| 41781. |
- Gil, Jorge, 1972, et al.
(författare)
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Exploring the Application of Urban Form Profiles in Freight Trip Generation
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This research aims to incorporate urban form characteristics in freight trip generation (FTG) models, and thus enable more interaction between practitioners through integration of their instruments and policies. From this perspective, the research addresses two questions: To what extent does the urban form profile of a location influence the freight trip generation patterns of local establishments? How much do the urban form profiles relate to the location preference of different types of establishment?
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| 41782. |
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| 41783. |
- Gil, Jorge, 1972
(författare)
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Street network analysis “edge effects”: Examining the sensitivity of centrality measures to boundary conditions
- 2017
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Ingår i: Environment and Planning B: Planning and Design. - : SAGE Publications. - 2399-8083 .- 2399-8091. ; 44:5, s. 819-836
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Tidskriftsartikel (refereegranskat)abstract
- With increased interest in the use of network analysis to study the urban and regional environment, it is important to understand the sensitivity of centrality analysis results to the so-called “edge effect”. Most street network models have artificial boundaries, and there are principles that can be applied to minimise or eliminate the effect of the boundary condition. However, the extent of this impact has not been systematically studied and remains little understood. In this article we present an empirical study on the impact of different network model boundaries on the results of closeness and betweenness centrality analysis of street networks. The results demonstrate that the centrality measures are affected differently by the edge effect, and that the same centrality measure is affected differently depending on the type of network distance used. These results highlight the importance, in any study of street networks, of defining the network's boundary in a way that is relevant to the research question, and of selecting appropriate analysis parameters and statistics.
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| 41784. |
- Gil, Jorge, 1972, et al.
(författare)
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Street Networks - Alternative models, measures & their merits
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Cities concentrate intensive human activities requiring highly complex networked infrastructure for movement, public transport and myriad other spatial interactions. The planning and management of multi-modal street networks for diverse users therefore requires an understanding of urban layout beyond motorised vehicle networks as simple linear conduits of movement. In seeking to address these issues, there has been a profusion of studies of street networks in recent years, with increasing attention from network scientists such as physicists, in addition to studies from transport, geographical and urban fields. These studies take different approaches to representing street networks, each with a different focus, sophistication and level of detail. The models used are based on paradigms grounded in different traditions, often with little reflection upon which is the appropriate representation of the system for a particular application. The different approaches typically generate different results without necessarily comparing means of representation and methods of analysis for different modes and contexts. A few studies have made comparisons but none has yet been done systematically across a wider set of approaches. In this international, inter-disciplinary contribution, we identify and characterise different representations of street networks, and associated measures, and compare analytic results for a sample area to bring out the commonalities, differences and relative merits of the different approaches. This review is a first step to build a foundation for deeper and more consistent understanding of the meaning and significance of the different models, and of their utility for particular applications.
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| 41785. |
- Gilardi, Raffaele, et al.
(författare)
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Reactivity of carbon based materials for powder metallurgy parts and hard metal powders manufacturing
- 2016
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Ingår i: Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy. - : Japan Society of Powder and Powder Metallurgy. - 0532-8799 .- 1880-9014. ; 63:7, s. 548-554
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Tidskriftsartikel (refereegranskat)abstract
- Carbon is a key element for powder metallurgy. For example, carbon is the basic alloying element in PM sintered steel, and carbon powders are used as a carbon source for the production of hard metals. However, there are only a few studies about the mechanisms of carbon dissolution and reactivity in dependence on the carbon sources with solid metals/oxides. This work presents the effect of the carbon source (different graphite and carbon black types) on the reactivity and efficiency of oxides reduction during the sintering of PM steels and on the synthesis of nanocrystalline WC powders. This experimental work sets the basis for optimizing the production of PM steel parts and nano-WC powders based on raw material selection and process conditions.
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| 41786. |
- Gilardi, Raffaele, et al.
(författare)
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The Role of Carbon Source in the Production of Ultrafine and Nanocrystalline WC-6Co Cemented Carbides
- 2015
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Ingår i: roceedings EURO PM2015 Congress & Exhibition, 4-7 October 2015, Reims, France. - 9781899072477 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Tungsten carbide powders are typically produced either by carburization of tungsten metal powders (W) or by carbothermal reduction of tungsten oxide powders (WO3). Different powders can be used as carburizing source like carbon black and graphite. Synthesis of nanostructured WC powders is achieved by a two-step process: mechanical activation of initial powders (by milling), followed by thermal activation of mixes. The properties and microstructure of the resulting tungsten carbide powders (WC) can be influenced both by the raw materials and by the mixing / carburization conditions (temperature and atmosphere). This work presents the effect of the carbon source reactivity (synthetic graphite and different carbon black types) on the synthesis of nanocrystalline WC powders and ultrafine WC-6Co cemented carbides. This experimental work sets the basis for optimizing the production of nano-WC powders based on raw material selection and process conditions.
