Characterization of Molecular Weight Distributions by the Standard Deviation

The standard deviation [sgrave] is known to be an absolute measure of Gaussian (G) distributions, because it (or multiples of it) always determines a constant fraction of the material. However, this is not true for distribution functions other than Gaussian. The weight fractions corresponding to weight standard deviations (±[sgrave]_w) of Schulz-Flory distributions depend on the polymolecularity index xw/xn, approaching a limiting value of W(x_w ± [sgrave]_w) = 86.5 for x_w/x_n →∞. The use of weight standard deviations is meaningless for generalized logarithmic normal (LN) distributions if x_w/x_n 52. The weight fractions W(X_n ± [sgrave]_n) around the number-average degree of polymerization of G and LN distributions first go through a maximum before decreasing with increasing x_w/x_n. The weight fractions W(x_n ± [sgrave]_n) decrease steadily with higher x_w/x_n.     

Total Synthesis of Nominal Gobienine A

The lichen‐derived glycoconjugate gobienine A is structurally more complex than most glycolipids isolated from higher plants by virtue of the all‐cis substituted γ‐lactone substructure embedded into its macrocyclic frame. A concise entry into this very epimerization‐prone and hence challenging structural motif is presented, which relies on an enantioselective cyanohydrin formation, an intramolecular Blaise reaction, a palladium‐catalyzed alkoxycarbonylation, and a diastereoselective hydrogenation of the tetrasubstituted alkene in the resulting butenolide. This strategy, in combination with ring‐closing olefin metathesis for the formation of the macrocyclic perimeter, allowed the proposed structure of gobienine A ( 1 ) to be formed in high overall yield. The recorded spectral data show that the structure originally attributed to gobienine A is incorrect and that it is not the epimerization‐prone ester site on the butanolide ring that is the locus of misassignment; rather, the discrepancy must be more profound.     

RP TLC Determination of the Lipophilicity of Anticancer-Active Propargyl Thioquinolines

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity of fifteen anticancer-active propargyl thioquinolines has been determined by reversed-phase thin-layer...     

A domain decomposition method on nested domains and nonmatching grids

A one directionally coupled problem on two nested domains is analyzed. The global domain and the subdomain are discretized by two triangulations that do not match on the subdomain. The connection between the two grids is established by using a stable projection operator onto the interface. An a priori error analysis is carried out and several numerical examples are given. The method is ideally suited for the case of a moving subdomain. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 374–387, 2004.     

Crystal field effects on the magnetic fluctuations in RAl2 and RNi2

Zero-field μSR spectra have been recorded for some ferromagnetic Laves phase compounds. A comparison of the temperature dependence of the exponential damping rate, λ(T), for our samples shows that λ(T) is strongly influenced by crystal field effects.     

Evaluation of the local anisotropy to exchange ratio D/J in amorphous DyxGd1−xNi

Values for the random anisotropy (D) and exchange (J) constants in amorphous Dy_xGd_1?xNi have been obtained from an analysis of the measured magnetization curves in terms of the H.P.Z. model. Within the molecular field approximation this model is suitable in high magnetic fields. In low fields, other properties, characteristic of random anisotropy systems, arise which are not taken into account in this model.     

A light neutral intermediate vector boson without large e+e−→ μ+μ− asymmetries

An effective SU(2)×U(1)×U(1)' electroweak theory is shown to permit the occurence of a pair of neutral intermediate vector bosons with masses 40 GeV?m_light?70 GeV, m^W.S._Z⁰<m_heavy?100 GeV. Neutrino neutral current interactions are shown to be the same as in the standard electroweak model, and e⁺e^?→μ⁺μ^? forward-backward asymmetries are within experimental bounds for m_light?40 GeV.