Diffraction catastrophes and semiclassical quantum mechanics for Veselago lensing in graphene

We study the effect of trigonal warping on the focussing of electrons by n-p junctions in graphene. We find that perfect focussing, which was predicted for massless Dirac fermions, is only preserved for one specific sample orientation. In the general case, trigonal warping leads to the formation of cusp caustics, with a different position of the focus for graphene's two valleys. We develop a semiclassical theory to compute these positions and find very good agreement with tight-binding simulations. Considering the transmission as a function of potential strength, we find that trigonal warping splits the single Dirac peak into two distinct peaks, leading to valley polarization. We obtain the transmission curves from tight-binding simulations and find that they are in very good agreement with the results of a billiard model that incorporates trigonal warping. Furthermore, the positions of the transmission maxima and the scaling of the peak width are accurately predicted by our semiclassical theory. Our semiclassical analysis can easily be carried over to other Dirac materials, which generally have different Fermi surface distortions.Comment: 6 pages, 4 figures, plus supplemental material. Important reference added and text update

Economic Growth and Longevity Risk with Adverse Selection

We study a closed economy featuring heterogeneous agents and exhibiting endogenous economic growth due to interfirm external effects. Individual agents differ in terms of their mortality profile. At birth, nature assigns a health status to each agent. Health type is private information and annuity firms can only observe an agent’s age. In the presence of longevity risk, agents want to annuitize their wealth conform the classic result by Yaari (1965). In the first-best case with perfect annuities, the market would feature a separating equilibrium (SE) in which each health type obtains an actuarially fair perfect insurance. In the SE all agents are savers throughout their lives. The informational asymmetry precludes the attainment of the first-best equilibrium, however, as healthy individuals have a strong incentive to misrepresent their type by claiming to be unhealthy. Using the equilibrium concept of Pauly (1974) and Abel (1986), we prove the existence of a second-best pooling equilibrium (PE) in which individuals of all types annuitize at a common pooling rate. As the unhealthy get close to their maximum attainable age, the pooling rate prompts such individuals to become net borrowers. But borrowing would reveal their health status, so the best the unhealthy can do is to impose a borrowing constraint on themselves during their autumn years. Using a plausibly calibrated version of the model we find that the growth- and welfare effects of PE versus SE are rather small, whilst those of PE versus no annuities at all (NAE) are rather large. An imperfect insurance is better than no insurance at all, both at the microeconomic and at the macroeconomic level.annuity markets, adverse selection, endogenous growth, overlapping generations, demography

Testing for inherited thrombophilia does not reduce the recurrence of venous thrombosis\ud

Background: Inherited thrombophilia is only weakly associated with recurrence in patients with a first venous thrombosis (VT). In spite of this, thrombophilia testing is often performed in these patients. Positive results may influence patient management such as prolonged anticoagulant treatment or intensified prophylaxis in high-risk situations. Objective: To investigate whether thrombophilia testing reduces the risk of recurrent VT by virtue of these management alterations. Methods: From a large case–control study of patients (MEGA study), aged 18–70 years, with a first VT between 1999 and 2004, we selected 197 patients who had had a recurrence during follow-up. We compared the incidence of thrombophilia testing to that of a control cohort of 324 patients. We calculated the odds ratio (OR) for recurrent thrombosis in tested vs. non-tested patients. Only patients who were tested before recurrence were regarded as tested. All first and recurrent thrombotic events were objectively confirmed. Results: Thrombophilia tests were performed in 35% of cases and in 30% of controls. The OR for recurrence was 1.2 [95% confidence interval (CI) 0.9–1.8] for tested vs. non-tested patients. After correction for age, sex, family history, geographic region, presence of clinical risk factors, and year of first VT, the OR remained unchanged. Discussion: Thrombophilia testing in patients with a first VT does not reduce the incidence of recurrence in clinical practice.\u