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| 41787. |
- Gilardi, Raffaele, et al.
(författare)
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The Role of Carbon Source in the Production of WC Powders
- 2014
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Ingår i: 9th International Conference on Tungsten, Refractory and Hardmaterials; Orlando; United States; 18 May 2014 through 22 May 2014. - 9780985339777 ; 1 Powder Production, s. 37-44
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Konferensbidrag (refereegranskat)abstract
- Tungsten carbide powders are typically produced either by carburization of tungsten metal powders (W) or by carbothermal reduction of tungsten oxide powders (WO3). Different powders can be used as carburizing source like carbon black and graphite. Synthesis of nanostructured WC powders is achieved by a two-step process: mechanical activation of initial powders (by milling), followed by thermal activation of mixes. The properties and microstructure of the resulting tungsten carbide powders (WC) can be influenced both by the raw materials and by the mixing /carburization process (temperature and atmosphere). This work presents a review of the studies carried out with several different graphite and carbon black powders for synthetizing nanosized WC from both W and WO3 powders. It is shown how the effectiveness of the mixing/carburization process for synthesis of nanostructured tungsten carbide powders is importantly affected by the type of carbon source used.
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| 41788. |
- Gilbert Gatty, Melina, 1986, et al.
(författare)
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Conformational Gating of Charge Separation in Porphyrin Oligomer-Fullerene Systems
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:50, s. 26482-26492
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Tidskriftsartikel (refereegranskat)abstract
- The rate of the photoinduced charge-separation in C-60-terminated butadiyne-linked porphyrin oligomers P-n (n = 4, 6) is strongly influenced by their molecular conformation. In these systems, the presence of the butadiyne linkers gives rise to a broad distribution of conformations in the ground state, due to an almost barrierless rotation of individual porphyrin units in the oligomer chain. The conformational states of these oligomers, either twisted or planar, could be selected by varying the excitation wavelength, thereby providing different initial excited states for charge separation. Charge separation in the different conformers was followed using both steady-state and 2D time-resolved emission using a streak camera system. Singular value decomposition (SVD) analysis applied on streak camera data provides here a powerful tool to study the conformational dependence of the charge separation in long PnC60 systems. Both the kinetics and spectral changes accompanying charge separation could be analyzed for different populations of conformation. From this analysis we show that, for both systems studied, twisted conformations undergo faster charge separation than planar conformations. This disparity in charge separation rates was ascribed mainly to the difference in driving force for charge separation between twisted and planar conformations. Charge separation was also studied in oligomers PnC60 coordinated to an octadentate ligand T8 that hinders the rotation of porphyrin subunits. The semicircular complexes PnC60-T8 show dramatic changes in their spectral properties, as well as slow excitation wavelength independent rate of charge separation and corresponding low efficiency compared to their linear counterparts. This slow charge separation rate was attributed to fast relaxation to the lowest excited vibronic state and lack of driving force for charge separation in these close to planar semicircular systems; i.e., the template systems behave like "normal" donor acceptor systems without slow conformational relaxation. This work illustrates how control of conformation can be used to tune the rate of charge separation.
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| 41789. |
- Gilbert Gatty, Melina, 1986, et al.
(författare)
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Hopping versus Tunneling Mechanism for Long-Range Electron Transfer in Porphyrin Oligomer Bridged Donor-Acceptor Systems
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:24, s. 7598-7611
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Tidskriftsartikel (refereegranskat)abstract
- Achieving long-range charge transport in molecular systems is interesting to foresee applications of molecules in practical devices. However, designing molecular systems with pre-defined wire-like properties remains difficult due to the lack of understanding of the mechanism for charge transfer. Here we investigate a series of porphyrin oligomer-bridged donor–acceptor systems Fc–Pn–C60 (n = 1–4, 6). In these triads, excitation of the porphyrin-based bridge generates the fully charge-separated state, Fc•+–Pn–C60•-, through a sequence of electron transfer steps. Temperature dependence of both charge separation (Fc–Pn*–C60 → Fc–Pn•+–C60•-) and recombination (Fc•+–Pn–C60•– → Fc–Pn–C60) processes was probed by time-resolved fluorescence and femtosecond transient absorption. In the long triads, two mechanisms contribute to recombination of Fc•+–Pn–C60•– to the ground state. At high temperatures (≥280 K), recombination via tunneling dominates for the entire series. At low temperatures (
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| 41790. |
- Gilbert Gatty, Melina, 1986, et al.
(författare)
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Photoinduced charge and energy transfer in molecular wires
- 2015
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Ingår i: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 1460-4744 .- 0306-0012. ; 44:4, s. 845-862
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Forskningsöversikt (refereegranskat)abstract
- Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed.
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