bluuebunny/crossref_metadata_2025 huggingface dataset:
A nonsmooth model for discontinuous shear thickening fluids: Analysis and numerical solution
Authors: De los Reyes Juan Carlos , Stadler Georg
Published: December 2014

We propose a nonsmooth continuum mechanical model for discontinuous shear thickening flow. The model obeys a formulation as energy minimization problem and its solution satisfies a Stokes type system with a nonsmooth constitute relation. Solutions have a free boundary at which the behavior of the fluid changes. We present Sobolev as well as H¨older regularity results and study the limit of the model as the viscosity in the shear thickened volume tends to infinity. A mixed problem formulation is discretized using finite elements and a semismooth Newton method is proposed for the solution of the resulting discrete system. Numerical problems for steady and unsteady shear thickening flows are presented and used to study the solution algorithm, properties of the flow and the free boundary. These numerical problems are motivated by recently reported experimental studies of dispersions with high particle-to-fluid volume fractions, which often show a sudden increase of viscosity at certain strain rates.
Combinatorics
Authors: Kahn Jeff , Steger Angelika , Sudakov Benjamin
Published: December 2014

Combinatorics is a fundamental mathematical discipline which focuses on the study of discrete objects and their properties. The current workshop brought together researchers from diverse fields such as Extremal and Probabilistic Combinatorics, Discrete Geometry, Graph theory, Combinatorial Optimization and Algebraic Combinatorics for a fruitful interaction. New results, methods and developments and future challenges were discussed. This is a report on the meeting containing abstracts of the presentations and a summary of the problem session.
Set Theory
Authors: Farah Ilijas , Friedman Sy-David , Magidor Menachem , Woodin W. Hugh
Published: December 2014

This stimulating workshop featured a broad selection of some of the most important recent developments in combinatorial set theory, the theory and applications of forcing, large cardinal theory and descriptive set theory.
Langlands Correspondence and Constructive Galois Theory
Authors: Dettweiler Michael , Heinloth Jochen , Yun Zhiwei
Published: December 2014

Recent progress in the Langlands programm provides a significant step towards the understanding of the arithmetic of global fields. The geometric Langlands program provides a systematic way to construct l-adic sheaves (resp. D-modules) on algebraic curves which subsumes the construction of classical sheaves, like rigid local systems, used in inverse Galois theory (by Belyi, Malle, Matzat, Thompson, Dettweiler, Reiter) for the construction of field extension of the rational function fields

\mathbb F_p(t)

or

\mathbb Q(t)

(recent work of Heinloth, Ngo, Yun and Yun). On the other hand, using Langlands correspondence for the field

\mathbb Q

, Khare, Larsen and Savin constructed many new automorphic representations which lead to new Galois realizations for classical and exceptional groups over

\mathbb Q

. It was the aim of the workshop, to bring together the experts working in the fields of Langlands correspondence and constructive Galois theory.
Representation Theory of Quivers and Finite Dimensional Algebras
Authors: Crawley-Boevey William , Iyama Osamu , Keller Bernhard , Krause Henning
Published: December 2014

Methods and results from the representation theory of quivers and finite dimensional algebras have led to many interactions with other areas of mathematics. Such areas include the theory of Lie algebras and quantum groups, commutative algebra, algebraic geometry and topology, and in particular the new theory of cluster algebras. The aim of this workshop was to further develop such interactions and to stimulate progress in the representation theory of algebras.
Enumerative Combinatorics
Authors: Bousquet-Mélou Mireille , Drmota Michael , Krattenthaler Christian , Noy Marc
Published: December 2014

Enumerative Combinatorics focusses on the exact and asymptotic counting of combinatorial objects. It is strongly connected to the probabilistic analysis of large combinatorial structures and has fruitful connections to several disciplines, including statistical physics, algebraic combinatorics, graph theory and computer science. This workshop brought together experts from all these various fields, including also computer algebra, with the goal of promoting cooperation and interaction among researchers with largely varying backgrounds.
Adaptive Statistical Inference
Authors: Low Mark , Munk Axel , Tsybakov Alexandre B.
Published: December 2014

This workshop in mathematical statistics highlights recent advances in adaptive methods for statistical estimation, testing and confidence sets. Related open mathematical problems are discussed with potential impact on the development of computationally efficient algorithms of data processing under prior uncertainty. Parcticular emphasis is on high dimensional models, inverse problems and discrtete structures.
Nonlinear Evolution Equations: Analysis and Numerics
Authors: Hochbruck Marlis , Nicaise Serge , Ostermann Alexander , Schnaubelt Roland
Published: December 2014

The workshop was devoted to the analytical and numerical investigation of nonlinear evolution equations. The main aim was to stimulate a closer interaction between experts in analytical and numerical methods for areas such as wave and Schrödinger equations or the Navier–Stokes equations and fluid dynamics.
Flat Surfaces and Dynamics on Moduli Space
Authors: Masur Howard , Möller Martin , Zorich Anton
Published: December 2014

