bluuebunny/crossref_metadata_2025 huggingface dataset:
Aircraft measurements of biomass burning aerosol over West Africa during DABEX
Authors: Johnson B. T. , Osborne S. R. , Haywood J. M. , Harrison M. A. J.
Published: July 2008

This paper investigates the properties of biomass burning aerosols over West Africa using data from the UK FAAM aircraft during the Dust and Biomass‐burning Experiment (DABEX). Aged biomass burning aerosols were widespread across the region, often at altitudes up to 4 km. Fresh biomass burning aerosols were observed at low altitudes by flying through smoke plumes from agricultural fires. The aircraft measured aerosol size distributions, optical properties, and vertical distributions. Single scattering albedo varied from 0.73 to 0.93 (at 0.55 μm) in aerosol layers dominated by biomass burning aerosol. We attribute much of this variation to the variable proportion of mineral dust and biomass burning aerosol. We estimate the single scattering albedo of aged biomass burning aerosol to be around 0.81 with an instrumental uncertainty of ±0.05. External mixing, and possibly internal mixing, between the biomass burning aerosol and mineral dust presents an additional source of uncertainty in this estimate. The size distributions of biomass burning aerosols were dominated by particles with radii smaller than 0.35 μm. A 20% increase of count mean radius was observed when contrasting fresh and aged biomass burning aerosols, accompanied by changes in the shape of the size distribution. These changes suggest growth by coagulation and condensation. Extinction coefficients, asymmetry parameters, and Angstrom exponents are calculated from Mie theory, using the lognormal fits to the measured size distributions and assumed refractive indices.
Identification of tropical convective tropopause and its association with cold point tropopause
Authors: Mehta Sanjay Kumar , Murthy B. V. Krishna , Rao D. Narayana , Ratnam M. Venkat , Parameswaran K. , Rajeev K. , Raju C. Suresh , Rao Kusuma G.
Published: July 2008

Using the MST radar observations at Gadanki (13.5°N, 79.2°E), a tropical station, the altitude of major convective outflow in the troposphere is identified and is considered to represent the convective tropopause. This is found to match well with the altitude of local minimum of potential temperature lapse rate obtained from simultaneous radiosonde observations. The convective tropopause altitudes are also compared with the cloud top altitudes obtained using satellite brightness temperature (BT) data and are found to match in the case of deep convection. The thickness of the tropical tropopause layer follows very closely the convective tropopause altitude and has little dependence on the cold point tropopause altitude. The thickness of the tropopause layer is found to shrink when convection reaches high altitudes. This occurs mainly during the monsoon months of July, September, and October.
Multiple‐scattering lidar from both sides of the clouds: Addressing internal structure
Authors: Davis A. B.
Published: July 2008

Multiple‐scattering (a.k.a. “off‐beam”) lidar is an emerging technology in cloud remote sensing. It delivers, as in classic lidar ceilometry, cloud base altitude but also the cloud's physical thickness H as well as its optical depth τ (averaged over horizontal scales on the order of H). The value of τ in fact must lie beyond the range accessible by standard (i.e., single‐scattering/on‐beam) lidar profiling, namely, up to 3–4. A refined diffusion‐theoretical model is presented here for signals from multiple‐scattering lidar and applied, on the one hand, to retrieval algorithm development and, on the other hand, signal‐to‐noise ratio (SNR) estimation. SNRs are computed for LANL's ground‐based Wide‐Angle Imaging Lidar (WAIL) system and NASA's space‐based Lidar‐In‐space Technology Experiment (LITE). The refinements are threefold and all about internal structure. First, the laser source is modeled as a collimated anisotropic exponentially distributed internal source rather than an isotropic point source at the cloud boundary; this opens the possibility of using δ‐Eddington rescaling to capture the forward peaked phase function more effectively within the diffusion framework. Second, stratification of the scattering coefficient is modeled as an increasing function of distance to cloud base; this strongly differentiates the signals when observed from above or from below. Finally, Cairns' rescaling is applied to this conservative scattering problem to account for the systematic effects of random (turbulence‐driven) internal variability at scales up to a few mean free paths.
Calculation of geomagnetically induced currents in the 400 kV power grid in southern Sweden
Authors: Wik M. , Viljanen A. , Pirjola R. , Pulkkinen A. , Wintoft P. , Lundstedt H.
Published: July 2008

Sweden has experienced many geomagnetically induced current (GIC) events in the past, which is obviously due to the high‐latitude location of the country. The largest GIC, almost 300 A, was measured in southern Sweden in the earthing lead of a 400 kV transformer neutral during the magnetic storm on 6 April 2000. On 30 October 2003, the city of Malmö at the southern coast suffered from a power blackout caused by GIC, leaving 50,000 customers without electricity for about 20–50 min. We have developed a model that enables calculation of GIC in the southern Swedish 400 kV power grid. This work constitutes the first modeling effort of GIC in Sweden. The model is divided into two parts. The electric field is first derived using a ground conductivity model and geomagnetic recordings from nearby stations. The conductivity model is determined from a least squares fit between measured and calculated GIC. GIC are calculated using a power grid model consisting of the topology of the system and of the transformer, transmission line, and station earthing resistances as well as of the coordinates of the stations. To validate the model, we have compared measured and calculated GIC from one site. In total, 24 events in 1998 to 2000 were used. In general the agreement is satisfactory as the correct GIC order of magnitude is obtained by the model, which is usually enough for engineering applications.
Estimation of nonlinear trends in water quality: An improved approach using generalized additive models
Authors: Morton Richard , Henderson Brent L.
Published: July 2008

