290 research outputs found
Cytological analysis of MRE11 protein during early meiotic prophase I in Arabidopsis and tomato
Early recombination nodules (ENs) are multiprotein complexes that are thought to be involved in synapsis and recombination, but little is known about their components or how they may be involved in these events. In this study, we describe the cytological behavior of a possible EN component, MRE11, a protein that is important for the repair of the numerous, programmed deoxyribonucleic acid double-strand breaks (DSBs) that occur early in the meiotic prophase. By immunofluorescence, many MRE11 foci were associated with chromosomal axes during early prophase I in both wild-type Arabidopsis and tomato primary microsporocytes. Similar patterns of MRE11 foci were observed in two Arabidopsis mutants (Atspo11-1 and Atprd1) that are defective in DSB formation and synapsis. In tomato chromosomes, MRE11 foci were more common in distal euchromatin than in proximal heterochromatin, consistent with known EN patterns. However, electron microscopic immunogold localization demonstrated that only about 10% of ENs were labeled, and most MRE11 label was associated with synaptonemal complex components. Thus, in plants, MRE11 foci are not dependent on DSB formation, and most MRE11 foci do not correspond to ENs. More generally, our results show that the simple presence of large numbers of fluorescent foci associated with synapsing chromosomes is insufficient evidence to equate these foci with ENs
SOA formation from the atmospheric oxidation of 2-methyl-3-buten-2-ol and its implications for PM<sub>2.5</sub>
The formation of secondary organic aerosol (SOA) generated by irradiating 2-methyl-3-buten-2-ol (MBO) in the presence and/or absence of NO<sub>x</sub>, H<sub>2</sub>O<sub>2</sub>, and/or SO<sub>2</sub> was examined. Experiments were conducted in smog chambers operated in either dynamic or static mode. A filter/denuder sampling system was used for simultaneously collecting gas- and particle-phase products. The structural characterization of gas and particulate products was investigated using BSTFA, BSTFA + PFBHA, and DNPH derivatization techniques followed by GC-MS and liquid chromatography analysis. This analysis showed the occurrence of more than 68 oxygenated organic compounds in the gas and particle phases, 28 of which were tentatively identified. The major components observed include 2,3-dihydroxyisopentanol (DHIP), 2-hydroxy-2-oxoisopentanol, 2,3-dihydroxy-3-methylbutanal, 2,3-dihydroxy-2-methylsuccinic acid, 2-hydroxy-2-methylpropanedioic acid, acetone, glyoxal, methylglyoxal, glycolaldehyde, and formaldehyde. Most of these oxygenated compounds were detected for the first time in this study. <br><br> While measurements of the gas-phase photooxidation products have been made, the focus of this work has been an examination of the particle phase. SOA from some experiments was analyzed for the organic mass to organic carbon ratio (OM/OC), the effective enthalpy of vaporization (ΔH<sub>vap</sub><sup>eff</sup>), and the aerosol yield. Additionally, aerosol size, volume, and number concentrations were measured by a Scanning Mobility Particle Sizer coupled to a Condensation Particle Counter system. The OM/OC ratio was 2.1 in the MBO/H<sub>2</sub>O<sub>2</sub> system. The ÎH<sub>vap</sub><sup>eff</sup> was 41 kJ mol<sup>â1</sup>, a value similar to that of isoprene SOA. The laboratory SOA yield measured in this study was 0.7% in MBO/H<sub>2</sub>O<sub>2</sub> for an aerosol mass of 33 Îźg m<sup>â3</sup>. Secondary organic aerosol was found to be negligible under conditions with oxides of nitrogen (NO<sub>x</sub>) present. Time profiles and proposed reaction schemes are provided for selected compounds. <br><br> The contribution of SOA products from MBO oxidation to ambient PM<sub>2.5</sub> was investigated by analyzing a series of ambient PM<sub>2.5</sub> samples collected in several places around the United States. In addition to the occurrence of several organic compounds in both field and laboratory samples, DHIP was found to originate only from the oxidation of MBO, and therefore this compound could potentially serve as a tracer for MBO SOA. Initial attempts have been made to quantify the concentrations of DHIP and other compounds based on surrogate compound calibrations. The average concentrations of DHIP in ambient PM<sub>2.5</sub> samples from Duke Forest in North Carolina ranged from zero during cold seasons to approximately 1 ng m<sup>â3</sup> during warm seasons. This appears to be the first time that DHIP has been detected in ambient PM<sub>2.5</sub> samples. The occurrence of several other compounds in both laboratory and field samples suggests that SOA originating from MBO can contribute under selected ambient conditions to the ambient aerosol mainly in areas where MBO emissions are high
The formation of secondary organic aerosol from the isoprene + OH reaction in the absence of NO<sub>x</sub>
The reaction of isoprene (C<sub>5</sub>H<sub>8</sub>) with hydroxyl radicals has been
studied in the absence of nitrogen oxides (NO<sub>x</sub>) to determine physical
and chemical characteristics of the secondary organic aerosol formed.
Experiments were conducted using a smog chamber operated in a steady-state
mode permitting measurements of moderately low aerosol levels. GC-MS analysis
was conducted to measure methyl butenediols in the gas phase and
polyols in the aerosol phase. Analyses were made to obtain several bulk
aerosol parameters from the reaction including values for the organic mass
to organic carbon ratio, the effective enthalpy of vaporization
(ÎH<sub>vap</sub><sup>eff</sup>), organic peroxide fraction, and the aerosol yield.
