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The regulation of acid secretion has been divided into cephalic and peripheral (gastric and intestinal) phases (1). The cephalic phase of gastric acid secretion originates in the central nervous system and impacts the hypothalamus; signals travel via the vagus nerve to the myenteric plexuses of the gastric mucosa. In the succeeding neural network, a variety of secondary neurons signal the gastric fundic and antral epithelia to influence gastric acid secretion by either primary or secondary action, namely, direct effects on parietal cells or gastric epithelial endocrine cells. The peripheral phase of acid secretion regulation involves local signaling within a variety of endocrine cells, transmitting regulatory information to the secretory cells of the gastric mucosa; the peripheral phase is more limited than the cephalic phase in terms of the possible mediators involved (2). Studies of isolated gastric endocrine cells have proved useful in defining the interactions of various signals in the regulation of gastric acid secretion, but such studies must be placed in context when considering their physiological implications. The isolated rabbit gastric gland is a more integrated model than that provided by isolated cells.With the isolation and purification (to between 85% and 95%) of functional enterochromaffin-like (ECL) cells from the rat gastric mucosa, a variety of receptors has been defined on this cell type. This has been done by measurement of calcium signals under superfusion conditions using video microscopy, and by histamine or pancreostatin release by radioimmunoassay under static conditions (3-5). When histamine release is measured in a static system, cross-talk is a problem. Superfusion of isolated, enriched ECL cells while measuring responses of intracellular calcium [Ca 2+ ] i eliminates cross-talk between possible contaminating gastric endocrine cells. Nevertheless, few (if any) inconsistencies have been found between the results of video-imaging and release measurements in this particular preparation. In this preparation, there are less than 2% D cells, and the addition of somatostatin antibody has not affected either calcium signaling or histamine release in response to a variety of agonists (3, 4).Histamine, released from ECL cells, is the most important direct stimulant of acid secretion, as shown by the broad efficacy of histamine-2 receptor antagonists as full inhibitors of gastrin and partial inhibitors of vagally stimulated acid secretion (6). The involvement of ECL cells in mediation of the cephalic (neural) phase of gastric acid secretion has been less clear. The atropine sensitivity of cephalic stimulation of acid secretion pointed

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SUMMARYGenetic algorithms (GAs) have become a popular optimization tool for many areas of research and topology optimization an effective design tool for obtaining efficient and lighter structures. In this paper, a versatile, robust and enhanced GA is proposed for structural topology optimization by using problemspecific knowledge. The original discrete black-and-white (0 -1) problem is directly solved by using a bit-array representation method. To address the related pronounced connectivity issue effectively, the four-neighbourhood connectivity is used to suppress the occurrence of checkerboard patterns. A simpler version of the perimeter control approach is developed to obtain a well-posed problem and the total number of hinges of each individual is explicitly penalized to achieve a hinge-free design. To handle the problem of representation degeneracy effectively, a recessive gene technique is applied to viable topologies while unusable topologies are penalized in a hierarchical manner. An efficient FEM-based function evaluation method is developed to reduce the computational cost. A dynamic penalty method is presented for the GA to convert the constrained optimization problem into an unconstrained problem without the possible degeneracy. With all these enhancements and appropriate choice of the GA operators, the present GA can achieve significant improvements in evolving into near-optimum solutions and viable topologies with checkerboard free, mesh independent and hinge-free characteristics. Numerical results show that the present GA can be more efficient and robust than the conventional GAs in solving the structural topology optimization problems of minimum compliance design, minimum weight design and optimal compliant mechanisms design. It is suggested that the present enhanced GA using problem-specific knowledge can be a powerful global search tool for structural topology optimization.

SummaryGrain size, number and starch content are important determinants of grain yield and quality. One of the most important biological processes that determine these components is the carbon partitioning during the early grain filling, which requires the function of cell wall invertase. Here, we showed the constitutive expression of cell wall invertase-encoding gene from Arabidopsis, rice (Oryza sativa) or maize (Zea mays), driven by the cauliflower mosaic virus (CaMV) 35S promoter, all increased cell wall invertase activities in different tissues and organs, including leaves and developing seeds, and substantially improved grain yield up to 145.3% in transgenic maize plants as compared to the wild-type plants, an effect that was reproduced in our 2-year field trials at different locations. The dramatically increased grain yield is due to the enlarged ears with both enhanced grain size and grain number. Constitutive expression of the invertaseencoding gene also increased total starch content up to 20% in the transgenic kernels. Our results suggest that cell wall invertase gene can be genetically engineered to improve both grain yield and grain quality in crop plants.

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