bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPETENCE DYNAMICS AND LEARNING PROCESSES IN PROJECT-BASED FIRMS: SHIFTING, ADAPTING AND LEVERAGING
Authors: SÖDERLUND JONAS
Published: March 2008

In times of increasing use of project-based structures, the capability of managing and organising projects becomes critical for competition. Previous research has documented the problems and possibilities of cross-project learning and various mechanisms that organisations can use to stimulate and facilitate learning. Moreover, research on project competence and project capabilities has positioned these capabilities within a knowledge-based theory of the firm. This paper tries to integrate these streams of research and attempts to broaden our current conceptual frameworks of how firms develop project competence. Based on an exploratory multiple-case study of six firms, it is suggested that a more fine-grained analysis of competence dynamics is required. We identify three different learning processes that contribute to the competence dynamics operating in project-based organisations. The first one labelled "shifting" revolves around the major shifts in the project operations of the firm. It is suggested that such major shifts play an important role in laying the foundation and rejuvenating the challenges of project organising. The second learning process identified, labelled "adapting", focuses on the continuous learning that takes place within project operations of the firm, between project generation, project organising, project leadership and project teamwork. The third and final learning process — "leveraging" — emphasises the role of knowledge transfer across projects; across similar projects, across different types of projects. It is suggested that empirical research into competence dynamics in project-based organisations should consider all three types of learning processes and further develop our understanding how these processes are linked to each other.
Social Networks and Health
Authors: Smith Kirsten P. , Christakis Nicholas A.
Published: March 2008

People are interconnected, and so their health is interconnected. In recognition of this social fact, there has been growing conceptual and empirical attention over the past decade to the impact of social networks on health. This article reviews prominent findings from this literature. After drawing a distinction between social network studies and social support studies, we explore current research on dyadic and supradyadic network influences on health, highlighting findings from both egocentric and sociocentric analyses. We then discuss the policy implications of this body of work, as well as future research directions. We conclude that the existence of social networks means that people's health is interdependent and that health and health care can transcend the individual in ways that patients, doctors, policy makers, and researchers should care about.
Macrophage Migration Inhibitory Factor in Cardiovascular Disease
Authors: Zernecke Alma , Bernhagen Jürgen , Weber Christian
Published: March 2008

The highly conserved and archetypical yet atypical cytokine macrophage migration inhibitory factor (MIF) fulfills pleiotropic immune functions in many acute and chronic inflammatory diseases. Recent evidence has emerged from both expression and functional studies to implicate MIF in various aspects of cardiovascular disease. The present review is aimed at providing a synopsis of the involvement of MIF in the inflammatory pathogenesis of atherosclerosis and its consequences, namely unstable plaque formation, remodeling after arterial injury, aneurysm formation, myocardial infarction, or ischemia-reperfusion injury. In addition, other forms of myocardial dysfunction and inflammation and the role of MIF in angiogenesis are reviewed. The functional data are reconciled with recent progress in the identification of heptahelical (CXC chemokine) receptors for MIF, its prototypic role as their noncanonical ligand, and its signal transduction profile operative in atherogenic and inflammatory recruitment of mononuclear cells and in the oxidative damage and apoptosis of cardiomyocytes. Its unique features and functions clearly distinguish MIF from other cytokines implicated in atherogenesis and make it a prime target for achieving therapeutic regression of atherosclerosis. The potential of targeting or exploiting MIF for therapeutic strategies or as a diagnostic marker in the management of cardiovascular diseases or disorders is scrutinized.
The Influence of Cloud and Surface Properties on the Arctic Ocean Shortwave Radiation Budget in Coupled Models*
Authors: Gorodetskaya Irina V. , Tremblay L-Bruno , Liepert Beate , Cane Mark A. , Cullather Richard I.
Published: March 2008

The impact of Arctic sea ice concentrations, surface albedo, cloud fraction, and cloud ice and liquid water paths on the surface shortwave (SW) radiation budget is analyzed in the twentieth-century simulations of three coupled models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. The models are the Goddard Institute for Space Studies Model E-R (GISS-ER), the Met Office Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO HadCM3), and the National Center for Atmosphere Research Community Climate System Model, version 3 (NCAR CCSM3). In agreement with observations, the models all have high Arctic mean cloud fractions in summer; however, large differences are found in the cloud ice and liquid water contents. The simulated Arctic clouds of CCSM3 have the highest liquid water content, greatly exceeding the values observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign. Both GISS-ER and HadCM3 lack liquid water and have excessive ice amounts in Arctic clouds compared to SHEBA observations. In CCSM3, the high surface albedo and strong cloud SW radiative forcing both significantly decrease the amount of SW radiation absorbed by the Arctic Ocean surface during the summer. In the GISS-ER and HadCM3 models, the surface and cloud effects compensate one another: GISS-ER has both a higher summer surface albedo and a larger surface incoming SW flux when compared to HadCM3. Because of the differences in the models’ cloud and surface properties, the Arctic Ocean surface gains about 20% and 40% more solar energy during the melt period in the GISS-ER and HadCM3 models, respectively, compared to CCSM3.

