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Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this paper, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems.
We report on the detection of a population of weak metal-line absorbers in the halo or nearby intergalactic environment of the Milky Way. Using high-resolution ultraviolet absorption-line spectra of bright quasars (QSO) obtained with the Space Telescope Imaging Spectrograph (STIS), along six sight lines we have observed unsaturated, narrow absorption in O I and Si II, together with mildly saturated C II absorption at high radial velocities (vertical bar v(LSR)vertical bar = 100-320 km s(-1)). The measured O I column densities lie in the range N(O I) 2 x 10(14) cm(-2) implying that these structures represent Lyman limit Systems and sub-Lyman limit System with H I column densities between 10(16) and 3 x 10(18) cm(-2), thus below the detection limits of current 21 cm all-sky surveys of high-velocity clouds (HVCs). The absorbers apparently are not directly associated with any of the large high column density HVC complexes, but rather represent isolated, partly neutral gas clumps embedded in a more tenuous, ionized gaseous medium situated in the halo or nearby intergalactic environment of the Galaxy. Photoionization modeling of the observed low ion ratios suggests typical hydrogen volume densities of n(H) > 0.02 cm(-3) and characteristic thicknesses of a several parsec down to subparsec scales. For three absorbers, metallicities are constrained in the range of 0.1-1.0 solar, implying that these gaseous structures may have multiple origins inside and outside the Milky Way. Using supplementary optical absorption-line data, we find for two other absorbers Ca II/O I column-density ratios that correspond to solar Ca/O abundance ratios. This finding indicates that these clouds do not contain significant amounts of dust. This population of low column density gas clumps in the circumgalactic environment of the Milky Way is indicative of the various processes that contribute to the circulation of neutral gas in the extended halos of spiral galaxies. These processes include the accretion of gas from the intergalactic medium and satellite galaxies, galactic fountains, and outflows. We speculate that this absorber population represents the local analog of weak Mg II systems that are commonly observed in the circumgalactic environment of low- and high-redshift galaxies.
We present a method for the rapid and simple extraction of DNA from marine sediments using electroelution. It effectively separates DNA from compounds, including humic substances, that interfere with subsequent DNA quantification and amplification. After extraction of the DNA from the sediment into an aqueous solution, the crude sample is encased in 2% agarose gel and exposed to an electrical current, which draws the DNA out of the gel into a centrifugal filter vial. After electroelution, the sample is centrifuged to remove contaminants <= 100 000 Da. Recovery of DNA using this method is quantitative and does not discriminate on the basis of size, as determined using DNA standards and DNA extracts from environmental samples. Amplification of DNA is considerably improved due to removal of PCR inhibitors. For Archaea, only these purified extracts yielded PCR products. This method allows for the use of relatively large volumes of sediment and is particularly useful for sediments containing low biomass such as deeply buried marine sediments. It works with both organic-rich and -poor sediment, as well as with sediment where calcium carbonate is abundant and sediment where it is limited; consequently, adjustment of protocols is unnecessary for samples with very different organic and mineral contents.
The nor-halimane diterpenoid tessmannic acid and its methyl, 2-methylisopropyl and 1-methylbutyl esters, the unusual isocoumarins 8-hydroxy-6-methoxy-3-pentylisocoumarin and 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, and 5- pentyl-3-methoxy-N-butylaniline were isolated from the stem and root bark extracts of Tessmannia densiflora Harms (Caesalpiniaceae) that showed mosquito larvicidal activity. The structures were determined on interpretation of spectroscopic data. Tessmannic acid and its methyl ester exhibited antibacterial and antifungal activity. The compounds also caused high larvae and adult Anopheles gambiae mosquitoe mortality effects, and stronger mosquito repellency than that shown by the standard repellent DEET, hence indicating Tessmannia species to be potential sources of bioactive natural products.
From the dichloromethane-methanol (1:1) extract of the seed pods of Derris trifoliata, a new flavanone derivative (S)-lupinifolin 4´-methyl ether was isolated. In addition, the known flavonoids lupinifolin and rotenone were identified. The structures were determined on the basis of spectroscopic evidence. Lupinfolin showed moderate in vitro antiplasmodial activity against the D6 (chloroquine-sensitive) and W2 (chloroquineresistant) strains of Plasmodium falciparum. The different parts of this plant showed larvicidal activities against Aedes aegypti and rotenoids were identified as the active principles.
From the seedpods of Tephrosia elata, a new β-hydroxydihydrochalcone named (S)-elatadihydrochalcone was isolated. In addition, the known flavonoids obovatachalcone, obovatin, obovatin methyl ether and deguelin were identified. The structures were determined on the basis of spectroscopic evidence. The crude extract and the flavonoids obtained from the seedpods of this plant showed antiplasmodial activities. The literature NMR data on β-hydroxydihydrochalcones is reviewed and the identity of some of the compounds assigned β-hydroxydihydrochalcone skeleton is questioned.
Previous studies that have examined the relationship between implicit and explicit motive measures have consistently found little variance overlap between both types of measures regardless of thematic content domain (i.e., power, achievement, affiliation). However, this independence may be artifactual because the primary means of measuring implicit motivescontent-coding stories people write about picture cuesare incommensurable with the primary means of measuring explicit motives: having individuals fill out self-report scales. To provide a better test of the presumed independence between both types of measures, we measured implicit motives with a Picture Story Exercise (PSE; McClelland, Koestner, Weinberger, 1989) and explicit motives with a cue- and response-matched questionnaire version of the PSE (PSE-Q) and a traditional measure of explicit motives, the Personality Research Form (PRF; Jackson, 1984) in 190 research participants. Correlations between the PSE and the PSE-Q were small and mostly nonsignificant, whereas the PSE- Q showed significant variance overlap with the PRF within and across thematic domains. We conclude that the independence postulate holds even when more commensurable measures of implicit and explicit motives are used.
Electrocoating of 2,2 dibutylpropylene dioxythiophene on carbon fiber microelectrodes (CFMEs) in different electrolytes in acetonitrile was performed, and surface morphology and electrochemical impedance spectroscopic investigation has been carried out. Impedance spectra showed the typical form of Z(IM) versus Z(RE) for transmission- line at frequencies 10 Hz, with transition to almost pure capacitive behaviour down to 10 mHz (the lower limit of frequency scan).
Predictions on displacement of suitable habitats due to climate change suggest that plant species with poor colonization ability may be unable to move fast enough to match forecasted climate-induced changes in habitat distribution. However, studies on early Holocene plant migration show fast migration of many plant species that are poor colonizers today. We hypothesize that warmer temperatures during the early Holocene yielded higher seed quality, contributing to explaining the fast migration. We studied how the 3 seed quality variables, seed mass, germinability, and requirements for break of seed dormancy, vary for seeds of 11 forest herb species with varying colonization capacity collected along a 1400-km latitudinal gradient. Within species, seed mass showed a positive correlation with latitude, whereas germinability was more positively correlated with temperature (growing degree hours obtained at time of seed collection). Only slow-colonizing species increased germinability with temperature, whereas only fast-colonizing species increased germinability with latitude. These interactions were only detectable when analyzing germinability of the seeds, even though this trait and seed mass were correlated. The requirement for dormancy break did not correlate with latitude or temperature. The results indicate that seed development of slow colonizers may be favoured by a warmer climate, which in turn may be important for their migration capacity.