Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition.

Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

The contribution from distant dust sources to the atmospheric particulate matter loadings at XiAn, China during spring.

Mass concentration data for PM(10) (particulate matter, PM, less than 10 mum) combined with an air mass back-trajectory clustering technique, a potential source contribution function (PSCF) model, and a concentration-weighted trajectory (CWT) method were used to evaluate the transport pathways and sources of XiAn PM(10) in spring 2001 to 2003. Three dust source areas: "Northwesterly Sources," "Northerly Sources," and a "Loess Plateau Source" and an anthropogenic "Southerly Source" contributing to the high particulate matter concentrations at XiAn were identified using these methods. The CWT method provided more compelling information on dust sources than the PSCF model, but there are clear advantages to using multiple interpretive tools. A comparison of the major dust transport pathways shows differences for XiAn versus Beijing, with "Northwesterly Sources" more important for XiAn and arid and semi-arid regions in Mongolia more important for Beijing.

Spectroscopic analysis of iron-oxide minerals in aerosol particles from northern China.

Diffuse reflectance spectrometry was used to study iron-oxide minerals and to investigate the reflectance characteristics of eolian dust collected during the spring of 2001 and 2002 on bulk filters from three sites in northern China. The first derivatives of the reflectance spectra were consistent with signals from two iron-oxide minerals, hematite and goethite, at wavelengths of 565 and 435 nm, respectively, and these values varied with the iron concentrations in the samples. The percent reflectances for the yellow, orange and red bands increased with the iron concentrations and with the first derivative values representing hematite and goethite while those for violet, blue and green bands decreased correspondingly. The results show that iron-oxide minerals play an important role in determining the aerosol particles' color and reflectance properties. Moreover, the relative amounts of the two iron-oxides in Asian dust apparently differ from those in African dust, suggesting that the iron-oxides may provide another tool for tracing the origins of eolian dust on a global scale.

A common aberration with water-immersion objective lenses.

We describe here an aberration that is frequently encountered with water-immersion but not oil-immersion objectives. The aberration is shown to be induced by tilt of the coverslip out of the plane normal to the optical axis. Model calculations taking into account the path-length distortions introduced by a tilted coverslip satisfactorily reproduce the observed effect on the images of small subresolution fluorescent beads.

239,240Pu and inorganic substances in aerosols from the vicinity of a waste isolation pilot plant: the importance of resuspension.

Aerosol samples were collected and analyzed to characterize the spatial and temporal variations in the concentrations of plutonium and selected inorganic substances in the atmosphere around the Waste Isolation Pilot Plant (WIPP). High-volume aerosol sampling was conducted at three sites: (1) On Site, (2) Near Field, and (3) Cactus Flats. 239,240Pu was determined by alpha spectrometry following chemical separations; mass loadings were determined gravimetrically. A separate set of low-volume aerosol samples was analyzed for major ions using ion chromatography and for trace elements by inductively-coupled plasma emission spectrometry and mass spectrometry. The average 239,240Pu activity concentrations in total suspended particle (TSP) samples (12 to 16 nBq m(-3)) were consistent with those previously reported, but they varied strongly with season, with the highest values generally in spring. Further, the 239,240Pu activity concentrations were comparable among the three sites, and therefore there was no evidence for elevated 239,240Pu activities due to WIPP operations. The fraction of the 239,240Pu activity concentrations in the PM10, samples (particles less than 10 microm diameter) relative to TSP was lower than the corresponding PM10/TSP ratios of either high-volume mass or several inorganics (sulfate, aluminum or lead), indicating that 239,240Pu tends to be on large particles. Aerosol mass loadings (microg m(-3)) and 239,240Pu activity concentrations were correlated for all sets of samples, but at On Site, the TSP samples showed higher mass to 239,240Pu ratios than the other sites. Thus activities or processes occurring at or near the WIPP site evidently produced aerosols that contributed to the mass loadings but contained less 239,244Pu than ambient aerosols. About 63% of the variability in 239,240Pu activity concentrations was explained by wind travel, sampling location, length of the sampling interval, and aerosol mass. 239,240Pu activity concentrations also were correlated with aluminum (an indicator of mineral dust), further implicating the resuspension of soils as an important determinant of 239,240Pu in aerosols. The 239,240Pu/Al ratios for the aerosols were higher than in soils, and this could be explained by the preferential binding of 239,240Pu to small soil particles that have large surface area to mass ratios and also have higher aluminum contents than larger particles.