Dynamics of the Teichmüller geodesic flow on the moduli space of curves and asymptotic monodromy of the Hodge bundle along this flow have numerous applications to dynamics and geometry of measured foliations, to billiards in polygons, to interval exchange transformations, and to geometry of flat surfaces.
A Universidade Federal de Minas Gerais no contexto do acesso aberto à informação científica: identificação de seus sistemas de informação
Authors: Souza Ráisa Mendes Fernandes de , Alvarenga Lídia
Published: December 2014

Os obstáculos enfrentados pela comunidade científica na disseminação e na garantia de acesso às próprias produções, contextualizados na necessidade de acesso aberto à informação científica, impulsionaram a criação dos Repositórios Institucionais - RIs. Trata-se de tecnologias adotadas por instituições de ensino e de pesquisa que visam gerir e disponibilizar a produção científica local. A pesquisa teve como objetivo geral caracterizar sistemas de informação da Universidade Federal de Minas Gerais analisando a percepção dos atores responsáveis por sua existência/manutenção dentro do contexto do acesso aberto à informação científica.  Tratou-se de uma pesquisa descritiva e qualitativa que tem por objeto os sistemas de informação criados dentro da universidade para o apoio ao ensino, à pesquisa e à extensão, nos quais contenham produções ou registros de produções, científicas ou não, da comunidade acadêmica local. Notou-se certa consciência dos atores entrevistados em relação à existência dos demais sistemas, apesar de tal consciência não ser a ideal. De forma geral, a UFMG possui Gestores e Depositantes suficientemente competentes para gerir um repositório maior, como é o caso de um RI. Como conclusão, faz-se necessária uma política de informação científica consolidada que nasça dos setores hierarquicamente superiores e que seja repassada aos setores inferiores para, assim, ser possível articular toda a comunidade universitária em prol de uma causa comum. O estudo ressalta a comunidade da UFMG e a otimização do acesso aberto às publicações da Universidade como escopo para possíveis estudos futuros.
Modelos e experiências de competência em informação em contexto universitário
Authors: Melo Alves Fernanda Maria , Alcará Adriana Rosecler
Published: December 2014

O artigo indica alguns estudos diacrônicos de revisão e de comparação sobre competência em informação a nível mundial e investiga alguns modelos em contexto universitário e suas respectivas aplicações, descrevendo experiências realizadas com estudantes, em diferentes universidades e países. Para tanto, realizou-se uma pesquisa bibliográfica e documental. Entre os resultados destaca-se a diversidade cronológica e geográfica dos modelos, bem como as suas diversas possibilidades de aplicação para a avaliação e o desenvolvimento da competência em informação de universitários.
A comprehensive parameterization of heterogeneous ice nucleation of dust surrogate: laboratory study with hematite particles and its application to atmospheric models
Authors: Hiranuma N. , Paukert M. , Steinke I. , Zhang K. , Kulkarni G. , Hoose C. , Schnaiter M. , Saathoff H. , Möhler O.
Published: December 2014

Abstract. A new heterogeneous ice nucleation parameterization that covers a wide temperature range (−36 to −78 °C) is presented. Developing and testing such an ice nucleation parameterization, which is constrained through identical experimental conditions, is important to accurately simulate the ice nucleation processes in cirrus clouds. The ice nucleation active surface-site density (ns) of hematite particles, used as a proxy for atmospheric dust particles, were derived from AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber measurements under water subsaturated conditions. These conditions were achieved by continuously changing the temperature (T) and relative humidity with respect to ice (RHice) in the chamber. Our measurements showed several different pathways to nucleate ice depending on T and RHice conditions. For instance, almost T-independent freezing was observed at −60 °C < T < −50 °C, where RHice explicitly controlled ice nucleation efficiency, while both T and RHice played roles in other two T regimes: −78 °C < T < −60 °C and −50 °C < T < −36 °C. More specifically, observations at T lower than −60 °C revealed that higher RHice was necessary to maintain a constant ns, whereas T may have played a significant role in ice nucleation at T higher than −50 °C. We implemented the new hematite-derived ns parameterization, which agrees well with previous AIDA measurements of desert dust, into two conceptual cloud models to investigate their sensitivity to the new parameterization in comparison to existing ice nucleation schemes for simulating cirrus cloud properties. Our results show that the new AIDA-based parameterization leads to an order of magnitude higher ice crystal concentrations and to an inhibition of homogeneous nucleation in lower-temperature regions. Our cloud simulation results suggest that atmospheric dust particles that form ice nuclei at lower temperatures, below −36 °C, can potentially have a stronger influence on cloud properties, such as cloud longevity and initiation, compared to previous parameterizations.
A case study of a low level jet during OPALE
Authors: Gallée H. , Barral H. , Vignon E. , Genthon C.
Published: December 2014

