Maximum estimates for oblique derivative problems with right hand side in L p , p<n

If u is a solution of the second order elliptic differential equation Lu=f in some Lipschitz domain in ⁿ , we estimate the maximum of u in terms of some oblique derivative prescribed on the boundary of the domain and in terms of the L ^p norm of f with p<n.     

Characterization and use of a Raman liquid-core waveguide sensor using preconcentration principles

A novel Raman sensor using a liquid-core optical waveguide is reported, implementing a Teflon-AF 2400 tube filled with water. An aqueous analyte mixture of benzene, toluene and p-xylene was introduced using a 1000 μl sample loop to the liquid-core waveguide (LCW) sensor and the analytes were preconcentrated on the inside surface of the waveguide tubing. The analytes were then eluted from the waveguide using an acetonitrile-water solvent mixture injected via a 30 μl eluting solvent loop. The preconcentration factor was experimentally determined to be 14-fold, in reasonable agreement with the theoretical preconcentration factor of 33 based upon the sample volume to elution volume ratio. Raman spectra of benzene, toluene and p-xylene were obtained during elution. It was found that analytically useful Raman signals for benzene, toluene and p-xylene were obtained at 992, 1004 and 1206 cm⁻¹, respectively. The relative standard deviation of the method was 3% for three replicate measurements. The limit of detection (LOD) was determined to be 730 ppb (parts per billion by volume) for benzene, exceptional for a system that does not resort to surface enhancement or resonance Raman approaches. The Raman spectra of these test analytes were evaluated for qualitative and quantitative analysis utility.     

Determining the scope of the organolanthanide-catalyzed, sequential intramolecular amination/cyclization reaction: formation of substituted quinolizidines, indolizidines, and pyrrolizidines

The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction was determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines. A methyl group was installed at diverse positions in the substrates to determine the sense and magnitude of diastereoselection. High diastereoselectivity (>20:1) was achieved for the formation of some quinolizidines and indolizidines. The sense of relative asymmetric induction was contrary to previously studied systems, and although some questions remain, a rationalization for these results is put forward.     

An overview of some recent developments in ionization methods for mass spectrometry

An overview of some recent advances in ionization sources for mass spectrometry is presented. Limitations were set so that the overview covers ionization techniques relevant to organic and biological analysis that have appeared in the literature since the year 2000. No effort is made to be comprehensive. Rather, a broad sweep overview of author-subjective highlights among a wide variety of sources is presented. These ionization sources include electron ionization, chemical ionization, various atmospheric plasma ionization sources, laser desorption sources, sonic spray and electrospray ionization sources.     

A top down approach to protein structural studies using chemical cross-linking and Fourier transform mass spectrometry

Mass spectrometric analysis of wild-type proteins that have been covalently modified by bifunctional cross-linking reagents and then digested proteolytically can be used to obtain low-resolution distance constraints, which can be useful for protein structure determination. Limitations of this approach include time-consuming separation steps, such as the separation of internally cross-linked protein monomers from covalent dimers, and a susceptibility to artifacts due to low levels of natural and man-made peptide modifications that can be mistaken for cross-linked species. The results presented here show that when a crude cross-linked protein mixture is injected into an electrospray ionization Fourier transform mass spectrometry (ESI-FTMS) instrument, the cross-link positions can be localized by fragmentation and mass spectrometry on the 'gas-phase purified' singly internally cross-linked monomer. Our results show that reaction of ubiquitin with the homobifunctional lysine-lysine cross-linking reagent dissuccinimidyl suberate (DSS) resulted in two cross-links consistent with the known ubiquitin tertiary structure (K6-K11 and K48-K63). Because no protein or peptide chemistry steps are needed, other than the initial cross-linking, this new top down approach appears well suited for high-throughput experiments with multiple cross-linkers and reaction conditions. Published in 2002 by John Wiley & Sons, Ltd.     

Algebras Generated by Semicentral Idempotents

Let be a unital K-algebra, where K is a commutative ring with unity. An idempotent is {\it left semicentral\/} if , and is {\it SCI-generated\/} if it is generated as a K-module by left semicentral idempotents. This paper develops the basic properties of SCI-generated algebras and characterizes those that are also prime, semiprime, primitive, or subdirectly irreducible. Minimal ideals and the socle of SCI-generated algebras are investigated. Conditions are found to describe a large class of SCI-generated algebras via generalized triangular matrix representations. SCI-generated piecewise domains are characterized. Examples are given that illustrate the breadth and diversity of the class of SCI-generated algebras.     

Thermostats: Analysis and application

Gaussian isokinetic and isoenergetic deterministic thermostats are reviewed in the correct historical context with their later justification using Gauss' principle of least constraint. The Nose-Hoover thermostat for simulating the canonical ensemble is also developed. For some model systems the Lyapunov exponents satisfy the conjugate pairing rule and a Hamiltonian formulation is obtained. We prove the conjugate pairing rule for nonequilibrium systems where the force is derivable from a potential. The generalized symplectic structure and Hamiltonian formulation is discussed. The application of such thermostats to the Lorentz gas is considered in some detail. The periodic orbit expansion methods are used to calculate averages and to categorize the generic transitions in the structure of the attractor. We prove that the conductivity in the nonequilibrium Lorentz gas is non-negative. (c) 1998 American Institute of Physics.     

Formation of Ni3Fe by mechanical alloying

Ni and Fe powders in a 7525 atomic proportion were mechanically alloyed using a high-energy ball mill.⁵⁷Fe Mössbauer measurements were made to determine the reaction mechanism for alloy formation by means of analysis of the evolution of the Fe hyperfine fields during milling. After a latent period of 2 hours, the spectral area of an Fe-like component decreased monotonically with milling time, disappearing after 8 hours. It was replaced by a well-resolved Zeeman pattern with hyperfine fieldH=29.1 T and outer lines of width 0.75 mm/s which is attributed to Fe in disordered Ni₃Fe. The evolution of hyperfine fields rules out alloy formation by dissolution of Ni in the Fe matrix or of Fe in the Ni matrix, so that formation must occur by reaction of Ni and Fe at the interfaces between their grains.