bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of solar radiation through clouds on melting glaciers: a comparison of parameterizations and their impact on melt modelling
Authors: Pellicciotti Francesca , Raschle Thomas , Huerlimann Thomas , Carenzo Marco , Burlando Paolo
Published: July 2011

We explore the robustness and transferability of parameterizations of cloud radiative forcing used in glacier melt models at two sites in the Swiss Alps. We also look at the rationale behind some of the most commonly used approaches, and explore the relationship between cloud transmittance and several standard meteorological variables. The 2 m air-temperature diurnal range is the best predictor of variations in cloud transmittance. However, linear and exponential parameterizations can only explain 30–50% of the observed variance in computed cloud transmittance factors. We examine the impact of modelled cloud transmittance factors on both solar radiation and ablation rates computed with an enhanced temperature-index model. The melt model performance decreases when modelled radiation is used, the reduction being due to an underestimation of incoming solar radiation on clear-sky days. The model works well under overcast conditions. We also seek alternatives to the use of in situ ground data. However, outputs from an atmospheric model (2.2 km horizontal resolution) do not seem to provide an alternative to the parameterizations of cloud radiative forcing based on observations of air temperature at glacier automatic weather stations. Conversely, the correct definition of overcast conditions is important.
Life, death and afterlife of the extrusion flow theory
Authors: Waddington Edwin D.
Published: July 2011

‘Extrusion flow’ describes any velocity field where maximum horizontal velocity occurs below the surface. By 1914, viscous flow and basal sliding over rough beds were accepted concepts. Between the world wars, there was little communication between naturalists describing complicated ice sheets, and physicists studying fundamental processes controlling flow. Max Demorest brought concepts from mechanics into glaciology and glacial geology; however, his extrusion flow theory, to explain how ice flowed out of central Greenland, overlooked force imbalance. Rudolf Streiff-Becker found an apparent large imbalance between ice flux discharged through a gate and net accumulation in the upstream catchment at Claridenfirn, Switzerland. Because he underestimated uncertainty in ice depth, he had to propose a strong undercurrent (extrusion flow) to evacuate the excess mass. Reassessment of his assumptions shows that extrusion was actually unnecessary. However, confluence of two lines of evidence for extrusion flow added stature to the concept. In 1952, John Nye showed that free extrusion flow was impossible due to force imbalance. Two forms of extrusion flow survive: capped extrusion flow is possible on local scales where longitudinal stress gradients allow upper ice to move slowly, and rigid- body rotational flow can allow deeper ice to move faster without strain.
Röthlisberger channel theory: its origins and consequences
Authors: Walder Joseph S.
Published: July 2011

The theory of channelized water flow through glaciers, most commonly associated with the names of Hans Röthlisberger and Ron Shreve and their 1972 papers in theJournal of Glaciology, was developed at a time when interest in glacier-bed processes was expanding, and the possible relationship between glacier sliding and water at the bed was becoming of keen interest. The R-channel theory provided for the first time a physically based conceptual model of water flow through glaciers. The theory also marks the emergence of glacier hydrology as a glaciological discipline with goals and methods distinct from those of surface-water hydrology.
A short history of the thermomechanical theory and modeling of glaciers and ice sheets
Authors: Blatter Heinz , Greve Ralf , Abe-Ouchi Ayako
Published: July 2011

Observations of glacier flow and explanations of its origin started as early as the 18th century. Several mechanisms were suggested before gravity-driven viscous flow became the accepted theory of glacier flow in the 1950s, the early years of the Journal of Glaciology. Since the viscosity of ice is strongly temperature-dependent, the topic of glacier and ice-sheet dynamics became essentially a fluid-dynamical problem. The availability of growing computing power turned the field of glacier mechanics and thermodynamics into a field of numerical modelling with increasing sophistication.
Emergent drumlins and their clones: from till dilatancy to flow instabilities
Authors: Clark Chris D.
Published: July 2011

Subglacial bedforms are a range of landforms (10-105m long) shaped mostly in glacial sediments and are abundant on ice-sheet beds. Numerous explanations for their generation, especially of drumlins, have been proposed. Rather than viewing them as resulting from erosion or deposition directly by ice, Smalley and Unwin (1968) proposed that both might occur simultaneously if, beneath the glacier, a layer of lubricating sediment existed and ‘flowed’, conducting geomorphic work (erosion, deposition, shaping) of its own. This idea appears to have steered the field, leading perhaps to final resolution of the centuries-old problem of drumlin genesis. Here I trace how the idea evolved, leading to the conclusion that subglacial bedforms are emergent phenomena arising from self-organization in the coupled flow of ice, sediment and water. The ubiquity and patterning of bedforms appears to be well explained by a naturally arising flow instability in the subglacial system, and which has been demonstrated by analytical and numerical modelling. A problem for the instability theory is an apparent mismatch between predicted and observed sedimentological properties of bedforms. A distinction is made between emergent drumlins, drumlin clones and obstacle drumlins which helps explain some apparent contradictions, and a conceptual framework is erected that might form a basis for confronting the theory with the wealth of observational evidence that exists.
Reliability of ice-core science: historical insights
Authors: Alley Richard B.
Published: July 2011