Abstract. A case study of a low level jet during the OPALE (Oxidant Production over Antarctic Land and its Export) summer campaign is presented. It has been observed at Dome C (East Antarctica) and is simulated accurately by the three-dimensional version of the Modèle Atmosphérique Régional (MAR). It is found that this low level jet is not related to an episode of thermal wind, conforting that Dome C may be a~place where turbulence on flat terrain can be studied.
Dimensions and aspect ratios of natural ice crystals
Authors: Um J. , McFarquhar G. M. , Hong Y. P. , Lee S.-S. , Jung C. H. , Lawson R. P. , Mo Q.
Published: December 2014

Abstract. During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the Tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign in mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between −87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were further distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. Dimensions and aspect ratios (AR, dimension of major axis divided by dimension of minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased as temperature increased. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' or L') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50±1.35 during three campaigns and 6.32±1.34 (5.46±1.34; 4.95±1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67 < T < −35 °C and at −40 < T < −15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L–W relationships of columns derived using current data exhibited a strong dependence on temperature; similar relationship determined in previous studies were within the range of the current data.
Transfer of organic carbon through marine water columns to sediments – insights from stable and radiocarbon isotopes of lipid biomarkers
Authors: Wakeham S. G. , McNichol A. P.
Published: December 2014

Abstract. Compound-specific 13C and 14C compositions of diverse lipid biomarkers (fatty acids, alkenones, hydrocarbons, sterols and fatty alcohols) were measured in sinking particulate matter collected in sediment traps and from underlying surface sediments in the Black Sea, the Arabian Sea and the Ross Sea. The goal was to develop a multiparameter approach to constrain relative inputs of organic carbon (OC) from marine biomass, terrigenous vascular-plant and relict-kerogen sources. Using an isotope mass balance, we calculate that marine biomass in sediment trap material from the Black Sea and Arabian Sea accounted for 66–100% of OC, with lower terrigenous (3–8%) and relict (4–16%) contributions. Marine biomass in sediments constituted lower proportions of OC (66–90%), with consequentially higher proportions of terrigenous and relict carbon (3–17 and 7–13%, respectively). Ross Sea data were insufficient to allow similar mass balance calculations. These results suggest that, whereas particulate organic carbon is overwhelmingly marine in origin, pre-aged allochthonous terrigenous and relict OC become proportionally more important in sediments, consistent with pre-aged OC being better preserved during vertical transport to and burial at the seafloor than the upper-ocean-derived marine OC.
Export fluxes in a naturally fertilized area of the Southern Ocean, the Kerguelen Plateau: seasonal dynamic reveals long lags and strong attenuation of particulate organic carbon flux (Part 1)
Authors: Rembauville M. , Salter I. , Leblond N. , Gueneugues A. , Blain S.
Published: December 2014

Abstract. A sediment trap moored in the naturally iron-fertilized Kerguelen plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth current speeds were low (∼10 cm s−1) and primarily tidal-driven (M2 tidal component) providing favorable hydrodynamic conditions for the collection of flux. Particulate organic carbon (POC) flux was generally low (<0.5 mmol m−2 d−1) although two episodic export events (<14 days) of 1.5 mmol m−2 d−1 were recorded. These increases in flux occurred with a 1 month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 ± 4.4 mmol m−2 yr−1 was relatively low considering the shallow deployment depth, but similar to deep-ocean (>2 km) fluxes measured from similarly productive iron-fertilized blooms. Comparison of the sediment trap data with complementary estimates of biomass accumulation and export indicate that ∼90% of the flux was lost between 200 and 300 m. We hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for rapid flux attenuation and the High Biomass Low Export regime characterizing the Kerguelen bloom. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.
Nitrogen fixation in the Southern Ocean: a case of study of the Fe-fertilized Kerguelen region (KEOPS II cruise)
Authors: González M. L. , Molina V. , Florez-Leiva L. , Oriol L. , Cavagna A. J. , Dehairs F. , Farias L. , Fernandez C.
Published: December 2014

