Protein structural effects in gas phase ion/molecule reactions with diethylamine.

The relationship between gas-phase protein structure and ion/molecule reactivity is explored in comparisons between native and disulfide-reduced aprotinin, lysozyme, and albumin. Reactions are performed in the atmospheric-pressure inlet to a quadrupole mass spectrometer employing a novel capillary interface-reactor. In reactions with equal concentrations of diethylamine, multiply protonated molecules generated by electrospray ionization (ESI) of 'native' proteins shifted to lower charge states than did multiply protonated molecules from ESI of the disulfide-reduced counterparts, suggesting that the disulfide-reduced protein ions are less reactive than native protein ions of the same charge state. Differences in reactivity may arise from protonation of different amino acid residues and/or differences in the proximities of charge sites in the two molecules. These results suggest that the reactivity of multiply charged proteins can be significantly affected by their gas-phase structure.     

Tunneling between thin film superconductors containing single flux vortices

Discrete conductance increments in the current-voltage characteristics of superconductor-insulator-superconductor tunnel junctions (of area $\text{?25 μ}\text{m}{}^2$) associated with single flux quanta (“vortices”) trapped in the thin film electrodes have been observed. These tunneling results were obtained for both Sn and Pb and provide, for the first time, a direct measure of the density of quasiparticle states corresponding to a single vortex. Simultaneous measurements of the Josephson critical current suppresion indicate that the vortex cores are on the average not aligned across the barrier on the scale of the coherence lenght. The measured vortex density of states is in disagreement with predictions of the normal cores model and previously published data.     

Generalized inverses of matrices over a finite field

For a given m × n matrix A of rank r over a finite field F, the number of generalized inverses, of reflexive generalized inverses, of normalized generalized inverses, and of pseudoinverses of A are determined by elementary methods. The more difficult problem of determining which m × n matrices A of rank r over F have normalized generalized inverses and which have pseudoinverses is solved. Moreover, the number of such matrices which possess normalized generalized inverses and the number which possess pseudoinverses are found.     

Complete reduction of fermion-antifermion bethe-salpeter equation with static kernel

The Bethe-Salpeter (BS) equation for a $\text{spin}\text{-}\text{1}\text{2}$ fermion-antifermion bound system is considered for the case in which the kernel is static and is the fourth component (i.e., three-scalar part) of a vector potential. Relative time (or relative energy) dependence can be eliminated easily. The 16 BS bispinor amplitudes are reexpressed in the usual way in terms of corresponding tensor amplitudes which satisfy 16 coupled integrodifferential equations. If Lorentz-, parity-, and charge-conjugation invariance are used, these equations can be reduced through a sequence of transformations to single eigenvalue equations, involving scalar and three-vector wavefunctions for singlet and triplet states, respectively. The effective Hamiltonians obtained in these equations are correct to all orders in the coupling constant and have a simple structure, consisting in general of a scalar, a spin-orbit, and a tensor part, which are explicitly exhibited.Although the equations could well be used for consideration of a general particleantiparticle system (e.g., quark-antiquark), for the present only positronium with a Coulomb interaction kernel is treated as an illustrative example. There exists a singlettriplet splitting in leading order mα⁶ ln α even though no spin-spin forces are directly introduced in the kernel. The splitting is calculated in detail in perturbation theory to order mα⁶ ln α and mα⁶.     

PBIB designs with m associate classes induced by full rank matrices modulo pm

This paper presents series of PBIB designs with m associate classes in which the treatment set is a subset of the Z(p^m)-module of n × 1 vectors over the ring of integers modulo p^m, p any prime. The association scheme of this series of designs is determined by the Fuller canonical form under row equivalence of n × 2 matrices [a,b] for vectors a and b in the treatment set. The blocking procedure utilizes full rank s × n matrices over Z(p^m), 1 ? s ? n ? 2, n ? 3. For m = 2, n = 3, s =1 and for each prime p, each PBIB is regular divisible and yields a finite proper uniform projective Hjelmslev plane with parameters j = p and k = p(p + 1).     

Hydration and contact ion pairing of Ca2+ with Cl- in supercritical aqueous solution

X-ray absorption fine structure (XAFS) spectroscopy was used to measure the first-shell structure about Ca2+ in high-temperature aqueous solution. XAFS spectra were acquired at the Ca K edge at temperatures up to 400 degrees C and pressures up to 350 bars. For the system at 400 degrees C, both Ca (4038.5 eV) and Cl (2822.4 eV) K-edge data were acquired and a global model was used to fit the two independent sets of XAFS data. Measurements were made at the bending magnet beamline (sector 20) at the Advanced Photon Source, Argonne. Above 250 degrees C, a significant number of Ca2+-Cl- direct contact ion pairs form in agreement with existing thermodynamic data for this system. For a 1 m CaCl2 solution at 400 degrees C, the mean coordination structure about Ca2+ contains 3.2+/-0.6 water molecules at an average Ca-O distance of 2.356+/-0.026 A and 1.8+/-0.7 Cl- at a Ca-Cl distance of 2.677+/-0.007 A. An evaluation of the Ca and Cl preedge and near-edge (x-ray absorption structure) spectra provided further confirmation of the change in the Ca2+ first-shell structure and symmetry. Overall these measurements provide a structural basis for understanding solvation of Ca2+ in hydrothermal systems. These results also provide important new insights into the structural aspects of Ca2+ ion pairing that are the basis of many biological processes under ambient conditions.     

Synthesis of Optimal Control for Cooperative Collision Avoidance for Aircraft (Ships) with Unequal Turn Capabilities

This paper presents a synthesis of an optimal control solution for cooperative collision avoidance strategies for aircraft (ships) with unequal turn capabilities in a close proximity coplanar encounter. The analytic expressions for the extremals are presented and their properties are analyzed. Simple algorithms for the synthesis of optimal control are developed. The structure of the synthesis is analyzed and its behavior with a change in the nondimensional turn rate ratio is studied. It is shown that Merz’s solution for identical aircraft (see Merz in Proc. Joint Automatic Control Conf., Paper 15-3, pp. 449–454, 1973; Navigation 20(2):144–152, 1973; Tarnopolskaya and Fulton in J. Optim. Theory Appl. 140(2):355–375, 2009) is a degenerate case of this more general solution. The results of this paper are useful for benchmarking and validating automated proximity management and collision avoidance systems.