A mathematical analysis of SFAP convolutional models

In this paper we compare, from a mathematical point of view, two well-recognized single fiber action potential (SFAP) convolutional models: the Nandedkar-Stalberg (N-S) model and the Dimitrov-Dimitrova (D-D) model. Junction waves appear in N-S SFAPs due to the onset and extinction of the monopoles whereas in D-D SFAPs these waves appear only when the dipoles reach the fiber/tendon junctions. D-D junction waves model more accurately the out-of-the-main-spike waveforms that appear in experimental SFAPs. The origin of junction waves lies in the discontinuities of the impulse responses. There are two kinds of these waves caused by the two types of existing discontinuities (in the impulse response function and in its derivative). We model each kind of discontinuity with a different mathematical function. Using these functions, the N-S and D-D impulse responses can be split and, therefore, the junction waves can be separated from the spike component of the SFAP. The expansion of the impulse response helps us to understand the differences between the N-S and D-D junction waves.     

Tumor necrosis factor-induced contraction of cultured rat mesangial cells: interaction with angiotensin II

The role of tumor necrosis factor alpha in the regulation of renal function, particularly glomerular filtration rate, has not been completely defined. This study was designed to assess the intrinsic role of this cytokine on glomerular filtration rate by analyzing its short-term effect on the degree of contraction in cultured rat mesangial cells, not only directly but also in the presence of angiotensin II. Contraction was evaluated both morphologically--by measuring planar cell surface area of cultured rat mesangial cells and glomerular cross-sectional area of isolated rat glomeruli--and biochemically--by analyzing myosin light-chain phosphorylation in cells. Tumor necrosis factor alpha significantly decreased planar cell surface area in a dose-dependent and time-dependent manner, an effect completely abolished by preincubation of the cells with platelet-activating factor receptor antagonists BN 52021 and alprazolam. This effect was also observed in the presence of angiotensin II, whether tumor necrosis factor alpha was added before or after angiotensin II, increasing the reduction in planar cell surface area induced by angiotensin II in both cases. Changes in planar cell surface area were evident not only when the absolute values of this parameter were considered but also when the percentage of contracted cells (cells with a planar cell surface area reduction > 10%) was analyzed. Tumor necrosis factor alpha also induced a significant reduction of glomerular cross-sectional area in isolated rat glomeruli. The results of the morphologic studies were supported by myosin light-chain phosphorylation experiments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of Gate Oxide in AlGaN/GaN High-Electron-Mobility Transistor pH Sensors

We report on a comparison of different gate oxides for AlGaN/GaN high-electron-mobility transistor (HEMT) pH sensors. The HEMTs show a linear increase in drain-source current as the pH of the electrolyte solutions introduced to the gate region is decreased. Three different gate oxides were examined, namely the native oxide on the AlGaN surface, a UV-ozone-induced oxide and an Sc₂O₃ gate deposited by molecular beam epitaxy. The Sc₂O₃ produced superior results in terms of resolution in measuring small changes in pH. The devices with Sc₂O₃ in the gate region exhibited a linear change in current between pH 3 and 10 of 37 μA/pH with a resolution of <0.1 pH over the entire pH range. In contrast, the native oxide devices showed a larger change in current, ∼70 μA/pH, but with a degraded resolution of ∼0.4 pH. Results for the UV-ozone oxide were intermediate in resolution, 0.2 pH. These HEMTs have promise for detecting pH changes in biological samples and can be readily integrated into a standard package for wireless data transmission.     

Ternary thiophene–X–thiophene semiconductor building blocks (X = fluorene, carbazole, phenothiazine): Modulating electronic properties and electropolymerization ability by tuning the X core

To achieve rationalization criteria for target-oriented molecular design of Th–X–Th (Th = thiophene) semiconductor building blocks, we have carried out an extensive investigation on the effects of the X core (X = fluorene, carbazole or phenothiazine) on the electronic properties and polymerization ability of Th–X–Th monomers and on the electronic and structural properties of the corresponding periodic conducting polymers –(Th–X–Th)_n–, obtained by electropolymerization and, for comparison's sake, by FeCl₃-catalyzed polymerization and/or Suzuki coupling. The effects of molecule bending and of solubilising bulky alkyl substituents have also been considered. The systematic, exhaustive template sequence combined with a rigorous, multitechnique investigation protocol affords a unique data library and a complete set of reliable interpretative/predictive guidelines.     

Dynamic brand-image-based production location decisions

In this paper, we study the dynamic production location decisions of a manufacturer of a certain branded product. Considering brand-image as a form of goodwill, we extend the well-known Nerlove-Arrow dynamic model by adding both country-image and price. Formulating an optimal control problem for a group of countries in which the cost of production is convexly increasing with country-image, we are able to develop optimal decision rules for a manufacturer regarding the location of production and pricing over time. The resulted optimal policy has a very interesting pattern. Assuming that the demand rises by more than the value of the new brand-image in percentage terms, then, if brand-image is increasing toward a stationary value level, the optimal policy should be to initially locate production in countries with high image and set a high price that signals high quality. Later, the production should gradually shift to countries with lower production costs and lower image and the price lowered until the stationary value level is reached. For brand-images beyond the stationary value level, the location of production should start in a country with low costs and country-image while setting prices that signal relatively low quality. Over time, production should be shifted to countries with gradually higher costs and images while setting higher prices until the brand-image approaches the level of stationary value.