The acid catalyzed nitration of methanol: formation of methyl nitrate via aerosol chemistry

The aqueous phase acid-catalyzed reaction of methanol (CH₃OH) with nitric acid (HNO₃) to yield methyl nitrate (CH₃ONO₂) under atmospheric conditions has been investigated using gas-phase infrared spectroscopy. Reactions were conducted in aqueous sulfuric acid solutions (50.5–63.6 wt.%) with [CH₃OH] = 0.00005–0.005 M and [HNO₃] = 0.02–0.21 M, at 278.2–328.6 K. Methyl nitrate production rates increased linearly with CH₃OH and HNO₃ concentrations and exponentially with sulfuric acid weight percent within the regime studied. Rates increased linearly with nitronium ion concentration, indicating that the reaction involves as the nitrating agent under these conditions. At 298 K, the rate of methyl nitrate production can be calculated from k _obs [CH₃OH][HNO₃], where k _obs  = 2.337 × 10⁻¹³(exp(0.3198*wt.% H₂SO₄)) when the solubility of CH₃ONO₂ in acidic solution is approximated by H* for pure water. The temperature dependence of the rate coefficient is related to solution composition, with activation energies of 59 and 49 kJ/mol at 51.1 and 63.6 wt.% H₂SO₄, respectively, when k is calculated from rate. The temperature dependence has also been parameterized for application to the atmosphere, but the small quantities of present in aerosol particles will result in methyl nitrate production rates too small to be of significance under most atmospheric conditions. An erratum to this article can be found at     

Earth-based 12.6-cm wavelength radar mapping of the Moon: New views of impact melt distribution and mare physical properties

We present results of a campaign to map much of the Moon’s near side using the 12.6-cm radar transmitter at Arecibo Observatory and receivers at the Green Bank Telescope. These data have a single-look spatial resolution of about 40 m, with final maps averaged to an 80-m, four-look product to reduce image speckle. Focused processing is used to obtain this high spatial resolution over the entire region illuminated by the Arecibo beam. The transmitted signal is circularly polarized, and we receive reflections in both senses of circular polarization; measurements of receiver thermal noise during periods with no lunar echoes allow well-calibrated estimates of the circular polarization ratio (CPR) and the four-element Stokes vector. Radiometric calibration to values of the backscatter coefficient is ongoing. Radar backscatter data for the Moon provide information on regolith dielectric and physical properties, with particular sensitivity to ilmenite content and surface or buried rocks with diameter of about one-tenth the radar wavelength and larger.Average 12.6-cm circular polarization ratio (CPR) values for low- to moderate-TiO₂ mare basalt deposits are similar to those of rough terrestrial lava flows. We attribute these high values to abundant few-centimeter diameter rocks from small impacts and a significant component of subsurface volume scattering. An outflow deposit, inferred to be impact melt, from Glushko crater has CPR values near unity at 12.6-cm and 70-cm wavelengths and thus a very rugged near-surface structure at the decimeter to meter scale. This deposit does not show radar-brightness variations consistent with levees or channels, and appears to nearly overtop a massif, suggesting very rapid emplacement. Deposits of similar morphology and/or radar brightness are noted for craters such as Pythagoras, Rutherfurd, Theophilus, and Aristillus. Images of the north pole show that, despite recording the deposition of Orientale material, Byrd and Peary craters do not have dense patterns of radar-bright ejecta from small craters on their floors. Such patterns in Amundsen crater, near the south pole, were interpreted as diagnostic of abundant impact melt, so the fraction of Orientale-derived melt in the north polar smooth plains, 1000 km farther from the basin center, is inferred to be much lower.     

Integrated, watershed-based management for sustainable water resources

Water scarcity is a becoming a critical issue globally, driven largely by the demands of an exponentially growing human population and complicated by the impacts of climate change on the amounts and distribution of precipitation. It is also due to mismanagement as scarce water resources are being used simultaneously for irrigation, power generation, public and industrial water supply, flood reduction, and wastewater disposal without consideration of the cumulative impacts to the water resources themselves. This paper outlines eight ecologically based principles and associated guidelines as the basis for integrated and watershed-based management of the world’s water resources.     

Feeding habits of age-0 striped bass,<Emphasis Type="Italic">Morone saxatilis</Emphasis>, in the mid-Hudson River estuary: Temporal,spatial, and ontogenetic variation

We quantified temporal and spatial variability in diets of 950 juvenile (age-0) striped bass in the Hudson River estuary. We used canonical correspondence analysis to assess the roles of temporal and spatial habitat variability in juvenile diet variation. We found that juvenile striped bass diets in the Hudson River were only modestly comparable to diets in other east coast estuaries. Among-year differences (51.4%) and spatial differences (41.9%) were substantially associated with juvenile striped bass diet. We found ontogeny (2.8%) and within-season variation (9.5%) to only weakly associate with diet variation. Our results indicate that an understanding of the temporal and spatial variation within the Hudson River estuary is vital in understanding variation in feeding by resident juvenile fish.     

