Klaus Halbach,Undulator Pioneer

I am indebted to Karl Brown for suggesting that I invite Klaus, who I did not know at the time, to a workshop on wiggler magnets in March 1977. I recall Karl saying to me something like, “Herman, if you want someone who knows about magnets, you should invite Klaus Halbach.” Klaus came and even made a contribution about some aspects of the design of electromagnet wigglers, the only type of wigglers that had been considered to that time. However, it was at that workshop that Klaus got his introduction to synchrotron radiation, mostly by listening to talks by Albert Hofmann and Andy Sesler, who explained the marvelous properties of undulator magnets as radiation sources. Klaus filed this information in his long-term memory banks while working on other topics, particularly the design of permanent magnet quadrupoles for proton linacs.     

Optimization for pattern classification using biased random search techniques

We demonstrate how optimization problems arise in the field of pattern classification, in particular in using piecewise-linear classification and classification based on an optimal linear separator. We motivate the need in this area for a general purpose optimization approach. We discuss ALOPEX, a biased random search approach, from the point of view of this need. While ALOPEX itself failed to fulfil our need, a newly-introduced generalization of it (iterated ALOPEX) was found to be appropriate for the optimization problems of our particular concern. We conclude the paper with a brief critical evaluation of this approach as compared to our original aims.     

C=1 conformal field theories on Riemann surfaces

We study the theory ofc=1 torus and ₂-orbifold models on general Riemann surfaces. The operator content and occurrence of multi-critical points in this class of theories is discussed. The partition functions and correlation functions of vertex operators and twist fields are calculated using the theory of double covered Riemann surfaces. It is shown that orbifold partition functions are sensitive to the Torelli group. We give an algebraic construction of the operator formulation of these nonchiral theories on higher genus surfaces. Modular transformations are naturally incorporated as canonical transformations in the Hilbert space.     

Commutator-finite orthomodular lattices

The class of orthomodular lattices which have only finitely many commutators is investigated. The following theorems are proved: contains the block-finite orthomodular lattices. Every irreducible element of is simple. Every element of is a direct product of a Boolean algebra and finitely many simple orthomodular lattices. The irreducible elements of which are modular, or are M-symmetric with at least one atom, have height two or less.     

Enzymatic polymerizations using surfactant microstructures and the preparation of polymer-ferrite composites

Applied Biochemistry and Biotechnology - Horseradish peroxidase has been used as a biocatalyst to synthesize a polymeric material from alkyl-substituted phenols. The synthesis is carried out in a...     

A novel intramolecularly stabilized nitronic acid, 2-aci-nitro-1,3-propanediol

A stable nitronic acid, 2-aci-nitro-1,3-propanediol, may be prepared from nitromethane and paraformaldehyde under fluoride ion catalysis.     

Conformational analysis of dimethylmethylphosphonate

The results of a CNDO/2 conformation analysis on dimethylmethylphosphonate are reported. Six stable conformers were found; their relative stabilities can be understood in terms of steric hindrance and gauche effect. Calculated barriers to internal rotation around P—O and O—C bonds are tabulated.     

Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes

The H₂, N₂/H₂, CO₂/H₂, N₂O/H₂, CO/H₂ and CH₄ chemical ionization mass spectra of thirteen C₈ to C₁₁ alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]⁺ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane-derived reagent system is estimated to be ～556 kJ mol^?1.     

Does ionized diacetylene have a positive proton affinity?

Singly and doubly charged C₄H₃^+/2+ ions generated upon electron ionization (EI) of the neutral precursors 1,3-butadiene, benzene, and exo-methylene cyclopropane, respectively, are examined by sector-field mass-spectrometry. Charge stripping of the mass-selected monocations affords the corresponding dications and charge exchange of the C₄H₃²⁺ dications allows for the reverse redox process. Refined analysis and additional MS/MS studies suggest that the monocations are mixtures of isomeric ions formed upon ionization, whereas only a single type of dication seems to be formed. As an average of energy-resolved measurements, a vertical ionization energy of IE_v(C₄H₃⁺)=16.5±0.4 eV is derived. In addition to the experimental work, density functional theory is used for a computational exploration of the mono- and dicationic species. The best theoretical estimates are IE_a(C₄H₃⁺)=16.33 eV and IE_v(C₄H₃⁺)=16.49 eV for the most stable isomer H₂C=C---CCH⁺. Combination of the experimental and theoretical findings leads to the conclusion that the diacetylene cation C₄H₂⁺ has indeed a positive proton affinity of PA(C₄H₂⁺)=1.50±0.42 eV.