On the completely positive and positive-semidefinite-preserving cones

The cone CP_n,q of completely positive linear transformations from $\text{M}{}_{\mathrm{n}}\text{(}\text{C}\text{)=}\text{M}{}_{\mathrm{n}}$ to $\text{M}$_q is shown to be isometrically isomorphic to $\text{P}$_nq, the cone of nq by nq positive semidefinite matrices. Generalizations of scalar and matrix results to $\text{CP}{}_{\mathrm{n,\; q}}\text{?}\text{HP}{}_{\mathrm{n,\; q}}\text{?}\text{L}\text{(}\text{M}{}_{\mathrm{n}}\text{,}\text{M}{}_{\mathrm{q}}\text{)}$ (where HP_n,q represents the hermitian-preserving linear transformations) are discussed. Relationships among the completely positives, the set of positive semidefinite preservers $\text{π(}\text{P}{}_{\mathrm{n}}\text{)}$, and its dual $\text{π(}\text{M}{}_{\mathrm{n}}\text{)}{}^1$ are given. Left and right facial ideals of CP are characterized. Properties of the joint angular field of values of a finite sequence of hermitian matrices H₁,…, H_m are studied, leading to a characterization of $\text{π(}\text{P}{}_{\mathrm{q}}\text{,}\text{P}{}_{\mathrm{n}}\text{)}$.     

Synthese,Struktur und magnetische Eigenschaften von [CrCl(μ-Cl)(TMEDA)]2

Synthesis, Structure, and Magnetic Properties of [CrCl(-μCl)(TMEDA)]₂ The title complex [CrCl(μ-Cl)(TMEDA)]₂ ( 1 ) is obtained in an equimolar reaction of CrCl₂(THF) with TMEDA in high yield. 1 crystallises in the monoclinic space group P2₁/c with a = 843.2(2), b = 1 109.(2), c = 1 147.4(3) pm, β = 102.99(2)° and Z = 2. The molecular structure of 1 contains two, slightly distorted quadratic pyramidal CrL₅-subunits, which are linked via two unsymmetrical Cl-bridges. The μ-Cl-functions take the apical position of one and a basal position of the second CrL₅-unit, wherein the apical Cr–Cl bond (277.6(1) pm) is destinctly longer than the basal Cr–Cl bond (240.6(1) pm). The terminal Cr–Cl bond is still shorter (237.5(1) pm). The Cr…Cr distance is far beyond any bonding interaction. This is confirmed by means of magnetic susceptibility measurements, which show four unpaired electrons per Cr centre; however, a small antiferromagnetic coupling of J/k = ?7.3 K can be calculated. This coupling is suggested to be originated by a 90°-σ-superexchange via the asymmetric μ-Cl functions.     

Discrete resistance changes in thin lipid membranes

Semispherical membranes were formed using a mixed lipid preparation extracted from beef brain gray matter. The membrane obtained had a thickness between several hundred angstroms and about one thousand angstroms as determined by the interference color of reflected light. The initial thick membrane and newly formed primary black membrane had a resistance greater than 10¹⁰ ohms, similar to that of the bulk lipid phase. However, when a small (< 15 mV) transmembrane potential was applied, the resistance decreased in a stepwise fashion to a final resistance of about 10⁵10⁶ ohms. The resultant thin membrane exhibited stepwise temperature-dependent fluctuations in conductance similar to those obtained with membranes to which substances such as the “excitability-inducing material” of Mueller and Rudin and certain ionophores have been added. Further, the membrane showed rectification when calcium was present on only one side of the membrane.     

More Efficient Parallel Totally Monotone Matrix Searching

We give a parallel algorithm for computing all row minima in a totally monotonen × nmatrix which is simpler and more work efficient than previous polylog-time algorithms. It runs inO(lg n lg lg n) time doingwork on aCRCW PRAM, inO(lg n(lg lg n)²) time doingwork on aCREW PRAM, and intime doingwork on anEREW PRAM. Since finding the row minima of a totally monotone matrix has been shown to be fundamental in the efficient solution of a host of geometric and combinatorial problems, our algorithm leads directly to improved parallel solutions of many algorithms in terms of their work efficiency.     

