Dehydrative glycosylation of tri-O-benzylated 1-hydroxyribofuranose catalyzed by a copper(II) complex

A phosphine/Cu(II) complex catalyzes the dehydrative glycosylation of tri-O-benzylated 1-hydroxyribofuranose to give the ribofuranoside with high stereoselectivity.     

Combined intra-intermolecular criss-cross cycloaddition of a new fluorinated unsymmetrical allenylazine with alkynes

The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.0^4,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis.     

Orbital formal normal forms for general Bogdanov-Takens singularity

We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence.     

Stage-specific and age-dependent profiles of zinc, copper, manganese, and selenium in rat seminiferous tubules

Stage-specific and age-dependent profiles of zinc, copper, manganese, and selenium in testis were examined in Wistar rats by both inductively coupled argon plasma-mass spectrometry (ICP-MS) with a microdissection technique and in situ elemental imaging of micro-PIXE analysis. The young adult animals (10 weeks old) contained higher levels of zinc and manganese in the seminiferous tubules at stages VII-VIII than stages XI through VI and IX-X and the levels were higher than those of the immature and old animals. Copper and selenium levels at stages VII-VIII of the young adult animals were also higher than those of the immature and old animals. In stages VII and VIII, zinc was higher in the central area of the seminiferous epithelium, where spermatozoa were localized, demonstrating a cell-specific property. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative studies of femtosecond to microsecond laser pulses on selective pigmented cell injury in skin

Threshold radiant exposures for grossly apparent immediate whitening and ultrastructural alterations of melanosomes in black guinea pig skin were determined for a series of red visible laser pulses ranging from 4 x 10(-4) to 6.5 x 10(-14) s. Threshold exposures for melanosomal injury were found to be independent of pulsewidth when the pulsewidths were below the estimated thermal relaxation time of melanosomes. Threshold radiant exposures for melanosomal injury were found to increase when the pulsewidths were approximately equal to or above the thermal relaxation time of melanosomes. At longer pulse durations, fracturing of melanosomes was not observed despite the longer exposures necessary for injury. Instead, perimelanosomal vacuoles were noted. These findings are consistent with the theory of selective photothermolysis and provide evidence for the thermal initiation of melanosomal disruption.     

Asymptotic properties of computationally efficient alternative estimators for a class of multivariate normal models

Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations.     

Lyapunov-type inequalities for nonlinear systems

In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations.     

Anodic stripping coulometry with collection for absolute trace analysis of lead, using flow-through electrochemical cells with porous working electrodes

Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10^–9 to 10^–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10^–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×10⁴. One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia     

Crystal and molecular structures of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine.

The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration.