Strong Connectivity of Polyhedral Complexes

A classical theorem of Robbins states that the edges of a graph may be oriented, in such a way that an oriented path exists between any source and destination, if and only if the graph is both connected and two-connected (it cannot be disconnected by the removal of an edge). In this paper, an algebraic version of Robbins' result becomes a lemma on Hilbert bases for free abelian groups, which is then applied to generalize his theorem to higher dimensional complexes. An application to cycle bases for graphs is given, and various examples are presented.     

An acyclic extension of the braid group

We relate Artin's braid groupB _℞=lim_→B_n to a certain groupF′ ofpl-homeomorphisms of the interval. Namely, there exists a short exact sequence 1→B _∞→A→F′→1 whereH _kA=0,k≥1.     

NAA characterization of the new Bovine Liver SRM

The National Institute of Standards and Technology (NIST) is preparing a freeze-dried powdered bovine liver tissue Standard Reference Material (SRM) to replace SRM 1577b Bovine Liver as the stock of this material was exhausted during 2006. Like the original SRM 1577 issued in 1972, this renewal focuses on the key elements for diagnostic, nutritional, and toxicological measurements that are important to medical, veterinary, and environmental sciences investigations. NIST’s approach for value assignment included extensive characterization by neutron activation analysis (NAA). Difficulties in the determination of some elements present at very low levels were overcome by use of radiochemical separations. Twentyone elements were characterized in SRM 1577c by NAA. The previous materials, SRM 1577 and 1577b, served as quality control.     

The infrared spectra of amorphous solid water and ice Ic between 10 and 140 K

Absorption spectra from 4000 to 1200 cm^?1 of amorphous solid water and polycrystalline ice I_c have been measured between 10 K and 140 K. Warm up and recooling of an H₂O sample prepared at 10 K gives rise to both irreversible and reversible changes in the peak frequency, band width, and peak height as well as the integrated intensity of the OH stretching band. These spectral effects are related to structural differences. The structure of amorphous solid water also depends on deposition conditions. The optical constants of amorphous so water are determined at 10 K and 80 K from a Kramers-Kronig analysis of the transmission spectra taking into account reflection and interference losses. The astrophysical implication of the temperature dependence of peak frequency and band width of the 3250 cm^?1 band in amorphous solid water is discussed briefly.     

A class of linear kinetic equations in a Krein space setting

Krein space methods are used to derive the unique solvability of a class of abstract kinetic equations on a half-space with accretive collision operators. At the same time a new proof is provided for the case of a positive self-adjoint collision operator. A Fokker-Planck type example is worked out as a new application.This work was performed while the author resided at the Dept. of Physics and Astronomy of the Free University of Amsterdam, The Netherlands.     

Infrared regularization of the massless scalar free field in two-dimensional space-time via Lorentz expansion

It is shown that Lorentz harmonics provide a natural basis for the expansion and infrared regularization of a massless scalar field in two dimensions. The negative metric operators separate out simply. Each Lorentz component of the field is partially local.     

Color models of hadrons

The evidence for a three-valued “color” degree of freedom in hadron physics is reviewed. The structure of color model is discussed. Consequences of color models for elementary particle physics are discussed, including saturation properties of hadronic states, π^o → 2ψ and related decays, leptoproduction, and lepton pair annihilation. Signatures are given which distinguish theories with isolated colored particles from those in which color is permanently bound.