Average Surface Concentration Research Articles

Dynamics of multicomponent vesicles in a viscous fluid

We develop and investigate numerically a thermodynamically consistent model of two-dimensional multicomponent vesicles in an incompressible viscous fluid. The model is derived using an energy variation approach that accounts for different lipid surface phases, the excess energy (line energy) associated with surface phase domain boundaries, bending energy, spontaneous curvature, local inextensibility and fluid flow via the Stokes equations. The equations are high-order (fourth order) nonlinear and nonlocal due to incompressibility of the fluid and the local inextensibility of the vesicle membrane. To solve the equations numerically, we develop a nonstiff, pseudo-spectral boundary integral method that relies on an analysis of the equations at small scales. The algorithm is closely related to that developed very recently by Veerapaneni et al. [81] for homogeneous vesicles although we use a different and more efficient time stepping algorithm and a reformulation of the inextensibility equation. We present simulations of multicomponent vesicles in an initially quiescent fluid and investigate the effect of varying the average surface concentration of an initially unstable mixture of lipid phases. The phases then redistribute and alter the morphology of the vesicle and its dynamics. When an applied shear is introduced, an initially elliptical vesicle tank-treads and attains a steady shape and surface phase distribution. A sufficiently elongated vesicle tumbles and the presence of different surface phases with different bending stiffnesses and spontaneous curvatures yields a complex evolution of the vesicle morphology as the vesicle bends in regions where the bending stiffness and spontaneous curvature are small.

Dimethyl sulfide production in a saline eutrophic lake, Salton Sea, California

The concentrations and distribution of volatile organic sulfur compounds were quantified over a 13-month period in the Salton Sea, a warm eutrophic saline lake in Southern California, U.S.A. The concentrations of dimethyl sulfide (DMS) appear to be the highest reported thus far for a natural body of water, with an average surface (0–2 m) concentration of 2.5 µmol L−1. DMS concentrations as high as 11 µmol L−1 were measured, and the concentrations of DMS correlated strongly with chlorophyll a (r2 = 0.62, n = 265, p < 0.05). Dimethyl disulfide was also measured; concentrations were much lower than DMS and often below detection (<0.01-0.32 µmol L−1). Carbon disulfide concentrations were low (<0.03 µmol L−1) and associated with strongly reduced conditions. Very high concentrations of dimethylsulfoniopropionate (DMSP), an osmolyte in marine algae, were also measured (average total DMSP of 2.4 µmol L−1), with concentrations strongly correlated with chlorophyll a (r2 = 0.88, n = 36, p < 0.05). The biomass of the Salton Sea is composed mostly of marine phytoplankton species that are high DMSP producers; based on the correlations of DMS, chlorophyll a, and DMSP, it appears that the DMS in the Salton Sea is directly linked to algal biomass through DMSP. As a result of its very high DMS concentrations, the average estimated volatilization at the Salton Sea (480 µmol m−2 d−1) was greater than estimates for other lakes and the open ocean. We calculate ~9.6 × 105 mol of DMS was volatilized off the surface of the Sea during the course of this study.

Secondary Organic Aerosol from Sesquiterpene and Monoterpene Emissions in the United States

Emissions of volatile organic compounds (VOC) from vegetation are believed to be a major source of secondary organic aerosol (SOA), which in turn comprises a large fraction of fine particulate matter in many areas. Sesquiterpenes are a class of biogenic VOC with high chemical reactivity and SOA yields. Sesquiterpenes have only recently been quantified in emissions from a wide variety of plants. In this study, a new sesquiterpene emission inventory is used to provide input to the Models-3 Community Multiscale Air Quality (CMAQ) model. CMAQ is used to estimate the contribution of sesquiterpenes and monoterpenes to SOA concentrations over the contiguous United States. The gas-particle partitioning module of CMAQ was modified to include condensable products of sesquiterpene oxidation and to update values of the enthalpy of vaporization. The resulting model predicts July monthly average surface concentrations of total SOA in the eastern U.S. ranging from about 0.2-0.8 microg m(-3). This is roughly double the amount of SOA produced in this region when sesquiterpenes are not included. Even with sesquiterpenes included, however, the model significantly underpredicts surface concentrations of particle-phase organic matter compared to observed values. Treating all SOA as capable of undergoing polymerization increases predicted monthly average surface concentrations in July to 0.4-1.2 microg m(-3), in closer agreement with observations. Using the original enthalpy of vaporization value in CMAQ in place of the values estimated from the recent literature results in predicted SOA concentrations of about 0.3-1.3 microg m(-3).

