1,721,566 research outputs found
Direct and large-eddy simulation of interactions between reacting flows and evaporating droplets
No full textReacting flows interacting with liquid droplets are of practical and scientific importance due
to their appearance in a multiplicity of industrial and domestic applications such as fire
suppression systems and humidified gas turbines. Experimental measurements are usually
limited to global quantities or local quantities at limited spatial locations, which provide
little detailed information for fundamental understanding of complex interactions.
Numerical simulations can overcome these limitations, but are restricted by the available
computer capacity. Therefore, most previous simulations in the field employ simplifications
such as a two-dimensional configuration, the Eulerian description of the dispersed phase, or
the Reynolds averaged Navier-Stokes (RANS) methodology, etc. Such simplified methods
are not appropriate for scrutinizing the local, unsteady interactions embedded in the
realistic multiphase reacting flows from the first principle. To this end, systematic
understanding of the multilateral, multiscale and multiphysics interactions among
turbulent flow, chemical reaction and dispersing droplets is still far from being achieved.Recently, the rapid development of the supercomputer hardware and software
technologies enables the application of high fidelity numerical techniques, i.e., direct
numerical simulation (DNS) and large eddy simulation (LES), to such complex flows. In
the present study, a hybrid Eulerian-Lagrangian methodology is developed and
implemented to investigate the multiphysics interactions. The well-designed parallel
algorithms enable us to look at both canonical and practical configurations, including a
temporal reacting shear layer, a turbulent reactive jet diluted with droplets and a simplified
small-scale domestic fire suppression system. All these configurations are characterised by
nonuniform droplet loading in the computational domain, fully three-dimensional
simulation and the Lagrangian description for droplets. The number of traced droplets
reaches the magnitude of 106 in some cases. DNS results with various physical parameters
have been obtained, showing self-consistency and correct trends. In LES, to avoid arbitrary
tuning of subgrid model coefficients, fully dynamic procedures have been designed
following the Germano procedure and implemented for the main six subgrid models. LES
of a heated plane jet, a reacting jet diluted with evaporating droplets and a simplified fire
suppression system has been performed and analysed. Droplet effects on turbulence and
combustion are quantified through examining the transport equations for the kinetic
energy and internal energy of the reacting flow
Learning Through Observation or Through Acquisition? Innovation Performance as an Outcome of Internal and External Knowledge Combination
No full textDue to copyright restrictions and/or publisher's policy full text access from Treasures at UT Dallas is limited to current UTD affiliates (use the provided Link to Article).Although the importance of external and internal knowledge combination for innovation is well recognized, the effectiveness of different patterns of combination requires further investigation. We consider spillovers of foreign direct investment (FDI) and external research and development (R&D) as two sources of external knowledge to domestic firms and argue that the effectiveness of incorporating the two external sources of knowledge varies conditional upon different levels of internal knowledge development (internal R&D). We argue that learning through observation and learning through acquisition are important mechanisms making such difference. Using a sample of manufacturing firms in China from 2002 to 2007, we find that rhythmic FDI spillover and external R&D positively affect innovation performance. However, the effect of rhythmic FDI spillover is stronger, whereas the effect of external R&D is weaker for firms with a moderate level of internal R&D than firms with a low or high level of internal R&D. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Naveen Jindal School of Managemen
Routing Optimization with Generalized Consistency Requirements
Get PDFThe consistent vehicle routing problem (ConVRP) aims to design synchronized routes on multiple days to serve a group of customers while minimizing the total travel cost. It stipulates that customers should be visited at roughly the same time (time consistency) by several familiar drivers (driver consistency). This paper generalizes the ConVRP for any level of driver consistency and additionally addresses route consistency, which means that each driver can traverse at most a certain proportion of different arcs of routes on planning days, which guarantees route familiarity. To solve this problem, we develop two set partitioning-based formulations, one based on routes and the other based on schedules. We investigate valid lower bounds on the linear relaxations of both of the formulations that are used to derive a subset of columns (routes and schedules); within the subset are columns of an optimal