In twenty-first-century climate runs, discrepancies in the surface net SW flux partly explain the range in the models’ sea ice area changes. Substantial decrease in sea ice area simulated during the twenty-first century in CCSM3 is associated with a large drop in surface albedo that is only partly compensated by increased cloud SW forcing. In this model, an initially high cloud liquid water content reduces the effect of the increase in cloud fraction and cloud liquid water on the cloud optical thickness, limiting the ability of clouds to compensate for the large surface albedo decrease. In HadCM3 and GISS-ER, the compensation of the surface albedo and cloud SW forcing results in negligible changes in the net SW flux and is one of the factors explaining moderate future sea ice area trends. Thus, model representations of cloud properties for today’s climate determine the ability of clouds to compensate for the effect of surface albedo decrease on the future shortwave radiative budget of the Arctic Ocean and, as a consequence, the sea ice mass balance.
Droughts and Persistent Wet Spells over the United States and Mexico
Authors: Mo Kingtse C. , Schemm Jae E.
Published: March 2008

Droughts and persistent wet spells over the United States and northwest Mexico have preferred regions of occurrence and persistence. Wet or dry conditions that persist more than 1 yr tend to occur over the interior United States west of 90°–95°W and northwest Mexico. In contrast, events over the eastern United States are less likely to occur and often last less than 6 months.

The long persistent drought and wet spells are often modulated by low-frequency sea surface temperature anomalies (SSTAs). The persistent dry or wet conditions over northwest Mexico and the Southwest are associated with decadal variability of SSTAs over the North Pacific. Persistent events over the northwestern mountains are associated with two decadal SSTA modes. One mode has loadings over three southern oceans and another one is an El Niño–Southern Oscillation (ENSO) like decadal mode. Wet and dry conditions over the Pacific Northwest and the Great Plains are often associated with ENSO.

The seasonal cycle of precipitation over the central-eastern United States, the East Coast, and the Ohio Valley is weak. Drought and wet spells over these regions are less persistent because the ENSO events have opposite impacts on precipitation for summer and winter.
Shifts in the Statistics of Daily Rainfall in South America Conditional on ENSO Phase
Authors: Ropelewski C. F. , Bell M. A.
Published: March 2008

There are several well-documented studies showing the shifts in seasonal mean rainfall and temperature conditional on El Niño–Southern Oscillation (ENSO) phase. Here the shifts in the seasonal histograms of daily rainfall over South America conditional on ENSO phase are examined. The authors are motivated to analyze daily rainfall statistics over seasons by the demands for information on the shorter temporal scales voiced by users of climate data. In the first stage of the analysis the Kolmogorov–Smirnov (K-S) test is used, comparing El Niño to La Niña histograms of daily station data, to identify regions where there are significant shifts in the histograms. The K-S statistic analyses of daily station data are then compared to the same analyses performed on existing publicly available gridded station datasets. The degree to which the station and gridded data agree in showing geographical regions of significance provides evidence that the gridded fields might provide guidance on the nature of the ENSO signal where station data are not available. Further, the analysis of the gridded datasets can be used to motivate and guide efforts to obtain more complete daily data where the gridded datasets suggest an ENSO signal. As an example a detailed comparison of one station in southern Brazil and its nearest neighbors in the gridded data are presented, suggesting that, despite biases, the gridded fields are generally consistent with the station data where both are available.

For many regions of the world neither daily station data nor daily gridded datasets are available for analysis. Thus despite documented and well-known regional biases in the precipitation fields available in the NCEP–NCAR reanalysis the extent to which shifts in the daily statistics of the NCEP–NCAR reanalysis precipitation are consistent with station and gridded station analyses is also examined. The preliminary work described here suggests that while the reanalysis does not ideally replicate the gridded station results the reanalysis may be useful as a tool for indicating candidate regions for further analysis with station or gridded data.
Volcanic Eruptions, Large-Scale Modes in the Northern Hemisphere, and the El Niño–Southern Oscillation
Authors: Christiansen Bo
Published: March 2008

The author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large-scale variability modes of sea level pressure in the Northern Hemisphere winter. The paper focuses on the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) to address the question about the physical nature of these modes. The hypothesis that the phase of the El Niño–Southern Oscillation (ENSO) may control the geographical extent of the dominant mode in the Northern Hemisphere is also investigated, as well as the related possibility that the impact of the eruptions may be different according to the phase of ENSO.

The author finds that both the AO and the NAO are excited in the first winter after the eruptions with statistical significance at the 95% level. Both the signal and the significance are larger for the NAO than for the AO. The excitation of the AO and the NAO is connected with the excitation of a secondary mode, which resembles an augmented Pacific–North American pattern. This mode has opposite polarity in the Atlantic and the Pacific and interferes negatively with the AO in the Pacific and positively in the Atlantic in the first winter after the eruptions, giving the superposition a strong NAO resemblance.

