754 research outputs found
Overall synthesis and conclusions
No full textThis chapter first systematically summarizes the most important findings and policy implications of each of the chapters included in this book volume. Next it synthesizes the overall findings and policy implications, and discusses future avenues for policy making and research. A first conclusion is that the chapters make clear that the ranges in policy relevant implications of AVs, within the scope of each chapter/topic, are still relatively broad. Secondly we conclude that research that is conceptually rich is more valuable for policy making. Thirdly we hypothesize that context matters for the uptake, impacts, and specific system design characteristics of real world AV implementation. Fourth we conclude that research on the global south has been limited so far. Fifth we argue that AVs, shared vehicles and electric vehicles (EVs) might stimulate each other in a positive way, in all directions. Finally we conclude that AVs will have wider societal implications, such as in the area of land use, accessibility, social exclusion, governmental expenditures, the labor market, and the environment. The more indirect the effects of AVs are, the more difficult they are to understand. For policy making a first conclusion is that the issues of ethics, cyber security and data protection deserve way more attention than they currently get. We also conclude that future motorway network extensions might not be no-regret anymore, because of possible congestion reductions due to AVs, but also because of decreasing marginal values of time. Finally we argue that countries that introduce AVs later than other countries can learn a lot from the real world experiences elsewhere.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Logistic
Seventeen-coordinate actinide helium complexes
Get PDFThe geometries and electronic structures of molecular ions featuring He atoms complexed to actinide cations are explored computationally using density functional and coupled cluster theories. A new record coordination number is established, as AcHe17 3+, ThHe17 4+ and PaHe17 4+ are all found to be true geometric minima, with the He atoms clearly located in the first shell around the actinide. Analysis of AcHen 3+ (n = 1–17) using the Quantum Theory of Atoms in Molecules (QTAIM) confirms these systems as having closed shell, charge-induced dipole bonding. Excellent correlations (R2 > 0.95) are found between QTAIM metrics (bond critical point electron densities and delocalisation indices) and the average Ac–He distances, and also with the incremental He binding energies
Transuranic computational chemistry
Get PDFRecent developments in the chemistry of the transuranic elements are surveyed, with particular emphasis on computational contributions. Examples are drawn from molecular coordination and organometallic chemistry, and from the study of extended solid systems. The role of the metal valence orbitals in covalent bonding is a particular focus, especially the consequences of the stabilization of the 5f orbitals as the actinide series is traversed. The fledgling chemistry of transuranic elements in the +II oxidation state is highlighted. Throughout, the symbiotic interplay of experimental and computational studies is emphasized; the extraordinary challenges of experimental transuranic chemistry afford computational chemistry a particularly valuable role at the frontier of the periodic table
Computational investigations of the speciation of Sr2+ in aqueous solution, and its interactions with the hydrated brucite (0001) surface
Get PDFThe fundamental objective of this research project was to develop a computational model, using high-level quantum chemical techniques based on density functional theory (DFT), which is able to describe the aquo and hydroxide complexes of strontium and their inter- actions with hydrated brucite surfaces, aiming to create a general approach which can be subsequently modified for the investigation of other radioactive ions/surfaces. The first two chapters of this PhD thesis are a general introduction on the project’s industrial relevance and on the computational methodology used. The subject of this study is strongly related to the decommissioning of the UK’s nuclear legacy fuel storage ponds and therefore the the- sis is organised such that, through the three main steps of the computational investigation, it eventually leads to an industrially relevant main conclusion. In the third chapter, the possible strontium hydroxide complexes in aqueous environment have been investigated, in order to establish likely candidate species for the interaction of nu- clear fission-generated strontium with the hydrated brucite surfaces in high pH spent nuclear fuel storage ponds. A combination of the COSMO continuum solvation model and one or two shells of explicit water molecules are employed for describing accurately the hydrolysis of Sr2+. The next chapter presents the periodic electrostatic embedded cluster model, developed for the brucite (0001) surface to be employed in the study of the adsorption reactions. Using the periodic electrostatic embedded cluster method (PEECM), implemented in the TURBOMOLE code, we have created