Comment on the use of GOES solar proton data and spectra in solar proton dose calculations.

There is a need to understand the calibration and response of the GOES solar particle detectors since the GOES data are being used to evaluate high energy solar particle events. We share some of our experience in utilizing these data in the analysis of solar particle ground-level events (GLEs). For the 29 September 1989 event, we have evaluated the solar proton and alpha particle spectral characteristics throughout the event. The results show that the solar cosmic ray spectrum is extremely hard at low energies with the magnitude of the slope increasing with increasing energy and with time.     

Polyhomologation: Synthesis of Novel Polymethylene Architectures by a Living Polymerization of Dimethylsulfoxonium Methylide

Not conventional polymerization of ethylene, but rather the title reaction has allowed access to the ω-functionalized tertiary polymethylene alcohols 1 . The ylide CH₂SOMe₂ is the methylene source in this living polymerization, and the chain length can be set by the initial ratio of ylide to organoborane.     

Vertically aligned Ni/NiO nanocomposites with abundant oxygen deficient hetero-interfaces for enhanced overall water splitting

The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water electrolysis and the elucidation of reaction mechanisms.In this work,we report the synthesis of well-controlled vertically aligned Ni/NiO nanocomposites consisting of Ni nanoclusters embedded in NiO,which result in highly efficient electrocatalysts for overall water splitting.We show that such a high catalytic efficiency toward both th...     

Cp2Fe(PR2)2PdCl2 (R = i-Pr, t-Bu) complexes as air-stable catalysts for challenging Suzuki coupling reactions

[reaction: see text] The use of Cp(2)Fe(PR(2))(2)PdCl(2) (R = i-Pr and t-Bu) in Suzuki coupling reactions were illustrated using a high throughput screening approach. The di-tbpfPdCl(2) catalyst was shown to be the more active catalyst for unactivated and sterically challenging aryl chlorides. Comparison studies using the commercial catalysts dppfPdCl(2), (Ph(3)P)(2)PdCl(2), (Cy(3)P)(2)PdCl(2), DPEPhosPdCl(2), dppbPdCl(2), dppePdCl(2), Pd(t-Bu(3)P)(2), and [Pd(mu-Br)(t-Bu(3)P)](2) were also done for selected cases to demonstrate the superior activities of di-tbpfPdCl(2) and di-isoppfPdCl(2).     

An internal doping method for the preparation of transparent hybrid xerogels containing nano-sized iron particles

Sol-gel copolymerization of iron tricarbonyl-2-(triisopropoxysilyl)-1,3-butadiene with 1,6-bistriethoxysilylhexane and 1,4-bistriethoxysilylbenzene followed by drying produced bridged polysilsesquioxane xerogels. These porous, transparent hybrid materials containing the iron metal precursor were irradiated (UV) and heated under vacuum resulting in the deposition of nano-sized iron particles doped in the xerogels. EDAX and electron diffraction techniques were used to characterize the iron phases. The TEM images of these doped xerogels provided additional information regarding the domain size of the iron phase.Using a combination of external doping of Cd²⁺ and S^2– ions and internal doping of Fe°, mixed Fe/CdS phases were prepared within the porous bridged polysilsesquioxane xerogels. The resulting doped xerogels were found to have retained their porous morphology.     

Convergence to stable laws for a class of multidimensional stochastic recursions

We consider a Markov chain ${\{X_n\}_{n=0}^\infty}$ on ${\mathbb R^d}$ defined by the stochastic recursion X _n  = M _n X _n-1 + Q _n , where (Q _n , M _n ) are i.i.d. random variables taking values in the affine group ${A(\mathbb R^d)=\mathbb R^d\rtimes {\rm GL}(\mathbb R^d)}$ . Assume that M _n takes values in the group of similarities of ${\mathbb R^d}$ , and the Markov chain has a unique stationary measure ν, which has unbounded support. We denote by |M _n | the expansion coefficient of M _n and we assume ${\mathbb E [|M|^\alpha]=1}$ for some positive α. We show that the partial sums ${S_n=\sum_{k=0}^n X_k}$ , properly normalized, converge to a normal law (α ≥ 2) or to an infinitely divisible law, which is stable in a natural sense (α < 2). These laws are fully nondegenerate, if ν is not supported on an affine hyperplane. Under an aperiodicity hypothesis, we prove also a local limit theorem for the sums S _n . If α ≤ 2, proofs are based on the homogeneity at infinity of ν and on a detailed spectral analysis of a family of Fourier operators P _v considered as perturbations of the transition operator P of the chain {X _n }. The characteristic function of the limit law has a simple expression in terms of moments of ν (α > 2) or of the tails of ν and of stationary measure for an associated Markov operator (α ≤ 2). We extend the results to the situation where M _n is a random generalized similarity.     

On the relative migratory aptitudes of carbon and heteroatoms in borate complexes. A surprising alpha-thia effect

Dimethylsulfoxonium methylide reacts with dicyclohexyl alpha-thiophenylmethyl)methylborane via 1,2-alkyl migration and alkyldithiaborolane via 1,2-sulfur migration.     

Improved theoretical description of protein folding kinetics from rotations in the phase space of relevant order parameters

A method is introduced to construct a better approximation for the reaction coordinate for protein folding from known order parameters. The folding of a two-state off-lattice alpha helical Go-type protein is studied using molecular dynamics simulations. Folding times are computed directly from simulation, as well as theoretically using an equation derived by considering Brownian-type dynamics for the putative reaction coordinate. Theoretical estimates of the folding time using the number of native contacts (Qn) as a reaction coordinate were seen to differ quite significantly from the true folding time of the protein. By considering the properties of the bimodal free energy surface of this protein as a function of Qn and another relevant coordinate for folding Q (the total number of contacts), we show that by introducing a rotation in the phase space of the order parameters Q and Qn, we can construct a new reaction coordinate q that leads to a fivefold improvement in the estimate of the folding rate. This new coordinate q, resulting from the rotation, lies along the line connecting the unfolded and folded ensemble minima of the free energy map plotted as a function of the original order parameters Q and Qn. Possible reasons for the remaining discrepancy between the folding time computed theoretically and from folding simulations are discussed.     

Tandem intramolecular Nicholas and Pauson-Khand reactions for the synthesis of tricyclic oxygen-containing heterocycles

[reaction: see text] Simple acyclic enynes can be easily converted into tricyclic ethers upon treatment with Co2(CO)8 followed by Nicholas and Pauson-Khand reactions. Tricyclic [5,8,5]- and [5,7,5]-systems can be prepared in high overall yields in only seven synthetic steps.