Noise and coupling induced synchronization in a network of chaotic neurons

The synchronization in four forced FitzHugh–Nagumo (FHN) systems is studied, both experimentally and by numerical simulations of a model. We show that synchronization may be achieved either by coupling of systems through bidirectional diffusive interactions, by introducing a common noise to all systems or by combining both ingredients, noise and coupling together. Here we consider white and colored noises, showing that the colored noise is more efficient in synchronizing the systems respect to white noise. Moreover, a small addition of common noise allows the synchronization to occur at smaller values of the coupling strength. When the diffusive coupling in the absence of noise is considered, the system undergoes the transition to subthreshold oscillations, giving a spike suppression regime. We show that noise destroys the appearance of this dynamical regime induced by coupling.     

The analysis of the magnetic properties in the intermetallic YxGd1−xNi3 compounds

In the paper an influence of Gd/Y substitution on the magnetic properties and exchange interactions of the Y_xGd_1−xNi₃ (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) polycrystalline compounds have been studied. The partial replacement of Gd by Y atoms is reflected in decreasing of the Curie temperature (T_C) as well as decreasing of effective the magnetic moment (μ_eff). It has been shown that such a behaviour strongly depends on the magnetic interactions. Exchange coupling parameters of R–R (A_RR), T–T (A_TT) and R–T (A_RT) have been evaluated from M(T) magnetization curves (2–300 K, 2 T) based on the mean field theory (MFT) calculation. The magnetocaloric effect (MCE) has been estimated from the family of magnetic isotherms. The magnetic entropy indicates relatively small change with the Gd/Y substitution. The value of ΔS_m(T,H) is higher for Gd-rich compounds and, respectively, decreases with Gd/Y substitution.     

LP and SDP branch-and-cut algorithms for the minimum graph bisection problem: a computational comparison

While semidefinite relaxations are known to deliver good approximations for combinatorial optimization problems like graph bisection, their practical scope is mostly associated with small dense instances. For large sparse instances, cutting plane techniques are considered the method of choice. These are also applicable for semidefinite relaxations via the spectral bundle method, which allows to exploit structural properties like sparsity. In order to evaluate the relative strengths of linear and semidefinite approaches for large sparse instances, we set up a common branch-and-cut framework for linear and semidefinite relaxations of the minimum graph bisection problem. It incorporates separation algorithms for valid inequalities of the bisection cut polytope described in a recent study by the authors. While the problem specific cuts help to strengthen the linear relaxation significantly, the semidefinite bound profits much more from separating the cycle inequalities of the cut polytope on a slightly enlarged support. Extensive numerical experiments show that this semidefinite branch-and-cut approach without problem specific cuts is a superior choice to the classical simplex approach exploiting bisection specific inequalities on a clear majority of our large sparse test instances from VLSI design and numerical optimization.     

Flow injection titration basing on the merging-zone technique

The proposed approach relies on titration of a sample that is gradually diluted in strictly controlled way in the flow injection system developed. On each step of sample dilution equal volumes of the sample and titrant solutions are simultaneously injected into two carrier streams and the zones are merged with each other. Then, they are mixed completely in the mixing chamber, merged with a stream of indicator and directed to a detector. It has been revealed that the method provides the results with accuracy better than ±3.3% (RE) and with mean repeatability lower than 1.0% (RSD). When the analyte concentration in a sample is too low to be determined directly, the procedure of titration with standard addition is exploited. The proposed approach has been successfully applied to the determination of total acidity in vinegars and magnesium and calcium in pharmaceutical products. The results obtained were comparable with those provided by the reference methods. The proposed procedure is characterized by low consumption of sample (usually less than 2 mL), titrant (about 3 mL) and indicator (about 0.6 mL). Average time of a single analysis is similar to time of traditional batch analysis.     

Determination of the Lipophilicity of Twenty-Seven Imidazo[2,1-c][1,2,4]triazine Derivatives with Strong Biological Activity by Reversed-Phase TLC. Comparison with Results Obtained by Use of Computational Algorithms

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity, log P, of 27 novel imidazo[2,1-c][1,2,4]triazine derivatives with strong biological activity has been determined...     