a quantum chemically treated cluster in an infinite array of point charges and validated this surface model by exploring the adsorption of Sr2+ and other s block cations on bare and hydrated surfaces, comparing the PEECM data with those from a periodic DFT study using the CRYSTAL code. In the fifth chapter, the results of the previous two chapters are combined to describe the Sr-surface interactions as realistically as possible. A theoretical reaction was created, in which the energy of the adsorbed Sr2+ ion on a hydrated brucite surface was compared with the energy of a solvated Sr2+ in the bulk solution, i.e. with the previously identified strontium complexes in aqueous phase. To achieve this, the PEECM model was extended with one and two layers of water molecules both in the quantum mechanical and point charge region, whose geometries are based on previous molecular dynamics studies. Several possible complexes are identified both in the presence or absence of solvatedOH− groups with different Sr-surface distances and complex conformation, and their adsorption energies were calculated in order to evaluate the general strength of the possible ion-surface interactions
Post hos nostra terra est: mapping the Late Roman ecumene with the Expositio totius mundi et gentium
Get PDFThis paper studies the landscape of the Late Roman ecumene as depicted by the Expositio totius mundi et gentium (Expos. mundi),1 written by an anonymous author in the middle of the 4th century CE. It will first contextualise the text and assess its structure, language and genre. The contribution will then focus on the distinction between Rome, the Sasanids and utopic societies in the east near Eden, the political and military organization of the Imperium Romanum as well as its economic framework and varying expressions of its culture. As
this paper will show, the anonymous author does not present detailed descriptions of Rome’s geographical landscape. Instead, the primary focus is on material resources of the Roman Empire, their potential for economic exploitation and the trading opportunities resulting from it. Rome’s cultivated landscapes are thereby regarded as important preconditions for its success on an economic, political and cultural level
All-electron CASPT2 study of Ce(eta(8)-C8H6)(2)
No full textCASSCF wave functions and CASPT2 energies are presented for the ground and 15 and 31 excited states of the D-2d and D-2h conformers respectively of the f-element sandwich molecule CePn(2) (Pn =eta(8)-C8H6) The ground states of both conformers are found to be strongly multiconfigurational, analogous to cerocene, CeCOT2 (COT = eta(8)-C8H8), as reported in Journal of Physical Chemistry A 113 (2009) 2896 Investigation of the nature of the multiconfigurational character shows that the analogy with cerocene is indeed strong It is shown that the occupations of the natural orbitals produce a more reliable description of the CePn(2) ground state than does the configurational admixture, and that these occupations can be used to deduce a value for the total f-density in the system. This density is found to be slightly lower than that of cerocene, and is in good agreement with that found experimentally. A density functional theory calculation of the same system is able to broadly capture the important features of the electronic structure, but is unable to replicate the experimental value of the total f-density CASPT2 calculations reproduce the energy of the first band in the UV/Vis spectrum of CePn*(2) (Pn* =eta(8)-(CMe6)-Me-8) to within 0 01 eV Although this extremely good agreement is probably somewhat fortuitous, it highlights the fact that multiconfigurational methods are required in order to model systems such as CePn(2) to a high level of accuracy. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserve
Are the Ground States of the Later Actinocenes Multiconfigurational? All-Electron Spin-Orbit Coupled CASPT2 Calculations on An(eta(8)-C8H8)(2) (An = Th, U, Pu, Cm)
No full textSpin-orbit free and spin-orbit coupled CASPT2 wave functions and energies are presented for the ground and low-lying excited states of four actinide element sandwich molecules; thorocene (ThCOT2), uranocene (UCOT2), plutonocene (PuCOT2), and curocene (CmCOT2). Spin-orbit coupling is found to make little difference to the equilibrium geometry of uranocene and plutonocene but has a significant effect on the energy spectrum of all the systems considered here other than thorocene. In all cases, however, the spin-orbit free ground states make the dominant contribution to their spin-orbit coupled counterparts. Following work presented in J. Phys. Chem. A 2009, 113, 2896, the variation in the multiconfigurational character of the ground-state wave functions as the 5f series is crossed is quantified via the occupation of the a(u)/b(1u) (e(2u)) metal-ring bonding and antibonding natural orbitals. The ground state of plutonocene is found to be nondegenerate with vertical bar M-J vertical bar = 0, in agreement with its temperature-independent paramagnetism
ChemInform Abstract: Does Covalency Increase or Decrease Across the Actinide Series? Implications for Minor Actinide Partitioning.
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