1,720,984 research outputs found
Urban Energy Fluxes in Built-Up Downtown Areas and Variations across the Urban Area, for Use in Dispersion Models
No full textSurface energy fluxes, at averaging times from 10 min to 1 h, are needed as inputs to most state-of-the-art dispersion models. The sensible heat flux is a major priority, because it is combined with the momentum flux to estimate the stability, the wind profile, and the turbulence intensities. Because of recent concerns about dispersion in built-up downtown areas of large cities, there is a need to estimate sensible heat flux in the midst of tall buildings. In this paper, the authors work with some high-quality and relevant but arguably underutilized data. The results of analysis of urban heat flux components from 10 locations in suburban and built-up downtown areas in Oklahoma City, Oklahoma, during the Joint Urban 2003 (JU2003) field experiment are presented here. At street level in the downtown area, in the midst of tall skyscrapers, the ground heat flux and the sensible heat flux are relatively large and the latent heat flux is relatively small when compared with concurrent fluxes observed in the upwind suburban areas. In confirmation of measurements in other cities, the sensible heat flux in the downtown area is observed to be slightly positive (10–20 W m[superscript −2]) at night, indicating nearly neutral or slightly unstable conditions. Also in agreement with observations in other cities is that the ground heat flux in the downtown area has a magnitude that is 3 or 4 times that in suburban or rural areas. These results should permit improved parameterizations of sensible heat fluxes in the urban downtown area with tall buildings.National Science Foundation (U.S.) (Award 0750878)Singapore. National Research FoundationSingapore-MIT Alliance for Research and TechnologySingapore-MIT Alliance. Center for Environmental Sensing and Monitorin
Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation
Full text linkThermal stratification (neutral, unstable and stable) plays an important role in determining the transport processes in and above urban street canyons. This paper summarizes the recent findings of the effect of thermal stratification on the transport of momentum, heat, and pollutants in the two-dimensional (2D) urban street canyons in the skimming flow regime. Special attention is paid to the results from large-eddy simulations (LESs), while other experimental and numerical results are referred to when necessary. With increasing Richardson number, Ri, the drag coefficient of the 2D street canyon as felt by the overlying atmosphere decreases in a linear manner. Under neutral and stable stratification, a nearly constant drag coefficient of 0.02 is predicted by the LESs. Under unstable stratification, the turbulent pollutant transport is dominated by organized turbulent motions (ejections and sweeps), while under stable stratification, the unorganized turbulent motion (inward interactions) plays a more important role and the sweeps are inhibited. The unstable stratification condition also enhances the ejections of turbulent pollutant flux, especially at the leeward roof-level corner, where the ejections dominate the turbulent pollutant flux, outweighing the sweeps. With increasing Ri, both the heat (area active scalar source) and pollutant (line passive scalar source) transfer coefficients decrease towards a state where the transfer coefficients become zero at Ri≈0.5. It should be noted that, due to the limit of the 2D street canyon configuration discussed in this paper, great caution should be taken when generalising the conclusions drawn here.Singapore. National Research FoundationSingapore-MIT Alliance for Research and Technology. Center for Environmental Sensing and Modelin
Live Geography -- Embedded Sensing for Standarised Urban Environmental Monitoring
No full textEnvironmental monitoring faces a variety of
complex technical and socio-political challenges, particularly in
the urban context. Data sources may be available, but mostly
not combinable because of lacking interoperability and
deficient coordination due to monolithic and closed data
infrastructures. In this work we present the Live Geography
approach that seeks to tackle these challenges with an open
sensing infrastructure for monitoring applications. Our system
makes extensive use of open (geospatial) standards throughout
the entire process chain – from sensor data integration to
analysis, Complex Event Processing (CEP), alerting, and
finally visualisation. We discuss the implemented modules as
well as the overall created infrastructure as a whole. Finally,
we show how the methodology can influence the city and its
inhabitants by „making the abstract real“, in other words how
pervasive environmental monitoring systems can change urban
social interactions, and which issues are related to establishing
such systems
Mapping urban climate and air quality for city planning, from multi-scale modeling to real-time air sensing
No full textLa pianificazione urbana si trova ad affrontare le sfide determinate dai cambiamenti climatici e dall’inquinamento urbano in città sempre più affollate, sia nei contesti emergenti sia in quelli consolidati. Ondate di calore e malattie respiratorie affliggono la salute e la qualità di vita dei cittadini. Come pianificare un’efficace risposta?
