Fabrication of materials for medical applications from solutions of biocompatible polymers

Technologically easy incorporation of biologically active compounds in a polymeric material in spinning from a compatible solution or dispersion in a polymer solution creates the conditions for directed regulation of the structure and fabrication of composite and porous materials. Additional modification in the stage of fabrication of spinning compositions or finished polymer articles allows regulating the kinetics of separation of the biologically active compounds. __________ Translated from Khimicheskie Volokna, No. 6, pp. 21–24, November–December, 2005.     

Blockade of tetrahydrobiopterin synthesis protects neurons after transient forebrain ischemia in rat: a novel role for the cofactor

The generation of nitric oxide (NO) aggravates neuronal injury. (6R)-5,6,7,8-Tetrahydro-L-biopterin (BH4) is an essential cofactor in the synthesis of NO by nitric oxide synthase (NOS). We attempted to attenuate neuron degeneration by blocking the synthesis of the cofactor BH4 using N-acetyl-3-O-methyldopamine (NAMDA). In vitro data demonstrate that NAMDA inhibited GTP cyclohydrolase I, the rate-limiting enzyme for BH4 biosynthesis, and reduced nitrite accumulation, an oxidative metabolite of NO, without directly inhibiting NOS activity. Animals exposed to transient forebrain ischemia and treated with NAMDA demonstrated marked reductions in ischemia-induced BH4 levels, NADPH-diaphorase activity, and caspase-3 gene expression in the CA1 hippocampus. Moreover, delayed neuronal injury in the CA1 hippocampal region was significantly attenuated by NAMDA. For the first time, these data demonstrate that a cofactor, BH4, plays a significant role in the generation of ischemic neuronal death, and that blockade of BH4 biosynthesis may provide novel strategies for neuroprotection.     

Error exponents of modulo-additive noise channels with sideinformation at the transmitter

Consider the optimum strategy for using channel state (“side”) information in transmission over a modulo-additive noise channel, with state-dependent noise, where the receiver does not have access to the side information (SI). Previous work showed that capacity-wise, the optimum transmitter shifts each code letter by a “prediction” of the noise sample based on the SI. We show that this structure achieves also the random-coding error exponent, and, therefore, is optimum at some range of rates below capacity. Specifically, the optimum transmitter predictor minimizes the Renyi entropy of the prediction error; the Renyi order depends on the rate, and goes to one (corresponding to Shannon entropy) for rates close to capacity. In contrast, it is shown that this “prediction strategy” may not be optimal at low transmission rates     

Least squares solutions of the HJB equation with neural network value-function approximators.

In this paper, we present an empirical study of iterative least squares minimization of the Hamilton-Jacobi-Bellman (HJB) residual with a neural network (NN) approximation of the value function. Although the nonlinearities in the optimal control problem and NN approximator preclude theoretical guarantees and raise concerns of numerical instabilities, we present two simple methods for promoting convergence, the effectiveness of which is presented in a series of experiments. The first method involves the gradual increase of the horizon time scale, with a corresponding gradual increase in value function complexity. The second method involves the assumption of stochastic dynamics which introduces a regularizing second derivative term to the HJB equation. A gradual reduction of this term provides further stabilization of the convergence. We demonstrate the solution of several problems, including the 4-D inverted-pendulum system with bounded control. Our approach requires no initial stabilizing policy or any restrictive assumptions on the plant or cost function, only knowledge of the plant dynamics. In the Appendix, we provide the equations for first- and second-order differential backpropagation.     

Quantification of social costs associated with construction projects: state-of-the-art review

