Galois Module Structure and the γ-Filtration

We describe a general method for calculating equivariant Euler characteristics. The method exploits the fact that the -filtration on the Grothendieck group of vector bundles on a Noetherian quasi-projective scheme has finite length; it allows us to capture torsion information which is usually ignored by equivariant Riemann–Roch theorems. As applications, we study the G-module structure of the coherent cohomology of schemes with a free action by a finite group G and, under certain assumptions, we give an explicit formula for the equivariant Euler characteristic in the Grothendieck group of finitely generated Z[G]-modules, when X is a curve over Z and G has prime order.     

Simulations of magnetorheological suspensions in Poiseuille flow

Particle-level simulations are conducted to study magnetorheological fluids in plane Poiseuille flow. The importance of the boundary conditions for the particles at the channel walls is examined by considering two extreme cases: no friction and infinite coefficient of friction. The inclusion of friction produces Bingham fluid behavior, as commonly observed experimentally for MR suspensions. Lamellar structures, similar to those reported for electrorheological fluids in shear flow, are observed in the post-yield region for both particle boundary conditions. The formation of these lamellae is accompanied by an increase in the bulk fluid velocity. The slip boundary condition produces higher fluid velocities and thicker lamellar structures.     

Interaction between explosive and analyte layers in explosive matrix-assisted plasma desorption mass spectrometry

An HMX/insulin two-layer system was chosen as a model for further investigation of the matrix properties of explosive materials for protein analytes in plasma desorption mass spectrometry. The dependencies of the molecular ion yield and average charge state as a function of the analyte thickness were studied. An increase in the charge state of multiply protonated molecular species was confirmed as the major matrix effect, with the average charge state z at the smallest thickness studied being higher than in matrix-assisted laser desorption/ionization and closer to the value obtained in electrospray ionization under standard acidic conditions. Observed charge state distributions are significantly narrower than the corresponding Poisson distributions, which suggests that the protonation of insulin is limited in plasma desorption by the number of basic sites in the molecule, similar to electrospray ionization. Both the curve displaying total molecular ion yield and the one showing the total charge (proton) yield as a function of the insulin thickness have maxima at a thickness different from an insulin monolayer. These observations diminish the significance of a matrix/analyte interface mechanism for the explosive matrix assistance. Instead, a mechanism related to the chemical energy release during conversion of the explosive after the ion impact is proposed. As additional mechanisms, enhanced protonation of the analyte through collisions with products of the explosive decay is considered, as well as electron scavenging by other products, which leads to a higher survival probability of positively charged protein molecular ions. Copyright 1999 John Wiley & Sons, Ltd.     

Discovery of phosphotyrosine-binding oligopeptides with supramolecular target selectivity

We demonstrate phage-display screening on self-assembled ligands that enables the identification of oligopeptides that selectively bind dynamic supramolecular targets over their unassembled counterparts. The concept is demonstrated through panning of a phage-display oligopeptide library against supramolecular tyrosine-phosphate ligands using 9-fluorenylmethoxycarbonyl-phenylalanine-tyrosine-phosphate (Fmoc-FpY) micellar aggregates as targets. The 14 selected peptides showed no sequence consensus but were enriched in cationic and proline residues. The lead peptide, KVYFSIPWRVPM-NH₂ (P7) was found to bind to the Fmoc-FpY ligand exclusively in its self-assembled state with K_D = 74 ± 3 μM. Circular dichroism, NMR and molecular dynamics simulations revealed that the peptide interacts with Fmoc-FpY through the KVYF terminus and this binding event disrupts the assembled structure. In absence of the target micellar aggregate, P7 was further found to dynamically alternate between multiple conformations, with a preferred hairpin-like conformation that was shown to contribute to supramolecular ligand binding. Three identified phages presented appreciable binding, and two showed to catalyze the hydrolysis of a model para-nitro phenol phosphate substrate, with P7 demonstrating conformation-dependent activity with a modest k_cat/K_M = 4 ± 0.3 × 10⁻⁴ M⁻¹ s⁻¹.

Phage-display screening on self-assembled tyrosine-phosphate ligands enables the identification of oligopeptides selective to dynamic supramolecular targets, with the lead peptide showing a preferred hairpin-like conformation and catalytic activity.     

Wave scattering effects in elastic percolation models

The study of the propagation of waves in randomly diluted models is presented. Porosity (crack-like) models are simulated by constructing typical elastic percolation networks with random microscopic heterogeneities in order to resemble rock media. Central and bond-bending forces (Born Hamiltonian) models are considered. For each experimental case, the elastic energy of the system is relaxed in equilibrium and then the model is excited by a pulse source in order to produce wave propagation. First, a review is presented of the well established velocity-porosity relationship from rock physics, which shows a linear trend from small porosities up to the critical porosity (percolation threshold) where the rocks fall apart. From the wave propagation analysis a general trend is observed for the attenuation of waves, from the small to the large porosity models, suggesting multiple scattering effects similar to those reported from effective-medium approximations of wave scattering due to random heterogeneities. Finally, the results are compared with those obtained from laboratory experiments on dry rocks with different porosities and different applied stress regimes.     

Constrained matrix optimization with applications

In this work we study a minimization problem for a matrix-valued function under linear constraints, in the case of a singular matrix. The proposed method differs from others on the restriction of the minimizing matrix to the range of the corresponding quadratic function. Moreover, we present two applications of the proposed minimization method in Linear Regression and B-spline smoothing.     

Observation of reentrant integer quantum Hall States in the lowest landau level

Measurements on very low disorder two-dimensional electrons confined to relatively wide GaAs quantum well samples with tunable density reveal a close competition between the electron liquid and solid phases near the Landau level filling factor ν=1. As the density is raised, the fractional quantum Hall liquid at ν=4/5 suddenly disappears at a well-width dependent critical density, and then reappears at higher densities with insulating phases on its flanks. These insulating phases exhibit reentrant ν=1 integer quantum Hall effects and signal the formation of electron Wigner crystal states. Qualitatively similar phenomena are seen near ν=6/5.     

Galois Structure of K-Groups of Rings of Integers

N/Kbe a Galois extension of number fields with finite Galois group G.We describe a new approach for constructing invariants of the G-module structure of the K groups of the ring of integers of N in the Grothendieck group of finitely generated projective Z[G]modules. In various cases we can relate these classes, and their function field counterparts, to the root number class of Fröhlich and Cassou-Noguès.     

Heuristics for the multi-level capacitated minimum spanning tree problem

The capacitated minimum spanning tree (CMST) problem is fundamental to the design of centralized communication networks. In this paper we consider the multi-level capacitated minimum spanning tree problem, a generalization of the well-known CMST problem. Based on work previously done in the field, three heuristics are presented, addressing unit and non-unit demand cases. The proposed heuristics have been also integrated into a mixed integer programming solver. Evaluation results are presented, for an extensive set of experiments, indicating the improvements that the heuristics bring to the particular problem.     

Aerosol-Assisted Plasma Deposition of Hydrophobic Polycations Makes Surfaces Highly Antimicrobial

The currently used multistep chemical synthesis for making surfaces antimicrobial by attaching to them hydrophobic polycations is replaced herein by an aerosol-assisted plasma deposition procedure. To this end, N,N-hexyl,methyl-PEI (HMPEI) is directly plasma-coated onto a glass surface. The resultant immobilized HMPEI coating has been thoroughly characterized and shown to be robust, bactericidal against Escherichia coli, and virucidal against human influenza virus.