Ice cores are remarkably faithful recorders of past climate, providing multiply duplicated reconstructions with small and quantifiable uncertainties. Ice core reconstructions in general do not rely on assumed quantitative time-invariance of empirical calibrations between climate and sedimentary characteristics, but instead rely on assuming little more than the constancy of physical law over time. The history of some of the discoveries that allow these ice-core climatic reconstructions is instructive for students, citizens and policymakers. Much important ice-core science was published in the Journal of Glaciology and the Annals of Glaciology, with scientific impacts much larger than indicated by mere citation counts.
Frost heave
Authors: Rempel Alan W.
Published: July 2011

The deformation of the ground surface that is produced by frost heave has motivated almost a century of concerted laboratory, field and theoretical studies. Well before the development of equipment capable of resolving the microscopic films that support liquid transport towards growing ice lenses, early investigators predicted their occurrence and noted their importance. Idealized experiments continue to prompt theoretical advances that have been combined to develop predictive models for the macroscopic frost-heave characteristics that are seen in the field. This contribution highlights steps on the road to our current understanding of the physical interactions that control how ice forms in unconsolidated porous media.
Glaciological advances made with interferometric synthetic aperture radar
Authors: Joughin Ian , Smith Ben E. , Abdalati Waleed
Published: July 2011

Spaceborne interferometric synthetic aperture radar (InSAR) techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half, revolutionizing the study of ice dynamics. Spaceborne interferometry has contributed to major progress in many areas of glaciological study by: providing the first comprehensive measurements of ice-stream flow velocity over the major outlets of Greenland and Antarctica; revealing that ice-stream and outlet-glacier flow can change rapidly (months to years); improving understanding of several ice-sheet and ice-shelf processes; providing velocity for flux-gate based mass-balance assessment; mapping flow of mountain glaciers; and capturing the geomorphic traces of past ice flow. We review the basic technique development, the measurement characteristics, and the extensive set of results yielded by these measurements.
Satellite remote sensing of sea-ice thickness and kinematics: a review
Authors: Kwok R.
Published: July 2011

Observations of sea-ice thickness and kinematics are essential for understanding changes in sea-ice mass balance, interactions between the ice cover and the ocean and atmosphere and for improving projections of sea-ice response in a warming climate. These parameters are not directly observable with current sensor technology, but are derived from satellite altimetry and imagery. While there is progress in the retrievals of Arctic sea-ice thickness from satellite altimetry, approaches to address Southern Ocean ice thickness require additional attention. On the other hand, procedures to derive sea-ice motion from satellite imagery are more mature and better understood and have been employed to produce useful results for more than a decade. Adequate sampling of sub-daily ice motion, however, remains a challenge. Generally, satellite instruments provide large-scale coverage but the frequency of temporal sampling is limited by orbit characteristics. In this review, I focus on the approaches, uncertainties, sampling limitations and validation issues associated with the estimation of sea-ice thickness and motion. I provide a summary of current and anticipated capabilities for monitoring sea-ice thickness and kinematics from space. The prospects for continuing these measurements into the next decade, from a satellite remote-sensing perspective, are discussed.
Arctic sea-ice change: a grand challenge of climate science
Authors: Kattsov Vladimir M. , Ryabinin Vladimir E. , Overland James E. , Serreze Mark C. , Visbeck Martin , Walsh John E. , Meier Walt , Zhang Xiangdong
Published: July 2011

Over the period of modern satellite observations, Arctic sea-ice extent at the end of the melt season (September) has declined at a rate of >11% per decade, and there is evidence that the rate of decline has accelerated during the last decade. While climate models project further decreases in sea- ice mass and extent through the 21st century, the model ensemble mean trend over the period of instrumental records is smaller than observed. Possible reasons for the apparent discrepancy between observations and model simulations include observational uncertainties, vigorous unforced climate variability in the high latitudes, and limitations and shortcomings of the models stemming in particular from gaps in understanding physical process. The economic significance of a seasonally sea-ice-free future Arctic, the increased connectivity of a warmer Arctic with changes in global climate, and large uncertainties in magnitude and timing of these impacts make the problem of rapid sea-ice loss in the Arctic a grand challenge of climate science. Meaningful prediction/projection of the Arctic sea-ice conditions for the coming decades and beyond requires determining priorities for observations and model development, evaluation of the ability of climate models to reproduce the observed sea-ice behavior as a part of the broader climate system, improved attribution of the causes of Arctic sea-ice change, and improved understanding of the predictability of sea-ice conditions on seasonal through centennial timescales in the wider context of the polar climate predictability.
Creep and plasticity of glacier ice: a material science perspective
Authors: Duval Paul , Montagnat Maurine , Grennerat Fanny , Weiss Jerome , Meyssonnier Jacques , Philip Armelle
Published: July 2011

