1,722,509 research outputs found
Particle bound reactive oxygen species (PB-ROS) emissions and formation pathways in residential wood smoke under different combustion and aging conditions
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<p><strong>Abstract. </strong>Wood combustion emissions can induce oxidative stress in the human respiratory tract by reactive oxygen species (ROS) in the aerosol particles, which are emitted either directly or formed through oxidation in the atmosphere. To improve our understanding of the particle bound ROS (PB-ROS) generation potential of wood combustion emissions, a suite of smog chamber (SC) and potential aerosol mass (PAM) chamber experiments were conducted under well determined conditions for different combustion devices and technologies, different fuel types, operation methods, combustion regimes, combustion phases and aging conditions. The PB-ROS content as well as the chemical properties of the aerosols were quantified by a novel ROS analyzer using the DCFH (2’,7’-dichlorofluorescin) assay and a high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS). For all eight tested combustion devices, primary PB-ROS concentrations substantially increased upon aging. The level of primary and aged PB-ROS emission factors (EF<sub>ROS</sub>) were dominated by the combustion device (within different combustion technologies) and to a greater extent by the combustion regimes: the variability within one device was much higher than the variability of EF<sub>ROS</sub> from different devices. Aged EF<sub>ROS</sub> under bad combustion conditions were ~2-80 times higher than under optimum combustion conditions. EF<sub>ROS</sub> from automatically operated combustion devices were on average one order of magnitude lower than those from manually operated appliances, which indicates that automatic combustion devices operated at optimum conditions to achieve near-complete combustion should be employed to minimize PB-ROS emissions. The use of an electrostatic precipitator decreased the primary and aged ROS emissions by a factor of ~1.5 which is however still within the burn-to-burn variability. The parameters controlling the PB-ROS formation in secondary organic aerosol were investigated by employing a regression model, including the fractions of the mass to charge ratios <em>m/z</em> 44 and 43 in secondary organic aerosol (SOA) (<em>f</em><sub>44-SOA </sub>and <em>f</em><sub>43-SOA</sub>), the OH exposure, and the total organic aerosol mass. The regression model results of the SC and PAM chamber aging experiments indicate that the PB-ROS content in SOA seems to increase with the SOA oxidation state, which initially increases with OH exposure and decreases with the additional partitioning of semi-volatile components with lower PB-ROS content at higher OA concentrations, while further aging seems to result in a decay of PB-ROS. The results and the special data analysis methods deployed in this study could provide a role model for PB-ROS analysis of further wood or any other combustion studies investigating different combustion conditions and aging methods.</p>
Analisi delle colonne di tubi in acciaio ad alte prestazioni (UHPC)
No full textLa colonna di tubi in acciaio rivestiti in calcestruzzo ad alte prestazioni è una sorta di struttura composita di nuovo tipo che viene realizzata riempiendo UHPC in tubi in acciaio.Può esercitare pienamente le proprietà di trazione del tubo di acciaio ed evitare l'elevata fragilità dell'UHPC.In questo modo, può migliorare le prestazioni di forza della struttura composita.Oggi, la ricerca sulla struttura UCFST si concentra principalmente sul suo comportamento statico, e la ricerca sul comportamento isteretico di questa nuova struttura composita è piuttosto rara.Pertanto, in questo documento, il comportamento ciclico delle colonne UCFST è stato studiato combinando lo studio sperimentale e l'analisi degli elementi finiti.I principali lavori svolti e le principali conclusioni raggiunte sono i seguenti:
(1) Facendo riferimento alle prove statiche esistenti delle colonne UCFST e alle prove quasi statiche delle normali colonne di tubi in acciaio riempiti in calcestruzzo, sono state effettuate le prove quasi statiche di otto colonne UCFST.Gli effetti del rapporto di compressione assiale e del rapporto di acciaio sul comportamento isteretico delle colonne sono stati studiati sperimentalmente. I risultati sperimentali hanno dimostrato che in tutti gli esemplari si sono verificati guasti integrali alla curvatura.E con l'aumento del rapporto di compressione assiale, la capacità di curvatura del campione è aumentata in primo luogo e poi diminuita, mentre la capacità di dissipazione dell'energia e della duttilità è diminuita molto.Inoltre, la capacità di flessione, di duttilità e di dissipazione dell'energia è aumentata in misura diversa con l'aumento del rapporto acciaio.
(2) Secondo i risultati di ricerca dei test statici delle colonne UCFST, il modello costitutivo del calcestruzzo confinato è stato selezionato in modo appropriato in primo luogo in questo foglio e il programma degli elementi finiti OpenSEES è stato adottato per stabilire modelli di colonne UCFST sotto carico ciclico.Inoltre, l'influenza del rapporto di compressione assiale, del rapporto di acciaio, dell'acciaio che produce forza e forza concreta sul comportamento di curvatura plastica delle colonne UCFST è stata analizzata espandidamente dal modello di elemento finito verificato.E i risultati dell'analisi degli elementi finiti hanno dimostrato che il rapporto acciaio, la forza di calcestruzzo e il rapporto di compressione assiale erano i parametri principali che influenzano la rigidità di elasticità delle colonne UCFST.Il momento di resa e la curvatura delle colonne UCFST sono stati influenzati principalmente dal rapporto di acciaio, dall'acciaio che produce forza e dalla forza di calcestruzzo di base.E i parametri come il rapporto di compressione assiale, il rapporto di acciaio, la resistenza in acciaio e così via influenzano il coefficiente di duttilità di curvatura delle colonne UCFST.
