Showing papers by "University of Maryland, Baltimore County published in 2002"

Environmental characterization of global sources of atmospheric soil dust identified with the nimbus 7 total ozone mapping spectrometer (toms) absorbing aerosol product

Abstract: [1] We use the Total Ozone Mapping Spectrometer (TOMS) sensor on the Nimbus 7 satellite to map the global distribution of major atmospheric dust sources with the goal of identifying common environmental characteristics The largest and most persistent sources are located in the Northern Hemisphere, mainly in a broad “dust belt” that extends from the west coast of North Africa, over the Middle East, Central and South Asia, to China There is remarkably little large-scale dust activity outside this region In particular, the Southern Hemisphere is devoid of major dust activity Dust sources, regardless of size or strength, can usually be associated with topographical lows located in arid regions with annual rainfall under 200–250 mm Although the source regions themselves are arid or hyperarid, the action of water is evident from the presence of ephemeral streams, rivers, lakes, and playas Most major sources have been intermittently flooded through the Quaternary as evidenced by deep alluvial deposits Many sources are associated with areas where human impacts are well documented, eg, the Caspian and Aral Seas, Tigris-Euphrates River Basin, southwestern North America, and the loess lands in China Nonetheless, the largest and most active sources are located in truly remote areas where there is little or no human activity Thus, on a global scale, dust mobilization appears to be dominated by natural sources Dust activity is extremely sensitive to many environmental parameters The identification of major sources will enable us to focus on critical regions and to characterize emission rates in response to environmental conditions With such knowledge we will be better able to improve global dust models and to assess the effects of climate change on emissions in the future It will also facilitate the interpretation of the paleoclimate record based on dust contained in ocean sediments and ice cores

Variability of Absorption and Optical Properties of Key Aerosol Types Observed in Worldwide Locations

Abstract: Aerosol radiative forcing is a critical, though variable and uncertain, component of the global climate. Yet climate models rely on sparse information of the aerosol optical properties. In situ measurements, though important in many respects, seldom provide measurements of the undisturbed aerosol in the entire atmospheric column. Here, 8 yr of worldwide distributed data from the AERONET network of ground-based radiometers were used to remotely sense the aerosol absorption and other optical properties in several key locations. Established procedures for maintaining and calibrating the global network of radiometers, cloud screening, and inversion techniques allow for a consistent retrieval of the optical properties of aerosol in locations with varying emission sources and conditions. The multiyear, multi-instrument observations show robust differentiation in both the magnitude and spectral dependence of the absorption—a property driving aerosol climate forcing, for desert dust, biomass burning, urban‐industrial, and marine aerosols. Moreover, significant variability of the absorption for the same aerosol type appearing due to different meteorological and source characteristics as well as different emission characteristics are observed. It is expected that this aerosol characterization will help refine aerosol optical models and reduce uncertainties in satellite observations of the global aerosol and in modeling aerosol impacts on climate.

The human-computer interaction handbook: fundamentals, evolving technologies and emerging applications