Variability in background levels of surface soil radionuclides in the vicinity of the US DOE waste isolation pilot plant.

Concentrations of radionuclides were measured in soils from a grid of locations surrounding the US Department of Energy Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico and from a grid on a reference site approximately 20 km southeast of the WIPP site. Each of the two grids has 16 sampling locations (grid nodes) systematically distributed within an area of 16.580 ha. Sampling was conducted prior to the arrival of the first waste shipment at WIPP. Thus, the 137Cs and 23,240Pu in the soil are expected to have been deposited as global fallout, although the Gnome Site, 8.8 km southwest of the WIPP, is also a potential source of 239,240Pu and fission products. The reference grid has significantly higher concentrations of fallout and natural radionuclides than the WIPP grid. Up to 80% of the total variability in radionuclide concentrations across the two grids is attributable to differences between grid nodes. Differences between replicates within a location account for 44-50% of the variability in concentrations of the uranium isotopes, but only 11-17% of the variability in the concentrations of the other radionuclides. Samples having similar abundance of radionuclides were spatially aggregated across the terrain. The activity concentrations of the radionuclides were strongly correlated with the concentrations of Al and Pb, and with the percentages of sand, silt and clay in the soil. Normalizing radionuclide concentrations to the concentration of Al or percent fine particles can help adjust for differences in soil textures among samples and facilitate the detection of gradients or temporal changes in soil concentrations.

Molecular characterization of Hop mosaic virus: its serological and molecular relationships to Hop latent virus.

The 3'-terminal sequence of hop mosaic virus (HpMV) genomic RNA was determined. A cDNA of approximately 1.8 kbp was amplified from the HpMV genome by 3' RACE using a degenerate primer, which was designed to anneal to the overlapping region of open reading frames (ORFs) 2 and 3 of eight carlavirus genomes. The sequence contained three ORFs, encoding proteins of 7-, 34-, and 11-kDa, which corresponded to ORFs 4, 5, and 6 of the carlavirus genome, respectively. The amino acid sequence of ORF 5, encoding the coat protein (CP) of HpMV, shows the highest identity (67%) to that of Hop latent virus (HpLV). The HpMV CP N-terminal sequence differs from that of HpLV, but the central and C-terminal sequences of the CP of both viruses are similar. The sequence similarity possibly causes the cross-reaction of heterologous antibodies of HpMV and HpLV. Phylogenetic analyses based on the CP amino acid and 3' non-coding region sequences indicate close relationships among HpMV, HpLV, and Potato virus M. We report here the first molecular characterization of HpMV genomic RNA.

Rhodopsin-transducin interface: studies with conformationally constrained peptides.

To probe the interaction between transducin (G(t)) and photoactivated rhodopsin (R*), 14 analog peptides were designed and synthesized restricting the backbone of the R*-bound structure of the C-terminal 11 residues of G(t)alpha derived by transferred nuclear Overhauser effect (TrNOE) NMR. Most of the analogs were able to bind R*, supporting the TrNOE structure. Improved affinities of constrained peptides indicated that preorganization of the bound conformation is beneficial. Cys347 was found to be a recognition site; particularly, the free sulfhydryl of the side chain seems to be critical for R* binding. Leu349 was another invariable residue. Both Ile and tert-leucine (Tle) mutations for Leu349 significantly reduced the activity, indicating that the Leu side chain is in intimate contact with R*. The structure of R* was computer generated by moving helix 6 from its position in the crystal structure of ground-state rhodopsin (R) based on various experimental data. Seven feasible complexes were found when docking the TrNOE structure with R* and none with R. The analog peptides were modeled into the complexes, and their binding affinities were calculated. The predicted affinities were compared with the measured affinities to evaluate the modeled structures. Three models of the R*/G(t)alpha complex showed strong correlation to the experimental data.