Some evidence is found that the correlations between the Atlantic and the Pacific are stronger in the negative ENSO phase than in the positive phase, although this difference is not statistically significant when all data since 1870 are considered. The author does not find any evidence that the impact of the volcanic eruptions is more hemispheric in the negative than in the positive ENSO phase.
Regional Model Simulations of the Bodélé Low-Level Jet of Northern Chad during the Bodélé Dust Experiment (BoDEx 2005)
Authors: Todd Martin C. , Washington Richard , Raghavan Srivatsan , Lizcano Gil , Knippertz Peter
Published: March 2008

The low-level jet (LLJ) over the Bodélé depression in northern Chad is a newly identified feature. Strong LLJ events are responsible for the emission of large quantities of mineral dust from the depression, the world’s largest single dust source, and its subsequent transport to West Africa, the tropical Atlantic, and beyond. Accurate simulation of this key dust-generating atmospheric feature is, therefore, an important requirement for dust models. The objectives of the present study are (i) to evaluate the ability of regional climate models (RCMs) and global analyses/reanalyses to represent this feature, and (ii) to determine the driving mechanisms of the LLJ and its strong diurnal cycle. Observational data obtained during the Bodélé Dust Experiment (BoDEx 2005) are utilized for comparison. When suitably configured, the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) RCM can represent very accurately many of the key features of the jet including the structure, diurnal cycle, and day-to-day variability. Surface winds are also well reproduced, including the peak winds, which activate dust emission. Model fidelity is, however, strongly dependent on the boundary layer parameterization scheme, surface roughness, and vertical resolution in the lowest layers. A model horizontal resolution of a few tens of kilometers is sufficient to resolve most of the key features of the LLJ, while in global analyses/reanalyses many features of the LLJ are not adequately represented. Idealized RCM simulations indicate that under strong synoptic forcing the surrounding orography of the Tibesti and Ennedi Mountains acts to focus the LLJ onto the Bodélé and to accelerate the jet by ∼40%. From the RCM experiments it is diagnosed that the pronounced diurnal cycle of the Bodélé LLJ is largely a result of varying eddy viscosity, with elevated heating/cooling over the Tibesti Mountains to the north as a second-order contribution.
The Summer Cyclone Maximum over the Central Arctic Ocean
Authors: Serreze Mark C. , Barrett Andrew P.
Published: March 2008

A fascinating feature of the northern high-latitude circulation is a prominent summer maximum in cyclone activity over the Arctic Ocean, centered near the North Pole in the long-term mean. This pattern is associated with the influx of lows generated over the Eurasian continent and cyclogenesis over the Arctic Ocean itself. Its seasonal onset is linked to the following: an eastward shift in the Urals trough, migration of the 500-hPa vortex core to near the pole, and development of a separate region of high-latitude baroclinicity. The latter two features are consistent with differential atmospheric heating between the Arctic Ocean and snow-free land. Variability in the strength of the cyclone pattern can be broadly linked to the phase of the summer northern annular mode. When the cyclone pattern is well developed, the 500-hPa vortex is especially strong and symmetric about the pole, with negative sea level pressure (SLP) anomalies over the pole and positive anomalies over middle latitudes. Net precipitation tends to be anomalously positive over the Arctic Ocean. When poorly developed, the opposite holds.
Understanding the Changes of Stratospheric Water Vapor in Coupled Chemistry–Climate Model Simulations
Authors: Oman Luke , Waugh Darryn W. , Pawson Steven , Stolarski Richard S. , Nielsen J. Eric
Published: March 2008

Past and future climate simulations from the Goddard Earth Observing System Chemistry–Climate Model (GEOS CCM), with specified boundary conditions for sea surface temperature, sea ice, and trace gas emissions, have been analyzed to assess trends and possible causes of changes in stratospheric water vapor. The simulated distribution of stratospheric water vapor in the 1990s compares well with observations. Changes in the cold point temperatures near the tropical tropopause can explain differences in entry stratospheric water vapor. The average saturation mixing ratio of a 20° latitude by 15° longitude region surrounding the minimum tropical saturation mixing ratio is shown to be a useful diagnostic for entry stratospheric water vapor and does an excellent job reconstructing the annual average entry stratospheric water vapor over the period 1950–2100. The simulated stratospheric water vapor increases over the 50 yr between 1950 and 2000, primarily because of changes in methane concentrations, offset by a slight decrease in tropical cold point temperatures. Stratospheric water vapor is predicted to continue to increase over the twenty-first century, with increasing methane concentrations causing the majority of the trend to midcentury. Small increases in cold point temperature cause increases in the entry water vapor throughout the twenty-first century. The increasing trend in future water vapor is tempered by a decreasing contribution of methane oxidation owing to cooling stratospheric temperatures and by increased tropical upwelling, leading to a near-zero trend for the last 30 yr of the twenty-first century.
Spatial Variability of Shortwave Irradiance for Snowmelt in Forests
Authors: Pomeroy John , Ellis Chad , Rowlands Aled , Essery Richard , Hardy Janet , Link Tim , Marks Danny , Sicart Jean Emmanuel
Published: March 2008

