Multiphase stabilization

We generalize the concept of stabilization of computing systems. According to this generalization, the actions of a system S are partitioned into n partitions, called phase 1 through phase n. In this case, system S is said to be n-stabilizing to a state predicate Q iff S has state predicates P.0, ..., P.n such that P.0=true, P.n=Q, and the following two conditions hold for every j, 1⩽j⩽n. First, if S starts at a state satisfying P.(j-1) and if the only actions of S that are allowed to be executed are those of phase j or less, then S will reach a state satisfying P.j. Second, the set of states satisfying P.j is closed under any execution of the actions of phase j or less. By choosing n=1, this generalization degenerates to the traditional definition of stabilization. We discuss three advantages of this generalization over the traditional definition. First, this generalization captures many stabilization properties of systems that are traditionally considered nonstabilizing. Second, verifying stabilization when n>1 is usually easier than when n=1. Third, this generalization suggests a new method of fault recovery, called multiphase recovery     

Quasi-adaptive fuzzy heating control of solar buildings

Significant progress has been made on maximising passive solar heat gains to building spaces in winter. Control of the space heating in these applications is complicated due to the lagging influence of the useful solar heat gain coupled with the wide range of construction materials and heating system choices. Additionally, and in common with most building control applications, there is a need to develop control solutions that permit simple and transparent set-up and commissioning procedures. This paper addresses the development and testing of a quasi-adaptive fuzzy logic control method that addresses these issues. The controller is developed in two steps. A feed-forward neural network is used to predict the internal air temperature, in which a singular value decomposition (SVD) algorithm is used to remove the highly correlated data from the inputs of the neural network to reduce the network structure. The fuzzy controller is then designed to have two inputs: the first input being the error between the set-point temperature and the internal air temperature and the second the predicted future internal air temperature. The controller was implemented in real-time using a test cell with controlled ventilation and a modulating electric heating system. Results, compared with validated simulations of conventionally controlled heating, confirm that the proposed controller achieves superior tracking and reduced overheating when compared with the conventional method of control.     

Petroleum sulphonates: Production and evalution as corrosion inhibitors

Sodium and calcium petroleum sulphonates have been prepared by sulphuric acid treatment of the Egyptian Morgan 350–450 °C petroleum fraction. Extraction and purification of the sulphonates from the sulphonated oil and the residual acid sludge is described. Corrosion studies revealed that the sodium petroleum sulphonates are more effective as corrosion inhibitors than the calcium salts in a neutral as well as in an acid medium. A maximum inhibition efficiency of about 75% was obtained by the sodium salt in an acid and a neutral medium, while the relevant value obtained by the calcium salt is 60 and 23% in an acid and a neutral medium respectively. It has been also found that both salts accelerated corrosion when used at relatively high concentration in a neutral medium. Results are discussed according to the current views of corrosion inhibition.     

Isoform-dependent differences in feedback regulation and subcellular localization of serine acetyltransferase involved in cysteine biosynthesis from Arabidopsis thaliana

Serine acetyltransferase (SATase; EC 2.3.1.30), which catalyzes the formation of O-acetyl-L-serine (OAS) from acetyl-CoA and L-serine, plays a regulatory role in the biosynthesis of cysteine by its property of feedback inhibition by cysteine in bacteria and certain plants. Three cDNA clones encoding SATase isoforms (SAT-c, SAT-p, and SAT-m) have been isolated from Arabidopsis thaliana. However, the significance of the feedback regulation has not yet been clear in these different isoforms of SATase from A. thaliana. We constructed the overexpression vectors for cDNAs encoding three SATase isoforms of A. thaliana and analyzed the inhibition of SATase activity by cysteine using the recombinant SATase proteins. In the case of SAT-c, the activity was feedback-inhibited by a low concentration of cysteine (the concentration that inhibits 50% activity; IC50 = 1.8 microM). By contrast, SAT-p and SAT-m were feedback inhibition-insensitive isozymes. We also determined the subcellular localization of three SATase isozymes by the transient expression of fusion proteins of each SATase N-terminal region with jellyfish green fluorescent protein (GFP) in 4-week-old Arabidopsis leaves. The SAT-c-GFP fusion protein was stayed in cytosol, whereas SAT-p-GFP and SAT-m-GFP fusion proteins were localized in chloroplasts and in mitochondria, respectively. These results suggest that these three SATase isoforms, which are localized in the different organelles, are subjected to different feedback regulation, presumably so as to play the particular roles for the production of OAS and cysteine in Arabidopsis cells. Regulatory circuit of cysteine biosynthesis in the plant cells is discussed.     

Unboundedness detection for a class of communicating finite-state machines

Let M and N be two communicating finite-state machines that exchange one type of message. We discuss an algorithm to decide whether the communication between M and N is bounded. The algorithm is based on constructing a finite representation of the reachability tree of M and N assuming that M and N progress at equal speeds.