Cometary particles: thin sectioning and electron beam analysis

Thin sections (500 to 1000 angstroms thick) of individual micrometeorites (5 to 15 micrometers) have been prepared with an ultramicrotome equipped with a diamond knife. Electron microscopic examination of these sections has revealed the internal structures of chondritic micrometeorites, and a subset of highly porous, fragile particles has been identified. Delicate meteoritic materials such as these are characteristic of debris from cometary meteors.     

Endocannabinoid hydrolysis generates brain prostaglandins that promote neuroinflammation

Phospholipase A(2)(PLA(2)) enzymes are considered the primary source of arachidonic acid for cyclooxygenase (COX)-mediated biosynthesis of prostaglandins. Here, we show that a distinct pathway exists in brain, where monoacylglycerol lipase (MAGL) hydrolyzes the endocannabinoid 2-arachidonoylglycerol to generate a major arachidonate precursor pool for neuroinflammatory prostaglandins. MAGL-disrupted animals show neuroprotection in a parkinsonian mouse model. These animals are spared the hemorrhaging caused by COX inhibitors in the gut, where prostaglandins are instead regulated by cytosolic PLA(2). These findings identify MAGL as a distinct metabolic node that couples endocannabinoid to prostaglandin signaling networks in the nervous system and suggest that inhibition of this enzyme may be a new and potentially safer way to suppress the proinflammatory cascades that underlie neurodegenerative disorders.     

Extreme oxygen sensitivity of electronic properties of carbon nanotubes

The electronic properties of single-walled carbon nanotubes are shown here to be extremely sensitive to the chemical environment. Exposure to air or oxygen dramatically influences the nanotubes' electrical resistance, thermoelectric power, and local density of states, as determined by transport measurements and scanning tunneling spectroscopy. These electronic parameters can be reversibly "tuned" by surprisingly small concentrations of adsorbed gases, and an apparently semiconducting nanotube can be converted into an apparent metal through such exposure. These results, although demonstrating that nanotubes could find use as sensitive chemical gas sensors, likewise indicate that many supposedly intrinsic properties measured on as-prepared nanotubes may be severely compromised by extrinsic air exposure effects.     

Sustainability and peasant farming systems: Observations from Zimbabwe

Many authors suggest the need to define ‘sustainable development’in operational terms. This paper looks at the problems ofattempting to ask whether peasant farming systems are sustainable.Any attempt at sustainability assessment needs to consider issuesrelated to the selected indicators or performance criteria, spatialscale or boundaries, and temporal scale. While there is certainlya need for more rigorous analysis of sustainability issues, thereis limited outlook for an approach based on indicators. Even if themany purely technical problems associated with specific indicatorscan be surmounted, will accurate bio-physical data advance ourknowledge about sustainability? Peasant systems arepolitically-guided management systems, whose boundaries are the state,not the field or the farm. Given the dynamic nature of peasant farmingsystems, where do we draw the line in assessing sustainability?Attempts at sustainability assessment 100 years ago or even 20–30years ago would have been completely superseded by events. We drawattention to the system as a whole, to a web of interconnections,causes and effects – of varying significance over both time andspace.     

Hemoglobin Gun Hill: deletion of five amino acid residues and impaired heme-globin binding

Hemoglobin Gun Hill, a new variant of adult hemoglobin, was found in a Caucasian and one of his three daughters. The abnormal hemoglobin had only half of the expected number of heme groups. Five amino acid residues appeared to be missing from the beta-globin chains. These residues occur in linear sequence in normal beta-chains in a region involved in heme-globin binding. A deletion of five amino acids in the beta-chains of hemoglobin Gun Hill is postulated. The most likely mechanism for the origin of such a hemoglobin variant would appear to be unequal crossing-over during meiosis.     

Preindustrial to modern interdecadal variability in coral reef pH

The oceans are becoming more acidic due to absorption of anthropogenic carbon dioxide from the atmosphere. The impact of ocean acidification on marine ecosystems is unclear, but it will likely depend on species adaptability and the rate of change of seawater pH relative to its natural variability. To constrain the natural variability in reef-water pH, we measured boron isotopic compositions in a approximately 300-year-old massive Porites coral from the southwestern Pacific. Large variations in pH are found over approximately 50-year cycles that covary with the Interdecadal Pacific Oscillation of ocean-atmosphere anomalies, suggesting that natural pH cycles can modulate the impact of ocean acidification on coral reef ecosystems.     

Origin and evolution of prebiotic organic matter as inferred from the Tagish Lake meteorite

The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration. At least some molecules of prebiotic importance formed during the alteration.