Replanning and analysis of partial setup strategies in printed circuit board assembly systems

This paper considers the operation of component placement equipment for the assembly of printed circuit boards (PCBs) in a medium-volume, medium-variety manufacturing environment. It focuses on the setup management and operational planning issues associated with productive use of these expensive resources. The concept of replanning is introduced to adapt to changes in the production environment by explicitly considering the initial state of the system. The partial setup strategy is suggested as a means of efficient adaptation and as a strategy that subsumes other setup strategies encountered in practice and the literature. These concepts are applied to the optimization of a single-placement machine producing multiple products. The results of using partial setups are compared with other commonly used strategies. Experimental results suggest significant gains at the singlemachine level. Future research is being pursued to improve the solution procedures and extend these replanning concepts to the line level.     

Root to shoot ratio of crops as influenced by CO2

Crops of tomorrow are likely to grow under higher levels of atmospheric CO₂. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO₂ concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO₂ concentration will affect roots and shoots of crop plants proportionally. Since elevated CO₂ can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO₂ on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO₂ and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO₂ enrichment will add substantially to the global change response data base.Abbreviations R:S root to shoot ratio, dry weight basis     

Iron supplementation moderates but does not cure the Belgrade anemia

Belgrade rats inherit microcytic, hypochromic anemia as an autosomalrecessive trait (gene symbol b). Erythrocytes and tissue are iron deficientin the face of elevated TIBC (total iron binding capacity) and percent ironsaturation; iron injections increased the number of erythrocytes but theirappearance remained abnormal. We have investigated iron supplements toimprove husbandry of b/b rats and to learn more about the underlying defectand its tissue distribution. Weekly IM (intramuscular) injections ofiron–dextran (Imferon at 30 mg kg) improved the anemia but did not alter thered cell morphology. Certain diets also improved the health of b/b rats whencompared to standard rat chows by the criteria of weight, survival toadulthood, hematology and reproduction. The critical nutritional factorturned out to be iron bioavailability, with ferrous iron added to the dietimproving the health of Belgrade rats without affecting the underlyingerythroid defect. Tissue iron measurements after dietary or parenteralsupplementation confirmed the iron deficient status of untreated b/b rats andestablished that dietary ferrous iron partially relieved this deficiency,with injections leading to greater amounts of tissue iron. Serum iron andTIBC were also found to be elevated in untreated b/b rats, with dietarysupplementation decreasing but not eliminating the elevation in TIBC. Thesestudies indicate that iron supplements can improve the health of b/b ratswithout altering the underlying defect and also suggest that the mutationcould alter iron uptake in the GI (gastrointestinal) tract.     

Sodium-dependent nucleoside transport in choroid plexus from rabbit. Evidence for a single transporter for purine and pyrimidine nucleosides.

The overall goal of this study was to determine the mechanisms by which nucleosides are transported in choroid plexus. Choroid plexus tissue slices obtained from rabbit brain were depleted of ATP with 2,4-dinitrophenol. Uridine and thymidine accumulated in the slices against a concentration gradient in the presence of an inwardly directed Na+ gradient. The Na(+)-driven uptake of uridine and thymidine was saturable with Km values of 18.1 +/- 2.0 and 13.0 +/- 2.3 microM and Vmax values of 5.5 +/- 0.3 and 1.0 +/- 0.2 nmol/g/s, respectively. Na(+)-driven uridine uptake was inhibited by naturally occurring ribo- and deoxyribonucleosides (adenosine, cytidine, and thymidine) but not by synthetic nucleoside analogs (dideoxyadenosine, dideoxycytidine, cytidine arabinoside, and 3'-azidothymidine). Both purine (guanosine, inosine, formycin B) and pyrimidine nucleosides (uridine and cytidine) were potent inhibitors of Na(+)-thymidine transport with IC50 values ranging between 5 and 23 microM. Formycin B competitively inhibited Na(+)-thymidine uptake and thymidine trans-stimulated formycin B uptake. These data suggest that both purine and pyrimidine nucleosides are substrates of the same system. The stoichiometric coupling ratios between Na+ and the nucleosides, guanosine, uridine, and thymidine, were 1.87 +/- 0.10, 1.99 +/- 0.35, and 2.07 +/- 0.09, respectively. The system differs from Na(+)-nucleoside co-transport systems in other tissues which are generally selective for either purine or pyrimidine nucleosides and which have stoichiometric ratios of 1. This study represents the first direct demonstration of a unique Na(+)-nucleoside co-transport system in choroid plexus.     

Pearson syndrome and mitochondrial encephalomyopathy in a patient with a deletion of mtDNA.

A patient is described who has features of Pearson syndrome and who presented in the neonatal period with a hypoplastic anemia. He later developed hepatic, renal, and exocrine pancreatic dysfunction. At the age of 5 years he developed visual impairment, tremor, ataxia, proximal muscle weakness, external ophthalmoplegia, and a pigmentary retinopathy (Kearns-Sayre syndrome). Muscle biopsy confirmed the diagnosis of mitochondrial myopathy. Analysis of mtDNA from leukocytes and muscle showed mtDNA heteroplasmy in both tissues, with one population of mtDNA deleted by 4.9 kb. The deleted region was bridged by a 13-nucleotide sequence occurring as a direct repeat in normal mtDNA. Both Pearson syndrome and Kearns-Sayre syndrome have been noted to be associated with deletions of mtDNA; they have not previously been described in the same patient. These observations indicate that the two disorders have the same molecular basis; the different phenotypes are probably determined by the initial proportion of deleted mtDNAs and modified by selection against them in different tissues.     

Characteristics of hamadryas-like male baboons living in anubis baboon troops in the Awash hybrid zone, Ethiopia.

In the twenty-two years since the Awash baboon hybrid zone was first described, about 25-30 hamadryas or hamadryas-like hybrid males have taken up residence in anubis baboon groups. Most enter as mature adults, though some may immigrate as juvenile followers. Long-term tracking of known immigrants indicates that they may reside for four years or more in their adopted troop, during which time they establish a series of comparatively short-term harems, and probably sire hybrid offspring. "Abductions" of anubis females to hamadryas troops, as postulated by early observers, were not seen, though their occurrence cannot be ruled out. Younger, more recent immigrants tend to be "purer" hamadryas in phenotype, perhaps reflecting a more distant origin, or a change in the composition of neighboring hamadryas populations. Coexisting hamadryas and anubis show no signs of reproductive isolation by behavioral barriers, and evidently belong to a single "recognition species."     

A structural model for the chromophore-binding domain of ovine rhodopsin

A putative model for the structure of the relatively independent carboxyl-terminal domain of (rhod)opsin has been developed by use of a combination of several secondary structure prediction methods. The validity of this approach was confirmed by comparing the secondary structure for bacteriorhodopsin as predicted by these methods with its known low resolution structure. The resulting predicted structure agreed well with the experimental data. The model obtained for opsin incorporates two transmembrane α-helical rods linked by an intradiscal loop. Each of the helical sections is interrupted by a short irregular region. One of these includes the lysyl residue to which the chromophore 11-cis retinal is attached. The second non-regular segment, almost opposite the first, contains a cysteinyl and a tryptophanyl residue which may be involved in protein—chromophore interaction. The proposed structure of this whole domain could prove instructive in the elucidation of the primary events of visual transduction.