The spatial variation of melt energy can influence snow cover depletion rates and in turn be influenced by the spatial variability of shortwave irradiance to snow. The spatial variability of shortwave irradiance during melt under uniform and discontinuous evergreen canopies at a U.S. Rocky Mountains site was measured, analyzed, and then compared to observations from mountain and boreal forests in Canada. All observations used arrays of pyranometers randomly spaced under evergreen canopies of varying structure and latitude. The spatial variability of irradiance for both overcast and clear conditions declined dramatically, as the sample averaging interval increased from minutes to 1 day. At daily averaging intervals, there was little influence of cloudiness on the variability of subcanopy irradiance; instead, it was dominated by stand structure. The spatial variability of irradiance on daily intervals was higher for the discontinuous canopies, but it did not scale reliably with canopy sky view. The spatial variation in irradiance resulted in a coefficient of variation of melt energy of 0.23 for the set of U.S. and Canadian stands. This variability in melt energy smoothed the snow-covered area depletion curve in a distributed melt simulation, thereby lengthening the duration of melt by 20%. This is consistent with observed natural snow cover depletion curves and shows that variations in melt energy and snow accumulation can influence snow-covered area depletion under forest canopies.
Mesocell Study Area Snow Distributions for the Cold Land Processes Experiment (CLPX)
Authors: Liston Glen E. , Hiemstra Christopher A. , Elder Kelly , Cline Donald W.
Published: March 2008

The Cold Land Processes Experiment (CLPX) had a goal of describing snow-related features over a wide range of spatial and temporal scales. This required linking disparate snow tools and datasets into one coherent, integrated package. Simulating realistic high-resolution snow distributions and features requires a snow-evolution modeling system (SnowModel) that can distribute meteorological forcings, simulate snowpack accumulation and ablation processes, and assimilate snow-related observations. A SnowModel was developed and used to simulate winter snow accumulation across three 30 km × 30 km domains, enveloping the CLPX mesocell study areas (MSAs) in Colorado. The three MSAs have distinct topography, vegetation, meteorological, and snow characteristics. Simulations were performed using a 30-m grid increment and spanned the snow accumulation season (1 October 2002–1 April 2003). Meteorological forcing was provided by 27 meteorological stations and 75 atmospheric analyses grid points, distributed using a meteorological model (MicroMet). The simulations included a data assimilation model (SnowAssim) that adjusted simulated snow water equivalent (SWE) toward ground-based and airborne SWE observations. The observations consisted of SWE over three 1 km × 1 km intensive study areas (ISAs) for each MSA and a collection of 117 airborne gamma observations, each integrating area 10 km long by 300 m wide. Simulated SWE distributions displayed considerably more spatial heterogeneity than the observations alone, and the simulated distribution patterns closely fit the current understanding of snow evolution processes and observed snow depths. This is the result of the MicroMet/SnowModel’s relatively finescale representations of orographic precipitation, elevation-dependant snowmelt, wind redistribution, and snow–vegetation interactions.
A Simple Data Assimilation System for Complex Snow Distributions (SnowAssim)
Authors: Liston Glen E. , Hiemstra Christopher A.
Published: March 2008

A methodology for assimilating ground-based and remotely sensed snow data within a snow-evolution modeling system (SnowModel) is presented. The data assimilation scheme (SnowAssim) is consistent with optimal interpolation approaches in which the differences between the observed and modeled snow values are used to constrain modeled outputs. The calculated corrections are applied retroactively to create improved fields prior to the assimilated observations. Thus, one of the values of this scheme is the improved simulation of snow-related distributions throughout the entire snow season, even when observations are only available late in the accumulation and/or ablation periods. Because of this, the technique is particularly applicable to reanalysis applications. The methodology includes the ability to stratify the assimilation into regions where either the observations and/or model has unique error properties, such as the differences between forested and nonforested snow environments. The methodologies are introduced using synthetic data and a simple simulation domain. In addition, the model is applied over NASA’s Cold Land Processes Experiment (CLPX), Rabbit Ears Pass, Colorado, observation domain. Simulations using the data assimilation scheme were found to improve the modeled snow water equivalent (SWE) distributions, and simulated SWE displayed considerably more realistic spatial heterogeneity than that provided by the observations alone.
Interannual Consistency in Fractal Snow Depth Patterns at Two Colorado Mountain Sites
Authors: Deems Jeffrey S. , Fassnacht Steven R. , Elder Kelly J.
Published: March 2008