Abstract. N2 fixation rates were measured during the KEOPS2 cruise in the HNLC area of Southern Ocean and in naturally iron-fertilized waters (Kerguelen Island 49.25° S, 69.58° E) using the 15N isotopic technique. We detected N2 fixation within the mixed layer at all stations, from the surface to 140 m depth. The data shows high variability with rates ranging between 0.42 and 20.11 nmol N L−1 d−1. The highest rates were concentrated in the euphotic layer and maximum values were obtained north of polar front (station F-L), which coincide with a positive N* ([NO3]–16[PO4]), high chlorophyll concentration and dissolved iron. N2 fixation rates were also obtained in stations with moderate (A3-2; E-4W) and also low (R-2) iron levels as well as Chl a, suggesting that beside the microbial biomass, its composition/structure is a driving factor controlling N2 fixation activities. Molecular analysis showed a diazotrophic community dominated by heterotrophic bacterioplankton. Size fractioned experiments indicated that most of N2 fixating activities came from <5 μm community and it was on line with molecular analysis revealing a low diversity diazotrophic community dominated by heterotrophic bacterioplankton. This study shows for first time N2 fixation is occurring in the Southern Ocean, at rates exceeding previous reports for high latitudes. Our findings suggest an indirect role of dFe in the regulation of N2 fixation through the enhancement of regenerated primary production and the availability of phytoplankton-derived dissolved organic matter, which in turn may stimulate heterotrophic bacterioplankton.
Effects of low pH stress on shell traits and proteomes of the dove snail, Anachis misera inhabiting shallow vent environments off Kueishan Islet, Taiwan
Authors: Chen Y. J. , Wu J. Y. , Chen C. T. A. , Liu L. L.
Published: December 2014

Abstract. The effects of naturally acidified seawater on a snail species, Anachis misera (Family: Columbellidae) were quantified in five shallow vent-based environments off Kueishan Islet, Taiwan. An absence of Anachis snails was observed in the most acidic North site (pH 7.22), and the size structure differed among the remaining East, South, Southwest and Northwest sites. If a positive correlation between shell length and shell width or total weight existed, the coefficient of determination (R2) of the equations was low, i.e., 0.207–0.444. Snails from the Northwest site (pH 7.33) exhibited a more globular shape than those of the South ones (pH 7.80). Standardized shell thickness T1 (thickness of body whorl : shell length) and T2 (thickness of penultimate whorl : shell length) from the Northwest site showed a decrease of 6.3 and 9.4%, respectively, compared to the South ones. In a similar vein, based on the 16 examined protein spots, protein expression profiles of snails in the South were distinct. With further characterization by principle component analysis, the separation was mainly contributed by the first (i.e., spots 8, 1, 15, and 12) and second (i.e., spots 15, 13, 12, 1, and 11) principal-components. As a whole, the shallow vent-based findings provide new information from subtropics on the effects of ocean acidification on gastropod snails in natural environments.
Forecast error covariance structure in coupled atmosphere–chemistry data assimilation
Authors: Park S. K. , Lim S. , Zupanski M.
Published: December 2014

Abstract. In this study, we examined the structure of an ensemble-based coupled atmosphere–chemistry forecast error covariance. The Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem), a coupled atmosphere–chemistry model, was used to create an ensemble error covariance. The control variable includes both the dynamical and chemistry model variables. A synthetic single observation experiment was designed in order to evaluate the cross-variable components of a coupled error covariance. The results indicate that the coupled error covariance has important cross-variable components that allow a physically meaningful adjustment of all control variables. The additional benefit of the coupled error covariance is that a cross-component impact is allowed, e.g., atmospheric observations can exert impact on chemistry analysis, and vice versa. Given the realistic structure of ensemble forecast error covariance produced by the WRF-Chem, we anticipate the ensemble-based coupled atmosphere–chemistry data assimilation will respond similarly to assimilation of real observations.
The terminator "toy"-chemistry test: a simple tool to assess errors in transport schemes
Authors: Lauritzen P. H. , Conley A. J. , Lamarque J.-F. , Vitt F. , Taylor M. A.
Published: December 2014

Abstract. This test extends the evaluation of transport schemes from prescribed advection of inert scalars to reactive species. The test consists of transporting two reacting chlorine-like species (Cl and Cl2) in the Nair and Lauritzen 2-D idealized flow field. The sources and sinks for the two species are given by a simple, but non-linear, "toy" chemistry. This chemistry mimics photolysis-driven processes near the solar terminator. As a result, strong gradients in the spatial distribution of the species develop near the edge of the terminator. Despite the large spatial variations in Cl and Cl2 the weighted sum Cly = Cl +2 Cl2 should always be preserved. The terminator test demonstrates how well the advection/transport scheme preserves linear correlations. Physics-dynamics coupling can also be studied with this test. Examples of the consequences of this test are shown for illustration.
Normal-mode function representation of global 3-D datasets: an open-access software for atmospheric research community
Authors: Žagar N. , Kasahara A. , Terasaki K. , Tribbia J. , Tanaka H.
Published: December 2014