Abstract: Foreword by Ben Shneiderman Introduction: A Moving Target: The Evolution of Human-Computer Interaction, Jonathan Grudin Humans in HCI Perceptual-Motor Interaction: Some Implications for Human-Computer Interaction, Timothy N. Welsh, Sanjay Chandrasekharan, Matthew Ray, Heather Neyedli, Romeo Chua, and Daniel J. Weeks Human Information Processing: An Overview for Human-Computer Interaction, Robert W. Proctor and Kim-Phuong L. Vu Mental Models in Human-Computer Interaction, Stephen J. Payne Task Loading and Stress in Human-Computer Interaction: Theoretical Frameworks and Mitigation Strategies, James L. Szalma, Gabriella M. Hancock, and Peter A. Hancock Choices and Decisions of Computer Users, Anthony Jameson Computers in HCI Input Technologies and Techniques, Ken Hinckley and Daniel Wigdor Sensor- and Recognition-Based Input for Interaction, Andrew D. Wilson Visual Displays, Christopher M. Schlick, Carsten Winkelholz, Martina Ziefle, and Alexander Mertens Haptic Interface, Hiroo Iwata Nonspeech Auditory and Crossmodal Output, Eve Hoggan and Stephen Brewster Network-Based Interaction, Alan Dix Wearable Computers, Daniel Siewiorek, Asim Smailagic, and Thad Starner Design of Fixed, Portable, and Mobile Information Devices, Michael J. Smith and Pascale Carayon Designing Human-Computer Interactions Visual Design Principles for Usable Interfaces: Everything Is Designed: Why We Should Think before Doing, Suzanne Watzman and Margaret Re Globalization, Localization, and Cross-Cultural User-Interface Design, Aaron Marcus and Emilie W. Gould Speech and Language Interfaces, Applications, and Technologies, Clare-Marie Karat, Jennifer Lai, Osamuyimen Stewart, and Nicole Yankelovich Multimedia User Interface Design, Alistair Sutcliffe Multimodal Interfaces, Sharon Oviatt Systems That Adapt to Their Users, Anthony Jameson and Krzysztof Z. Gajos Mobile Interaction Design in the Age of Experience Ecosystems, Marco Susani Tangible User Interfaces, Hiroshi Ishii and Brygg Ullmer Achieving Psychological Simplicity: Measures and Methods to Reduce Cognitive Complexity, John C. Thomas and John T. Richards Information Visualization, Stuart Card Collaboration Technologies, Gary M. Olson and Judith S. Olson Human-Computer Interaction and the Web, Helen Ashman, Declan Dagger, Tim Brailsford, James Goulding, Declan O'Sullivan, Jan-Felix Schmakeit, and Vincent Wade Human-Centered Design of Decision-Support Systems, Philip J. Smith, Roger Beatty, Caroline C. Hayes, Adam Larson, Norman D. Geddes, and Michael C. Dorneich Online Communities, Panayiotis Zaphiris, Chee Siang Ang, and Andrew Laghos Virtual Environments, Kay M. Stanney and Joseph V. Cohn Privacy, Security, and Trust: Human-Computer Interaction Challenges and Opportunities at Their Intersection, John Karat, Clare-Marie Karat, and Carolyn Brodie Application-/Domain-Specific Design Human-Computer Interaction in Health Care, Francois Sainfort, Julie A. Jacko, Molly A. McClellan, and Paula J. Edwards Why We Play: Affect and the Fun of Games-Designing Emotions for Games, Entertainment Interfaces, and Interactive Products, Nicole Lazzaro Motor Vehicle-Driver Interfaces, Paul A. Green Human-Computer Interaction in Aerospace, Steven J. Landry User-Centered Design in Games Randy J. Pagulayan, Kevin Keeker, Thomas Fuller, Dennis Wixon, Ramon L. Romero, and Daniel V. Gunn Designing for Diversity Older Adults and Information Technology: Opportunities and Challenges, Sara J. Czaja, and Chin Chin Lee Human-Computer Interaction for Kids, Amy Bruckman, Alisa Bandlow, Jill Dimond, and Andrea Forte Information Technology for Communication and Cognitive Support, Alan F. Newell, Alex Carmichael, Peter Gregor, Norman Alm, Annalu Waller, Vicki L. Hanson, Graham Pullin, and Jesse Hoey Perceptual Impairments: New Advancements Promoting Technological Access, Julie A. Jacko, V. Kathlene Leonard, Molly A. McClellan, and Ingrid U. Scott Universal Accessibility and Low-Literacy Populations: Implications for Human-Computer Interaction Design and Research Methods, William M. Gribbons Computing Technologies for Deaf and Hard of Hearing Users, Vicki L. Hanson The Development Process Section A Requirements Specification User Experience Requirements Analysis within the Usability Engineering Lifecycle, Deborah J. Mayhew and Todd J. Follansbee Task Analysis, Catherine Courage, Jhilmil Jain, Janice (Ginny) Redish, and Dennis Wixon Contextual Design, Karen Holtzblatt Grounded Theory Method in Human-Computer Interaction and Computer-Supported Cooperative Work, Michael J. Muller and Sandra Kogan An Ethnographic Approach to Design, Jeanette Blomberg and Mark Burrell Section B Design and Development Putting Personas to Work: Employing User Personas to Focus Product Planning, Design, and Development, John Pruitt and Tamara Adlin Prototyping Tools and Techniques, Michel Beaudouin-Lafon and Wendy E. Mackay Scenario-Based Design, Mary Beth Rosson and John M. Carroll Participatory Design: The Third Space in Human-Computer Interaction, Michael J. Muller and Allison Druin Unified User Interface Development: A Software Refactoring Perspective, Anthony Savidis and Constantine Stephanidis Usability + Persuasiveness + Graphic Design = eCommerce User Experience, Deborah J. Mayhew Human-Computer Interaction and Software Engineering for User Interface Plasticity, Joelle Coutaz and Gaelle Calvary Section C Testing, Evaluation, and Technology Transfer Usability Testing, Joseph S. Dumas and Jean E. Fox Usability for Engaged Users: The Naturalistic Approach to Evaluation, David Siegel Survey Design and Implementation in HCI, A. Ant Ozok Inspection-Based Evaluations, Gilbert Cockton, Alan Woolrych, Kasper Hornbaek, and Erik Frokjaer Model-Based Evaluation, David Kieras Spreadsheet Tool for Simple Cost-Benefit Analyses of User Experience Engineering, Deborah J. Mayhew Technology Transfer, Kevin M. Schofield Emerging Phenomena in HCI Augmenting Cognition in HCI: Twenty-First Century Adaptive System Science and Technology, Kelly S. Hale, Kay M. Stanney, and Dylan D. Schmorrow Social Networks and Social Media, Molly A. McClellan, Julie A. Jacko, Francois Sainfort, and Layne M. Johnson Human-Computer Interaction for Development: Changing Human-Computer Interaction to Change the World, Susan M. Dray, Ann Light, Andrew M. Dearden, Vanessa Evers, Melissa Densmore, Divya Ramachandran, Matthew Kam, Gary Marsden, Nithya Sambasivan, Thomas Smyth, Darelle van Greunen, and Niall Winters Author Index Subject Index

