Insurance Cycles, Spanning and Regulation

This paper offers a novel explanation of the financial underwriting cycle in the property-liability insurance industry. By doing so it resolves that significant anomaly in asset pricing theory posed by cycles in the efficient pricing of insurance coverage. In contrast to the reliance on a variety of institutional or capital market failures underlying all previous explanations of this cycle, we directly augment the complete-markets environment of traditional asset-pricing models through the presence of a single source of risk that cannot be fully hedged through existing financial markets. We realistically interpret this source of risk as unforecastable noise in the implementation of insurance regulations. Cycles in the value of underwriting insurance coverage can arise in this simple variant of a standard complete-markets pricing model owing to the effect of such regulatory risk. We offer a sufficient condition for a stable cycle to endogenously exist in market equilibrium and illustrate this condition in the context of a representative insurance firm and a regulator pursuing a countercyclical policy with noisy implementation. Interestingly, while insurance pricing is efficient in the absence of the regulator, cyclic pricing and underwriting profitability can be induced by a countercyclical regulator policy designed to stabilize the very cycle it creates

Anti-correlations in the degree distribution increase stimulus detection performance in noisy spiking neural networks

Neuronal circuits in the rodent barrel cortex are characterized by stable low firing rates. However, recent experiments show that short spike trains elicited by electrical stimulation in single neurons can induce behavioral responses. Hence, the underlying neural networks provide stability against internal fluctuations in the firing rate, while simultaneously making the circuits sensitive to small external perturbations. Here we studied whether stability and sensitivity are affected by the connectivity structure in recurrently connected spiking networks. We found that anti-correlation between the number of afferent (in-degree) and efferent (out-degree) synaptic connections of neurons increases stability against pathological bursting, relative to networks where the degrees were either positively correlated or uncorrelated. In the stable network state, stimulation of a few cells could lead to a detectable change in the firing rate. To quantify the ability of networks to detect the stimulation, we used a receiver operating characteristic (ROC) analysis. For a given level of background noise, networks with anti-correlated degrees displayed the lowest false positive rates, and consequently had the highest stimulus detection performance. We propose that anti-correlation in the degree distribution may be a computational strategy employed by sensory cortices to increase the detectability of external stimuli. We show that networks with anti-correlated degrees can in principle be formed by applying learning rules comprised of a combination of spike-timing dependent plasticity, homeostatic plasticity and pruning to networks with uncorrelated degrees. To test our prediction we suggest a novel experimental method to estimate correlations in the degree distribution

‘Jugglers’, ‘copers’ and ‘strugglers’: academics’ perceptions of being a head of department in a post-1992 UK university and how it influences their future careers

This study investigates the experiences of academics who became department heads in a post-1992 UK university and explores the influence that being in the position has on their planned future academic career. Drawing on life history interviews undertaken with 17 male and female heads of department, the paper constitutes an in-depth study of their careers in the same university. The findings suggest that academics who become department heads not only need the capacity to assume a range of personal and professional identities, but need flexibility to regularly adopt and switch between them. Whether individuals can successfully balance and manage such multiple identities, or whether they experience major conflicts within or between them, greatly affects their experiences of being a head of department and seems to influence their subsequent career decisions. The paper concludes by proposing a conceptual framework and typology to interpret the career trajectories of academics that became department heads in the case university

Entanglement between Demand and Supply in Markets with Bandwagon Goods

Whenever customers' choices (e.g. to buy or not a given good) depend on others choices (cases coined 'positive externalities' or 'bandwagon effect' in the economic literature), the demand may be multiply valued: for a same posted price, there is either a small number of buyers, or a large one -- in which case one says that the customers coordinate. This leads to a dilemma for the seller: should he sell at a high price, targeting a small number of buyers, or at low price targeting a large number of buyers? In this paper we show that the interaction between demand and supply is even more complex than expected, leading to what we call the curse of coordination: the pricing strategy for the seller which aimed at maximizing his profit corresponds to posting a price which, not only assumes that the customers will coordinate, but also lies very near the critical price value at which such high demand no more exists. This is obtained by the detailed mathematical analysis of a particular model formally related to the Random Field Ising Model and to a model introduced in social sciences by T C Schelling in the 70's.Comment: Updated version, accepted for publication, Journal of Statistical Physics, online Dec 201

Structure of the Quark Propagator at High Temperature

In the high temperature, chirally invariant phase of QCD, the quark propagator is shown to have two sets of poles with different dispersion relations. A reflection property in momentum space relates all derivatives at zero-momentum of the particle and hole energies, the particle and hole damping rates, and the particle and hole residues. No use is made of perturbation theory.Comment: 8 pages, Latex twocolum

