EC71-799 Engineering the Irrigation Pumping Plant

Extension Circular 71-799: Engineering the irrigation pumping plant; pumps selection, pump drives, setting up the drives, power units, and direction for matching an electric motor to an irrigation pump

Dimer-mediated cation diffusion in the stoichiometric ionic conductor Li3N

Non-equilibrium molecular dynamics has been used to model cation diffusion in stoichiometric Li3N over the temperature range 50 < T/K < 800. The resulting diffusion coefficients are in excellent agreement with the available experimental data. We present a detailed atomistic account of the diffusion process. Contrary to the conclusions drawn from previous studies, our calculations show that it is unnecessary to invoke the presence of a small concentration of intrinsic defects in order to initiate diffusion. The structure can be considered to consist of alternating layers of composition Li2N and Li. As the temperature increases an increasing number of cations leave the Li2N layers and migrate either to the interlayer space or to the Li layer. Those that move into the interlayer space form Li2 dimers with cations in the Li2N layers and those that move into the neighboring layer form dimers with cations therein. The two types of dimer are aligned parallel and perpendicular to [001], respectively and have lifetimes of ∼3 ps. The vacancies so created facilitate rapid diffusion in the Li2N layers and the interlayer cation motion results in slower diffusion perpendicular to the layers

Diffusion in Li₂O studied by non-equilibrium molecular dynamics for 873 <T/K <1603

The use of non-equilibrium molecular dynamics facilitates the calculation of the cation diffusion constant of Li2O at temperatures too low to be accessible by other methods. Excellent agreement with experimental diffusion coefficients has been obtained over the temperature range 873 < T/K < 1603. Diffusion below 1200 K was shown to be dominated by a concerted nearest-neighbour hopping process, whereas in the high-temperature superionic region an additional mechanism involving a six-coordinate interstitial cation site in the anti-fluorite structure becomes increasingly dominant. Our model thus accounts for the transition from the superionic regime to the non-superionic regime.</p

The Big Society and the Conjunction of Crises: Justifying Welfare Reform and Undermining Social Housing

The idea of the “Big Society” can be seen as culmination of a long-standing debate about the regulation of welfare. Situating the concept within governance theory, the article considers how the UK coalition government has justified a radical restructuring of welfare provision, and considers its implications for housing provision. Although drawing on earlier modernization processes, the article contends that the genesis for welfare reform was based on an analysis that the government was forced to respond to a unique conjunction of crises: in morality, the state, ideology and economics. The government has therefore embarked upon a programme, which has served to undermine the legitimacy of the social housing sector (most notably in England), with detrimental consequences for residents and raising significant dilemmas for those working in the housing sector

Impersonation-as-a-Service: Characterizing the Emerging Criminal Infrastructure for User Impersonation at Scale

In this paper we provide evidence of an emerging criminal infrastructure enabling impersonation attacks at scale. Impersonation-as-a-Service (ImpaaS) allows attackers to systematically collect and enforce user profiles (consisting of user credentials, cookies, device and behavioural fingerprints, and other metadata) to circumvent risk-based authentication system and effectively bypass multi-factor authentication mechanisms. We present the ImpaaS model and evaluate its implementation by analysing the operation of a large, invite-only, Russian ImpaaS platform providing user profiles for more than $260'000$ Internet users worldwide. Our findings suggest that the ImpaaS model is growing, and provides the mechanisms needed to systematically evade authentication controls across multiple platforms, while providing attackers with a reliable, up-to-date, and semi-automated environment enabling target selection and user impersonation against Internet users as scale.Comment: Presented at ACM CCS 2020. Appendix on "Deriving a Threat Model from Observation" available at https://michelecampobasso.github.io/publication/2020-11-10-impaa

A Visual One-Time Password Authentication Scheme Using Mobile Devices

16th International Conference, ICICS 2014, Hong Kong, China, December 16-17, 2014The use of passwords for user authentication has become ubiquitous in our everyday lives. However, password theft is becoming a common occurrence due to a variety of security problems associated with passwords. As such, many organizations are moving towards adopting alternative solutions like one-time passwords, which are only valid for a single session. Nevertheless, various one-time password schemes also suffer from a number of drawbacks in terms of their method of generation or delivery. This paper presents the design of a challenge-response visual one-time password authentication scheme that is to be used in conjunction with the camera on a mobile device. The main purpose of the proposed scheme is to be able to send a challenge over a public channel for a user to obtain a session key, while safeguarding the user’s long-term secret key. In this paper, we present the authentication protocol, the various design considerations and the advantages provided by the scheme.Department of Computin

