Radar reflectivity of titan

The present understanding of the atmosphere and surface conditions on Saturn's largest moon, Titan, including the stability of methane, and an application of thermodynamics leads to a strong prediction of liquid hydrocarbons in an ethane-methane mixture on the surface. Such a surface would have nearly unique microwave reflection properties due to the low dielectric constant. Attempts were made to obtain reflections at a wavelength of 3.5 centimeters by means of a 70-meter antenna in California as the transmitter and the Very Large Array in New Mexico as the receiving instrument. Statistically significant echoes were obtained that show Titan is not covered with a deep, global ocean of ethane, as previously thought. The experiment yielded radar cross sections normalized by the Titan disk of 0.38 +/- 0.15, 0.78 +/- 0.15, and 0.25 +/- 0.15 on three consecutive nights during which the sub-Earth longitude on Titan moved 50 degrees. The result for the combined data for the entire experiment is 0.35 +/- 0.08. The cross sections are very high, most consistent with those of the Galilean satellites; no evidence of the putative liquid ethane was seen in the reflection data. A global ocean as shallow as about 200 meters would have exhibited reflectivities smaller by an order of magnitude, and below the detection limit of the experiment. The measured emissivity at similar wavelengths of about 0.9 is somewhat inconsistent with the high reflectivity.     

Radar images of Mars

Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO(2) or H(2)O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.     

Book reviews

Marilyn Holly is an Associate Professor of Philosophy at the University of Florida. Her special interests include political philosophy, ethics and ecology, Jungian thought, and Native American spirituality in its relation to the environment. She is currently at work on a monograph-length piece on the latter topic. She has taught an undergraduate course in ethics and ecology, and plans to do so again. The following essay emerged from her search for a suitable text for such a course.     

Robust RNAi-based resistance to mixed infection of three viruses in soybean plants expressing separate short hairpins from a single transgene

Transgenic plants expressing double-stranded RNA (dsRNA) of virus origin have been previously shown to confer resistance to virus infections through the highly conserved RNA-targeting process termed RNA silencing or RNA interference (RNAi). In this study we applied this strategy to soybean plants and achieved robust resistance to multiple viruses with a single dsRNA-expressing transgene. Unlike previous reports that relied on the expression of one long inverted repeat (IR) combining sequences of several viruses, our improved strategy utilized a transgene designed to express several shorter IRs. Each of these short IRs contains highly conserved sequences of one virus, forming dsRNA of less than 150 bp. These short dsRNA stems were interspersed with single-stranded sequences to prevent homologous recombination during the transgene assembly process. Three such short IRs with sequences of unrelated soybean-infecting viruses (Alfalfa mosaic virus, Bean pod mottle virus, and Soybean mosaic virus) were assembled into a single transgene under control of the 35S promoter and terminator of Cauliflower mosaic virus. Three independent transgenic lines were obtained and all of them exhibited strong systemic resistance to the simultaneous infection of the three viruses. These results demonstrate the effectiveness of this very straight forward strategy for engineering RNAi-based virus resistance in a major crop plant. More importantly, our strategy of construct assembly makes it easy to incorporate additional short IRs in the transgene, thus expanding the spectrum of virus resistance. Finally, this strategy could be easily adapted to control virus problems of other crop plants.     

Insecticidal potency of novel compounds on multiple insect species of medical and veterinary importance

BACKGROUND: Vector‐borne diseases continue to present significant threats to human, animal and plant health. Mosquitoes, houseflies, sand flies and stable flies are well‐known vectors of several human and animal pathogens. The toxicity of selected semiochemicals with molecular structures indicative of insecticidal activity was determined against these insect species with the aim of developing novel insecticides toxic to multiple insect species. RESULTS: Three semiochemicals, namely beta‐damascone, cyclemone A and melafleur, showed remarkable toxicity to three mosquitoes, Aedes aegypti L., Ae. albopictus (Skuse) and Anopheles quadrimaculatus Say, the housefly, Musca domestica L., the stable fly, Stomoxys calcitrans L., and the sand fly, Lutzomyia shannoni (Dyar). The chemicals were equally toxic to several field‐collected permethrin‐tolerant housefly strains. When formulated as 500 mL L^?1 emulsifiable concentrates, the chemicals demonstrated stability and toxicity on filter paper and camouflage military fabrics, with persistence up to 8 days under laboratory conditions. The chemicals were equally effective under field conditions when evaluated on unpainted plywood panels, although a higher dosage was required under field conditions to achieve similar efficacy. CONCLUSION: Laboratory quantification of LC₅₀ values and field efficacy of three semiochemicals as formulated compounds on mosquitoes, houseflies, stable flies and sand flies showed that these semiochemicals could serve as potent insecticides for multiple insect species. Copyright © 2010 Society of Chemical Industry     