Abstract. The paper presents new software for the analysis of global dynamical fields in (re)analyses, weather forecasts and climate models. A new diagnostic tool, developed within the MODES project, allows one to diagnose properties of balanced and inertio-gravity (IG) circulation across many scales. In particular, the IG spectrum, which has only recently become observable, can be studied simultaneously in the mass field and wind field and considering the whole model depth in contrary to majority of studies. The paper presentation includes the theory of normal-mode function expansion, technical details of the Fortran 90 code, examples of namelists which control the software execution and outputs of the software application on the reanalysis dataset ERA Interim. The applied libraries and default compiler are from the open-source domain. A limited understanding of Fortran suffices for the successful implementation of the software. The presented application of the software to the ERA Interim dataset show some features of the large-scale circulation after it has been split into the balanced and IG components. The global energy distribution is dominated by the balanced energy with IG modes making less than 10% of the total wave energy. However, on subsynoptic scales IG energy dominates and it is associated with the main features of tropical variability on all scales. The presented energy distribution and features of the zonally-averaged and equatorial circulation provide a reference for the validation of climate models.
Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices
Authors: Funk C. , Hoell A. , Shukla S. , Bladé I. , Liebmann B. , Roberts J. B. , Robertson F. R. , Husak G.
Published: December 2014

Abstract. In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent East African droughts to a stronger Walker circulation, resulting from warming in the Indo–Pacific warm pool and an increased east-to-west sea surface temperature (SST) gradient in the western Pacific, we show that the two dominant modes of East African boreal spring rainfall variability are tied to SST fluctuations in the western central Pacific and central Indian Ocean, respectively. Variations in these two rainfall modes can thus be predicted using two SST indices – the western Pacific gradient (WPG) and central Indian Ocean index (CIO), with our statistical forecasts exhibiting reasonable cross-validated skill (rcv ≈ 0.6). In contrast, the current generation of coupled forecast models show no skill during the long rains. Our SST indices also appear to capture most of the major recent drought events such as 2000, 2009 and 2011. Predictions based on these simple indices can be used to support regional forecasting efforts and land surface data assimilations to help inform early warning and guide climate outlooks.
Identifying areas susceptible to desertification in the Brazilian Northeast
Authors: da Silva Pinto Vieira R. M. , Tomasella J. , dos Santos Alvalá R. C. , Sestini M. F. , Affonso A. G. , Rodriguez D. A. , Barbosa A. A. , do Amaral Cunha A. P. M. , de Fátima Valles G. , Crepani E. , de Oliveira S. B. P. , Benício de Souza M. S. , Calil P. M. , de Carvalho M. A. , de Morisson Valeriano D. , Campello F. C. B. , Santana M. O.
Published: December 2014

Abstract. Approximately 57% of the Brazilian Northeast region is recognized as semiarid land and has been undergoing intense land use processes in the last decades, which have resulted in severe degradation of its natural assets. Therefore, the objective of this study is to identify the areas that are susceptible to desertification in this region based on the eleven driving factors of desertification (pedology, geology, geomorphology, topography data, land use and land cover change, aridity index, livestock density, rural population density, fire hot spot density, human development index (HDI), conservation units) which were model-simulated for two different periods: 2000 and 2010. Each indicator were assigned weights ranging from 1 to 2 (representing the best and the worst conditions), representing classes indicating low, moderate and high susceptibility to desertification. The result indicates that 94% of the Brazilian Northeast region is under moderate to high susceptibility to desertification. The areas that were susceptible to soil desertification increased by approximately 4.6% (83.35 km2) from 2000 to 2010. The implementation of the methodology provide the technical basis for decision making that involves mitigating actions, as well as the first comprehensive national assessment within the United Nations Convention to Combat Desertification framework.
Exploring the Realities of Curriculum-by-Random-Opportunity: The Case of Geriatrics on the Internal Medicine Clerkship Rotation
Authors: Diachun Laura , Charise Andrea , Goldszmidt Mark , Hui Yin , Lingard Lorelei
Published: December 2014

BackgroundWhile major clerkship blocks may have objectives related to specialized areas such as geriatrics, gay and lesbian bisexual transgender health, and palliative care, there is concern that teaching activities may not attend sufficiently to these objectives. Rather, these objectives are assumed to be met “by random opportunity”.(1) This study explored the case of geriatric learning opportunities on internal medicine clinical teaching units, to better understand the affordances and limitations of curriculum by random opportunity.MethodsUsing audio-recordings of morning case review discussions of 13 patients > 65 years old and the Canadian geriatric core competencies for medical students, we conducted a content analysis of each case for potential geriatric and non-geriatric learning opportunities. These learning opportunities were compared with attendings’ case review teaching discussions. The 13 cases contained 40 geriatric-related and 110 non-geriatric-related issues. While many of the geriatric issues (e.g., delirium, falls) were directly relevant to the presenting illness, attendings’ teaching discussions focused almost exclusively on non-geriatric medical issues, such as management of diabetes and anemia, many of which were less directly relevant to the reason for presenting to hospital.ResultsThe authors found that the general medicine rotation provides opportunities to acquire geriatric competencies. However, the rare uptake of opportunities in this study suggests that, in curriculum-by-random-opportunity, presence of an opportunity does not justify the assumption that learning objectives will be met.ConclusionsMore studies are required to investigate whether these findings are transferrable to other vulnerable populations about which undergraduate students are expected to learn through curriculum by random opportunity.
Genome-wide regulatory dynamics of translation in the Plasmodium falciparum asexual blood stages
Authors: Caro Florence , Ahyong Vida , Betegon Miguel , DeRisi Joseph L
Published: December 2014

