Macro-instabilities of a Suspension in an Axially Agitated Mixing Tank

This paper deals with an experimental assessment of the occurrence of flow macro-instabilities in a mechanically stirred suspension and visual observation of the origination and extinction of macro-vortices. The mean frequency of the occurrence of macro-instabilities in operational conditions was also observed. The experiments were carried out in a cylindrical vessel with an inner diameter of 0.19 m, and an axial stirrer with six pitched 45° blades (PBT) was used. The diameter of the stirrer was equal to half of the vessel diameter. The mean frequencies of the occurrence of macro-instabilities were determined at the stirrer frequency for just suspended conditions in dependence on solids concentration and impeller clearance (height of the stirrer above the bottom of the vessel).Two regions of origin of macro-instabilities and one region of extinction were determined visually. It was found that the mean frequency of occurrence of macro-instabilities increases with increasing stirrer frequency at constant concentration of solids. At constant stirrer speed, the frequency of occurrence of macro-instabilities decreases with increasing concentration of solids. At higher concentration of solids, a sharp change toward lower mean frequencies of macro-instabilities was observed

Diversity of O Antigens within the Genus Cronobacter: from Disorder to Order

Cronobacter species are Gram-negative opportunistic pathogens that can cause serious infections in neonates. The lipopolysaccharides (LPSs) that form part of the outer membrane of such bacteria are possibly related to the virulence of particular bacterial strains. However, currently there is no clear overview of O-antigen diversity within the various Cronobacter strains and links with virulence. In this study, we tested a total of 82 strains, covering each of the Cronobacter species. The nucleotide variability of the O-antigen gene cluster was determined by restriction fragment length polymorphism (RFLP) analysis. As a result, the 82 strains were distributed into 11 previously published serotypes and 6 new serotypes, each defined by its characteristic restriction profile. These new serotypes were confirmed using genomic analysis of strains available in public databases: GenBank and PubMLST Cronobacter. Laboratory strains were then tested using the current serotype-specific PCR probes. The results show that the current PCR probes did not always correspond to genomic O-antigen gene cluster variation. In addition, we analyzed the LPS phenotype of the reference strains of all distinguishable serotypes. The identified serotypes were compared with data from the literature and the MLST database (www.pubmlst.org/cronobacter/). Based on the findings, we systematically classified a total of 24 serotypes for the Cronobacter genus. Moreover, we evaluated the clinical history of these strains and show that Cronobacter sakazakii O2, O1, and O4, C. turicensis O1, and C. malonaticus O2 serotypes are particularly predominant in clinical cases

OPTIMAL REGIONAL PLANNING APPROACH IN SOLID WASTE MANAGEMENT

Solid waste consists of all the sol id material that an urban society can no longer useconstructively or economically and must be discarded in a way that is harmful to theenvironment. As a community becomes intensively urbanized, the problem of solid wastemanagement gets more and more aggravated. Cost of providing waste management servicesis rising hoth as a result of scarcity of land and due to the tightening environmentalregulations. An approach of waste management receiving wide attention recently is toreduce the waste disposal costs hy establishing centralized facilities. Centrally operatedfacilities have the advantage of economics of scale that cannot be owned by smallermunicipalities.This paper investigates problems associated with the new approach of rcgionalizauon andwaste diversion. It also investigates the application of linear programming (LP) and mixedinteger programming (MIP) techniques for the optimal allocation of waste stream andfacility scheduling of a regional solid waste management system over a fixed planningperiod. Waste disposal options include landfilling and waste diversion through recyclingand coruposting. The regional system consists of multiple cities. landfills. material recoveryfacilities. cornposting facilities and transfer stations.This paper investigates problems associated with the new approach of rcgionalizauon andwaste diversion. It also investigates the application of linear programming (LP) and mixedinteger programming (MIP) techniques for the optimal allocation of waste stream andfacility scheduling of a regional solid waste management system over a fixed planningperiod. Waste disposal options include landfilling and waste diversion through recyclingand coruposting. The regional system consists of multiple cities. landfills. material recoveryfacilities. cornposting facilities and transfer stations.Mathematical models used for the optimization arc formulated to minimize the net presentvalue of the cost of providing waste management services in a region. The opiimizauonmodel used consists of a set of constraints defining the waste now mass balance andcapacity limitation of the facilities. It is seen that the LP approach is simple and efficient incomputation time hut the usage is limited due LO its inability to handle discrete size forfacilities and mutually exclusive situations. The MIP approach allows for formulating allpossible options into a single model run. However. as the size or the problem increases. MIPapproach may introduce a large number of binary variables into the model, increasing thetime requirement to reach the optimum solution.

A historical note on the complexity of scheduling problems

In 1972 E.M. Livshits and V.I. Rublinetsky published a paper in Russian, in which they presented linear-time reductions of the partition problem to a number of scheduling problems. Unaware of complexity theory, they argued that, since partition is not known to have a simple algorithm, one cannot expect to find simple algorithms for these scheduling problems either. Their work did not go completely unnoticed, but it received little recognition. We describe the approach and review the results

Use of cement suspension as an alternative matrix material for textile-reinforced concrete

Textile-reinforced concrete (TRC) is a material consisting of high-performance concrete (HPC) and tensile reinforcement comprised of carbon roving with epoxy resin matrix. However, the problem of low epoxy resin resistance at higher temperatures persists. In this work, an alternative to the epoxy resin matrix, a non-combustible cement suspension (cement milk) which has proven stability at elevated temperatures, was evaluated. In the first part of the work, microscopic research was carried out to determine the distribution of particle sizes in the cement suspension. Subsequently, five series of plate samples differing in the type of cement and the method of textile reinforcement saturation were designed and prepared. Mechanical experiments (four-point bending tests) were carried out to verify the properties of each sample type. It was found that the highest efficiency of carbon roving saturation was achieved by using finer ground cement (CEM 52.5) and the pressure saturation method. Moreover, this solution also exhibited the best results in the four-point bending test. Finally, the use of CEM 52.5 in the cement matrix appears to be a feasible variant for TRC constructions that could overcome problems with its low temperature resistance

Integrating Abstraction Techniques for Formal Verification of Analog Designs

The verification of analog designs is a challenging and exhaustive task that requires deep understanding of physical behaviours. In this paper, we propose a qualitative based predicate abstraction method for the verification of a class of non-linear analog circuits. In the proposed method, system equations are automatically extracted from a circuit diagram by means of a bond graph. Verification is applied based on combining techniques from constraint solving and computer algebra along with symbolic model checking. Our methodology has the advantage of avoiding exhaustive simulation normally encountered in the verification of analog designs. To this end, we have used Dymola, Hsolver, SMV and Mathematica to implement the verification flow. We illustrate the methodology on several analog examples including Colpitts and tunnel diode oscillators