bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual Perception and Awareness
Authors: Celesia Gastone G.
Published: December 2010

The study of visual processing and abnormalities due to lesions of cortical structures sheds light on visual awareness/consciousness and may help us to better understand consciousness. We report on clinical observations and psychophysical testing of achromatopsia/prosopagnosia, visual agnosia, and blindsight. Achromatopsia and prosopagnosia reveal that visual cortices have functionally specialized processing systems for color, face perception, and their awareness, and that furthermore these systems operate independently. Dysfunction is limited to some aspects of visual perception; someone with achromatopsia, although not conscious of color, is aware of the objects’ form, motion, and their relationship with sound and other sensory percepts. Perceptual awareness is modular, with neuronal correlates represented by multiple separate specialized structures or modules. Visual agnosia shows that awareness of a complete visual percept is absent, though the subject is aware of single visual features such as edges, motion, etc., an indication that visual agnosia is a disruption of the binding process that unifies all information into a whole percept. Blindsight is characterized by the subject’s ability to localize a visual target while denying actually seeing the target. Blindsight is mediated by residual islands of the visual cortex, which suggests that sensory modules responsible for awareness can function only when structurally intact. We conclude (1) that perceptual awareness (consciousness?) is modular, and (2) that perceptual integration is also modular, which suggests that integration among distinct cortical regions is a parallel process with multiple communication pathways. Any hypothesis about consciousness must include these observations about the presence of multiple parallel, but spatially and temporally different, mechanisms.
Time-Varying Cortical Connectivity Estimation from Noninvasive, High-Resolution EEG Recordings
Authors: Astolfi Laura , Cincotti Febo , Mattia Donatella , De Vico Fallani Fabrizio , Vecchiato Giovanni , Salinari Serenella , Vecchiato Gianni , Witte Herbert , Babiloni Fabio
Published: December 2010

Objective: In this paper, we propose a body of techniques for the estimation of rapidly changing connectivity relationships between EEG signals estimated in cortical areas, based on the use of adaptive multivariate autoregressive modeling (AMVAR) for the estimation of a time-varying partial directed coherence (PDC). This approach allows the observation of rapidly changing influences between the cortical areas during the execution of a task, and does not require the stationarity of the signals. Methods: High resolution EEG data were recorded from a group of spinal cord injured (SCI) patients during the attempt to move a paralyzed limb. These data were compared with the time-varying connectivity patterns estimated in a control group during the real execution of the movement. Connectivity was estimated with the use of realistic head modeling and the linear inverse estimation of the cortical activity in a series of regions of interest by using time-varying PDC. Results: The SCI population involved a different cortical network than those generated by the healthy subjects during the task performance. Such a network differs for the involvement of the parietal cortices, which increases in strength near to the movement imagination onset for the SCI when compared to the normal population. Conclusions: The application of time-varying PDC allows tracking the evolution of the connectivity between cortical areas in the analyzed populations during the proposed tasks. Such details about the temporal evolution of the connectivity patterns estimated cannot be obtained with the application of the standard estimators of connectivity.
Patterns of Implicit Learning Below the Level of Conscious Knowledge
Authors: Yordanova Juliana , Verleger Rolf , Wagner Ullrich , Kolev Vasil
Published: December 2010

The objective of the present study was to evaluate patterns of implicit processing in a task where the acquisition of explicit and implicit knowledge occurs simultaneously. The number reduction task (NRT) was used as having two levels of organization, overt and covert, where the covert level of processing is associated with implicit associative and implicit procedural learning. One aim was to compare these two types of implicit processes in the NRT when sleep was or was not introduced between initial formation of task representations and subsequent NRT processing. To assess the effects of different sleep stages, two sleep groups (early- and late-night groups) were used where initial training of the task was separated from subsequent retest by 3 h full of predominantly slow wave sleep (SWS) or rapid eye movement (REM) sleep. In two no-sleep groups, no interval was introduced between initial and subsequent NRT performance. A second aim was to evaluate the interaction between procedural and associative implicit learning in the NRT. Implicit associative learning was measured by the difference between the speed of responses that could or could not be predicted by the covert abstract regularity of the task. Implicit procedural on-line learning was measured by the practice-based increased speed of performance with time on task. Major results indicated that late-night sleep produced a substantial facilitation of implicit associations without modifying individual ability for explicit knowledge generation or for procedural on-line learning. This was evidenced by the higher rate of subjects who gained implicit knowledge of abstract task structure in the late-night group relative to the early-night and no-sleep groups. Independently of sleep, gain of implicit associative knowledge was accompanied by a relative slowing of responses to unpredictable items suggesting reciprocal interactions between associative and motor procedural processes within the implicit system. These observations provide evidence for the separability and interactions of different patterns of processing within implicit memory.
Function-Related Gamma Oscillations and Conscious Perception
Authors: Carozzo Simone , Garbarino Sergio , Serra Sebastiano , Sannita Walter G.
Published: December 2010

