Using Session Types for Reasoning About Boundedness in the Pi-Calculus

The classes of depth-bounded and name-bounded processes are fragments of the pi-calculus for which some of the decision problems that are undecidable for the full calculus become decidable. P is depth-bounded at level k if every reduction sequence for P contains successor processes with at most k active nested restrictions. P is name-bounded at level k if every reduction sequence for P contains successor processes with at most k active bound names. Membership of these classes of processes is undecidable. In this paper we use binary session types to decise two type systems that give a sound characterization of the properties: If a process is well-typed in our first system, it is depth-bounded. If a process is well-typed in our second, more restrictive type system, it will also be name-bounded.Comment: In Proceedings EXPRESS/SOS 2017, arXiv:1709.0004

Structural change in the dairy sectors of Germany and the Netherlands - A markov analysis

With the milk quota announced to be abolished in the future, the dairy sector is going to face a significant policy regime shift. This paper sets out to analyze the impact of milk quotas on the dairy farm structure of two important milk producing member states: Germany and the Netherlands. Based on proper behavioral assumptions, non stationary Markov chain models are specified and estimated using a generalized cross entropy procedure, which takes into account both sample and prior information. Moreover four mobility indicators characterizing structural change are developed and calculated. Structural change in the dairy sector as measured by the mobility measures is faster in West Germany than in the Netherlands. However, in the transition region East Germany structural change outpaces that of the traditional German and Dutch dairy sectors by a factor two or more. The introduction of milk quotas as of April 1, 1984 reduced overall farm mobility for the Netherlands, but increased mobility in West Germany. However, in both cases the milk quotas lead to an increase in upward mobility

Context-Free Session Types for Applied Pi-Calculus

We present a binary session type system using context-free session types to a version of the applied pi-calculus of Abadi et. al. where only base terms, constants and channels can be sent. Session types resemble process terms from BPA and we use a version of bisimulation equivalence to characterize type equivalence. We present a quotiented type system defined on type equivalence classes for which type equivalence is built into the type system. Both type systems satisfy general soundness properties; this is established by an appeal to a generic session type system for psi-calculi.Comment: In Proceedings EXPRESS/SOS 2018, arXiv:1808.0807

SnS can be modally characterized

AbstractWe show that a modal mu-calculus with label set {1,…,n} can define the Rabin recognizable tree languages up to an equivalence similar to the observational equivalence of Milner

Molecular states in a one-electron double quantum dot

The transport spectrum of a strongly tunnel-coupled one-electron double quantum dot electrostatically defined in a GaAs/AlGaAs heterostructure is studied. At finite source-drain-voltage we demonstrate the unambiguous identification of the symmetric ground state and the antisymmetric excited state of the double well potential by means of differential conductance measurements. A sizable magnetic field, perpendicular to the two-dimensional electron gas, reduces the extent of the electronic wave-function and thereby decreases the tunnel coupling. A perpendicular magnetic field also modulates the orbital excitation energies in each individual dot. By additionally tuning the asymmetry of the double well potential we can align the chemical potentials of an excited state of one of the quantum dots and the ground state of the other quantum dot. This results in a second anticrossing with a much larger tunnel splitting than the anticrossing involving the two electronic ground states.Comment: 4 pages, 4 figures; EP2DS-16 conference contributio

Estimating Investment Equations in Imperfect Capital Markets

Numerous studies have tried to provide a better understanding of firm-level investment behaviour using econometric models. The model specification of more recent studies has been based on two main approaches. The first, the real options approach, focuses on irreversibility and uncertainty in perfect capital markets; of particular interest is the range of inaction caused by sunk costs. The second, the neo-institutional finance theory, emphasises capital market imperfections and firms’ released liquidity constraints. Empirical applications of the latter theory often refer to linear econometric models to prove these imperfections and thus do not account for the range of inaction caused by irreversibility. In this study, a generalised Tobit model based on an augmented q model is developed with the intention of considering the coexistence of irreversibility and capital market imperfections. Simulation-based experiments allow investigating the properties of this model. It can be shown how disregarding irreversibility reduces effectiveness of simpler linear models.q model, uncertainty, capital market imperfections, generalised Tobit model

Studerendes oplevelse af reorganisering af problem-baseret læring på Aalborg Universitet

På Aalborg Universitet skete der i 2010 en omorganisering af stu-dieordningerne på Det Teknisk-Naturvidenskabelige Fakultet. Blandt ændringerne var, at de traditionelle projekter fyldte mindre, en større adskillelse af den formelle sammenhæng mellem kurser og projekter og en opdeling af kurserne i blokke på 5 ECTS. Vi sammenlignede erfaringerne med både den nye og den gamle model hos 10.-semesterstuderende på tre uddannelser og konkluderede, at de adspurgte studerende lagde stor vægt på projektarbejdet både i den gamle og den nye model, men at der var en signifikant lavere oplevelse af sammenhæng på et semester nu ift. før. De studerende prioriterede nu kursuseksamen højere til sidst i semesteret. Overordnet viste undersøgelsen også, at forholdet mellem det fagorienterede og det problemorienterede i de to PBL-modeller, og PBL-modeller generelt, ofte ikke var som modellerne overordnet gav udtryk for. Eksempelvis havde den nye model flere fagorienterede kurser og var derfor fra én synsvinkel et skridt mod en mere fagorienteret PBL-model; på den anden side havde de studerende i den nye model tidsmæssigt stadig mest fokus på det problemorienterede projekt og de fagorienterede kurser indeholdt PBL-lignende miniprojekter. De studerendes adfærd i en ændret undervisningsmodel var således mere kompleks, end man umiddelbart kunne antage. In 2010 Aalborg University reorganized the curriculum at the Faculty of Engineering and Science. The new curriculum scheduled less time for group projects and there was a formal separation between project and course work in each semester. The courses were also divided into 5 ECTS blocks. We compared student experiences of the old and new curriculums for three study programmes. Our results reveal that whereas in the old curriculum, students would prioritize the projects, with the new curriculum there was more focus on course work and linked examinations and the students found each semester more fragmented than before. This led us to question whether the new model had more subject-oriented courses, which would suggest a move towards a subject based PBL (problem based learning) model, or whether the students still spent most time on projects because the subject based courses contained PBL mini projects. Generally the study showed that the relationship between subject and problem solving in the two curricula models was not always obvious, and that the students’ behaviour in a changed teaching model was more complex than one might at first anticipate