Molecular orbitals of Si2O 7 6− , Si3O 10 8− , etc., and mixed (B,Al,P,Si) m applied to clusters and X-ray spectroscopy data of silicates

The Si, Al L_{II, III} and OK_α emission and quantum yield spectra were obtained for 24 silicates. It was found that in minerals of a homogeneous anion composition the Si L_{II, III} line has double-humped structure, and when in addition to SiO ₄ ^4? ions of other composition (BeO ₄ ^6? , AlO ₄ ^5? etc.) are present it has triple-humped structure. The process of crystal-glass transition was studied by X-ray spectroscopy. The result is that in spite of the original form of the Si L_{II, III} line of the mineral this line changes its structure in glass and exhibits a typical double-humped structure. The CNDO/2 approach was used to calculate the electronic structure of basic structural groups of silicates from SiO ₄ ^4? to Si₅O ₁₆ ^12? by replacing one or two of the Si atoms by Be, B, Al and P. A qualitative interpretation of the X-ray spectra is presented.     

Contrasting patterns of precipitation seasonality during the Holocene in the south‐ and north‐central Mediterranean

Pollen‐based quantitative estimates of seasonal precipitation from Lake Pergusa and lake‐level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid‐Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south‐central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north‐central Italy, where the mid‐Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non‐linear responses to orbitally driven insolation decrease in addition to seasonal and inter‐hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd.     

Impact of wildfire on source water contributions in Devil Creek,CA: evidence from end‐member mixing analysis

A geochemical and end‐member mixing analysis (EMMA) is undertaken in Devil Canyon catchment, located in southern California, to further understanding of watershed behaviour and source water contributions after an acute and extensive wildfire. Physical and chemical transformations in post‐fire watersheds are known to increase overland flow and decrease infiltration, mainly due to formation of a hydrophobic layer at, or near, the soil surface. However, less is known about subsurface flow response in burned watersheds. The current study incorporates EMMA to evaluate and quantify source water contributions before, and after, a catchment affected by wildfires in southern California during the fall of 2003. Pre‐ and post‐fire stream water data were available at several sampling sites within the catchment, allowing the identification of contributing water sources at varying spatial scales. Proposed end‐member observations (groundwater, overland flow, shallow subsurface flow) were also collected to constrain and develop the catchment mixing model. Post‐fire source water changes are more evident in the smaller and faster responding sub‐basin (interior sampling point). Early post‐fire storm events are dominated by overland flow with no significant soil water or groundwater flow contribution. Inter‐storm streamwater in this smaller basin shows an increase in groundwater and a decrease in soil water. In the larger, baseflow‐dominated system, source water components appear less affected by fire. A slight increase in lateral flow is observed with only a slight decrease in baseflow. Changes in the post‐fire flow regimes affect nutrient loading and chemical response of the basin. Relatively rapid recovery of the chaparral ecosystem is evidenced, with active re‐growth and evapotranspiration evidenced by the fourth post‐fire rainy season. Copyright © 2008 John Wiley & Sons, Ltd.     

Photochemical changes in chemical markers of sedimentary organic matter source and age

Several chemical markers of organic matter source and age are shown to be susceptible to light-induced alteration. To test for the photochemical lability of markers previously employed for sediments from the Louisiana coastal zone, we subjected sediments under resuspension conditions to simulated sunlight, and monitored changes in C:N and Br:OC ratios, δ¹³C, Δ¹⁴C, and lignin composition. Markers of terrigenous origin (high C:N, lignin) decreased and δ¹³C became enriched in sediments containing primarily terrigenous organic matter, while a marker of marine organic matter (Br:OC) decreased in samples containing significant contributions from this source. Preferential loss of ¹⁴C from all sediments indicated enhanced photochemical lability of organic matter of relatively recent origin, consistent with the changes in chemical markers. Most, but not all, experimental alterations are consistent with field distributions of these markers. Relatively small experimental changes in the markers in combination with confounding processes in the environment, however, prevent these parallel trends from providing any more than a consistency test for the importance of photochemical reactions in this region.     