<br><br>
The gas phase analysis showed the presence of methacrolein, methyl vinyl
ketone, and four isomers of the methyl butenediols. These gas-phase
compounds may serve as precursors for one or more of several compounds
detected in the aerosol phase including 2-methylglyceric acid, three
2-methyl alkenetriols, and two 2-methyl tetrols. In contrast to most
previous studies, the 2-methyl tetrols (and the 2-methyl alkenetriols) were
found to form in the absence of acidic sulfate aerosol. However, reaction
conditions did not favor the production of HO<sub>2</sub> radicals, thus allowing
RO<sub>2</sub>+RO<sub>2</sub> reactions to proceed more readily than if higher
HO<sub>2</sub> levels had been generated.
<br><br>
SOA/SOC (i.e. OM/OC) was found to average 1.9 in the absence of NO<sub>x</sub>.
The effective enthalpy of vaporization was measured as 38.6 kJ mol<sup>−1</sup>,
consistent with values used previously in modeling studies. The yields in
this work (using an independent technique than used previously) are lower than
those of Kroll et al. (2006) for similar aerosol masses. SOC yields reported
in this work range from 0.5â1.4% for carbon masses between 17 and
49 ÎźgC m<sup>−3</sup>
The use of light to enhance weaver ant Oecophylla longinoda Latreille (Hymenoptera: Formicidae) queen catches
Production of live weaver ant (Oecophylla longinoda and O. smaragdina) colonies is being developed as the ants provide several ecosystem services in agriculture and as they are used in education and research laboratories. Founding queens needed for colony production can be caught in artificial nests made of live leaves that are curled on trees. In this study we investigated if the catch rate of O. longinoda queens in artificial nests could be improved by attracting queens to trees with a light source (electric torches). We compared catch rates of 50 artificial nests on each of eight citrus trees, four of them with light and four without light. During two mating seasons covering 9 mating flights we caught a total of 178 queens. However, 3.8 times more queens were caught in the trees with light compared to trees without light. We conclude that queen catches can be highly improved by combining artificial nests with an attracting light source
Influence of aerosol acidity on the chemical composition of secondary organic aerosol from β-caryophyllene
The secondary organic aerosol (SOA) yield of β-caryophyllene photooxidation is enhanced by aerosol acidity. In the present study, the influence of aerosol acidity on the chemical composition of β-caryophyllene SOA is investigated using ultra performance liquid chromatography/electrospray ionization-time-of-flight mass spectrometry (UPLC/ESI-TOFMS). A number of first-, second- and higher-generation gas-phase products having carbonyl and carboxylic acid functional groups are detected in the particle phase. Particle-phase reaction products formed via hydration and organosulfate formation processes are also detected. Increased acidity leads to different effects on the abundance of individual products; significantly, abundances of organosulfates are correlated with aerosol acidity. To our knowledge, this is the first detection of organosulfates and nitrated organosulfates derived from a sesquiterpene. The increase of certain particle-phase reaction products with increased acidity provides chemical evidence to support the acid-enhanced SOA yields. Based on the agreement between the chromatographic retention times and accurate mass measurements of chamber and field samples, three β-caryophyllene products (i.e., β-nocaryophyllon aldehyde, β-hydroxynocaryophyllon aldehyde, and β-dihydroxynocaryophyllon aldehyde) are suggested as chemical tracers for β-caryophyllene SOA. These compounds are detected in both day and night ambient samples collected in downtown Atlanta, GA and rural Yorkville, GA during the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS)
Ant colonies: building complex organizations with minuscule brains and no leaders
Thus far the articles in the series JOD calls the âOrganization Zooâ have employed the notion of a âzooâ metaphorically to describe an array of human institutions. Here we take the term literally to consider the design of the most complex organizations in the living world beside those of humans, a favorite of insect zoos around the world: ant colonies. We consider individuality and group identity in the functioning of ant organizations; advantages of a flat organization without hierarchies or leaders; self-organization; direct and indirect communication; job specialization; labor coordination; and the role of errors in innovation. The likely value and limitations of comparing ant and human organizations are briefly examined
Cosmic Ray Rejection and Readout Efficiency for Large-Area Arrays
We present an algorithm to optimally process uniformly sampled array image
data obtained with a nondestructive readout. The algorithm discards full wells,
removes cosmic ray (particle) hits and other glitches, and makes a nearly
optimum estimate of the signal on each pixel. The algorithm also compresses the
data. The computer requirements are modest, and the results are robust. The
results are shown and compared to results of Fowler sampled and processed data.
Non-ideal detector performance may require some additional code, but this is
not expected to cost much processing time. Known types of detector faults are
addressed.Comment: This paper has been accepted for publication in the PAS
Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)
M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging
Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m
telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along
with spectra from the International Ultraviolet Explorer and Lick 1-m
telescopes. The wide-field UIT image shows FUV emission from (a) an elongated
nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c)
a bright inner ring of H II regions at the perimeter of the inner disk (R = 48
arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the
ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc).
The HST/FOC image resolves the NUV emission from the nuclear region into a
bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30
deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk
indicates an approximately 10^7 or 10^8 yr-old stellar population from
low-level starbirth activity blended with some LINER activity. Analysis of the
H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers
of stars and gas in M94 indicates that most of the star formation is being
orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring,
oval disk, and outer ring. The inner starburst ring and bi-symmetric knots at
intermediate radius, in particular, argue for bar-mediated resonances as the
primary drivers of evolution in M94 at the present epoch. Similar processes may
be governing the evolution of the ``core-dominated'' galaxies that have been
observed at high redshift. The gravitationally-lensed ``Pretzel Galaxy''
(0024+1654) at a redshift of approximately 1.5 provides an important precedent
in this regard.Comment: revised figure 1 (corrected coordinate labels on declination axis);
19 pages of text + 19 figures (jpg files); accepted for publication in A
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