Fairness and the axioms of control predicates

Many recent axiomatic definitions for structured programming languages include control predicates,at(S), in(S), andafter(S), which are an abstraction of location counters. The usual axioms identify control locations so as to imply that no time (i.e., no state transition) is needed to pass from the end of one statement to the next, and in particular from the end of a loop body back to the test at the head of the loop. Here, an axiomatic framework for control predicates is examined. It is shown that if all the axioms are to be maintained with common representation mappings, there are difficult new requirements which need to be satisfied by an implementation for fair concurrent models of computation. Several approaches to resolving the difficulty are considered, and in particular it is suggested to replace some axioms of the formPQ byPeventually(Q), whereP andQ are control predicates, thereby separating control states previously identified.The North has receded, but the South has not yet arrived.-Reuven Miran, 42 Degrees in the Shade Every three lines intersect at a point, if the point is thick enough.-Folk theoremNote: A talk based on this paper was presented at the Colloquium on Temporal Logic and Specification, Altrincham, Cheshire, April 1987.C.R. Categories: D.3.1 [Programming languages] Formal definitions and theory: semantics; D..3.3 [Programming languages] Language constructs: control structures; F.3.1. [Logics and meanings of programs] Specifying and verifying and reasoning about programs.     

Surface properties of Ca,Ti-doped CeO2 and their influence on the reverse water-gas shift reaction

CeO₂-based materials can be found in a variety of catalytic processes, including the reverse water-gas shift (RWGS) reaction. Nevertheless, the interaction of molecular gases with the surfaces of such materials is still not clear. Recently, some progress was reported on the incorporation of neodymium (Nd) and calcium (Ca) into ceria and their effect on H₂O and CO₂ adsorption. Titanium (Ti), which has a much smaller ionic radius, has the ability to change the interaction landscape, both as a co-dopant to Ca and as a sole dopant in the CeO₂ system. In this study, the interactions of environmental gases (i.e., water vapor and CO₂) on the surface of Ti-doped CeO₂ and Ca,Ti co-doped CeO₂ were investigated. Ti addition to CeO₂ was shown to decrease water vapor uptake by up to 25% all while maintaining similar heats of adsorption. In the case of CO₂ adsorption, Ti addition to CeO₂ had lowered the uptake by more than 50% as well as lowering the heat of adsorption. Co-doping with Ti and Ca showed small decrease in H₂O uptake accompanied with increased heat of adsorption. For CO₂, the changes to the uptake and energetics were small and did not indicate a specific trend. The RWGS catalytic performance showed improvement by the addition of Ti in certain levels. The relationship between the doping, surface properties, gas-surface interactions, and catalytic performance is discussed.     

Role of acetylcholine in negative patterning in turtles (Chrysemys picta).

Turtles were run on a negative patterning task involving 2 positive elements, a key with white stripes on a black background, and a solid red key, and a compound stimulus combining the 2 elements, white stripes on a red background. Injections of scopolamine, methylscopolamine, or saline were started at the same time that the compound stimulus was introduced, after the animals had been autoshaped to press the key for each of the elements. Scopolamine disrupted the learning of negative patterning, but methylscopolamine had no effect. In contrast, learning of a simple discrimination between the elements was not affected by scopolamine. These results show that muscarinic cholinergic receptors are involved in the learning of negative patterning in turtles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of explosives by nuclear magnetic resonance spectrometry

In order to evaluate the applicability of NMR to the analysis of explosives, the method was used to analyse explosives from actual cases. The results were then compared with results from other analytical methods, mainly TLC and GC/MS. For unexploded samples NMR was found to be a simple, fast and reliable method, often allowing the identification of mixtures without pre-separation. Some post-explosion samples were also successfully analysed by NMR. Although sensitivity problems still exist, NMR showed a surprisingly promising prospects for the difficult field of post-explosion analysis.     