Frequency-domain techniques describe oscillations as a fundamental behavior of neurons and brain signals. Oscillations synchronize over large portions of cortex and mediate in the spatiotemporally coherent activation of neuron assemblies required for brain processing to occur. Oscillations in the gamma band (~20.0–80.0 Hz) originate from the tonic excitation of inhibitory interneuron networks, sustain rhythms and frequency constancy, and are enhanced during sensory, motor, or “cognitive” processes through frequency-dependent and function-related neuronal synchronization. Experimental work indicates a role of gamma activity in conscious perception. Further investigation is, nevertheless, warranted as gamma-band synchronization plays a functional role in low-level phase coding as well as in high-complexity neural processes related to perception, such as selective attention, focused arousal, multistable or ambiguous perceptive conditions, visuomotor integration, and associative learning.
Consciousness as the Emergent Property of the Interaction Between Brain, Body, and Environment
Authors: Casadio Maura , Giannoni Psiche , Masia Lorenzo , Morasso Pietro , Sanguineti Vittorio , Squeri Valentina , Vergaro Elena
Published: December 2010

Neuromotor rehabilitation, typically seen with stroke patients, is usually mistakenly focused on the recovery of movements while disregarding the insufficient or missing awareness of the affected part of the body. Thus, the functional recovery of sensorimotor abilities is fundamentally a problem of consciousness. The paper addresses the implications of this concept in the design of optimal robot-assistance in the training of patients, according to the assumption that consciousness is the emergent property of the interaction between brain, body, and environment. Optimal assistance is formulated as a process that follows three basic guidelines: (1) limitation of the assistance level to the minimum value capable of allowing patients to initiate the movements; (2) trial-to-trial reduction of assistance in order to promote the emergence of voluntary control; (3) nonmonotonic modulation from session to session in order to promote memory consolidation.
Influence of atmospheric nutrients on primary productivity in a coastal upwelling region
Authors: Mackey Katherine R. M. , van Dijken Gert L. , Mazloom Simran , Erhardt Andrea M. , Ryan John , Arrigo Kevin R. , Paytan Adina
Published: December 2010

Atmospheric deposition is an important source of nutrients to the coastal and open ocean; however, its role in highly productive upwelling regions like coastal California has not been determined. Approximately 0.1%–0.2% of new production is attributable to atmospheric deposition of nitrogen (N) annually, but if the estimate is expanded to encompass the effects of iron (Fe), aerosols may support 1%–2% of new production on average, and up to 5% on days with high deposition fluxes. Laboratory culture and in situ incubation experiments confirm the bioavailability of N from dry deposition in this region. A significant positive relationship between aerosol optical thickness and chlorophyll a derived from the Moderate Resolution Imaging Spectroradiometer is observed for the summer months and is stronger offshore than near the coast. Moreover, the portion of productivity supported by atmospheric deposition is higher on days without upwelling and during El Niño periods when nutrient input from upwelling is suppressed, a phenomenon that could become more prevalent due to climate warming. Expanding the results from California, we estimate that dry deposition could increase productivity in other major coastal upwelling regions by up to 8% and suggest that aerosols could stimulate productivity by providing N, Fe, and other nutrients that are essential for cell growth but relatively deplete in upwelled water.
A model‐data intercomparison of CO2 exchange across North America: Results from the North American Carbon Program site synthesis
Authors: Schwalm Christopher R. , Williams Christopher A. , Schaefer Kevin , Anderson Ryan , Arain M. Altaf , Baker Ian , Barr Alan , Black T. Andrew , Chen Guangsheng , Chen Jing Ming , Ciais Philippe , Davis Kenneth J. , Desai Ankur , Dietze Michael , Dragoni Danilo , Fischer Marc L. , Flanagan Lawrence B. , Grant Robert , Gu Lianhong , Hollinger David , Izaurralde R. César , Kucharik Chris , Lafleur Peter , Law Beverly E. , Li Longhui , Li Zhengpeng , Liu Shuguang , Lokupitiya Erandathie , Luo Yiqi , Ma Siyan , Margolis Hank , Matamala Roser , McCaughey Harry , Monson Russell K. , Oechel Walter C. , Peng Changhui , Poulter Benjamin , Price David T. , Riciutto Dan M. , Riley William , Sahoo Alok Kumar , Sprintsin Michael , Sun Jianfeng , Tian Hanqin , Tonitto Christina , Verbeeck Hans , Verma Shashi B.
Published: December 2010

Our current understanding of terrestrial carbon processes is represented in various models used to integrate and scale measurements of CO2 exchange from remote sensing and other spatiotemporal data. Yet assessments are rarely conducted to determine how well models simulate carbon processes across vegetation types and environmental conditions. Using standardized data from the North American Carbon Program we compare observed and simulated monthly CO2 exchange from 44 eddy covariance flux towers in North America and 22 terrestrial biosphere models. The analysis period spans ∼220 site‐years, 10 biomes, and includes two large‐scale drought events, providing a natural experiment to evaluate model skill as a function of drought and seasonality. We evaluate models' ability to simulate the seasonal cycle of CO2 exchange using multiple model skill metrics and analyze links between model characteristics, site history, and model skill. Overall model performance was poor; the difference between observations and simulations was ∼10 times observational uncertainty, with forested ecosystems better predicted than nonforested. Model‐data agreement was highest in summer and in temperate evergreen forests. In contrast, model performance declined in spring and fall, especially in ecosystems with large deciduous components, and in dry periods during the growing season. Models used across multiple biomes and sites, the mean model ensemble, and a model using assimilated parameter values showed high consistency with observations. Models with the highest skill across all biomes all used prescribed canopy phenology, calculated NEE as the difference between GPP and ecosystem respiration, and did not use a daily time step.
Responses of CO2 flux components of Alaskan Coastal Plain tundra to shifts in water table
Authors: Olivas Paulo C. , Oberbauer Steven F. , Tweedie Craig E. , Oechel Walter C. , Kuchy Andrea
Published: December 2010

