130,557 research outputs found
A 2-D computational model describing the heat transfer, reaction kinetics and regeneration characteristics of a ceramic diesel particulate trap
No full textA 2-D CFD model was developed to describe the heat transfer, and reaction kinetics in a honeycomb structured ceramic diesel particulate trap. This model describes the steady state as well as the transient behavior of the flow and heat transfer during the trap regeneration processes. The trap temperature profile was determined by numerically solving the 2-D unsteady energy equation including the convective, heat conduction and viscous dissipation terms. The convective terms were based on a 2-D analytical flow field solution derived from the conservation of mass and momentum equations (Opris, 1997). The reaction kinetics were described using a discretized first order Arrhenius function. The 2-D term describing the reaction kinetics and particulate matter conservation of mass was added to the energy equation as a source term in order to represent the particulate matter oxidation. The filtration model describes the particulate matter accumulation in the trap. This model includes the diffusion, direct interception, and inertia mechanisms, and are linked together to capture the overall filtration characteristics of the trap (Opris and Johnson, 1998). The effect of trap material proper-ties on trap regeneration behavior was studied with and without a Cu fuel additive for controlled and uncontrolled regeneration tests. The theoretical results compared well to the experimental data. The regeneration model indicated that the fundamental difference between SiC and Cordierite is to be found in the trap design (wall thickness = 0.8 mm for the tested SiC vs. 0.43 mm with Cordierite), and trap material properties (thermal conductivity, density and specific heat where 11 W/m/K, 1600 kg/m3, and 750 J/kgK with SiC, and 0. 1 W/m/K, 1000 kg/m3 and 600 J/ kgK with Cordierite). These differences are largely responsible for the regeneration behavior difference. Using the regeneration model, it was determined that the temperature gradients (dT/dt) for similar conditions, were up to five times larger with Cordierite, when compared to SiC. The regeneration times with SiC were more than twice as long for the tested conditions. These results were also confirmed experimentally (Gantawar et al., 1996 and Awara et al., 1996), and are consistent with the difference in trap design and material properties. For all tested conditions (SiC and Cordierite, with and without the fuel additive, controlled and uncontrolled regeneration tests), the computed results indicated that the regeneration process is driven by the local exhaust gas temperature. Since all regeneration processes were initiated by ramping the engine (flow rates and temperatures) from a low reaction rate condition (∼300°C) to a higher reaction rate condition (\u3e 450-500°C), the regeneration process was always initiated at the trap inlet. However, as the local reactions increased the local gas temperatures, and as some of the released energy was convected downstream in the channel, the maximum temperatures were always calculated (and measured) towards the end of the inlet channel indicating a local energy storage. Consequently, the reaction rates increased locally even more, yielding a local particulate oxidation rate higher than the rest of the inlet channel. For all tested cases, the particulate matter was first oxidized towards the end of the inlet channel. As regions of the inlet cell were partially or completely oxidized, the reaction front moved to upstream regions where there was availability of particulate matter. Consequently, the reaction front moved from downstream to upstream locations. The parametric study performed in this research indicated that an optimum trap configuration can be achieved by changing the material properties (e.g. thermal conductivity similar to SiC\u27s and density and specific heat similar to Cordierite\u27s). From a filtration/trap pressure drop point of view, the trap pore size could be increased to approximately 30 μm and a trap porosity of approximately 45%
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
The R&D Tax Incentives
No full textThis article sets out some background information and reflections of the author on the R&D tax incentive schemes included in the Common Corporate Tax Base (CCTB) Proposal. In particular the author analyzes the stimulus to private R&D through ad hoc tax incentives included in the CCTB Proposal and dives into the actual provisions included in the Proposal highlighting the most relevant issues connected with their design and interpretation. Moreover, the author explores the interaction between the CCTB Proposal and the granting by Member States of domestic R&D tax incentives
La professionalità dell'insegnante tra competenze e processi di aggiornamento
No full textL'oggetto del saggio riguarda la competenza e le pratiche professionali degli insegnanti, dove ho delineato forme e direzioni che alla luce degli attuali bisogni devono orientare i loro processi di aggiornamento permanent
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