This paper advocates the use of Generalized Additive Models (GAMs) for the estimation of nonlinear trends in water quality in the presence of serially correlated errors. The GAM methodology is applicable to a range of physical, chemical and biological water quality variates. Comparison with the estimate based on Seasonal Kendall's Slope and robust regression is discussed. An example is given concerning log‐transformed stream electrical conductivity, which is adjusted for flow. The monthly data have first order autocorrelation exceeding 0.5 and the trend is markedly nonlinear. Seasonal effects are shown to have been changing over time.
A vertical dispersion model for solute exchange induced by underflow and periodic hyporheic flow in a stream gravel bed
Authors: Qian Qin , Voller Vaughan R. , Stefan Heinz G.
Published: July 2008

Interstitial flows in stream gravel beds are driven by stream slope and controlled by hydraulic conductivity (underflows) or induced by pressure differentials on the streambed surface (hyporheic flows). They enhance solute exchange between surface water and a streambed. To study the solute transport in a stream gravel bed, a 2‐D transient advection–dispersion mass transfer model was formulated. The velocity field includes an underflow and a spatially periodic hyporheic flow, e.g., due to standing surface waves or bed forms. Two dimensionless scaling parameters emerged: R measures the relative strength of hyporheic flow to underflow in the streambed and λ is the ratio of dispersivity of the gravel bed to the pressure wavelength along the streambed. In the analysis of mass transfer of nonconservative substances into a streambed, an explicit 2‐D analysis of interstitial flow is often undesirable. Therefore the numerical solutions for the 2‐D concentration fields under periodic boundary conditions were reduced to 1‐D vertical concentration profiles (by streamwise averaging of the solute concentrations). The profiles were matched to the solution of an unsteady vertical 1‐D dispersion equation that introduces a depth variable “enhanced dispersion coefficient DE(y)” that lumps all forms of interstitial advective and dispersive transport in the streambed. Functions DE(y) were determined for many combinations of independent parameters by inverse modeling, and the dependence of DE(y) on the dimensionless parameters R and λ was determined from these results. Analytical relationships for DE(y, R, λ) have been proposed and validated against available experimental data. Knowledge of DE(y) allows the estimation of solute/mass transfer rates in streambeds under wavy boundary conditions, without explicit analysis of the interstitial flow. This is a distinct advantage for applications in stream water quality and/or pore water quality studies.
Coupled hydrologic and vegetation dynamics in wetland ecosystems
Authors: Muneepeerakul Chitsomanus P. , Miralles‐Wilhelm Fernando , Tamea Stefania , Rinaldo Andrea , Rodriguez‐Iturbe Ignacio
Published: July 2008

The stochastic nature of long‐term dynamics of soil moisture, water table, and vegetation in wetland ecosystems driven by precipitation are investigated through this modeling study. A simple model is presented here to couple the hydrologic and vegetation dynamics via transpiration and ecosystem carrying capacity. The simulation results portray possible competition outcomes between plant species having different survival strategies in response to the fluctuating soil moisture and water tables under different rainfall conditions. Long‐range correlations in the dynamics were detected in several of the key variables of wetland ecosystems, as the result of their dependence on the long‐ memory structure of the water table. The statistical structure of the modeled water table fluctuations is found to be similar to that obtained from a real case study, validating the ability of the model in capturing water table dynamics and suggesting its potential toward the quantification of the long‐term dynamics of wetland vegetation.
Inverse procedure for calibrating parameters that control land subsidence caused by subsurface fluid withdrawal: 1. Methods
Authors: Liu Yi , Helm Donald C.
Published: July 2008

Land subsidence prediction depends on a selected theoretical model and the calibration of its parameter values. An inverse model is developed that calibrates five parameters of a compacting confined aquifer system: K′v (vertical hydraulic conductivity of the aquitards), S′skv (aquitard nonrecoverable skeletal specific storage), S′ske (aquitard recoverable skeletal specific storage), Ssk (skeletal specific storage of the aquifer), and p′max 0 (initial preconsolidation stress within the aquitards). This inverse model combines a procedure for finding an initial set of parameter values and an inverse adjustment procedure. Initial values are estimated by using a new graphic method for the analysis of field data. The follow‐up inverse procedure is a computer algorithm that combines the Newton‐Raphson method with Helm's one‐dimensional finite difference subsidence model (COMPAC). COMPAC offers two options: a constant‐parameter simulation and a stress‐dependent parameter simulation. The classical least squares criterion is employed as the objective function of this inverse procedure. Three characteristics of the objective function are considered. This inverse model is applied to calculations of an idealized compacting confined aquifer system using Helm's model. This investigation shows that the final values for the five parameters lead to simulated compaction error of less than 1%. This contrasts to the initial error of more than 60%. These results indicate that the proposed inverse procedure (model) can be applied to actual field data.
Inverse procedure for calibrating parameters that control land subsidence caused by subsurface fluid withdrawal: 2. Field application
Authors: Liu Yi , Helm Donald C.
Published: July 2008

