The Contact Process Seen from a Typical Infected Site

This paper studies contact processes on general countable groups. It is shown that any such contact process has a well-defined exponential growth rate, and this quantity is used to study the process. In particular, it is proved that on any nonamenable group, the critical contact process dies out. Research supported by GAČR grant 201/06/1323 and the German Science Foundation. Part of this work was carried out when the author was employed as a postdoc at the University of Tübingen.     

Capillary scale monolithic trap column for desalting and preconcentration of peptides and proteins in one- and two-dimensional separations

Monolithic columns based on poly-(styrene-divinylbenzene) (PS-DVB) were utilized both for preconcentration (in 10 mm x 0.20 mm I.D. format) and analytical separation (in 60 mm x 0.20 and 0.10 mm I.D. format) of peptides and proteins in column switching micro-scale high-performance liquid chromatography. A special holder for short monolithic preconcentration columns was designed and pressure durability tests approved long-term stability up to 400 bar. An 11-20% decrease in the average peak widths of nine peptides was obtained upon combining a preconcentration column with an analytical column as compared with a setup using an analytical column only. Trapping efficiency, especially for small and hydrophilic peptides, was optimized by using 0.10% heptafluorobutyric acid instead of 0.050% trifluoroacetic acid as solvent additive during sample loading. Using a 10 mm x 0.20 mm I.D. preconcentration column, loadabilities between 0.5 and 1.6 microg were determined by frontal analysis of proteins and bioactive peptides, respectively. A 100-fold concentration followed by direct on-line intact mass determination is demonstrated for diluted (3 micromolL(-1)) protein solutions. The applicability of the monolithic preconcentration column for multidimensional chromatography was tested by off-line two-dimensional separation, combining strong cation-exchange chromatography and ion-pair reversed-phase chromatography. Peptide identification data from digested protein mixtures demonstrated reproducibilities of 46-75% in triplicate analyses, and confident peptide identifications of low abundant peptides even in the presence of a 650-fold molar excess of high abundant peptides.     

Entropy-Driven Phase Transition in Low-Temperature Antiferromagnetic Potts Models

We prove the existence of long-range order at sufficiently low temperatures, including zero temperature, for the three-state Potts antiferromagnet on a class of quasi-transitive plane quadrangulations, including the diced lattice. More precisely, we show the existence of (at least) three infinite-volume Gibbs measures, which exhibit spontaneous magnetization in the sense that vertices in one sublattice have a higher probability to be in one state than in either of the other two states. For the special case of the diced lattice, we give a good rigorous lower bound on this probability, based on computer-assisted calculations that are not available for the other lattices.     

Spectral and surface investigations of Ca2V2O7:Eu3+ nanophosphors prepared by citrate-gel combustion method: a potential red-emitting phosphor for near-UV light-emitting diodes

In the present work, red-emitting Ca₂V₂O₇:xEu³⁺ (x = 0.5–6.0 mol%) nanophosphors, in the form of powders, were synthesized by the citrate-gel combustion method using metal nitrates as precursors and citric acid as fuel. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy were used to study the structure, morphology and spectral properties of the samples. The chemical compositions and electronic states of the powders were analyzed with X-ray photoelectron spectroscopy. The average crystallite sizes estimated using the XRD data were found to be in the range of 30–45 nm, and were cross verified by TEM. The lattice parameters determined by the POWD program were approximated as a = 7.242 Å, b = 6.674 Å, c = 6.932 Å and V = 291.24 Å³, respectively. Under UV (395 nm) (PL) and electron (CL) excitation, the nanophosphors show characteristic emission from the Eu³⁺ ion (⁵D₀ → ⁷F_j, j = 1–5) with the main peaks at 612 and 616 nm. The maximum emission intensity was recorded from the sample with an Eu³⁺ concentration of 4 mol% and a critical energy distance of 19.084 Å between the donor and the acceptor. Above this concentration, there was a reduction in the intensity due to dipole–dipole induced concentration quenching effects. The potential applications of this phosphor as a high color-purity phosphor in light-emitting diodes are evaluated.     