Major advances in understanding the plasticity of ice have been made during the past 60 years with the development of studies of the flow of glaciers and, recently, with the analysis of deep ice cores in Antarctica and Greenland. Recent experimental investigations clearly show that the plastic deformation of the ice single crystal and polycrystal is produced by intermittent dislocation bursts triggered by long-range interaction of dislocations. Such dislocation avalanches are associated with the formation of dislocation patterns in the form of slip lines and slip bands, which exhibit long-range correlations and scale invariance. Long-range dislocation interactions appear to play an essential role in primary creep of polycrystals and dynamic recrystallization. The large plastic anisotropy of the ice crystal is at the origin of large strain and stress heterogeneities within grains. The use of full- field approaches is now a compulsory proceeding to model the intracrystalline heterogeneities that develop in polycrystals. Ice is now highly regarded among the materials science community. It is considered a model material for understanding deformation processes of crystalline materials and polycrystal modeling.
Shear resistance and continuity of subglacial till: hydrology rules
Authors: Iverson Neal R.
Published: July 2011

The field observations of G.S. Boulton stimulated widespread interest in deformable beds. Shear resistance of till in its critical state is insensitive to strain rate and increases linearly with effective pressure. During unsteady deformation, pseudo-viscous shear resistance can be caused by dilation of consolidated tills and resultant pore-pressure decline. This effect is probably uncommon, however, because susceptible tills of low hydraulic diffusivity are also those least likely to consolidate significantly during effective-pressure transients. Stick-slip motion at Whillans Ice Stream, Antarctica, indicates that its basal till must weaken during rapid slip and strengthen during longer periods of slower slip. Recurrence intervals for rapid-slip episodes there (6-18hours) indicate that till-strength variations, if driven by changes in pore pressure either related or unrelated to basal freezing, are focused in the uppermost several centimeters of the bed. Ploughing of grains at the bed surface and associated excess pore pressures in adjacent till can account for rate-weakening during rapid slip, with pore-pressure decay causing strengthening between slip episodes. By promoting shallow, sluggish subglacial water flow and low effective pressure, soft beds may help sustain themselves by slowing their own transport. Soft-bed shear resistance, kinematics and continuity are problems rooted in subglacial hydrology.
Immune Suppression in Tumors as a Surmountable Obstacle to Clinical Efficacy of Cancer Vaccines
Authors: Wieërs Grégoire , Demotte Nathalie , Godelaine Danièle , Van der Bruggen Pierre
Published: July 2011

Human tumors are usually not spontaneously eliminated by the immune system and therapeutic vaccination of cancer patients with defined antigens is followed by tumor regressions only in a small minority of the patients. The poor vaccination effectiveness could be explained by an immunosuppressive tumor microenvironment. Because T cells that infiltrate tumor metastases have an impaired ability to lyse target cells or to secrete cytokine, many researchers are trying to decipher the underlying immunosuppressive mechanisms. We will review these here, in particular those considered as potential therapeutic targets. A special attention will be given to galectins, a family of carbohydrate binding proteins. These lectins have often been implicated in inflammation and cancer and may be useful targets for the development of new anti-cancer therapies.
Stability Proxies for Water-in-Oil Emulsions and Implications in Aqueous-based Enhanced Oil Recovery
Authors: Alvarado Vladimir , Wang Xiuyu , Moradi Mehrnoosh
Published: July 2011

Several researchers have proposed that mobility control mechanisms can positively contribute to oil recovery in the case of emulsions generated in Enhanced-Oil Recovery (EOR) operations. Chemical EOR techniques that use alkaline components or/and surfactants are known to produce undesirable emulsions that create operational problems and are difficult to break. Other water-based methods have been less studied in this sense. EOR processes such as polymer flooding and LoSalTM injection require adjustments of water chemistry, mainly by lowering the ionic strength of the solution or by decreasing hardness. The decreased ionic strength of EOR solutions can give rise to more stable water-in-oil emulsions, which are speculated to improve mobility ratio between the injectant and the displaced oil. The first step toward understanding the connection between the emulsions and EOR mechanisms is to show that EOR conditions, such as salinity and hardness requirements, among others, are conducive to stabilizing emulsions. In order to do this, adequate stability proxies are required. This paper reviews commonly used emulsion stability proxies and explains the advantages and disadvantage of methods reviewed. This paper also reviews aqueous-based EOR processes with focus on heavy oil to contextualize in-situ emulsion stabilization conditions. This context sets the basis for comparison of emulsion stability proxies.
Direct Sensor Orientation of a Land-Based Mobile Mapping System
Authors: Rau Jiann-Yeou , Habib Ayman F. , Kersting Ana P. , Chiang Kai-Wei , Bang Ki-In , Tseng Yi-Hsing , Li Yu-Hua
Published: July 2011

