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Vertical Scales (vertical + scale)

Distribution by Scientific Domains
Life Sciences22%

Selected Abstracts

Psychometric Properties of IRT Proficiency Estimates

EDUCATIONAL MEASUREMENT: ISSUES AND PRACTICE, Issue 3 2010
Michael J. Kolen
Psychometric properties of item response theory proficiency estimates are considered in this paper. Proficiency estimators based on summed scores and pattern scores include non-Bayes maximum likelihood and test characteristic curve estimators and Bayesian estimators. The psychometric properties investigated include reliability, conditional standard errors of measurement, and score distributions. Four real-data examples include (a) effects of choice of estimator on score distributions and percent proficient, (b) effects of the prior distribution on score distributions and percent proficient, (c) effects of test length on score distributions and percent proficient, and (d) effects of proficiency estimator on growth-related statistics for a vertical scale. The examples illustrate that the choice of estimator influences score distributions and the assignment of examinee to proficiency levels. In particular, for the examples studied, the choice of Bayes versus non-Bayes estimators had a more serious practical effect than the choice of summed versus pattern scoring. [source]

The Impact of Vertical Scaling Decisions on Growth Interpretations

EDUCATIONAL MEASUREMENT: ISSUES AND PRACTICE, Issue 4 2009
Derek C. Briggs
Most growth models implicitly assume that test scores have been vertically scaled. What may not be widely appreciated are the different choices that must be made when creating a vertical score scale. In this paper empirical patterns of growth in student achievement are compared as a function of different approaches to creating a vertical scale. Longitudinal item-level data from a standardized reading test are analyzed for two cohorts of students between Grades 3 and 6 and Grades 4 and 7 for the entire state of Colorado from 2003 to 2006. Eight different vertical scales were established on the basis of choices made for three key variables: Item Response Theory modeling approach, linking approach, and ability estimation approach. It is shown that interpretations of empirical growth patterns appear to depend upon the extent to which a vertical scale has been effectively "stretched" or "compressed" by the psychometric decisions made to establish it. While all of the vertical scales considered show patterns of decelerating growth across grade levels, there is little evidence of scale shrinkage. [source]

Cover Picture: Plasma Process.

PLASMA PROCESSES AND POLYMERS, Issue 2 2006
Polym.
Cover: AFM scans (5µm,×,5µm) of 500 nm thick films as deposited on Si from processes a) RFICP (full vertical scale: 12.6 nm), b) MIRA (full vertical scale: 44.9 nm), and c) DECRP (full vertical scale: 27.7 nm). Further details can be found in the Full Paper by P. Supiot,* C. Vivien, A. Granier, A. Bousquet, A. Mackova, D. Escaich, R. Clergereaux, P. Raynaud, Z. Stryhal, and J. Pavlik on page 100. [source]

The Impact of Vertical Scaling Decisions on Growth Interpretations

EDUCATIONAL MEASUREMENT: ISSUES AND PRACTICE, Issue 4 2009
Derek C. Briggs
Most growth models implicitly assume that test scores have been vertically scaled. What may not be widely appreciated are the different choices that must be made when creating a vertical score scale. In this paper empirical patterns of growth in student achievement are compared as a function of different approaches to creating a vertical scale. Longitudinal item-level data from a standardized reading test are analyzed for two cohorts of students between Grades 3 and 6 and Grades 4 and 7 for the entire state of Colorado from 2003 to 2006. Eight different vertical scales were established on the basis of choices made for three key variables: Item Response Theory modeling approach, linking approach, and ability estimation approach. It is shown that interpretations of empirical growth patterns appear to depend upon the extent to which a vertical scale has been effectively "stretched" or "compressed" by the psychometric decisions made to establish it. While all of the vertical scales considered show patterns of decelerating growth across grade levels, there is little evidence of scale shrinkage. [source]

Assemblage structure, but not diversity or density, change with depth on a northeast Pacific seamount

MARINE ECOLOGY, Issue 2010
Craig R. McClain
Abstract Although depth-related patterns in assemblage structure are documented in several deep-sea systems, variation in diversity, assemblage structure, and abundance with depth on individual seamounts remains unexplored. Knowledge of alpha- and beta-diversity on single seamounts is needed for any robust generalization about large-scale biodiversity patterns on seamounts. Here, we explore bathymetric variation in benthic megafauna, based on ROV video transects, on Davidson seamount (1246,3656 m) in the Northeast Pacific Ocean. We found that substantial change in assemblage structure can occur over vertical scales on an individual seamount. Changes of 50% in assemblage composition (beta-diversity, faunal turnover) were observed over as little as a ,1500 m depth interval down the flanks of the seamount, although bathymetric clines in composition were not uniform across major taxa. Diversity and density exhibit no consistent bathymetric pattern and can vary greatly on a single isobath. Our findings suggest that ecological and evolutionary processes may vary considerably on a single seamount. As such, seamounts should be viewed as patchworks of habitats where high beta-diversity may ultimately increase total biodiversity. [source]