The Arctic stores close to 14% of the global soil carbon, most of which is in a poorly decomposed state as a result of water‐saturated soils and low temperatures. Climate change is expected to increase soil temperature, affecting soil moisture and the carbon storage and sink potential of many Arctic ecosystems. Additionally, increased temperatures can increase thermokarst erosion and flooding in some areas. Our goal was to determine the effects that water table shifts would have on the CO2 sink potential of the Alaskan Coastal Plain tundra. To evaluate the effects of different water regimes, we used a large hydrological manipulation at Barrow, Alaska, where we maintained flooded, drained, and intermediate water levels in a naturally drained thaw lake basin over a period of three seasons: one pretreatment (2006) and two treatment (2007–2008) seasons. To assess CO2 flux components, we used 24 h chamber‐based measurements done on a weekly basis. Increased water table strongly lowered ecosystem respiration (ER) by reducing soil oxygen availability. Flooding decreased gross primary productivity (GPP), most likely by submerging mosses and graminoid photosynthetic leaf area. A decrease in water table increased GPP and ER; however, the increase in root and microbial activity was greater than the increase in photosynthesis, negatively affecting net ecosystem exchange. In the short term, ER is the CO2 flux component that responds most strongly to changes in water availability. Our results suggest that drying of the Alaskan Coastal Plain tundra in the short term could double ER rates, shifting the historic role of some Arctic ecosystems from a sink to a source of CO2.
Ancient Perspectives on Arctic Climate Change and Ice Sheet Dynamics: APEX Fourth International Conference and Workshop: Arctic Paleoclimate Proxies and Chronologies; Höfn, Iceland, 26–30 May 2010
Authors: Applegate Patrick , Fisher Timothy G.
Published: December 2010

The Arctic is particularly sensitive to climate change. In a warming world, reductions in ice‐covered area on land and sea increase the amount of solar radiation absorbed at the Earth's surface. Thus, temperatures should increase more rapidly at high northern latitudes than elsewhere. Modern observations of temperature increases, reductions in the mass balances of the Greenland ice sheet and small glaciers, and loss of sea ice extent confirm climate scientists' expectations of enhanced Arctic response to climate change.
House Hearing on Climate Change Presents Sharply Different Views
Authors: Showstack Randy
Published: December 2010

With Republicans about to assume the majority and take over leadership positions in the U.S. House of Representatives when the next Congress convenes in January 2011, the House Committee on Science and Technology organized what may be the Democrats' last congressional hearing on climate change this session. Billed as “A Rational Discussion of Climate Change: The Science, the Evidence, the Response,” the 17 November hearing featured three panels of scientists focusing on the basic science of climate change and impacts of carbon dioxide (CO2) on temperature and ocean acidity.

In addition to the scientific information presented by witnesses, there was much back and forth debate, sometimes testy, among panelists with sharply different perspectives. Comments from the House members ranged across the board, from trying to set a tone of objectivity to impassioned remarks.
Climate Variability and Change in South America: ENSO, Decadal Variability and Climate Change in South America: Trends, Teleconnections, and Potential Impacts; Guayaquil, Ecuador, 12–14 October 2010
Authors: McPhaden Michael J. , Vera Carolina Susana , Guingla Rodney Martínez
Published: December 2010

El Niño and the Southern Oscillation (ENSO) have profound effects on South American climate. Warm ENSO events (El Niños) and cold ENSO events (La Niñas), which occur on year‐to‐year time scales, are associated with droughts, floods, and other extreme weather events across the continent. Anthropogenic greenhouse gas warming of the planet will also likely have a profound effect on South America, through both gradual shifts in the baseline climate and increases in extreme events, including possible changes in the ENSO cycle.

There are indications that climate change may already be having an impact in South America, with temperature trends observed in the Galápagos and in the altiplano of the northern Andes and in the shrinking of tropical mountain glaciers. There has also been a shift in the behavior of El Niño, with an increased tendency for warm sea surface temperature anomalies to be concentrated in the central Pacific rather than in the eastern Pacific during the past 2 decades. These central Pacific (or “Modoki,” which means “similar but different” in Japanese) El Niños have a different signature than eastern Pacific El Niños in terms of teleconnection patterns on weather variability in South America and in terms of effects on marine ecosystems and fisheries along the west coast of the continent. However, the instrumental climate record is relatively short, and many of the observed trends could simply be the result of natural decadal climate variability that is unresolved in observations.
Outreach and Communications Highlights at the AGU Fall Meeting
Authors: Chell Kaitlin
Published: December 2010

Did you know that there is more to the AGU Fall Meeting in San Francisco than just scientific sessions? AGU also is offering a wide variety of outreach and communications workshops, career opportunity events, informative workshops for teachers, and film screenings at this year's Fall Meeting on 13–17 December and on Sunday, 12 December, just prior to the meeting.

