The benthic boundary layer approach and its application to Lake Päijänne,Finland

Resuspension of bottom sediments is the net result of a wide variety of different fluid mechanical processes with characteristic time and length scales that extend over six orders of magnitude. The sum of these effects is most heavily concentrated in a layer adjacent to the bottom called the benthic boundary layer (BBL). The physics of BBL must be understood before improved solutions to the resuspension problem are possible. Traditionally in lakes, sedimentation and resuspension have been modelled with the aid of equations which ignore the time and space variations of near bottom processes. This can lead to wrong estimates of material transport. With the exception of few recent studies, benthic boundary layer approach has been mainly applied to marine environments. The instrumentation has been a major problem for development of the theory and its applications, but during recent years some new instruments have been giving promising results. This paper discusses the applicability of the theory in Finnish lakes and presents results from Lake Päijänne.     

Boundary layer properties of highly dissected leaves: an investigation using an electrochemical fluid tunnel

Abstract. A method for modelling heat and mass transfer by diffusion-controlled electrode reactions in a fluid tunnel is described. In this procedure, a nickelplated leaf functions as a test electrode, and the convective transfer of ions to the leaf cathode in an electrolyte-filled flow tunnel is measured as a function of flow rate. The method permits the simulation of water vapour and heat transfer, and in particular, the determination of boundary layer conductances, by analogy with observed ion transfer. The approach is applicable to many problems in modelling heat and mass transfer between leaves and their surroundings, and is especially useful in examining the properties of leaves in which surface characteristics or overall shape are complex. Using this method, the properties of the highly dissected leaves of Achillea lanulosa with regard to forced convection were investigated. The leaves showed high transfer conductances, indicating that the effective unit of heat transfer was probably the individual leaf subelements. Conductances tended to be greater and effective characteristic dimensions smaller for the larger, more open leaves of a lower altitude population in contrast with leaves from high altitude plants. While the results provide insight into the properties of these complex leaf shapes, difficulties in interpreting the findings are discussed, and a number of exploratory approaches are suggested for data analysis and interpretation.     

Selection of the conodont Idiognathodus simulator (Ellison) as the event marker for the base of the global Gzhelian Stage (Upper Pennsylvanian, Carboniferous)

Studies carried out for more than 10 years by the Task Group to establish GSSPs at the base of the Moscovian–Kasimovian and Kasimovian–Gzhelian boundaries have resulted in the proposal that the level at which the conodont species Idiognathodus simulator (Ellison, 1941) first appears be selected to mark the base of the Gzhelian Stage. This expands this eastern European chronostratigraphic unit to a global scale.I. simulator (sensu Barrick et al., 2008) has been identified so far in Midcontinent and eastern North America, the Moscow and Donets basins and southern Urals of eastern Europe, and in south-central China. Correlation of this level based on this species and other conodont species can be reinforced in some areas by ammonoid and fusulinid data.     

Effects of leaf shape plasticity on leaf surface temperature

干旱区植物叶片形态可塑性是植物适应高温干旱环境的重要生存策略, 但目前仍缺乏直观的数据予以证明。该研究应用热成像技术和图像分析技术, 同步测定真实叶片与模拟叶片的叶温、形态及风速、辐射和温度等环境参数。研究结果显示: 在干旱、高温环境下, 除了蒸腾, 叶片形态变化也是调控叶温的重要因子。干旱区植物叶片变小, 有利于加速叶片与环境的物质及热量交换, 从而达到降低叶温的目的。样地数据显示, 在高温、低风速环境下, 叶片宽度每减少1 cm, 叶片表面温度降低约2.1 ℃, 而模拟叶片叶宽度每减少1 cm, 叶片表面温度降低0.60-0.86 ℃。该研究对深入理解植物生存策略与环境适能力具有重要意义。     

Role of electrostatics in the binding of charged metallophthalocyanines to neutral and charged phospholipid membranes

Binding of the cationic tetra(tributylammoniomethyl)-substituted hydroxoaluminum phthalocyanine (AlPcN₄) to bilayer lipid membranes was studied by fluorescence correlation spectroscopy (FCS) and intramembrane field compensation (IFC) methods. With neutral phosphatidylcholine membranes, AlPcN₄ appeared to bind more effectively than the negatively charged tetrasulfonated aluminum phthalocyanine (AlPcS₄), which was attributed to the enhancement of the coordination interaction of aluminum with the phosphate moiety of phosphatidylcholine by the electric field created by positively charged groups of AlPcN₄. The inhibitory effect of fluoride ions on the membrane binding of both AlPcN₄ and AlPcS₄ supported the essential role of aluminum-phosphate coordination in the interaction of these phthalocyanines with phospholipids. The presence of negative or positive charges on the surface of lipid membranes modulated the binding of AlPcN₄ and AlPcS₄ in accord with the character (attraction or repulsion) of the electrostatic interaction, thus showing the significant contribution of the latter to the phthalocyanine adsorption on lipid bilayers. The data on the photodynamic activity of AlPcN₄ and AlPcS₄ as measured by sensitized photoinactivation of gramicidin channels in bilayer lipid membranes correlated well with the binding data obtained by FCS and IFC techniques. The reduced photodynamic activity of AlPcN₄ with neutral membranes violating this correlation was attributed to the concentration quenching of singlet excited states as proved by the data on the AlPcN₄ fluorescence quenching.     

The effect of dielectric polarization of the electrode on anomalous temperature effects in the electrical double layer

Monte Carlo simulations and a modified Poisson–Boltzmann (MPB) theory are used to investigate the temperature dependence of the capacitance (around the potential of zero charge) of an electric double layer in the presence of surface polarization due to a dielectric boundary. Within the context of the restricted primitive model planar double layer, whose solvent dielectric constant is ε₂, the cases when the electrode is an insulator (ε₁ = 1), when the electrode and the electrolyte have the same permittivity (ε₁ = ε₂, no polarization), and when the electrode is a conductor (ε₁ → ∞) are studied for the case where the electrolyte concentration is 0.1 M. The simulations reveal a capacitance anomaly, that is, a positive temperature dependence of the capacitance at low temperatures for the former two situations. The MPB theory also shows this effect for these two situations and is in qualitative or better agreement with the simulation data. In these two cases, both the simulations and theory show a dramatic increase of the diffuse layer potential in the temperature regime where capacitance anomaly occurs. However, in the latter situation, where the electrode is metallic, the capacitance always has a negative temperature derivative for the MPB theory and probably also for the simulation data.