Op zoek naar Dracula: Plaatsen van verbeelding in Transsylvanië en Whitby

Jaarlijks trekken diverse toeristen Transsylvanië binnen, op zoek naar sporen van Graaf Dracula. Zij worden gedreven door Bram Stokers Dracula (1897) of een van de vele verfilmingen uit de 20ste en 21ste eeuw. In dit artikel is onderzocht waarom mensen de behoefte hebben om fictieve verhalen, zoals Dracula, te verbinden met fysieke, herleidbare locaties, en waarom zij deze locaties vervolgens zelf willen bezoeken. Op basis van participerende observatie tijdens twee Dracula Tours en eenentwintig diepte-interviews, wordt geconcludeerd dat de innerlijke beleving van de Dracula-toerist getypeerd wordt door een dynamiek tussen twee, deels tegenovergestelde processen. Enerzijds worden Dracula-toeristen gedreven door de wens om een concrete vergelijking te maken tussen het landschap dat zij bezoeken en het beeld dat zij van dat landschap hebben gevormd op basis van het boek of de films. Anderzijds wordt de rationele benadering van het willen traceren en willen vergelijken van werkelijkheid en verbeelding gecontrasteerd met een meer intuïtief, emotioneel verlangen naar een tijdelijk symbiose tussen beide werelden. Beide processen hebben een uitgesproken fysiek karakter. Zij vinden plaats door middel van een zintuiglijke waarneming van de lokale omgeving en leiden tot een gemeenschappelijk doel: de verankering van verbeelding in de fysieke werkelijkheid

Op zoek naar James Bond : Mediapelgrimages, fans en masculiniteit

In de films en boeken van James Bond wordt veel gereisd. 007 heeft een ‘license to travel’, zo lijkt het wel. Veel Bond-fans treden in de voetsporen van hun held, en bezoeken de opnamelokaties van films als Never Say Never Again, Die Another Day en Quantum Of Solace. In dit artikel wordt onderzocht wat deze mensen drijft. Waarom gaan zij op zoek naar de wereld van James Bond? En welke sociaal-culturele waarden liggen in deze handelingen besloten

De populaire verbeelding

__Inleidend__ Wie op een mooie zomerdag Exeter College bezoekt, een van de oudste colleges van Oxford, loopt grote kans een groep toeristen tegen het lijf te lopen. Op zich is dat geen unicum: de meeste colleges trekken een geregelde stroom toeristen aan. Maar de aandacht van deze bezoekers gaat niet zozeer uit naar de fraaie, neogotische kapel, of naar het uitzicht op Radcliffe Square. De fotocamera’s zijn allemaal gericht op een hoek van het gazon: op een schijnbaar betekenisloos stukje grasveld. Opvallend is dat het gangbare geklets van toeristen heeft plaatsgemaakt voor een gewijde stilte, waarin slechts het klikken van de camera’s hoorbaar is. Wat wil het geval? Het is precies op deze plaats dat Inspector Morse – het centrale karakter van de gelijknamige tv-serie - getroffen werd door een hartaanval. In de laatste aflevering van deze wereldwijd populaire detective was te zien hoe Inspector Morse neerzakte, precies híer op het gazon in Exeter College, om enkele uren later te overlijden in het nabijgelegen ziekenhuis

The Tragedy of Annuitization

We construct a tractable discrete-time overlapping generations model of a closed economy and use it to study government redistribution of accidental bequests and private annuities in general equilibrium. Individuals face longevity risk as there is a positive probability of passing away before the retirement period. We find non-pathological cases where it is better for longrun welfare to waste accidental bequests than to give them to the elderly. Next we study the introduction of a perfectly competitive life insurance market offering actuarially fair annuities. There exists a tragedy of annuitization: although full annuitization of assets is privately optimal it is not socially beneficial due to adverse general equilibrium repercussions.Longevity risk, Risk sharing, Overlapping generations, Intergenerational transfers, Annuity markets

Stories that move: Fiction, imagination, tourism

The subject of this article is media tourism: the phenomenon of people travelling to places which they associate with novels, films or television series. Existing knowledge about this phenomenon is fragmented and principally based on individual case studies of eye-catching examples. This article aims to go beyond the limited scope of case studies and to explore an underlying, more generic process. It investigates the stories that are remembered by individuals, the associations between these stories and existing places, and decisions about whether or not to undertake travel to these places. Based on a series of in-depth interviews, the article concludes that every human being has a small treasure trove of stories which they love and which are considered part of their identity. The interviews suggest that there is a strong relationship between the recollection of beloved stories and tourist practices – in terms of both destination decision making and tourist experience