As part of its new strategic plan, AGU is committed to engaging its members, shaping policy, and informing society about the excitement of Earth and space science and its role in developing solutions for the sustainability of the planet. Outreach and communications events are critical to accomplishing these goals. AGU members can become involved in public outreach, public policy, or media‐related activities by participating in these events at the Fall Meeting. Here are highlights of outreach and communications events at the Fall Meeting:
Seagrass sediments as a global carbon sink: Isotopic constraints
Authors: Kennedy Hilary , Beggins Jeff , Duarte Carlos M. , Fourqurean James W. , Holmer Marianne , Marbà Núria , Middelburg Jack J.
Published: December 2010

Seagrass meadows are highly productive habitats found along many of the world's coastline, providing important services that support the overall functioning of the coastal zone. The organic carbon that accumulates in seagrass meadows is derived not only from seagrass production but from the trapping of other particles, as the seagrass canopies facilitate sedimentation and reduce resuspension. Here we provide a comprehensive synthesis of the available data to obtain a better understanding of the relative contribution of seagrass and other possible sources of organic matter that accumulate in the sediments of seagrass meadows. The data set includes 219 paired analyses of the carbon isotopic composition of seagrass leaves and sediments from 207 seagrass sites at 88 locations worldwide. Using a three source mixing model and literature values for putative sources, we calculate that the average proportional contribution of seagrass to the surface sediment organic carbon pool is ∼50%. When using the best available estimates of carbon burial rates in seagrass meadows, our data indicate that between 41 and 66 gC m−2 yr−1 originates from seagrass production. Using our global average for allochthonous carbon trapped in seagrass sediments together with a recent estimate of global average net community production, we estimate that carbon burial in seagrass meadows is between 48 and 112 Tg yr−1, showing that seagrass meadows are natural hot spots for carbon sequestration.
Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity
Authors: Basu Nandita B. , Destouni Georgia , Jawitz James W. , Thompson Sally E. , Loukinova Natalia V. , Darracq Amélie , Zanardo Stefano , Yaeger Mary , Sivapalan Murugesu , Rinaldo Andrea , Rao P. Suresh C.
Published: December 2010

Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro‐climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long‐term monitoring data from the Mississippi‐Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter‐annual variations in loads (LT) for total‐N (TN) and total‐P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow‐weighted concentration, = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LT‐QT relationship. These responses are characteristic of transport‐limited systems. In contrast, in the absence of legacy sources in less‐managed catchments, values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter‐annual variations in LT can be robustly predicted given discharge variations arising from hydro‐climatic or anthropogenic forcing, and (2) water‐quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water‐quality impacts, and on acceleration of global biogeochemical cycles.
Salinity dependence of the thermoelectric coupling coefficient in brine‐saturated sandstones
Authors: Leinov E. , Vinogradov J. , Jackson M. D.
Published: December 2010

We report measurements of the thermoelectric coupling coefficient in intact sandstone samples saturated with NaCl brine at concentrations ranging from 1 × 10−4 to 1 M. Our measurements account for temperature‐dependent electrode effects. We also present a model for the salinity dependence of the thermoelectric coupling coefficient which yields a close match to the experimental data. At low salinity, the measured coupling coefficient exhibits the salinity dependence predicted for a perfect membrane, while at high salinity, the coupling coefficient follows that predicted for an uncharged porous medium. Measured values of the coupling coefficient range from 0.370 mVK−1 at low salinity (1 × 10−4 M), to 0.055 mVK−1 at high salinity (1 M).
Imprint of the El Niño Modoki on decadal sea level changes
Authors: Behera Swadhin , Yamagata Toshio
Published: December 2010

Decadal variation in sea level is shown to manifest as higher than normal sea level in the central Pacific flanked by lower than normal sea level on either side of the basin during the early 21st century. This abnormal condition is evidently aided by frequent occurrences of El Niño Modoki events and associated wind convergence to the dateline during 2000–2004. The sea level rise in central Pacific succeeded a phase of lower than normal sea level associated with La Niña Modoki events toward the end of 20th century. A correlation analysis confirms the dominant influence of El Niño/La Niña Modoki on the sea level rise in the central Pacific as compared to that of the El Niño/La Niña. This influence can even be seen in remote regions such as the coasts of California and Mauritius through atmospheric teleconnections.
Polar Ultraviolet Imager observation of auroral breakup
Authors: Liou Kan
Published: December 2010

