Wave attenuation in waveguide containing two-layer semiconductor-dielectric structure as a function of conductivity and thickness of semiconductor

The interaction of H₁₀ waves with a two-layer semiconductor-dielectric structure of finite dimensions in a rectangular wave guide is examined. The wave attenuation is calculated as a function of the conductivity and thickness of the semiconductor. It is shown that the use of semiconductor-dielectric structures makes it possible to increase the range of attenuation variation with modulation of semiconductor conductivity.Saratov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 8, pp. 712–724, August, 1992.     

Modeling fixed and fluidized reactors for cassava starch saccharification with immobilized enzyme

Cassava starch saccharification in fixed-and fluidized-bed reactors using immobilized enzyme was modeled in a previous paper using a simple model in which all dextrins were grouped in a single substrate. In that case, although good fit of the model to experimental data was obtained, physical inconsistency appeared as negative kinetic constants. In this work, a multisubstrate model, developed earlier for saccharification with free enzyme, is adapted for immobilized enzyme. This latter model takes into account the formation of intermediate substrates, which are dextrins competing for the catalytic site of the enzyme, reversibility of some reactions, inhibition by substrate and product, and the formation of isomaltose. Kinetic parameters to be used with this model were obtained from initial velocity saccharification tests using the immobilized enzyme and different liquefied starch concentrations. The new model was found to be valid for modeling both fixed- and fluidized-bed reactors. It did not present inconsistencies as the earlier one had and has shown that apparent glucose inhibition is about seven times higher in the fixed-bed than in fluidized-bed reactor.

     

Stability of immobilized amyloglucosidase in the process of cassava starch saccharification

Applied Biochemistry and Biotechnology - The half-life of immobilized amyloglucosidase was determined in a fluidized-bed reactor operating continuously with a 30% w/v liquefied cassava starch...     

β-Cyclodextrin production by simultaneous fermentation and cyclization

Production of β-cyclodextrin (CD) with high-dextrose equivalent (DE) starch hydrolysates by simultaneous fermentation and cyclization (SFC) gives higher yields than using only the enzyme CGTase, because fermentation eliminates glucose and maltose that inhibit CD production, while at the same time, produces ethanol that increases yield. A 10% (w/v) solution of cassava starch, liquefied with α-amylase, was incubated with CGTase using: only the enzyme, added ethanol (from 1 to 5%), and added yeast,S. cerevisiae (12% w/v), plus nutrients, the latter being the SFC process. Reaction conditions were: 38αC, pH 6.0, DE from 2 to 25, and 3.3 mL of CGTase/L. The yield of β-CD has decreased with an increase in DE, and maximum reaction yields were found for DE equal to 3.54, reaching 5.6, 14.7, and 11.5 mM β-CD, respectively. For an increase of DE, of approx 6 times (from 3.54 to 23.79), β-CD yield decreased 6 times for the first, and second reaction media with 3% (v/v) ethanol, and only approx 3 times for SFC (from 11.5 to 3.73 mM), showing that this process is less sensitive to variations in the DE     

Response of axisymmetric separated flow to its spatially localized perturbation

The flow past an axisymmetric body with laminar boundary-layer separation in a low-velocity air stream has been studied. The hot-wire technique was employed to identify the variation of velocity field induced by a local stationary perturbation of separation region at the stern of the experimental model. A large-scale influence upon the near-wall flow due to a cylinder roughness element provided on the model surface was observed. The obtained data substantiate the possibility of controlling the laminar boundary-layer separation on an axisymmetric body using a local external forcing.     

Algebras of Log-Integrable Functions and Operators

We show that certain spaces of \(\log \)-integrable functions and operators are complete topological \(*\)-algebras with respect to a natural metric space structure. We explore connections with the Nevanlinna class of holomorphic functions.     

Methods and Supports for Immobilization and Stabilization of Cyclomaltodextrin Glucanotransferase from Thermoanaerobacter

Thermoanaerobacter cyclomaltodextrin glucanotransferase (CGTase) was immobilized using different supports and immobilization methods to study the effect on activity recovery. The enzyme covalently attached into glyoxyl-silica showed low activity recovery of 1.5%. The hydrophobic adsorption of the enzyme on Octadecyl-Sepabeads yielded also low activity recovery, 3.83%, and the enzyme could easily leak from the support at low ionic strength, although the immobilization yield was satisfactory, approximately 76%. The CGTase encapsulated in a sol–gel matrix gave an activity recovery of 6.94% and maximum cyclization activity at 60 °C, at pH 6.0. The half-time life at 60 °C, pH 6.0, in the presence of substrate was 100 min, which was lower than that of the free enzyme. The best activity recovery in this work (6.94%) is approximately five times smaller than that obtained previously using glyoxyl-agarose as support and covalent immobilization. Thus, the best support and method we tested so far for immobilization of CGTase is covalent attachment on glyoxyl-agarose.     

The structure and dynamics of multilayer networks

In the past years, network theory has successfully characterized the interaction among the constituents of a variety of complex systems, ranging from biological to technological, and social systems. However, up until recently, attention was almost exclusively given to networks in which all components were treated on equivalent footing, while neglecting all the extra information about the temporal- or context-related properties of the interactions under study. Only in the last years, taking advantage of the enhanced resolution in real data sets, network scientists have directed their interest to the multiplex character of real-world systems, and explicitly considered the time-varying and multilayer nature of networks. We offer here a comprehensive review on both structural and dynamical organization of graphs made of diverse relationships (layers) between its constituents, and cover several relevant issues, from a full redefinition of the basic structural measures, to understanding how the multilayer nature of the network affects processes and dynamics.     

Global response of laminar flow separation to local flow perturbations (review)

In the present paper, we summarize our experimental data on flow separation control on wings at low subsonic velocities. The focus is on the reduction of the separation region by stationary and nonstationary controlled flow perturbations. Wind-tunnel data obtained for test models of different aspect ratios prove that the entire separated flow can be modified by forcing its narrow parts much smaller in size than the transverse extent of the separation region. Such an approach to flow control at laminar separation comes from non-local interaction of the large-scale flow structure with spatially concentrated disturbances.