A land-based mobile mapping system (MMS) is flexible and useful for the acquisition of road environment geospatial information. It integrates a set of imaging sensors and a position and orientation system (POS). The positioning quality of such systems is highly dependent on the accuracy of the utilized POS. This limitation is the major drawback due to the elevated cost associated with high-end GPS/INS units, particularly the inertial system. The potential accuracy of the direct sensor orientation depends on the architecture and quality of the GPS/INS integration process as well as the validity of the system calibration (i.e., calibration of the individual sensors as well as the system mounting parameters). In this paper, a novel single-step procedure using integrated sensor orientation with relative orientation constraint for the estimation of the mounting parameters is introduced. A comparative analysis between the proposed single-step and the traditional two-step procedure is carried out. Moreover, the estimated mounting parameters using the different methods are used in a direct geo-referencing procedure to evaluate their performance and the feasibility of the implemented system. Experimental results show that the proposed system using single-step system calibration method can achieve high 3D positioning accuracy.
Visual Odometry Based on Structural Matching of Local Invariant Features Using Stereo Camera Sensor
Authors: Núñez Pedro , Vázquez-Martín Ricardo , Bandera Antonio
Published: July 2011

This paper describes a novel sensor system to estimate the motion of a stereo camera. Local invariant image features are matched between pairs of frames and linked into image trajectories at video rate, providing the so-called visual odometry, i.e., motion estimates from visual input alone. Our proposal conducts two matching sessions: the first one between sets of features associated to the images of the stereo pairs and the second one between sets of features associated to consecutive frames. With respect to previously proposed approaches, the main novelty of this proposal is that both matching algorithms are conducted by means of a fast matching algorithm which combines absolute and relative feature constraints. Finding the largest-valued set of mutually consistent matches is equivalent to finding the maximum-weighted clique on a graph. The stereo matching allows to represent the scene view as a graph which emerge from the features of the accepted clique. On the other hand, the frame-to-frame matching defines a graph whose vertices are features in 3D space. The efficiency of the approach is increased by minimizing the geometric and algebraic errors to estimate the final displacement of the stereo camera between consecutive acquired frames. The proposed approach has been tested for mobile robotics navigation purposes in real environments and using different features. Experimental results demonstrate the performance of the proposal, which could be applied in both industrial and service robot fields.
La réalité de la microfinance à l'échelle régionale : l'exemple de l'Aquitaine
Authors: Brana Sophie , Jégourel Yves
Published: July 2011

Reposant sur une base de données unique totalisant près de 4000 prêts provenant de 33 institutions de microfinance (IMF) localisées sur la région Aquitaine, cet article poursuit trois objectifs : identifier les IMF opérant sur le territoire aquitain, évaluer à quels besoins celles-ci répondent et préciser enfin la nature de la relation de crédit qui s’instaure entre ces différentes institutions et leurs bénéficiaires. Utilisant un modèle probit, nous montrons que les déterminants de l’octroi d’un microcrédit restent relativement conventionnels, proches de ceux adoptés dans le secteur bancaire traditionnel. Nous mettons, en outre, en lumière que la microfinance touche deux catégories de clients, les uns partiellement exclus du secteur bancaire tandis que les autres en sont totalement exclus. Nous soulignons, enfin, l’importance du dispositif d’accompagnement en amont de la relation de prêt pour que la microfinance atteigne pleinement ses ambitions sociales.
L'écologie industrielle comme processus de développement territorial : une lecture par la proximité
Authors: Beaurain Christophe , Brullot Sabrina
Published: July 2011

A l’échelle d’un territoire, une démarche d’écologie industrielle (EI), appelée symbiose industrielle, permet de réduire l’impact des activités économiques sur l’environnement. Cet article vise essentiellement à mettre en évidence l’apport d’une lecture par le corpus théorique de la proximité de ces démarches. Après avoir rappelé brièvement le cadre théorique traditionnellement utilisé pour appréhender les symbioses industrielles, nous développons l’idée que l’écologie industrielle relève d’une dynamique de développement territorial. Nous soulignons ainsi la pertinence d’une mobilisation des notions utilisées par le groupe de la Proximité pour illustrer le caractère dynamique d’une démarche d’EI. Nous insistons plus particulièrement sur le rôle décisif des projets de territoire et des interactions créatrices de ressources spécifiques dans la mise en œuvre de ces démarches.
Vers un nouveau modèle systémique dans l'analyse de la création d'activités et d'emplois en espace rural
Authors: Verbeck Cédric , Lenain Marie-Anne , Blasquiet-Revol Hélène
Published: July 2011

Bien qu’inégal selon les territoires, le redressement démographique des espaces ruraux se confirme. Le maintien et la création d’activités et d’emplois sont donc plus que jamais nécessaires au développement économique de ces territoires. Les termes de "création d’emplois" et de "création d’activités" sont rarement définis et recouvrent des objets flous. Les chercheurs se sont approprié le thème de façon diversifiée au sein d’approches et de disciplines variées. Cet article identifie, par une revue de littérature, les cadres théoriques des différentes disciplines sur le sujet de la création d’activités et d’emplois en territoire rural. A partir de cet état de l’art, il propose un nouveau modèle systémique dans l’analyse de la création d’activités et d’emplois dans les espaces ruraux. Ce triptyque est construit autour des aspects du créateur d’activités, des acteurs de l’accompagnement et des territoires ruraux.
Macular Dystrophy in Kabuki Syndrome: A New Clinical Feature?
Authors: Lindfield Dan , Griffiths Michael F. P. , Thompson Dorothy A. , Moore Anthony T.
Published: July 2011