The NASA's Polar satellite completed its mission in March 2008. During its 12 year operation, the Ultraviolet Imager (UVI) on‐board Polar acquired a large number of auroral images in FUV bands with unprecedented spatial and temporal resolutions. The purpose of this brief report is to provide a list of auroral substorm onset identified with UVI to the community for full use. A total of 2003 auroral substorm onsets are identified in the Northern Hemisphere between 1996 and 2000 and 536 onsets in Southern Hemisphere in 2007. Distributions of the onset locations are near Gaussian, with a population mean of 65.9° (standard deviation σ = 2.2°) in magnetic latitude (MLat) and 22.6 (σ = 1.1) in magnetic local time (MLT) for the northern hemispheric events and 68.0° (σ = 2.3°) in MLat and 22.6 (σ = 1.1) in MLT for the southern hemispheric events. A comparison with previously published IMAGE onset results suggests that substorms occur more frequently and intensely in the descending than in the ascending phase of solar cycle. The list of onset events includes the onset times and locations, and is provided as a supplement.
Hemispheric asymmetries in the ionospheric response observed in the American sector during an intense geomagnetic storm
Authors: de Abreu A. J. , Fagundes P. R. , Sahai Y. , de Jesus R. , Bittencourt J. A. , Brunini C. , Gende M. , Pillat V. G. , Lima W. L. C. , Abalde J. R. , Pimenta A. A.
Published: December 2010

The main purpose of this investigation is to study the ionospheric F region response induced by the intense geomagnetic storm that occurred on 7–8 September 2002. The geomagnetic index Dst reached a minimum of −181 nT at 0100 UT on 8 September. In this study, we used observations from a chain of 12 GPS stations and another chain of 6 digital ionosonde stations. It should be mentioned that, soon after the sudden commencement (SC) at 1637 UT on 7 September, the TEC variations at midlatitude stations in both hemispheres showed an F region positive storm phase. However, during the recovery phase, a strong hemispheric asymmetry was observed in the ionospheric response. While a TID type soliton was observed to propagate in the Southern American sector, no TID activity was seen in the Northern American sector. Also, in the Southern Hemisphere, the TEC variations were less affected by the geomagnetic storm. The Northern Hemisphere observations showed a strong and long‐lasting negative F region storm phase starting at about 1000 UT on 8 September (lasting for about 24 h). A perusal of TEC phase fluctuations and equatorial spread‐F (ESF) ionospheric sounding data indicates that, on the disturbed night of 7–8 September, some stations showed the occurrence of ESF starting at about 0000 UT (2000 LT) on 8 September, whereas other stations showed that the ESF occurrence started much later, at about 0800 UT (0500 LT). This hemispheric asymmetric response of the ionospheric F region possibly indicates the presence of different mechanisms for the generation of ESF along the various latitudinal regions during the disturbed period.
On the radiation budget in regional climate simulations for West Africa
Authors: Kothe S. , Ahrens B.
Published: December 2010

This paper discusses the simulated monthly radiation budget of West Africa by eight regional climate models and the impact of three uncertainty sources in the simulations: cloud fraction, surface albedo, and surface temperature. The models were driven by the European Centre for Medium‐Range Weather Forecasts ERA‐Interim reanalysis data within the European Union project ENSEMBLES. The simulated budgets were compared to the satellite‐based Global Energy and Water Cycle Experiment Surface Radiation Budget and ERA‐Interim data sets. The simulations tended to underestimate the net solar radiation and the outgoing long‐wave radiation, and they showed a regionally varying over‐ or underestimation in all budget components (up to 75%). The evaluation showed that uncertainty in the cloud fraction is the most important of the uncertainty sources over the ocean (with explained error variances between 25% and 60% depending on the budget component averaged over all models). Over land, the surface albedo and surface temperature were, on average, of similar importance as the cloud fraction. The latter result differed from that in a recent study for Europe, indicating that the importance of land surface on the radiation budget is regionally dependent. The relatively simple factor of surface albedo still explains a substantial part of the solar budget error variance in this study: more than 10% over ocean and more than 20% over land, peaking to more than 60% over the Sahelian and Saharan areas. It is worth improving on that in the models, in view of the complexity of other factors like cloud inhomogeneity and direct and indirect aerosol effects.
Highly nonlinear ozone formation in the Houston region and implications for emission controls
Authors: Xiao Xue , Cohan Daniel S. , Byun Daewon W. , Ngan Fong
Published: December 2010

Photochemical modeling with high‐order sensitivity analysis is applied to simulate the nonlinear responses of ozone to NOx and VOC emissions from different source regions in the Houston‐Galveston‐Brazoria area and their interactions. First‐order responses of daytime ozone to Houston NOx emissions are typically positive but are negative in the core region, indicating a NOx‐inhibited chemical regime there. Houston anthropogenic VOC emissions exert a spatially smaller impact on ozone but are important to high ozone concentrations in the core region. Highest ozone concentrations in the Houston region typically occur where the impacts of the Houston Ship Channel NOx emissions coincide with those of NOx emitted from the rest of the Houston region. Daytime ozone is found to exhibit a more nonlinear responsiveness to precursor emissions in Houston than has been reported in other regions, including a strongly concave response to local NOx emissions and strong interactions between the impacts of NOx and VOC emissions changes. Due to this intense nonlinearity, moderate perturbations (10–30%) in either NOx or VOC emissions inventories could flip whether Houston ozone is modeled to be more responsive to VOC control or NOx control. Thus the accuracy of emission inventories could strongly influence predictions of ozone response to emission reductions.
Regional assessment of microphysical properties of marine boundary layer cloud using the PATMOS‐x dataset
Authors: Rausch John , Heidinger Andrew , Bennartz Ralf
Published: December 2010

