| 1. |
- Zheng, Dehua, et al.
(författare)
-
Intramolecular Iron-Mediated C-H Bond Heterolysis with an Assist of Pendant Base in a [FeFe]-Hydrogenase Model
- 2014
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:48, s. 16817-16823
-
Tidskriftsartikel (refereegranskat)abstract
- Although many metalloenzymes containing iron play a prominent role in biological C-H activation processes, to date iron-mediated C(sp(3-)H heterolysis has not been reported for synthetic models of Fe/S-metalloenzymes. In contrast, ample precedent has established that nature's design for reversible hydrogen activation by the diiron hydrogenase ([FeFe]-H(2)ase) active site involves multiple irons, sulfur bridges, a redox switch, and a pendant amine base, in an intricate arrangement to perform H-H heterolytic cleavage. In response to whether this strategy might be extended to C-H activation, we report that a [FeFe]-H2ase model demonstrates iron-mediated intramolecular C-H heterolytic cleavage via an agostic C-H interaction, with proton removal by a nearby pendant amine, affording Fe-II-[ Fe'(II)-CH- S] three-membered-ring products, which can be reduced back to 1 by (CpCo)-Co-2 in the presence of HBF4. The function of the pendant base as a proton shuttle was confirmed by the crystal structures of the N-protonated intermediate and the final deprotonated product in comparison with that of a similar but pendant-amine-free complex that does not show evidence of C-H activation. The mechanism of the process was backed up by DFT calculations.
|
|
| 2. |
- Cullinane, Kevin, et al.
(författare)
-
Benchmarking the performance of Swedish Rail Freight Rolling Stock: A Conceptual Approach to Setting Tariffs using Data Envelopment Analysis
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There are many ways to improve the efficiency of a railway system. Many are inherently long-term and involve significant investment. This paper proposes the more immediate, simpler and cheaper approach of incentivising the use of better rolling stock through appropriate infrastructure charging and thereby reducing the number of problems arising and the costs imposed on other rail users, the infrastructure providers and society. It is posited that infrastructure charges should be differentiated to reflect differences in the performance of rolling stock and that this can be achieved purely and simply on the basis of technical and other characteristics. Utilising an existing database, the performance benchmarking of rolling stock is proposed as the basis for formulating and justifying a performance-based tariff structure. Data Envelopment Analysis (DEA) is the preferred method of analysis by which relative measures (in index form) of rolling stock performance can be derived and benchmark performance identified. The paper provides a theoretical conceptualisation of how this might be applied to rail freight rolling stock in order to develop a tariff structure for infrastructure charges which is functionally dependent upon the derived relative benchmark values of performance (quality). The proposed approach has several advantages: no supplementary data collection is required; once the strategic decision is taken as to the level of marginal (social) cost to be recouped, the setting of the tariff becomes deterministic and only needs to be periodically reviewed; following its introduction, the analysis required for reviewing tariffs is relatively straightforward; DEA output provides management with useful information on achieving improved performance; and the potential exists for applying this proposed approach to both passenger rolling stock and within a multinational context. The paper concludes that the proposed approach will greatly simplify the basis upon which infrastructure charges are levied on rail users, while maintaining the possibility of differentiating the tariff structure by specific train path, network link and/or capacity utilisation. It also reinforces the principle of marginal cost pricing. Ultimately, the implementation of this approach will support the objective to increase long-term robustness and reduce disruptions to railways.
|
|
| 3. |
- Cullinane, Kevin, et al.