Seasonal CO2 rectifier effect and large‐scale extratropical atmospheric transport

In atmospheric transport models, the covariation of the atmospheric transport and annually neutral biospheric CO2 flux is usually evident as the annual zonal mean surface CO2 concentration gradient. Using the NIES transport model and CO2 flux from the Biome‐BGC model, the covariations of different transport mechanisms and CO2 flux were examined and quantified. Including the covariation of the total transport (processes included in the NIES model) and CO2 flux, the annual average pole to pole CO2 concentration gradient is 3.5 ppm and interhemispheric difference of the average extratropical surface concentration is 2.5 ppm. The conventional covariation mechanism of the seasonal variation of planetary boundary layer mixing height and CO2 flux accounts for approximately 45% of the CO2 concentration gradient. Another important contribution to the CO2 concentration gradient in this model is the covariation of the extratropical anomaly transport (mainly by cyclones and anticyclones) and the biospheric flux, which accounts for about 55%. This alternate physical mechanism is the association of stronger meridional (north–south) anomaly transport (under strong baroclinic instability condition) with higher CO2 concentration from soil respiration in the winter and weaker anomaly transport (weak baroclinic instability condition) with lower CO2 concentration from photosynthetic uptake in the summer. The net result of the meridional transport and flux covariation is a north–south annual zonal mean CO2 concentration gradient.

Facile electrocatalytic redox of hemoglobin by flower-like gold nanoparticles on boron-doped diamond surface

The flower-like gold nanoparticles together with spherical and convex polyhedron gold nanoparticles were fabricated on boron-doped diamond (BDD) surface by one-step and simple electrochemical method through easily controlling the applied potential and the concentration of HAuCl4. The recorded X-ray diffraction (XRD) patterns confirmed that these three shapes of gold nanoparticles were dominated by different crystal facets. The cyclic voltammetric results indicated that the morphology of gold nanoparticles plays big role in their electrochemical behaviors. The direct electrochemistry of hemoglobin (Hb) was realized on all the three different shapes of nanogold-attached BDD surface without the aid of any electron mediator. In pH 4.5 acetate buffer solutions (ABS), Hb showed a pair of well defined and quasi-reversible redox peaks. However, the results obtained demonstrated that the redox peak potential, the average surface concentration of electroactive heme, and the electron transfer rates of Hb are greatly dependent upon the surface morphology of gold nanoparticles. The electron transfer rate constant of hemoglobin over flower-like nanogold/BDD electrode was more than two times higher than that over spherical and convex polyhedron nanogold. The observed differences may be ascribed to the difference in gold particle characteristics including surface roughness, exposed surface area, and crystal structure.

Direct electrochemistry and electrocatalysis of horseradish peroxidase in α-zirconium phosphate nanosheet film