Cloud droplet number concentration and geometrical thickness of marine boundary layer clouds are inferred from 25 years of National Oceanic and Atmospheric Administration's AVHRR Pathfinder Atmospheres‐Extended (PATMOS‐x) Level 2b retrievals of optical thickness and cloud droplet effective radius over the period 1982 through 2009. A novel approach to addressing nonphysical values of cloud droplet number concentration N owing to satellite orbital drift is applied by normalizing estimated droplet number concentrations with respect to local observation time. Cloud geometrical thickness H is also normalized to a common reference time by scaling H against diurnal values from a passive microwave liquid water path climatology. The effectiveness of the methods applied to correct N and H are evaluated. Both quantities are spatially and temporally characterized in several subtropical subsidence regions for likely drizzle‐free observations. Estimated liquid water path from PATMOS‐x is further validated against 20 years of liquid water path values from the Special Sensor Microwave/Imager (SSM/I). Good agreement between SSM/I and PATMOS‐x is found in coastal regions. Cloud droplet number concentrations in excess of 300 cm−3 are found along the western boundaries of the American and African continents, with greatly lower values found further out to sea with no observed long‐term trends in cloud properties.
Global spherical harmonic models of the internal magnetic field of the Moon based on sequential and coestimation approaches
Authors: Purucker Michael E. , Nicholas Joseph B.
Published: December 2010

Three new models of the global internal magnetic field of the Moon based on Lunar Prospector (LP) fluxgate magnetometer observations are developed for use in understanding the origin of the Moon's crustal magnetic field and for modeling its interaction with the solar wind. The models are at spherical harmonic degree 170, corresponding to 64 km wavelength resolution, from 30 km mean altitude LP observations. Coverage is complete except for a few areas near each pole. Original signal amplitudes are best preserved in the sequential approach map, whereas feature recognition is superior in the coestimation and harmonic wave number correlation maps. Spherical harmonic degrees less than 15, corresponding to 666 km wavelength, are largely absent from the Moon's internal magnetic field. We interpret this bound in terms of the Moon's impact history. A derived magnetization map suggests magnetizations may locally exceed 0.2 A/m in the lunar crust at the survey resolution if the magnetic crust is as thick as 40 km.
Composition of Titan's lower atmosphere and simple surface volatiles as measured by the Cassini‐Huygens probe gas chromatograph mass spectrometer experiment
Authors: Niemann H. B. , Atreya S. K. , Demick J. E. , Gautier D. , Haberman J. A. , Harpold D. N. , Kasprzak W. T. , Lunine J. I. , Owen T. C. , Raulin F.
Published: December 2010

The Cassini‐Huygens probe gas chromatograph mass spectrometer (GCMS) determined the composition of the Titan atmosphere from ∼140 km altitude to the surface. After landing, it returned composition data of gases evaporated from the surface. Height profiles of molecular nitrogen (N2), methane (CH4), and molecular hydrogen (H2) were determined. Traces were detected on the surface of evaporating methane, ethane (C2H6), acetylene (C2H2), cyanogen (C2N2), and carbon dioxide (CO2). The methane data showed evidence that methane precipitation occurred recently. The methane mole fraction was (1.48 ± 0.09) × 10−2 in the lower stratosphere (139.8–75.5 km) and (5.65 ± 0.18) × 10−2 near the surface (6.7 km to the surface). The molecular hydrogen mole fraction was (1.01 ± 0.16) × 10−3 in the atmosphere and (9.90 ± 0.17) × 10−4 on the surface. Isotope ratios were 167.7 ± 0.6 for 14N/15N in molecular nitrogen, 91.1 ± 1.4 for 12C/13C in methane, and (1.35 ± 0.30) × 10−4 for D/H in molecular hydrogen. The mole fractions of 36Ar and radiogenic 40Ar are (2.1 ± 0.8) × 10−7 and (3.39 ± 0.12) × 10−5, respectively. 22Ne has been tentatively identified at a mole fraction of (2.8 ± 2.1) × 10−7. Krypton and xenon were below the detection threshold of 1 × 10−8 mole fraction. Science data were not retrieved from the gas chromatograph subsystem as the abundance of the organic trace gases in the atmosphere and on the ground did not reach the detection threshold. Results previously published from the GCMS experiment are superseded by this publication.
Hydroclimatology of the 2008 Midwest floods
Authors: Budikova D. , Coleman J. S. M. , Strope S. A. , Austin A.
Published: December 2010