Optimization strategies for sediment reduction practices on roads in steep,forested terrain

Many forested steeplands in the western United States display a legacy of disturbances due to timber harvest, mining or wildfires, for example. Such disturbances have caused accelerated hillslope erosion, leading to increased sedimentation in fish‐bearing streams. Several restoration techniques have been implemented to address these problems in mountain catchments, many of which involve the removal of abandoned roads and re‐establishing drainage networks across road prisms. With limited restoration funds to be applied across large catchments, land managers are faced with deciding which areas and problems should be treated first, and by which technique, in order to design the most effective and cost‐effective sediment reduction strategy. Currently most restoration is conducted on a site‐specific scale according to uniform treatment policies. To create catchment‐scale policies for restoration, we developed two optimization models – dynamic programming and genetic algorithms – to determine the most cost‐effective treatment level for roads and stream crossings in a pilot study basin with approximately 700 road segments and crossings. These models considered the trade‐offs between the cost and effectiveness of different restoration strategies to minimize the predicted erosion from all forest roads within a catchment, while meeting a specified budget constraint. The optimal sediment reduction strategies developed by these models performed much better than two strategies of uniform erosion control which are commonly applied to road erosion problems by land managers, with sediment savings increased by an additional 48 to 80 per cent. These optimization models can be used to formulate the most cost‐effective restoration policy for sediment reduction on a catchment scale. Thus, cost savings can be applied to further restoration work within the catchment. Nevertheless, the models are based on erosion rates measured on past restoration sites, and need to be updated as additional monitoring studies evaluate long‐term basin response to erosion control treatments. Copyright © 2006 John Wiley & Sons, Ltd.     

The binary star population of the young cluster NGC 1818 in the Large Magellanic Cloud

We determine the binary star fraction as a function of radius in NGC 1818, a young rich cluster in the Large Magellanic Cloud, using Hubble Space Telescope images in bands F336W (∼ U ) and F555W (∼ V ). Our sample includes binaries with M _primary ∼ 2–5.5 M_⊙ and M _secondary ≳ 0.7 M_primary. The binary fraction increases towards the cluster centre, from ∼ 20 ± 5 per cent in the outer parts, to ∼ 35 ± 5 per cent inside the core. This increase is consistent with dynamical mass segregation and need not be primordial. We compare our results with expectations from N -body models, and discuss the implications for the formation and early evolution of such clusters.     

Ferric-ferrous ratios,H2O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

 Complete chemical analyses, including ferric and ferrous iron, H₂O contents and δD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc, (2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava in the Leucite Hills, Wyoming. The Fe₂O₃ contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe³⁺ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less than would be expected for a site fully occupied by hydroxyl. Cation- and anion-based normalization procedures provide accurate mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe³⁺/Fe^T, and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western Mexico and eastern California have the highest Fe³⁺/Fe^T ratios (56–87%), reflecting high magmatic oxygen fugacities (ΔNNO = +2 to +5), in contrast to those from Uganda (25–40%) and the Leucite Hills (23%). There is no correlation between the OH content and the Fe³⁺/Fe^T ratio in the micas. Values of KMg/Fe²⁺D (± 2σ errors) were calculated for three phlogopite-olivine pairs (0.12 ± 0.12, 0.26 ± 0.14, 0.09 ± 0.12), two biotite-hornblende pairs (0.73 ± 0.08 and 1.22 ± 0.10) and a single phlogopite-augite pair (1.15 ± 0.12). Values of KF/OHD for two biotite and hornblende pairs could not be determined without significant error because of the extremely low F contents (< 0.2 wt%) of the four phases. The δD values obtained in this study encompass a large range (−137 to −43‰). The phlogopite and biotite separates from Uganda have δD values of −70 to −49‰, which overlap those believed to represent “primary” mantle. There is a larger range in δD values (−137 to −43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in δ¹⁸O values (5.2–6.2‰) is consistent with “normal” mantle. It is unlikely, therefore, that the variable δD values reflect heterogeneity in the mantle source region of the minette magmas. Nor can the extremely low δD values reflect degassing of H₂ or H₂O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous phenocrysts. The very low δD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect on the δ¹⁸O value, f _{O 2}, a _{H 2O} or bulk composition of the host magmas. Received: 5 January 1995 / Accepted: 19 March 1996     

Mars landscape evolution: influence of stratigraphy on geomorphology in the north polar region

Lithology and physical properties of strata exposed at the Earth's surface have direct influence on the erosion and geomorphic expression of landforms. While this is well known on our planet, examples on Mars are just coming to light among the tens of thousands of airphoto-quality images (resolutions 1.5–12 m/pixel) acquired since 1997 by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC). Specific examples occur among martian north polar layered materials, which MOC images reveal are divided into two distinct stratigraphic units: a lower, dark-toned layered unit and a younger, upper, lighter-toned layered unit. The lower unit is less resistant to wind erosion than the upper unit. The upper unit most likely consists of stratified dust and ice, while the lower unit contains abundant, poorly cemented sand. Sand is more easily mobilized by wind than dust; the lower resistance to erosion of the lower unit results from the presence of sand. Where wind erosion in polar troughs has penetrated to the lower unit, geomorphic change has proceeded more rapidly: sand has been liberated from the lower unit, and arcuate scarps have formed as the upper unit has been undermined. Wind erosion of the lower unit thus influences the geomorphology of the north polar region; this result likely explains the genesis of the large polar trough, Chasma Boreale, and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades. The properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30–50% less than previously estimated.