Holdup and extraction characteristics of jojoba meal

Holdup and drainage characteristics have been determined for three jojoba meals of different nature and size distribution, using hexane and isopropanol as solvents. Density and viscosity properties of the oil-solvent solutions have been measured. The experimental information should be of value in the design of solvent extraction equipment for jojoba nuts.     

A GENERAL ALGORITHMIC APPROACH TO THE OPTIMAL SYNTHESIS OF ENERGY-EFFICIENT DISTILLATION TRAIN DESIGNS

Significant energy savings in conventional distillation trains can be achieved by (i) altering the processing sequence, and (ii) performing intercolumn energy matches through an appropriate choice of the column pressures. Prior works have shown that the best thermally-coupled distillation systems usually feature near-minimum utility costs. By choosing the least utility cost as the design target, the synthesis of a heat-integrated distillation train is formulated as a mixed-integer linear programming problem to find simultaneously all the best separation strategy, column pressures and HX-network. Every feasible high-order intercolumn heat match is considered in the model. The search for the global optimum is made by applying a standard branch-and-bound technique for MILP problems. The proposed formulation has successfully been applied to a five-component mixture separation problem.     

Minimum utility usage in heat exchanger network synthesis A transportation problem

This paper formulates the minimum utility calculation for a heat exchanger network synthesis as a “transportation problem” from linear programming, allowing one to develop an effective interactive computing aid for this problem. The approach is to linearize cooling/heating curves and partition the only at potential pinch points. In this formulation user imposed constraints are readily included, the latter permitting selected stream/stream matches disallowed in total or in part.By altering the formulation of the objective function, the paper also shows how to solve a minimum utility cost problem, where each utility is available at a single temperature level. A procedure is included to handle a utility which passes through a temperature change when being used.Extending the partitioning procedure permits the formulation to accommodate match dependent approach temperatures, an extension which is useful when heat transfer through a third fluid only is allowed for some matches.     

Synthesizing heat exchanger networks having restricted stream/stream matches using transportation problem formulations

This paper presents an algorithm which is readily computer implementable for the synthesis of heat exchanger networks. The algorithm permits the user to impose constraints disallowing in part or in total the matching of any of the stream pairs. Earlier work showed how to discover minimum utility use for these restricted match problems. Constraining utility use to any feasible limit desired, this paper shows how to discover networks requiring the fewest stream/stream matches and among those to discover networks of simply topology. If required, the algorithm will generate cyclic and/or split stream networks. The algorithm involves the formulation, solving and post processing of a series of linear “transportation” problems. Such problems are linear programming problems of special structure which can be solved extremely rapidly using existing computer codes.     

GENERAL APPLICABILITY OF A METHOD FOR OBTAINING YEAST PROTOPLASTS USING A LYTIC PREPARATION FROM STREPTOMYCES

The ability of a lytic preparation from Streptomyces WL-6 to produce yeast protoplasts was analysed. True protoplasts were found to be produced from strains of the following yeasts: Trigonopsis variabilis, Toruiopsis stellata, Candida puicherrima, Saccharomyces carisbergensis, Saccharomyces cerevisiae and Saccharomyces meilis. The time necessary to obtain 100% protoplasts varied from 35 to 50 min.     

Towards molecular spintronics

The ability to manipulate electron spin in organic molecular materials offers a new and extremely tantalizing route towards spin electronics, both from fundamental and technological points of view. This is mainly due to the unquestionable advantage of weak spin-orbit and hyperfine interactions in organic molecules, which leads to the possibility of preserving spin-coherence over times and distances much longer than in conventional metals or semiconductors. Here we demonstrate theoretically that organic spin valves, obtained by sandwiching an organic molecule between magnetic contacts, can show a large bias-dependent magnetoresistance and that this can be engineered by an appropriate choice of molecules and anchoring groups. Our results, obtained through a combination of state-of-the-art non-equilibrium transport methods and density functional theory, show that although the magnitude of the effect varies with the details of the molecule, large magnetoresistance can be found both in the tunnelling and the metallic limit.     