The inverse procedure (InvCOMPAC) that was developed in part 1 of this two‐part paper is applied to two aquifer systems at two sites in Shanghai. The present part 2 illustrates how to calibrate transient land subsidence parameter values on the basis of in situ data. The new graphic‐analytic method yields initial parameter values for use in the inverse procedure. For the upper and lower confined aquifer systems at multiple‐extensometer sites F09 and F16 in Shanghai, their final parameter values are calibrated further by InvCOMPAC, a computer‐based inverse model. The simulation error of transient subsidence over a period of 13 and 20 years, respectively, at sites F09 and F16 is decreased to 11.8 and 13.9%, respectively, from an initial graphic‐analytic result of 72.1 and 415.3%. This demonstrates that InvCOMPAC is applicable to complex field conditions. The new graphic‐analytic method is necessary in order to find a realistic set of initial parameter values. Calibrated parameter values are used to predict future subsidence in the field. Predictions indicate that a large amount of ongoing residual nonrecoverable compaction will occur and will not equilibrate with the anticipated decline of groundwater levels at these sites. The reason is that the vertical nonrecoverable skeletal specific storage of the aquitards is 2−3 orders of magnitude larger than the vertical recoverable skeletal specific storage of both the aquitards and the aquifer. The vertical hydraulic conductivity is too small for the aquitards to drain sufficiently quickly for them to reach a new equilibrium in response to water level declines. It is recommended that groundwater levels be kept above the past maximum preconsolidation pressure levels within the aquitards. This will prevent continued nonrecoverable compaction from occurring.
Not all water becomes wine: Sulfur inputs as an opportune tracer of hydrochemical losses from vineyards
Authors: Hinckley Eve‐Lyn S. , Kendall Carol , Loague Keith
Published: July 2008

California's widespread and economically important vineyards offer substantial opportunities to understand the interface between hydrology and biogeochemistry in agricultural soils. The common use of native sulfur (S) as a fumigant or soil additive provides a novel way to isotopically differentiate among sulfate (SO42−) pools, allowing the estimation of water and SO42− budgets. The objectives of this study were (1) to characterize the near‐surface hydrological flow paths in a vineyard during irrigation and storm events and (2) to determine how those flow paths affect the fate and transport of SO42− across seasons. Integrating hydrological theory with measurements of SO42− concentration and sulfate‐S isotopic ratios (expressed as [SO42−] and δ34S, respectively) in inputs, soil water, and leachate provided a means of determining flow paths. Low [SO42−] and δ34S in leachate during 4‐h irrigation events reflect minimal engagement of the soil matrix, indicating that preferential flow was the dominant path for water in the near surface. In contrast, high [SO42−] and δ34S values during 8‐h irrigation and storm events reflect near‐complete engagement of the soil matrix, indicating that lateral flow was the dominant pathway. Because hydrologic response and SO42− mobility are tightly coupled in these soils, the magnitude of water fluxes through the near surface controls S cycling both on and off site. These results indicate that preferential flow is an important loss pathway to consider in managing both water resources and water quality (reactive elements) in vineyard land use systems.
Variation of mean sea surface temperature and modulation of El Niño–Southern Oscillation variance during the past 150 years
Authors: Fang Yue , Chiang John C. H. , Chang Ping
Published: July 2008

Evidence is presented that the dominant non‐trend mode of interdecadal global SST variations is linked to significant modulation of ENSO variance during the past 150 years. The mode resembles the interhemispheric SST pattern linked to Sahel rainfall changes, with colder northern hemisphere conditions co‐incident with higher ENSO variance. Simulations of an intermediate coupled global climate model demonstrate that this global SST pattern can drive the interdecadal changes to ENSO variance. The influence on the ENSO dynamics comes primarily from the portion of the SST change local to the tropical Pacific, which is warm over the entire equatorial Pacific particularly in the southeast during times of stronger ENSO activity. We speculate that the warming equatorial SST causes ENSO events occur earlier and thus have longer time to develop, as well as enhancing the vertical temperature gradient and thus increasing the effectiveness of oceanic entrainment.
Analysis of seafloor seismograms of the 2003 Tokachi‐Oki earthquake sequence for earthquake early warning
Authors: McGuire Jeffrey J. , Simons Frederik J. , Collins John A.
Published: July 2008

Earthquake Early Warning (EEW) algorithms estimate the magnitude of an underway rupture from the first few seconds of the P‐wave to allow hazard assessment and mitigation before the S‐wave arrival. Many large subduction‐zone earthquakes initiate 50–150 km offshore, potentially allowing seafloor instruments sufficient time to identify large ruptures before the S‐waves reach land. We tested an EEW algorithm using accelerograms recorded offshore Hokkaido in the region of the 2003 Mw 8.1 Tokachi‐Oki earthquake and its aftershocks. A wavelet transform of the first ∼4 s of the P‐wave concentrates information about earthquake magnitude from both waveform amplitude and frequency content. We find that wavelets with support of a few seconds provide discriminants for EEW that are both accurate enough to be useful and superior to peak acceleration or peak velocity. Additionally, we observe a scaling of wavelet coefficient magnitude above Mw 6.0 indicating that, at least for the mainshock (Mw 8.1) and largest aftershock (Mw 7.1), the final size of a rupture could have been estimated from the initial portion of the seismogram.
Eco‐geomorphic implications of hillslope aspect: Inferences from analysis of landscape morphology in central New Mexico
Authors: Istanbulluoglu Erkan , Yetemen Omer , Vivoni Enrique R. , Gutiérrez‐Jurado Hugo A. , Bras Rafael L.
Published: July 2008