Computational study of lithium-ion mobility in stoichiometric solid-state systems

Lithium-ion mobility in solid-state systems is an important field with significance for a range of technological interests, especially in the field of energy materials. The binary lithium compounds Li2O and Li3N have been studied using modern computational techniques to elucidate their diffusion properties. The macroscopic diffusion coefficients have been calculated and the underlying microscopic diffusion processes elucidated using molecular-dynamics-based techniques. In both systems studied the diffusion has been modelled over a wider temperature range than previously attempted. The agreement between the calculated diffusion coefficients and the best available experimental data surpasses previous computational studies. The level of agreement achieved is due to the use of force-field non-equilibrium molecular dynamics (FF-NEMD). This method, which has only recently been applied to solid-state diffusion, allows rates of diffusion that are typically too low to be studied with equilibrium molecular dynamics to be modelled. NEMD uses a fictitious external field to increase the frequency of the rare diffusion events in a predictable manner without changing the nature of the diffusion mechanisms. In the case of Li2O the transition from the non-superionic to the superionic regime has been modelled. The dominant mechanism in each regime has been determined: in the non-superionic regime a concerted mechanism dominates and in the superionic regime an interstitial-mediated mechanism dominates. For Li3N the anisotropic nature of the lithium diffusion coefficient has been modelled. The diffusion mechanisms dominant for different directions have also been elucidated. The rapid diffusion in the (001) plane of the hexagonal structure has been explained by the presence of vacancies on the in-plane Li sites, both in this thesis and in previous works. Previous studies have explained this by the presence of contaminants leading to non-stoichiometric Li3N. However, in this thesis the under occupation of these sites has been explained by the formation of Li2 dumbbells, or site sharing, largely about the interlayer Li sites, but also about the in-plane Li sites. The existence of these dumbbells explains the experimental diffusion coefficients of stoichiometric Li3N.</p

Computational study of lithium-ion mobility in stoichiometric solid-state systems

Lithium-ion mobility in solid-state systems is an important field with significance for a range of technological interests, especially in the field of energy materials. The binary lithium compounds Li2O and Li3N have been studied using modern computational techniques to elucidate their diffusion properties. The macroscopic diffusion coefficients have been calculated and the underlying microscopic diffusion processes elucidated using molecular-dynamics-based techniques. In both systems studied the diffusion has been modelled over a wider temperature range than previously attempted. The agreement between the calculated diffusion coefficients and the best available experimental data surpasses previous computational studies. The level of agreement achieved is due to the use of force-field non-equilibrium molecular dynamics (FF-NEMD). This method, which has only recently been applied to solid-state diffusion, allows rates of diffusion that are typically too low to be studied with equilibrium molecular dynamics to be modelled. NEMD uses a fictitious external field to increase the frequency of the rare diffusion events in a predictable manner without changing the nature of the diffusion mechanisms. In the case of Li2O the transition from the non-superionic to the superionic regime has been modelled. The dominant mechanism in each regime has been determined: in the non-superionic regime a concerted mechanism dominates and in the superionic regime an interstitial-mediated mechanism dominates. For Li3N the anisotropic nature of the lithium diffusion coefficient has been modelled. The diffusion mechanisms dominant for different directions have also been elucidated. The rapid diffusion in the (001) plane of the hexagonal structure has been explained by the presence of vacancies on the in-plane Li sites, both in this thesis and in previous works. Previous studies have explained this by the presence of contaminants leading to non-stoichiometric Li3N. However, in this thesis the under occupation of these sites has been explained by the formation of Li2 dumbbells, or site sharing, largely about the interlayer Li sites, but also about the in-plane Li sites. The existence of these dumbbells explains the experimental diffusion coefficients of stoichiometric Li3N.</p

A New Platydoris Gastropoda Nudibranchia From The Galapagos Islands

Volume: 17Start Page: 209End Page: 21

A PRELIMINARY LIST OF KNOWN OPISTHOBRANCHS FROM THE GALAPAGOS ISLANDS COLLECTED BY THE AMERIPAGOS EXPEDITION

Volume: 15Start Page: 147End Page: 15