An approach to emulating separable graphs

A technique foremulating multicomputer interconnection networks that are based onseparable graphs (graphs having bounded degree and sublinear multicolor recursive bisectors) is presented. Efficient emulations among interconnection networks are necessary for porting programs designed for one network to another.Emulations are formalized asgraph embeddings, where the nodes (processors) of theguest graph (emulated network) are assigned to nodes of thehost graph (emulator), while the edges (communication links) of the guest are routed via paths in the host. The communication slowdown in an emulation depens on thedilation (length of the longest routing path) and thecongestion (number of paths that contend for a host edge) of the embedding. Theexpansion of the embedding (the ratio of the sizes of the host to guest) determines the inefficiency of processor utilization. Cell trees are introduced as interconnection networks whose special communication properties enable them to serve as intermediate devices in these emulations. Nodes in cell trees are organized into equinumerous parts calledcells; the cells are labeled by nodes of a complete binary tree. Communication in cell trees is restricted to two specific and distinct primitives:cell communication is confined within cells, whiletransfer communication occurs between adjacent cells. Rather than solved directly, the emulation problem for the original guest-host pair is decomposed into two independent parts: emulating the guest by the cell tree, and emulating the cell tree by the host.In emulations of separable graphs by cell trees, the node assignment that ensures small dilation is derived from the separator-based decomposition of guest graphs. The congestion-free edge routing is achieved by coordinatingglobal andlocal phases, which are based on two characteristic cell-tree communication primitives.The technique is instantiated by emulating cell trees on specific host graphs. Withshuffle-like hypercube-derivative networks as hosts new constant-expansion emulations are obtained that have both dilation and congestion logarithmic in the size of the multicolor bisector of guest graphs. These emulations are the first such to have optimal (up to constants)congestion; they provide the firstoptimal algorithm for emulating arbitrary separable graphs on shuffle-like networks. The application of the technique tohypercubes as hosts also produces optimal emulations that differ from those previously known by having smaller expansion constants.This research was supported in part by NSF Grants CCR-88-12567 and CCR-90-13184, and by the University of Massachusetts Graduate School Fellowship for the academic year 1991-92. A preliminary version of this paper was presented at the 3rd ACM Symposium on Parallel Algorithms and Architectures, July 22–24, 1991, in Hilton Head, South Carolina, USA.     

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.     

Chromosomal location of the genetic determinants for bacteriocins produced by Lactobacillus gasseri K7

The production of similar or even identical bacteriocins by different lactic acid bacteria is not a rare event. To take advantage of this finding, genetic determinants of the Lactobacillus K7 bacteriocins were tested for putative homologies with previously described bacteriocins of the Lactobacillus acidophilus group through polymerase chain reaction (PCR). Among specific primer pairs of seven known bacteriocins, derived from their respective sequences, only acidocin LF221 A and B primers amplified fragments in chromosomal DNA of K7 strain that revealed strong similarity over small regions of LF221 bacteriocins. Treatment of Lactobacillus K7 with ethidium bromide and mitomycin C was ineffective in generating non-bacteriocinogenic derivatives and had no impact on plasmid loss either. Classification studies elucidated Lactobacillus K7 as a member of the Lactobacillus gasseri species.     

Gas–liquid mass transfer in periodically operated trickle-bed reactors: Influence of the liquid-phase physical properties and flow modulation

The influence of periodic operation on trickle-bed reactor (TBR) hydrodynamics and gas–liquid mass transfer was investigated. Two-phase pressure drop, dynamic liquid hold-up and gas–liquid mass transfer coefficient (k_La) were determined at various liquid flow rates and for different modes of liquid flow variation (increasing and decreasing liquid flow rate). The results reveal the considerable influence of type of liquid flow rate modulation on k_La values (deviations of up to 80% in k_La). Simulation studies on gas-limited reaction in a periodically operated TBR indicate that an enhancement in conversion of about 14% can be expected from an appropriate selection of the operating mode, thus clearly demonstrating the quantitative process intensification feasible through increased gas–liquid mass transfer.     

