Semichiral Sigma Models with 4D Hyperkaehler Geometry

Semichiral sigma models with a four-dimensional target space do not support extended N=(4,4) supersymmetries off-shell arXiv:0903.2376, arXiv:0912.4724. We contribute towards the understanding of the non-manifest on-shell transformations in (2,2) superspace by analyzing the extended on-shell supersymmetry of such models and find that a rather general ansatz for the additional supersymmetry (not involving central charge transformations) leads to hyperk\"ahler geometry. We give non-trivial examples of these models.Comment: 19 page

On the delivery robustness of train timetables with respect to production replanning possibilities

Measuring timetable robustness is a complex task. Previous efforts have mainly been focused on simulation studies or measurements of time supplements. However, these measurements don't capture the production flexibility of a timetable, which is essential for measuring the robustness with regard to the trains' commercial activity commitments, and also for merging the goals of robustness and efficiency. In this article we differentiate between production timetables and delivery timetables. A production timetable contains all stops, meetings and switch crossings, while a delivery timetable only contains stops for commercial activities. If a production timetable is constructed such that it can easily be replanned to cope with delays without breaking any commercial activity commitments it provides delivery robustness without compromising travel efficiency. Changing meeting locations is one of the replanning tools available during operation, and this paper presents a new framework for heuristically optimising a given production timetable with regard to the number of alternative meeting locations. Mixed integer programming is used to find two delivery feasible production solutions, one early and one late. The area between the two solutions represents alternative meeting locations and therefore also the replanning enabled robustness. A case study from Sweden demonstrates how the method can be used to develop better production timetables

The Maraca: a tool for minimizing resource conflicts in a non-periodic railway timetable

While mathematical optimization and operations research receive growing attention in the railway sector, computerized timetabling tools that actually make significant use of optimization remain relatively rare. SICS has developed a prototype tool for non-periodic timetabling that minimizes resource conflicts, enabling the user to focus on the strategic decisions. The prototype is called the Maraca and has been used and evaluated during the railway timetabling construction phase at the Swedish Transport Administration between April and September 2010

EyeSpot: leveraging gaze to protect private text content on mobile devices from shoulder surfing

As mobile devices allow access to an increasing amount of private data, using them in public can potentially leak sensitive information through shoulder surfing. This includes personal private data (e.g., in chat conversations) and business-related content (e.g., in emails). Leaking the former might infringe on users’ privacy, while leaking the latter is considered a breach of the EU’s General Data Protection Regulation as of May 2018. This creates a need for systems that protect sensitive data in public. We introduce EyeSpot, a technique that displays content through a spot that follows the user’s gaze while hiding the rest of the screen from an observer’s view through overlaid masks. We explore different configurations for EyeSpot in a user study in terms of users’ reading speed, text comprehension, and perceived workload. While our system is a proof of concept, we identify crystallized masks as a promising design candidate for further evaluation with regard to the security of the system in a shoulder surfing scenario

Opportunities and challenges with new railway planning approach in Sweden

Long lead times in railway planning can give rise to a significant discrepancy between the original plan and the traffic eventually operated, resulting in inefficient utilization of capacity. Research shows that the railway sector in Sweden would benefit from a different planning approach in which capacity consuming decisions are pushed forward in time whenever possible. This approach is currently being implemented at Trafikverket, the Swedish Transport Administration. With it follows a number of mathematical opportunities and challenges, some of which will be presented in this paper

Two Models of Interest Arbitration

Published in cooperation with the American Bar Association Section of Dispute Resolutio

Digitala tjänster för co-modal trafiksynkronisering i Göta älv-området

Detta dokument sammanfattar det som har framkommit under en mindre förstudie inom ramen för projektet "Utveckling av innovativa, kundorienterade IT-baserade järnvägstjänster". Målet med förstudien var att undersöka dagens förutsättningar för att synkronisera co-modala skärningspunkter, med broöppningar som konkret exempel. Studien har tittat på vilken information som påverkar beslut om broöppningar med avsikt att kunna ge en indikation på vilka mekanismer och vilken information som skulle behövas från Trafikverkets perspektiv för att möjliggöra smidigare broöppningar för sjöfarten. Den faktor som enligt förstudien påverkar broöppningsmöjligheterna mest är bristen på tydliga riktlinjer för hur olika trafikslag ska prioriteras

Spectroscopy and level detuning of few-electron spin states in parallel InAs quantum dots

We use tunneling spectroscopy to study the evolution of few-electron spin states in parallel InAs nanowire double quantum dots (QDs) as a function of level detuning and applied magnetic field. Compared to the much more studied serial configuration, parallel coupling of the QDs to source and drain greatly expands the probing range of excited state transport. Owing to a strong confinement, we can here isolate transport involving only the very first interacting single QD orbital pair. For the (2,0)-(1,1) charge transition, with relevance for spin-based qubits, we investigate the excited (1,1) triplet, and hybridization of the (2,0) and (1,1) singlets. An applied magnetic field splits the (1,1) triplet, and due to spin-orbit induced mixing with the (2,0) singlet, we clearly resolve transport through all triplet states near the avoided singlet-triplet crossings. Transport calculations, based on a simple model with one orbital on each QD, fully replicate the experimental data. Finally, we observe an expected mirrored symmetry between the 1-2 and 2-3 electron transitions resulting from the two-fold spin degeneracy of the orbitals.Comment: 17 pages, 8 figure

Progress on Securing Nuclear Weapons and Materials: The Four-Year Effort and Beyond

On the eve of the Nuclear Security Summit in Seoul, South Korea, a new study finds that an international initiative to secure all vulnerable nuclear stockpiles within four years has reduced the dangers they pose. But the new analysis, by researchers in Harvard University’s Project on Managing the Atom, also concludes that much will remain to be done to ensure that all nuclear weapons and material are secure when the current four-year effort comes to an end. “At the end of four years, the global risks of nuclear theft will be significantly lower than they were before,” said co-author Matthew Bunn, associate professor of public policy at Harvard Kennedy School. “But there will still be a great deal left to do to make sure that all the world’s stocks of nuclear weapons and the materials needed to make them are protected from the full range of plausible terrorist and criminal threats – in a way that will last.” The other co-authors of the report are Martin B. Malin, executive director of the Project on Managing the Atom in the Kennedy School’s Belfer Center for Science and International Affairs, and Eben Harrell, research associate in the Managing the Atom project. The study, “Progress on Securing Nuclear Weapons and Materials: the Four-Year Effort and Beyond,” was released in advance of the Seoul summit on March 26-27, 2012, being attended by leaders or senior officials from 54 countries and four international organizations