α-zirconium phosphate nanosheets (ZrPNS) derived via the delamination of layered α-zirconium phosphate (α-ZrP) have been proven to be efficient support matrixes for the immobilization of horseradish peroxidase (HRP). X-ray powder diffraction (XRD) results revealed that ZrPNS in HRP–ZrPNS film remained unorderly structured for the effect of HRP. Fourier transform infrared (FTIR) spectra results revealed that HRP remained the secondary structure in HRP–ZrPNS film. The direct electrochemistry of HRP was realized in HRP–ZrPNS film on a glassy carbon electrode (GCE), showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the HRP heme FeIII/FeII redox couple. The average surface concentration (Γ⁎) of electroactive HRP in HRP–ZrPNS film was estimated to be 1.35×10−10 mol cm−2, which indicated a high loading of enzyme molecules in HRP–ZrPNS film. Based on these, a third generation reagentless biosensor was constructed for the determination of hydrogen peroxide (H2O2). The response time of the biosensor was less than 3 s, and the linear response range of the biosensor for H2O2 was from 1.3×10−6 to 1.6×10−2 M with a correlation coefficient of 0.9997.

Spectral and nonlinear optical properties of metal complexes with 1,2-naphthalocyanine in silicate gel matrices

We have studied the influence of the method for embedding metal (Yb or Zn) complexes with 1,2-naphthalocyanine into nanoporous silicate xerogels (directly during sol-gel synthesis or by impregnation of the xerogel) and the nature of the Yb3+ exoligand (anionic Cl− or acetylacetone) on the spectral properties and structure of impurity molecular centers. It is shown that the degree of protonation and/or aggregation of the studied metal complexes is determined by the average surface concentration of HO-Si≡ silanol groups of the gel-matrix nanopores. It is established that the Yb complex with 1,2-naphthalocyanine and the anionic ligand Cl− penetrates to the greatest extent from solution into the inner cavities of the xerogel (degree of impregnation). This is due to quasichemical interaction of pigment molecules with the dehydroxylated nanopore surface containing ≡Si-O-Si≡ siloxane bridges. It is shown that the investigated metal complexes in both liquid solutions and solid-state silicate gel-matrices have a limiting effect on powerful optical radiation.

Improved Electromigration Lifetime for Copper Interconnects using Tantalum Implant

ABSTRACTIn this study, a novel method is explored for improving the electromigration lifetime of Cu wires, using Ta implantation into Cu. For high implant doses (2E15 cm−2), the electromigration lifetime is improved by over 5X using this method. An increase in lifetime is achieved, even for an average surface concentration of Ta on the order of 0.1 atm%. We propose that the improvement in electromigration lifetime is due to the reduction of defects at the SiN/Cu interface due to the presence of Ta. The line-to-line leakage at high voltages (&gt; 5V) increases with the Ta implant, with higher leakage at higher Ta concentrations, so the Ta dose must be limited to avoid excessive leakage.

Galvinoxyl monolayers on Au(111) studied by STM, EPR, and cyclic voltammetry

Galvinoxyl layers on Au(111) have been studied by scanning tunnelling microscopy (STM), electron paramagnetic resonance (EPR), and cyclic voltammetry (CV). We observe two phases: configuration I having a molecular density of $1.57\ifmmode\pm\else\textpm\fi{}0.16\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}\mathrm{mol}∕{\mathrm{cm}}^{2}$ and a rectangular lattice ($15\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ by $7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$) observed at room temperature and down to $140\phantom{\rule{0.3em}{0ex}}\mathrm{K}$; configuration II with a slightly smaller molecular density of $1.37\ifmmode\pm\else\textpm\fi{}0.14\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}\mathrm{mol}∕{\mathrm{cm}}^{2}$ and oblique cells ($22.5\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ by $5.4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$) arranged alternatingly in stacks yielding a molecular layer with lower symmetry and comparatively large crystallographic unit cell. The latter is only observed upon cooling down to $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and subsequent annealing to room temperature. For both assemblies typical domain sizes in the range of $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ have been found. The EPR results confirm that the radical character is preserved upon adsorption and that the intermolecular distance is smaller than $11\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. The interaction between the overlapping singly occupied spin orbitals is high, indicating no participation of the unpaired electron in the binding to the surface or laterally between neighboring radicals. The average surface concentration deduced from CV measurements is in excellent agreement with the surface coverages deduced from STM topographies. In aqueous electrolyte the adsorbate undergoes a one-electron oxidation with concomitant loss of a proton as determined from oxidation potential vs $p\mathrm{H}$ curves in a similar fashion as known for the free radical in solution. This indicates no dramatic change of the electronic properties of the radical upon adsorption. Structure models are proposed with molecules standing upright like ``bicycles in rows.''

Migration stability of α-tocopherol in irradiated UHMWPE

The oxidation resistance of irradiated ultra-high molecular weight polyethylene (UHMWPE) components used in total joint arthroplasty can be improved by adding α-tocopherol (vitamin E) through diffusion. To ensure long-term oxidative stability, a minimum α-tocopherol concentration needs to be maintained throughout these components. Migration of α-tocopherol out of the components is one mechanism that could compromise long-term oxidative stability. We hypothesized that α-tocopherol could elute out during standard implant fabrication steps such as cleaning as well as during in vivo use. We doped 85 kGy irradiated UHMWPE with α-tocopherol at 120 °C and homogenized at 120 °C. We determined the extent of elution of α-tocopherol or its effect on oxidative stability following cleaning in isopropyl alcohol (IPA) and following 5 million cycles (MC) of simulated normal gait in bovine serum. There was no significant elution of α-tocopherol in repeated and prolonged cleaning in IPA as measured by average surface and bulk α-tocopherol concentrations. There was no change in the oxidative stability following 5 MC of hip simulator testing, indicating minimal elution during simulated normal gait.

Uniformity in a thin-zone multi-pulse TAP experiment: numerical analysis

The thin-zone TAP reactor (TZTR) model of a multi-pulse experiment is computationally validated based on a more general three-zone reactor model. The analysis is focused on the uniformity of gaseous and surface concentrations in the catalyst zone, which is a key property of TZTR model. It is shown that if the TZTR model is valid for the first pulse in a multi-pulse experiment then it is valid for all subsequent pulses. For a typical reactor packing (the ratio of the thin-zone thickness to the length of reactor is 1/30) and with the first pulse conversion up to 97%, the gaseous and surface concentration profiles can be considered uniform and characterized by their spatial average values only. The reaction rate in the catalyst zone may also be characterized by its spatial average value and directly related to the spatial average gaseous and surface concentrations, in the same way as an elementary rate is related to concentrations. As a result of these unique characteristics, the TZTR may be considered a “perfectly-mixed” reactor even at high conversion.

Arctic haze over Central Europe

An extraordinary aerosol situation over Leipzig, Germany in April 2002 was investigated with a comprehensive set of ground-based volumetric and columnar aerosol data, combined with aerosol profiles from lidar, meteorological data from radiosondes and air mass trajectory calculations. Air masses were identified to stem from the Arctic, partly influenced by the greater Moscow region. An evaluation of ground-based measurements of aerosol size distributions during these periods showed that the number concentrations below about 70 nm in diameter were below respective long-term average data, while number, surface and volume concentrations of the particles larger than about 70 nm in diameter were higher than the long-term averages. The lidar aerosol profiles showed that the imported aerosol particles were present up to about 3 km altitude. The particle optical depth was up to 0.45 at 550 nm wavelength. With a one-dimensional spectral radiative transfer model top of the atmosphere (TOA) radiative forcing of the aerosol layer was estimated for a period with detailed vertical information. Solar aerosol radiative forcing values between −23 and −38 W m−2 were calculated, which are comparable to values that have been reported in heavily polluted continental plumes outside the respective source regions. The present report adds weight to previous findings of aerosol import to Europe, pointing to the need for attributing the three-dimensional aerosol burden to natural and anthropogenic sources as well as to aerosol imports from adjacent or distant source regions. In the present case, the transport situation is further complicated by forward trajectories, indicating that some of the observed Arctic haze may have originated in Central Europe. This aerosol was transported to the European Arctic before being re-imported in the modified and augmented form to its initial source region.

Scanning surface potential microscopic studies of photo-voltaic Langmuir–Blodgett assemblies containing an A–S–D triad molecule

Scanning surface potential microscopy was applied to detect the photo-voltaic response of Langmuir–Blodgett (LB) monolayer assemblies containing an amphiphilic A–S–D triad molecule (ASD) with two different concentrations. The triad acts as a charge separation unit in the same way as the photosynthetic reaction center. In addition, the photo-induced multistep electron transfer systems can be organized in the LB monolayers: first electrons and holes are separated across the monolayer through the ASD triads upon photo-excitation and then the resultant electrons and holes are further separated by lateral diffusion among the concentrated A and the D moieties, respectively. The change in surface potential was clearly observed on an LB assembly with the high ASD concentration in a mixed ASD monolayer with ω-tricosenoic acid (T) (the molar ratio of ASD:T=1:5), while the photo-response could not be observed on an LB monolayer with the low ASD concentration (the molar ratio of ASD:T=1:30). It was interesting to note that the average surface concentration of ASD in the latter diluted monolayer was decreased only to 1 6 of that of the former concentrated monolayer. If the photo-response depended linearly on the ASD concentration, the surface potential would be readily detected in the latter monolayer. The nonlinearity can be attributed to the effect of succeeding lateral diffusion of the separated charges among the ASD triads. To clarify the effect of the lateral diffusion, the other type of LB assemblies, i.e., A/A–S–D double layers, was fabricated by alternate deposition of an additional acceptor (A) layer and the ASD layer. In the A/A–S–D assemblies, significant photo-induced surface potential change was observed with an A layer of a high A concentration (A:T=1:2) even when the ASD concentration was low in the ASD layer (ASD:T=1:30). This result supported an idea that the additional A layer enhanced lateral electron diffusion and resulted in electron accumulation in A layer and hole accumulation in the diluted ASD layer in the A/A–S–D system.

Surface Segregation of Chromium in a Copper-Chromium Alloy and its Effect on Formation of a Native Oxide Layer

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) has been used for studying the surface segregation of chromium in a copper-0.4 mass% chromium alloy. The influence of the chromium segregation on native oxide layers formed on the surface in this alloy has also been studied. According to a simple layered model assuming thin homogeneous layers, the average surface concentration chromium was found to increase up to about 15 at% on the alloy surface by annealing up to about 1000 K under ultra high vacuum. The AR-XPS results for the alloy surface with chromium segregation, which was exposed to air, showed that the growth of the native oxide layer of copper was not significantly suppressed by segregated chromium. This small influence of chromium segregation on the native oxide layer is considered to result from the relatively high oxidation rate of copper and the microscopic heterogeneity of chromium segregation on the alloy surface.

On Trace Metal Geochemistry in the Danube River and Western Black Sea

Trace metal concentrations were measured in the Danube River estuary and in the shelf area of the north-western Black Sea. Total dissolved concentrations (<0·45μM) of the freshwater in the river end-member were found to be: Cd=117pM, Pb=81pM, Co=266pM, Zn=6nM, Mn=19nM, Ni=15nM, Cu=36nM, Al=384nM and Fe=20nM. These concentrations are surprisingly low for an area where serious contamination has been suspected. This is particularly true of Cd, Pb and Zn, which are generally anthropogenic in polluted regions. The observed low concentrations, in particular for Fe, Mn, Co and Al can be attributable to the precipitation of hydrated oxides as a consequence of high pH of the Danube River. Concentrations of metals in the particulate fraction are similar to those in other major rivers of the world.The evolution of the total dissolved trace metal concentrations in the surface waters within the salinity gradient suggests: (1) no noticeable exchange between the particulate and the dissolved fraction for Cu, Ni and Zn; and (2) evidence for a low solid to liquid exchange for the other metals (Cd, Fe, Mn, Co and Pb) which brings about a two-fold increase in their concentrations from lower to higher salinity. Another source of dissolved material is suspected at around salinity 15. This source may be from localized-patches in the sediment where specific redox conditions may induce a vertical flux of dissolved metals: the bottom waters above these patches are characterized by a diminution of the dissolved O2and high concentrations of metals.The colloidal fraction (between 10kD and 0·45μm) was established on a limited number of samples for Cd, Cu, Mn and Fe and was found to be significant: 40% of Cu, 40% of Cd, ∼50% of Mn and 60% of Fe of the so-called dissolved phase are actually associated with colloidal material. It represents at least 40% of the total dissolved concentration in the fresh water and in the mixing zone. This proportion decreases linearly with salinity for Cd and Cu. Fe is mostly in colloidal form with a maximum (∼80%) between salinity 5 and 10.The surface distribution of the total dissolved metals throughout the study area show a limited influence of the Danube on the concentrations observed for the ‘open sea’ (salinity=18). Most of the riverine flux seems to follow the general circulation to the south-west area. These ‘open Black Sea’ concentrations are the same order of magnitude as average surface concentrations in the Mediterranean Sea.