Macrobenthos relative to the oxygen minimum zone on the East Indian margin,Bay of Bengal

The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone [OMZ – DO (dissolved oxygen), concentration <0.5 ml·1^?1] at 110 stations off the North East Indian margin (16⁰ and 20⁰ N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1^?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m^?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l^?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m^?2). Species richness [E(S₁₀₀)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S₁₀₀) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l^?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S₁₀₀), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally.     

An instrument for commissioning the active and adaptive optics of modern telescopes: the Infrared Test Camera for the Large Binocular Telescope

We describe the design, integration, and operation of the infrared test cameras for the commissioning of the Large Binocular Telescope. The design and construction phase lasted slightly more than one year from February 2007 to April 2008 and was the result of a joint collaboration among INAF Osservatorio Astronomico di Bologna, Università di Bologna Dipartimento di Astronomia (Italy) and the Max-Planck-Institut für Astronomie (Heidelberg, Germany). Thereafter, the camera was delivered to the LBT Observatory (USA) for commissioning of the telescope active optics and, more recently, for commissioning of the first light adaptive optics.     

Comet classification with new methods for gas and dust spectroscopy

We present the results of a program of comet long-slit spectroscopy with the Kast Dual Spectrograph on the 3-m Shane Telescope at Lick Observatory. A total of 26 comets, from a variety of dynamical families, were observed on 39 different nights from 1996 to 2007. A new statistical method extracted the twilight sky from comet frames, because traditional sky subtraction techniques were inadequate. Because previously published Haser model parent and daughter scale lengths did not fit the data well, unbiased ranges of scale lengths were searched for the best-fitting pairs. Coma gas production rates for OH, CN, C₂, C₃, NH, NH₂, and OH confirmed the widely reported carbon-chain depletion for a sub-class of comets, most notably high-perihelion Jupiter-family comets observed at r_h > 1.5 AU, with different behaviors for C₂ and C₃. Our long-slit spectroscopy data was also adapted for the A(θ)fρ dust production parameter. The assumption that A(θ)fρ is constant throughout the nucleus was not upheld. High dust-to-gas ratios for comets with large perihelia were not a selection effect, and suggest that the dust was released earlier in the formation of the coma than the gas. The dust-to-gas ratio did not exhibit any evolutionary traces between different comet dynamical families. The comet survey illuminates the diversity among comets, including the unusually carbon poor Comet 96P/Machholz.     

Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets

We used chemical equilibrium and chemical kinetic calculations to model chemistry of the volatiles released by heating different types of carbonaceous, ordinary and enstatite chondritic material as a function of temperature and pressure. Our results predict the composition of atmospheres formed by outgassing during accretion of the Earth and other terrestrial planets. Outgassing of CI and CM carbonaceous chondritic material produces H₂O-rich (steam) atmospheres in agreement with the results of impact experiments. However, outgassing of other types of chondritic material produces atmospheres dominated by other gases. Outgassing of ordinary (H, L, LL) and high iron enstatite (EH) chondritic material yields H₂-rich atmospheres with CO and H₂O being the second and third most abundant gases. Outgassing of low iron enstatite (EL) chondritic material gives a CO-rich atmosphere with H₂, CO₂, and H₂O being the next most abundant gases. Outgassing of CV carbonaceous chondritic material gives a CO₂-rich atmosphere with H₂O being the second most abundant gas. Our results predict that the atmospheres formed during accretion of the Earth and Mars were probably H₂-rich unless the accreted material was dominantly CI and CM carbonaceous chondritic material. We also predict significant amounts of S, P, Cl, F, Na, and K in accretionary atmospheres at high temperatures (1500-2500 K). Finally, our results may be useful for interpreting spectroscopic observations of accreting extrasolar terrestrial planets.