We investigate the influence of hillslope aspect on landscape morphology in central New Mexico, where differences in soils, vegetation, and landforms are observed between mesic north‐facing and xeric south‐facing slopes. Slope–area and curvature–area relations, derived from a Digital Elevation Model (DEM), are used to characterize the opposing hillslope morphologies. In all geologies and elevation ranges studied, topographic data reveal significantly steeper slopes in north‐facing aspects, and shallower slopes in south‐facing aspects. North‐facing slope curvatures are also greater than south‐facing curvatures. Using a conceptual slope‐area model, we suggest that for a given drainage area, steeper north‐facing slopes imply lower soil erodibility. We argue that this interpretation, consistent with recent views of ecosystem control on semiarid erosion rates, shows the influence hillslope aspect on topography and its associated vegetation communities. Observed valley asymmetry in the region reinforces this concept and suggests a long‐term legacy of aspect‐modulated ecogeomorphic processes.
Natural abundance measurements of 13C indicate increased deep soil carbon mineralization after forest disturbance
Authors: Diochon Amanda , Kellman Lisa
Published: July 2008

Northern forest soils represent globally important stores of carbon (C), yet there is no consensus about how they are altered by the widespread practice of harvesting that dominates many forested landscapes. Here we present the first study to systematically investigate the utility of δ13C and C content depth profiles to infer temporal changes in belowground carbon cycling processes following disturbance in a pure C3 ecosystem. We document carbon concentration and δ13C depth profile enrichment trends consistent with a kinetic fractionation arising from soil organic carbon (SOC) humification across a northern forest chronosequence (1, 15, 45, 80 and 125+ yrs). Reduced soil C storage that coincided with observed soil profile δ13C‐enrichment patterns which intensified following clearcut harvesting, pointed to losses of SOC in the deeper (>20 cm) mineral soil. This study suggests the δ13C approach may assist in identifying mechanisms responsible for soil C storage changes in disturbed C3 forest ecosystems.
On the cause of Saturn's plasma periodicity
Authors: Burch J. L. , Goldstein J. , Mokashi P. , Lewis W. S. , Paty C. , Young D. T. , Coates A. J. , Dougherty M. K. , André N.
Published: July 2008

Periodic plasma enhancements are examined for all Cassini orbits from December 29, 2005 through September 7, 2006. The events, which have UT durations of 3–4 hours, are centered near SLS3 longitude 10° at radial distances near 15 RS and at larger W longitudes at larger distances, reaching 180°W by 49 RS. Magnetic‐field data within the events and outside 30 to 35 RS show signatures of neutral‐sheet crossings and magnetic reconnection (i.e., plasmoids). We conclude that plasmoids move outward from 30–35 RS along a spiral path that rotates with the planet. The duration of these events is similar to that of SKR events, and they are ordered in the SKR‐based SLS3 longitude system. A conceptual model, in which the plasmoids are triggered in the pre‐midnight quadrant following (with a predictable delay) the appearance of SKR at the magnetopause and then propagate outward in a rotating spiral pattern, can explain the connection among periodicities observed in Saturn's charged particles, magnetic fields, and kilometric radiation.
Solar‐minimum quiet time ion energization and outflow in dynamic boundary related coordinates
Authors: Peterson W. K. , Andersson L. , Callahan B. C. , Collin H. L. , Scudder J. D. , Yau A. W.
Published: July 2008

We report hemispheric average fluxes and energies of outflowing energetic (0.015 < E/q < 33 keV) H+, O+, and He+ ions in dynamic boundary‐related coordinates, from observations obtained by the Polar/TIMAS instrument near 6000 km altitude in the southern hemisphere during quiet geomagnetic intervals at solar minimum. We discuss our observations in terms of known energization and transport processes. We find that only a small fraction of energetic ions escape from the ionosphere directly into the polar cap and at quiet times the characteristic energies of escaping H+ are between 30 and 300 eV in the cusp region and between 30 eV and 1.2 keV in the midnight sector. For O+ we conclude the characteristic energy in the cusp is ∼100 eV and between 150 and 600 eV in the midnight sector. Our data suggest that the relative energization and acceleration of O+ is significantly different in the noon quadrant. The observations and analysis presented here also suggest that O+ has activity dependent transport paths from the ionosphere to the ring current that have not previously been identified.
Performance of the ground‐based total ozone network assessed using satellite data
Authors: Fioletov V. E. , Labow G. , Evans R. , Hare E. W. , Köhler U. , McElroy C. T. , Miyagawa K. , Redondas A. , Savastiouk V. , Shalamyansky A. M. , Staehelin J. , Vanicek K. , Weber M.
Published: July 2008

