Dynamics of a driven probe molecule in a liquid monolayer

We study dynamics of a probe molecule, driven by an external constant force in a liquid monolayer on top of solid surface. In terms of a microscopic, mean-field-type approach, we calculate the terminal velocity of the probe molecule. This allows us to establish the analog of the Stokes formula, in which the friction coefficient is interpreted in terms of the microscopic parameters characterizing the system. We also determine the distribution of the monolayer particles as seen from the stationary moving probe molecule and estimate the self-diffusion coefficient for diffusion in a liquid monolayer.Comment: Latex, 7 pages, 1 figur

A multi-gene phylogeny of Lactifluus (Basidiomycota, Russulales) translated into a new infrageneric classification of the genus

Infrageneric relations of the genetically diverse milkcap genus Lactifluus (Russulales, Basidiomycota) are poorly known. Currently used classification systems still largely reflect the traditional, mainly morphological, characters used for infrageneric delimitations of milkcaps. Increased sampling, combined with small-scale molecular studies, show that this genus is underexplored and in need of revision. For this study, we assembled an extensive dataset of the genus Lactifluus, comprising 80 % of all known species and 30 % of the type collections. To unravel the infrageneric relationships within this genus, we combined a multi-gene molecular phylogeny, based on nuclear ITS, LSU, RPB2 and RPB1, with a morphological study, focussing on five important characteristics (fruit body type, presence of a secondary velum, colour reaction of the latex/context, pileipellis type and presence of true cystidia). Lactifluus comprises four supported subgenera, each containing several supported clades. With extensive sampling, ten new clades and at least 17 new species were discovered, which highlight the high diversity in this genus. The traditional infrageneric classification is only partly maintained and nomenclatural changes are proposed. Our morphological study shows that the five featured characteristics are important at different evolutionary levels, but further characteristics need to be studied to find morphological support for each clade. This study paves the way for a more detailed investigation of biogeographical history and character evolution within Lactifluus

Developement of real time diagnostics and feedback algorithms for JET in view of the next step

Real time control of many plasma parameters will be an essential aspect in the development of reliable high performance operation of Next Step Tokamaks. The main prerequisites for any feedback scheme are the precise real-time determination of the quantities to be controlled, requiring top quality and highly reliable diagnostics, and the availability of robust control algorithms. A new set of real time diagnostics was recently implemented on JET to prove the feasibility of determining, with high accuracy and time resolution, the most important plasma quantities. With regard to feedback algorithms, new model–based controllers were developed to allow a more robust control of several plasma parameters. Both diagnostics and algorithms were successfully used in several experiments, ranging from H-mode plasmas to configuration with ITBs. Since elaboration of computationally heavy measurements is often required, significant attention was devoted to non-algorithmic methods like Digital or Cellular Neural/Nonlinear Networks. The real time hardware and software adopted architectures are also described with particular attention to their relevance to ITER.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

QSO 2237+0305 VR light curves from Gravitational Lenses International Time Project optical monitoring

We present VR observations of QSO 2237+0305 conducted by the GLITP collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma (Spain). The PSF fitting method and an adapted version of the ISIS subtraction method have been used to derive the VR light curves of the four components (A-D) of the quasar. The mean errors range in the intervals 0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the faintest component (D) having the largest uncertainties. We address the relatively good agreement between the A-D light curves derived using different filters, photometric techniques, and telescopes. The new VR light curves of component A extend the time coverage of a high magnification microlensing peak, which was discovered by the OGLE team.Comment: 15 pages, 3 figures, ApJ accepted (Feb 19

Elasticity of smectic liquid crystals with focal conic domains

We study the elastic properties of thermotropic smectic liquid crystals with focal conic domains (FCDs). After the application of the controlled preshear at different temperatures, we independently measured the shear modulus G' and the FCD size L. We find out that these quantities are related by the scaling relation G' ~ \gamma_{eff}/L where \gamma_{eff} is the effective surface tension of the FCDs. The experimentally obtained value of \gamma_{\rm eff} shows the same scaling as the effective surface tension of the layered systems \sqrt{KB} where K and B are the bending modulus and the layer compression modulus, respectively. The similarity of this scaling relation to that of the surfactant onion phase suggests an universal rheological behavior of the layered systems with defects.Comment: 14 pages, 7 figures, accepted for publication in JPC

Molecular Weight Dependence of Spreading Rates of Ultrathin Polymeric Films

We study experimentally the molecular weight $M$ dependence of spreading rates of molecularly thin precursor films, growing at the bottom of droplets of polymer liquids. In accord with previous observations, we find that the radial extension R(t) of the film grows with time as R(t) = (D_{exp} t)^{1/2}. Our data substantiate the M-dependence of D_{exp}; we show that it follows D_{exp} \sim M^{-\gamma}, where the exponent \gamma is dependent on the chemical composition of the solid surface, determining its frictional properties with respect to the molecular transport. In the specific case of hydrophilic substrates, the frictional properties can be modified by the change of the relative humidity (RH). We find that \gamma \approx 1 at low RH and tends to zero when RH gets progressively increased. We propose simple theoretical arguments which explain the observed behavior in the limits of low and high RH.Comment: 4 pages, 2 figures, to appear in PR

Soil structure evolution under two soil management systems in a clay oxisol from Cerrado region.

The sustainability of crop production in oxisols of Cerrado Region depends on the understanding of soil structural evolution processes. Modifications in soil structure were followed for 4 years allowing the comparison of two soil management systems: conventional plowing with heavy disk harrow (CCL), and zero-tillage (PDC). Structural characterization was achieved by morpho-structural analysis, allowing the identification of horizons and homogeneous pedological units (HPU). From samples taken from most representative HPUs it were performed: pH, acidity, CEC, nutrient status, bulk and particle densities, pore size distribution from pF curves, pedo-structural characteristics from soil swelling curves, organic matter status, and micromorphological observations. Morphological differences were identified between surface horizons. Under CCL, the structural state evolved to a compaction, with well developed angular blocky HPUs, high inter-aggregate cohesion and a sufficient macroporal space. Root growth and crop performance, however, were menaced by the lack of pore continuity. In PDC, results have shown an improvement in soil structure, with moderate resistance and inter-aggregate cohesion, and well developed subangular blocky HPUs. Pore space, besides being not different from compacted horizons found in CCL, have a favorable continuity. Significant gains in yields were observed in PDC, showing a better nutrient status. Benefit/cost relationship in PDC has enhanced net income, reflecting the better structural condition. Soil structure evolution studies were important to verify the improvement in soil quality and health under no-till, an alternative soil management system for sustainable crop production in Brazilian Cerrado Region.Scientific registration n.: 1056. Symposium n.: 2. Presentation: poster