Tropospheric Aerosol Optical Thickness from the GOCART Model and Comparisons with Satellite and Sun Photometer Measurements

Abstract: The Georgia Institute of Technology‐Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model is used to simulate the aerosol optical thickness t for major types of tropospheric aerosols including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt The GOCART model uses a dust emission algorithm that quantifies the dust source as a function of the degree of topographic depression, and a biomass burning emission source that includes seasonal and interannual variability based on satellite observations Results presented here show that on global average, dust aerosol has the highest t at 500 nm (0051), followed by sulfate (0040), sea salt (0027), OC (0017), and BC (0007) There are large geographical and seasonal variations of t, controlled mainly by emission, transport, and hygroscopic properties of aerosols The model calculated total ts at 500 nm have been compared with the satellite retrieval products from the Total Ozone Mapping Spectrometer (TOMS) over both land and ocean and from the Advanced Very High Resolution Radiometer (AVHRR) over the ocean The model reproduces most of the prominent features in the satellite data, with an overall agreement within a factor of 2 over the aerosol source areas and outflow regions While there are clear differences among the satellite products, a major discrepancy between the model and the satellite data is that the model shows a stronger variation of t from source to remote regions Quantitative comparison of model and satellite data is still difficult, due to the large uncertainties involved in deriving the t values by both the model and satellite retrieval, and by the inconsistency in physical and optical parameters used between the model and the satellite retrieval The comparison of monthly averaged model results with the sun photometer network [Aerosol Robotics Network (AERONET)] measurements shows that the model reproduces the seasonal variations at most of the sites, especially the places where biomass burning or dust aerosol dominates

Is the Growth of Small Firms Constrained by Internal Finance

Abstract: This paper examines the long-standing theory that the growth of small firms is often constrained by the quantity of internal finance. Under plausible assumptions, when financing constraints are binding, an additional dollar of internal finance should generate slightly more than an additional dollar of growth in assets. This quantitative prediction should not hold for the relatively small number of firms which access external equity. We test these predictions with a panel of more than 1, 600 small firms and find that the growth of most firms is constrained by internal finance. Our results have implications for several different research literatures, including models of firm growth.

Capital market imperfections, high-tech investment, and new equity financing

Abstract: Highly variable returns, asymmetric information and a lack of collateral should cause small high-tech firms to have poor access to debt. New equity financing has several advantages over debt, but may be costly compared to internal finance. We examine an unbalanced panel of over 2,400 publicly traded US high-tech companies over the period 1981–98. Most small high-tech firms obtain little debt financing. New equity financing, in the form of the initial public offering, is very important and permits a major increase in firm size. After going public, comparatively few firms make heavy use of external finacing.