Molecular characterization of Hop latent virus and phylogenetic relationships among viruses closely related to carlaviruses.

The complete nucleotide sequence of the hop latent virus (HpLV) genome was determined. The viral RNA genome is 8,612 nucleotides long, excluding the poly(A) tail, and contains six open reading frames (ORFs), which encode putative proteins of 224-kDa (ORF 1), 25-kDa (ORF 2), 11-kDa (ORF 3), 7-kDa (ORF 4), 34-kDa (ORF 5), and 12-kDa (ORF 6). ORF 5 encodes the coat protein as demonstrated by N-terminal sequencing of three proteolytic peptides derived from the virus particle. The genome organization of HpLV is similar to that of other species in the genus Carlavirus, and the overall sequence of HpLV is more similar to that of Potato virus M than to sequences of other carlaviruses reported to date. The amino acid sequences of the putative methyltransferase, RNA helicase, and RNA-dependent RNA polymerase encoded in ORF 1 and an 'accessory' helicase encoded in ORF 2 of the HpLV genome were compared with those of viruses in the 'tymo' lineage: the genera Carlavirus, Potexvirus, Allexivirus, Foveavirus, Trichovirus, Capillovirus, Vitivirus, and Tymovirus. The phylogenetic relationships among the viruses in these genera are discussed. This is the first molecular characterization of a carlavirus infecting hop plants.

Orientation-dependent visibility of long thin objects in polarization-based microscopy.

Under conditions of directional illumination, the visibility of long, thin objects depends very strongly on the direction and polarization of the incident light. Solutions to Maxwell's equations for the case of an infinite cylinder in an electromagnetic field are well known, and have been used by others in the past for theoretical analysis of light scattering by long, thin objects. The existence of those solutions allows us to calculate the expected angular distribution and polarization of the light scattered from long, thin objects illuminated by a plane wave at any angle. In this paper we show for the first time how one can incorporate these solutions of Maxwell's equations into a quantitative description of the expected appearance of filamentous biological structures in polarization-based microscopy. Our calculations for unidirectional polarized illumination show that thin, dielectric linear objects such as microtubules (or shallow interfaces) observed with finite aperture optics 1) are totally invisible when the angle (phi) between the object's long axis and incident illumination is outside the range magnitude of 90 - phi < or = sin-1 [1.33/N.A.obj]degrees; and 2) are seen with maximum intensity when phi = 90 degrees for incident illumination and scattered light polarized, either both parallel or both perpendicular to the long axis of the object; whereas 3) two maxima appear at phi approximately equal to 90 +/- 25 degrees for polarization of the incident illumination parallel to, but the scattered light perpendicular to the long axis, or vice versa; and 4) in either of these latter conditions, the objects are invisible when the illumination is near normal incidence. These counterintuitive predictions were exactly borne out by our experimental measurements of light-scattering intensity from flagellar axonemes as a function of orientation in a polarizing microscope. These calculations and measurements provide a foundation for furthering our understanding of textural or form birefringence. Calculations based on a solid cylinder model accurately predict the shapes of the measured intensity versus orientation curves. However, the relative intensities of axonemes viewed with different polarizer-analyzer settings differ from those calculated for a homogeneous solid cylinder. Thus we find that these relative intensities can provide a sensitive probe for the structure of biological objects with diameters much smaller than the wavelength of light.

Imaging properties of axicon in a scanning optical system.

The imaging properties of a scanning optical system that incorporates an axicon are presented. Beamshape characteristics including the axial distribution of the J(0) beam and its control and aberration effects arising from off-axis illumination are experimentally studied. These parameters are relevant when the axicon is used in an imaging system operating in the beam-scanning mode. The J(0) pattern produced by a blazed axicon transmittance grating is also presented.

Reducing elution method for copper(II) in cation-exchange chromatography by hydroxylamine hydrocloride solution.

The cation-exchange Chromatographic behaviour of copper and several other metals in hydroxylamine hydrochloride solution has been investigated. At 50 degrees copper(II) is reduced to copper(I) which is eluted quickly in a narrow band and easily separated from other metals such as zinc, nickel, cobalt and iron.