488 research outputs found
Erratum: Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory (vol 77, art no 121404, 2008)
No full textErratum of original article: Karen Johnston, Jesper Kleis, Bengt I. Lundqvist, and Risto M. Nieminen, Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory, Phys. Rev. B 77, 121404 (2008)
Picard - an electrostatic particle in cell simulation code
No full textThis is a particle-in-cell plasma code 'picard' that was developed
by Jesper Lindkvist and Herbert Gunell with start in 2016 using
resources provided by the Swedish National Infrastructure for
Computing (SNIC) at the High Performance Computing Center North
(HPC2N), Umeå University, Sweden. Jesper Lindkvist was funded by
the Swedish National Space Board (SNSB project 201/15) and
Herbert Gunell by the Swedish National Space Agency (SNSA
project 108/18).
A paper based on the first version was published in A&A .
The present version has been updated to include ionisation as a source of cometary ions, and hdf5 files are used for writing the output. The changes in this version were made by Herbert Gunell.
The files included are:
picard.tgz Package containing all source file, some matlab m-files
that can be used for plotting of the results, and an input
file that was used for a simulation that will be used in an
upcoming publication by Herbert Gunell and Charlotte Götz.
fig-cur.mp4 Videoclip showing results from the simulation defined by the input file, specifically
three-dimensional current paths from different angles.
@author : Jesper Lindkvist
Email : [email protected]
@author : Herbert Gunell
Email : [email protected]
Type Theory Unchained: Extending Agda with User-Defined Rewrite Rules
No full textDependently typed languages such as Coq and Agda can statically guarantee the correctness of our proofs and programs. To provide this guarantee, they restrict users to certain schemes a- such as strictly positive datatypes, complete case analysis, and well-founded induction a- that are known to be safe. However, these restrictions can be too strict, making programs and proofs harder to write than necessary. On a higher level, they also prevent us from imagining the different ways the language could be extended. In this paper I show how to extend a dependently typed language with user-defined higher-order non-linear rewrite rules. Rewrite rules are a form of equality reflection that is applied automatically by the typechecker. I have implemented rewrite rules as an extension to Agda, and I give six examples how to use them both to make proofs easier and to experiment with extensions of type theory. I also show how to make rewrite rules interact well with other features of Agda such as-equality, implicit arguments, data and record types, irrelevance, and universe level polymorphism. Thus rewrite rules break the chains on computation and put its power back into the hands of its rightful owner: Yours.Programming Language
First-principles calculations of polymer interactions
No full textThis thesis reports on studies of interactions in sparse matter by first-principles calculations, in particular polymeric systems. The focus is on the three unbranched simple polymers: polyethylene (PE), isotactic polypropylene (PP) and isotactic polyvinylchloride (PVC), which together represent an important class of materials that form complexes stabilized by weak but long-range dispersive interactions. The latter ones are not included in traditional density functional theory (DFT). Due to the missing nonlocal description traditional implementations of DFT predicts, e.g., the PEcrystal to be unstable, contradicting both experiments and intuition.Two schemes are applied which extend the applicability of DFT to such sparse systems:1. A systematic correction scheme that applies to parallel well-separated polymers is proposed. From the length-averaged electron densities of the polymers and their static polarizabilities, both calculated with the traditional DFT, the dynamic response and in turn the asymptotic dispersive interaction of the polymers are modeled. Simple expressions for the orientation dependent polymerpolymer interaction energy are obtained, and even simpler expressions are found by enforcing the polymers to be cylindrically symmetric. Explicit results are given for PE, PP, PVC.2. The nonlocal correlation energy for pairs of PE-molecules is calculated also for short and intermediate separations using the recently developed general geometry (gg) DFT scheme [Phys. Rev. Lett. 92, 246401, 2004]. The gg-scheme models the electrodynamic response on the basis of the electron density only and applies also at binding distance and out. This allows us to calculate the cohesive energy landscape for the PE crystal, showing promising agreement with experimental values for equilibrium lattice constants.For well separated PE-chains (center-to-center distance > 8 Å) the two approaches turn out to be consistent with each other
Van der Waals density-functional description of polymers and other sparse materials
No full textPolymers are abundant in nature --- rubber, tar and latex have been known to mankind for thousands of years. Early in the 20th century, a systematic synthesis of polymers was developed, but the great potential of synthesized polymers was recognized first during World War II. Since then,
polymeric materials of enormous variety have been developed and constructed, and research has been devoted to improve the production and to develop new polymeric materials. A prediction of the materials behavior of such complex systems requires insight at all length scales. Proper microscopic quantum-mechanical calculations are prerequisites but out of reach of covering all length scales.