Binge drinking trajectories from adolescence to emerging adulthood in a high-risk sample: predictors and substance abuse outcomes.

Abstract: This study describes binge drinking trajectories from adolescence to emerging adulthood in 238 children of alcoholics and 208 controls. Mixture modeling identified three trajectory groups: early-heavy (early onset, high frequency), late-moderate (later onset, moderate frequency), and infrequent (early onset, low frequency). Nonbingers were defined a priori. The early-heavy group was characterized by parental alcoholism and antisociality, peer drinking, drug use, and (for boys) high levels of externalizing behavior, but low depression. The infrequent group was elevated in parent alcoholism and (for girls) adolescent depression, whereas the nonbinger and late-moderate groups showed the most favorable adolescent psychosocial variables. All 3 drinking trajectory groups raised risk for later substance abuse or dependence compared with the nonbingers, with the early-heavy group at highest risk.

Texturing and Modeling: A Procedural Approach

Abstract: From the Publisher: This the classic text/tutorial/reference introducing and defining the procedural approach to texturing and modeling and computer graphics in general. This Second Edition is completely revised and updated to the current computer graphics marketplace. It contains a toolbox of procedures upon which programmers can build a library of textures and objects, and includes extensive explanations of how these functions work and how to design new functions. New chapters include: Cellular Texture Generation, Volumetric Cloud Modeling with Implicit Functions, Interacting with Virtual Actors, and Rendering with Adaptive Level of Detail.

A Long-Term Record of Aerosol Optical Depth from TOMS Observations and Comparison to AERONET Measurements

Abstract: Observations of backscattered near-ultraviolet radiation from the Total Ozone Mapping Spectrometer (TOMS) on board the Nimbus-7 (1979‐92) and the Earth Probe (mid-1996 to present) satellites have been used to derive a long-term record of aerosol optical depth over oceans and continents. The retrieval technique applied to the TOMS data makes use of two unique advantages of near-UV remote sensing not available in the visible or nearIR: 1) low reflectivity of all land surface types (including the normally bright deserts in the visible), which makes possible aerosol retrieval over the continents; and 2) large sensitivity to aerosol types that absorb in the UV, allowing the clear separation of carbonaceous and mineral aerosols from purely scattering particles such as sulfate and sea salt aerosols. The near-UV method of aerosol characterization is validated by comparison with Aerosol Robotic Network (AERONET) ground-based observations. TOMS retrievals of aerosol optical depth over land areas (1996‐2000) are shown to agree reasonably well with AERONET sun photometer observations for a variety of environments characterized by different aerosol types, such as carbonaceous aerosols from biomass burning, desert dust aerosols, and sulfate aerosols. In most cases the TOMS-derived optical depths of UV-absorbing aerosols are within 30% of the AERONET observations, while nonabsorbing optical depths agree to within 20%. The results presented here constitute the first long-term nearly global climatology of aerosol optical depth over both land and water surfaces, extending the observations of aerosol optical depth to regions and times (1979 to present) not accessible to ground-based observations.

X-Ray spectral variability and rapid variability of the soft X-ray spectrum Seyfert 1 galaxies Arakelian 564 and Ton S180

Abstract: The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were monitored for 35 days and 12 days, respectively, with ASCA and RXTE (and EUVE for Ton S180). These represent the most intensive X-ray monitoring of any such soft-spectrum Seyfert 1 to date. Light curves were constructed for Ton S180 in six bands spanning 0.1-10 keV and for Ark 564 in five bands spanning 0.7-10 keV. The short-timescale (hours-days) variability patterns were very similar across energy bands, with no evidence of lags between any of the energy bands studied. The fractional variability amplitude was almost independent of energy band, unlike hard-spectrum Seyfert 1 galaxies, which show stronger variations in the softer bands. It is difficult to simultaneously explain soft Seyfert galaxies stronger variability, softer spectra, and weaker energy dependence of the variability relative to hard Seyfert galaxies. There was a trend for soft- and hard-band light curves of both objects to diverge on the longest timescales probed (~weeks), with the hardness ratio showing a secular change throughout the observations. This is consistent with the fluctuation power density spectra that showed relatively greater power on long timescales in the softest bands. The simplest explanation of all of these is that two continuum emission components are visible in the X-rays: a relatively hard, rapidly variable component that dominates the total spectrum and a slowly variable soft excess that only shows up in the lowest energy channels of ASCA. Although it would be natural to identify the latter component with an accretion disk and the former with a corona surrounding it, a standard thin disk could not get hot enough to radiate significantly in the ASCA band, and the observed variability timescales are much too short. It also appears that the hard component may have a more complex shape than a pure power law. The most rapid factor of 2 flares and dips occurred within ~1000 s, in Ark 564 and a bit more slowly in Ton S180. The speed of the luminosity changes rules out viscous or thermal processes and limits the size of the individual emission regions to 15 Schwarzschild radii (and probably much less), that is, to either the inner disk or small regions in a corona.