Scaling turbulent atmospheric stratification.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008
I: Turbulence, waves
Abstract In this first of a three-part series, we argue that the dynamics of turbulence in a stratified atmosphere should depend on the buoyancy over a wide range of vertical scales and on energy flux over a wide range of horizontal scales; it should be scaling, but anisotropic, not isotropic. We compare the leading statistical theories of atmospheric stratification which are conveniently distinguished by the elliptical dimension Ds which quantifies their degree of spatial stratification. This includes the mainstream isotropic 2-D (large scales), isotropic 3-D (small scales) theory but also the more recent linear gravity wave theories (Ds = 7/3) and the classical fractionally integrated flux (FIF) 23/9-D unified scaling model. In the latter, the horizontal wind has a k,5/3 spectrum as a function of horizontal wavenumber determined by the energy flux and a k,11/5 energy spectrum as a function of vertical wavenumber determined by the buoyancy force variance flux. In this model, the physically important notion of scale is determined by the turbulent dynamics, it is not given a priori (i.e. the by usual Euclidean distance). The 23/9-D FIF model is the most physically and empirically satisfying, being based on turbulent (spectral) fluxes. The FIF model as originally proposed by Schertzer and Lovejoy is actually a vast family of scaling models broadly compatible with turbulent phenomenology and with the classical turbulent laws of Kolmogorov, Corrsin and Obukov. However, until now it has mostly been developed on the basis of structures localized in space,time. In this paper, we show how to construct extreme FIF models with wave-like structures which are localized in space but unlocalized in space,time, as well as a continuous family of intermediate models which are akin to Lumley,Shur models in which some part of the localized turbulent energy ,leaks' into unlocalized waves. The key point is that the FIF requires two propagators (space,time Green's functions) which can be somewhat different. The first determines the space,time structure of the cascade of fluxes; this must be localized in space,time in order to satisfy the usual turbulence phenomenology. In contrast, the second propagator relates the turbulent fluxes to the observables; although the spatial part of the propagator is localized as before, in space,time it can be unlocalized. (It is still localized in space, now in wave packets.) We display numerical simulations which demonstrate the requisite (anisotropic, multifractal) statistical properties as well as wave-like phenomenologies. In parts II and III we will examine the empirical evidence for the spatial and temporal parts, respectively, of the model using state-of-the-art lidar data of aerosol backscatter ratios (which we use as a surrogate for passive scalar concentration). Copyright © 2008 Royal Meteorological Society [source]

Contour-advective semi-Lagrangian algorithms for many-layer primitive-equation models

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 596 2004
A. R. Mohebalhojeh
Abstract For an f -plane many-layer primitive-equation isopycnal model, three ,contour-advective semi-Lagrangian' (CASL) algorithms and a standard pseudo-spectral (PS) algorithm are compared as regards their representation of balance and imbalance during the evolution of a highly complex vortical flow with substantial activity in small horizontal and vertical scales. The three CASL algorithms employ (q,h,,), (q,,,,), and (q,,,,) as their prognostic variables, where q is the Rossby potential vorticity, h is layer thickness, , is horizontal divergence, , and , represent departures of vorticity from, respectively, geostrophic and Bolin,Charney balance. It is demonstrated that the CASL algorithm with (q,,,,) improves on the algorithm with (q,h,,) across nearly the whole range of applicability of the algorithms, i.e. practically up to the limit where overturning and diabatic effects may dominate. Unlike in the PS algorithm, the improvement is achieved without sacrificing the accuracy of the vortical part of the flow by excessive damping. Copyright © 2004 Royal Meteorological Society [source]

Distribution of benthic communities in the fjord-like Bathurst Channel ecosystem, south-western Tasmania, a globally anomalous estuarine protected area

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2010
Neville S. Barrett
Abstract 1.Benthic assemblages in the fjord-like Bathurst Channel estuarine system, south-western Tasmania, vary over horizontal scales of 1,5,km and vertical scales of 1,10,m. Multivariate analysis indicated a total of eight major assemblages that characterize different sections and depths of the channel. 2.Because tannins in the low-salinity surface water layer block light, foliose algae reach 5,m depth in the marine western region but do not penetrate below 1,m in the east. By contrast, sessile invertebrates are most abundant below 5,m depth in the west and below 2,m in the east. Deeper assemblages are unlikely to be continuous with assemblages in deeper waters off the Tasmanian coast as they are highly constrained by depth within particular sections of the estuary. 3.While the species composition of the Bathurst Channel biota is most similar to that found elsewhere in Tasmania, the structural character of the biota in terms of major taxonomic groups is more closely allied to that found in fjords of south-western Chile and south-western New Zealand. These three regions all possess wilderness settings, high rainfall that is channelled through estuaries as a low-salinity surface layer, deep-water emergence of fauna, rapid change in biotic communities over short horizontal and vertical distances, and high levels of local endemism. They also include some of the most threatened aquatic ecosystems on earth due to increasing human activity from a near pristine base, and the potentially catastrophic impacts of climate change. Copyright © 2009 John Wiley & Sons, Ltd. [source]