A novel method for isolating and analyzing organic acids in biological cultures

Applied Biochemistry and Biotechnology -     

Plasmon-based nanolenses assembled on a well-defined DNA template

The controlled and reproducible synthesis of closely spaced noble metal nanoparticle groupings is an essential step toward the rational design of nanostructures for surface enhanced Raman scattering with single-molecule sensitivity. In this communication, we demonstrate the facile synthesis of 5, 8, and 18 nm gold particle groupings on a well-defined DNA template by hybridizing monoconjugated gold-DNA building blocks. The obtained nanometer interparticle gaps should yield local intensity enhancements up to 4 orders of magnitude as estimated by Generalized Mie Theory. By tuning the particle size and relative curvatures, we calculate that the maximum enhancement can be optimized and localized on a specific part of the nanostructure. These groupings act as plasmon-based nanolenses assembled on a biomolecular backbone that can be functionalized in proximity to the region of highest field.     

Incomplete block-matrix factorization iterative methods for convection-diffusion problems

Standard Galerkin finite element methods or finite difference methods for singular perturbation problems lead to strongly unsymmetric matrices, which furthermore are in general notM-matrices. Accordingly, preconditioned iterative methods such as preconditioned (generalized) conjugate gradient methods, which have turned out to be very successful for symmetric and positive definite problems, can fail to converge or require an excessive number of iterations for singular perturbation problems.This is not so much due to the asymmetry, as it is to the fact that the spectrum can have both eigenvalues with positive and negative real parts, or eigenvalues with arbitrary small positive real parts and nonnegligible imaginary parts. This will be the case for a standard Galerkin method, unless the meshparameterh is chosen excessively small. There exist other discretization methods, however, for which the corresponding bilinear form is coercive, whence its finite element matrix has only eigenvalues with positive real parts; in fact, the real parts are positive uniformly in the singular perturbation parameter.In the present paper we examine the streamline diffusion finite element method in this respect. It is found that incomplete block-matrix factorization methods, both on classical form and on an inverse-free (vectorizable) form, coupled with a general least squares conjugate gradient method, can work exceptionally well on this type of problem. The number of iterations is sometimes significantly smaller than for the corresponding almost symmetric problem where the velocity field is close to zero or the singular perturbation parameter =1.The 2 ^nd author's research was sponsored by Control Data Corporation through its PACER fellowship program.The 3 ^rd author's research was supported by the Netherlands organization for scientific research (NWO).On leave from the Institute of Mathematics, Academy of Science, 1090 Sofia, P.O. Box 373, Bulgaria.     

Molecular weight determination for 1,2,1,2-polypropadiene

By using standard bromination conditions, the insoluble 1,2,1,2-polypropadiene (formed by Ni(acac)₂ or Co(acac)_{2 or 3}, C₃H₄, (iBu)₃Al catalysts) is transformed into a soluble bromopolypropadiene. Using this technique, determination of molecular weight becomes possible. It was found that the molecular weight increases with polymerization time until a steady value is reached. As the polymer yield continues to increase when a constant molecular weight has been reached, chain transfer must occur. The molecular weight of polybromopropadiene was independent of the concentrations of the catalyst components. From experiments with crosslinked polymers and from theoretical considerations, it was deduced that the low solubility of the original 1,2,1,2-polypropadiene is due to its high crystallinity.     

Three-dimensional negative index of refraction at optical frequencies by coupling plasmonic waveguides

We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. Control of waveguide coupling yields a metamaterial consisting of a one-dimensional multilayer stack that exhibits an isotropic index of -1 at a free-space wavelength of 400?nm. The concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.     

Efficient planewise‐like preconditioners for solving 3D problems

We deal with the numerical solution of large linear systems resulting from discretizations of three‐dimensional boundary value problems. It has been shown recently that, if the use of presently available planewise pre‐conditionings is as pathological as thought by many people, except for some trivial anisotropic problems, linewise preconditionings could fairly outperform pointwise methods of approximately the same computational complexity. We propose here a zebra (or line red–black) like numbering strategy of the grid points that leads to a rate of convergence comparable to the one predicted for ideal planewise preconditionings. The keys to the success of this strategy are threefold. On the one hand, one gets rid of the, time and memory consuming, task of computing some accurate approximation to the inverse of each pivot plane matrix. On the other hand, at each PCG iteration, there is no longer a need to solve linear systems whose matrices have the same structure as a two‐dimensional boundary value problem matrix. Finally, it is well suited to parallel computations. Copyright © 1999 John Wiley & Sons, Ltd.     

Erbium as a probe of everything?

Erbium is a lanthanide ion with unique electronic and optical properties. In its trivalent state it is composed of an incompletely filled 4f inner shell and two closed outer shells. By employing these properties in specific material systems, Er can be used to probe point defects, oxygen, OH, Er, radiation defects, network structure, excitons, optical density of states, optical modes, and photonic bandstructure.     

Review and analysis of renewable feedstocks for the production of commodity chemicals

Applied Biochemistry and Biotechnology - Several biomass feedstocks were analyzed for their suitability in chemicals production by industry. Feedstocks included dedicated feedstock crops,...     

An experimental investigation of a wall jet in a torus

Results of an experimental investigation of the velocity profile of a turbulent gas injected in a toroidal configuration are presented. The measurements surprisingly show that it is possible to describe the radial distribution of the azimuthal velocity in terms of a plane wall jet discharging in an external stream. The growth of the inner boundary layer, the width of the jet, and the velocity profile are in accordance with the known experimental data on this subject. A fundamentally different relation has been deduced for the decay of the maximum velocity. Up to now Sigalla's formula \(U_m /U_j \propto \sqrt {a/x}\) is generally accepted. Our data based on an essentially extended range of x/a, correlate with the exponential relation $$U_m /U_j = exp\left[ { - 154(Re_x )^{ - 0.777} \frac{x}{a}} \right].$$