Validation of MODIS aerosol retrieval over ocean

Abstract: The MODerate resolution Imaging Spectroradiometer (MODIS) algorithm for determining aerosol characteristics over ocean is performing with remarkable accuracy. A two-month data set of MODIS retrievals co-located with observations from the AErosol RObotic NETwork (AERONET) ground-based sunphotometer network provides the necessary validation. Spectral radiation measured by MODIS (in the range 550 - 2100 nm) is used to retrieve the aerosol optical thickness, effective particle radius and ratio between the submicron and micron size particles. MODIS-retrieved aerosol optical thickness at 660 nm and 870 nm fall within the expected uncertainty, with the ensemble average at 660 nm differing by only 2% from the AERONET observations and having virtually no offset. MODIS retrievals of aerosol effective radius agree with AERONET retrievals to within +/- 0.10 micrometers, while MODIS-derived ratios between large and small mode aerosol show definite correlation with ratios derived from AERONET data.

Extended versus Ensemble Kalman Filtering for Land Data Assimilation

Abstract: The performance of the extended Kalman filter (EKF) and the ensemble Kalman filter (EnKF) are assessed for soil moisture estimation. In a twin experiment for the southeastern United States synthetic observations of near-surface soil moisture are assimilated once every 3 days, neglecting horizontal error correlations and treating catchments independently. Both filters provide satisfactory estimates of soil moisture. The average actual estimation error in volumetric moisture content of the soil profile is 2.2% for the EKF and 2.2% (or 2.1%; or 2.0%) for the EnKF with 4 (or 10; or 500) ensemble members. Expected error covariances of both filters generally differ from actual estimation errors. Nevertheless, nonlinearities in soil processes are treated adequately by both filters. In the application presented herein the EKF and the EnKF with four ensemble members are equally accurate at comparable computational cost. Because of its flexibility and its performance in this study, the EnKF is a promising ...

Non‐spherical aerosol retrieval method employing light scattering by spheroids

Abstract: Received 4 December 2001; revised 5 February 2002; accepted 8 February 2002; published 24 May 2002. [1] Numerous studies indicate the need to account for particle non-sphericity in modeling the optical properties of dustlike aerosols. The methods for simulating the scattering of light by various non-spherical shapes have rapidly evolved over the last two decades. However, the majority of aerosol remote-sensing retrievals still rely on the Mie theory because retrievals accounting for particle non-sphericity are not as well defined methodologically and are demanding computationally. We propose a method for the retrieval of the optical properties of non-spherical aerosol based on the model of a shape mixture of randomly oriented polydisperse spheroids. This method is applied to angular and spectral radiation measurements from the Aerosol Robotic Network (AERONET) in locations influenced by desert dust. Comparisons with Mie-based retrievals show a significant improvement in dust-particle phase functions, size distributions, and refractive indices. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0933 Exploration Geophysics: Remote sensing; 0994 Exploration Geophysics: Instruments and techniques

Optical Properties of Atmospheric Aerosol in Maritime Environments

Abstract: Systematic characterization of aerosol over the oceans is needed to understand the aerosol effect on climate and on transport of pollutants between continents. Reported are the results of a comprehensive optical and physical characterization of ambient aerosol in five key island locations of the Aerosol Robotic Network (AERONET) of sun and sky radiometers, spanning over 2‐5 yr. The results are compared with aerosol optical depths and size distributions reported in the literature over the last 30 yr. Aerosol found over the tropical Pacific Ocean (at three sites between 208S and 208N) still resembles mostly clean background conditions dominated by maritime aerosol. The optical thickness is remarkably stable with mean value of ta(500 nm) 5 0.07, mode value at tam

