Extension of tabled 0L-systems and languages

This paper introduces a new family of languages which originated from a study of some mathematical models for the development of biological organisms. Various properties of this family are established and in particular it is proved that it forms a full abstract family of languages. It is compared with some other families of languages which have already been studied and which either originated from the study of models for biological development or belong to the now standard Chomsky hierarchy. A characterization theorem for context-free languages is also established.This research has been supported by NSF Grant GJ 998.     

Strategic capital budgeting: asset replacement under market uncertainty

In this paper the impact of product market uncertainty on the optimal replacement timing of a production facility is studied. The existing production facility can be replaced by a technologically more advanced and thus more cost-effective one. We take into account strategic interactions among the firms competing in the product market by analyzing the problem in a duopolistic setting. We calculate the value of each firm and show that i) a preemptive (simultaneous) replacement occurs when the associated sunk cost is low (high), ii) despite the preemption effect uncertainty always raises the expected time to replace, and iii) the relationship between the probability of optimal replacement within a given time interval and uncertainty is decreasing for long time intervals and humped for short time intervals. Furthermore it is shown that result ii) carries over to the case where firms have to decide about starting production rather than about replacing existing facilities. Correspondence to: Grzegorz PawlinaThis research was undertaken with support from the European Union's Phare ACE Programme 1997. The content of the publication is the sole responsibility of the authors and in no way represents the views of the Commission or its services. The authors would like to thank Kuno Huisman, Enrico Pennings, two anonymous referees, and participants of the Advances in Game Theory Conference in Hilvarenbeek, EFMA 2002 in London, and the Workshop on Recent Topics in Real Options Valuation in Krems for helpful comments.G. Pawlina     

Membrane Systems with Marked Membranes

Membrane computing is a biologically inspired computational paradigm. Motivated by brane calculi we investigate membrane systems which differ from conventional membrane systems by the following features: (1) biomolecules (proteins) can move through the regions of the systems, and can attach onto (and de-attach from) membranes, and (2) membranes can evolve depending on the attached molecules. The evolution of membranes is performed by using rules that are motivated by the operation of pinocytosis (the pino rule) and the operation of cellular dripping (the drip rule) that take place in living cells. We show that such membrane systems are computationally universal. We also show that if only the second feature is used then one can generate at least the family of Parikh images of the languages generated by programmed grammars without appearance checking (which contains non-semilinear sets of vectors). If, moreover, the use of pino/drip rules is non-cooperative (i.e., not dependent on the proteins attached to membranes), then one generates a family of sets of vectors that is strictly included in the family of semilinear sets of vectors. We also consider a number of decision problems concerning reachability of configurations and boundness.     

Contrast Restoration by Adaptive Countershading

The ABSTRACT is to be in fully-justified italicized text, between two horizontal lines, in one-column format, below the author and affiliation information. Use the word “Abstract” as the title, in 9-point Times, boldface type, left-aligned to the text, initially capitalized. The abstract is to be in 9-point, single-spaced type. The abstract may be up to 3 inches (7.62 cm) long. Leave one blank line after the abstract, then add the subject categories according to the ACM Classification Index (see http://www.acm.org/class/1998/ ).     

Instrumental variables for nonlinearity recovering in block-oriented systems driven by correlated signals

The goal of the paper is to identify the Hammerstein-type systems excited and disturbed by correlated random processes. The problem is semi-parametric in the sense that the nonlinear static characteristic is recovered without prior knowledge about the linear dynamic block, i.e. when its order is unknown. The method is based on the instrumental variables technique, with the instruments generated by input inverse filtering. It is proved that, in contrast to the least-squares-based approach, the proposed algorithm leads to an asymptotically unbiased, strongly consistent estimate. Constructive procedures of instrumental variables generation are given for some popular cases.     

Anti‐corrosion additive for concrete

The Building Research Institute in Warsaw has developed an organic concrete additive, known as Dikszopt, which is derived from tanning oak extract. Tests, mostly in the laboratory but some in application trials, show that it has a remarkable ability to protect reinforcing steel against corrosion, notably in carbonized concrete. It also appears to improve the consistency of the concrete mix and retard the setting time, as discussed in this article from the Institute.     

