonant in staccato.

Methods

Using high-speed imaging we examined the initiation of vocal fold vibration in aspirated and unaspirated productions of the consonant /p/ as well as in the staccato tones.

Results

The number vibrations failing to produce vocal fold collision were significantly higher in the aspirated /p/ than in the unaspirated /p/ and in the staccato tones. High frequency ripple in the audio waveform was significantly delayed in the aspirated /p/.

Conclusions

Initiation of vocal fold collision and the appearance of high-frequency ripple in the vowel /i/ are slightly delayed in aspirated productions of a preceding consonant /p/.     

Effects of MnO<Subscript>2</Subscript> nano-particles on the conductivity of PMMA-PEO-LiClO<Subscript>4</Subscript>-EC polymer electrolytes

Li-ion rechargeable batteries based on polymer electrolytes are of great interest for solid state electrochemical devices nowadays. Many studies have been carried out to improve the ionic conductivity of polymer electrolytes, which include polymer blending, incorporating plasticizers and filler additives in the electrolyte systems. This paper describes the effects of incorporating nano-sized MnO₂ filler on the ionic conductivity enhancement of a plasticized polymer blend PMMA–PEO–LiClO₄–EC electrolyte system. The maximum conductivity achieved is within the range of 10⁻³ S cm⁻¹ by optimizing the composition of the polymers, salts, plasticizer, and filler. The temperature dependence of the polymer conductivity obeys the VTF relationship. DSC and XRD studies are carried out to clarify the complex formation between the polymers, salts, and plasticizer.     

Depth-profiling the composition of bimetallic nanoparticles using medium energy ion scattering

The near monolayer depth resolution of medium energy ion scattering is utilized to develop a probe of the depth dependent composition of bimetallic nanoparticles supported on planar oxide supports. The approach fits spectra of scattered ion intensity versus ion energy at well-defined scattering angles taking into account the asymmetric line shape in such spectra and also the depth dependent loss processes encountered by incident ions as they pass through the bimetallic particles.     

Elemental composition of fine particulate matter (PM2.5) in Skopje,FYR of Macedonia

Aerosol samples were collected at an urban background site in Skopje, Former Yugoslavic Republic of Macedonia, during four measurement campaigns from December 2006 to October 2007. An impactor was used to collect particulate matter (PM_2.5) aerosol particles and the samples were analyzed for the concentrations of particulate mass, black carbon (BC), and 17 elements. The 12‐h average PM_2.5 concentrations varied in the range 10–140 µg m^?3 with the highest concentrations measured during wintertime pollution episodes and during the summer period. Pair‐wise correlations and crustal enrichment were studied and the data set was analyzed by factor analysis and positive matrix factorization. Major aerosol components were identified as mineral dust (main observed tracers Si, K, Ca, Ti, Fe, Sr, and Rb), combustion (BC, S, K, V, and Ni), traffic‐related aerosol (Pb and Zn), and secondary sulfate combined with mineral dust. Combustion sources dominated during wintertime and were likely due to heavy oil combustion, biomass burning, and other industrial activities within the city area. Mineral dust was observed throughout the year, but the concentrations peaked during the unusually hot and dry summer of 2007. It is concluded that Skopje suffers from serious air pollution due to central and residential heating, the transport sector, and industrial activities within the city, and contributions from mineral dust increase the PM_2.5 concentrations under dry periods. Topography and meteorological conditions aggravate the problems and make the air quality comparable with the conditions in other highly polluted cities in Southern Europe and worldwide. Copyright © 2011 John Wiley & Sons, Ltd.     

Coloring graphs from random lists of fixed size

Let G = G(n) be a graph on n vertices with maximum degree bounded by some absolute constant Δ. Assign to each vertex v of G a list L(v) of colors by choosing each list uniformly at random from all k‐subsets of a color set of size . Such a list assignment is called a random ‐list assignment. In this paper, we are interested in determining the asymptotic probability (as ) of the existence of a proper coloring ? of G, such that for every vertex v of G. We show, for all fixed k and growing n, that if , then the probability that G has such a proper coloring tends to 1 as . A similar result for complete graphs is also obtained: if and L is a random ‐list assignment for the complete graph K_n on n vertices, then the probability that K_n has a proper coloring with colors from the random lists tends to 1 as .Copyright © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 44, 317‐327, 2014     

Extreme value copula estimation based on block maxima of a multivariate stationary time series

The core of the classical block maxima method consists of fitting an extreme value distribution to a sample of maxima over blocks extracted from an underlying series. In asymptotic theory, it is usually postulated that the block maxima are an independent random sample of an extreme value distribution. In practice however, block sizes are finite, so that the extreme value postulate will only hold approximately. A more accurate asymptotic framework is that of a triangular array of block maxima, the block size depending on the size of the underlying sample in such a way that both the block size and the number of blocks within that sample tend to infinity. The copula of the vector of componentwise maxima in a block is assumed to converge to a limit, which, under mild conditions, is then necessarily an extreme value copula. Under this setting and for absolutely regular stationary sequences, the empirical copula of the sample of vectors of block maxima is shown to be a consistent and asymptotically normal estimator for the limiting extreme value copula. Moreover, the empirical copula serves as a basis for rank-based, nonparametric estimation of the Pickands dependence function of the extreme value copula. The results are illustrated by theoretical examples and a Monte Carlo simulation study.