The ionized gas and nuclear environment in NGC 3783. I. Time-averaged 900 kilosecond Chandra grating spectroscopy

Abstract: We present results from a 900 ks exposure of NGC 3783 with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The resulting X-ray spectrum, which covers the 0.5-10 keV energy range, has the best combination of signal-to-noise ratio and resolution ever obtained for an AGN. This spectrum reveals absorption lines from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also possible absorption lines from H-like and He-like Ar and Ca as well as H-like C. We also identify inner-shell absorption from lower ionization ions such as Si VII-Si XII and S XII-S XIV. The iron absorption spectrum is very rich; L-shell lines of Fe XVII-Fe XXIV are detected, as well as probable resonance lines from Fe XXV. A strong complex of M-shell lines from iron ions is also detected in the spectrum. The absorption lines are blueshifted relative to the systemic velocity by a mean velocity of -590 ± 150 km s-1. We resolve many of the absorption lines, and their mean FWHM is 820 ± 280 km s-1. We do not find correlations between the velocity shifts or the FWHMs with the ionization potentials of the ions. Most absorption lines show asymmetry, having more extended blue wings than red wings. In O VII we have resolved this asymmetry to be from an additional absorption system at approximately -1300 km s-1. The two X-ray absorption systems are consistent in velocity shift and FWHM with the ones identified in the UV lines of C IV, N V, and H I. Equivalent width measurements for all absorption and emission lines are given and column densities are calculated for several ions. We resolve the narrow Fe Kα line at 6398.2 ± 3.3 eV to have an FWHM of 1720 ± 360 km s-1, which suggests that this narrow line may be emitted from the outer part of the broad-line region or the inner part of the torus. We also detect a "Compton shoulder" redward of the narrow Fe Kα line, which indicates that it arises in cold, Compton-thick gas.

Alternative Measures of Competitive Balance in Sports Leagues

Abstract: The most commonly used measures of competitive balance in sports leagues do not cap- ture season-to-season changes in relative standings. This article describes an alternative measure of competitive balance, the Competitive Balance Ratio (CBR), that reflects team- specific variation in winning percentage over time and league-specific variation. Based on estimation of a model of the determination of annual attendance in professional base- ball during the past 100 years, variation in the CBR explains more of the observed varia- tion in attendance than other alternatives measures of competitive balance, suggesting that CBR is a useful metric. Competitive balance is thought to be an important determinant of demand for sporting events. Competitive balance reflects uncertainty about the outcomes of professional sporting events. The conventional wisdom holds that to induce fans to purchase tickets to a game or tune in to a broadcast, there must be some uncertainty regarding the outcome. Neale (1964) called this the League Standing Effect. If a league lacks competitive balance, fan interest in the weaker teams will fall and, eventually, fan interest in the stronger teams will also decline. Thus, greater com- petitive balance should lead to greater demand, other things held equal. Quirk and Fort (1997) attribute the demise of the All American Football Conference, which started play in 1946 and merged with the National Football Conference in late 1949, to a lack of competitive balance. One commonly used measure of competitive balance is the dispersion of win- ning percentage within sports leagues. This measure of competitive balance has been used extensively by Scully (1989), Quirk and Fort (1997), and others to assess the performance of teams in sports leagues. Formally, this measure of competitive balance uses the standard deviation of winning percentage (WPCT), defined as the ratio of wins to total games played, as a measure of competitive balance. Consider a

MODIS Cloud screening for remote sensing of aerosols over oceans using spatial variability

Abstract: ] A cloud masking algorithm based on the spatial variability ofreflectances at the top of the atmosphere in visible wavelengths wasdeveloped for the retrieval of aerosol properties by MODIS. It isshown that the spatial pattern of cloud reflectance as observed fromspace, is very different from that of aerosols. Clouds show a veryhigh spatial variability in the scale of hundred meters to fewkilometers, whereas aerosols in general are very homogeneous. Theconcept of spatial variability of reflectances at the top of theatmosphere is mainly applicable over the ocean where the surfacebackground is sufficiently homogeneous for the separation betweenaerosols and clouds. Aerosol retrievals require a particular cloudmasking approach since a conservative mask will screen out strongaerosol episodes and a less conservative mask could allow forcloud contamination that tremendously affect the retrieved aerosoloptical properties (e.g. aerosol optical depth and effective radii). Adetailed study on the effect of cloud contamination on aerosolretrievals is performed and parameters are established determiningthe threshold value for the MODIS aerosol cloud mask (3X3-STD)over the ocean. The 3X3-STD algorithm discussed in this paper isthe operational cloud mask used for MODIS aerosol retrievals overthe ocean. I

