Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ     

Influence of surface chemistry and protein concentration on the adsorption rate and S-layer crystal formation

Bacterial crystalline surface layers (S-layers) are the outermost envelope of prokaryotic organisms representing the simplest biological membranes developed during evolution. In this context, the bacterial protein SbpA has already shown its intrinsic ability to reassemble on different substrates forming protein crystals of square lattice symmetry. In this work, we present the interaction between the bacterial protein SbpA and five self-assembled monolayers carrying methyl (CH(3)), hydroxyl (OH), carboxylic acid (COOH) and mannose (C(6)H(12)O(6)) as functional groups. Protein adsorption and S-layer formation have been characterized by atomic force microscopy (AFM) while protein adsorption kinetics, mass uptake and the protein layer viscoelastic properties were investigated with quartz crystal microbalance with dissipation monitoring (QCM-D). The results indicate that the protein adsorption rate and crystalline domain area depend on surface chemistry and protein concentration. Furthermore, electrostatic interactions tune different protein rate adsorption and S-layer recrystallization pathways. Electrostatic interactions induce faster adsorption rate than hydrophobic or hydrophilic interactions. Finally, the shear modulus and the viscosity of the recrystallized S-layer on CH(3)C(6)S, CH(3)C(11)S and COOHC(11)S substrates were calculated from QCM-D measurements. Protein-protein interactions seem to play a main role in the mechanical stability of the formed protein (crystal) bilayer.     

A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

Simultaneous measurement of mechanical and surface properties in thermoresponsive, anchored hydrogel films

Hydrogel films have been used extensively in the preparation of biosensors and biomedical devices. The characteristics of the aqueous interface of the polymer layer are significant for the biosensor or device function; likewise, the changing mechanical properties of thermoresponsive polymers are an important feature that affects the polymer behavior. Atomic force microscopy was used here to characterize both the surface and the mechanical properties of polymeric hydrogel films prepared from a thermoresponsive terpolymer of N-isopropylacrylamide and acrylic acid with benzophenonemethacrylate as a photoreactive cross-linker comonomer. The force-distance curves thus obtained were analyzed to assess both the surface forces and the mechanical response that were associated with the hydrogel. These properties were investigated as a function of temperature, in water and in Tris buffer, for different degrees of polymer cross-linking. For samples in water, the distance over which the surface forces were effective was found to remain constant as the temperature was increased from 26 to 42 °C, even though the mechanical response indicated that the samples had been heated past the lower critical solution temperature, or LCST. The bulk of the polymer becomes less soluble above the LCST, although this does not seem to affect the surface properties. This may be due to the segregation of the acrylic acid-rich polymer segments near the gel surface, which is in agreement with reports for related systems.