Kabuki syndrome is a rare and genetically heterogenous condition that has both systemic and ophthalmic complications. Macular dystrophy has not previously been noted in conjunction with this syndrome. The authors present a 14-year-old girl with Kabuki syndrome with macular dystrophy and confirmatory electrodiagnostics.
Pathologies and analytical study of mosaic materials from Carmona and Italica
Authors: Palomar T. , García-Heras M. , Saiz-Jiménez C. , Márquez C. , Villegas M. A.
Published: July 2011

This work reports on the characterization of Roman mosaic samples from Carmona and Italica (Spain). A physico-chemical study of both glass tesserae and mortar fragments to determine their composition, to evaluate their state of conservation and to study their production technology was carried out. Samples were characterized by means of a binocular microscope, SEM-EDS, visible spectrophotometry, XRD and petrographic analysis. The tesserae were made from soda lime silicate glass, even though one of them showed high contents of lead and copper oxides. The samples from Carmona showed deterioration pathologies associated to the humidity affecting the mosaic during burial, while those from Italica presented traces of biodeterioration. The data also indicated that the glass used in the tesserae had a lower technical quality than that used in tableware pieces of similar chronology.
Proceso de molturación mecánica en medio seco, húmedo y criogénico de polvo de hierro dúctil nanoestructurado
Authors: Cinca N. , Hurtado E. , Cano I. G. , Guilemany J. M.
Published: July 2011

El principal objetivo de este estudio, es obtener una efectiva reducción del tamaño de partícula y de grano de un polvo de hierro nanoestructurado mediante la molturación mecánica en diferentes medios de molienda. La principal dificultad radica en la gran ductilidad del material. Las variables a estudiar en el proceso han sido la velocidad de rotación, la relación polvo/bolas y el porcentaje de agente de control añadido. El polvo se ha estudiado por difracción laser para caracterizar la distribución de tamaños de partículas, microscopía electrónica de barrido (SEM), microscopía electrónica de transmisión (TEM) y difracción de Rayos X. Del estudio comparativo se destaca: la molienda en seco ha dado lugar a una reducción más efectiva tanto del tamaño de partícula (43%) como del tamaño de grano (62%), mientras que en condiciones húmedas se ha conseguido disminuir la cantidad de óxido, así como obtener una distribución más homogénea del polvo resultante, aunque la reducción del tamaño de partícula no ha sido tan efectiva; finalmente, los resultados en medio criogénico producen reducciones en tamaños en tiempos más cortos y por tanto resultan prometedores.
Aplicación del permanganato potásico para la eliminación de cianuros de cobre en aguas residuales de la planta de lixiviación en una mina de oro (II): Ensayos en planta piloto
Authors: Sancho J. P. , Fernández B. , Ayala J. , García M. P. , Lavandeira A.
Published: July 2011

La búsqueda de un tratamiento que permita la detoxificación de las aguas residuales generadas durante los procesos industriales, ha sido una constante para todas las empresas en general y para las explotaciones mineras auríferas en particular, cuyas aguas residuales suelen contener elevadas concentraciones de compuestos cianurados con una elevada toxicidad. En el trabajo de investigación previo, desarrollado en el laboratorio, se demostró la eficacia del permanganato potásico como agente oxidante de aguas residuales cianuradas, procedentes de una planta hidrometalúrgica de oro, consiguiendo la destrucción de los complejos cianurados de cobre presentes en solución y la posterior eliminación del metal por precipitación como hidróxido. En este trabajo se presentan las conclusiones obtenidas tras la implantación del proceso desarrollado en el laboratorio, a escala de planta piloto.
Coagulación de finos en la flotación de la fluorita
Authors: Sarquís P. E. , González M. , Moyano A. , Bazán V.
Published: July 2011

La fluorita es un mineral de mucha importancia en la industria metalúrgica. Se presenta acompañada de silicatos, carbonatos y óxidos. Para la obtención de concentrados comerciales, más de 95 % de CaF2, el mineral se procesa en plantas de flotación donde se usa ácido oleico como colector de la fluorita. Para que el ácido oleico actúe selectivamente es común el uso de reactivos depresores: silicato de sodio, tanino y carbonato de sodio. Estos agentes tienen un efecto dispersante que se evidencia en la separación de sólido-líquido sobre las colas de las plantas. El agua recuperada contiene finos que al ingresar al circuito afectan notoriamente la eficiencia de la flotación. Se estudió el efecto de iones coagulantes para clarificar el agua de retorno. El problema de estos iones está relacionado con sus reacciones con el colector por la formación de compuestos y, posiblemente, sobre la selectividad. Se agregaron cantidades variables de iones Al3+, Fe3+ y Ca2+ y se evaluó la recuperación de fluorita, la selectividad y en el contenido de sólidos en el agua de los efluentes. Los resultados muestran que algunos iones no solamente no mejoran la calidad del agua sino que además son perjudiciales en la flotación. Otros, por el contrario, contribuyen a reducir el contenido de finos en suspensión. Por lo tanto, y si bien hay una pérdida en la recuperación, este efecto se puede contrarrestar con un pequeño aumento en el consumo de colector.
Modelado del crecimiento de picaduras en tuberías enterradas que transportan hidrocarburos utilizando técnicas estadísticas
Authors: Velázquez J. C. , Caleyo F. , Valor A. , Hallen J. M.
Published: July 2011