Dobson and Brewer spectrophotometer and filter ozonometer data available from the World Ozone and Ultraviolet Data Centre (WOUDC) were compared with satellite total ozone measurements from TOMS (onboard Nimbus 7, Meteor 3, and Earth Probe satellites), OMI (AURA satellite) and GOME (ERS‐2 satellite) instruments. Five characteristics of the difference with satellite data were calculated for each site and instrument type: the mean difference, the standard deviation of daily differences, the standard deviation of monthly differences, the amplitude of the seasonal component of the difference, and the range of annual values. All these characteristics were calculated for five 5‐year‐long bins and for each site separately for direct sun (DS) and zenith sky (ZS) ozone measurements. The main percentiles were estimated for the five characteristics of the difference and then used to establish criteria for “suspect” or “outlier” sites for each characteristic. About 61% of Dobson, 46% of Brewer, and 28% of filter stations located between 60°S and 60°N have no “suspect” or “outlier” characteristics. In nearly 90% of all cases, Dobson and Brewer sites demonstrated 5‐year mean differences with satellites to be within ±3% (for DS observations). The seasonal median difference between all Brewer DS measurements at 25°–60°N and GOME and OMI overpasses remained within ±0.5% over a period of more than 10 years. The satellite instrument performance was also analyzed to determine typical measurement uncertainties. It is demonstrated that systematic differences between the analyzed satellite instruments are typically within ±2% and very rarely are they outside the ±3% envelope. As the satellite instrument measurements appear to be better than ±3%, ground‐based instruments with precision values worse than ±3% are not particularly useful for the analyses of long‐term changes and comparison with numerical simulations.
Measurements of low amounts of precipitable water vapor by millimeter wave spectroscopy: An intercomparison with radiosonde, Raman lidar, and Fourier transform infrared data
Authors: Fiorucci Irene , Muscari Giovanni , Bianchi Cesidio , Di Girolamo Paolo , Esposito Francesco , Grieco Giuseppe , Summa Donato , Bianchini Giovanni , Palchetti Luca , Cacciani Marco , Di Iorio Tatiana , Pavese Giulia , Cimini Domenico , de Zafra Robert L.
Published: July 2008

Observations of very low amounts of precipitable water vapor (PWV) by means of the Ground‐Based Millimeter wave Spectrometer (GBMS) are discussed. Low amounts of column water vapor (between 0.5 and 4 mm) are typical of high mountain sites and polar regions, especially during winter, and are difficult to measure accurately because of the lack of sensitivity of conventional instruments to such low PWV contents. The technique used involves the measurement of atmospheric opacity in the range between 230 and 280 GHz with a spectral resolution of 4 GHz, followed by the conversion to precipitable water vapor using a linear relationship. We present the intercomparison of this data set with simultaneous PWV observations obtained with Vaisala RS92k radiosondes, a Raman lidar, and an IR Fourier transform spectrometer. These sets of measurements were carried out during the primary field campaign of the Earth Cooling by Water vapor Radiation (ECOWAR) project which took place at Breuil‐Cervinia (45.9°N, 7.6°E, elevation 1990 m) and Plateau Rosa (45.9°N, 7.7°E, elevation 3490 m), Italy, from 3 to 16 March 2007. GBMS PWV measurements show a good agreement with the other three data sets exhibiting a mean difference between observations of ≃9%. The considerable number of data points available for the GBMS versus lidar PWV correlation allows an additional analysis which indicates negligible systematic differences between the two data sets.
Aerosol characteristics over urban Cairo: Seasonal variations as retrieved from Sun photometer measurements
Authors: El‐Metwally M. , Alfaro S. C. , Abdel Wahab M. , Chatenet B.
Published: July 2008

During the Cairo Aerosol Characterization Experiment an automated Sun photometer belonging to the NASA Aerosol Robotic Network has been implemented for the first time in the megacity of Cairo, Egypt. The inversion of the measurements performed by this instrument several times a day and over a duration of more than 1 year (from the end of October 2004 to the end of January 2006) provides a way of determining the temporal variability of aerosol characteristics such as size distribution, complex refractive index, single‐scattering albedo, and asymmetry parameter. The analysis of the results reveals that Cairo's aerosol is a mixture of three individual components produced by different mechanisms: “background pollution” aerosol produced by local urban activities, “pollution‐like” aerosol resulting from biomass burning in the Nile delta, and “dust‐like” aerosol released by wind erosion in the Sahara. It is also shown that the variations in the overall aerosol properties are in fact due to changes in the proportions of this mixture. In particular, short‐duration dust storms and biomass‐burning episodes explain the largest observed aerosol optical depths (AOD) (AOD > 0.7) through the extreme enhancements of concentrations in dust‐like aerosols characterized by low Ångström's exponent values (α < 0.5) and in “biomass‐burning” aerosols (1.0 < α < 1.5). When averaged over longer (monthly and yearly) time periods, the effects of these high‐frequency modifications are smoothed. In particular, an average “mixed aerosol” type is defined for the whole duration of the measurements period. The low single‐scattering albedo (SSA) of this average aerosol and its marked spectral dependence clearly indicate that, at least on a yearly basis, the aerosol is dominated by its two light absorbing pollution components (background pollution and pollution‐like) and to such an extent that it compares well with values obtained in other polluted megacities (e.g., Mexico City). This general dominance of the absorbing components can be challenged at shorter timescales. Indeed, the occurrence of several dust storms in springtime, and particularly in April, causes a significant increase in SSA and a parallel decrease in spectral dependence during this month. Conversely, the October biomass‐burning events are not able to cause such important deviations from the yearly averaged mixed aerosol model that its optical properties can no longer be used for this month.
Circumpolar transport of a volcanic cloud from Hekla (Iceland)
Authors: Carn S. A. , Prata A. J. , Karlsdóttir S.
Published: July 2008