The characterization of the transcriptome and proteome of Plasmodium falciparum has been a tremendous resource for the understanding of the molecular physiology of this parasite. However, the translational dynamics that link steady-state mRNA with protein levels are not well understood. In this study, we bridge this disconnect by measuring genome-wide translation using ribosome profiling, through five stages of the P. falciparum blood phase developmental cycle. Our findings show that transcription and translation are tightly coupled, with overt translational control occurring for less than 10% of the transcriptome. Translationally regulated genes are predominantly associated with merozoite egress functions. We systematically define mRNA 5′ leader sequences, and 3′ UTRs, as well as antisense transcripts, along with ribosome occupancy for each, and establish that accumulation of ribosomes on 5′ leaders is a common transcript feature. This work represents the highest resolution and broadest portrait of gene expression and translation to date for this medically important parasite.
History of Path Analysis
Authors: Mulaik Stanley A.
Published: December 2014

Sewell Wright was a geneticist who originated the method of path analysis for studying causal hypotheses with correlations and partical correlations and who struggled to get it accepted in a climate of British and logical expiricism that was hostile to the concept of causality. The method subsequently developed into the modern method of structural equation modeling.
History of Factor Analysis: A Statistical Perspective
Authors: Bartholomew David J.
Published: December 2014

This article provides a brief, semi‐technical history of factor analysis from 1904 to recent times. It begins with the pioneering work of Charles Spearman and finishes with the modern approach of covariance structure modeling, which has incorporated factor analysis into a larger statistical setting.
History of Multivariate Analysis of Variance
Authors: Hershberger Scott L.
Published: December 2014

Multivariate analysis of variance (MANOVA) can be thought of as a multivariate generalization of analysis of variance (ANOVA), in which more than one dependent variable is used to evaluate group differences. Wilks introduced lambda (Λ) in 1932 as a statistical test of the equality of group centroids. Wilks's Λ was derived from the likelihood ratio of the null and non‐null hypotheses usually specified in MANOVA. Subsequently, other MANOVA test criteria were developed, although all share with Λ the difficulty of unusually complex sampling distributions. Instead of using Λ directly, either an approximate chi‐square orFratio transformation of Λ is preferred.
Model Identifiability
Authors: Huang Guan‐Hua
Published: December 2014

A model is identifiable if there is a one‐to‐one correspondence between the probability distribution of the data and the values of model parameters. When applying a nonidentifiable model, different people may draw different conclusions from the same model of the observed data. Before one can meaningfully discuss the estimation of a model, model identifiability must be verified.
Linear Statistical Models for Causation: A Critical Review
Authors: Freedman D. A.
Published: December 2014

We review the basis for inferring causation by means of linear statistical models. Parameters should be stable under interventions, and so should error distributions. There are also statistical conditions that must be satisfied. Stability is difficult to establisha priori, and the statistical conditions are equally problematic. Therefore, causal relationships are seldom to be inferred from a data set by running regressions, unless there is substantial prior knowledge about the mechanisms that generated the data.
Goodness of Fit Indices
Authors: Mulaik Stanley A.
Published: December 2014

Goodness of fit is assessed by tests of exact fit and indices of approximation. The chi squared statistic is a test of exact fit. Many indices of approximation are based on estimates of the normalized noncentrality parameter, which is a measure of the degree of lack of fit for the model to the data that is invariant of sample size. Discussed are commonly used indices such as the CFI, the RMSEA, the GFI index, and Steiger's Γ1.
Model Selection
Authors: Cortina Lilia M.
Published: December 2014

Given the complexity inherent in behavioral phenomena, there are typically multiple plausible models that can account for any set of observations. The task, then, is to select the model that shows superior qualities in terms of fit, parsimony, interpretability, and consistency with theory. Even then, the researcher cannot claim to have identified the one ‘true’ model, because selection of an excellent model could artifactually result from failure to consider every possible alternative.
Catastrophe Theory
Authors: Wagenmakers E.‐J. , Maas H. L. J. , M. Molenaar P. C.
Published: December 2014

Catastrophe theory describes how small, continuous changes in control parameters (i.e., independent variables that influence the state of a system) can have sudden, discontinuous effects on dependent variables. Such discontinuous, jumplike changes are called
phase‐transitions
or
catastrophes
. Examples include the sudden collapse of a bridge under slowly mounting pressure, and the freezing of water when temperature is gradually decreased. This entry expands on the ideas inherent in catastrophe models.
Graphical Chain Models
Authors: Wermuth Nanny
Published: December 2014