Calcium Ions Regulate K+ Uptake into Brain Mitochondria: The Evidence for a Novel Potassium Channel

The mitochondrial response to changes of cytosolic calcium concentration has a strong impact on neuronal cell metabolism and viability. We observed that Ca²⁺ additions to isolated rat brain mitochondria induced in potassium ion containing media a mitochondrial membrane potential depolarization and an accompanying increase of mitochondrial respiration. These Ca²⁺ effects can be blocked by iberiotoxin and charybdotoxin, well known inhibitors of large conductance potassium channel (BK_Ca channel). Furthermore, NS1619 – a BK_Ca channel opener – induced potassium ion–specific effects on brain mitochondria similar to those induced by Ca²⁺. These findings suggest the presence of a calcium-activated, large conductance potassium channel (sensitive to charybdotoxin and NS1619), which was confirmed by reconstitution of the mitochondrial inner membrane into planar lipid bilayers. The conductance of the reconstituted channel was 265 pS under gradient (50/450 mM KCl) conditions. Its reversal potential was equal to 50 mV, which proved that the examined channel was cation-selective. We also observed immunoreactivity of anti-β₄ subunit (of the BK_Ca channel) antibodies with ~26 kDa proteins of rat brain mitochondria. Immunohistochemical analysis confirmed the predominant occurrence of β₄ subunit in neuronal mitochondria. We hypothesize that the mitochondrial BK_Ca channel represents a calcium sensor, which can contribute to neuronal signal transduction and survival.     

Numerical modelling of radiative heat transfer in an internal indirect reforming-type SOFC

The present paper describes numerical modelling of the radiative heat transfer process in the module chamber of an internal indirect reforming-type SOFC. The ability to do internal reforming is one of the characteristics of high-temperature fuel cells, SOFC. As in any high-temperature system, radiative heat transfer is important. In this article, heat transfer between the fuel reformer surface and all other surfaces facing the reformer surfaces is modelled. Governing equations for radiative heat transfer are described using Hottel's zone method. The resulting radiation–conduction conjugate heat transfer problems are numerically solved with a combination of Gauss–Seidel and Newton–Raphson methods. The steam reforming reaction occurring inside the fuel reformer is described using Achenbach model. The obtained results indicate that, for the development of effective indirect internal reforming, the position of the reformer in the module chamber and emissivity of the surfaces of the reformer, cell and other elements in the SOFC module all play a key role.     

Structure and properties of 6061 + 26 mass% Si aluminum alloy produced via coupled rapid solidification and KOBO-extrusion of powder

Experiments on mechanical consolidation of rapidly solidified (RS) powder of 6061 + 26 mass% Si alloy were performed using the oscillating-die extrusion method. The RS powder was wrapped in thin-wall 6061-alloy cup 35 mm in diameter and vacuum-compressed by means of 100 ton press. Bars 8 mm in diameter were extruded with cross-section reduction of λ = 19 without any preheating of the charge. Tubes with a diameter/wall thickness of 14 mm/1 mm and cross-section reduction of λ = 33 were also manufactured with success. TEM/STEM observations revealed a very fine structure of as-extruded material and bimodal distribution of quasi-spherical silicon particles. Statistical analysis revealed a silicon fine fraction of 0.1–0.7 μm and a coarse fraction 2.1–2.5 μm in diameter. Examination by means of TEM did not reveal any significant changes in the morphology of the silicon particles, even when a high extrusion ratio and the material annealing after deformation were used. Hot compression tests on as-extruded rods (λ = 19) and preliminary annealed samples were performed at a constant true strain rate of 5 × 10^?3 s^?1 within the temperature range of 293–823 K. High strength of the material and relatively high ductility of samples deformed by compression up to ?_t ? 0.4 were observed. The maximum flow stress value for as-extruded material was reduced with deformation temperature from ～390 to ～3.5 MPa for 293 and 823 K, respectively. Annealing of the samples at 773 K/30 min was found to reduce the maximum flow stress by 30–40%. Tensile strengths of similar as-cast alloys and materials manufactured by means of other powder metallurgy methods were shown for the purpose of comparison.     

Wetting Behavior and Reactivity of Molten Silicon with h-BN Substrate at Ultrahigh Temperatures up to 1750 °C

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.