Decision problems for convex languages

We examine decision problems for various classes of convex languages, previously studied by Ang and Brzozowski, originally under the name “continuous languages”. We can decide whether a language L is prefix-, suffix-, factor-, or subword-convex in polynomial time if L is represented by a DFA, but these problems become PSPACE-complete if L is represented by an NFA. If a regular language is not convex, we find tight upper bounds on the length of the shortest words demonstrating this fact, in terms of the number of states of an accepting DFA. Similar results are proved for some subclasses of convex languages: the prefix-, suffix-, factor-, and subword-closed languages, and the prefix-, suffix-, factor-, and subword-free languages. Finally, we briefly examine these questions where L is represented by a context-free grammar.     

Cluster computing of mechanisms dynamics using recursive formulation

This paper presents the O(n) recursive algorithm for forward dynamics of closed loop kinematic chains adapted to parallel computations on a cluster of workstations. The Newton–Euler equations of motion are formulated in terms of relative coordinates. Closed loop kinematic chains are transformed into open loop chains by cut joint technique. Cut joint constraint and Lagrange multipliers are introduced to complete the equations of motion. Constraint stabilization is performed using the Baumgarte stabilization technique with application to multibody systems with large number of degrees of freedom. Numerical simulations are carried out to study the influence of the degrees of freedom of the multibody system on computational efficiency of the algorithm using the Message Passing Interface (MPI). We also consider the ways of minimization of communication overhead which has significant impact on efficiency in case of cluster computing.     

The influence of zinc ions discharged in a non-aqueous cell on a copper catalyst on the rate of cyclohexanol dehydrogenation reaction

Results of studies on the influence of a copper catalyst modification with zinc ions on the activity in the reaction of cyclohexanol dehydrogenation are presented. The modification has been performed by electrochemical discharging-insertion of zinc ions on a copper electrode in a non-aqueous cell. It has been demonstrated that the catalyst activity depends on the amount of discharged zinc ions as well as on the nature and concentration of the electrolyte. In the case of zinc ions discharged from a solution of ZnCl₂ in propylene carbonate, the yield of cyclohexanone increased up to five times and using Zn(BF₄)₂ in dimethylformamide almost twenty times. The activity of the system in the competing reaction of dehydration was low, hence the selectivity in the dehydrogenation reaction was high.     

Defect Equilibria and Transport in YBa2Cu3O7-x at Elevated Temperatures: II, Nonstoichiometry

Aspects of nonstoichiometry for the Y-Ba-Cu (1: 2: 3) system are considered. The general formula YBa₂Cu₃O_7-x has been assumed for considerations of nonstoichiometry in 1: 2:3 oxide cuprates. Assuming that copper ions may occupy different lattice positions (independently of their valency), the equilibrium constants for oxygen intercalation were determined:     

Relationship between the rock mass deformation and places of occurrence of seismological events

Static effort of rock mass very rarely causes of rock burst in polish coal mines. Rock bursts with source in the seismic tremor within the roof rock layers are prevailing. A seismic tremor is an effect of rupture or sliding in roof layers above the exploited panel in coal seam, sometime in a distance from actual exploitation. Sliding, as a rule occurs in fault zone and tremors in it are expected, but monolithic layer rupture is very hard to predict. In a past few years a practice of analyzing state of deformation in high energy seismic tremors zones has been employed. It let gathering experience thanks to witch determination of dangerous shape of reformatted roof is possible. In the paper some typical forms of roof rocks deformations leading to seismic tremor occurrence will be presented. In general these are various types of multidirectional rock layers bending. Real examples of seismic events and rock bursts will be shown.     

