Extending the random-phase approximation for electronic correlation energies: The renormalized adiabatic local density approximation

The adiabatic connection fluctuation-dissipation theorem with the random phase approximation (RPA) has recently been applied with success to obtain correlation energies of a variety of chemical and solid state systems. The main merit of this approach is the improved description of dispersive forces while chemical bond strengths and absolute correlation energies are systematically underestimated. In this work we extend the RPA by including a parameter-free renormalized version of the adiabatic local density (ALDA) exchange-correlation kernel. The renormalization consists of a (local) truncation of the ALDA kernel for wave vectors $q>2k_F$, which is found to yield excellent results for the homogeneous electron gas. In addition, the kernel significantly improves both the absolute correlation energies and atomization energies of small molecules over RPA and ALDA. The renormalization can be straightforwardly applied to other adiabatic local kernels.Comment: 5 page

Static correlation beyond the random phase approximation: Dissociating H2 with the Bethe-Salpeter equation and time-dependent GW

We investigate various approximations to the correlation energy of a H$_2$ molecule in the dissociation limit, where the ground state is poorly described by a single Slater determinant. The correlation energies are derived from the density response function and it is shown that response functions derived from Hedin's equations (Random Phase Approximation (RPA), Time-dependent Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW (TDGW)) all reproduce the correct dissociation limit. We also show that the BSE improves the correlation energies obtained within RPA and TDHF significantly for intermediate binding distances. A Hubbard model for the dimer allow us to obtain exact analytical results for the various approximations, which is readily compared with the exact diagonalization of the model. Moreover, the model is shown to reproduce all the qualitative results from the \textit{ab initio} calculations and confirms that BSE greatly improves the RPA and TDHF results despite the fact that the BSE excitation spectrum breaks down in the dissociation limit. In contrast, Second Order Screened Exchange (SOSEX) gives a poor description of the dissociation limit, which can be attributed to the fact that it cannot be derived from an irreducible response function

Local interpolation in Hilbert spaces of Dirichlet series

We denote by \Hp the Hilbert space of ordinary Dirichlet series with square-summable coefficients. The main result is that a bounded sequence of points in the half-plane $\sigma >1/2$ is an interpolating sequence for \Hp if and only if it is an interpolating sequence for the Hardy space $H^2$ of the same half-plane. Similar local results are obtained for Hilbert spaces of ordinary Dirichlet series that relate to Bergman and Dirichlet spaces of the half-plane $\sigma >1/2$

Occlusion prevents the use of vascular loops for blood sampling and dosing in minipigs

Continous blood sampling and intravenous dosing are difficult in pigs, especially minipigs. A skin loop containing the jugular vein or the carotid artery has been used for solving this problem in other species of animals, but it has never beenattempted in the pig. In this study eight such skin loops were made on minipigs, which technically caused only a few problems. Shortening the loop and widening the distance between the two parallel incisions reduced problems of necrosisand improper wound healing. A juvenile pig did not show such problems. However, in all loops excessive formation of fibrotie tissue occluded the vessel after approximately six days. We, therefore, conclude that although the surgical technique ispossible: further modification, e.g, by insertion of a rigid artificial vessel or an in-dwelling catheter, is necessary, before vascular loops can he used as a method for continuous sampling and dosing in minipigs

Excitons in van der Waals heterostructures: The important role of dielectric screening

The existence of strongly bound excitons is one of the hallmarks of the newly discovered atomically thin semi-conductors. While it is understood that the large binding energy is mainly due to the weak dielectric screening in two dimensions (2D), a systematic investigation of the role of screening on 2D excitons is still lacking. Here we provide a critical assessment of a widely used 2D hydrogenic exciton model which assumes a dielectric function of the form {\epsilon}(q) = 1 + 2{\pi}{\alpha}q, and we develop a quasi-2D model with a much broader applicability. Within the quasi-2D picture, electrons and holes are described as in-plane point charges with a finite extension in the perpendicular direction and their interaction is screened by a dielectric function with a non-linear q-dependence which is computed ab-initio. The screened interaction is used in a generalized Mott-Wannier model to calculate exciton binding energies in both isolated and supported 2D materials. For isolated 2D materials, the quasi-2D treatment yields results almost identical to those of the strict 2D model and both are in good agreement with ab-initio many-body calculations. On the other hand, for more complex structures such as supported layers or layers embedded in a van der Waals heterostructure, the size of the exciton in reciprocal space extends well beyond the linear regime of the dielectric function and a quasi-2D description has to replace the 2D one. Our methodology has the merit of providing a seamless connection between the strict 2D limit of isolated monolayer materials and the more bulk-like screening characteristics of supported 2D materials or van der Waals heterostructures.Comment: 14 pages, 13 figure

Variations on Some Rossian Themes

In this dissertation, I develop and defend some of W. D. Ross’s moral views. Ross’s views, I argue, are often highly plausible, though it is also often the case that variations on (or modifications to) his views are needed in order to remain philosophically tenable. In my dissertation, I explain why these variations are necessary and what they should look like. In chapter 1, I discuss Ross’s theory of moral rightness in his most important work, The Right and the Good. In chapters 2 and 3, I correct various misunderstandings about Ross’s position: I argue that he is no more a particularist about absolute duty than a utilitarian or a Kantian is, and on many definitions of “pluralism” present in the literature, he is not in fact a pluralist, as he is typically assumed to be. In chapter 4, I discuss several objections that Ross later comes to make to his own theory of rightness; I argue, however, that none of them are any good. In chapter 5, I argue against Ned Markosian’s recent claim that “Rossian Minimalism” is the best theory of rightness that makes use of the concept of a prima facie duty: Ross’s own theory (or, at least, a “world” version of it) is, I maintain, superior to Rossian Minimalism. In chapter 6, I address some objections to Ross’s theory suggested by Michael Stocker and Michael Slote and demonstrate that the best way of responding to them is by transforming Ross’s theory into a “dual-ranking” one. In chapter 7, I discuss Ross’s theory of the subjective sense of “right” (chapters 1-6 are primarily concerned with Ross’s theory of the objective sense of the term). I show that Ross’s theory is problematic, and I offer a better theory in its place. In chapter 8, I turn to Ross’s theory of moral goodness. I argue that his theory is more plausible than other theories suggested in the literature, but it suffers from the “nepotism problem.” I show that Ross’s solution to this problem is unsatisfactory and suggest a better way forward

