Dynamics in aqueous solutions of poly(vinyl alcohol) and its hydrophobically modified anionic analogues

Summary The dynamics of aqueous solutions of unmodified poly(vinyl alcohol) (PVA) and of hydrophobically modified anionic analogues with two different degrees of hydrophobic substitution (HMPVA1 and HMPVA2) is studied with the aid of viscometry and dynamic light scattering (DLS). The viscosity results reveal a pronounced polyelectrolyte effect in dilute solutions of HMPVA1, while strong association effects, even at very low concentrations, are observed in solutions of the analogue with the highest hydrophobicity. The relaxation times for solutions of PVA are practically independent of concentration over the considered range. For the hydrophobically modified analogues, both the fast and the slow relaxation times increase with increasing concentration for both systems, but the concentration dependencies of the relaxation times are much stronger for HMPVA2 due to enhanced hydrophobic associations. Received: 19 July 2002/Revised version: 10 October 2002/ Accepted: 10 October 2002 RID="a" ID="a" Present address: Jotun NS, P 0 Box 2021, N-3235 Sandefiord, Noraay Correspondence to Rolf Andreas Lauten     

Verifying a distributed list system: A case history

The background for this paper is twofold: One is the definition of a caching protocol for shared memory parallel computers called SCI, and the other is the usage of rewriting techniques in program verification. The paper concentrates on a linked list system, which is a central aspect of the caching protocol. We first describe an informal proof of this system, including a rather large invariant. Thereafter we show how the list system and the invariant can both be described in the formalism of rewriting logic, and we use this to carry through a significant part of the verification mechanically, using the OBJ3 interpreter.     

Overcoming organizational challenges to secure knowledge management

Incident management systems have the potential to improve security dramatically but often experience problems stemming from organizational, interpersonal and social constraints that limit their effectiveness. These limits may cause underreporting of incidents, leading to erroneous perceptions of the actual safety and security situation of the organization. The true security situation may be better understood and underreporting may be reduced if underlying systemic issues surrounding security incident management are taken into account. A dynamic simulation, based on the parallel experience of industrial incident management systems, illustrates the cumulative effects of rewards, learning, and retributions on the fate of a hypothetical knowledge management system designed to collect information about events and incidents. Simulation studies are part of an ongoing research project to develop sustainable knowledge and knowledge transfer tools that support the development of a security culture.

Effect of selenium on the growth of some selected green and blue-green algae

An algal assay procedure using microplate technique was carried out to assess the effect of selenium on the growth of some green and blue-green algae. Sodium selenite pentahydrate (Na₂SeO₃.5H₂O) and selendioxide (Se₂O₄) were tested as selenium. The test algae were Selenastrum capricornutum, Scenedesmus obliquus, Chlorella sp., Monoraphidium convolutum, Monoraphidium contortum, Monoraphidium griffithii, Anabaena flos-aquae, Micro-cystis aeruginosa, and Oscillatoria agardhii. The blue-green algae are toxin-producing strains. Cell number and in vivo chlorophyll fluorescence were the growth parameters of green and blue-green algae respectively. Dose-response curves quantify the selenium toxicity in terms of EC₅₀. The lowest selenium concentrations giving no detectable growth (EC₁₀₀) were visually inspected. The test algae showed distinctly different responses to various selenium treatments. Selenium at concentrations < 0.1 mg L⁻¹ stimulates, to varying degrees, the growth of all the green algae with one exception: S. capricornutum was dramatically inhibited at all treatments. O. agardhii, A. flos-aquae and M. aeruginosa showed marginal growth stimulation up to 0.1 mg Se L⁻¹, 1.0 mg Se L⁻¹ and 3.2 mg Se L⁻¹ respectively. In terms of EC₅₀, the compound selendioxide was more toxic to greens than sodium selenite. The reverse was indicated for the blue-greens. In general, the EC₅₀ presented a wide range (0.08–7.2 mg Se L⁻¹), with the lowest values reported for S. obliquus and the highest for M. aeruginosa. All the test algae, except S. obliquus, maintained observable growths at higher selenium levels (EC₁₀₀>1.0<100mg Se L⁻¹).     

居德布兰河谷旅游项目—河边桑拿

河边桑拿位于一条美丽的河边,可以全景观赏远山的景色。它建在菲多斯景观酒店附近,供酒店的客人使用。桑拿房有一面玻璃墙,朝向景区。建筑物建在地形中,除玻璃墙外,四周用青草覆盖。     

A new phase diagram for layered antiferromagnetic films

Magnetic multilayer films provide convenient model systems for studying the physics of antiferromagnetic films and surfaces. Here we report on the magnetic reversal and domain structure in antiferromagnetically coupled Co/Pt multilayers that are isomorphic to layered antiferromagnetic films with perpendicular magnetic anisotropy. We observe two distinct remanent states and reversal modes of the system. In mode 1 the magnetization in each layer reverses independently, producing an antiferromagnetic remanent state that shows full lateral correlation and vertical anticorrelation across the interlayers. In mode 2 the reversal in adjacent layers is locally synchronized with a remanent state that is vertically correlated but laterally anticorrelated in ferromagnetic stripe domains. Theoretical energy calculations of the two ground states identify a new phase boundary that is in good agreement with our experimental results.     

The Red Queen in organizational creation and development

We synthesize organization learning theory and organizationalecology to predict systematic patterns in the founding and growthof organizations over time. Our central argument is that competitiontriggers organizational learning, which in turn intensifiescompetition that again triggers an adaptive response. We modelthis self-exciting dynamic—sometimes referred to as the‘Red Queen’ in general evolutionary theory—toexplain organizational founding and growth rates among the thousandsof retail banks that have operated in Illinois at any time from1900–1993. We find strong evidence that Red Queen evolutionled some organizations to grow quickly and to place strong competitivepressure on rivals. Red Queen evolution also helped establishbarriers to entry. However, this same evolutionary process appearsto make organizations more susceptible to ‘competencytraps’, ultimately slowing their growth rates and invitingnew market entry. Organizations confronted by a widely varyingdistribution of competitors grow more slowly and are more likelyto face new entrants. Overall, the results suggest that processesof organizational creation and growth emerge from ecologiesof learning organizations. More generally, we discuss the useof ecological theory and models to study the empirical consequencesof organizational learning.     

SESAM-69—A general purpose finite element method program

The multilevel superelement method in combination with extensive data generators materialized in the program system SESAM-69 introduce a new dimension to the concept of the Finite Element Method (FEM).The paper describes the superelement method and the program system SESAM-69 in brief terms. However, the major part contains some of the program analytics in connection with this method. The multilevel superelement method is an extension of the better known substructure technique, or reduction procedure. The method applies to both statics and dynamics.