Fractal dimensions derived from log–log variograms are useful for characterizing spatial structure and scaling behavior in snow depth distributions. This study examines the temporal consistency of snow depth scaling features at two sites using snow depth distributions derived from lidar datasets collected in 2003 and 2005. The temporal snow accumulation patterns in these two years were substantially different, but both years represent nearly average 1 April accumulation depths for these sites, with consistent statistical distributions. Two distinct fractal regions are observed in each log–log variogram, separated by a scale break, which indicates a length scale at which a substantial change in the driving processes exists. The lag distance of the scale break is 15 m at the Walton Creek site and 40 m at the Alpine site. The datasets show consistent fractal dimensions and scale break distances between the two years, suggesting that the scaling features observed in spatial snow depth distributions are largely determined by physiography and vegetation characteristics and are relatively insensitive to annual variations in snowfall. Directional variograms also show consistent patterns between years, with smaller fractal dimensions aligned with the dominant wind direction at each site.
The Interactions of Gravity Waves with Mesocyclones: Preliminary Observations and Theory
Authors: Coleman Timothy A. , Knupp Kevin R.
Published: March 2008

Apparent interactions between ducted gravity waves and preexisting mesocyclones are investigated. Preliminary analyses of Weather Surveillance Radar-1988 Doppler (WSR-88D) observations from several cases reveal that the intersection of fine lines, whose propagation speed is consistent with that of gravity waves, and existing mesocyclones leads to an increase in the rotational velocity of the mesocyclone. Utilizing simplified ducted wave kinematics and the vorticity equation, changes in vorticity associated with convergence–divergence and perturbation wind shear within the gravity wave are examined. Convergence ahead of wave ridges may be significant, causing mesocyclone intensification through vorticity stretching. It will also be shown that a wave may significantly change the vertical wind shear and streamwise vorticity in storm inflow. A simple one-dimensional model is presented, which shows that vorticity decreases temporarily ahead of the wave ridge, then increases rapidly behind the ridge as positive tilting and stretching act together. The mesocyclone vorticity reaches a peak just ahead of the wave ridge, then begins to rapidly decrease behind the ridge. Model results compared very well to actual measurements in a sample case in which a mesocyclone interacted with two gravity waves of different amplitudes.
Assessing the Capability of a Regional-Scale Weather Model to Simulate Extreme Precipitation Patterns and Flooding in Central Texas
Authors: Lowrey Marla R. Knebl , Yang Zong-Liang
Published: March 2008

A regional-scale weather model is used to determine the potential for flood forecasting based on model-predicted rainfall. Extreme precipitation and flooding events are a significant concern in central Texas, due to both the high occurrence and severity of flooding in the area. However, many current regional prediction models do not provide sufficient accuracy at the watershed scale necessary for flood mitigation efforts. The Weather Research and Forecasting (WRF) model, created with the purpose of improving upon the current fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5), is specifically designed for regional grid spacings of 1–10 km. Previous research by the authors resulted in the development of a regional-scale prediction system over the San Antonio River basin, using a geographic information system (GIS) database, a hydrologic model, and a hydraulic model. Observed precipitation drives the prediction system; the authors hypothesize that the WRF model has the potential to predict flooding, at a lead time of several days, with a level of accuracy near that of observed precipitation. Causes of model error are also investigated, to determine the relative errors caused by model physics, initialization interval, buffer zone and domain size, and small-amplitude random errors. Results show that the Betts–Miller–Janjić cumulus and Lin et al. microphysics schemes, 48-h initialization interval, and two-domain configuration covering minimal ocean and having a parent-to-nest area ratio of greater than 10 best simulates a recent (July 2002) large storm event over the San Antonio River basin. This particular storm was selected because it produced extreme rainfall volumes and intensities, and also because its meteorological characteristics are typical of central Texas storm events. Location errors in rainfall are most significant because of their typically nonlinear patterns (increasing location error does not linearly modify streamflow output). Errors in intensity and timing show a more predictable (linear) watershed response that may be useful in the estimation of streamflow ranges for flood forecasting.
A dental health education exercise
Authors: Clewett John A.
Published: March 2008

A dental health educational exercise was carried out on a class of primary school children. A verbal questionnaire was conducted, some formal instruction on dental health was given and group activities on oral hygiene were performed. An attempt was made to promote dental awareness and induce motivation. The amount of learning derived from the exercise was assessed from an analysis of essays written by the children.
The Relationship Between Cultural Competence and Ethnocentrism of Health Care Professionals
Authors: Capell Jen , Dean Elizabeth , Veenstra Gerry
Published: March 2008