Flux Stabilization in 6 Dimensions: D-terms and Loop Corrections

We analyse D-terms induced by gauge theory fluxes in the context of 6-dimensional supergravity models. On the one hand, this is arguably the simplest concrete setting in which the controversial idea of `D-term uplifts' can be investigated. On the other hand, it is a very plausible intermediate step on the way from a 10d string theory model to 4d phenomenology. Our specific results include the flux-induced one-loop correction to the scalar potential coming from charged hypermultiplets. Furthermore, we comment on the interplay of gauge theory fluxes and gaugino condensation in the present context, demonstrate explicitly how the D-term arises from the gauging of one of the compactification moduli, and briefly discuss further ingredients that may be required for the construction of a phenomenologically viable model. In particular, we show how the 6d dilaton and volume moduli can be simultaneously stabilized, in the spirit of KKLT, by the combination of an R symmetry twist, a gaugino condensate, and a flux-induced D-term.Comment: 24 pages, 1 figure v2:minor correction

Crises and collective socio-economic phenomena: simple models and challenges

Financial and economic history is strewn with bubbles and crashes, booms and busts, crises and upheavals of all sorts. Understanding the origin of these events is arguably one of the most important problems in economic theory. In this paper, we review recent efforts to include heterogeneities and interactions in models of decision. We argue that the Random Field Ising model (RFIM) indeed provides a unifying framework to account for many collective socio-economic phenomena that lead to sudden ruptures and crises. We discuss different models that can capture potentially destabilising self-referential feedback loops, induced either by herding, i.e. reference to peers, or trending, i.e. reference to the past, and account for some of the phenomenology missing in the standard models. We discuss some empirically testable predictions of these models, for example robust signatures of RFIM-like herding effects, or the logarithmic decay of spatial correlations of voting patterns. One of the most striking result, inspired by statistical physics methods, is that Adam Smith's invisible hand can badly fail at solving simple coordination problems. We also insist on the issue of time-scales, that can be extremely long in some cases, and prevent socially optimal equilibria to be reached. As a theoretical challenge, the study of so-called "detailed-balance" violating decision rules is needed to decide whether conclusions based on current models (that all assume detailed-balance) are indeed robust and generic.Comment: Review paper accepted for a special issue of J Stat Phys; several minor improvements along reviewers' comment

Storage rot of seed yam resulting from speargrass injuries

Postharvest rot due to injury is a major contributing factor to the declining quality of stored seed yams ( Dioscorea spp.). Among the several known injuries, the piercing effect of speargrass rhizomes has become a serious constraint for yam production in Ghana. The objective of this study was to assess injuries on seed yams resulting from piercing of speargrass rhizomes and their effects on postharvest rots in Ghana. Eighty farmer fields from Mem, Watro, Asanteboa and Abour in the Atebubu-Amantin Municipal in the Bono East Region of Ghana were screened for speargrass incidence and injury on harvested tubers, for laboratory analysis of pathogens in 2016 and 2017. The tubers were sorted into four categories of seed yam based on weight. Thirty seed yams each of two selected white yam cultivars (Dente and Kpamyo) with visible speargrass rhizome-pierced-tubers (VSRPT) and non-speargrass rhizome pierced healthy tubers (NSRPHT) were randomly selected and stored in a ban for weekly assessment of rot. The rotten tissues from the localised area of VPSRT were subjected to pathological investigations in the laboratory. The incidence of injury seemingly increased with increasing tuber weight. It was 0% for < 100 g samples and averagely 14% for > 1 kg samples, irrespective of cultivars and locations. Incidence of rot from NSRPHT sample was observed 5 weeks after storage (WAS) for both cultivars; and 2 WAS from the VSRPT sample and 40% higher than NSRPHT at 8 WAS. Eight and six known rot pathogens were isolated from the rotten tissues of VSRPT of Dente and Kpamyo, respectively. Injury from the piercing of speargrass rhizome significantly contributed to hastening of tuber rots; while tuber injury increased with increasing speargrass density. Appropriate management of speargrass is essential for commercial seed yam growers to reduce tuber damage which affects yam quality, storage and marketing.La pourriture post-r\ue9colte due \ue0 une d\ue9chirure est un facteur majeur contribuant \ue0 la baisse de la qualit\ue9 des ignames des semences stock\ue9es ( Dioscorea spp.). Parmi les nombreuses d\ue9chirures connues, l\u2019effet per\ue7ant des rhizomes de la gerbe d\u2019herbe est devenu une contrainte s\ue9rieuse pour la production d\u2019igname au Ghana. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer les d\ue9chirures sur les ignames de semence r\ue9sultant du per\ue7age des rhizomes de gerbe d\u2019herbe et leurs effets sur les pourritures post-r\ue9colte au Ghana. Quatre-vingts champs d\u2019agriculteurs de Mem, