bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐cooperative power control and spectrum allocation in cognitive radio networks: a game theoretic perspective
Authors: Duong Nguyen Duy , Madhukumar A. S.
Published: February 2012

The invention of cognitive radio (CR) concept aims to overcome the spectral scarcity issues of emerging radio systems by exploiting under‐utilization of licensed spectrum. Determining how to allocate unused frequency bands among CR is one of the most important problems in CR networks. Because different CRs may have different quality‐of‐service requirements, they may have different objectives. In voice communication, high‐speed transmission is the most important factor; hence, voice radios always try to maximize their transmission rate. However, in data communication, the most important factor is the bit error rate. The data radios always try to maximize their signal‐to‐interference‐plus‐noise ratio (SINR). In this paper, two non‐cooperative games named interference minimization game and capacity maximization game, which reflect the target of data radios and voice radios, respectively, are proposed. From the simulations, after these games are applied, the average SINRs of all players at each channel are improved. The average SINR of players in each channel after applying the capacity maximization game is smaller than that after applying the interference minimization game. However, in comparison with that after applying the interference minimization game, the average capacity of players after applying capacity maximization approach is larger. Copyright © 2012 John Wiley & Sons, Ltd.
Internalization of serotonin 5‐HT1A autoreceptors as an imaging biomarker of antidepressant response
Authors: Zimmer Luc , Descarries Laurent
Published: February 2012

Serotonin (5‐hydroxytryptamine, 5‐HT) and its various receptors are involved in numerous CNS functions. Among the currently known 5‐HT receptors, the 5‐HT1A receptor is the best characterized subtype. It is tightly implicated in the pathogenesis of mood disorders, notably in depression, and thus represents an important target for drug therapy. Binding to 5‐HT1A receptors can be visualized and quantified by positron emission tomography (PET), facilitating the translation from animal research to man. Using the 5‐HT1A radiotracer [18F]MPPF, recent PET studies in cat and human have provided evidence that internalization of 5‐HT1A autoreceptors is amenable to in vivo neuroimaging at the very onset of specific serotonin reuptake inhibitor (SSRI) administration. The in vivo detection of this phenomenon in human is promising in terms of clinical management, particularly as an early biomarker of responsiveness to SSRI treatment. However, several questions are still pending regarding the correlation between 5‐HT1A internalization at the onset of the treatment and the ensuing therapeutic efficacy. WIREs Membr Transp Signal 2012,1:239–245. doi: 10.1002/wmts.11

For further resources related to this article, please visit the WIREs website.
Protein farnesylation and disease
Authors: Novelli Giuseppe , D'Apice Maria Rosaria
Published: February 2012

Prenylation consists of the addition of an isoprenoid group to a cysteine residue located near the carboxyl terminal of a protein. This enzymatic posttranslational modification is important for the maturation and processing of proteins. Both processes are necessary to mediate protein‐protein and membrane‐protein associations, in addition to regulating the localisation and function of proteins. The severe phenotype of animals deficient in enzymes involved in both prenylation and maturation highlights the significance of these processes. Moreover, alterations in the genes coding for isoprenylated proteins or enzymes that are involved in both prenylation and maturation processes have been found to be the basis of severe human diseases, such as cancer, neurodegenerative disorders, retinitis pigmentosa, and premature ageing syndromes. Recent studies on isoprenylation and postprenylation processing in pathological conditions have unveiled surprising aspects of these modifications and their roles in different cellular pathways. The identification of these enzymes as therapeutic targets has led researchers to validate their effects in vitro and in vivo as antitumour or antiageing agents. This review attempts to summarise the basic aspects of protein isoprenylation and postprenylation, integrating our data with that observed in other studies to provide a comprehensive scenario of progeroid syndromes and the therapeutic avenues.
Activation of spleen tyrosine kinase is required for TNF‐α‐induced endothelin‐1 upregulation in human aortic endothelial cells
Authors: Kim Yoon Ji , Koo Tai Yeon , Yang Won Seok , Han Nam Jeong , Jeong Jin Uk , Lee Sang Koo , Park Su-Kil
Published: February 2012

Endothelin‐1 (ET‐1) promotes atherosclerosis. We tested whether spleen tyrosine kinase (Syk) mediates tumor necrosis factor‐α (TNF‐α)‐induced ET‐1 upregulation in human aortic endothelial cells (HAECs) and sought to identify the signal pathways involved. TNF‐α‐induced reactive oxygen species (ROS) activated Syk and phosphatidylinositol 3‐kinase (PI3K), which was required for the activation of AP‐1 and subsequent ET‐1 gene transcription. ROS mediated c‐Jun NH2‐terminal kinase (JNK) is also required for AP‐1 activation, but Syk and PI3K regulated AP‐1 activation independently of JNK. Through regulation of ET‐1 production, Syk could be implicated in atherosclerosis.
Asp563 of the horizontal helix of subunit NuoL is involved in proton translocation by the respiratory complex I
Authors: Steimle Stefan , Willistein Max , Hegger Patricia , Janoschke Marco , Erhardt Heiko , Friedrich Thorsten
Published: February 2012

The NADH:ubiquinone oxidoreductase couples the electron transfer from NADH to ubiquinone with the translocation of protons across the membrane. It contains a 110 Å long helix running parallel to the membrane part of the complex. Deletion of the helix resulted in a reduced H+/e− stoichiometry indicating its direct involvement in proton translocation. Here, we show that the mutation of the conserved amino acid D563L, which is part of the horizontal helix of the Escherichia coli complex I, leads to a reduced H+/e− stoichiometry. It is discussed that this residue is involved in transferring protons to the membranous proton translocation site.
Postponement strategy for international transfer of products in a global supply chain: A system dynamics examination
Authors: Choi Kanghwa , Narasimhan Ram , Kim Soo Wook
Published: February 2012

This paper contributes to research on “postponement” strategy in the context of a global production–distribution system of an automobile manufacturer. It proposes a model that integrates multiple considerations germane to global supply chains. Postponement is important in this context because it is necessary to consider international transfers and tariffs, and it is important to appropriately account for the impact of postponement on total costs. Consideration of several key variables such as shipping point, customs tariff, and cost differences between countries is essential to derive full benefits from postponement strategy in global supply chains. International transfer of goods among countries in global automobile industry is complex and dynamic because of the multitude of factors that must be considered. The paper develops insights regarding postponement strategy in global supply chains via a system dynamics simulation model. The model draws on the experiences of a Korean automobile manufacturer with operations in developing and developed countries.

The results of the system dynamics simulations show that the choice of optimal shipping point and the right level of postponement under the “decoupling points” strategy in global operations has a significant effect on overall cost efficiency, when decoupling point and postponement timing are considered simultaneously. The results also show that there are key differences in executing the postponement strategy when shipping to a developing country as opposed to a developed country.

This insight has practical implications for global operations and is helpful in developing a sophisticated framework for executing the postponement strategy as manufacturing firms expand their operations globally.
Intermittency and inertial particle entrainment at a turbulent interface: the effect of the large-scale eddies
Authors: Good G. H. , Gerashchenko S. , Warhaft Z.
Published: February 2012

We present measurements of mean and conditional number densities, radial distribution functions (r.d.f.s), velocities and accelerations of sub-Kolmogorov-scale water droplets entraining at a shearless turbulence–turbulence interface (TTI) and a turbulence–non-turbulence interface (TNI). We thus look at statistics of an inhomogeneous inertial particle field in both homogeneous and inhomogeneous turbulence. As in a previous communication (Gerashchenko, Good & Warhaft J. Fluid Mech., vol. 818, 2011, pp. 293–303), an active grid produces high-Reynolds number turbulence $({\mathit{Re}}_{\lambda } = 275)$ on either one or both sides of a splitter plate in a wind tunnel. Sprays seed droplets on one side of the splitter plate, while screens dampen turbulence in the adjacent flow for the TNI. Gravitational and inertial effects are isolated by turning of the apparatus with respect to gravity. We parameterize the droplets under homogeneous conditions, where it is demonstrated that both the sweeping and loitering effects on the droplet settling velocities are present. In the inhomogeneous conditions, we show that the droplets are entrained in bulk, resulting in large-scale clusters and preserving the droplet-ambient conditions of the seeded side of the flows.
Barley seed coating with free and immobilized alkaline phosphatase to improve P uptake and plant growth
Authors: PILAR-IZQUIERDO MARÍA C. , ORTEGA NATIVIDAD , PEREZ-MATEOS MANUEL , BUSTO MARÍA D.
Published: February 2012

Coating barley seeds with free and immobilized alkaline phosphatase was investigated as a potential means to enhance plant utilization of accumulated soil phosphorus (P). Two coating techniques were studied: film-coating and pelleting. The highest phosphatase activity retention in the coating layer, ranging from 0·48 to 0·67, was observed when seeds were film-coated with phosphatase–polyresorcinol complex (PPC). The germination of seeds film-coated or pelleted with alkaline phosphatase ranged from 0·84 to 0·97 or 0·14 to 0·25, respectively. Low germination of the pelleted seeds was attributed to freezing the seeds in liquid nitrogen (N) for the layer coating formation. Pelleted seeds were not used in the remainder of the studies. Under pot culture conditions, an increase in the soil inorganic P was detected when the seeds were film-coated with phosphatase. Moreover, the film-coating significantly increased the P uptake by plants (between 25 and 31% after 35 days after planting (DAP)). The present study showed that the seed film-coating with free and immobilized phosphatase increased the phosphatase activity in the rhizosphere and the P uptake by plants.
Intrauterine Growth and Neuropsychological Performance in Very Low Birth Weight Preschoolers
Authors: Raz Sarah , DeBastos Angela K. , Newman Julie Bapp , Batton Daniel
Published: February 2012

In this study we examined the association between intrauterine growth, indexed either as a categorical variable or continuous dimension, and neuropsychological outcome, in a very low birth weight (VLBW) sample of 143 preschoolers. When the commonly used split at the 10th percentile rank was applied to classify intrauterine growth restriction (IUGR), we found that the growth restricted group (n= 25) exhibited significantly poorer performance in the global motor domain, but not on any other neuropsychological measure. In contrast, when adequacy of intrauterine growth was indexed by standardized birth weight, a continuous dimension, this early risk factor explained a unique portion of the variance in global cognitive abilities and visuospatial skills, as well as in global, fine, and gross motor skills. These findings are consistent with recent magnetic resonance imaging data disclosing global neurodevelopmental changes in the brains of preterm infants with IUGR. When cases classified with IUGR (<10th percentile) were excluded, the relationship between adequacy of intrauterine growth and global cognitive abilities remained significant despite range restriction. Hence, an association between appropriateness of intrauterine growth and global intellectual outcome may be observed even within the population of VLBW preschoolers with adequate standardized birth weight. (JINS, 2012,18, 200–211)
AN ORDERING OF MEASURES OF THE WELFARE COST OF INFLATION IN ECONOMIES WITH INTEREST-BEARING DEPOSITS
Authors: Cysne Rubens Penha , Turchick David
Published: February 2012

This paper builds on Lucas [Econometrica 68 (2000), 247–274] and on Cysne [Journal of Money, Credit and Banking 35 (2003), 221–238] to derive and order six alternative measures of the welfare costs of inflation (five of them already existing in the literature) for any vector of opportunity costs. We provide examples and closed-form solutions for each welfare measure based both on log–log and on semilog money demands, whenever possible in terms of elementary functions. Estimates of the maximum relative error a researcher can incur when using any of these measures are given. Everything is done for economies with or without interest-bearing deposits.
Dimensional Quantification of Embedded Voids or Objects in Three Dimensions Using X-Ray Tomography
Authors: Patterson Brian M. , Escobedo-Diaz Juan P. , Dennis-Koller Darcie , Cerreta Ellen
Published: February 2012

Scientific digital imaging in three dimensions such as when using X-ray computed tomography offers a variety of ways to obtain, filter, and quantify data that can produce vastly different results. These opportunities, performed during image acquisition or during the data processing, can include filtering, cropping, and setting thresholds. Quantifying features in these images can be greatly affected by how the above operations are performed. For example, during binarization, setting the threshold too low or too high can change the number of objects as well as their measured diameter. Here, two facets of three-dimensional quantification are explored. The first will focus on investigating the question of how many voxels are needed within an object to have accurate geometric statistics that are due to the properties of the object and not an artifact of too few voxels. These statistics include but are not limited to percent of total volume, volume of the individual object, Feret shape, and surface area. Using simple cylinders as a starting point, various techniques for smoothing, filtering, and other processing steps can be investigated to aid in determining if they are appropriate for a specific desired statistic for a real dataset. The second area of investigation is the influence of post-processing, particularly segmentation, on measuring the damage statistics in high purity Cu. The most important parts of the pathways of processing are highlighted.
Do members make a difference? A study of Transnational Civil Society Organizations
Authors: Kotzian Peter , Steffek Jens
Published: February 2012

Civil Society Organizations (CSOs) play an active role in European and global governance, and many commentators see them as a link that connects the international level with citizens. But not all CSOs active at the international level do have a substantial number of members. The question we investigate in this article is to what extent membership distinguishes these CSOs from other transnational actors. To what extent do member and non-member CSOs differ in their roles and activities? Is it plausible to argue, as it quite often happens, that CSOs with members are more legitimate than others? On the basis of a survey of 60 exemplary CSOs we find that membership CSOs neither differ substantially from non-member CSOs in their political behavior, nor do they differ in important aspects of legitimacy, such as transparency or efforts to include beneficiaries.
Non-Graphical Solutions for Cattell’s Scree Test
Authors: Raîche Gilles , Walls Theodore A. , Magis David , Riopel Martin , Blais Jean-Guy
Published: February 2012

Most of the strategies that have been proposed to determine the number of components that account for the most variation in a principal components analysis of a correlation matrix rely on the analysis of the eigenvalues and on numerical solutions. The Cattell’s scree test is a graphical strategy with a nonnumerical solution to determine the number of components to retain. Like Kaiser’s rule, this test is one of the most frequently used strategies for determining the number of components to retain. However, the graphical nature of the scree test does not definitively establish the number of components to retain. To circumvent this issue, some numerical solutions are proposed, one in the spirit of Cattell’s work and dealing with the scree part of the eigenvalues plot, and one focusing on the elbow part of this plot. A simulation study compares the efficiency of these solutions to those of other previously proposed methods. Extensions to factor analysis are possible and may be particularly useful with many low-dimensional components.
Deep magmatic degassing versus scrubbing: Elevated CO2emissions and C/S in the lead‐up to the 2009 eruption of Redoubt Volcano, Alaska
Authors: Werner Cynthia , Evans William C. , Kelly Peter J. , McGimsey Robert , Pfeffer Melissa , Doukas Michael , Neal Christina
Published: February 2012

We report CO2, SO2, and H2S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO2emission rates up to 9018 t/d and C/S ratios ≥30 measured in the months prior to the eruption were critical for fully informed forecasting efforts. Observations of ice‐melt rates, meltwater discharge, and water chemistry suggest that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. These fluids scrubbed only a few hundred tonnes/day of SO2, not the >2100 t/d SO2expected from degassing of magma in the mid‐ to upper crust (3–6.5 km), where petrologic analysis shows the final magmatic equilibration occurred. All data are consistent with upflow of a CO2‐rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO2by near‐surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid‐crustal magma followed by nearly complete loss of SO2in a deep magmatic‐hydrothermal system. Alternatively, high C/S ratios could be attributed to decompressional degassing of low silica andesitic magma that intruded into the mid‐crust in the 5 months prior to eruption, thereby mobilizing the pre‐existing high silica andesite magma or mush in this region. The latter scenario is supported by several lines of evidence, including deep long‐period earthquakes (−28 to −32 km) prior to and during the eruption, and far‐field deformation following the onset of eruptive activity.
Seismic anisotropy in the south western Pacific region from shear wave splitting
Authors: Király Eszter , Bianchi Irene , Bokelmann Götz
Published: February 2012

We perform shear‐wave splitting measurements to determine seismic anisotropy in the upper mantle under the remote and still not well‐understood South Western Pacific Region, more precisely the New Hebrides subduction zone. We obtained 29 good and 35 fair splitting measurements at 8 stations and 93 good and fair Null measurements from the data provided by various networks. According to the splitting parameters, the seismic stations are grouped into “eastern” and “western” stations. Anisotropy of the subducting plate (“western” stations) appears to be the result of absolute plate motion (APM) of the Australian plate. From fast orientations alone, it would be difficult to judge which process is responsible for the anisotropic structure: either the absolute plate motion or trench‐parallel “toroidal” flow. Their delay times reveal that these anisotropic parameters can be explained without the presence of the subduction zone, and the APM provides a simple explanation for the observed anisotropy. On the other hand, delay times at “eastern” stations are higher than that of “western” stations. These stations are located close to the subduction zone, and the nearly trench‐parallel orientation of fast polarization axes and their higher splitting delay times indicate the presence of subduction zone. Anisotropy at “eastern” stations is apparently due to the additional effect from “toroidal” flow near the subduction zone, which increases the total anisotropy.
Changes in winter precipitation extremes for the western United States under a warmer climate as simulated by regional climate models
Authors: Dominguez F. , Rivera E. , Lettenmaier D. P. , Castro C. L.
Published: February 2012

We find a consistent and statistically significant increase in the intensity of future extreme winter precipitation events over the western United States, as simulated by an ensemble of regional climate models (RCMs) driven by IPCC AR4 global climate models (GCMs). All eight simulations analyzed in this work consistently show an increase in the intensity of extreme winter precipitation with the multi‐model mean projecting an area‐averaged 12.6% increase in 20‐year return period and 14.4% increase in 50‐year return period daily precipitation. In contrast with extreme precipitation, the multi‐model ensemble shows a decrease in mean winter precipitation of approximately 7.5% in the southwestern US, while the interior west shows less statistically robust increases.
Geothermobarometry of the 2010 Eyjafjallajökull eruption: New constraints on Icelandic magma plumbing systems
Authors: Keiding Jakob K. , Sigmarsson Olgeir
Published: February 2012

The 2010 Eyjafjallajökull eruption in Iceland produced mildly alkaline basalt that was emitted during the initial flank eruptive phase, whereas tephra predominately of benmorite composition was erupted during the second explosive phase from the summit of the volcano. These latter magmas show pervasive magma mingling between basalts and silicic magma. Glass and coexisting equilibrium mineral analyses have been used to define pressure‐temperature crystallization paths for the eruption based on melt, clinopyroxene‐melt and plagioclase‐melt thermobarometry. Temperature calculations show that the early basaltic eruptions from the flank eruption have magmatic temperatures of around 1170°C (±25°C) and a narrow temperature range (<30°C) at any given depth. In contrast, benmoritic products crystallized at lower temperatures (1000–1060°C). Pressure estimates yield an average pressure of 5.6–6.4 kbar (±1.5 kbar) for the basaltic tephra and variable but lower pressures for the benmoritic samples ranging down to 0.6 kbar. The mafic magma mainly crystallized in the deeper crust (16–18 km), whereas mingled magma from the summit eruption crystallized at more shallow crustal levels (2–5 km) suggesting multistage magma ascent. Magmatic water concentrations were estimated with plagioclase‐melt hygrometry. The maximum average water content of 1.8 wt % H2O, obtained in one of the summit samples, is in agreement with melt inclusion observations. Water concentration of this or lower levels is demonstrated to only have limited effect on the pressure‐temperature calculations.
Subtidal circulation on the Alabama shelf during the Deepwater Horizon oil spill
Authors: Dzwonkowski Brian , Park Kyeong
Published: February 2012

Water column velocity and hydrographic measurements on the inner Alabama shelf are used to examine the flow field and its forcing dynamics during the Deepwater Horizon oil spill disaster in the spring and summer of 2010. Comparison between two sites provides insight into the flow variability and dynamics of a shallow, highly stratified shelf in the presence of complicating geographic and bathymetric features. Seasonal currents reveal a convergent flow with strong, highly sheared offshore flow near a submarine bank just outside of Mobile Bay. At synoptic time scales, the flow is relatively consistent with typical characteristics of wind‐driven Ekman coastal circulation. Analysis of the depth‐averaged along‐shelf momentum balance indicates that both bottom stress and along‐shelf pressure gradient act to counter wind stress. As a consequence of the along‐shelf pressure gradient and thermal wind shear, flow reversals in the bottom currents can occur during periods of transitional winds. Despite the relatively short distance between the two sites (14 km), significant spatial variability is observed. This spatial variability is argued to be a result of local variations in the bathymetry and density field as the study region encompasses a submarine bank near the mouth of a major freshwater source. Given the physical parameters of the system, along‐shelf flow in this region would be expected to separate from the local isobaths, generating a mean offshore flow. The local, highly variable density field is expected to be, in part, responsible for the differences in the vertical variability in the current profiles.
Comparing optimized CO emission estimates using MOPITT or NOAA surface network observations
Authors: Hooghiemstra P. B. , Krol M. C. , Bergamaschi P. , de Laat A. T. J. , van der Werf G. R. , Novelli P. C. , Deeter M. N. , Aben I. , Röckmann T.
Published: February 2012

This paper compares two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) or CO total columns from the Measurement of Pollution in the Troposphere (MOPITT) instrument are assimilated in a 4D‐Var framework. Inferred emission estimates from the two inversions are consistent over the Northern Hemisphere (NH). For example, both inversions increase anthropogenic CO emissions over Europe (from 46 to 94 Tg CO/yr) and Asia (from 222 to 420 Tg CO/yr). In the Southern Hemisphere (SH), three important findings are reported. First, due to their different vertical sensitivity, the stations‐only inversion increases SH biomass burning emissions by 108 Tg CO/yr more than the MOPITT‐only inversion. Conversely, the MOPITT‐only inversion results in SH natural emissions (mainly CO from oxidation of NMVOCs) that are 185 Tg CO/yr higher compared to the stations‐only inversion. Second, MOPITT‐only derived biomass burning emissions are reduced with respect to the prior which is in contrast to previous (inverse) modeling studies. Finally, MOPITT derived total emissions are significantly higher for South America and Africa compared to the stations‐only inversion. This is likely due to a positive bias in the MOPITT V4 product. This bias is also apparent from validation with surface stations and ground‐truth FTIR columns. Our results show that a combined inversion is promising in the NH. However, implementation of a satellite bias correction scheme is essential to combine both observational data sets in the SH.
GPS observations at quasi‐conjugate points during solar minimum
Authors: Momani Mohammad Awad
Published: February 2012

This paper aims at investigating the climatology of ionospheric TEC at quasi‐conjugate points located at different latitude ranges during low solar activity in 2007 with focus on the annual/hemispheric and semiannual asymmetry. Data from four pairing GPS stations are used for investigating the symmetry/or asymmetry between the conjugate hemispheres. The stations are selected based on data availability and manipulation possibility, and based on location of the conjugate point that was obtained by IGRF/DGRF model parameters. Our observations were in good agreement with plenty of studies conducted in this area. The results show evident annual asymmetry, hemispheric differences, and also weak semiannual asymmetry in GPS‐TEC at all GPS stations. The annual asymmetry is occurring at all latitudes from equatorial to polar cap regions. The asymmetry was quantified based on differencing of the annual mean‐TEC between the conjugate hemispheres (i.e., TECN°‐TECS°) which show differences in the range between 10 and 30%. The annual asymmetry is mainly driven by several factors, mainly: the geomagnetic field configuration, the Sun‐Earth distance, and lower atmosphere tidal forcing. The hemispheric asymmetry of the TEC in conjugate hemispheres follows the control of solar declination and is a manifestation of the seasonal variations. The semiannual anomaly (also equinoctial asymmetry) was seen at SBA/RESO and also SUWN/KARR with more activity seen in March equinox compared with September. The occurrence of semiannual anomaly suggests close couplings of the ionosphere in both hemispheres.
Sources and sinks of methane and carbon dioxide exchanges in mountain forest in equatorial Africa
Authors: Delmas R. A. , Servant J. , Tathy J. P. , Cros B. , Labat M.
Published: February 2012

Sources and sinks of methane were studied in the Mayombe forest, a tropical evergreen forest located in a mountainous region in central Africa. Important methane emissions, reaching 6×1013 molecules/cm2/s, were measured in flooded lowlands where soil characteristics: pH and redox potential, favor the growth of methanogenic bacteria. However, basically, soils of this region constitute a sink of atmospheric methane with uptake rates ranging from 1010 to 1011 molecules/cm2/s. Methane emission from termite nests was also studied; it appeared to be a minor component of the methane budget. CH4 concentrations were measured inside the forest and in the surrounding atmosphere, CO2 being used as a qualitative tracer of air exchanges. In spite of intense but scattered and size‐limited sources this environment seems to be a net sink of atmospheric methane.
Light hydrocarbons in the tropospheric boundary layer over tropical Africa
Authors: Rudolph J. , Khedim A. , Bonsang B.
Published: February 2012

Fifty measurements of nonmethane hydrocarbons (NMHC) and several other trace gases were made over an equatorial rain forest in February 1988 as part of the DECAFE experiment. The measurements were made independently by two different laboratories. Each laboratory used its own sample containers, gas chromatographic measurement procedure, and calibration. Also, the altitudinal distribution of the samples differed. Apart from propene and i‐pentane for which a substantial difference in the absolute calibration existed between the two laboratories, the average results were very similar, and the vertical profiles were identical within the scatter of the data. For NMHC with longer atmospheric residence times (e.g., ethane and acetylene) the average results agreed within a few percent. In the boundary layer, only small gradients could be found. In all cases where a significant vertical gradient existed, there was an increase of the mixing ratios with increasing altitude. This can be explained by the different origin of the air masses at different altitudes. Above the boundary the trace gas mixing ratios decrease. The observed NMHC pattern can primarily be described as photochemically aged emissions from biomass burning. The observed depletion of the photochemically reactive NMHC also agrees with the occurrence of enhanced ozone levels in the boundary layer.
Atmospheric measurements of peroxyacetyl nitrate and other organic nitrates at high latitudes: Possible sources and sinks
Authors: Singh H. B. , O'Hara D. , Herlth D. , Bradshaw J. D. , Sandholm S. T. , Gregory G. L. , Sachse G. W. , Blake D. R. , Crutzen P. J. , Kanakidou M. A.
Published: February 2012

Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO2, HNO3, peroxypropionyl nitrate (PPN), CH3ONO2, NOy) were performed at high latitudes over North America and Greenland during July–August 1988, at all altitudes between 0 and 6 km as part of an Arctic Boundary Layer Expedition (ABLE 3A). Complementing these were measurements of C1 to C5 hydrocarbons, O3, chemical tracers (C2Cl4, CO), and important meteorological parameters. PAN was found to be an important reactive nitrogen species in the free troposphere, with 95% of the mixing ratios falling in the range of 5 to 450 ppt. PAN increased systematically with height with mixing ratios of 100–700 ppt at 6 km and 0–50 ppt in the boundary layer. The free tropospheric PAN reservoir was present over the entire high‐latitude region sampled (50° to 82°N latitude and 60° to 160°W longitude). In the boundary layer, PAN mixing ratios were higher over land than over the North Pacific Ocean. Significant levels of PAN were measured within stratospheric intrusions, forest fire plumes, and episodes of remote pollution. Other organic nitrates such as PPN and CH3ONO2 were found to be a small fraction of PAN (0–10%). PAN and O3 were strongly correlated both in their fine and gross structures, and the latitudinal distribution of PAN in the free troposphere followed that of O3. A two dimensional global photochemical model is used to compare measurements and model results. Model simulations, correlations between reactive nitrogen species (e.g. PAN and NOy) and anthropogenic tracers (C2H2, CO, C2Cl4), and the composition of NOy itself support the view that the reactive nitrogen measured during ABLE 3 A is predominantly of anthropogenic origin with a minor stratospheric component. Transported industrial pollution, biomass burning, and the unique seasonal dynamics of the Arctic/sub‐Arctic region play a dominant role in defining this reactive nitrogen abundance. This PAN (and NOy) reservoir may contribute to the summertime maximum in deposited nitrate observed over Greenland.
Relationship of peroxyacetyl nitrate to active and total odd nitrogen at northern high latitudes: Influence of reservoir species on NOx and O3
Authors: Singh H. B. , Herlth D. , O'Hara D. , Zahnle K. , Bradshaw J. D. , Sandholm S. T. , Talbot R. , Crutzen P. J. , Kanakidou M.
Published: February 2012

Measurements of peroxyacetyl nitrate (PAN), NO, NO2, HNO3, NOy, (total odd nitrogen), and O3 were made in the high‐latitude troposphere over North America and Greenland (35° to 82°N) during the Arctic Boundary Layer Expedition (ABLE 3A) (July–August 1988) throughout 0‐to 6‐km altitudes. These data are analyzed to quantitatively describe the relationships between various odd nitrogen species and assess their significance to global tropospheric chemistry. In the free troposphere, PAN was as much as 25 times more abundant than NOx. PAN to NOx ratio increased with increasing altitude and latitude. PAN was found to be the single most abundant reactive nitrogen species in the free troposphere and constituted a major fraction of NOy, PAN to NOy ratios were about 0.1 in the boundary layer and increased to 0.4 in the free troposphere. A 2‐D global photochemical model with C1‐C3 hydrocarbon chemistry is used to compare model predictions with measured results. A sizable portion (≈50%) of the gaseous reactive nitrogen budget is unaccounted for, and unknown organic nitrates and pernitrates are expected to be present. Model calculations (August 1, 70°N) show that a major fraction of the observed NOx (50 to 70% of median) may find its source in the available PAN reservoir. PAN and the unknown reservoir species may have the potential to control virtually the entire NOx availability of the high latitude troposphere. It is predicted that the summer NOx and O3 mixing ratios in the Arctic/sub‐Arctic troposphere would be considerably lower in the absence of the ubiquitous PAN reservoir. Conversely, this PAN reservoir may be responsible for the observed temporal increase in tropospheric O3 at high latitudes.
The Mauna Loa Observatory photochemistry experiment
Authors: Ridley B. A. , Robinson E.
Published: February 2012

Concurrent measurements of selected odd nitrogen constituents, hydrocarbons, peroxides, organic acids, formaldehyde, and other species were made from May 1 to June 4, 1988, at the Mauna Loa Observatory. An introduction to the experiment and a description of some of its objectives are presented.
Ozone and Aitken nuclei over equatorial Africa: Airborne observations during DECAFE 88
Authors: Andreae M. O. , Chapuis A. , Cros B. , Fontan J. , Helas G. , Justice C. , Kaufman Y. J. , Minga A. , Nganga D.
Published: February 2012

We determined the distribution of ozone (O3) and Aitken condensation nuclei (CN) over the rain forest in equatorial Africa during February 12–25, 1988. A pronounced O3 maximum with levels up to 70 ppbv was present in a layer between 1 and 3 km altitude throughout the period. It coincided with a CO maximum and with high levels of CO2 and gaseous organic acids. In general, the vertical distribution of CN was similar to that of O3, with number densities ranging up to approximately 3000 cm−3. Dense haze was visible within this layer. O3 and CN decreased sharply above the haze layer to values typical of the remote troposphere. Survey flights showed little change in levels of O3 and CN or in their vertical distribution over distances of hundreds of kilometers. Meteorological observations suggest that this ozone and particulate enriched layer is formed from air masses which originate in northern Africa and subsequently advect over dry tropical regions where biomass burning emits large amounts of aerosols, CO, NO, and hydrocarbons. These air masses then become trapped in the equatorial region between the near‐surface monsoon flow from the southeast and the permanent easterly flow above 3–4 km. Differences in the vertical distribution of O3 and CN result from the removal of O3 by surface uptake and reactions with NO and hydrocarbons, leading to surface O3 concentrations near zero and a steep O3 gradient through the subcloud layer at night. During the day this gradient is reduced by convective mixing. CN concentrations showed no pronounced gradients in the subcloud layer, consistent with the absence of a strong sink for CN at the ground. CN gradients near the surface suggest emission of particles from the forest vegetation or from biomass burning.
Enhancement of atmospheric radiation by an aerosol layer
Authors: Michelangeli Diane V. , Allen Mark , Yung Yuk L. , Shia Run‐Lie , Crisp David , Eluszkiewicz Janusz
Published: February 2012

The presence of a stratospheric haze layer may produce increases in both the actinic flux and the irradiance below this layer. Such haze layers result from the injection of aerosol‐forming material into the stratosphere by volcanic eruptions. Simple heuristic arguments show that the increase in flux below the haze layer, relative to a clear sky case, is a consequence of “photon trapping.” We explore the magnitude of these flux perturbations, as a function of aerosol properties and illumination conditions, with a new radiative transfer model that can accurately compute fluxes in an inhomogeneous atmosphere with nonconservative scatterers having arbitrary phase function. One calculated consequence of the El Chichon volcanic eruption is an increase in the midday surface actinic flux at 20°N latitude, summer, by as much as 45% at 2900 Å. This increase in flux in the UV‐B wavelength range was caused entirely by aerosol scattering, without any reduction in the overhead ozone column.
The influence of surface kinetics on the growth of stratospheric ice crystals
Authors: MacKenzie A. Robert , Haynes Peter H.
Published: February 2012

A model of the growth of polar stratospheric ice crystals is described, taking account of the interstitial supersaturation, the effect of radiative heat transfer, heat conduction, mass diffusion and surface kinetic processes. This last effect has commonly been neglected in treatments of solid particle growth derived from models of liquid droplet aerosols. Numerical solutions for a wide range of conditions indicate that surface kinetic effects can be the dominant rate—limiting process for small particles and low supersaturations. Outside of these conditions the surface resistance remains a significant fraction of the total resistance to growth. Limits to the application of our formula, including its application to type I particles, are outlined.
Organic acids over equatorial Africa: Results from DECAFE 88
Authors: Helas Gunter , Bingemer Heinz , Andreae Meinrat O.
Published: February 2012

Gaseous short chain organic acids were measured during the dry season (February) in and above the rain forest of the northern Congo. Samples were taken at ground level and during several flights up to 4 km altitude. The organic acids were concentrated from the atmosphere by using “mist scrubbers,” which expose a mist of deionized water to the air to be probed. The organic acids absorbed in the water were subsequently analyzed by ion chromatography. Formic, acetic, and pyruvic acids were identified in the samples. At ground level, average mixing ratios of gaseous formic and acetic acid of 0.5±0.6 and 0.6±0.7 parts per billion by volume (ppbv) (1 s), respectively, were found. Boundary layer mixing ratios, however, were significantly higher (3.7±1.0 and 2.7±0.9 ppbv). This indicates a downward net flux of these atmospheric trace components from the boundary layer to the surface. Free tropospheric samples taken above the cloud convection layer show lower mixing ratios again (0.9±0.3 and 0.7±0.1 ppbv). On the basis of this vertical distribution, direct emission by vegetation is not considered to be the dominant source. Biomass burning and photochemical oxidation of biogenic precursors are the major processes contributing to the enhancement of organic acids observed in the boundary layer. The organic acids parallel the profiles of ozone and CO, which suggests that their generation processes are closely related. Pyruvic acid is not correlated with formic acid, indicating that the oxidation of isoprene is not of major importance. In emissions from biomass fires, CO correlates well with formic and acetic acid, and thus some of the enhancement of organic acids in the boundary layer can be explained due to burning. However, an additional gas phase source for organic acids must exist to explain the observed ratio of formic to acetic acid. This is most likely the ozonolysis of olefins which were released as pyrolysis products from biomass burning.
Twilight variation of vertical column abundances of OClO and BrO in the north polar region
Authors: Wahner Andreas , Schiller Cornelius
Published: February 2012

Measurements of vertical column abundances of OClO and BrO obtained during the Airborne Arctic Stratospheric Expedition 1989 are used for comparison with simple model calculations. The diurnal variation of these molecules is examined using data taken during morning and evening twilight and during nighttime. The comparison suggests that air masses inside the Arctic vortex contain ClO mixing ratios of several 100 pptv and in some cases up to 600 pptv, in agreement with in situ measurements. The measured OClO and BrO vertical column abundances are consistent with BrO mixing ratios of 7–12 pptv. The magnitude as well as the variation of the measured OClO and BrO vertical column abundances during twilight agree in most cases with the calculated vertical column abundances. Nevertheless, the model calculations are inconsistent with the observed high nighttime BrO vertical column abundances of 6–10 × 1013 cm−2.
Alkyl nitrate and selected halocarbon measurements at Mauna Loa Observatory, Hawaii
Authors: Atlas E. , Schauffler S. M. , Merrill J. T. , Hahn C. J. , Ridley B. , Walega J. , Greenberg J. , Heidt L. , Zimmerman P.
Published: February 2012

Measurements of ≥C3 alkyl nitrates, perchlorethylene, and bromoform were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The median mixing ratios of these compounds in free tropospheric air (3.4 km) were 2.3, 3.2, and .20 pptv, respectively. A diurnal variation in the concentration of these compound at Mauna Loa was driven by the local upslope/downslope circulation and by differences in the concentration of these species between the boundary layer and the free troposphere. Longer term variation was closely related to synoptic‐scale circulation of the North Pacific and to differences in the sources of air masses reaching Hawaii. Alkyl nitrates and their hydrocarbon precursors were present in nearly constant proportions during the experiment. This suggested the possibility that nitrate:hydrocarbon ratios may be determined near source regions and remain steady during long‐range transport. Reasonable correlation was observed also between alkyl nitrates and peroxyacetyl nitrate (PAN), but a more complex relationship was found between methyl and higher alkyl nitrates. In general, ≥C3 alkyl nitrates were a significant component of the organic nitrate reservoir at Mauna Loa. However, ≥C3 alkyl nitrates only accounted for <2% of total NOy. This evidence suggests that simple alkyl nitrates are not the source of “missing” odd nitrogen in the remote atmosphere.
Use of weather types to disaggregate general circulation model predictions
Authors: Hay Lauren E. , McCabe Gregory J. , Wolock David M. , Ayers Mark A.
Published: February 2012

General circulation models (GCMs) simulate climatic conditions with a grid cell resolution on the order of 100,000 km2. This resolution is inadequate to assess the effects of climatic change on water resources at a regional scale. A method has been developed that uses weather‐type analysis as a tool to spatially disaggregate GCM predictions to make them useful for water resource studies. The method has been applied to the Delaware River basin to predict the effects of doubling atmospheric carbon dioxide on precipitation patterns in the region. An application of the technique to the Delaware River basin indicates that future climatic conditions will show minimal changes in weather‐type frequency, implying that air circulation patterns will remain unchanged. Results of this study indicate that changes in regional precipitation patterns under a doubling of atmospheric carbon dioxide will be a result of within‐type changes in weather characteristics.
Land‐surface schemes for future climate models: Specification, aggregation, and heterogeneity
Authors: Henderson‐Sellers Ann , Pitman Andrew J.
Published: February 2012

The development of biosphere models for future global climate models will require the successful prediction of the natural vegetation “congruent” to the climate. A highly generalized (nine class) grouping of Holdridge life zones has been used here as a means of investigating three‐step “coupling” of a land‐surface scheme into a global climate model. Another requirement for future modeling is the development of a method of spatial aggregation of land‐surface data to the required global model resolution while retaining the necessary degree of variability in the data for subsequent climate simulations. It is shown that the aggregation of data rather than the selection of a dominant ecotype is likely to improve future simulations. A third vital component of future modeling is the representation of important sub‐grid scale processes, especially those associated with hydrological exchanges between the land surface and the atmosphere. It is shown that the incorporation of a scheme for representing sub‐grid scale precipitation and lakes improves the level of realism in the land‐surface models and should improve the overall climate simulations.