The study examined the relationship between cultural competence and ethnocentrism among health care professionals. Physical therapists, occupational therapists, and nurses ( N = 71) from three hospitals in Vancouver, British Columbia, Canada, participated in the survey research project. The survey questionnaire incorporated the Inventory for Assessing the Process of Cultural Competence Among Healthcare Professionals—Revised and the Generalized Ethnocentrism Scale. Cultural competence scores and ethnocentrism scores were inversely related (r = –.28, p = .017). Results suggest that cultural competence may not be entirely distinct from ethnocentrism. The construct of cultural competence warrants further study vis-à-vis its correlates and its impact on clinical outcomes.
Chairman Fred Hampton Way
Authors: “Kamau" LaRaviere Troy
Published: March 2008

I begin this article at the site of the murder of Black Panther Party Leader Fred Hampton. I then visit the school where I teach and I recall elements of my life history that explain how I became aware of the political repression and murder of Fred Hampton. I then focus on how I brought a discussion of Hampton's work into the classroom and how this discussion created a moment where I believe students had a conscious recognition of what I was doing: working against common practice to provide them with a politically relevant school experience. I provide additional examples of politically relevant teaching from my classroom, I discuss research on the subject, and I call for increased efforts by teachers to offer politically relevant instruction to their students.
The Agonistic Approach
Authors: Vitus Kathrine
Published: March 2008

The agonistic approach—aimed at embracing opposing perspectives as part of a qualitative research process and acknowledging that process as fundamentally political—sheds light on both the construction of and the resistance to research identities. This approach involves reflexively embedding interview situations into the ethnographic context as a tool for analyzing how this context conditions and limits positions for research participants, thereby setting the stage for potential agonisms between the researcher and field participants. The author—an ethnic Danish researcher—uses the agonistic approach to examine the identity construction problems and resistance dynamics in interviews with ethnic minority boys at a crime-preventive recreation centre. Applying an agonistic analysis to apparently “uninformative” interview data not only creates insight into local discursive resources, practices, cultural understandings, and power relations but also transforms what initially appears to constitute methodological problems—in terms of “data gaps” from participant resistance—into important, substantial empirical material.
Desire and Drive in Researcher Subjectivity: The Broken Mirror of Lacan
Authors: Brown Tony
Published: March 2008

This article offers an account of how a researcher's subjectivity might be seen as being stitched into the fabric of practitioner research. It uses Lacan's notion of the mirror phase in suggesting that the subject of reflection is not quite what he or she might seem to be. The Freudian concept of desire is considered in relation to the motivations that reflective research models produce. This is contrasted with his concept of drive read against a research attitude where excessive belief in the linguistic forms of such research risks usurping the life one might seek to locate. The article draws on a contemporary reading of the terms as offered by the Lacanian social commentator Slavoj Žižek. Two examples are provided of teachers carrying out practitioner research for higher degrees. These document the awkwardness the teachers experience in building conceptions of self through reflective work as personal ideas are processed in social space.
Heavy-Traffic Limits of Queueing Networks with Polling Stations: Brownian Motion in a Wedge
Authors: Jennings Otis B.
Published: March 2008

We consider two serial single-server stations in heavy traffic. There are two job types: All jobs visit station 1 and then station 2. Station 1 processes jobs in an exhaustive service or gated service fashion; station 2 uses an arbitrary nonidling service discipline. Neither station incurs switchover delays. We prove two heavy-traffic limit theorems (HTLT) for the diffusion-scaled, two-dimensional total workload process: one for when the first station implements exhaustive service and the other for when gated service is employed. Our limiting processes are two-dimensional Brownian motions in a wedge, a type of reflected Brownian motion (RBM). The limiting process under exhaustive service is equal in distribution to the limiting process that one obtains when the first station performs one of two buffer priority policies.
Optimal Control of Distributed Parallel Server Systems Under the Halfin and Whitt Regime
Authors: Tezcan Tolga
Published: March 2008

We consider a distributed parallel server system that consists of multiple server pools and a single customer class. We show that the minimum-expected-delay faster-server-first (MED-FSF) routing policy asymptotically minimizes the stationary distribution of the total queue length and the stationary delay probability in the Halfin and Whitt regime. We propose the minimum-expected-delay load-balancing (MED-LB) routing policy to balance the utilizations of all the servers in a distributed system with no unnecessary idling. We show that this policy balances both the long-run and finite-time average utilizations over all the server pools in the Halfin and Whitt regime. We next show that, under either the MED-FSF or the MED-LB policy, a distributed system performs as well as the corresponding inverted V-system. Finally, we show that, operating under the MED-LB policy, both the distributed system and the inverted V-system have similar performances to a corresponding M/M/n system. We illustrate the quality of our asymptotic results for several parallel server systems via simulation experiments.
Refinement Derivatives and Values of Games
Authors: Montrucchio Luigi , Semeraro Patrizia
Published: March 2008