In primo luogo mappando, ovvero aumentando la conoscenza a livello locale. Tuttavia il mapping è limitato dall’esistente gap di comunicazione tra la pianificazione e la conoscenza settoriale (climatologia, scienze ambientali, epidemiologia). Esiste inoltre un gap di scala: mentre soluzioni di mitigazione e, in particolare di adattamento, sono studiate a scala prevalentemente locale, i modelli sono disponibili a scala vasta, e non consentono una mappatura a scala di quartiere, delle persone. Quali strumenti suggerire quindi alla pianificazione al fine di mappare e migliorare il clima urbano e la qualità dell’aria della città?
Il sensing, l’interpretazione dell’osservazione diretta a scala locale, potrebbe fornire una soluzione, attraverso l’ipotesi di una rete di sensori pervasiva e diffusa nella città. Infatti, grazie ai recenti avanzamenti della tecnologia e l’abbassamento dei costi, da poche precise stazioni di monitoraggio è possibile pensare ad un drastico cambio di paradigma dal modeling verso il sensing: la costituzione di una rete intelligente di sensori diffusa nella città, e che apre a nuova conoscenza e a scenari partecipativi, grazie al potenziale coinvolgimento dei cittadini che diventano attori consapevoli. Come usare quindi il sensing?
L’impatto e le opportunità per la pianificazione urbana e ambientale sono vaste: una mappatura del clima urbano e della qualità dell’aria, ad alta risoluzione e a scala locale, ha la potenzialità di contribuire a studi urbani sulla concentrazione di inquinanti e calore nell’ambiente urbano, consentendo analisi su variazioni spaziali e temporali di eventuali hotspots urbani. Essendo inoltre i dati raccolti in real-time, è possibile immaginare la creazione di una piattaforma intelligente per una comunicazione e collaborazione interdisciplinare, utile a vari attori, pianificatori, decisori, cittadini, contribuendo alla finalità ultima di pianificare città resilienti, “sensienti” e “responsive”.
La ricerca ha inteso quindi esplorare le opportunità del sensing nella mappatura del clima urbano della qualità dell’aria: mappare tramite sensing potrebbe configurarsi come un modo per trasferire la conoscenza climatica e ambientale nel linguaggio della pianificazione, migliorando scala e risoluzione del modeling, e colmando l’esistente gap tra climatologia, meteorologia, studi ambientali sull’aria, pianificazione e disegno urbano. Esplorare l’impatto sulla pianificazione, come può essa beneficiare dal city sensing, include anche la ricerca del possibile coinvolgimento e partecipazione dei cittadini, spinto dal crescente interesse per le tematiche ambientali, della salute e della qualità della vita urbana.
I limiti dell’air sensing, tra i quali la tecnologia e i costi, sono le principali barriere per l’utilizzo diffuso allo stato attuale in ambito urbano. Pertanto, oltre ad evidenziare le opportunità, la ricerca mira a esplorare potenziali ostacoli e le strategie per superarli, fornendo raccomandazioni per anticiparne una sua futura integrazione negli strumenti della pianificazione.Urban planning is facing the environmental questions posed by climate change and air pollution in urbanized and increasingly crowded areas in both the developed and developing world: how can cities alleviate their responsibility and address proper measures? While current studies are exploring mitigation and particularly adaptation solutions to be applied to target locations, data and urban models are mostly available at the regional/city level, with little information available at the local/neighborhood level, and the “people's level”.
However, new available sensing technologies are pushing a paradigm shift: from traditional top-down climate/environmental modeling and scarce governmental monitoring to innovative diffused sensor networks and participatory sensing scenarios. The opportunities for spatial and environmental planning are vast: mapping at a local scale and at a fine-grained resolution can enhance UHI and pollution concentration studies, and allow hotspots spatial and temporal variation studies. In addition, real-time information supports the creation of an urban smart information platform for interdisciplinary communication and collaboration, ultimately used by planners and decision makers, for planning more sentient, resilient, and responsive cities.
