1,721,044 research outputs found
The use of finite element field analysis in investigating industrial electrostatic hazards
No full textLarge vessels containing electrostatically charged flammable mists or dust clouds form part of many industrial processes. Consequently, high internal space potentials and electric fields are possible, promoting electrostatic discharges. The risk of ignition is often addressed by nitrogen inertion or by adding explosion protection systems. A preferred cost-effective alternative is to analyse the process with the aim of determining the maximum electric field that can be generated inside the vessel, for comparison with breakdown strength of air at which electrostatic discharges can occur. This field can seldom be measured directly. It can, however, be determined by performing simple measurements of the charge concentration and vessel dimensions to model the electrostatic conditions using a finite element, field analysis package. The package has been routinely used in hazard analyses by Wolfson Electrostatics, allowing the potential distributions and electric fields inside vessels to be displayed, using interactive graphics, as contour lines, vectors or graphs. Two hazard investigations in which the package was used are described in this paper
Electrostatic ignition assessment of flammable clouds in large vessels by finite-element potential and electric field analysis
No full textThe Holocene vegetation history of Erhai Lake, Yunnan Province southwestern China: The role of climate and human forcings
No full textA pollen diagram from a 6.62 m sediment sequence in Lake Erhai in northwest Yunnan, China was obtained to examine the roles of climate change and human impact on the development of the Erhai lake-catchment system since 12950 cal. yr BP. The record extends back into the Younger Dryas, where the dominance of Betula and deciduous Quercus points to a relatively cold and wet winter climate. After 11 750 cal. yr BP, a warming climate coupled with enhanced summer monsoon precipitation results in the expansion of Tsuga and evergreen broadleaved trees (Cyclobalanopsis, Lithocarpus and Castanopsis). An increase in evergreen oaks and dry-tolerant species after 10 320 cal. yr BP suggests a greater seasonality in rainfall, reflecting a southward shift in the winter front across the region. This trend of increasing temperatures and seasonality is seen to continue through into the mid-Holocene and the onset of the Holocene optimum. A marked decline in arboreal taxa coupled with increased levels of grass (Poaceae) and other disturbance taxa provides the first evidence for human impact in the catchment at c. 6370 cal. yr BP. This early phase of forest clearance leads to the collapse of the natural altitudinal vegetation gradient that existed in the catchment from the Lateglacial. The subsequent expansion of secondary pine forest suggests that these early clearances were part of a sustained period of shifting agriculture. Archaeological and historical records for the region point to a gradual increase in immigration into the region throughout the late Holocene. The increased pressure on the catchment is reflected in the pollen record by a series of clearance phases, which increase in intensity after 2140 cal. yr BP, linked presumably to intensification of agriculture and early urbanization. This trend continues through the last millennium, before a sharp increase in arboreal pollen at the top of the core reflects a phase of reforestation that took place in the catchment over the last 25 years
Coupling temporal and spatial dimensions of global sediment flux through lake and marine sediment records
No full textA major obstacle to our ability to assess future impacts of climate and human activities on the global sediment system is the lack of suitable timescales over which long-term processes and system properties may be observed. A long-term view offers the opportunity to observe pre-impact states, trajectories and the history of responses to forcings. The paper explores the scope of sediment archives in lakes and the continental margin as sources of information to inform about spatio-temporal characteristics of total suspended sediment (TSS) flux across spatial scales ranging from small catchments (<103 km2) to regional–continental basins (103–106 km2), and over timescales varying from decades to millennia. Numerous published studies, representing many geographical regions, provide estimates for sedimentation rates over full- or part-Holocene timescales, based largely on 14C and 210Pb dating. Results from small–medium drainage basins show that, during the Holocene, climate has been largely subordinate to human impact in controlling long-term shifts in sediment loads, though the evidence for short-term climate impacts is also clear. The rise in sediment delivery following major human impact is typically 5–10-fold higher than under undisturbed conditions, but may be higher depending upon the environment and intensity of impact. Sediment-source studies suggest that surface soil rarely dominates the sediment load, and that channel and gully sources often dominate even in small basins. For larger drainage basins, the forcing–response mechanisms are less clear and there is evidence to suggest that values for modern fluxes lie close to long-term averages. A more systematic analysis of the relative magnitude of change in sediment flux in different basin sizes reveals a global trend where relative changes diminish with increasing basin size. The findings suggest that small basins are most responsive to impacts and will show the largest changes in sediment flux. In contrast, large basins with effective storage zones and very slow reaction times lead to far weaker levels of spatio-temporal coupling. One implication is that the most rapid increases in sediment flux to the coast are caused by disturbance in small–medium drainage basins feeding directly to the coast. Overall, lake and marine sediment archives provide a range of useful information, often with high temporal resolution, that is difficult to obtain by other means. Future studies may be able to use these datasets to provide a typological classification of sediment regimes according to different spatio-temporal characteristics of their forcing–response mechanisms
Assessment of industrial electrostatic hazards using finite-element electric field analysis
No full textCharged clouds, generated in industrial processes, can lead to large values of space potential and electric field inside a vessel. Isolated masses of airborne liquid within can carry induced charge to the wall resulting in electrostatic discharges. Critical values of space potential can be found using a relationship between the jet safety factor and the material hazard coefficient. A computer package is described which allows complex space potential profiles and electric fields to be modelled for a prescribed space charge density. This allows the central space potential, a key indicator of electrostatic risk, to be evaluated. Examples are presented of two recent hazard investigations made by Wolfson Electrostatics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Holocene human-environment interaction in sub-tropical south-west China: a case-study from Erhai lake catchment Yunnan Province
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