A comparison of airborne and surface trace gas measurements during the Southern Oxidants Study (SOS)

The NOAA Twin Otter conducted more than a dozen overflights of ground‐level air quality monitoring stations during the 1995 Southern Oxidants Study (SOS) Nashville/Middle Tennessee Ozone Project Field Intensive. Surface and aircraft observations of ozone and ozone precursors were examined to identify systematic sampling errors, and to assess the degree to which surface measurements may be considered representative of the larger planetary boundary layer (PBL). Overall agreement between surface and aircraft trace gas measurements was excellent in the well developed mixed layer, especially in rural‐regional background air and under stagnant conditions, where surface concentrations change only slowly. On July 2, surface level measurements were representative of the larger mixed layer over distances as far as 70 km in background air, and 30 km in the weakly advected urban plume. Vertical variations in trace gas concentrations were often minimal in the well‐mixed PBL, and measurements at the surface always agreed well with aircraft observations up to 460 m above ground level. Under conditions of rapidly varying surface concentrations (e.g., during episodes of power plant plume fumigation and early morning boundary layer development), agreement between surface and aloft is dependent upon the spatial (aircraft) and temporal (ground) averaging intervals used in the comparison. Under these conditions, surface sites may be representative of the PBL only to within a few kilometers. Under clear skies in the well‐mixed PBL, regression of aircraft trace gas data collected within 5 km of the ground sites against 15–20 min average surface concentrations centered on the times of the overflights yielded the following relationships: [O3]aircraft = ([O3]surface × 0.9374) + 4.86 ppbv (r2 = 0.9642); [CO]aircraft = ([CO]surface × 0.8914) + 16.4 ppbv (r2=0.9673); [SO2]aircraft = ([SO2]surface × 0.9414) − 0.069 ppbv (r2 = 0.9945). Although O3, CO, and SO2 measurements at the surface and aloft generally agreed well, isolated examples of unexplained measurement discrepancies emerged, illustrating the need for side‐by‐side instrument comparisons. NOY measurements agreed poorly between surface and aircraft: [NOY]aircraft = ([NOY]surfacex × 0.9184) + 4.56 ppbv (r2 = 0.9188).

Dynamics of Pyridine Adsorption on Gold(111) Terraces in Acid Solution from in-Situ Scanning Tunneling Microscopy under Potentiostatic Control

The adsorption of pyridine (Py) on Au(111) terraces produced from aqueous 0.1 M HClO4 + 10-3 M Py at 298 K was studied in the potential range 0.15 V < E < 0.55 V (vs SHE) by in-situ scanning tunneling microscopy. When E ≥ Epzc, the potential of zero charge of the substrate, both ordered and disordered domains can be observed. Ordered domains correspond to vertically adsorbed Py molecules forming a (4 × 4) hexagonal lattice with the nearest neighbor distance d = 0.38 nm, and corrugation z = 0.04 nm. The ordered adsorbate structure disappears for E < Epzc, but it is recovered several minutes after stepping E backward to E > Epzc, as expected for a reversible potential-step-induced surface process. The surface concentration of adsorbed Py molecules resulting from the (4 × 4) lattice is close to 1 × 10-9 mol/cm2, a figure exceeding the average integral surface concentration value obtained from electroadsorption measurements. Therefore, disordered domains would be related to a mobile diluted Py adsorbate coexisting with ordered Py adsorbate domains leading to a nonhomogeneous Py adsorbate layer at the positively charged Au(111) terraces.

