A model for preferential concentration

The preferential concentration of inertial particles in a turbulent velocity field occurs when the particle and fluid time constants are commensurate. We propose a straightforward mathematical model for this phenomenon and use the model to study various scaling limits of interest and to study numerically the effect of interparticle collisions. The model comprises Stokes’ law for the particle motions, and a Gaussian random field for the velocity. The primary advantages of the model are its amenability to mathematical analysis in various interesting scaling limits and the speed at which numerical simulations can be performed. The scaling limits corroborate experimental evidence about the lack of preferential concentration for a large and small Stokes number and make new predictions about the possibility of preferential concentration at large times and lead to stochastic differential equations governing this phenomenon. The effect of collisions is found to be negligible for the most part, although in some cases they have an interesting antidiffusive effect

Þinghald að fornu : fornleifarannsóknir 2003

No abstract available

Chronic dermatomycoses of the foot as risk factors for acute bacterial cellulitis of the leg: A case-control study

Objective: To assess the role of foot dermatomycosis ( tinea pedis and onychomycosis) and other candidate risk factors in the development of acute bacterial cellulitis of the leg. Methods: A case-control study, including 243 patients ( cases) with acute bacterial cellulitis of the leg and 467 controls, 2 per case, individually matched for gender, age (+/-5 years), hospital and admission date (+/-2 months). Results: Overall, mycology-proven foot dermatomycosis was a significant risk factor for acute bacterial cellulitis (odds ratio, OR: 2.4; p < 0.001), as were tinea pedis interdigitalis (OR: 3.2; p < 0.001), tinea pedis plantaris (OR: 1.7; p = 0.005) and onychomycosis (OR: 2.2; p < 0.001) individually. Other risk factors included: disruption of the cutaneous barrier, history of bacterial cellulitis, chronic venous insufficiency and leg oedema. Conclusions: Tinea pedis and onychomycosis were found to be significant risk factors for acute bacterial cellulitis of the leg that are readily amenable to treatment with effective pharmacological therapy. Copyright (C) 2004 S. Karger AG, Basel

Þinghald að fornu : fornleifarannsóknir 2003

No abstract available

Dynamics and statistics of heavy particles in turbulent flows

We present the results of Direct Numerical Simulations (DNS) of turbulent flows seeded with millions of passive inertial particles. The maximum Taylor's Reynolds number is around 200. We consider particles much heavier than the carrier flow in the limit when the Stokes drag force dominates their dynamical evolution. We discuss both the transient and the stationary regimes. In the transient regime, we study the growt of inhomogeneities in the particle spatial distribution driven by the preferential concentration out of intense vortex filaments. In the stationary regime, we study the acceleration fluctuations as a function of the Stokes number in the range [0.16:3.3]. We also compare our results with those of pure fluid tracers (St=0) and we find a critical behavior of inertia for small Stokes values. Starting from the pure monodisperse statistics we also characterize polydisperse suspensions with a given mean Stokes.Comment: 13 pages, 10 figures, 2 table

Transport properties of dense fluid argon

We calculate using molecular dynamics simulations the transport properties of realistically modeled fluid argon at pressures up to $\simeq 50GPa$ and temperatures up to $3000K$. In this context we provide a critique of some newer theoretical predictions for the diffusion coefficients of liquids and a discussion of the Enskog theory relevance under two different adaptations: modified Enskog theory (MET) and effective diameter Enskog theory. We also analyze a number of experimental data for the thermal conductivity of monoatomic and small diatomic dense fluids.Comment: 8 pages, 6 figure

Rhyolitic tephra horizons in northwestern Europe and Iceland from the AD 700s-800s: a potential alternative for dating first human impact

The distribution and geochemistry of four rhyolitic tephra horizons from Iceland dated to the ad 700s–800s is assessed. These include the rhyolitic phase of the Landnám tephra (ad 870s), the ad 860 layer, a previously unrecorded tephra called the GA4–85 layer (c. ad 700–800) and the Tjïrnuvík tephra (c. ad 800s). The ad 860 and GA4–85 layers were first found in peat bogs in north Ireland. They are here correlated with equivalent horizons on Iceland which were found below the Landnám tephra (c. ad 870s). This time period is considered important in the North Atlantic region, because it coincides with a phase of human settlement in Iceland and the Faroe Islands. The establishment of a detailed tephrochronology may provide a tool for exact dating of sediment successions and sediments associated with archaeological excavations. Caution must be taken especially on Iceland where the Landnám tephra is often used for dating archaeological sites. This investigation show that several rhyolitic tephra horizons occur close in time to the Landnám tephra, and that mistakes can be made if detailed geochemical analyses are not carried out, especially in areas which are distal to the source of the Landnám tephra (the Veidivötn and Torfajökull volcanic systems, southern Iceland)

A survey among dermatologists: diagnostics of superficial fungal infections - what is used and what is needed to initiate therapy and assess efficacy?

BACKGROUND: Superficial fungal infections are common. It is important to confirm the clinical diagnosis by mycological laboratory methods before initiating systemic antifungal treatment, especially as antifungal sensitivity and in vitro susceptibility may differ between different genera and species. For many years, the gold standard for diagnosis of superficial fungal infections has been direct fungal detection in the clinical specimen (microscopy) supplemented by culturing. Lately, newer molecular based methods for fungal identification have been developed. OBJECTIVE: This study was initiated to focus on the current usage of mycological diagnostics for superficial fungal infections by dermatologists. It was designed to investigate whether it was necessary to differentiate between initial diagnostic tests and those used at treatment follow-up in specific superficial fungal infections. METHODS: An online questionnaire was distributed among members of the EADV mycology Task Force and other dermatologists with a special interest in mycology and nail disease. RESULTS: The survey was distributed to 62 dermatologists of whom 38 (61%) completed the whole survey, 7 (11%) partially completed and 17 (27%) did not respond. Nearly, all respondents (82-100%) said that ideally they would use the result of direct microscopy (or histology) combined with a genus/species directed treatment of onychomycosis, dermatophytosis, Candida- and Malassezia-related infections. The majority of the dermatologists used a combination of clinical assessment and direct microscopy for treatment assessment and the viability of the fungus was considered more important at this visit than when initiating the treatment. Molecular based methods were not available for all responders. CONCLUSION: The available diagnostic methods are heterogeneous and their usage differs between different practices as well as between countries. The survey confirmed that dermatologists find it important to make a mycological diagnosis, particularly prior to starting oral antifungal treatment in order to confirm the diagnose and target the therapy according to genus and species