A definition of setwise differentiability for set functions is given through refining the partitions of sets. Such a construction is closely related to the one proposed by Rosenmuller [Rosenmuller, J. 1977. Extreme Games and Their Solutions. Springer-Verlag, Berlin], Epstein [Epstein, L. 1999. A definition of uncertainty aversion. Rev. Econom. Stud. 66 579–608], and Epstein and Marinacci [Epstein, L., M. Marinacci. 2001. The core of large differentiable TU games. J. Econom. Theory 100 235–273]. We present several classes of transferable utility (TU) games that are differentiable and study differentiation rules. The last part of this paper applies refinement derivatives to the computation of value of games. Following Hart and Mas-Colell [Hart, S., A. Mas-Colell. 1989. Potential, value and consistency. Econometrica 57 589–614], we define an operator through the refinement derivative of the potential of the game. We show that this operator is a value, when restricted to the spaces pM∞ and POT2. The latter space is closely related to Myerson's balanced contributions axiom.
On Decomposition Methods for a Class of Partially Separable Nonlinear Programs
Authors: DeMiguel Victor , Nogales Francisco J.
Published: March 2008

We study two different decomposition algorithms for the general (nonconvex) partially separable nonlinear program (PSP): bilevel decomposition algorithms (BDAs) and Schur interior-point methods (SIPMs). BDAs solve the problem by breaking it into a master problem and a set of independent subproblems, forming a type of bilevel program. SIPMs, on the other hand, apply an interior-point technique to solve the problem in its original (integrated) form, but then use a Schur complement approach to solve the Newton system in a decentralized manner. Our first contribution is to establish a theoretical relationship between these two types of decomposition algorithms. This is a first step toward closing the gap between the incipient local convergence theory of BDAs and the mature local convergence theory of interior-point methods. Our second contribution is to show how SIPMs can be modified to solve problems for which the Schur complement matrix is not invertible in general. The importance of this contribution is that it substantially enlarges the class of problems that can be addressed with SIPMs.
Facets of Two-Dimensional Infinite Group Problems
Authors: Dey Santanu S. , Richard Jean-Philippe P.
Published: March 2008

In this paper, we lay the foundation for the study of the two-dimensional mixed integer infinite group problem (2DMIIGP). We introduce tools to determine if a given continuous and piecewise linear function over the two-dimensional infinite group is subadditive and to determine whether it defines a facet of 2DMIIGP. We then present two different constructions that yield the first known families of facet-defining inequalities for 2DMIIGP. The first construction uses valid inequalities of the one-dimensional integer infinite group problem (1DIIGP) as building blocks for creating inequalities for the two-dimensional integer infinite group problem (2DIIGP). We prove that this construction yields all continuous piecewise linear facets of the two-dimensional group problem that have exactly two gradients. The second construction we present has three gradients and yields facet-defining inequalities of 2DMIIGP whose continuous coefficients are not dominated by those of facets of the one-dimensional mixed integer infinite group problem (1DMIIGP).
Packing d-Dimensional Bins in d Stages
Authors: Caprara Alberto
Published: March 2008

We consider the d-dimensional bin-packing problem, the most relevant generalization of classical bin packing, and show a general result about the asymptotic worst-case ratio of a wide class of approximation algorithms that construct solutions in d stages, containing many heuristics previously considered in the literature. Moreover, we give the exact value of the asymptotic worst-case ratio between the optimal solution and the best solution obtainable by packing the items in d stages, showing how to achieve such a ratio efficiently. The key property behind our result is the asymptotic optimality of the fractional relaxation of (one-dimensional) bin packing, an important by-product of the approximation schemes for the problem from the 1980s, which, to the best of our knowledge, is used here for the first time only for the sake of the analysis. For the two-dimensional case, we push the approximablity threshold below 2 after more than 20 years (reaching 1.691…), but also improve and widely simplify the analysis of the previous best method from the 1980s. Moreover, for d ≥ 3 we improve the previous approximability threshold by a factor of 1.691…, a notable improvement when d is small.
Etiological Relationships in Atopy: A Review of Twin Studies
Authors: Thomsen Simon Francis , Kyvik Kirsten Ohm , Backer Vibeke
Published: March 2008

The genetics of asthma and atopy has been studied frequently in twin populations from various parts of the world. However, emphasis has been put on univariate analysis of questionnaire data, whereas clinical and intermediate traits only sporadically have been studied, especially in multivariate settings. This review focuses on multivariate twin studies of atopy and related traits. We conclude that the genetic liability to most atopic traits is significantly correlated but that trait-specific genes also play a role. Previous studies have estimated the genetic correlation between upper and lower respiratory allergic symptoms, that is, asthma and hay fever, to be between .47 and .95. Furthermore, atopic traits share a portion of their genetic determinants with other complex disorders like obesity and behavioral traits. A correlation of about .3 and .34 has been reported between genes associated with asthma and obesity, and between genes associated with asthma and depression, respectively. We emphasize that multivariate methods applied to twin studies, especially when genetic marker information is available, provide a valuable framework within which complex etiological mechanisms underlying atopy can be disentangled.
Heritability of Self-Reported Asthma and Allergy: A Study in Adult Dutch Twins, Siblings and Parents
Authors: Willemsen Gonneke , van Beijsterveldt Toos C. E. M. , van Baal Caroline G. C. M. , Postma Dirkje , Boomsma Dorret I.
Published: March 2008