This article reviews the early twentieth century origins of graphical models and outlines the subsequent major developments from path analysis and conditional independence to the use of graphical models in representing relations among random variables, and, more recently, chains of such multivariate relations.
Saturated Model
Authors: Hershberger Scott L.
Published: December 2014

A saturated model is a model that perfectly fits the data because it has as many parameters as there are values to be fitted. Saturated models are also just‐identified models, and can provide useful information in the search for a more parsimonious, unsaturated model in which some of the parameters of the saturated are not estimated. Saturated and unsaturated models must be hierarchically nested in order to evaluate the unsaturated model's fit to the data.
Clinical Trials, Early Cancer and Heart Disease
Authors: Schneiderman Marvin A. , Gehan Edmund A.
Published: December 2014

Early developments in controlled clinical trials at the National Institutes of Health (NIH) took place mainly at the National Cancer Institute (NCI) and what was then the National Heart Institute (NHI) (subsequently the National Heart, Lung, and Blood Institute (NHLBI))beginning in the 1950s. This article reviews the developments from the early 1950s to the late 1960s at both institutes, summarizing the early efforts in clinical trials, the organizations set up to conduct and monitor the clinical trials, and the developments in statistical methodology that have formed the basis for conducting many of the present day randomized controlled trials. The early history of clinical trials at these institutes has been reviewed in more detail at NCI by Gehan & Schneiderman and at NHLBI by Halperin et al.
Catastrophical Risk
Authors: Chichilnisky Graciela
Published: December 2014

This article analyses decision under uncertainty, motivated by problems emerging from global environmental risks. These are typically low‐probability events with major irreversible consequences. For such risks the Von Neumann–Morgenstern (NM) Axioms for decision‐making under uncertainty are not appropriate, since they are insensitive to low‐probability events. The article introduces an alternative set of axioms that require sensitivity to both low and large probability events. Through a representation theorem in functional analysis, the results characterize all the operators whose maximization leads to the fulfillment of these axioms. They involve a convex combination of expected utility and a criterion based on the desire to avoid low‐probability and potentially catastrophical events. It is shown that the new axioms help resolve the Allais paradox. Open questions about risk aversion, games under uncertainty and calculus of variations are discussed.
Fire Risk, Industrial
Authors: Thomas Ian
Published: December 2014

Fire represents both a benefit and a threat to society. Fire is essential and is used constructively in providing many of the materials and services essential to modern living. However, unwanted fires represent a threat that is generally immediately recognized and instils fear into those threatened. Fire generally represents a small but not insignificant risk in modern societies. It represented a greater risk in the past when open fires were common in domestic and industrial situations, but even today unwanted fires are responsible for considerable loss of life, property and services. The consequences of unwanted fires include injuries and death to people and animals involved, loss of contents and building structures and consequential damage to businesses and services. Many of these losses are not recorded, or alternatively, not made publicly available, and so the consequences associated with them are unable to be estimated accurately. However, in many countries considerable effort is expended in recording details of unwanted fires, including locations, causes and consequences. However, international collection of such information is restricted to very basic information such as the overall losses and costs of fires and the number of fire ‐related fatalities per annum.
Flood Risk Management, Quantitative Methods
Authors: Gelder P. H. A. J. M
Published: December 2014

In this article, quantitative methods for flood risk management are discussed. Reliability analysis of flood defense systems and the probabilistic flood risk management approach are outlined. The application of quantitative methods offers the designer a way to unify the design of engineering structures, processes, and management systems. For this reason, there is a growing interest in the use of these methods in the design and safety assessment of flood defenses. This article describes the background of probabilistic analyses, uncertainties, and systems analysis for flood risk management.
Risk Assessment, Probabilistic
Authors: Thompson Kimberly M.
Published: December 2014

A primary criticism of environmental risk assessment as it has been practiced in the last 20 years has been the failure of analysts to properly account for issues of variability and uncertainty. Many risk assessments focused on producing ‘point estimates’ of risks have provided risk managers and decision makers with information that is at best incomplete and at worst dangerously misleading. As the field of risk assessment has matured, techniques for better treatment of variability and uncertainty have been developed and incorporated into what is known as ‘probabilistic’ risk assessments. In contrast to the point estimate approach, where single values are assumed for each model input, the probabilistic approach quantifies the possible range of values that each input may take, as well as the probability associated with each value. Modern computational power then allows the analyst to generate a multidimensional distribution of risk that reflects both the variability of risk across different individuals in the population as well as the uncertainty associated with each estimate.
Bienyeme‐Galton‐Watson Branching Process
Authors: Athreya K.B.
Published: December 2014

