A fast algorithm for the Cyber 205 to simulate the 3D Ising model

We describe a computer program that performs the Metropolis algorithm for the 3D Ising model at a peak speed of 98 million spin updates per second on a 2-pipe CDC Cyber 205. This speed is achieved using the special vector capabilities of the Cyber 205 and multispin coding techniques.     

e + e −→W − e + v and non-standard gauge couplings: Another look

The cross section for singleW ^? production ine ⁺ e ^? collisions is exactly computed for an arbitraryW magnetic moment. It is found that this process may give a first look at theW Wγ vertex just below the twoW threshold. A detailed comparison is made with previous calculations that used the equivalent photon approximation.     

The vacuum of supersymmetric SU(3) × SU(2) × U(1)

We show that in supersymmetric SU(3) × SU(2) × U(1) it is possible to break SU(2) with an Higgs singlet and at the same time to avoid vacuum expectation values for s-fermions. With rather simple constraints we obtain important restrictions on the values of the model parameters.     

Chemometrics in analytical chemistry—part II: modeling,validation, and applications

Analytical and Bioanalytical Chemistry - The contribution of chemometrics to important stages throughout the entire analytical process such as experimental design, sampling, and explorative data...     

Mercury determination by CV-AAS in wastewater and sewage sludge from a stabilization pond system

The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110 degrees C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 microgl(-1) have been found at the entrance of the system and 0.74 +/- 0.0 microgl(-1) at the exit, while in sludge the results were between 0.29 +/- 0.12 microgkg(-1) in the facultative pond and 0.04 +/- 0.02 microgkg(-1) in the second maturation pond (exit).     

Oxidation ofn-butane and propene on exhydrotalcite Mg, Al, Fe mixed oxides

Oxidative dehydrogenation ofn-butane and propene has been studied on six Mg−Al−Fe oxide catalysts prepared by thermal decomposition of layered double hydroxides with a hydrotalcite-like structure, possessing Mg²⁺ and Al³⁺ ions in the brucite-like layers, and hexacyanoferrate in the interlayers. In all cases, CO₂ and H₂O are formed, together with minor amounts of ethylene and methane. On the solids prepared from hexacyanoferrate(II), formation of benzene is also observed.     

Preliminary study of nickel,ferric, lead,and copper oxinates in reactions of reextraction through the exchange of ligands: The use of chloroform solutions of the copper oxinate in the spectrophotometric determination of cyanide

In this paper a systematic study of four metallic oxinates (ferric, nickel, lead, and copper complexes) is carried out, determining some characteristics of the organic solutions of these complexes in reactions of reextraction by the exchange of ligands. These reactions are based on the decoloration produced in organic solutions of colored complexes when they are mixed with aqueous solutions of anions. The study of some characteristics and the qualitative tests shows that only the copper oxinate is interesting for quantitative purposes because its solutions in chloroform are decolored at very low concentrations of oxalate ethylenediamine tetraacetate, sulfide, and cyanide.The application of this study to the indirect spectrophotometric determination of cyanide is carried out. The decoloration varies linearly with the cyanide concentration between 10 and 50 ppm for a phase volume ratio 1:1. Finally, the error, reproducibility of the method, nature of the exchange reaction, and interferences of foreign ions are also established.     

The nature of the indenyl effect

The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.     

Preparation,structural, and spectroscopic study of tetrakis(4-methylpyridinium) β-octamolybdate

The title compound, (C₆H₈N)₄[Mo₈O₂₆], has been prepared and its crystal structure determined by X-ray crystallography. The compound is triclinic,P¯1,Z=1 witha=10.167(1),b=10.745(1),c=10.027(8) Å,=85.05(1),=106.73(3), =107.75(1)°,V=999.1(7) ų,F(000)=748,D _x=2.59 andD _o=2.61(1) Mg/m³. The [Mo₈O₂₆]^4– anion shows slight differences in several bond lengths and angles when compared with other related octamolybdates. The planar cations are connected to the polyanions through bifurcated hydrogen bonds. The MoO₆ octahedra are distorted and the distortion has been evaluated using three different equations. The spectroscopic study shows that the cations are protonated and the polyanion presents the well-known infrared spectrum for octamolybdates.     

Elemental composition of lichens at Nahuel Huapi National Park,Patagonia, Argentina

Five species of epiphytic lichens were sampled from urban and periurban areas of Bariloche, a non industrial city located on the East side of the Nahuel Huapi National Park, North-Western Patagonia, Argentina, and from pristine areas of the Park. Each individual lichen was analyzed using Instrumental Neutron Activation Analysis. The results of the analysis showed high concentrations of lithophile elements, with very good correlations among them. The relative concentration of these elements in all lichen species is in good agreement with the elemental composition of sediments collected in the Park. Elemental concentrations which are not related to detritical inputs are also presented.