Esta investigación, resume los resultados de un estudio, enfocado en contribuir a resolver las necesidades de predicción de crecimiento de picadura en ductos que transportan hidrocarburos. Primero, se describe el desarrollo de un modelo determinista, considerando las propiedades físicas y químicas del suelo y el tipo de recubrimiento que protege la tubería. Este modelo fue utilizado para realizar simulaciones de Monte Carlo, logrando establecer las distribuciones de probabilidad de profundidad de picadura y su velocidad de crecimiento en suelos. Finalmente, se detalla el desarrollo de un modelo estocástico basado en cadenas de Markov. Este modelo tiene como objetivo, predecir la evolución en el tiempo de las distribuciones de profundidad de picadura.
Os docentes de Biblioteconomia, Documentação e Ciência da Informação no Brasil: alguns resultados de estudo exploratório sobre as representações da profissão bibliotecária
Authors: Walter Maria Tereza Machado Teles , Baptista Sofia Galvão
Published: July 2011

As representações da profissão bibliotecária são analisadas sob a perspectiva dos docentes, em estudo exploratório. Os dados parciais apresentados refletem a opinião dos entrevistados acerca de sua percepção dos alunos, do curso, da profissão e dos organismos representativos dos bibliotecários. De modo geral, os professores manifestaram que os alunos não entram nos cursos por vocação, são originários de classes socioeconômicas menos favorecidas, possuem formação básica frágil e não estão interessados na carreira, mas somente no diploma. Apontaram problemas decorrentes da forma como são conduzidos os cursos, do modo como alguns professores atuam e de como trabalham para que os alunos adquiram conhecimentos e mudem suas atitudes.
A contribuição de B. Dervin para a Ciência da Informação no Brasil
Authors: Araújo Carlos Alberto Ávila , Pereira Giselle Alves , Fernandes Janaína Rozário
Published: July 2011

O artigo apresenta os resultados de uma pesquisa que buscou ver o impacto de Brenda Dervin na produção científica brasileira em Ciência da Informação. Buscou-se referências à autora em todos os artigos publicados em sete periódicos nacionais, entre os anos de 2003 e 2007. Dervin é citada em 27 dos 872 artigos analisados. Das 19577 referências bibliográficas destes artigos, 42 são de trabalhos de Dervin. Essas referências foram analisadas buscando-se identificar a freqüência de cada uma das obras da autora citadas, ano, idioma, natureza e casos de co-autoria. Os artigos citantes foram analisados em termos de temática e procedência institucional dos autores. Por fim, analisou-se a importância das citações à autora para as discussões empreendidas nos artigos citantes. Entre os resultados encontrados destacam-se: a obra mais citada, Information needs and uses, teve 16 referências; a maior contribuição da autora se dá no âmbito dos estudos de usuários da informação; a instituição brasileira que mais a cita é a UFMG; o tipo de citação mais comum é a conceitual.
Análise das disciplinas de tecnologia da informação ofertadas nos currículos dos cursos de arquivologia da região sul do Brasil
Authors: Araujo Nelma Camêlo , Crestosmo Simone
Published: July 2011

Este artigo é parte de uma pesquisa realizada nas Universidades do Sul do Brasil que ministram disciplinas de Tecnologia da Informação nos Cursos de Arquivologia. Os objetivos da pesquisa foram identificar por meio da proposta pedagógica dos Cursos as disciplinas que contém conteúdo de Tecnologia da Informação, bem como identificar a percepção dos docentes que ministram essas disciplinas serealmenteas mesmas capacitam os estudantes dos cursos a estarem preparados para o mercado de trabalho
Cultura escrita: práticas de leitura e do impresso
Authors: Cavalcante Lidia Eugenia
Published: July 2011

A história da cultura escrita e das práticas de leitura é o tema discutido neste artigo. Visa compreender a trajetória do livro impresso em sua materialidade, bem como os processos delineados a partir da incontestável presença cultural e política desse suporte para a sociedade moderna. Busca evidenciar as práticas, os fenômenos e as mutações que sustentam tal suporte por séculos, abordando a “crise do livro”, suas causas e efeitos. Por conseguinte, trata das particularidades da cultura escrita, que se efetivaram no Siècle des Lumières e se consagraram no “agir” do espírito dos autores e dos leitores daquela época, cuja propagação influenciou definitivamente o mundo ocidental. Analisa as condições sociológicas e históricas do lugar do leitor moderno entre Ciência, Filosofia e Romance, continuamente transformado pela renovação do pensamento e da cultura.
Les facteurs de développement des bibliothèques publiques québécoises depuis 1959
Authors: Gazo Dominique
Published: July 2011

Cet article est une revue de littérature qui propose de distinguer les différents facteurs de développement des bibliothèques publiques québécoises. La législation, l'action gouvernementale, les modes administratifs, le financement et les normes sont étudiés tout à tour afin de rendre compte du processus de développement des bibliothèques publiques au Québec.
A cada leitor seu texto: dos livros às redes
Authors: Almeida Marco Antônio de
Published: July 2011