Short-term effects of storage time and temperature on pH, pCO2, and pO2 in porcine arterial blood

There is evidence that pre-analytical handling may be an important determinant of blood gas variables. To study this possibility we investigated the influence of storage time (5, 15, 30, 45, and 60 minutes after blood sampling) and storage temperature (4oC and 20oC) on the variation in pH, pCO2, and pO2 in porcine blood. We found that the median pH decreased (P<0.001), but did not exhibit clinically significant changes. The median pCO2 increased with duration of storage (P<0.001) and the median pO2 was variable at 4oC (P=0.002), and decreased at 20oC (P<0.001). The variations in pCO2 and pO2 were higher at 20oC than at 4oC. This study demonstrates that time delay before analysis of blood gas can be a cause of increased variation, and should be minimised in order to avoid false results and to ensure correct conclusions. If a delay of more than five minutes in analysis is expected, the specimen should be placed on crushed ice

Assessing the influence of additive manufacturing and digital inventories on an Oil & Gas company's inventory management strategy

The oil and gas (O&G) industry is increasingly considering using additive manufactured (AM) for spare part management. As O&G companies seek to align their inventory management (IM) strategies, adopting digital inventories (DI) in combination with AM has emerged as a promising solution to current IM challenges in the industry. O&G operators may leverage AM and DI to reduce physical inventories, supply chain risk, inventory-related costs and lead times. However, approaches that describe how companies may implement the DI in operations and existing IM strategies are lacking. As such, this thesis will investigate how Norwegian O&G operators may implement DI to existing IM strategies. Seven companies with experience with AM and currently participate in a DI ecosystem have been interviewed as part of the research for the thesis. The aim of the interviews was to explore the current challenges, best practices, and essential aspects for enabling the successful implementation of DIs. The interview findings are compared against relevant literature to understand the DI ecosystem comprehensively. Key challenges in the ecosystem are unsuitable procurement processes, lack of commercial models, AM spare part (SP) qualification and a lack of demand for AM projects. ERP integration and assessments of AM suitability for stored SP are discussed as key enablers of DI implementation. The benefits and challenges associated with ERP integration will be discussed, thereby providing insight towards how O&G companies may utilise existing ERP systems to maximise the value of DI. A set of frameworks for identifying SP with characteristics suitable for AM is presented. The frameworks may be used to reduce physical inventories. Two decision models visualising critical decisions and stages for a SP ordered through a DI are presented. The first decision model considers decisions and stages for a given SP ordered through a DI. The second model may be adopted by O&G operators aiming to reduce physical inventories. In conclusion, the thesis's main contribution is expanding knowledge of implementing DI as a part of IM strategies for Norwegian O&G operators. The findings highlight a need to address current procurement processes and develop attractive commercial models for all actors in the DI ecosystem. ERP integration and assessment of stored SP suitable for AM are identified as essential enablers of DI implementation

Human-AI Collaboration in Public Services: The case of sick leave case handling in the Norwegian Labour and Welfare Administration

Public service delivery has seen a surge in demand from society in recent years, especially after the Covid-19 pandemic. It is crucial for public service organizations to keep up with digitization efforts to meet these demands. The most important information systems innovation for the public sector is artificial intelligence (AI). Not all processes in public service delivery can be fully automated by AI, requiring human presence to ensure human discretion and fair judgment. This study investigates the needs for human-AI collaboration in public services. To further narrow the study, it focuses on the case of sick leave case handling in the Norwegian Labour and Welfare Administration (NAV). Human-AI collaboration in public services is a field of research that has gained increased interest recently, but there is a need for further research in this area. To help shed more light on this topic, we formulated the following research question: "What are caseworkers’ needs for Human-AI collaboration in public services?" To help us answer the research question, we formulated three sub-questions related to the caseworkers’ needs for AI when handling sick leave cases, their expectations for the future working with AI, and how our contributions can facilitate meeting their needs. A case study was conducted, with semi-structured interviews and focus group interviews with 16 public service practitioners as data-gathering methods. The research is set in the organization NAV, specifically in the area of sick leave case handling. We conducted a systematic literature review on the topic of transparency in human-AI interaction, which we found to be a central topic in the human-AI collaboration literature. We found multiple aspects of AI to encompass the topic of transparency, which forms the basis for the background theory used in this study. Findings show that caseworkers have quite similar needs relating to human-AI collaboration. They think that AI could mostly assist in the internal processes of the organization. Bias in AIs decisions, based on data available, was a concern amongst the caseworkers. The caseworkers suggested that humans should be in the loop to allow more trust in the systems, and thought that not all processes should be automated. Findings point towards simplifying and streamlining caseworkers’ work processes, by using AI-assisted tools in their systems. Based on the findings and recommendations, we suggest further research into the responsible development and deployment of AI, different government legislations, and how human-AI collaboration differs cross-culturally. From this study, we propose implications for practice in NAV. To leave the human in control, and to improve caseworkers’ decision-making processes, a human-centered approach to human-AI collaboration is suggested. Public sector organizations could streamline and simplify work processes through human-AI collaboration, which could help reach some of the UN’s sustainable development goals