solution for each formulation. We then solve the reduced problem of either one of the formulations to achieve an optimal solution. Numerical results show that our exact method can effectively solve most of the medium-sized ConVRP instances in the literature and can also solve some newly generated instances involving up to 50 customers. Our exact solutions explore some managerial findings with respect to the adoption of consistency measures in practice. First, maintaining reasonably high levels of consistency requirements does not necessarily always lead to a substantial increase in cost. Second, a high level of time consistency can potentially be guaranteed by adopting a high level of driver consistency. Third, maintaining high levels of time consistency and driver consistency may lead to lower levels of route consistency
TOMOGRAPHY OF THE FERMI-LAT gamma-RAY DIFFUSE EXTRAGALACTIC SIGNAL VIA CROSS CORRELATIONS WITH GALAXY CATALOGS
No full textBuilding on our previous cross-correlation analysis (Xia et al. 2011) between the isotropic.-ray background (IGRB) and different tracers of the large-scale structure of the universe, we update our results using 60 months of data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi). We perform a cross-correlation analysis both in configuration and spherical harmonics space between the IGRB and objects that may trace the astrophysical sources of the IGRB: QSOs in the Sloan Digital Sky Survey (SDSS) DR6, the SDSS DR8 Main Galaxy Sample, luminous red galaxies (LRGs) in the SDSS catalog, infrared-selected galaxies in the Two Micron All Sky Survey (2MASS), and radio galaxies in the NRAO VLA Sky Survey (NVSS). The benefit of correlating the Fermi-LAT signal with catalogs of objects at various redshifts is to provide tomographic information on the IGRB, which is crucial in separating the various contributions and clarifying its origin. The main result is that, unlike in our previous analysis, we now observe a significant (>3.5 sigma) cross-correlation signal on angular scales smaller than 1 degrees in the NVSS, 2MASS, and QSO cases and, at lower statistical significance (similar to 3.0 sigma), with SDSS galaxies. The signal is stronger in two energy bands, E > 0.5 GeV and E > 1 GeV, but it is also seen at E > 10 GeV. No cross-correlation signal is detected between Fermi data and the LRGs. These results are robust against the choice of the statistical estimator, estimate of errors, map cleaning procedure, and instrumental effects. Finally, we test the hypothesis that the IGRB observed by Fermi-LAT originates from the summed contributions of three types of unresolved extragalactic sources: BL Lacertae objects (BL Lacs), flat spectrum radio quasars (FSRQs), and star-forming galaxies (SFGs). We find that a model in which the IGRB is mainly produced by SFGs (72(-37)(+23) 2 sigma errors), with BL Lacs and FSRQs giving a minor contribution, provides a good fit to the data. We also consider a possible contribution from misaligned active galactic nuclei, and we find that, depending on the details of the model and its uncertainty, they can also provide a substantial contribution, partly degenerate with the SFG one
Towards a better binder for pervious concrete: A case study on the flexural strength of fibre-reinforced high-strength cementitious paste (F-HSCP) under different curing conditions
No full textAdding fibres can help increase the performance of the binder and, thus, the mechanical performance of the pervious concrete. However, their performance under various curing conditions is questionable. This study investigates the mechanical performance and microstructure evolution of fibre-reinforced high-strength cementitious paste (F-HSCP) incorporating Ultra-High Molecular Weight Polyethylene fibre (UF), Glass fibre (GF), and Steel fibre (STF) across four curing conditions: standard 28-day water curing (W-Type), steam curing for 48 h (S-Type), 90 °c, 48-hour hot water bath curing (H-Type), and 8-hour, 1 MPa pressure, 180 °c autoclaved curing (A-Type). Key findings indicate that W-Type curing is the best way to uniformly enhance the flexural strength up to 23.9 MPa. A-Type curing reduced strength by approximately 14 % (to 20.5 MPa) due to non-uniform hydration products. UF at low dosages benefits from S- and H-Type curing, achieving 22.47 MPa at 0.7 % fibre dosage, which provides higher flexural strength than other curing methods. GF reinforcement proved to be unsuitable, with A-Type curing causing a 12.86 % reduction in initial cracking strength at 2.0 % dosage and reaching only minimal ultimate strength improvements (<5 %) across all conditions. Conversely, STF demonstrated superior performance with strengthened fibre-matrix bonds, where a 3 % dosage increased initial crack strength by 21.87 % under S-Type curing, while a 4 % dosage enhanced ultimate flexural strength by 224.31 % and achieved good toughness. These insights offer critical guidance for maximising fibre efficiency in F-HSCP across various curing conditions, which is critical for its binding effect in pervious concrete
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
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