Cooperativity, sensitivity, and noise in biochemical signaling

Cooperative interactions in the binding of multiple signaling molecules is a common mechanism for enhancing the sensitivity of biological signaling systems. It is widely assumed this increase in sensitivity of the mean response implies the ability to detect smaller signals. Extending the classic work of Berg and Purcell [Biophys. J. 20, 193 (1977)] on the physical limits of chemoreception, we show that the random arrival of diffusing signaling molecules at receptor sites constitutes a noise source that is not reduced by cooperativity. Cooperativity makes reaching this limit easier, but cannot reduce the limit itself.     

The Use of Starch Drying Kinetics Curves for Experimental Determination of Its Specific Surface Area

The most popular method for the calculation of specific surface area is its determination from water vapour sorption isotherms. The study presented here has been designed for the purpose of optimisation and selection of the conditions of drying so as to allow the determination of specific surface area from plotted curves of the drying process. The results indicate that drying curves can be used as the basis for the determination of specific surface area, the values of which do not differ statistically significantly (α = 0.05) from those determined from isotherms of water vapour sorption (adsorption/desorption).     

Structure, Conformation, and Stereodynamics of N-Nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes and N-Nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ones(1)

The variable temperature (1)H, (13)C, and (19)F NMR spectra were measured for the title N-nitrosamines. The observed unusually low N-N rotation barriers (12-15 kcal/mol) result from a significant deviation of the nitrosamino system from planarity. A pyramidal character of the amino nitrogen was confirmed by the X-ray crystal structures of two compounds and by bathochromic shifts of the n-pi absorption bands in the UV spectra. The nonplanarity of the nitrosamino moiety is due to the strong pseudoallylic A((1,3)) strain caused by the steric interaction of the NNO group with the neighboring aryl substituents fixed in the equatorial positions of the bicyclic skeleton. In addition, the barriers to the C-C rotation of aryl groups were examined at temperatures lower than required to "freeze" the N-N rotation and different DeltaG() values were observed for the aryls oriented syn and anti to the nitroso oxygen.     

Estimation of trioctylphosphine oxide (TOPO) diffusion coefficients by dynamic adsorption measurements in model extraction systems

Equilibrium interfacial tension and surface excess isotherms for trioctylphosphine oxide (TOPO) were determined and interpreted. Despite its high hydrophobicity, TOPO adsorbs at the hydrocarbon/water interfaces and decreases effectively the interfacial tension. The interfacial activity of TOPO is affected by the type of organic diluent and the composition of the aqueous phase, i.e., the kind (HNO(3), KNO(3)) and the concentration of nonorganic electrolyte present in the system. Significant lowering of TOPO interfacial activity is observed with an increase of the aqueous phase acidity. The dynamic interfacial tension for TOPO was measured by using the drop volume technique. With the aid of the Ward and Tordai equation the values of the diffusion coefficients of TOPO were estimated. The values determined were in the right order of magnitude compared with the literature data.     

Epitope-targeted proteome analysis: towards a large-scale automated protein–protein-interaction mapping utilizing synthetic peptide arrays

We describe the development of a process for the genome-wide mapping of interactions between protein domains and peptide ligands entirely based on high-throughput biochip technologies. A phage library displaying protein domains from a randomly fragmented and cloned cDNA library will be "panned" on an array of synthetic peptide ligands. After multiplexed affinity enrichment, peptide-specific phage populations will be automatically eluted, propagated, labelled and identified by hybridisation to a DNA microarray. Peptide arrays are synthesized in situ by SPOT synthesis on a planar substrate. By utilizing a commercially available library of human brain cDNA plus a set of distinct model domains cloned into T7-phage, we could show that a single panning round on an array of known peptide ligands for these model domains synthesized on a cellulose membrane can yield an enrichment of better than a factor of 1,000. This is sufficient to detect peptide-specific enrichment of Cy3(post-panning) against Cy5(pre-panning)-labelled phage DNA inserts on a cDNA microarray. Thus, the proof-of-principle of our approach could be successfully demonstrated and first interaction data are being collected.