Este artigo faz considerações sobre a relação entre livros, leituras e leitores considerando as mudanças na materialidade dos meios de comunicação social e cultural e nas formas de organização textual, produção, distribuição e recepção de conhecimentos e informações. Centra-se nas formas como os textos escritos se tornam objetos manuscritos, escritos, impressos e informatizados, e de que maneira estas materializações dos textos criam determinadas formas de leitura e de tipos de leitores.
Art et archives: une perspective archivistique
Authors: Lemay Yvon
Published: July 2011

Bien que les artistes contemporains aient été nombreux depuis la fin des années 1980 à utiliser des documents d’archives dans leurs travaux, le phénomène a été peu étudié jusqu’ici par les archivistes. Le but de cet article est de présenter les grandes lignes d’un projet de recherche que nous avons amorcé sur le sujet, plus particulièrement sur l’usage d’archives photographiques. Dans un premier temps, nous effectuons une revue de la littérature afin de montrer l’importance de cette tendance dans le milieu de l’art. Deuxièmement, nous esquissons les bases d’une typologie visant à mieux comprendre les motivations des créateurs et les orientations de leur production. Troisièmement, nous présentons cinq aspects qui sont autant de raisons de s’intéresser à l’utilisation artistique des archives d’un point de vue archivistique. Nous terminerons en soulignant la contribution de ce projet à l’avancement de la discipline et l’approche contextuelle qui a été privilégiée.
Aerosol flux measurements above a mixed forest at Borden, Ontario
Authors: Gordon M. , Staebler R. M. , Liggio J. , Vlasenko A. , Li S.-M. , Hayden K.
Published: July 2011

Abstract. Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. Chemically speciated flux measurements were made at a height of 29 m at the same location between 19 July and 2 August, 2006 using a Quadrupole Aerosol Mass Spectrometer (Q-AMS). The Q-AMS measured an average sulphate deposition velocity of 0.3 mm s−1 and an average nitrate deposition velocity of 4.8 mm s−1. The FMPS, mounted at a height of 33 m (approximately 10 m above the canopy top) and housed in a temperature controlled enclosure, measured size-resolved particle concentrations from 3 to 410 nm diameter at a rate of 1 Hz. For the size range 18 < D < 452 nm, 60 % of fluxes were upward. The exchange velocity was between −0.5 and 2.0 mm s−1, with median values near 0.5 mm s−1 for all sizes between 22 and 310 nm. The size distribution of the apparent production rate of particles at 33 m peaked at a diameter of 75 nm. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day.
Black carbon in the atmosphere and snow, from pre-industrial times until present
Authors: Skeie R. B. , Berntsen T. , Myhre G. , Pedersen C. A. , Ström J. , Gerland S. , Ogren J. A.
Published: July 2011

Abstract. The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65° N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m−2 and for the snow-albedo effect 0.016 W m−2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.
Sulphur dioxide as a volcanic ash proxy during the April–May 2010 eruption of Eyjafjallajökull Volcano, Iceland
Authors: Thomas H. E. , Prata A. J.
Published: July 2011

Abstract. The volcanic ash cloud from the eruption of Eyjafjallajökull volcano in April and May 2010 resulted in unprecedented disruption to air traffic in Western Europe causing significant financial losses and highlighting the importance of efficient volcanic cloud monitoring. The feasibility of using SO2 as a tracer for the ash released during the eruption is investigated here through comparison of ash retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) with SO2 measurements from a number of infrared and ultraviolet satellite-based sensors. Results demonstrate that the eruption can be divided into an initial ash-rich phase, a lower intensity middle phase and a final phase where considerably greater quantities both ash and SO2 were released. Comparisons of ash-SO2 dispersion indicate that despite frequent collocation of the two species, there are a number of instances throughout the eruption where separation is observed. This separation occurs vertically due to the more rapid settling rate of ash compared to SO2, horizontally through wind shear and temporally through volcanological controls on eruption style. The potential for the two species to be dispersed independently has consequences in terms of aircraft hazard mitigation and highlights the importance of monitoring both species concurrently.
Artifacts in measuring aerosol uptake kinetics: the roles of time, concentration and adsorption
Authors: Renbaum L. H. , Smith G. D.
Published: July 2011