Lieb–Robinson Bounds,Arveson Spectrum and Haag–Ruelle Scattering Theory for Gapped Quantum Spin Systems

We consider translation invariant gapped quantum spin systems satisfying the Lieb–Robinson bound and containing single-particle states in a ground state representation. Following the Haag–Ruelle approach from relativistic quantum field theory, we construct states describing collisions of several particles, and define the corresponding S-matrix. We also obtain some general restrictions on the shape of the energy–momentum spectrum. For the purpose of our analysis, we adapt the concepts of almost local observables and energy–momentum transfer (or Arveson spectrum) from relativistic QFT to the lattice setting. The Lieb–Robinson bound, which is the crucial substitute of strict locality from relativistic QFT, underlies all our constructions. Our results hold, in particular, in the Ising model in strong transverse magnetic fields.     

Ab initio and molecular mechanics (MM2 and MM3) calculations of nonconjugated positively charged nitrogen-containing compounds

High-level ab initio calculations have been performed on N-methyl-N-methyleneammonium and related compounds to obtain accurate rotational barriers, structures, and vibrational frequencies. The 6-31G** basis set has been utilized at the Hartree-Fock level of theory for these calculations because little experimental data are available. The MM2(91) and MM3(94) force fields have been parameterized to include these nonconjugated charged nitrogen-containing compounds. Molecular mechanics geometries and vibrational frequencies compare well with the ab initio results. © 1995 John Wiley & Sons, Inc.     

Rapid detection of neurotoxic insecticides in food using disposable acetylcholinesterase-biosensors and simple solvent extraction

The extensive use of pesticides to protect agricultural crops necessitates reliable tools for the detection of residues in food and water, thus ensuring environmental protection and consumer safety. Neuroinhibitors such as organophosphates and carbamates in particular, represent a potential hazard to human health. These compounds are frequently found in food, but conventional methods of analysis are limited as they are either time consuming or not sufficiently sensitive. As a result, a rapid and sensitive biosensor test based on AChE-inhibition was developed. The disposable AChE-biosensor was directly applied in solvent extracts of food samples using isooctane as extraction solvent. A complete assay could be performed in less than 2 h. Recovery rates of 84% were obtained in tests with spiked orange juice samples. Tests in food samples with a lower water content resulted in reduced recovery rates (44% for peach pap baby food). Phosphorothionate insecticides in food could be detected after direct oxidation with N-bromosuccinimide and solvent extraction. The assay displayed a detection limit of 2 microg/kg paraoxon, which was sufficient for the monitoring of maximum residue limits in food according to EU regulations.     

A COMPARISON OF PHOTO-KILLING AMONG CAROTENE AND CYTOCHROME c ACCUMULATING STRAINS OF THE SMUT FUNGUS Ustilago violacea AT SPECIFIC WAVELENGTHS FROM 400 TO 650 nm

Abstract— Variously pigmented strains of Ustilago violacea were exposed to monochromatic light from 400 to 650 nm in 50-nm increments to determine which wavelengths were most effective for photo-killing. In addition, liquid nitrogen temperature absorption spectra were determined for intact cells of the fungal strains. The high cytochrome c containing pink strains 1.C429, AB278a-1, 1.C425 and 2.C427 were more sensitive to cytochrome absorption wavelengths than were their low cytochrome c counterparts 15.10, 1.C2 y , 1.C2 w and 1.C427, while the carotene accumulating strains 1.C2 y and AB278a-1 were more resistant to photo-killing than their carotene lacking counterparts 15.10, 1.C2 w , 1.C427 and 1.C429, 1.C415, 2.C428 even at wavelengths not absorbed by carotenes. The results suggest that cytochrome c and other cytochromes are photosensitizers and that carotene-related protection is through the quenching of the photosensitizers as well as by absorption.     

A review of analytical methods for the determination of sulfolane and alkanolamines in environmental studies

Sulfolane and alkanolamines are used extensively in the processing of sour natural gases. Over many years of operation, there have been inadvertent leaks of these chemicals to groundwater and wetlands surrounding gas processing facilities, leading to uptake by vegetation. Because sulfolane and alkanolamines are extremely water-soluble, their analysis has presented challenges, particularly requirements for suitable extraction from biological matrixes and soil, along with sensitive detection using commonly available instrumentation. Analytical methods usually use gas chromatography or liquid chromatography with a variety of detector systems. Sample preparation techniques may include extraction with organic solvents, water, or a combination of these. In some cases, direct aqueous injections have been used. Derivatization of alkanolamines has been used to improve the chromatographic separations and detection. More recent procedures, using positive-ion electrospray ionization mass spectrometry (MS), have been useful for the confirmation of uptake of the alkanolamines and transformation products by wetland vegetation. Future developments will likely center on further MS analyses for identification of metabolites and transformation products in aquatic environments.