Concentration effect of Tm on cathodoluminescence properties of SiO2:Tm and SiO2:Ho,Tm systems

Cathodoluminescence (CL) properties of SiO₂ powders activated with thulium (Tm³⁺) and holmium (Ho³⁺) ions prepared by a sol–gel process were investigated. Different molar concentrations of Tm³⁺ co-doped with Ho³⁺ were studied. The 460 nm peak was monitored and the influence of the beam energy and concentration of Tm³⁺ ions on the emission properties of this peak was also monitored. The peculiar behavior whereby the 460 nm emission peak decreases and the increase in the 705 and 865 nm peaks with the increase in the concentration of Tm³⁺ ions is reported. The relationship between the accelerating beam voltage and the CL intensity of the blue emission peak (460 nm peak) is established. Morphology, particle size and optical properties were characterized with Scanning electron microscopy (SEM), UV/VIS Lambda 750 S spectrometer and Auger electron spectroscopy (AES) equipped with Ocean Optics S2000, respectively.     

A comparative study on structural,morphological and luminescence characteristics of Zn3(VO4)2 phosphor prepared via hydrothermal and citrate-gel combustion routes

Comparison of structural, morphological and spectroscopic properties of zinc vanadate Zn₃(VO₄)₂ phosphor synthesized via two different methods, viz. citrate-gel combustion and hydrothermal reaction, is presented. Highly crystalline and pure phase micro-rods are achieved by citrate-gel combustion route. The hydrothermal reaction products exhibit ribbon like structures. X-ray photoelectron spectroscopic investigation reveals the presence of multiple oxidation states of vanadium in the hydrothermally synthesized phosphor. Luminescence properties have also been compared and the effect of divalent cationic substitution (Ca, Mg) is presented.     

Improved GaSb surfaces using a (NH4)2S/(NH4)2S04 solution

Bulk (1 0 0) n-GaSb surfaces have been treated with a sulphur based solution ((NH₄)₂S/(NH₄)₂SO₄) to which sulphur has been added, not previously reported for the passivation of GaSb surfaces. Au/n-GaSb Schottky barrier diodes (SBDs) fabricated on the treated material show significant improvement compared to that of the similar SBDs on the as-received material as evidenced by the lower ideality factor (n), higher barrier height (?_b) and lower contact resistance obtained. Additionally, the reverse leakage current, although not saturating, has been reduced by almost an order of magnitude at −0.2 V. The sample surfaces were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The native oxide, Sb–O, present on the as-received material is effectively removed on treating with ([(NH₄)₂S/(NH₄)₂SO₄]+S) and (NH₄)₂S. Analysis of the as-received surface by XPS, prior to and after argon sputtering, suggests that the native oxide layer is ≤8.5 nm.     

Finding the convex hull facet by facet

Finding the convex hull of a finite set of points in Euclidean space was one of the first problems explored in the field of computational geometry. In two dimensions a variety of algorithms have been developed and analyzed. For higher dimensions the problems are less well understood. Several “convex hull” problems are defined, solved, and analyzed here in terms of the size of the input and output. In all cases these solutions are the best of the known algorthms. The problems include enumerating the facets of the convex hull, computing the facial lattice of the convex hull and producing a new compact structure representing the combinatorial type of the convex hull. In addition, deciding the combinatorial equivalence of two polytopes is shown to be coNP-hard.     

Men and measures: capturing knowledge requirements in firms through qualitative system modelling

Knowledge Management (KM) is an issue of great and increasing importance in most if not all areas of managerial endeavour. In this paper, we are concerned with the particular practical difficulty within KM of mapping knowledge in a managed system. This is an important practical issue because without a view of the terrain of explicit and tacit knowledge in the managed system, we have little prospect of planning our managerial interaction. Few if any practical methods exist which reflect the strongly systemic nature of business organizations. We begin by establishing our position with regard to the numerous definitions and perspectives of knowledge in managed systems, and indeed in regard to the disagreements that rack KM over the nature of knowledge itself, where it lies and the role of humans as creators, users and guardians of that knowledge. We relate the nature of system knowledge to well-known taxonomies of knowing what, knowing how, knowing why, knowing who together with the integrated from of knowing in the managed system as a whole. The method presented, Systems Based KM (or SBKM), is based on a non-positivist qualitative method deriving from System Dynamics and it is presented through the medium of a case study of a professional firm.