Inverse scheduling with maximum lateness objective

We study a range of counterparts of the single-machine scheduling problem with the maximum lateness criterion that arise in the context of inverse optimization. While in the forward scheduling problem all parameters are given and the objective is to find the optimal job sequence for which the value of the maximum lateness is minimum, in inverse scheduling the exact values of processing times or due dates are unknown, and they should be determined so that a prespecified solution becomes optimal. We perform a fairly complete classification of the corresponding inverse models under different types of norms that measure the deviation of adjusted parameters from their given estimates.     

Structural study of the initial growth of nanocrystalline CdS thin films in a chemical bath

Nanocrystalline cadmium sulfide CdS thin films with relevance for optical applications were synthesized from aqueous solutions by chemical bath deposition. Grazing incidence X-ray diffraction shows that the films formed on glass or silicon substrates are made up of nanocrystalline particles. About 80% of the particles have a diameter of 5 ± 1 nm. The nanoparticles have either sphalerite or wurtzite structure. The presence of the sphalerite phase is a signature of a highly non-equilibrium state of the nanocrystalline film. Kinetic studies show that the size of the nanocrystals and the relative fraction of the two phases do not depend on the deposition time once it exceeds a duration of 30 min. For longer times, the particle characteristics remain constant while the thickness of the film grows. Thermodynamical analysis of ionic equilibria allows to choose the reaction bath composition for the formation of cadmium hydroxide Cd(OH)₂. The experiments provide strong evidence that the beginning of the deposition of CdS is accompanied by a formation of cadmium hydroxide Cd(OH)₂.     

Presynaptic Release of Glutamate by Heteroexchange Under Altered Gravity Conditions

The study focused on the release of glutamate by reversal of Na^?+?-dependent glutamate transporters that was investigated in cortical synaptosomes isolated from Wistar rats subjected to centrifuge-induced hypergravity of 10×g for 1 h. Transportable competitive inhibitor of glutamate transporters—DL-threo-beta-hydroxyaspartate (DL-THA) induced the release of L-[¹⁴C]glutamate via heteroexchange that consisted of 22.5 ± 1.7% of total label in normal gravity and 23.7 ± 1.7% in altered gravity conditions. Inhibition of the ability of synaptic vesicles to accumulate the neuromediator by preliminary treatment of synaptosomes with the protonophore (FCCP) augmented the release of cytosolic L-[¹⁴C]glutamate evoked by DL-THA from 44.0 ± 2.0% to 52.0 ± 2.3% of total label for G-loaded animals as compared to controls. Thus, combined application of DL-THA and FCCP revealed the increase in transporter-mediated release of glutamate that might be evidence for hypoxic injury of neurons.     

Electrochemical studies of the electron states of disordered electrochromic oxides

In this paper, we show that electrochemical quasi-steady state potential curves of disordered tungsten, titanium, cerium and iridium oxides exhibit fine structure in striking agreement with the density of electronic states, as obtained from ab initio calculations for the crystalline counterparts. The ability to probe the electronic structure by our electrochemical technique is restricted to disordered non-metallic materials. It is highly probable that the probed electronic states are required to be localized, in order for the technique to give a good picture of their density. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. By combining electrochemical and electrical conductivity measurements for the case of tungsten oxide, we have verified the localized character of the probed states and estimated their localization radius.     

Controlled synthesis of amphiphilic siloxane-siloxane block copolymers with carboxyl functions

Summary Poly[2-(carboxymethylthio)ethyl]methylsiloxane-block-polydimethylsiloxane, 1, and poly{[2-(carboxymethylthio)ethyl]methylsiloxane-co-dimethylsiloxane}-block-polydimethylsiloxane, 2, were synthesized by ene-thiol addition of mercaptoacetic acid to respective precopolymers 3 and 4, containing vinyl groups bound to silicon. The precopolymers 3 and 4 were obtained by sequential anionic copolymerization of hexamethylcyclotrisiloxane, D₃, with 2,4,6-trimethyl-2,4,6-trivinyl-cyclotrisiloxane, 5, and D₃ with 2,4,4,6,6,-pentamethyl-2-vinylcyclotrisiloxane, 6, respectively. The method permits to synthesise the block copolymers with a narrow molecular weight distribution and a high block purity. The ene-thiol addition was performed on free radical route, using AIBN as initiator. The reaction proceeds selectively, leading to the transformation of vinyl groups in the precopolymers into the β-adducts. Received: 15 December 1999/Revised version: 25 February 2000/Accepted: 24 March 2000     