Abstract. In laboratory studies of organic aerosol particles reacting with gas-phase oxidants, high concentrations of radicals are often used to study on the timescale of seconds reactions which may be occurring over days or weeks in the troposphere. Implicit in this approach is the assumption that radical concentration and time are interchangeable parameters, though this has not been established. Here, the kinetics of OH- and Cl-initiated oxidation reactions of model single-component liquid (squalane) and supercooled (brassidic acid and 2-octyldodecanoic acid) organic aerosols are studied by varying separately the radical concentration and the reaction time. Two separate flow tubes with residence times of 2 and 66 s are used, and [OH] and [Cl] are varied by adjusting either the laser photolysis fluence or the radical precursor concentration ([O3] or [Cl2], respectively) used to generate the radicals. It is found that the rates measured by varying the radical concentration and the reaction time are equal only if the precursor concentrations are the same in the two approaches. Further, the rates depend on the concentrations of the precursor species with a Langmuir-type functional form suggesting that O3 and Cl2 saturate the surface of the liquid particles. It is believed that the presence of O3 inhibits the rate of OH reaction, perhaps by reacting with OH radicals or by O3 or intermediate species blocking surface sites, while Cl2 enhances the rate of Cl reaction by participating in a radical chain mechanism. These results have important implications for laboratory experiments in which high concentrations of gas-phase oxidants are used to study atmospheric reactions over short timescales and may explain the variability in recent measurements of the reactive uptake of OH on squalane particles in reactor systems used in this and other laboratories.
Effect of humidity on the composition of isoprene photooxidation secondary organic aerosol
Authors: Nguyen T. B. , Roach P. J. , Laskin J. , Laskin A. , Nizkorodov S. A.
Published: July 2011

Abstract. The effect of relative humidity (RH) on the composition and concentrations of gas-phase products and secondary organic aerosol (SOA) generated from the photooxidation of isoprene under high-NOx conditions was investigated. Experiments were performed with hydrogen peroxide as the OH precursor and in the absence of seed aerosol. The relative yields of most gas-phase products were the same regardless of initial water vapor concentration with exception of hydroxyacetone and glycolaldehyde, which were considerably affected by RH. A significant change was observed in the SOA composition, with many unique condensed-phase products formed under humid (90 % RH) vs. dry (<2 % RH) conditions, without any detectable effect on the rate and extent of the SOA mass growth. There is a 40 % reduction in the number and relative abundance of distinct particle-phase nitrogen-containing organic compounds (NOC) detected by high resolution mass spectrometry. The suppression of condensation reactions, which produce water as a product, is the most important chemical effect of the increased RH. For example, the total signal from oligomeric esters of 2-methylglyceric acid was reduced by about 60 % under humid conditions and the maximum oligomer chain lengths were reduced by 7–11 carbons. Oligomers formed by addition mechanisms, without direct involvement of water, also decreased at elevated RH but to a much smaller extent. The observed reduction in the extent of condensation-type oligomerization at high RH may have substantial impact on the phase characteristics and hygroscopicity of the isoprene aerosol. The reduction in the amount of organic nitrates in the particle phase has implications for understanding the budget of NOC compounds.
A high-resolution emission inventory of primary pollutants for the Huabei region, China
Authors: Zhao B. , Wang P. , Ma J. Z. , Zhu S. , Pozzer A. , Li W.
Published: July 2011

Abstract. Huabei is a part of eastern China located between 32° N and 42° N latitude. Administratively it is a region including Beijing and Tianjin Municipalities, Hebei and Shanxi Provinces, and Inner-Mongolia Autonomous Region. Over the past decades, the region has experienced dramatic changes in air quality and climate, and has become a major focus of environmental research in China. Here we present a new inventory of air pollutant emissions in Huabei for the year 2003 developed as part of the project Influence of Pollution on Aerosols and Cloud Microphysics in North China (IPAC-NC). Our estimates are based on the data from the statistical yearbooks of state and provinces as well as local districts including major sectors and activities of power generation, industrial energy consumption, industrial processing, civil energy consumption, crop straw burning, oil and solvent evaporation, manure, and motor vehicles. The emission factors are selected from a variety of literature and those from local measurements in China are used whenever available. The estimated total emissions in the Huabei administrative region in 2003 are 4.73 Tg SO2, 2.72 Tg NOx (in equivalent NO2), 1.77 Tg VOC, 24.14 Tg CO, 2.03 Tg NH3, 4.57 Tg PM10, 2.42 Tg PM2.5, 0.21 Tg EC, and 0.46 Tg OC. For model convenience, we consider a larger Huabei region with Shandong, Henan and Liaoning Provinces included in our inventory. The estimated total emissions in the larger Huabei region in 2003 are: 9.55 Tg SO2, 5.27 Tg NOx (in equivalent NO2), 3.82 Tg VOC, 46.59 Tg CO, 5.36 Tg NH3, 10.74 Tg PM10, 5.62 Tg PM2.5, 0.41 Tg EC, and 0.99 Tg OC. The estimated emission rates are projected into grid cells at a horizontal resolution of 0.1° latitude by 0.1° longitude. Our gridded emission inventory consists of area sources, which are classified into industrial, civil, traffic, and straw burning sectors, and large industrial point sources, which include 345 sets of power plants, iron and steel plants, cement plants, and chemical plants. The estimated regional NO2 emissions are about 2–3 % (administrative Huabei region) or 5 % (larger Huabei region) of the global anthropogenic NO2 emissions. We compare our inventory (IPAC-NC) with a global emission inventory EDGAR-CIRCE and an Asian emission inventory INTEX-B. While the total emissions in Huabei are comparable with each other, large differences up to a factor of 2–3 for local emissions in the areas such as the Beijing and Tianjin megacities are found. We expect that our inventory will provide more practical spatial distributions of air pollutant emissions in the Huabei region of China and can be applied for air pollution and chemistry research on this region in the future.