The late spring/early summer flooding that occurred in the American Midwest between May and June 2008 resulted from a combination of large‐scale atmospheric circulation patterns that supported a steady influx of moisture into the area. A low pressure system centered over the central‐western United States steered a strong jet and associated storms along its eastern edge from the west to southwest and an anomalously strong Great Plains Low Level Jet brought continuous warm and moist air into the area from the Gulf of Mexico into the area. We examine and quantify here the impact these circulation patterns had on the hydroclimatology of the Midwest highlighting the magnitude, frequency, geographic distribution, and temporal evolution of precipitation that ultimately magnified the flooding. Historical precipitation records were used to assess the regional rainfall characteristics at various geographic and time scales. Five distinct hydroclimatic characteristics contributed to the definition of the 2008 flood including persistent high surface soil moisture conditions prior to flooding exasperated by anomalously high rainfall, extreme rainfall totals covering extensive areas, increased frequency of shorter‐term, smaller‐magnitude events, persistent multiday heavy precipitation events, and extreme flood‐producing rain storms. The major flooding lasted for approximately 24 days and most greatly impacted the state of Iowa, southern Wisconsin, and central Indiana. Its occurrence during the May–June period makes the event especially unusual for this region.
The 2009 exceptional Amazon flood and interannual terrestrial water storage change observed by GRACE
Authors: Chen J. L. , Wilson C. R. , Tapley B. D.
Published: December 2010

The Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission provides a new capability for measuring extreme climate events, such as floods and droughts associated with large‐scale terrestrial water storage (TWS) change. GRACE gravity measurements show significant TWS increases in the lower Amazon basin in the first half of 2009, clearly associated with the exceptional flood season in that region. The extended record of GRACE monthly gravity solutions reveals the temporal and spatial evolution of both nonseasonal and interannual TWS change in the Amazon basin over the 7 year mission period from April 2002 to August 2009. GRACE observes a very dry season in 2002–2003 and an extremely wet season in 2009. In March 2009 (approximately the peak of the recent Amazon flood), total TWS surplus in the entire Amazon basin is ∼624 ± 32 Gt, roughly equal to U.S. water consumption for a year. GRACE measurements are consistent with precipitation data. Interannual TWS changes in the Amazon basin are closely connected to ENSO events in the tropical Pacific. The 2002–2003 dry season is clearly tied to the 2002–2003 El Niño and the 2009 flood to the recent La Niña event. The most significant contribution of this study in the area of water resources is to confront the hydrological community with the latest results of the GRACE satellite mission and further demonstrates the unique strength of GRACE and follow‐up satellite gravity observations for measuring large‐scale extreme climate events.
Screening for Obesity‐Related Complications Among Obese Children and Adolescents: 1999–2008
Authors: Benson Lacey J. , Baer Heather J. , Kaelber David C.
Published: December 2010

Obesity is becoming an increasingly prevalent problem among American children. Screening for obesity associated comorbid conditions has been shown to be inconsistent. The current study was undertaken to explore patterns of ordering screening tests among obese pediatric patients. We analyzed electronic medical records (EMR) from 69,901 patients ages 2–18 years between June 1999 and December 2008. Obese children who had documented diagnoses of obesity were identified based on International Classification of Diseases, Ninth Revision codes. Screening rates for glucose, liver, and lipid abnormalities were assessed. Regression analysis was used to examine impact of patient characteristics and temporal trends were analyzed. Of the 9,251 obese diagnosed patients identified, 22% were screened for all three included obesity‐related conditions: diabetes, liver, and lipid abnormalities; 52% were screened for glucose abnormalities; 30% for liver abnormalities; and 41% for lipid abnormalities. Increasing BMI and age were associated with increased rates of screening. Females and Hispanic patients were more likely to be screened. The majority of screening was ordered under “basic metabolic panel,” “hepatic function panel,” and “full lipid profile” for each respective condition. The percentages of patients screened generally increased over time, although the percentages screened for diabetes and lipid abnormalities seemed to plateau or decrease after 2004. Even after diagnosis, many obese patients are not receiving recommended laboratory screening tests. Screening increased during the study period, but remains less than ideal. Providers could improve care by more complete laboratory screening in patients diagnosed with obesity.
Predicting Treatment Initiation in a Family‐Based Adolescent Overweight and Obesity Intervention
Authors: Dhingra Akshay , Brennan Leah , Walkley Jeff
Published: December 2010

Little is known about factors associated with treatment initiation in overweight and obese adolescents. This study investigated parent‐reported adolescent demographic, adolescent health, and parent motivation factors associated with initiation of a family‐based adolescent overweight and obesity intervention. A telephone survey was completed by 349 parents calling to register their interest in participating in a cognitive behavioral lifestyle intervention for adolescent overweight and obesity. A total of 172 families (49.3%) returned their consent form to initiate treatment. A binomial logistic regression, with predictors entered in three blocks: (i) adolescent demographic (adolescent age, gender, adolescent BMI‐for‐age z‐score, parent BMI); (ii) adolescent health (perceived adolescent physical and mental health, presence of an adolescent physical health problem or mental health problem, medication intake); and (iii) parent motivation (perceived adolescent weight category, concern about adolescent weight, importance of adolescent weight, confidence in adolescent capacity to change weight, priority of adolescent weight loss, discrepancy between adolescent current and ideal weight, previous weight loss attempts), was significant (χ2 (16) = 35.19, P = 0.004) accounting for 12.4–16.5% (95% confidence interval) of treatment initiation variance. Parent‐reported adolescent physical health problem, parent perception of adolescent weight category, parent priority of adolescent weight loss, and parent perception of discrepancy between adolescent current and ideal weight were significant in the model. These findings indicate that data collected at intake are associated with treatment initiation and highlight the role of assessing and enhancing treatment motivation from initial contact.
Steepest descent reaction path integration using a first-order predictor–corrector method
Authors: Hratchian Hrant P. , Frisch Michael J. , Schlegel H. Bernhard
Published: December 2010