Autoxidation of cholesteryl linoleate in aqueous colloidal suspension

The autoxidation of the cholesteryl moiety of cholesteryl linoleate stabilized in aqueous colloidal suspension with sodium dodecyl sulfate has been studied at 85C. The overall rate of this oxidation is more rapid than that for unesterified cholesterol and oxidation also occurs to a greater extent for the linoleate ester. These results are in contrast to those for more saturated fatty acyl esters of cholesterol which show diminished susceptibility to attack by oxygen in such a system. Autoxidation of cholesteryl linoleate by an intramolecular free-radical mechanism is considered. Presented at the AOCS Meeting in Houston, Texas, April, 1965. Work conducted during the tenure of a Summer Research Student Pellowship.     

Effect of Frothers on Bubble Size and Foam Stability in Potash Ore Flotation Systems

The objective of this project was to compare the effect of a selective flotation frother (MIBC) and powerful frothers (DEMPH and DF‐1012) on bubble size and foamability in water and in brine. In water, the bubble size is clearly reduced by flotation frothers which prevent bubbles from coalescing. The present study shows that the bubbles do not coalesce in brine and, therefore, frothers do not affect the size of bubbles in brine. The dynamic foamabality index measured in brine is much lower than that in water for weak frothers (e.g. MIBC); for both tested strong frothers the foamability measurements in brine reveal formation of meta‐stable foams.     

Bubble coalescence and its effect on dynamic foam stability

The size of bubbles generated using a single‐hole sparger, a multi‐hole sparger and a flotation cell were measured. While the size of bubbles generated from the single‐hole sparger does not depend on frother concentration, the bubble size strongly depends on frother concentration when the multi‐hole sparges, or flotation cell, are utilized. The bubbles size ceases to depend on frother at the concentrations exceeding the value characteristic for each frother and referred to as the critical coalescence (CCC). All the bubble size vs. frother concentration curves converge on a single curve. Aqueous solutions of the frothers that are characterized by low CCC values from foams quite stable under dynamic conditions. Since bubble coalescence can be inhibited by frother concentrations exceeding the CCC, sparing systems can be studied and compared only at frother concentrations that exceed CCC.     

Noble metals supported on carbon black composites as catalysts for the wet-air oxidation of phenol

Pt, Pd and Ru catalysts supported on carbon black composites (CBC) were characterized in the wet air oxidation of phenol solution using a fixed-bed reactor working in a trickle-flow regime under relatively mild conditions: temperature, 393-433 K; pressure, 50-80 bar; liquid hourly space velocity (LHSV), 0.5-6 h⁻¹. The activity of the catalysts decreases in the following order: Pt/CBC>Pd/CBC≈Ru/CBC?CBC. The physicochemical properties of the CBC are affected by its reaction with oxygen during the oxidation process. Combustion of the CBC material in the aqueous phase proceeds at a lower temperature than that in the gas phase; its surface properties change according the same rules as during low temperature oxidation by gaseous air.     

Supercritical carbon dioxide processing of conducting composites of polypyrrole and porous crosslinked polystyrene

Conducting composites (∼3 mm in thickness) of polypyrrole (PPy) and porous crosslinked polystyrene (PCPS) were prepared by first impregnating PCPS with iodine (I₂), and then contacting it with pyrrole (Py). Both these steps were carried out with and without supercritical carbon dioxide. The use of supercritical CO₂ as a solvent for I₂ and Py facilitated the transport and deposition of these substances in the pores of the permanently porous host and produced composites with conductivities as high as 10⁻³ S cm⁻¹. Moreover, the deposition of I₂ in the pores could be controlled via the CO₂ pressure. The bulk and surface conductivities of the composite exhibited percolation behavior with respect to the amount of the I₂ deposited, whereas the volume conductivity exhibited a stepwise transition at approximately 100 wt% PPy+I₂ complex formed (with respect to the original mass of PCPS). Optical micrographs suggest that non-uniform distributions of PPy are obtained in the pores below this transition.The percolation threshold was as low as 10 wt% so that the stability and mechanical strength of the composites were approximately the same as those of the host PCPS. This was verified by TGA and compressive strength measurements. The temperature dependence of the conductivity conformed with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport. However, the data could be correlated equally well with the CELT model.