As a first step in the direction of such a general description, we treat one of the simplest polymer systems by help of first-principles density-functional theory (DFT) calculations. Specifically, interactions of chains of simple linear nonbranched polyethylene (PE) are investigated. PE represents an important class
of systems that form complexes stabilized by weak but
long-ranged dispersive interactions. Traditional DFT
does not include the latter and predicts the PE crystal to be unstable, contradicting both experiments and intuition.
A recently proposed density functional (vdW-DF), with a
consistent account of the dispersive interactions for general geometries [Phys. Rev. Lett. {\bf 92}, 246401, 2004], is implemented to infinite crystalline systems and applied to crystalline PE. The vdW-DF does not only lead to a stable PE crystal structure but also predicts
crystal-parameter values in promising agreement with
experimental data. This motivates our application of
vdW-DF to other technologically important sparse-matter systems, including dimers of parallel PE, PP, and PVC polymers, hydrogen and potassium intercalation in graphite
and bundles of nanotubes.
The adopted first-principles methods are based on
electron-structure calculations and differ significantly from the simplified force-field approaches. These have potential parameters fitted to experimental data at the
equilibrium separation and are widely used for complex polymer systems. Here they are explicitly shown to give general intermolecular parameters that lack any solid physical foundation, and which thus has no guaranteed success for systems outside the training set or at separation beyond the equilibrium separation.
The first-principles insight gained makes possible a
a well-founded interatomic description and in turn better predictive power of these fast force-field schemes
First-principles calculations of polymer interactions
No full textThis thesis reports on studies of interactions in sparse matter by first-principles calculations, in particular polymeric systems. The focus is on the three unbranched simple polymers: polyethylene (PE), isotactic polypropylene (PP) and isotactic polyvinylchloride (PVC), which together represent an important class of materials that form complexes stabilized by weak but long-range dispersive interactions. The latter ones are not included in traditional density functional theory (DFT). Due to the missing nonlocal description traditional implementations of DFT predicts, e.g., the PEcrystal to be unstable, contradicting both experiments and intuition.
Two schemes are applied which extend the applicability of DFT to such sparse systems:
1. A systematic correction scheme that applies to parallel well-separated polymers is proposed. From the length-averaged electron densities of the polymers and their static polarizabilities, both calculated with the traditional DFT, the dynamic response and in turn the asymptotic dispersive interaction of the polymers are modeled. Simple expressions for the orientation dependent polymerpolymer interaction energy are obtained, and even simpler expressions are found by enforcing the polymers to be cylindrically symmetric. Explicit results are given for PE, PP, PVC.
2. The nonlocal correlation energy for pairs of PE-molecules is calculated also for short and intermediate separations using the recently developed general geometry (gg) DFT scheme [Phys. Rev. Lett. 92, 246401, 2004]. The gg-scheme models the electrodynamic response on the basis of the electron density only and applies also at binding distance and out. This allows us to calculate the cohesive energy landscape for the PE crystal, showing promising agreement with experimental values for equilibrium lattice constants.