Modelling of unsteady-state hydrodynamics in periodically operated trickle-bed reactors:Influence of the liquid-phase physical properties

Process intensification using periodic operation of trickle bed reactors (TBRs) is still a long way from replacing conventional steady-state operation in industrial use, despite the numerous benefits described in the literature. Complex interactions between hydrodynamics, mass transfer and reaction phenomena make the design of periodically operated TBRs an almost insurmountable challenge. The development of hydrodynamic models able to provide reliable quantitative predictions of flow behaviour and possessing a sound physical basis, is an essential prerequisite for obtaining the necessary insights into this complexity. In this work, the two-phase pressure drop and dynamic liquid hold-up during max/min and on/off periodical operation were predicted using a model based on the relative permeability concept. In order to demonstrate the utility of this approach, a systematic investigation of the quantitative influence of the liquid-phase physical properties was carried out. The results obtained show that the modelling of the hydrodynamics in periodically operated TBRs using the relative permeability concept is feasible. By selecting suitable permeability parameters, unsteady-state hydrodynamics for different periodic operating modes can be predicted successfully.     

Non-destructive ultrasonic investigation of the structure state of steam pipelines

The main purpose of the work is to study the dependence of the ultrasonic wave parameters on the structure state in tubes of boilers at thermo-electric power station. The changes of the velocity, spectra and attenuation of ultrasonic surface waves are caused by degradation of the structure and can be used for residual life estimation of the equipment.     

Ability of Lactobacillus gasseri K 7 to inhibit Escherichia coli adhesion in vitro on Caco-2 cells and ex vivo on pigs' jejunal tissue

The ability of Lactobacillus (Lb.) gasseri K 7 to inhibit adhesion of Escherichia coli O8:K88 to intestinal mucosa was studied on cultured Caco-2 cells and ex vivo on pigs' small intestinal tissue. Lactobacilli were added simultaneously with E. coli, before E. coli and after E. coli for competition, exclusion and displacement assays. The concentration of lactobacilli on fully differentiated Caco-2 cells was 4.5+/-0.3 x 10(8) cfu/well, while the concentration of E. coli varied from 1.5 x 10(6) to 4.3 x 10(8) cfu/well. The number of E. coli adhered to Caco-2 monolayer (cfu/well) was lineary correlated (R(2)=0.97) to the concentration of added cells. In the assay simulating exclusion, E. coli adhesion was reduced by Lb. gasseri K 7 strain by 0.1 to 0.6 log cfu/well. The binding of E. coli was inhibited even more when incubated simultaneously with lactobacilli, particularly at the lowest concentration of E. coli (ratio E. coli/lactobacilli 1:248), where five-times reduction (or 0.7 log) was observed. When adhesion to tissue derived from pigs' jejunum was tested, concentration of E. coli was constant (6.9+/-0.14 x 10(7) cfu/ml), while the concentration of Lb. gasseri K 7 was 5.9 x 10(7) and 1.3 x 10(7) cfu/ml in two independent experiments, respectively. The adhesion of E. coli and Lb. gasseri K 7 cells to jejunal mucosa was similar (1.0+/-0.17 x 10(6) and 1.54+/-0.10 x 10(6) cfu/cm(2)) when the concentrations of single strains in suspensions were approximately the same. No significant competition, exclusion or displacement of E. coli by lactobacilli was observed on jejunal tissue. In conclusion, Lb. gasseri K 7 was found to be effective in reducing E. coli adhesion to Caco-2 enterocytes, but it was not able to do so in ex vivo conditions tested for pig jejunal tissue.     

Novel alginate based nanocomposite hydrogels with incorporated silver nanoparticles

Alginate colloid solution containing electrochemically synthesized silver nanoparticles (AgNPs) was investigated regarding the nanoparticle stabilization and possibilities for production of alginate based nanocomposite hydrogels in different forms. AgNPs were shown to continue to grow in alginate solutions for additional 3 days after the synthesis by aggregative mechanism and Ostwald ripening. Thereafter, the colloid solution remains stable for 30 days and could be used alone or in mixtures with aqueous solutions of poly(vinyl alcohol) (PVA) and poly(N-vinyl-2-pyrrolidone) (PVP) while preserving AgNPs as verified by UV–Vis spectroscopy studies. We have optimized techniques for production of Ag/alginate microbeads and Ag/alginate/PVA beads, which were shown to efficiently release AgNPs decreasing the Escherichia coli concentration in suspensions for 99.9% over 24 h. Furthermore, Ag/hydrogel discs based on alginate, PVA and PVP were produced by freezing-thawing technique allowing adjustments of hydrogel composition and mechanical properties as demonstrated in compression studies performed in a biomimetic bioreactor.