Structures and waves in a nonlinear heat-conducting medium

The paper is an overview of the main contributions of a Bulgarian team of researchers to the problem of finding the possible structures and waves in the open nonlinear heat conducting medium, described by a reaction-diffusion equation. Being posed and actively worked out by the Russian school of A. A. Samarskii and S.P. Kurdyumov since the seventies of the last century, this problem still contains open and challenging questions.Comment: 23 pages, 13 figures, the final publication will appear in Springer Proceedings in Mathematics and Statistics, Numerical Methods for PDEs: Theory, Algorithms and their Application

Migration, Transfers and Child Labor

We examine agricultural child labor in the context of emigration, transfers, and the abil-ity to hire outside labor. We start by developing a theoretical background based on Basu and Van, (1998), Basu, (1999) and Epstein and Kahana (2008) and show how hiring labor from outside the household and transfers to the household might induce a re-duction in children’s working hours. Analysis using Living Standards Measurement Survey (LSMS) data on the Kagera region in Tanzania lend support to the hypothesis that both emigration and remittances reduce child labor.child labor, emigration, transfers, Tanzania

Prediction of sanding in subsurface hydrocarbon reservoirs.

Sand production in oil and gas wells can occur if the fluid velocity exceeds a certain value. Due to drilling operations, the mechanical stresses can exceed the load bearing capacity of the rock. As the local stresses exceed certain level, a certain amount of rock is fractured into sand. Then, the sand is carried by the fluid through the wellbore depending on the flow rate. The amount of the solids can be less than a few grams per cubic meter of reservoir fluid or an essential amount. In the later case erosion of the rock and removing sufficient quantities of rock can occur. This can produce subsurface cavities which collapse and destroy the well. When sanding is unavoidable it is necessary to estimate the characteristics of the process. Our aim was to generate a simple one-dimensional local model, which predicts the volume of sanding, the radius and the porosity of the yielded zone. Such model will help the company in the development of complex 3D models

Dynamics of nearly spherical vesicles in an external flow

We analytically derive an equation describing vesicle evolution in a fluid where some stationary flow is excited regarding that the vesicle shape is close to a sphere. A character of the evolution is governed by two dimensionless parameters, $S$ and $\Lambda$, depending on the vesicle excess area, viscosity contrast, membrane viscosity, strength of the flow, bending module, and ratio of the elongation and rotation components of the flow. We establish the ``phase diagram'' of the system on the $S-\Lambda$ plane: we find curves corresponding to the tank-treading to tumbling transition (described by the saddle-node bifurcation) and to the tank-treading to trembling transition (described by the Hopf bifurcation).Comment: 4 pages, 1 figur

Good and bad institutions:is the debate over? Cross-country firm-level evidence from the textile industry

Using firm-level data from nine developing countries, we demonstrate that certain institutions, like restrictive labour market regulations, that are considered bad for economic growth might be beneficial for production efficiency, whereas good business environment, which is considered beneficial for economic growth, might have an adverse impact on production efficiency. We argue that our results suggest that there might be significant difference in the macro- and micro-impacts of institutional quality, such that the classification of institutions into 'good' and 'bad might be premature

Protonation of citraconic and glutaconic acid in perchloric acid media

The protonation process of citraconic and glutaconic acid in perchloric acid media was followed using the method of UV spectroscopy. The observed changes in the UV spectra of investigated acids confirmed that the protonation process in perchloric acid with concentration from 5 to 10 mol/dm3 occurred. Glutaconic acid behaved as weak organic base in perchloric acid media and existed in its monoprotonated form. On the other hand, citraconic acid existed in its protonated form and as protonated anhydride at higher perchloric acid concentration. Using the absorbance data the thermodynamic dissociation constants were calculated applying the methods of Yates and McClelland, Bunnett and Olsen, and the “excess acidity” function method. The solvatation parameters m, m* and were evaluated, as well. In order to correct the medium effect the method of characteristic vector analysis was applied. The possible site where the protonation may take place was discussed using the partial atomic charge values determined according to AM1 and PM3 semiempirical methods

STUDIES ON CYTOMEGALOVIRAL (CMV) INFECTIONS IN NEWBORN CHILDREN

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Binding of His-tagged fluorophores to lipid bilayers and giant vesicles

His-tagged molecules can be attached to lipid bilayers via certain anchor lipids, a method that has been widely used for the biofunctionalization of membranes and vesicles. To measure the coverage by the membrane-bound molecules, it is useful to study molecules that are fluorescent as well. Here, we use two such molecules, green fluorescence protein (GFP) and green-fluorescent fluorescin isothiocyanate (FITC), both of which are tagged with a chain of six histidines that bind to achor lipids within the bilayers. This His-tag is much smaller in size than the GFP molecule but somewhat larger than the FITC dye. The lipid bilayers form giant unilamellar vesicles (GUVs), the behavior of which can be directly observed in the optical microscope. Several protocols for the preparation of GUVs have been developed. We apply and compare three well-established protocols based on polyvinyl alcohol (PVA) hydrogel swelling, electroformation on platinum wires, and electroformation on indium tin oxide (ITO) glass. For the same nanomolar concentration in the exterior solution, the coverage by His-tagged FITC is much lower than the one by His-tagged GFP. However, for both GFP and FITC, we find that the binding of the His-tagged molecules to the anchor lipids depends strongly on the preparation method. The highest binding affinitiy is obtained for electroformation on platinum wires. PVA gel swelling gives rise to a somewhat smaller binding affinity whereas electroformation on ITO glass leads to essentially no binding. Furthermore, the binding affinitiy is also observed to depend on the pH of the aqueous solution, with a relatively weak and strong pH-dependence for His-tagged GFP and His-tagged FITC, respectively