Instruction-level parallel processing

The performance of microprocessors has increased steadily over the past 20 years at a rate of about 50% per year. This is the cumulative result of architectural improvements as well as increases in circuit speed. Moreover, this improvement has been obtained in a transparent fashion, that is, without requiring programmers to rethink their algorithms and programs, thereby enabling the tremendous proliferation of computers that we see today. To continue this performance growth, microprocessor designers have incorporated instruction-level parallelism (ILP) into new designs. ILP utilizes the parallel execution ofthe lowest level computer operations-adds, multiplies, loads, and so on-to increase performance transparently. The use of ILP promises to make possible, within the next few years, microprocessors whose performance is many times that of a CRAY-IS. This article provides an overview of ILP, with an emphasis on ILP architectures-superscalar, VLIW, and dataflow processors-and the compiler techniques necessary to make ILP work well.     

Neurotoxicity of a fragment of the amyloid precursor associated with Alzheimer's disease

Amyloid deposition in senile plaques and the cerebral vasculature is a marker of Alzheimer's disease. Whether amyloid itself contributes to the neurodegenerative process or is simply a by-product of that process is unknown. Pheochromocytoma (PC12) and fibroblast (NIH 3T3) cell lines were transfected with portions of the gene for the human amyloid precursor protein. Stable PC12 cell transfectants expressing a specific amyloid-containing fragment of the precursor protein gradually degenerated when induced to differentiate into neuronal cells with nerve growth factor. Conditioned medium from these cells was toxic to neurons in primary hippocampal cultures, and the toxic agent could be removed by immunoabsorption with an antibody directed against the amyloid polypeptide. Thus, a peptide derived from the amyloid precursor may be neurotoxic.     

Tissue plasminogen activator reduces neurological damage after cerebral embolism

Intravenous administration of tissue plasminogen activator immediately after the injection of numerous small blood clots into the carotid circulation in rabbit embolic stroke model animals caused a significant reduction in neurological damage. In vitro studies indicate that tissue plasminogen activator produced substantial lysis of clots at concentrations comparable to those expected in vivo, suggesting that this may be the mechanism of action of this drug. Drug-induced hemorrhages were not demonstrable. Tissue plasminogen activator may be of value for the immediate treatment of embolic stroke.     

Polar lightning and decadal-scale cloud variability on Jupiter

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter.     

Haplotypes of “<Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter solanacearum” suggest long-standing separation

Three haplotypes of the recently discovered bacterium species “Candidatus Liberibacter solanacearum” are described and related to geographic ranges. The first two are associated with Zebra Chip/Psyllid Yellows of potatoes and other solanaceous plants, vectored by the tomato/potato psyllid Bactericera cockerelli in North and Central America and New Zealand. The third is associated with diseased carrots in Finland and vectored by the carrot psyllid Trioza apicalis. The haplotypes are described by SNPs on the 16s rRNA, 16s/23s ISR and 50s rplJ and rplL ribosomal protein genes. These SNPs are inherited as a package across the three genes. Haplotype “a” has been found primarily from Honduras and Guatemala through western Mexico to Arizona and California, and in New Zealand. Haplotype “b” is currently known from eastern Mexico and northwards through Texas to south central Washington. These haplotypes show some range overlap in Texas, Kansas and Nebraska. The haplotypes are not yet known to elicit biological differences in the plant or insect hosts. These apparently stable haplotypes suggest separate bacterial populations of long standing.     

Iron mobilization by heathland plant extracts

Aqueous extracts of leaves and shoots of Calluna vulgaris, Erica tetralix, and Betula pendula were reacted with iron compounds in the laboratory. Extracts of B. pendula were found to be most active in solubilizing iron. The iron mobilizing capacity of extracts of C. vulgaris depended upon plant age, season, and soil conditions. C. vulgaris shoots were found to be more readily leached of their soluble organic matter than those of B. pendula but yielded little soluble inorganic material. C. vulgaris extracts were the most acid (pH 4.2–4.5) of those examined.     

Accumulation of Cadmium,Chromium, and Zinc by the Moss Sphagnum Papillosum Lindle

In a series of laboratory experiments employing radiotracer methodology, the uptake of Cd,Cr, and Zn by Sphagnum papillosum Lindle moss from solutions of deionized water and bogwater was investigated. Bioaccumulation of the metals was a passive process, since living anddead moss accumulated metal equally. No significant differences were found in metal uptake ratesfrom single metal solutions and mixed metal solutions, suggesting insignificant competitionbetween the metals occurred at the low concentration range used (10-10 to 10-7 M). Metaluptake conformed with Freundlich adsorption isotherms. Concentration factors of metals inSphagnum papillosum in bog water (103 for Cd and Zn, 102 for Cr) were lower than in deionizedwater (104 for Cd and Zn, 103 for Cr), possibly due to metal complexation by dissolved organicmatter, competition by other major cations present in the bog water (Na+, K+, Mg2+, Ca2+) orcomplexation by chlorides in the bog water. While earlier studies have demonstrated the potentialof using sphagnum mosses for monitoring environmental metal contamination, these experimentsare the first to assess metal uptake in moss using low, environmentally realistic metalconcentrations. The results confirm that mosses would be very effective bioindicators ofenvironmental metal concentrations because the concentration of metal in the moss rapidly anddirectly reflects the metal concentrations in the ambient water.