Beginning Readers' Motivation for Reading in Relation to Parental Beliefs and Home Reading Experiences.

Abstract: Sixty-five 6-year-olds (first graders) from different sociocultural backgrounds and their mothers participated in a study examining children's motivation for reading in relation to parental beliefs and home literacy experiences. Each child completed an individually administered Motivations for Reading Scale that assessed several theoretical dimensions of reading motivation, including enjoyment/interest in reading, perceived competence as a reader, and sense of the value of reading. Parents were interviewed regarding their beliefs about reasons for reading, their beliefs about their child's interest in learning to read, and their ratings of the frequency of their child's experiences with printed materials. Results revealed that the beginning readers had generally positive views about reading and that no differences in motivation were associated with income level, ethnicity, or gender. Empirical support was provided for the distinctness of the dimensions of value, enjoyment, and perceived competence. Parent...

Online communities: focusing on sociability and usability

Abstract: 1 Background Millions of people meet online to chat, to find like-minded people, to debate topical issues, to play games, to give or ask for information, to find support, to shop, or just to hang-out with others. They go to chat-rooms, bulletin boards, join discussion groups or they create their group using instant messaging software. Short messaging (also known as ‘texting’) is also gaining popularity in some parts of the world. These online social gatherings are known by a variety of names including ‘online community’, a name coined by early pioneers like Howard Rheingold, who describes these online communities as ‘cultural aggregations that emerge when enough people bump into each other often enough in cyberspace’ (Rheingold, 1994, p. 57). 1.1 The scope of this chapter There is no accepted definition of online community. The term means different things to different people (Preece, 2000) so this chapter starts by examining definitions and descriptions of online community from different disciplines, and briefly traces how the topic has emerged. Section 2 outlines research from social psychology, sociology, communications studies, computer-supported cooperative work (CSCW) and human-computer interaction (HCI) that informs our understanding of why people interact they way they do in online communities. Section 3 brings many of these ideas together in the context of design and evaluation of online communities, outlines a design methodology and proposes a frame work for supporting social interaction (i.e., sociability) and designing usability. Section 4 returns to research and briefly reviews

Energy-Aware TDMA-Based MAC for Sensor Networks

Abstract: Networking unattended sensors is expected to have a significant impact on the efficiency of many military and civil applications. Sensors in such systems are typically disposable and expected to last until their energy drains. Therefore, energy is a very scarce resource for such sensor systems and has to be managed wisely in order to extend the life of the sensors for the duration of a particular mission. In this chapter, we present a novel approach for energy-aware management of sensor networks that maximizes the lifetime of the sensors while maintaining desired quality of service attributes related to sensed data delivery. The approach is to dynamically set routes and arbitrate medium access to minimize energy consumption and maximize sensor life. We give a brief overview of the energy-aware routing and a description of a Time-Division-Multiple-Access (TDMA) -based Medium AccessControl (MAC) protocol. We discuss algorithms for assigning time slots for the communicating sensor nodes. The approach is evaluated through simulation. Simulation results have confirmed the effectiveness of our new approach.

Different activation dynamics in multiple neural systems during simulated driving.

Abstract: Driving is a complex behavior that recruits multiple cognitive elements. We report on an imaging study of simulated driving that reveals multiple neural systems, each of which have different activation dynamics. The neural correlates of driving behavior are identified with fMRI and their modulation with speed is investigated. We decompose the activation into interpretable pieces using a novel, generally applicable approach, based upon independent component analysis. Some regions turn on or off, others exhibit a gradual decay, and yet others turn on transiently when starting or stopping driving. Signal in the anterior cingulate cortex, an area often associated with error monitoring and inhibition, decreases exponentially with a rate proportional to driving speed, whereas decreases in frontoparietal regions, implicated in vigilance, correlate with speed. Increases in cerebellar and occipital areas, presumably related to complex visuomotor integration, are activated during driving but not associated with driving speed.

