Rings, towers, cages of ZnO

Theoretical electronic structure studies on (ZnO)_n (n= 2–18, 21) have been carried out to show that the transition from an elementary ZnO molecule to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our first principles electronic structure calculations carried out within a gradient corrected density functional framework show that small Zn_nO_n (n=2–7) clusters form single, highly stable rings. Zn₃O₃ and the symmetric cage Zn₁₂O₁₂ are shown to be particularly stable clusters. Among larger clusters, the most stable are oblong cages, Zn₁₅O₁₅, Zn₁₈O₁₈, and Zn₂₁O₂₁, which are reminiscent of nanotubes.     

Boron-nitrogen macrocycles: a new generation of calix[3]arenes

The simple condensation reaction of 3,5-di-tert-butyl salicylaldehyde and 3-aminophenylboronic acid leads to a trimeric macrocyclic compound. The ability of this molecule to include small organic molecules was in a first approximation analyzed by (1)H NMR spectroscopy and X-ray crystallography.     

Multiresidue procedures for determination of triazine and organophosphorus pesticides in water by use of large-volume PTV injection in gas chromatography

Summary Two procedures, based on large-volume injection with a programmed-temperature vaporizer (PTV), have been developed for the determination of several triazine and organophosphorus pesticides. The use of PTV for injection in gas chromatography (GC) has enabled the introduction of up to 200 μL sample extract into the GC, thus increasing the sensitivity of the method. PTV injection has been combined off-line with two different microextraction procedures—liquid-liquid partition and solid-phase extraction. A simple and rapid off-line liquid-liquid microextraction procedure (5 mL water/1 mL methyltert-butyl ether) was applied to surface water samples spiked at levels between 0.01 and 5μg L⁻¹. Recoveries of the overall procedure were >80% and the precision was better than 15%. Detection limits were <30 ngL⁻¹ from 200-μL injections in GC-NPD analysis of triazines and GC-FPD analysis of organophosphorus pesticides. Off-line automated solid-phase extraction with C₁₈ cartridges has been applied to water samples (50 mL) spiked at 0.01, 0.1 and 1 μg L⁻¹. The overall procedure was satisfactory (recoveries >80% and coefficients of variation <12%) and the limits of detection ranged from 1 to 9 ng L⁻¹. Finally, several surface water samples were anlysed, and triazine herbicides were detected at concentrations of approx. 0.1–0.2 μg L⁻¹. The results were similar to those obtained by conventional solvent extraction then GC-MSD after splitless injection of 2 μL.     

INAA of Aerosol Samples in Mexico City

Total solid particles (TSP), respirable particles (RP) PM10 and 17 metallic pollutants were measured in dwellings in the Metropolitan Zone of Mexico Valley (MZMV) by gravimetry and instrumental neutron activation analysis (INAA). Monitoring was performed in Northeast, Center, Southeast and Southwest Zones in the winter and spring seasons. In general, the average concentration of contaminants (derived from industrial activities) that we have determined have increased with time. TSP and RP PM10 are often above the US and Mexican norms.     

Estimates on the Distribution of the Condition Number of Singular Matrices

We exhibit some new techniques to study volumes of tubes about algebraic varieties in complex projective spaces. We prove the existence of relations between volumes and Intersection Theory in the presence of singularities. In particular, we can exhibit an average Bezout Equality for equidimensional varieties. We also state an upper bound for the volume of a tube about a projective variety. As a main outcome, we prove an upper bound estimate for the volume of the intersection of a tube with an equidimensional projective algebraic variety. We apply these techniques to exhibit upper bounds for the probability distribution of the generalized condition number of singular complex matrices.     

Cyclic Amino(Ylide) Silylene: A Stable Heterocyclic Silylene with Strongly Electron‐Donating Character

An isolable heterocyclic silylene ( 4 ) with two different π‐donating substituents, namely a classical amino group and a more electropositive and stronger carbon‐based π‐donating phosphonium ylide, was synthesized and fully characterized. The combination of these two different π‐donating substituents confers high thermal stability and an unusual nucleophilic character on silylene 4 . Therefore, silylene 4 behaves as a strong donor ligand toward transition metals with a donating character comparable to N‐heterocyclic carbenes, in contrast to classical N‐heterocyclic silylenes, which generally present a weak donating character.     

Inactivation of influenza virus by solar radiation

Influenza virus is readily transmitted by aerosols and its inactivation in the environment could play a role in limiting the spread of influenza epidemics. Ultraviolet radiation in sunlight is the primary virucidal agent in the environment but the time that influenza virus remains infectious outside its infected host remains to be established. In this study, we calculated the expected inactivation of influenza A virus by solar ultraviolet radiation in several cities of the world during different times of the year. The inactivation rates reported here indicate that influenza A virions should remain infectious after release from the host for several days during the winter "flu season" in many temperate-zone cities, with continued risk for reaerosolization and human infection. The correlation between low and high solar virucidal radiation and high and low disease prevalence, respectively, suggest that inactivation of viruses in the environment by solar UV radiation plays a role in the seasonal occurrence of influenza pandemics.     

A characterization of quintic helices

A polynomial curve of degree 5, α,$\alpha ,$ is a helix if and only if both ∥α^′∥$\parallel {\alpha }^{\prime }\parallel$ and ∥α^′∧α^″∥$\parallel {\alpha }^{\prime }\wedge {\alpha }^{″}\parallel$ are polynomial functions.     

High hole mobility of 1,2-bis[4'-(diphenylamino)biphenyl-4-yl]-1,2-diphenylethene in field effect transistor

Triphenylamine-functionalized tetraphenylethene shows aggregation-induced emission feature with unity solid-state fluorescence efficiency. Its amorphous film can function in a p-type FET device with field effect mobility up to 2.6 × 10(-3) cm(2)/Vs.     

Some Results of Backward Itô Formula

Abstract

We use the notion of backward integration, with respect to a general Lévy process, to treat, in a simpler and unifying way, various classical topics as: Girsanov theorem, first order partial differential equations, the Liouville (or Lyapunov) equations and the stochastic characteristic method.