(författare)
-
Improving the Quality of Sweden’s Rail Freight Rolling Stock: The use of DEA in Benchmarking and Pricing
- 2017
-
Ingår i: Benchmarking : An International Journal. - 1463-5771 .- 1758-4094. ; 24:6, s. 1552-1570
-
Tidskriftsartikel (refereegranskat)abstract
- The paper provides a theoretical conceptualization of how data envelopment analysis can be applied to rail freight rolling stock in order to develop a tariff for track access charges which is functionally dependent upon the derived relative benchmark values of performance. Design/methodology/approach: It is posited that track access charges should be differentiated to reflect differences in the performance of rolling stock and that this can be achieved purely on the basis of technical and other characteristics. The performance benchmarking of rolling stock is proposed as the basis for formulating and justifying a performance-based tariff structure. Using Data Envelopment Analysis (DEA), relative index measures of rolling stock performance can be derived, benchmark performance identified and a tariff structure developed. Findings – A workable approach to implementing the concept, utilising existing in-house databases, is found to be feasible and a template for tariff-setting is established. Research limitations/implications – In the absence of access to in-house technical data on rolling stock which is commercially sensitive, no empirical application of the concept is possible. Originality/value – There are many ways to improve the efficiency of a railway system. Many are inherently long-term and involve significant investment. Using Sweden as an example, this paper proposes the more immediate, simpler and cheaper approach of incentivising the use of better rolling stock through appropriate track access charging. Such an approach should reduce the number of problems arising on the rail network and the costs imposed on other rail users, the infrastructure providers and society. Ultimately, the implementation of this approach would support the objective of increasing long-term robustness and reducing disruptions to railways
|
|
| 4. |
- Cullinane, Kevin, et al.
(författare)
-
RAIL FREIGHT QUALITY -THE CONTEXT OF SWEDISH RAIL FREIGHT AND A ROLLING STOCK INDEX
- 2015
-
Ingår i: Nationell konferens i transportforskning 2015. ; 21-22 oktober Karlstads universitet
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There are many ways to improve the efficiency of a railway system. Many involve huge sums of money. However, an interim, less expensive method is to more strongly encourage the use of more efficient and less environmentally damaging rolling stock. There are many rail operators using the Swedish rail system. Some are dedicated to using up-to-date stock which is less prone to breakdowns, is gentler on the tracks and better for the environment. Other companies, however, are less concerned with the modernity of their stock and the impact it has on the whole railway system or the environment. A method is needed to encourage the use of the former and discourage the use of the latter. Without a way of analysing, benchmarking and monitoring performance, however, it is difficult to move forward. Fees can have a controlling function in all phases of the allocation of capacity. A more differentiated fee model means that the fee is raised and differentiated by vehicle characteristics and to train path connected to capacity utilization. This strategy will allow the connection to the marginal cost principle is reinforced (which is consistent with the legislature's intentions). This will be done by taking into account actual differences in vehicle wear, and partly by fees clearer reflects the capacity utilization of the railway infrastructure at different times and on different locations. This approach would strengthen and make visible the link between traffic operation and maintenance needs, and emphasize the importance of capacity utilized effectively. The aim is to increase long-term robustness and reduce disruptions to railways. The Swedish Transport Administration suggest that differentiated track and train path charges becomes key element of the fee structure (Trafikverket, 2013). Trafikverket (2013) also state that track access charges could also be designed to cover the social marginal cost of environmental impacts and noise emissions or differentiated by such costs. Quality charges were introduced in 2012. The Swedish Transport Administration believes that these could become effective instruments to complement other charges by affecting actors' behavior in the operational stage, i.e. during the implementation of the timetable. The quality of the train is measured in terms of the number of delay minutes, namely the additional delay that occurs between two timetable points during the journey. The current development of differentiated infrastructure charges generates a complicated and complex interrelated fee structure where costs, environmental, social and quality factors are included. We propose that several of these factors and components in fact could be integrated into an index construct of rolling stock to facilitate simple understanding of the rolling stock characteristics and performance as well as act as a benchmarking index. Given this background, the aim of this paper is to evaluate the need for a method of incentivising the use of more sustainable rolling stock in the Swedish rail freight sector and propose a possible benchmarking index. Key words: rail quality, differentiated charges, rolling stock
|
|
| 5. |
- Hamed, Tareq Abu, et al.
(författare)
-
Multiscale in modelling and validation for solar photovoltaics
- 2018
-
Ingår i: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
|
|