Asymptotic and finite element approximations for heat transfer in rotating compressible flow over an infinite porous disk

The laminar boundary layer equations for the compressible flow due to the finite difference in rotation and temperature rates are solved for the case of uniform suction through the disk. The effects of viscous dissipation on the incompressible flow are taken into account for any rotation rate, whereas for a compressible fluid they are considered only for a disk rotating in a stationary fluid. For the general case, the governing equations are solved numerically using a standard finite element scheme. Series solutions are developed for those cases where the suction effect is dominant. Based on the above analytical and numerical solutions, a new asymptotic finite element scheme is presented. By using this scheme one can significantly improve the pointwise accuracy of the standard finite element scheme.     

Design of Light-Induced Molecular Switcher for the Driver of the Quantum Cellular Automata (QCA) Based on the Transition through the Intramolecular Charge Transfer (ICT) Structure

The design of light-induced switcher for the molecular QCA driver was discussed. The driver-cell with two connected chromophores was proposed as a basic model of the molecular light-induced trigger. One of the chromophores will conjugate with a left diagonal and the second chromophore will conjugate with a right diagonal. Some differences between two chromophores can allow selective controlling of the switch to the left or to the right. The following three-steps mechanism for QCA switcher was suggested – light-induced transition through ICT area (a), initiation of the driver‘s polarization (b) and the beginning of the signal transition to the other cells (c). The principal physical characteristics of the driver‘s trigger was proposed, and the corresponding chemical implementation was discussed. Three kinds of processes leading to ICT were discussed as mechanisms suggested for potential switchers: 1) Irradiation leading to the ICT excited state; 2) Chemical reaction with ICT transition state; 3) Excited State Intramolecular Proton Transfer (ESIPT). The common features of these processes are the non-radiative transition to the initial state after excitation, with the back transition going through the highly polar charge transfer (CT) area.     

四基色投影显示

我们采用多芯片HTPS屏结构,已开发出一种四基色前投式投影样机。这种投影机建立在对一种现行高端品牌产品的光学平台进行改进的基础之上。在KESHETTM芯片中,用ColorPeakTM算法,把标准720p输入信号转换成所需要的多基色输入信号,结果使色域和亮度都有了显著的提高。     

Attenuation of the Photobaric-Photoacoustic Signal in Leaves by Oxygen-Consuming Processes

Charland et al. (Biochim. Biophys. Acta 1992 , 1098, 261–265) obtained photoacoustic data from sugar maple tree leaves, in which the photobaric part of the photoacoustic signal declined in time following a transition from high light to low light level, which they interpreted as indicating stromal and plasmal oxygen-consuming processes. Here, a simple mathematical model of oxygen diffusion, which includes a continuous distribution of oxygen-consuming sinks in the diffusion path from the photosynthetic membrane to the inner air phase, is presented. The model explains the main features of the dependence of the steady-state signal on the modulation frequency and the light intensity, although the numerical agreement between the data and the results of the model is only semi-quantitative, which is discussed. It turns out that at sufficiently high light intensity, or at a short time after a previous exposure to a high light level, the effect of oxygen consumption tends to zero because a high stromal oxygen concentration is built up which is saturating for the uptake process. Within this limitation, the merit of the photoacoustic signal as an indicator for photosynthetic oxygen evolution is preserved, answering recent doubts.     

Reaction-bonded B4C/SiC composites synthesized by microwave heating

The reaction-bonding technique was used to synthesize boron carbide (B₄C) - silicon carbide (SiC) composites by microwave heating. Preforms of porous B₄C were obtained by compaction followed or not by partial densification. Then, the material was infiltrated by molten silicon under a microwave heating. The influence of the thermal cycles (T: 1400-1500°C, t: 5-120 minutes) is low. The hardness of boron carbide is comparable to that of alumina (15-19 GPa) for a much lower density (≈2.5 g/cm³ for B₄C-based material instead of 3.95 g/cm³ for alumina). These properties make this composite, obtained by microwave heating, a good candidate for ballistic applications.