Hekla volcano (Iceland) erupted on 17 August 1980 and emplaced a sulfur dioxide (SO2) cloud into the north polar stratosphere at a maximum altitude of ∼15 km. The SO2 is tracked using satellite data from the ultraviolet (UV) Nimbus‐7 Total Ozone Mapping Spectrometer (N7/TOMS) and the infrared (IR) High‐resolution Infrared Radiation Sounder (HIRS/2) on the NOAA TIROS Operational Vertical Sounder (TOVS) platform. The eruption emitted ∼0.5–0.7 Tg of SO2, which later split into three distinct clouds, one of which circled the North Pole at the perimeter of an atypically persistent Arctic cyclone for six days, impacting airspace on three continents. Separate clouds drifted across eastern Russia, Alaska, and Canada. Maximum SO2 columns derived from TOMS and HIRS/2 accurately define the volcanic cloud's path and fit trajectories produced by the NOAA Hybrid Single‐Particle Lagrangian Integrated Trajectory (HYSPLIT) model, providing confidence in the model. When combined with the SO2 measurements, trajectory altitudes derived from HYSPLIT provide robust estimates of the altitudes of the SO2 clouds (8–15 km), which would be elusive using either the satellite data or the trajectory model in isolation. Near‐coincident, spectrally discrete UV and IR retrievals are compared in the volcanic cloud and indicate good agreement between TOMS and HIRS/2 SO2 columns for pixels with similar viewing geometry. Hekla eruptions, which follow a pattern of early explosive venting of volcanic gases with significant stratospheric injection, could play a role in promoting Arctic ozone loss, depending on the phase of the North Atlantic Oscillation during the eruption.
Acute Treatment with Rosuvastatin Protects Insulin Resistant (C57BL/6J ob/ob) Mice against Transient Cerebral Ischemia
Authors: Mayanagi Keita , Katakam Prasad V , Gáspár Tamas , Domoki Ferenc , Busija David W
Published: July 2008

The purpose of this study was to investigate the short-term effects of rosuvastatin (RSV), a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on transient, focal cerebral ischemia in C57BL/6J ob/ob mice with insulin resistance (IR). Male ob/ob, lean, or wild-type (WT) mice were treated with RSV (10 mg/kg per day, i.p.) or vehicle for 3 days. Ischemia was induced by 60 mins of middle cerebral artery occlusion (MCAO) and cortical blood flow (CBF) was monitored by laser-Doppler flowmetry. Infarct volumes were measured 24 h after reperfusion. IR mice exhibited a higher infarct volume compared with Lean or WT mice, and RSV reduced infarct volume only in obese mice (40% ± 3% versus 32% ± 3%, P < 0.05). Blood cholesterol and insulin levels were elevated in ob/ob mice but were unaffected by RSV. The CBF reductions during MCAO were similar in all groups and were not affected by RSV. Although RSV did not increase cortical endothelial NO synthase (eNOS) levels in the ob/ob mice, it attenuated the increased cortical expression of intracellular adhesion molecule-1 (ICAM-1) after MCAO from ob/ob mice. Thus, RSV protects against stroke in IR mice by a mechanism independent of effects on the lipid profile, CBF, or eNOS but dependent on suppression of post-MCAO ICAM-1 expression.
Antifungal‐protein production in maize (Zea mays) suspension cultures
Authors: Perri Fabio , Della Penna Serena , Rufini Francesca , Patamia Maria , Bonito Mariantonietta , Angiolella Letizia , Vitali Alberto
Published: July 2008

The growing emergency due to the phenomenon of drug resistance to micro‐organisms has pushed forward the search for new potential drug alternatives to those already in use. Plants represent a suitable source of new antifungal molecules, as they produce a series of defensive proteins. Among them are the PRPs (pathogenesis‐related proteins), shown to be effective in vitro against human pathogens. An optimized and established cell‐suspension culture of maize (Zea mays) was shown to constitutively secrete in the medium a series of PRPs comprising the antifungal protein zeamatin (P33679) with a final yield of approx. 3 mg/litre. The in‐vitro‐produced zeamatin possessed antifungal activity towards a clinical strain of the human pathogenic yeast Candida albicans, an activity comparable with the one reported for the same protein extracted from maize seeds. Along with zeamatin, other PRPs were expressed: a 9 kDa lipid‐transfer protein, a 26 kDa xylanase inhibitor and a new antifungal protein, PR‐5. A fast, two‐step chromatographic procedure was set up allowing the complete purification of the proteins considered, making this cell line a valuable system for the production of potential antifungal agents in a reliable and easy way.
Voice Loudness and Gender Effects on Jitter and Shimmer in Healthy Adults
Authors: Brockmann Meike , Storck Claudio , Carding Paul N. , Drinnan Michael J.
Published: July 2008

Purpose

The aim of this study was to investigate voice loudness and gender effects on jitter and shimmer in healthy young adults because previous descriptions have been inconsistent.

