A line-balancing strategy for designing flexible assembly systems

We present a rough-cut analysis tool that quickly determines a few potential cost-effective designs at the initial design stage of flexible assembly systems (FASs) prior to a detailed analysis such as simulation. It uses quantitative methods for selecting and configuring the components of an FAS suitable for medium to high volumes of several similar products. The system is organized as a series of assembly stations linked with an automated material-handling system moving parts in a unidirectional flow. Each station consists of a single machine or of identical parallel machines. The methods exploit the ability of flexible hardware to switch almost instantaneously from product to product. Our approach is particularly suitable where the product mix is expected to be stable, since we combine the hardware-configuration phase with the task-allocation phase. For the required volume of products, we use integer programming to select the number of stations and the number of machines at each station and to allocate tasks to stations. We use queueing network analysis, which takes into account the mean and variance of processing times among different products to determine the necessary capacity of the material-handling system. We iterate between the two analyses to find the combined solution with the lowest costs. Work-in-process costs are also included in the analysis. Computational results are presented.     

Cu(I)-thionein release from copper-loaded yeast cells

Summary The release of intact CU(I)₈-thionein from copper-resistant copper-loaded yeast cells, strain X 2180-1Aa, has been shown. This copper(I)-thiolate-rich protein was characterized and compared with the chemical and physicochemical properties of intracellular yeast Cu-thionein. The same molecular mass and stoichiometry of 8 mol copper atoms/mol protein was found. No detectable difference between the Cu-thioneins was seen in luminescence emission, electronic absorption in the ultraviolet region, chiroptical data or amino acid composition. The importance of stable Cu(I)-thiolates in Cu-thionein as a safe vehicle for transporting copper in a non-reactive manner is confirmed.     

Analysis of Adenosine Immunoreactivity, Uptake, and Release in Purified Cultures of Developing Chick Embryo Retinal Neurons and Photoreceptors

We have investigated the presence of endogenous adenosine and of mechanisms for adenosine uptake and release in chick embryo retinal neurons and photoreceptors grown in purified cultures in the absence of glial cells. Simultaneous autoradiographic and immunocytochemical analysis showed that endogenous adenosine and the uptake mechanism for this nucleoside colocalize in practically all the photoreceptors, but only in approximately 20% of the neurons. Approximately 25% of the neurons showed either immunocytochemical labeling or autoradiographic labeling, while greater than 50% of the neurons were unlabeled with both techniques. [3H]Adenosine uptake was saturable and could be inhibited by nitrobenzylthioinosine and dipyridamole and by pretreatment of the [3H]adenosine with adenosine deaminase. Although these observations indicate that the uptake is specific for adenosine, only 35% of accumulated radioactivity was associated with adenosine, with the remaining 65% representing inosine, hypoxanthine, and nucleotides plus uric acid. Adenosine as well as several of its metabolites were released by the cells under basal as well as K(+)-stimulated conditions. Potassium-enhanced release was blocked by 10 mM CoCl2 or in Ca2(+)-free, Mg2(+)-rich solutions. The results indicate that retinal cells that synthesize, store, and release adenosine differentiate early during embryogenesis and are therefore consistent with a hypothetical role for adenosine in retinal development.     

Fusion of liposomes and rat brain microsomes examined by two assays

Summary Liposomes are prepared from rat brain microsomal lipid and loaded with either Tb³⁺ or dipicolinic acid (DPA) to test fusion with the Tb-DPA assay. They are also loaded with octadecyl Rhodamine B chloride (R₁₈) to test fusion with the R₁₈ assay. The addition of either Ca²⁺ or Mg²⁺ to loaded liposomes develops fluorescence with both assays. The fluorescence elicited by Mg²⁺ is similar to that elicited by Ca²⁺ if assessed with R₁₈, but much higher if determined by Tb-DPA. The Ca²⁺-dependent fluorescence of the Tb-DPA complex is not suppressed by the addition of EDTA, and therefore it is internal to vesicles. The contrary is true for the Mg²⁺-dependent fluorescence. Rat brain microsomes can be disrupted by adding octylgucoside and reconstituted by removing it by dialysis. We use this procedure to load microsomes with DPA. This allows the use of the Tb-DPA assay for testing the fusion of rat brain microsomes. Reconstituted microsomes fuse with liposomes. This fusion has characteristics similar to those of liposome-liposome fusion. However, no microsome-microsome fusion could be detected with either method. The two methods give different results, owing to the chemical properties of the assays. Indeed Tb-DPA implies the retention of vesicle content, whereas this is not required by the R₁₈ assay.     