The study of the growth and development of many species of animals, plants and other organisms over time may be approached in the following manner. At some point in time a set of individuals called ancestors or the zeroth generation is identified. These produce offspring and the collection of offspring of all the ancestors constitutes the first generation. The offspring of these first generation individuals constitute the second generation and so on. If one specifies the rules by which the offspring production takes place then one could study the behavior of the long time evolution of such a process, called a
branching process
. Questions of interest are the long term survival of such a process or its extinction, the growth rate of such a population, fluctuation of population sizes, effects of control mechanicisms etc. In this article several simple mathematical models and some results for these will be discussed. Many of the assumptions made, especially the one about independence of lines of descent, are somewhat idealistic and unrealistic. Nevertheless, the models do prove useful in answering some general questions, since many results about long term behavior deviate somewhat from the basic assumptions.
Control Theory
Authors: Young Peter C.
Published: December 2014

Control theory is concerned with the mathematical characterization and analysis of deterministic and stochastic dynamic systems for the purpose of identification, estimation and control. It emphasizes the importance of feedback processes, both as an integral aspect of all dynamic systems and as a means of artificially controlling or optimizing the behavior of such systems. In relation to environmetrics, the main importance of control theory relates to the impact that it has had on the analysis of environmental time series and the modeling of environmental systems. In addition, however, its powerful ability to improve our understanding of how dynamic systems behave in feedback terms can have a profound effect on how environmetric models are interpreted in physically meaningful terms.
Copula Modeling for Extremes
Authors: Genest Christian , Nešlehová Johanna
Published: December 2014

This article introduces extreme‐value copulas, reviews models from this class, and describes their main properties. The associated rank‐based estimation procedures and model validation techniques are also presented.
Counting process: Theory
Authors: Olofsson Peter
Published: December 2014

A counting process is a nonnegative, integer‐valued, increasing stochastic process that is used to count the number of occurrences of some event as time goes by. Special cases include pure birth processes, renewal processes, and the Poisson process.
Covariogram, Examples of
Authors: Hu Juan
Published: December 2014

Covariogram is a term for covariance function of a second‐order process and is instrumental for spatial interpolation. This article provides some examples of isotropic covariograms for stationary‐spatial processes that have been used in kriging.
Criticality, Self‐Organized
Authors: Li Bai‐Lian
Published: December 2014

The causes and possible relations between the abundance of fractal structures (
see
Fractal dimensions) and 1/
f
signals found in nature have puzzled scientists for years. Based on observations of computer simulations of the cellular automata sandpile model, the term self‐organized criticality (SOC) was invented by theoretical physicists and was used to explain a universal dynamic organizing process governing various fractal growths in space and time. SOC describes that systems organize themselves so their internal dynamics produce critical behavior over a very wide range of length scales. The term consists of two parts.
Self‐organization
has been used to describe the ability of certain nonequilibrium systems to develop structures and patterns often without explicit pressure or involvement from outside the systems.
Criticality
is a technical word used in connection with phase transitions, and has a very precise meaning, in which the system becomes critical when all members of the system influence each other and events of all sizes occur.
Cylindrical Data
Authors: Anderson‐cook Christine M. , Otieno B. Sango
Published: December 2014

Cylindrical data are a form of directional data, where two responses are considered. An angular or circular response is combined with a linear response to form observations, which can be thought of as a location in polar coordinates or on the surface of a unit cylinder. There are several alternatives for modeling the responses including circular‐linear relationships. Depending on the nature of the relationship between the two responses, some model forms can be more natural than others. Environmental examples of cylindrical data include plant and animal migration, as well as wind direction with another environmental measure such as ozone concentration or temperature.
Demographic Stochastic Models
Authors: Ver Hoef Jay M.
Published: December 2014

Population viability analysis is the application and study of extinction effects in ecological population modeling. Population viability analysis has important applications for studying the global and local extinction of populations. It attempts to identify threats to populations and then evaluate the probability that the population will persist to some future time.
Dynamic Modeling: Introduction
Authors: Dowd Michael
Published: December 2014

Dynamic modeling describes the quantitative representation of time‐dependent systems, usually as systems of differential equations or discrete versions thereof. Dynamic models may be nonlinear, high dimensional, spatially explicit, and can exhibit complex behavior. They are most commonly deterministic, but can be stochastic. They are key elements for many scientific disciplines, and the foundation for environmental prediction. Dynamic modeling in environmetrics considers uncertainty analysis, as well as inference on the state of the system and its parameters using available observations.
Ensemble
Authors: Li Bo
Published: December 2014

This article introduces the concept of ensemble, mainly in the context of environmental and climate studies. It summaries several different types of ensembles and discusses why in general the ensemble is a popular and useful tool for problems with a large degree of freedom. Finally, it illustrates this concept through an example of past temperature reconstruction.