Method

Fifty-seven healthy adults (28 women, 29 men) aged 20–40 years were included in this cross-sectional single-cohort study. Three phonations of /a/ at soft, medium, and loud individual loudness were recorded and analyzed using PRAAT software (P. Boersma & D. Weeninkk, 2006). Voice loudness and gender effects on measured sound pressure level, fundamental frequency, jitter, and shimmer were assessed through the use of descriptive and inferential (analysis of variance) statistics.

Results

Jitter and shimmer significantly increased with decreasing voice loudness, especially in phonations below 75 dB and 80 dB. In soft and medium phonation, men were generally louder and showed significantly less shimmer. However, men had higher jitter measures when phonating softly. Gender differences in jitter and shimmer at medium loudness may be mainly linked to different habitual voice loudness levels.

Conclusion

This pragmatic study shows significant voice loudness and gender effects on perturbation. In clinical assessment, requesting phonations above 80 dB at comparable loudness between genders would enhance measurement reliability. However, voice loudness and gender effects in other age groups, in disordered voices, or when a minimal loudness is requested should be further investigated.
Effects of Training on Naïve Listeners' Judgments of the Speech Intelligibility of Children With Severe-to-Profound Hearing Loss
Authors: Ellis Lee W. , Beltyukova Svetlana A.
Published: July 2008

Purpose

This study examined the effects of feedback training, familiarization training, and no training on naïve listeners' word identification (WI) and magnitude estimation scaling (MES) judgments of the speech intelligibility of children with severe-to-profound hearing impairments.

Method

Depending on the training group, listeners received a pretest, an immediate posttest, and/or a delayed posttest.

Results

Results indicated that repeated exposure, with or without training, led to improved WI scores. Beyond the effects of repeated exposure, listeners' WI judgments of the intelligibility of speech significantly increased immediately after training in which listeners received feedback regarding the accuracy of their WI responses. The MES results were less straightforward—listeners in the feedback group perceived speech samples as less intelligible after the training, perceptions of speech intelligibility stayed almost the same for the familiarization training group, and participants in the control group perceived speech samples as more intelligible at the posttest. For the training groups that were not pretested, perceptions improved from the immediate to delayed posttest.

Discussion

Results may have both theoretical and clinical significance, particularly as they relate to contrasting theories of perceptual learning and the extent to which listener characteristics may be reflected in intelligibility judgments.
Rasch Analysis of Word Identification and Magnitude Estimation Scaling Responses in Measuring Naïve Listeners' Judgments of Speech Intelligibility of Children With Severe-to-Profound Hearing Impairments
Authors: Beltyukova Svetlana A. , Stone Gregory M. , Ellis Lee W.
Published: July 2008

Purpose

Speech intelligibility research typically relies on traditional evidence of reliability and validity. This investigation used Rasch analysis to enhance understanding of the functioning and meaning of scores obtained with 2 commonly used procedures: word identification (WI) and magnitude estimation scaling (MES).

Method

Narrative samples of children with hearing impairments were used to collect data from listeners with no previous experience listening to or judging intelligibility of speech. WI data were analyzed with the Rasch rating scale model. MES data were examined with Rasch partial credit model when individual scales were unknown, and the Rasch rating scale model was used with reported individual scales.

Results

Results indicated that both procedures have high reliability and similar discriminatory power. However, reliability and separation were lower for MES when scales were unknown. Both procedures yielded similar speech sample ordering by their difficulty. However, sampling gaps were noted as well as item misfit issues.

Conclusions

Functioning wise, both WI and MES procedures were highly reliable in measuring speech intelligibility, and measurement precision may be increased by asking participants to report their individual scales when using MES. Meaning wise, operationalization of speech intelligibility did not change when either WI or MES procedure was used. However, the sample selection procedure needs to be further refined to allow for a wider selection of stimuli.
Acoustic Correlates of Fatigue in Laryngeal Muscles: Findings for a Criterion-Based Prevention of Acquired Voice Pathologies
Authors: Boucher Victor J.
Published: July 2008

Purpose

The objective was to identify acoustic correlates of laryngeal muscle fatigue in conditions of vocal effort.

Method

In a previous study, a technique of electromyography (EMG) served to define physiological signs of “voice fatigue” in laryngeal muscles involved in voicing. These signs correspond to spectral changes in contraction potentials. A corpus of vocalizations from the 7 participants in the EMG study was used to explore the effects of muscle fatigue on voice acoustics. Each participant produced vocalizations at regular intervals (50 in all) extending across a day (12–14 hr). The participants also produced 5 min of loud speech with peaks of 74 dBA at 1 m between each vocalization. Twenty acoustic parameters were measured using the Multi-Dimensional Voice Program (Kay Elemetrics, Lincoln Park, NJ).

