Fluctuator Model of Memory Dip in Hopping Insulators

We show that the non-equilibrium dynamic in two-dimensional hopping insulators close to metal-dielectric transition is sensitive to electric fields confinement inside the sample, which leads to a nearly thermally activated conductance behavior and a strong non-equilibrium conductance response to the gate voltage, including a memory dip in a field dependence of conductance.     

To react or not to react? Intrinsic stochasticity of human control in virtual stick balancing

Understanding how humans control unstable systems is central to many research problems, with applications ranging from quiet standing to aircraft landing. Increasingly, much evidence appears in favour of event-driven control hypothesis: human operators only start actively controlling the system when the discrepancy between the current and desired system states becomes large enough. The event-driven models based on the concept of threshold can explain many features of the experimentally observed dynamics. However, much still remains unclear about the dynamics of human-controlled systems, which likely indicates that humans use more intricate control mechanisms. This paper argues that control activation in humans may be not threshold-driven, but instead intrinsically stochastic, noise-driven. Specifically, we suggest that control activation stems from stochastic interplay between the operator''s need to keep the controlled system near the goal state, on the one hand, and the tendency to postpone interrupting the system dynamics, on the other hand. We propose a model capturing this interplay and show that it matches the experimental data on human balancing of virtual overdamped stick. Our results illuminate that the noise-driven activation mechanism plays a crucial role at least in the considered task, and, hypothetically, in a broad range of human-controlled processes.     

“Greening Up” Cross-Coupling Chemistry

New methodologies that enable palladium catalyzed cross-coupling reactions to be performed under environmentally benign conditions (in water and/or at room temperature) have been developed. Described approaches involve in situ activation of carbon–halogen or carbon–hydrogen bonds using zinc metal, or cationic palladium, respectively.     

Silica Colloidal Membranes with Enantioselective Permeability

Robust mesoporous membranes composed of silica spheres were surface-modified with chiral selector moieties, including small molecules, macrocycles, and polymers. Diffusion rates of enantiomers of a chiral dye through the resulting asymmetrically modified colloidal membranes were measured and the corresponding permselectivities were calculated. The membranes showed enantioselectivities in the range of 1.2–1.8, which were not significantly affected by the structure of the surface-immobilized chiral electors. This selectivity is on par with most reported polymer-based solid membranes and bulk liquid membranes. The enantioselectivity results from the surface-facilitated mechanism of transport of enantiomers through the mesopores.     

Electropolymerized flavin adenine dinucleotide as an advanced NADH transducer

Electropolymerizing the prosthetic group (flavin adenine dinucleotide, FAD) responsible in the active sites of dehydrogenases for NAD(+)|NADH regeneration, we succeeded in mimicking enzyme activity. Poly(FAD) characterized by an additional polymer-type redox reaction has been discovered as a highly effective electrocatalyst for NADH oxidation: operating at the lowest potentials reported for NADH transducers (0.00 V, pH 7.4), poly(FAD) is characterized by the electrochemical rate constant of 1.8 +/- 0.6 x 10(-3) cm s(-1), which is at the level of the NADH mass-transfer constant. Flow injection analysis of NADH with the poly(FAD)-modified wall-jet electrode as a detector has been characterized by a linear calibration range prolonged down to 5 x 10(-7) M and a sensitivity of 0.08 A M(-1) cm(-2), which taking into account the dispersion coefficient ( approximately 3), is at the diffusion-limiting value. In contrast to the low molecular weight mediators able to exhibit similar electrocatalytic properties, poly(FAD)-modified electrodes are characterized by the dramatically improved stability and, thus, can be considered as the most advantageous NADH transducers for analytical chemistry.     

Few-Layer Graphene Modified by Bridge-Like Defects as Li-Storing Cells

The paper presents some results of computer simulations and density functional theory calculations of the energetic and structural characteristics of few-layer graphene nanostructures as storing cells for Li. Modeling and calculations allow to reveal some peculiarities in such systems, which can be considered as causes of known dimension instabilities and shortening of the life-time of Li- based electrical power devices. Results of the computational study and calculations predict, that all these problems can be in significant measure solved by modifying of few-layer graphene nanostructures by bridge -like defects, which make them much more stiffer and stable against the deformation.     

Thermal instability in freshwater lakes under ice: Effect of salt gradients or solar radiation?

The phenomenon of “temperature dichotomy”, or anomalous heating of surface water under the ice up to temperatures exceeding 4 °C is known to take place occasionally in solar-heated ice-covered freshwater lakes and has usually been explained by the stabilizing effect of the weak vertical salinity gradient created by the melt water flux from the ice and supporting the unstable temperature distribution. Here, we report an observation of the local temperature maximum in the upper part of the water column of ice-covered Lake Vendyurskoe (northwestern Russia). The observation was accompanied by vertically resolved measurements of the conductivity allowing estimation of the dissolved salts effect on the vertical density distribution. The results demonstrate insufficiency of the salt gradient to support the vertical stability of water column. Therefore, we suggest the vertically inhomogeneous radiation absorption to be the probable stabilizing mechanism here, similarly to radiatively heated boundary layers in the ocean, the atmosphere and star interiors. An analytical solution of the heat transfer equation is derived describing the temperature profile evolution in ice-covered lakes subject to solar radiation heating above the maximum density temperature. Observed daytime temperature profiles agree well with the analytical model that suggests the absence of convective mixing. According to the model, the temperature maximum is formed within a day that supports the hypothesis about the stabilizing effect of the solar radiation absorption. We conclude that in temperate lakes the warm layer should have diurnal character and should be destroyed during the nighttime by convection. In polar lakes, in turn, the warm layer can exist during essentially longer periods that is supported by application of the model to the previously published data from Lake Peters, Alaska. In this case, the ice melting rate can be significantly affected by the increased temperature gradient beneath the ice. Apart from potential effects on the ice melting rate and the spring plankton development in lakes, the regime represents a rare geophysical example of instability driven solely by radiative heating with many useful analogies in planetary and stellar physics.     

Management criteria for lake ecosystems applied to case studies of changes in nutrient loading and climate change

The aim of this paper is twofold: to present and discuss practically useful management criteria from different perspectives of lake management (fishery, recreation, conservation, monitoring of water quality and use of water for irrigation and drinking), and to put these criteria into the context of a holistic lake ecosystem model, LakeWeb, which accounts for production, biomasses, predation and abiotic/biotic feedbacks related to nine key functional groups of organisms constituting the lake ecosystem. These are phytoplankton, benthic algae, macrophytes, bacterioplankton, herbivorous zooplankton, predatory zooplankton, zoobenthos, prey fish and predatory fish. The LakeWeb model also includes a mass‐balance model for phosphorus and calculates bio‐uptake and retention of phosphorus in these groups of organisms. It also includes submodels for the depth of the photic zone and lake temperature. The LakeWeb model is driven by few and readily accessible driving variables and it has been extensively tested and shown to capture fundamental lake foodweb interactions very well, which should lend credibility to the scenarios discussed in this paper regarding the conditions in Lake Batorino, Belarus. The LakeWeb model offers a tool to address important, often very complex, scientific problems in a realistic manner. The first scenario describes the changes after 1990 when there was a drastic reduction in the use of fertilizers in agriculture because of political changes and the corresponding changes in lake characteristics and foodweb structures utilizing the given management criteria. The second scenario describes, for comparative purposes, the probable alterations in the lake foodweb related to global climatic changes; in this case, warming and increased temperature variations. This study indicates that there are several similarities between eutrophication and increases in temperatures, which are discussed in this paper along with the mechanistic reasons related to such changes by using a set of general management criteria.