The present study assessed the prevalence of asthma and allergy, and estimated the importance of genetic and environmental influences on asthma and allergy liability and their association. Longitudinal data on self-reported, doctor-diagnosed asthma and allergy were collected in over 14,000 individuals registered with the Netherlands Twin Register. Structural equation modeling was used for univariate and bivariate genetic analyses on data from twins, their siblings, and parents. Results showed no sex, age, and minimal birth cohort effects for asthma prevalence (11.8%). For allergy, prevalence was higher in women (19.8%) than in men (13.9%). Allergy prevalence at ages 22, 23, and 24 years increased from the 1970 to the 1980 birth cohort. The prevalence of allergy, but not of asthma, was higher in nontwin siblings than in twins. No assortative mating was observed. High (broad-sense) heritabilities were found for asthma (75%) and allergy (66%), with evidence for nonadditive genetic effects in asthma. The association between asthma and allergy (correlation = .65) was largely due to common genes (70%). No sex differences in genetic architecture were found. In conclusion, the prevalence of allergy but not of asthma increased in recent years. Individual differences in the liability to asthma, allergy and their co-occurrence are for a large part accounted for by differences in genetic background. Nonadditive gene action is important, which may have consequences for gene hunting strategies.
An Exploration of Gene–Environment Interaction and Asthma in a Large Sample of 5-Year-Old Dutch Twins
Authors: van Beijsterveldt Toos C. E. M. , Boomsma Dorret I.
Published: March 2008

A consistent finding from twin studies is that the environment shared by family members does not contribute to the variation in susceptibility to asthma. At the same time, it is known that environmental risk factors that are shared by family members are associated with the liability for asthma. We hypothesize that the absence of a main effect of shared environmental factors in twin studies can be explained by gene–environment interaction, that is, that the effect of an environmental factor shared by family members depends on the genotype of the individual. We explore this hypothesis by modeling the resemblance in asthma liability in twin pairs as a function of various environmental risk factors and test for gene–environment interaction. Asthma data were obtained by parental report for nearly 12,000 5-year-old twin pairs. A series of environmental risk factors was examined: birth cohort, gestational age, time spent in incubator, breastfeeding, maternal educational level, maternal smoking during pregnancy, current smoking of parents, having older siblings, and amount of child care outside home. Results revealed that being a boy, born in the 1990s, premature birth, longer incubator time, and child care outside home increased the risk for asthma. With the exception of premature birth, however, none of these factors modified the genetic effects on asthma. In very premature children shared environmental influences were important. In children born after a gestation of 32 weeks or more only genetic factors were important to explain familial resemblance for asthma.
Asthma and Mode of Birth Delivery: A Study in 5-Year-Old Dutch Twins
Authors: van Beijsterveldt Toos C. E. M. , Boomsma Dorret I.
Published: March 2008

Several studies report caesarean section (CS) to be a risk factor for childhood asthma. We used data from a large cohort of 5-year-old twins to examine the relationship between mode of birth delivery and asthma. The extent to which an infant is exposed to maternal vaginal flora may protect against the risk of developing asthma. Therefore, we expect a lower rate of asthma in twins born by vaginal delivery (VD) than those born by CS, and a lower rate of asthma in first-born twins compared to second-born twins by VD. Information on mode of delivery was obtained at the time of birth in a survey completed by the mother shortly after delivery. Information on history of asthma diagnosis by a physician was obtained by parental report when the twins were 5 years old. Complete data were available for 6330 first-born and 5438 second-born twins from birth cohorts 1991–2000. Full term first-born twins born by CS had a significantly higher risk of asthma compared to those born by VD, odds ratio = 1.59 (95% CI = 1.23–2.06). No significant differences were observed between CS and VD first-born twins when gestational age was less than 37 weeks, and no significant differences were observed between CS and VD second-born twins at any gestational age. No differences in asthma prevalence were found between first- and second-born twins both born by VD. CS may increase the risk of asthma to full term infants, however, the underlying mechanism is unclear.
A Note on Twin–Singleton Differences in Asthma
Authors: Thomsen Simon Francis , Kyvik Kirsten Ohm , Backer Vibeke
Published: March 2008

Twins constitute a valuable resource for genetic studies of asthma. However, critics argue that twins are ‘special’ in terms of prenatal environment and upbringing and therefore nonrepresentative. In respect to asthma a small range of studies report differential morbidity in twins compared with singletons. We review some of the possible explanations for these findings and conclude that results from twin studies of asthma can be extrapolated to the general population.