Results

The analyses showed no consistent correlations between acoustic parameters and estimates of muscle fatigue. However, in all cases, nonlinear jumps occurred in the frequency of amplitude tremor at points where fatigue estimates showed a critical shift. These jumps were robust despite changes in F0 in some individuals.

Conclusion

A brief rise in voice tremor can correspond to a critical change in laryngeal muscle tissues seen as a condition where continued vocal effort can increase the risk of lesions or other conditions affecting voice.
The Breadth of Coarticulatory Units in Children and Adults
Authors: Goffman Lisa , Smith Anne , Heisler Lori , Ho Michael
Published: July 2008

Purpose

To assess, in children and adults, the breadth of coarticulatory movements associated with a single rounded vowel.

Method

Upper and lower lip movements were recorded from 8 young adults and 8 children (aged 4–5 years). A single rounded versus unrounded vowel was embedded in the medial position of pairs of 7-word/7-syllable sentences.

Results

Both children and adults produced movement trajectories associated with lip rounding that were very broad temporally (i.e., movement duration lasting 45% to 56% of the sentence). Some effects appeared to extend across the entire utterance. There were no differences between children and adults in the extent of the coarticulatory effect. However, children produced relatively variable movements associated with lip rounding.

Conclusions

These data support the hypothesis that, for young children and adults, broad chunks of output have been planned by the onset of implementation of a sentence. This implies that, based on a change in a single phoneme, the motor commands to the muscles are altered for the production of the entire sentence.
Prevalence of Stuttering in African American Preschoolers
Authors: Proctor Adele , Yairi Ehud , Duff Melissa C. , Zhang Jie
Published: July 2008

Purpose

In this study, the authors sought to determine the prevalence of stuttering in African American (AA) 2- to 5-year-olds as compared with same-age European Americans (EAs).

Method

A total of 3,164 children participated: 2,223 AAs and 941 EAs. Data were collected using a 3-pronged approach that included investigators' individual interactions with each child, teacher identification, and parent identification of stuttering.

Results

No statistically significant difference for stuttering was found between AA and EA children. Using the investigator and teacher method of identification, the prevalence of stuttering was 2.52% for the entire sample. For both racial groups, boys exhibited a higher prevalence of stuttering than girls. Of the 3 predictors (age, race, sex) of stuttering, only sex was a significant predictor.

Conclusions

AA 2- to 5-year-olds are not overrepresented in the stuttering population for this age group. When data are combined for both racial groups, the prevalence of stuttering is 2.52%. More boys than girls stuttered in this sample of preschoolers.
Exploring Genetic and Environmental Effects in Dysphonia: A Twin Study
Authors: Simberg Susanna , Santtila Pekka , Soveri Anna , Varjonen Markus , Sala Eeva , Sandnabba N. Kenneth
Published: July 2008

Purpose

To explore the existence of genetic effects as well as the interaction between potential genetic effects and a voice-demanding occupation on dysphonia.

Method

One thousand seven hundred and twenty-eight Finnish twins (555 male; 1,173 female) born between 1961 and 1989 completed a questionnaire concerning vocal symptoms and occupation. The zygosity determination resulted in 125 monozygotic and 108 dizygotic full twin pairs. A composite variable called
dysphonia
was formed by summing 6 vocal symptoms based on the results of a factor analysis. Twin model fitting was used to explore the contribution of genetic and environmental effects on the dysphonia variable.

Results

Individual differences in dysphonia were explained by genetic effects (35%) and nonshared environmental effects (65%). Shared environmental effects were estimated at 0%. Also, the authors found that for the participants who worked in voice-demanding occupations, the causes of dysphonia were more environmental, whereas the etiology of the symptoms was more strongly affected by genes in the participants with less voice-demanding occupations. However, this gene–environment interaction was not statistically significant.

Conclusion

Both genetic and environmental factors have an impact on the etiology of voice problems. Environmental factors, either independently or interacting with genetic factors, seem to play the key role, especially if the person has a voice-demanding occupation.
Nonnative Speech Perception Training Using Vowel Subsets: Effects of Vowels in Sets and Order of Training
Authors: Nishi Kanae , Kewley-Port Diane
Published: July 2008

Purpose

K. Nishi and D. Kewley-Port (2007) trained Japanese listeners to perceive 9 American English monophthongs and showed that a protocol using all 9 vowels (fullset) produced better results than the one using only the 3 more difficult vowels (subset). The present study extended the target population to Koreans and examined whether protocols combining the 2 vowel sets would provide more effective training.

Method

Three groups of 5 Korean listeners were trained on American English vowels for 9 days using one of the 3 protocols: fullset only, first 3 days on subset then 6 days on fullset, or first 6 days on fullset then 3 days on subset. Participants' performance was assessed by pre- and posttraining tests, as well as by a midtraining test.

Results

(a) Fullset training was effective for Koreans as well as Japanese, (b) no advantage was found for the 2 combined protocols over the fullset-only protocol, and (c) sustained “nonimprovement” was observed for training using one of the combined protocols.

Conclusions

In using subsets for training on American English vowels, care should be taken not only in the selection of subset vowels but also in the training orders of subsets.