Space-based measurements of stratospheric mountain waves by CRISTA 1. Sensitivity, analysis method, and a case study

Abstract: [1] The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured stratospheric temperatures and trace species concentrations with high precision and spatial resolution during two missions. The measuring technique is infrared limb-sounding of optically thin emissions. In a general approach, we investigate the applicability of the technique to measure gravity waves (GWs) in the retrieved temperature data. It is shown that GWs with wavelengths of the order of 100–200 km horizontally can be detected. The results are applicable to any instrument using the same technique. We discuss additional constraints inherent to the CRISTA instrument. The vertical field of view and the influence of the sampling and retrieval imply that waves with vertical wavelengths ∼3–5 km or larger can be retrieved. Global distributions of GW fluctuations were extracted from temperature data measured by CRISTA using Maximum Entropy Method (MEM) and Harmonic Analysis (HA), yielding height profiles of vertical wavelength and peak amplitude for fluctuations in each scanned profile. The method is discussed and compared to Fourier transform analyses and standard deviations. Analysis of data from the first mission reveals large GW amplitudes in the stratosphere over southernmost South America. These waves obey the dispersion relation for linear two-dimensional mountain waves (MWs). The horizontal structure on 6 November 1994 is compared to temperature fields calculated by the Pennsylvania State University (PSU)/National Center for Atmospheric Research (NCAR) mesoscale model (MM5). It is demonstrated that precise knowledge of the instrument's sensitivity is essential. Particularly good agreement is found at the southern tip of South America where the MM5 accurately reproduces the amplitudes and phases of a large-scale wave with 400 km horizontal wavelength. Targeted ray-tracing simulations allow us to interpret some of the observed wave features. A companion paper will discuss MWs on a global scale and estimates the fraction that MWs contribute to the total GW energy (Preusse et al., in preparation, 2002).

A High-Resolution X-Ray Image of the Jet in M87

Abstract: We present the first high-resolution X-ray image of the jet in M87 using the Chandra X-Ray Observatory. There is clear structure in the jet and almost all of the optically bright knots are detected individually. The unresolved core is the brightest X-ray feature but is only 2-3 times brighter than knot A (123 from the core) and the inner knot HST-1 (10 from the core). The X-ray and optical positions of the knots are consistent at the 01 level, but the X-ray emission from the brightest knot (A) is marginally upstream of the optical emission peak. Detailed Gaussian fits to the X-ray jet one-dimensional profile show distinct X-ray emission that is not associated with specific optical features. The X-ray/optical flux ratio decreases systematically from the core, and X-ray emission is not clearly detected beyond 20'' from the core. The X-ray spectra of the core and the two brightest knots, HST-1 and A, are consistent with a simple power law (Sν ∝ ν-α) with α = 1.46 ± 0.05, practically ruling out inverse Compton models as the dominant X-ray emission mechanism. The core flux is significantly larger than expected from an advective accretion flow, and the spectrum is much steeper, indicating that the core emission may be due to synchrotron emission from a small-scale jet. The spectral energy distributions of the knots are well fitted by synchrotron models. The spectral indices in the X-ray band, however, are comparable to that expected in the Kardashev-Pacholczyk synchrotron model but are much flatter than expected in the pitch-angle isotropization model of Jaffe and Perola. The break frequencies derived from both models drop by factors of 10-100 with distance from the core.

Ancient lowlands on Mars

Abstract: [1] Mars Orbiter Laser Altimeter (MOLA) data provide compelling evidence that the martian lowlands, below the smooth and sparsely cratered northern plains, are extremely old, far older than the plains which cover them. The evidence is in the form of a very large population of “Quasi-Circular Depressions” (QCDs), many of which are very evident in the MOLA elevation data but generally not visible in available imagery. We interpret these “invisible” QCDs to be buried impact basins. Cumulative number versus diameter curves for lowland QCDs suggests the buried lowland surface is older than the visible highland surface and that the lowland plains are a relatively thin (1–2 km) veneer overlying this much older surface. We conclude that the martian lowlands have been low and stable for nearly all of martian history.