On minimum cost isolated failure immune networks

A telecommunications network is isolated failure immune (IFI) if and only if communication between operative sites can be completed as long as network failures are isolated. It is known that the class of minimal IFI networks is equivalent to the class of spanning 2-trees. To the best of our knowledge, this work is the first computational study dealing with the construction of a minimum cost IFI network. The problem is known to be NP-complete. We develop a tabu search based heuristic for solving the minimum cost spanning 2-tree (MCS2T) problem. The complex structure of 2-trees makes the tabu search heuristic highly dependent on the starting solution. We develop four heuristic algorithms to obtain diversified good starting solutions. They are: completion of a 2-tree from a spanning tree, two greedy approaches, and a method based on the recursive definition of a 2-tree. We also formulate an integer programming problem (IP) whose objective function value is a lower bound to the MCS2T problem. We solve the IP by developing a constraint generation scheme. The algorithms were tested on complete random graphs with Euclidean distances and on two real data sets (Civil Aeronautics Board) with instances of 10, 15, 20 and 25 nodes. As a result of this research for small problems (10 and 15 nodes), the heuristic solutions are on average within 0.8% from the optimal solution and for large problems (20 and 25 nodes), the average error is less than 2.8%.     

Automatic three-dimensional spectrogoniometer for determination of optical properties and surface parameters

An automatic three-dimensional spectrogoniometer is presented. The wavelength of ligth and angles of incidence and observation are variable, making it capable of performing different optical characterizations in an integrated way.     

Synthesis of Cr x Ti1−2x Nb x O2O20≤x≤0.5 rutile solid solutions from alkoxides

In this study, Cr _x Ti_1–2x Nb _x O₂ (0 x 0.5) rutile solid solutions have been synthesized from gels built from hydrolysis-condensation of Cr (III) acetylacetonate, NbCl₅ and Ti (IV) isopropoxide mixture (polymeric gel). Characterization of these solid solutions was carried out by X-ray diffraction, ultraviolet-visible and infrared spectroscopy, differential thermal and thermogravimetric analysis and CIELAB (Commission Internationale del'Eclairage L^*a^*b^*) parameter measurements. The results obtained by the polymeric gel method were compared with those obtained by traditional ceramic synthesis. This comparison reveals some differences with regard to synthesis temperatures and reaction mechanisms. The formation of Cr _x Ti_1–2x Nb _x O₂ (0 x 0.5) rutile solid solutions by the ceramic method requires temperatures of about 1200°C and soaking times of several days. These solid solutions are synthesized at 1000°C in 24 h by the polymeric gel method. In ceramic synthesis, the CrNbO₄ compound with rutile structure appears as an intermediate compound in the formation of rutile solid solutions. In polymeric gel synthesis, however, the CrNbO₄ rutile compound was not detected in the samples.     

Plasma-enhanced fluorination of YBa2Cu3O7−δ ceramics

The radiofrequency plasma technique involving mixtures of CF₄+O₂ gases has been applied to the surface treatment of high T_c superconducting oxides (YBa₂Cu₃O_7–). Investigation of the various experimental parameters of the process has shown that the improvement of the critical current density, J _c, mainly depends on the inlet precursor composition CF₄+%O₂, on the total pressure and on the reaction time. The presence of fluorine in the bulk of the ceramics has been observed from electron microprobe analysis, together with an increase of the Cu³⁺ content. The plasma-enhanced fluorination (PEF) treatment improves the superconducting properties of the materials: both values of the resistivity in the normal state and of the superconducting transition width are reduced and the critical transition temperature is improved by about 1 K.     

Phosphofructokinase from mantle tissue of Mytilus galloprovincialis. Purification and effects of phosphorylation on the enzymatic activity

Phosphofructokinase purified from mantle tissue of the sea mussel Mytilus galloprovincialis, was phosphorylated "in vitro" by the catalytic subunit of cyclic AMP-dependent protein kinase. The incorporation of phosphate gave rise to an activation of the enzyme by increasing its affinity for fructose-6-phosphate, by decreasing its sensitivity to the inhibition by ATP and by enhancing the effect of allosteric activators (5'-AMP and fructose-2,6-bisphosphate). In addition, the effects of phosphorylation on the catalytic activity are pH-dependent.     

Network flow and 2-satisfiability

We present two algorithms for network flow on networks with infinite capacities and finite integer supplies and demands. The first algorithm runs inO(mK) time on networks withm edges, whereK=O(m²/log⁴ m) is the value of the optimal flow, and can also be applied to the capacitated case by lettingK be the sum of thefinite capacities alone. The second algorithm runs inO(wm logK) time for arbitraryK, where w is a new parameter, thewidth of the network. These algorithms as well as other uses of the notion of width lead to results for several questions on the 2-satisfiability problem: minimizing the weight of a solution, finding the transitive closure, recognizing partial solutions, enumerating all solutions. The results have applications to stable matching, wherew corresponds to the number of people andm to the instance size (usuallym w²).     

3D-line clipping algorithms — a comparative study

Some well-known line-polyhedron intersection methods are summed up and new accelerating modifications presented. Results of comparison of known and newly developed methods are included. New methods use the fact that each line can be described as the intersection of two planes.     

Valence band density of states of small cobalt particles on Si(111) substrate

Small Co particles were prepared by sputter etching of a 4–5 nm thick island-like Co film deposited on Si(111) substrate. The density of states (DOS) of the valence band was measured by means of ultraviolet photoemission (UPS) during the sputter etching to monitor the formation of small Co particles. It was found that at a given thickness of the Co island the Fermi level was shifted by 1.8-1.9 eV toward higher binding energy and theDOS decreased or no states were detectable at the Fermi level. This effect was explained by the formation of small Co particles with electronic structure which is significantly different from that of the bulk Co.     

Objective meat quality measurements of ham: A practical classification method on the slaughterline

Meat quality is one of the principal problems in Spanish dry cured ham productuon. At the experimental level, there are well developed objective instrumental measurements which can be made on the slaughterline and then, by applying the correct statistical treatment, these measurements can be used to classify hams with an acceptable degree of accuracy. These treatments, however, are not easy to apply in the industry.

In this work, 312 pork carcasses were tested at three industrial abbatoirs. Ham meat quality was determined by internal light scattering (FOP), electrical conductivity (EC) and pH measurements in Semimembranosus (SM) muscle at 45 min and 24 h post mortem. The results obtained were: 21 (6.7%) DFD; 168 (53.9%) slightly DFD; 104 (33.3%) normal; 11 (3.5%) slightly PSE; and 8 (2.6%) PSE.

A simplified method has been developed for classifying hams into quality categories, by deriving a theoretical quality value (Q) based on a simple statistical treatment of values for FOP, EC and pH. The multiple linear regression coefficient of Q was R² = 0.85 (P<0.001) with respect to the experimental variables.     

Minimum cost design of laterally loaded welded rectangular cellular plates

Material and fabrication costs are included in the cost function. The fabrication cost is calculated by three formulae relating to the preparation, welding and additional costs. The design constraints are related to bending stresses, the local buckling of ribs due to bending and shear and to the limitation of the plate thicknesses. The local buckling of the compressed face plate elements is considered by an effective width calculation. In the numerical examples, the variables are the plate dimensions and the numbers of ribs in two directions. The optimization is carried out for steel Fe 360 and Fe 510 and for various values of the fabrication cost factor. The computations are performed by using the backtrack discrete combinatorial method, Rosenbrock's Hillclimb method and the FSQP method developed by Zhou and Tits (1992), and the results are compared with each other.Partly presented at the international conference Structural Optimization '93, Rio de Janeiro, August 2–6, 1993.