Ptuba: a tool for the visualization of helix surfaces in proteins

Projection of transmembrane helices using a Uniform B-spline Algorithm is a tool for the visualization of interactions between helices in membrane proteins. It allows the user to generate projections of 3D helices, no matter what their deviations from a canonical helix might be. When associated with adapted coloring schemes it facilitates the comprehension of helix-helix interactions. Examples of transmembrane proteins were chosen to illustrate the advantages that this method provides. In the glycophorin A dimer we can easily appreciate the structural features behind homodimerisation. Using the structure of the fumarate reductase we analyze the contact surfaces inside a helical bundle and thanks to structures from a molecular dynamics simulation we see how modifications in structure and electrostatics relate to their interaction. We propose the use of this tool as an aid to the visualization and analysis of transmembrane helix surfaces and properties.     

Autothermal reactors with internal heat exchang—I Numerical and experimental studies in the multiple steady-state region

Detailed numerical and experimental studies in the multiple steady-state region of an autothermal reactor with internal countercurrent heat exchange were conducted. The mildly exothermic water-gas shift reaction was used in the studies. In this distributed-parameter system multiple steady states were found experimentally. Although significant radial and longitudinal temperature gradients exist, one-dimensional (radially-lumped) simulations predict mean behavior quite well. For two-dimensional simulations, Legendre polynomial trial functions give faster convergence than Jacobi polynomials when using orthogonal collocation methods. Inflections in the radial temperature gradients were measured near the hot spot although not predicted by the simulations. Significant temperature jumps at the inner wall upstream of the hot spot were also measured. Production of hydrogen could be conducted at surprisingly mild conditions if the reactor could be controlled in a stable mode essentially identical to the middle unstable steady state.     

Mineral migration from stainless steel, cast iron and soapstone (steatite) Brazilian pans to food preparations

Culinary utensils may release some inorganic elements during food preparation. Mineral migration can be beneficial for as long as it occurs in amounts adequate to the needs of the consumer or no toxicological implications are involved. In this study, the migrations of Fe, Mg, Mn, Cr, Ni and Ca, along seven cooking cycles were evaluated for two food preparations (polished rice and commercial tomato sauce, the latter as an acid food), performed in unused stainless steel, cast iron and soapstone pans, taking refractory glass as a blank. Minerals were determined by inductively coupled plasma optical emission spectrometry (ICP OES). The utensils studied exhibited different rates, patterns and variability of migration depending on the type of food. Regression analysis of the data revealed that, as a function of the number of cycles, the iron pans released increasing amounts of iron when tomato sauce was cooked (y = 70.76x + 276.75; R2 = 0.77). The soapstone pans released calcium (35 and 26 mg/kg), magnesium (25 and 15 mg/kg) into the tomato sauce and rice preparations, respectively. Additionally, the commercial tomato sauce drew manganese (3.9 and 0.6 mg/kg) and some undesirable nickel (1.0 mg/kg) from the soapstone material, whereas the stainless steel pans released nickel at a lower rate than steatite and in a diminishing fashion with the number o cooking cycles, while still transferring some iron and chromium to the food. We conclude that while cast iron and glass could be best for the consumer's nutritional health, stainless steel and steatite can be used with relatively low risk, provided acid foods are not routinely prepared in those materials.     

A quadratic optimization method for connectivity and coverage control in backbone-based wireless networks

The use of directional wireless communications to form flexible mesh backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional homogeneous wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure backbone network requirements such as coverage and connectivity in a dynamic wireless environment. This paper considers the use of mobility control, as the dynamic reposition of backbone nodes, to provide assured coverage-connectivity in dynamic environments. This paper presents a novel approach to the joint coverage-connectivity optimization problem by formulating it as a quadratic minimization problem. Quadratic cost functions for network coverage and backbone connectivity are defined in terms of the square distance between neighbor nodes, which are related to the actual energy usage of the network system. Our formulation allows the design of self-organized network systems which autonomously achieve energy minimizing configurations driven by local forces exerted on network nodes. The net force on a backbone node is defined as the negative energy gradient at the location of the backbone node. A completely distributed algorithm is presented that allows backbone nodes to adjust their positions based on information about neighbors’ position only. We present initial simulation results that show the effectiveness of our force-based mobility control algorithm to provide network configurations that optimize both network coverage and backbone connectivity in different scenarios. Our algorithm is shown to be adaptive, scalable and self-organized.