Communities that surround an operating construction site often find themselves subjected to negative impacts such as annoyances and economic losses. The latter often called “social costs”, refer to the monetary equivalent of consumed resources, loss of income and loss of enjoyment experienced by parties not engaged in the contractual agreement, solely due to a construction process. Social costs take many forms including loss of revenue, productivity and time, consumption of non-renewable resources and accelerated deterioration of secondary roads.Social costs, while widely acknowledged, are rarely considered in the design, planning or bid evaluation phases of construction projects in North America. This is attributed to the difficulty associated with quantifying social costs using standard estimating methods and the fact that these costs are borne by the community rather than the contractual parties. This paper outlines 22 sources of social costs associated with construction projects in urban environments. The concept of ‘social indicators' is introduced as a mean to link adverse impacts generated by construction activities and valuation methods. Thereafter, seven methodologies developed in the fields of economics and actuary are presented and their suitability for quantifying specific classes of social costs associated with construction projects are investigated. The capacity of current bid evaluation methods to account for social costs is also examined. It is concluded that a methodical approach for the incorporation of social costs in the bid evaluation process will be a key step towards a more sustainable-oriented construction industry. A generic framework for the development of such an approach is presented. Finally, the concept of developing a standard reference document to estimate social costs is examined and a sample format proposed.     

Surface energy of polyester and viscose fibres modified with polyfluoroalkyl acrylates

The comparative effectiveness of using polyfluoroalkyl acrylates of different structure to decrease the surface energy of viscose and polyester fibres was investigated. It was found that polyfluoroalkyl acrylates with a linear alkyl radical of optimum length (6–8 fluorinated atoms) were the most effective in decreasing the surface energy of viscose and polyester fibres; branching of the fluoroalkyl radical and appearance of oxygen atoms in the perfluorinated radical decreased the effectiveness of the modifier polymer. The index of the critical surface tension of heptane—oil mixtures was used as the criterion for evaluating the effectiveness of the polyfluoroalkyl acrylates in reducing the wettability of the fibre. The most effective modifier among the new polyfluoroalkyl acrylates was selected based on the results of the studies — polyperfluorodecyl acrylate. __________ Translated from Khimicheskie Volokna, No. 3, pp. 9–12, May–June, 2007.     

ATP hydrolysis induces an intermediate conformational state in GroEL

The conformational properties of the molecular chaperone GroEL in the presence of ATP, its non-hydrolyzable analog 5'-adenylimidodiphosphate (AMP-PNP), and ADP have been analyzed by differential scanning calorimetry (DSC), Fourier-transform infra-red (FT-IR) and fluorescence spectroscopy. Nucleotide binding to one ring promotes a decrease in the Tm value of the GroEL thermal transition that is reversed when both rings are filled with nucleotide, indicating that the sequential occupation of the two protein rings by these nucleotides has different effects on the GroEL thermal denaturation process. In addition, ATP induces a conformational change in GroEL characterized by (a) the appearance of a reversible low temperature endotherm in the DSC profiles of the protein, and (b) an enhanced binding of the hydrophobic probe 8-anilino-naphthalene-1-sulfonate (ANS), which strictly depends on ATP hydrolysis. The similar sensitivity to K+ of the temperature range where activation of the GroEL ATPase activity, the low temperature endotherm, and the increase of the ANS fluorescence are abserved strongly indicates the existence of a conformational state of GroEL during ATP hydrolysis, different from that generated on ADP or AMP-PNP binding. To achieve this intermediate conformation, GroEL mainly modifies its tertiary and quaternary structures, leading to an increased exposure of hydrophobic surfaces, with minor rearrangements of its secondary structure.     

Preparation of magnesite ore in mining

It is shown that the chemical composition of the mined magnesite ore is interrelated with its lumpiness. It is established that the content of harmful admixtures in fine fractions exceeds that in coarse fractions by a factor of 2–3. The discovered dependences have been used in a series of full-scale tests that reflect the main laws of segregation of the raw material in storage. The results have made it possible to use the effect of segregation for primary preparation of the ore in the mining stage. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 7, pp. 35 – 38, July, 2000.     

Film materials with controlled release of biologically active substances

The properties of spun composites containing polyvinyl alcohol, a proteolytic enzyme (protease C or Terrilytin) and the high-molecular-weight antimicrobial polyhexamethyleneguanidine hydrochloride were investigated. The effect of the composition of the spinning compositions and spinning temperature on the properties of the film materials — the activity, stability, and rate of release of biologically active substances — was investigated. The possibility of obtaining polyvinyl alcohol films with controlled release of biologically active substances was demonstrated. Translated from Khimicheskie Volokna, pp. 44–48, September–October, 1998.