Search for fullerenes C 60and C 70in Cretaceous–Tertiary boundary sediments from Turkmenistan, Kazakhstan, Georgia, Austria, and Denmark

Fullerenes C 60and C 70have been found previously in sediments from the Cretaceous-Tertiary boundary (KTB) sites of Woodside Creek and Flaxbourne River (both New Zealand). Additional discoveries from Caravaca (Spain), Sumbar and Malyi Balkhan (Turkmenistan) and Stevns Klint (Denmark) are reported here. Fullerenes were not found in the KTB sediment from Elendgraben (Austria), nor in acid-demineralized sediments from Koshak (Kazakhstan) and Tetri Tskaro (Georgia). The average surface concentration of C 60at these sites is estimated to be 11.7×10 −3 g /cm 2(11.7 ng/cm 2), which implies 1.1 ppm normalized to the average elemental carbon surface concentration at KTB sites. Global wildfires following the Chicxulub impact 65 Myr ago are the most likely process by which these fullerenes were formed.

Surface modifications and erosion yields of silicon and titanium doped graphites due to low energy D+ bombardment

Influences of low energy D+ ion bombardment and target temperature on surface topography, surface concentration and erosion yield of carbon based binary compounds were investigated. The samples contained 10 at.% Si and 10 at.% Ti, respectively. The surface concentration was determined in situ by Auger electron spectroscopy and the topography ex situ by scanning electron microscopy. During low energy D+ bombardment a pronounced conelike surface developed with silicon respective titanium rich ‘caps’ protecting the underlaying carbon rich shafts from erosion. The average dopant surface concentration was up to 7 × the bulk concentration. The erosion mechanism was determined by surface concentration and chemical state of the surface: At high temperatures carbidic bindings dominated, while at room temperature a mixture of graphite and carbide covered the surface.

Dissolved organic carbon and its utilization in a riverine wetland ecosystem

Variations in dissolved organic carbon (DOC) concentrations of surface waters and subsurface interstitial groundwater of riparian and wetland soils to 1.2 m depth were evaluated in a riverine wetland ecosystem over one year. DOC was monitored at seven sites within the wetland pond, two sites on the inflow stream, and one site on the outflow stream. Surface concentrations in the inflow stream ranged from 0.74 to 11.6 mg C L−1 and those of the outflow from 2.1 to 8.0 mg C L−1 Average DOC from stream floodplain hydrosoils (3.1 to 32.1 mg C L−1 was greater than DOC from the sediments below the stream channel (1.6 to 6.8 mg C L−1 Surface DOC within the wetland varied seasonally, with greatest fluctuations in concentrations through the summer and autumn (range 4.8 to 32.6 mg C L−1 ) during intensive macrophyte growth and bacterial production. DOC was less variable during the winter months (1.7 to 3.3 mg C L−1 Within the wetland pond, average DOC concentrations (7.1 to 48.2 mg C L−1) in the subsurface waters were significantly greater (p < 0.05) than average surface concentrations. The microbial availability of surface and subsurface DOC to bacteria was evaluated from losses of DOC by wetland bacteria grown on the DOC. Bacterial growth efficiencies ranged from 5 to 20% and were negatively correlated to the percentage of DOC removed by bacteria (r2=0.93). Throughout the ecosystem, DOC concentrations were greatest in the subsurface waters, but at most depths this DOC was a less suitable substrate than surface DOC for utilization by bacteria.