For well separated PE-chains (center-to-center distance > 8 Å) the two approaches turn out to be consistent with each other
35 frågor och svar inför en edering av Jesper Swedbergs Swensk Ordabok
No full textIn this paper, the author accounts for his work on editing an early 18th centurydictionary manuscript, bishop Jesper Swedberg’s Swensk Ordabok. A similar project– i.e. editing an old, hitherto unpublished dictionary manuscript – has beenperformed in Sweden only once before. This means that there is no tradition onwhich the solution of many problems concerning the edition of Swedberg'sdictionary could be based. For instance, there are no less than five manuscriptversions. Which of them should be selected as the basis manuscript of the edition,and to what extent should the differences between the manuscripts be accounted forin the edition? As argued by the author, none of the manuscripts written bySwedberg himself can serve as the basis manuscript, since they are all incomplete.Also, a relatively restricted account of the differences between the manuscripts issuggested; otherwise, the readability of the edition would be too low
Van der Waals interaction of simple, parallel polymers
No full textWe study the mutual interactions of simple parallel polymers within the framework of density-functional theory (DFT). As the conventional implementations of DFT do not treat the long-range dispersion fvan der Waals (vdW) interactions, we develop a systematic correction scheme for the nonlocal energy contribution of the polymer interaction at the intermediate to the asymptotic separations. We primarily focus on the three polymers, polyethylene, isotactic polypropylene, and isotactic polyvinylchloride, but the scheme presented applies also more generally to other simple polymers. From first-principle calculations we extract the geometrical and electronic structures of the polymers and the local part of their interaction energy, as well as the static electric response. The dynamic electrodynamic response is modeled on the basis of these static calculations, from which the nonlocal vdW interaction of the polymers is extracted
Exploration and reflection in interactive art: Glass pond
No full textGlass Pond is an interactive artwork designed to engender exploration and reflection through an intuitive, tangible interface and a simulation agent. It is being developed using iterative methods. A study has been conducted with the aim of illuminating user experience, interface, design, and performance issues.The paper describes the study methodology and process of data analysis including coding schemes for cognitive states and movements. Analysis reveals that exploration and reflection occurred as well as composing behaviours (unexpected). Results also show that participants interacted to varying degrees. Design discussion includes the artwork's (novel) interface and configuration. Copyright the author(s) and CHISIG
Real Estate Agent as a profession : A study regarding the occupation´s professional categorization
No full textTitel: Fastighetsmäklare som profession - En studie om yrkets professionskategorisering Nivå: Kandidatuppsats i ämnet Fastighetsvetenskap Författare: Jesper Arnshed Handledare: Karin Staffansson Pauli Datum: Maj 2021 Syfte: Med utgångspunkt i de fördelar som tillkommer av att nå en högre profession, är syftet med denna studie att undersöka fastighetsmäklarbranschens syn på kategoriseringen av mäklarprofessionen Metod: Denna studie har applicerat en kvalitativ forskningsmetodik. Med hjälp av semistrukturerade intervjuer har empirisk data kopplats till den teoretiska bakgrunden, om de bakomliggande aspekterna som bidrar till fastighetsmäklarens professionskategorisering. Resultat & Slutsats: Resultatet visar att mäklarens strävan mot högre profession delvis försvåras till följd av glappet mellan teori och praktik, samt de odefinierade regel- och ramverk som mäklare har att förhålla sig till. Om den nya lagändringen istället hade varit förankrad i de reella utmaningar och faktorer som påverkar förtroendet och yrkesintegriteten för mäklaren, finns där stora möjligheter för yrkesgruppen att nå en högre profession. Uppsatsens bidrag till ämnet: Studien har bidragit med ytterligare förståelse för mäklarens profession och vad som förhindrar en högre kategorisering. Förslag till framtida forskning: Efterhand som lagändringen har blivit implementerad vore det intressant att studera vilka förändringar som fått genomslag i branschen och för mäklaren.Title: Real Estate Agent as a profession - A study about the occupation´s professional categorization Level: Bachelor's thesis within Real Estate Science Author: Jesper Arnshed Supervisor: Karin Staffansson Pauli Date: May 2021 Aim: Based on the benefits of reaching a higher profession, the aim of this study is to examine the real estate industry's view on the categorization of the broker´s profession. Method: This study has applied a qualitative research methodology. With the help of semi-structured interviews, additional dimensions have supplemented the theoretical background, about the underlying aspects that are derived from the real estate agent's professional classification. Result & Conclusions: The result shows that the brokers´ aim towards a higher profession is partly prevented due to the gap between theory and practice, and the undefined rules and regulations that brokers must deal with. If the new law change had instead been rooted in the real challenges and aspects that affect the trust and professional integrity among brokers, there are great opportunities for the occupational group to reach a higher profession. Contribution of the thesis: The study contributed with additional understanding to the broker´s profession and what prevents a higher categorization. Suggestions for future research: As the changes in the law are implemented, it would be interesting to study what changes have had an impact in the industry and for the broker.
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