(3) In base ai risultati delle prove quasi -statiche e dell'analisi degli elementi finiti, la curva di curvatura della curva del momento -curvatura delle colonne UCFST può essere ben simulata utilizzando il modello a tre linee.Per quanto riguarda la teoria della colonna CFST, le formule di calcolo semplificate di ciascun punto caratteristico della curva scheletrica di curvatura del momento delle colonne UCFST sono state ottenute con il metodo di montaggio dei dati.E i punti caratteristici includono la rigidità di elasticità, il momento di resa, la curvatura della resa e la rigidità di fase di rafforzamento.Infine, i dati delle prove quasi statiche e dell'analisi degli elementi finiti sono stati utilizzati per verificare il modello tri -line sulla curva di curvatura del momento -curvatura delle colonne UCFST proposte in questo documento, che può fornire un riferimento per la ricerca sul comportamento sismico delle colonne UCFST in futuro.Ultra-high performance concrete (UHPC)-filled steel tube (UCFST) column is a kind of new-type composite structure which is made by filling UHPC into steel tube. It can fully exert the tensile properties of steel tube and avoid the high brittleness of UHPC. Thus, it can improve the force-bearing performance of the composite structure. Nowadays, research on UCFST structure mainly focuses on its static behavior, and the research on hysteretic behavior of this new composite structure is quite rare. Therefore, in this paper, the cyclic behavior of UCFST columns were studied by combining the experimental study and finite element analysis. The main work carried out and the main conclusions obtained are as follows:
(1) Referring to the existing static tests of UCFST columns and quasi-static tests of normal concrete-filled steel tube (CFST) columns, the quasi-static tests of eight UCFST columns were carried out. The effects of axial compression ratio and steel ratio on the hysteretic behavior of the columns were investigated experimentally. The experimental results showed that integral bending failure were occurred in all the specimens. And with the increase of axial compression ratio, the bending capacity of the specimen increased firstly and then decreased, while the ductility and energy dissipation capacity decreased a lot. Furthermore, the bending capacity, ductility and energy dissipation capacity all increased in different magnitude as the steel ratio increased.
(2) According to the research results of UCFST columns static tests, the constitutive model of confined concrete was selected appropriately firstly in this paper and the finite element program OpenSEES was adopted to establish UCFST column models under cyclic load. Furthermore, the influence of axial compression ratio, steel ratio, steel yielding strength and concrete strength on the plastic bending behavior of UCFST columns was analyzed expandingly by the verified finite element model. And the results of finite element analysis showed that steel ratio, core concrete strength and axial compression ratio were the main parameters that affect the elasticity stiffness of UCFST columns. The yield moment and yield curvature of UCFST columns were mainly affected by steel ratio, steel yielding strength and core concrete strength. And the parameters such as axial compression ratio, steel ratio, steel strength and so on would affect the curvature ductility coefficient of UCFST columns.
(3) According to the results of quasi-static tests and finite element analysis, the bending moment-curvature skeleton curve of UCFST columns can be the well simulated by using the tri-line model. Referring to CFST column theory, the simplified calculation formulas of each characteristic point in the moment-curvature skeleton curve of UCFST columns were obtained by data fitting method. And the characteristic points included the elasticity stiffness, the yield moment, the yield curvature and the strengthening phase stiffness. Finally, the data of quasi-static tests and finite element analysis were used to verify the tri-line model on the bending moment-curvature curve of UCFST columns proposed in this paper, which can provide reference for the research on the seismic behavior of UCFST columns in the future
Numerical investigation of the effect of holes on dynamic fracturing in multi-flawed granite
No full textA numerical study is conducted using the improved continuum-based discrete element method (CDEM) to investigate the effect of holes on the dynamic fracturing of multi-flawed rocks. The specimen geometries contain a perpendicular crack-like flaw, a hole-like flaw, and an inclined crack-like flaw. A fracture model is implemented into the improved CDEM that combines the nonlinear pressure-dependent shear strength and tensile strength of rocks. The digital image correlation method combined with ultra-high-speed photography is applied in a split Hopkinson pressure bar system to verify the accuracy of the proposed model. The experimental results show that the improved CDEM accurately reproduces dynamic crack behavior in rocks. The simulation results show that hole-like flaws significantly affect crack behavior compared with the two investigated crack-like flaws. However, this effect gradually weakens with increasing loading stresses. This study provides important insight into the dynamic fracturing of multi-flawed rocks
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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