The performance of a thermometer screen on an automatic weather station

The performance of a Didcot-type thermometer screen on an Automatic Weather Station and a conventional Stevenson screen were compared, both with each other and against an aspirated Assmann psychrometer. Maximum temperature in the Didcot screen exceeded the conventional screen maximum by up to 1 K on calm, sunny days, and Didcot minimum temperatures were as much as 1.5 K less than the screen minima on still, clear nights; mean temperature discrepancies between screens were + 0.3 and − 0.4 K for maxima and minima, respectively. The apparent psychrometric constant for the Didcot screen was 1.0 mbar K⁻¹ which increased to 1.2 mbar K⁻¹ when u < 2 m s⁻¹ in contrast to the value of 0.799 mbar K⁻¹ frequently used for the Stevenson screen.     

In vitro inhibition of the activation of Pro-matrix Metalloproteinase 1 (Pro-MMP-1) and Pro-matrix metalloproteinase 9 (Pro-MMP-9) by rice and soybean Bowman-Birk inhibitors

The in vitro inhibitory activity of the rice Bowman-Birk inhibitor (rBBI) or soybean Bowman-Birk inhibitor (sBBI) against trypsin-catalyzed activation of pro-matrix metalloproteinase 1 or 9 (pro-MMP-1 or pro-MMP-9), respectively, was investigated using electrophoresis with silver staining, heparin-enhanced zymography, biotinylated gelatin, Biotrak assay, and fluorescence quenched substrate hydrolysis. rBBI at concentrations of 0.08-0.352 mg/mL dose-dependently inhibited the in vitro activation of 45 microg/mL pro-MMP-1 by trypsin. Heparin-enhanced zymography analysis of pro-MMP-1, trypsin-activated MMP-1, and a mixture of pro-MMP-1-trypsin-rBBI showed clear zones associated with trypsin-activated MMP-1 and the absence of clear zones in lanes containing pro-MMP-1 or a mixture of pro-MMP-1, trypsin, and rBBI. The results of the Biotrak assay also indicated that rBBI dose-dependently suppressed the activation of pro-MMP-1 by trypsin. sBBI dose-dependently inhibited the activation of 100 microg/mL of pro-MMP-9 by trypsin. Biotinylated gelatin assays demonstrated that pro-MMP-9 or pro-MMP-9 in the presence of trypsin and BBI did not hydrolyze gelatin, whereas p-aminophenylmercury acetate (APMA)-activated MMP-9 and trypsin-activated MMP-9 caused significant hydrolysis of gelatin. Quenched fluorescence substrate hydrolysis for total MMP activity showed that pro-MMP-1 or pro-MMP-9 did not hydrolyze the substrate Mca-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH2; active MMP-1 or MMP-9 hydrolyzed the substrate, but lower substrate hydrolysis was obtained when pro-MMP-1 or pro-MMP-9 was incubated with trypsin in the presence of increasing concentrations of rBBI. The results are discussed in light of the role of MMP-1 and MMP-9 in the process of angiogenesis and the potential of rBBI or sBBI as a functional food ingredient.     

Turf-banked terrace treads and risers, turf exfoliation and possible relationships with advancing treeline

Fine-scale geomorphic/pedogenic processes at alpine treeline may facilitate the initial stages of conifer invasion of alpine tundra. Turf-banked terraces and turf exfoliation associated with solifluction may provide both the topographic protection and the seedbed necessary for conifer establishment above treeline. The morphometry, stoniness and surface penetrability of turf-banked terraces were recorded. Whereas differences among sites exist due to topographic constraints, differences in soil penetrability depend on turf exfoliation. Exfoliated turf risers are significantly more penetrable than non-exfoliated solifluction risers and adjacent treads. These penetrable microsites provide favorable conditions for seed germination. The process of turf exfoliation may play a role in conifer advance into tundra during climatic change.