Stereoselective total synthesis of dihydrocorynantheol

[reaction: see text] A stereoselective synthesis of the indole alkaloid dihydrocorynantheol (1) from indole-3-acetic acid has been achieved by a sequence involving 9 as a key intermediate. The synthesis of the unsaturated lactam ring in 9 highlights a series of catalytic organometallic reactions featuring two ring-closing metatheses and a zirconocene-catalyzed carbomagnesation. Since no protecting groups were used, the present synthesis of 1 is exceedingly concise, consisting of only eight distinct operations.     

Complexation of small molecules by open-ended resorcarene hosts

[structure: see text] Sterically hindered tetraaminomethylated resorcarenes form inclusion complexes in CDCl(3) with acetonitrile and acetaldehyde, which are kinetically stable on the NMR time scale at 233 K.     

Dialkylzinc-assisted alkynylation of nitrones

[reaction: see text]. Reaction of nitrones with terminal alkynes takes place readily in the presence of a substoichiometric amount of diethylzinc in toluene, affording N-propargyl-hydroxylamines in excellent yields and purity.     

Rigid tetranitroresorcinarenes

[reaction: see text]. o-alkylation of C2V-symmetrical resorcinarene tetraesters 2 with 2 equiv of 1,3-difluoro-4,6-dinitrobenzene readily affords conformationally rigid octanitro resorcinarene 3, which is a potential scaffold for the design of supramolecular structures.     

Simulation of indentation fracture in crystalline materials using mesoscale self-assembly

A new physical model based on mesoscale self-assembly is developed to simulate indentation fracture in crystalline materials. Millimeter-scale hexagonal objects exhibiting atom-like potential functions were designed and allowed to self-assemble into two-dimensional (2D) aggregates at the interface between water and perfluorodecalin. Indentation experiments were performed on these aggregates, and the stresses and strains involved in these processes were evaluated. The stress field in the aggregates was analyzed theoretically using the 2D elastic Hertz solution. Comparison of the experimental results with theoretical analysis revealed that fracture develops in regions subjected to high shear stress and some, albeit low, tensile stress. The potential for the broader application of the model is illustrated using indentation of assemblies with point defects and adatoms introduced at predetermined locations, and using a two-phase aggregate simulating a compliant film on a stiff substrate.     

Method of Gaussian equivalent representation: a new technique for reducing the sign problem of functional integral methods

We report on the specific features of the sign problem in the classical auxiliary field methodology and the strategies employed for its alleviation. In particular, we focus on a new technique based on the method of Gaussian equivalent representation of Efimov and Nogovitsin [Physica (Amsterdam) 234A, 506 (1996)]] with which we could ameliorate the convergence properties significantly. We believe that this technique can also provide an interesting possibility to reduce the sign problem of other methods of computer simulation based on a functional integral approach.     

Improved measurement of Vub with inclusive semileptonic B decays

We report a new measurement of the Cabibbo-Kobayashi-Maskawa parameter Vub made with a sample of 9.7 x 10(6) BB- events collected with the CLEO II detector. Using heavy quark theory, we combine the observed yield of leptons from semileptonic B decay in the end-point momentum interval 2.2-2.6 GeV/c with recent CLEO II data on B-->X(s)gamma to find Vub = (4.08+/-0.34+/-0.44+/-0.16+/-0.24)x10(-3), where the first two uncertainties are experimental and the last two are from theory.     

Conical harmonic generation in isotropic materials

A novel class of nonlinear optical processes is described in which radiation at the nth harmonic is generated through the use of a (2n+1)-order nonlinearity. Utilizing an odd-order nonlinearity, this process allows for the generation and amplification of both odd- and even-order harmonics in isotropic materials. Additionally, this process can always be phase matched in normal-dispersion materials without the use of birefringence. Experimental results are presented in which conical third-harmonic emission is generated from a sapphire sample.     

Neutrino cross sections and future observations of ultrahigh-energy cosmic rays

We show that future detectors of ultrahigh-energy cosmic-ray neutrinos will be able to measure neutrino-nucleon cross section, sigma(nu N), at energies as high as 10(11) GeV or higher. We find that the flux of upgoing charged leptons per unit surface area produced by neutrino interactions below the surface is inversely proportional to sigma(nu N). This contrasts with the rate of horizontal air showers (HAS) due to neutrino interactions in the atmosphere, which is proportional to sigma(nu N). Thus, by comparing the HAS and upgoing air shower rates, the neutrino-nucleon cross section can be inferred. Taken together, upgoing and horizontal rates ensure a healthy total event rate, regardless of the value of sigma(nu N).     

Correction of systematic errors in the fabrication of fiber Bragg gratings

We suggest a novel method for significant improvement of fiber Bragg grating (FBG) spectral characteristics based on compensation of repeatable errors during the grating writing process. The method is based on an open loop scheme in which a test grating is written first and then a corrected design is obtained and implemented by writing another (compensated) grating. The results are presented for a FBG dispersion compensator.