The research aims to investigate the potential of mapping urban climate and air quality with the help of air sensing; mapping by air sensing can be a way of transferring the climatic and environmental knowledge into planning languages, bridging the gap between urban climatology, meteorology, air studies, city planning and urban design.
Limits of air sensing, in its technology and cost, are the biggest barriers for current planning processes. Therefore, exploring air sensing opportunity, obstacles and strategies to overcome them, and providing recommendations for its integration into urban planning, is the final scope of this research.DIPARTIMENTO DI ARCHITETTURA E STUDI URBANI26POLETTI, ANGELASALERNO, ROSSELL
Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation
Full text linkA validated large-eddy simulation model was employed to study the effect of the aspect ratio and ground heating on the flow and pollutant dispersion in urban street canyons. Three ground-heating intensities (neutral, weak and strong) were imposed in street canyons of aspect ratio 1, 2, and 0.5. The detailed patterns of flow, turbulence, temperature and pollutant transport were analyzed and compared. Significant changes of flow and scalar patterns were caused by ground heating in the street canyon of aspect ratio 2 and 0.5, while only the street canyon of aspect ratio 0.5 showed a change in flow regime (from wake interference flow to skimming flow). The street canyon of aspect ratio 1 does not show any significant change in the flow field. Ground heating generated strong mixing of heat and pollutant; the normalized temperature inside street canyons was approximately spatially uniform and somewhat insensitive to the aspect ratio and heating intensity. This study helps elucidate the combined effects of urban geometry and thermal stratification on the urban canyon flow and pollutant dispersion.Singapore National Research Foundation (Singapore-MIT Alliance for Research and Technology (SMART)
The rise of low-cost sensing for managing air pollution in cities
Full text linkEver growing populations in cities are associated with a major increase in road vehicles and air pollution. The overall high levels of urban air pollution have been shown to be of a significant risk to city dwellers. However, the impacts of very high but temporally and spatially restricted pollution, and thus exposure, are still poorly understood. Conventional approaches to air quality monitoring are based on networks of static and sparse measurement stations. However, these are prohibitively expensive to capture tempo-spatial heterogeneity and identify pollution hotspots, which is required for the development of robust real-time strategies for exposure control. Current progress in developing low-cost micro-scale sensing technology is radically changing the conventional approach to allow real-time information in a capillary form. But the question remains whether there is value in the less accurate data they generate. This article illustrates the drivers behind current rises in the use of low-cost sensors for air pollution management in cities, whilst addressing the major challenges for their effective implementation
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
Predicting vehicular emissions in high spatial resolution using pervasively measured transportation data and microscopic emissions model
No full textAir pollution related to traffic emissions pose an especially significant problem in cities; this is due to its adverse impact on human health and well-being. Previous studies which have aimed to quantify emissions from the transportation sector have been limited by either simulated or coarsely resolved traffic volume data. Emissions inventories form the basis of urban pollution models, therefore in this study, Global Positioning System (GPS) trajectory data from a taxi fleet of over 15,000 vehicles were analyzed with the aim of predicting air pollution emissions for Singapore. This novel approach enabled the quantification of instantaneous drive cycle parameters in high spatio-temporal resolution, which provided the basis for a microscopic emissions model. Carbon dioxide (CO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and particulate matter (PM) emissions were thus estimated. Highly localized areas of elevated emissions levels were identified, with a spatio-temporal precision not possible with previously used methods for estimating emissions. Relatively higher emissions areas were mainly concentrated in a few districts that were the Singapore Downtown Core area, to the north of the central urban region and to the east of it. Daily emissions quantified for the total motor vehicle population of Singapore were found to be comparable to another emissions dataset. Results demonstrated that high-resolution spatio-temporal vehicle traces detected using GPS in large taxi fleets could be used to infer highly localized areas of elevated acceleration and air pollution emissions in cities, and may become a complement to traditional emission estimates, especially in emerging cities and countries where reliable fine-grained urban air quality data is not easily available. This is the first study of its kind to investigate measured microscopic vehicle movement in tandem with microscopic emissions modeling for a substantial study domain. Keywords: Air quality; Transportation; Emissions; Microscopic emissions model; Microscopic vehicle movemen
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
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