Effect of oxygen pressure on synthesis and export of nitrogenous solutes by nodules of cowpea

Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures of O₂ (pO₂; 1–80%, v/v, in N₂) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO₂ tested. In sub-ambient pO₂ (1 and 2.5%) nodules contained specific activities of uricase (urate: O₂ oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those from air. On a cell basis, uninfected cells in nodules from 1% O₂ contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in sub-ambient O₂, the activities of other enzymes of ureide synthesis were relatively unaffected by pO₂. Short-term effects of pO₂ on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO₂ (1, 2.5 or 5%, v/v in N₂) and¹⁵N₂. Despite a fall in total¹⁵N₂ fixation, ureide synthesis and export was maintained at a high level except in 1% O₂ where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules which allow the balance between O₂ supply and demand to be maintained over a wide range of pO₂, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of fixed nitrogen. This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance Bureau postgraduate fellowship (to F.D.D.).     

Morphological and structural adaptation of nodules of cowpea to functioning under sub- and supra-ambient oxygen pressure

Nodules of cowpea (Vigna unguiculata (L.) Walp. cv. Vita 3:Bradyrhizobium CB 756) from 28-d-old plants cultured for 23 d with their root systems maintained in O₂ levels from 1 to 80% (v/v, in N₂) in the external gas phase showed a range of structural changes which have been interpreted in relation to an over- or under-supply of O₂. A response to the partial pressure of O₂ in the gas phase (pO₂) was noted with respect to nodule size, lenticel development, the relative distributions of cortical and infected central tissue, the differentiation of cortex, especially the inner cortex, the frequency and size of infected and uninfected interstitial cells, the volume of extracellular spaces both in cortex and infected tissue, and in the frequency of bacteroids. As a consequence of these changes the surface area of inner cortex relative to the nitrogenase-containing units of fixing tissue (infected cells or bacteroids) was increased by as much as 20-fold. Effectiveness of bacteroid functioning increased from 0.10 ± 0.02 · 10^-9 μmol acetylene reduced per bacteroid in air-grown nodules to 0.9 ± 0.16 · 10^-9 (same units) per bacteroid in those cultured in 1% O₂. This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian International Development Assistance Bureau postgraduate fellowship (to F.D.D.). The authors wish to thank Dr. W.F.C. Blumer for his considerable help with morphometric analysis, Dr. J. Kuo for guidance in the use of histological techniques, and to Dr. J.S. Pate for the suggestion that lenticel development might be quantified by surface staining of nodules.     

Arg74 in HLA-DRBI and DRB3 controls a DR3-related epitope

TR81 is a specificity closely related to or identical with DR3. In Caucasoids two amino acids, Tyr at position 26 and Arg at position 74 of HLA class II DR chains, have been found to be associated with the presence of TR81. Recently, a variant of DRBI *03 identified in American Blacks has been shown to possess Arg at position 74 but Phe at position 26. This codon combination is found to be present in four other cell lines where it still specifies the TR81 determinant. This suggests that the TR81 specificity is uniquely dependent on the presence of Arg at position 74.     

Modulation of microvascular growth and morphogenesis by reconstituted basement membrane gel in three-dimensional cultures of rat aorta: A comparative study of angiogenesis in Matrigel,collagen, fibrin,and plasma clot