DFL: A dataflow language based on Petri nets and nested relational calculus

In this paper we propose DFL—a formal, graphical workflow language for dataflows, i.e., workflows where large amounts of complex data are manipulated, and the structure of the manipulated data is reflected in the structure of the workflow. It is a common extension of (1) Petri nets, which are responsible for the organization of the processing tasks, and (2) nested relational calculus, which is a database query language over complex objects, and is responsible for handling collections of data items (in particular, for iteration) and for the typing system. We demonstrate that dataflows constructed in a hierarchical manner, according to a set of refinement rules we propose, are semi-sound, i.e., initiated with a single token (which may represent a complex scientific data collection) in the input node, terminate with a single token in the output node (which represents the output data collection). In particular they never leave any “debris data” behind and an output is always eventually computed regardless of how the computation proceeds.     

Dendrite coherency of Al-Si-Cu alloys

The dendrite coherency point of Al-Si-Cu alloys was determined by thermal analysis and rheological measurement methods by performing parallel measurements at two cooling rates for aluminum alloys across a wide range of silicon and copper contents. Contrary to previous findings, the two methods yield significantly different values for the fraction solid at the dendrite coherency point. This disparity is greatest for alloys of low solute concentration. The results from this study also contradict previously reported trends in the effect of cooling rate on the dendritic coherency point. Consideration of the results shows that thermal analysis is not a valid technique for the measurement of coherency. Analysis of the results from rheological testing indicates that silicon concentration has a dominant effect on grain size and dendritic morphology, independent of cooling rate and copper content, and thus is the factor that determines the fraction solid at dendrite coherency for Al-Si-Cu alloys.     

Stability of a shaft made from a shape memory alloy undergoing martensite transitions under the action of torque strength and an axial force

The phenomenon is analyzed of the global stability failure of an actuating body force exciter in the form of a cylindrical tube undergoing direct and reversed martensite transitions under the action of a combined axial force and torque. The stability ranges are plotted in the “axial force-torque” coordinates. For the direct transition, it is shown that these ranges may be non-convex. It is shown that a certain increase of the torque value above zero may cause an essential increase in the axial compressing force.     

Selective pressures for and against genetic instability in cancer: a time-dependent problem

Genetic instability in cancer is a two-edge sword. It can both increase the rate of cancer progression (by increasing the probability of cancerous mutations) and decrease the rate of cancer growth (by imposing a large death toll on dividing cells). Two of the many selective pressures acting upon a tumour, the need for variability and the need to minimize deleterious mutations, affect the tumour's 'choice' of a stable or unstable 'strategy'. As cancer progresses, the balance of the two pressures will change. In this paper, we examine how the optimal strategy of cancerous cells is shaped by the changing selective pressures. We consider the two most common patterns in multistage carcinogenesis: the activation of an oncogene (a one-step process) and an inactivation of a tumour-suppressor gene (a two-step process). For these, we formulate an optimal control problem for the mutation rate in cancer cells. We then develop a method to find optimal time-dependent strategies. It turns out that for a wide range of parameters, the most successful strategy is to start with a high rate of mutations and then switch to stability. This agrees with the growing biological evidence that genetic instability, prevalent in early cancers, turns into stability later on in the progression. We also identify parameter regimes where it is advantageous to keep stable (or unstable) constantly throughout the growth.     

Analytical Study of Turbulent Pollutant Dispersion near a Low Hill

An analytical methodology is developed to study the pollutant dispersion in a turbulent wind flow over a two-dimensional hill with a small slope. As in a typical boundary layer problem, the flow domain is divided into an inner and an outer region: the inviscid outer region is further subdivided into an upper and a middle layer while the viscous inner region is subdivided into a shear stress and an inner surface layer. Based on the Reynolds-averaged Navier–Stokes equations and the continuity equations, closed form analytical solutions of the stream functions and velocities are readily obtained for all regions in the domain. The velocity information is then imported into the diffusion equation, and the pollutant concentration distribution is readily solved. For reasons of turbulent shear, a variational method with adjustments to the streamline coordinate system is used to obtain an accurate solution of the pollutant concentration. Results show that when the source is located in the upper layer, the concentrations decrease with distance along the upwind side of the hill and tend to reach a constant value rapidly near the hilltop. Similar results are observed when the source is located in the middle layer. However, due to the reduction of wind speed in the middle layer, the concentrations become saturated at a later upslope position as compared to the source in the upper layer. This methodology is shown to be able to provide a quick and accurate estimate of local pollutant patterns and can be applied to any flow field provided that the streamlines can be specified through the velocities.