The theoretical treatment of chemical reactions inevitably includes the integration of reaction pathways. After reactant, transition structure, and product stationary points on the potential energy surface are located, steepest descent reaction path following provides a means for verifying reaction mechanisms. Accurately integrated paths are also needed when evaluating reaction rates using variational transition state theory or reaction path Hamiltonian models. In this work an Euler-based predictor–corrector integrator is presented and tested using one analytic model surface and five chemical reactions. The use of Hessian updating, as a means for reducing the overall computational cost of the reaction path calculation, is also discussed.
Terahertz electro-absorption effect enabling femtosecond all-optical switching in semiconductor quantum dots
Authors: Hoffmann M. C. , Monozon B. S. , Livshits D. , Rafailov E. U. , Turchinovich D.
Published: December 2010

We demonstrate an instantaneous all-optical manipulation of optical absorption in InGaAs/GaAs quantum dots (QDs) via an electro-absorption effect induced by the electric field of an incident free-space terahertz signal. A terahertz signal with the full bandwidth of 3 THz was directly encoded onto an optical signal probing the absorption in QDs, resulting in the encoded temporal features as fast as 460 fs. The instantaneous nature of this effect enables femtosecond all-optical switching at very high repetition rates, suggesting applications in terahertz-range wireless communication systems with data rates of at least 0.5 Tbit/s.
Energy decay of solutions to the Cauchy problem for a nondissipative wave equation
Authors: Benaissa Abbes , Benazzouz Sohbi
Published: December 2010

In this paper, we consider energy decay for nondissipative wave equation in unbounded domain (the usual energy is not decreasing). We use an approach introduced by Guesmia, which leads to decay estimates (known in the dissipative case) when the integral inequalities method by Komornik [Exact Controllability and Stabilization. The Multiplier Method. Masson–Wiley, Paris, 1994] cannot be applied due to the lack of dissipativity. First, we study the stability of a wave equation with a weak nonlinear dissipative term based on the equation: \documentclass[12pt]{minimal}\begin{document}$u^{\prime \prime }-\Delta _{x}u+\lambda ^{2}(x) u+\sigma (t) g(u^{\prime })+ \theta (t)h(\nabla _{x} u)=0$\end{document}u′′−Δxu+λ2(x)u+σ(t)g(u′)+θ(t)h(∇xu)=0 in \documentclass[12pt]{minimal}\begin{document}${\mathchoice{\bf \hbox{$\displaystyle \rm I \hspace{-1.5pt}\rm R$}}{\bf \hbox{$\textstyle {\rm I} \hspace{-1.5pt}\rm R$}}{\bf \hbox{$\scriptstyle \rm I\hspace{-1.0pt}\rm R$}}{\bf \hbox{$\scriptscriptstyle \rm I \hspace{-1.0pt}\rm R$}}}^{n}$\end{document}IRn. We consider the general case with a function h satisfying a smallness condition, and we obtain decay of solutions under weak growth assumptions on the feedback function and without any control of the sign of the derivative of the energy related to the above equation. In the second case, we consider the case h(∇u) = −∇Φ∇u. We prove some precise decay estimates of equivalent energy.
Atomic scale studies of spall behavior in nanocrystalline Cu
Authors: Dongare Avinash M. , Rajendran Arunachalam M. , LaMattina Bruce , Zikry Mohammed A. , Brenner Donald W.
Published: December 2010

The micromechanisms related to ductile failure during dynamic loading of nanocrystalline Cu are investigated in a series of large-scale molecular dynamics simulations. Void nucleation, growth, and coalescence is studied for a nanocrystalline Cu system with an average grain size of 6 nm under conditions of impact of a shock piston with velocities of 250, 500, 750, and 1000 m/s and compared to that observed in single crystal copper. Higher impact velocities result in higher strain rates and higher values of spall strengths for the metal as well as nucleation of larger number of voids in smaller times. For the same impact velocity, the spall strength of the nanocrystalline metal, however, is lower than that for single crystal copper. The results obtained for void nucleation and growth in nanocrystalline Cu for various impact velocities and for single crystal copper [001] suggests two distinct stages of evolution of voids. The first stage (I) corresponds to the fast nucleation of voids followed by the second stage (II) attributed to growth and coalescence of voids. The first stage is found to be dependent on the microstructure of the system as well as the shock pressure/strain rate, whereas, the second stage of void growth is independent of the strain rate and microstructure of the system and dependent only on the number of voids nucleated.