Summary Rings of rat aorta cultured in Matrigel, a reconstituted gel composed of basement membrane molecules, gave rise to three-dimensional networks composed of solid cellular cords and occasional microvessels with slitlike lumina. Immunohistochemical and ultrastructural studies showed that the solid cords were composed of endothelial sprouts surrounded by nonendothelial mesenchymal cells. The angiogenic response of the aortic rings in Matrigel was compared to that obtained in interstitial collagen, fibrin, or plasma clot. Morphometric analysis demonstrated that the mean luminal area of the microvascular sprouts and channels was significantly smaller in Matrigel than in collagen, fibrin, or plasma clot. The percentage of patent microvessels in Matrigel was also markedly reduced. Autoradiographic studies of³H-thymidine-labeled cultures showed reduced DNA synthesis by developing microvessels in Matrigel. The overall number of solid endothelial cords and microvessels was lower in Matrigel than in fibrin or plasma clot. A mixed cell population isolated from Matrigel cultures formed a monolayer in collagen or fibrin-coated dishes but rapidly reorganized into a polygonal network when plated on Matrigel. The observation that gels composed of basement membrane molecules modulate the canalization, proliferation, and organization into networks of vasoformative endothelial cells in three-dimensional cultures supports the hypothesis that the basement membrane is a potent regulator of microvascular growth and morphogenesis. This work was supported by grants from the W. W. Smith Charitable Trust and grants CA14137 and HL43392 from the National Institutes of Health, Bethesda, MD.     

Characterization of waldmeister, a novel developmental mutant in Arabidopsis thaliana

A novel Arabidopsis thaliana (L.) Heynh. developmental mutant,waldmeister (wam), is described. This mutant was found in theprogeny arising from an Ac-Ds tagging experiment, but does notappear to be tagged by an introduced transposon. This recessivenuclear mutation maps between GAPB and ap1 on chromosome 1 andshows extreme morphological and physiological changes in bothfloral and vegetative tissues. Changes to the vegetative phenotypeinclude altered leaf morphology, multiple rosettes, stem fasciation,retarded senescence and disturbed geotropic growth. Changesto the floral phenotype include delayed flowering, increasednumber of inflorescences, determinate inflorescences, alterednumber and morphology of floral organs, chimeric floral organs,and ectopic ovules . wam was crossed to a number of previouslydescribed floral mutants: apetela 2, apetela 3, pistillata,agamous, and leafy. The phenotype of the double mutant was ineach case additive. In the case of agamous, however, the indeterminaterepetitive floral structure of agamous was lacking, emphasizingthe determinate inflorescence growth of wam. The extreme phenotypeof the wam mutant is suggestive of a disturbance to a gene ofglobal importance in the regulation of plant growth and development. Key words: Arabidopsis thaliana, waldmeister, developmental mutant, flower mutant     

Characterization of the Glutamate Receptors Mediating Release of Somatostatin from Cultured Hippocampal Neurons

Abstract: l -Glutamate, NMDA, dl -α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate (KA) increased the release of somatostatin-like immunoreactivity (SRIF-LI) from primary cultures of rat hippocampal neurons. In Mg²⁺-containing medium, the maximal effects (reached at ∼100 µ M ) amounted to 737% (KA), 722% (glutamate), 488% (NMDA), and 374% (AMPA); the apparent affinities were 22 µ M (AMPA), 39 µ M (glutamate), 41 µ M (KA), and 70 µ M (NMDA). The metabotropic receptor agonist trans -1-aminocyclopentane-1,3-dicarboxylate did not affect SRIF-LI release. The release evoked by glutamate (100 µ M ) was abolished by 10 µ M dizocilpine (MK-801) plus 30 µ M 1-aminophenyl-4-methyl-7,8-methylenedioxy-5 H -2,3-benzodiazepine (GYKI 52466). Moreover, the maximal effect of glutamate was mimicked by a mixture of NMDA + AMPA. The release elicited by NMDA was sensitive to MK-801 but insensitive to GYKI 52466. The AMPA- and KA-evoked releases were blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX) or by GYKI 52466 but were insensitive to MK-801. The release of SRIF-LI elicited by all four agonists was Ca²⁺ dependent, whereas only the NMDA-evoked release was prevented by tetrodotoxin. Removal of Mg²⁺ caused increase of basal SRIF-LI release, an effect abolished by MK-801. Thus, glutamate can stimulate somatostatin release through ionotropic NMDA and AMPA/KA receptors. Receptors of the KA type (AMPA insensitive) or metabotropic receptors appear not to be involved.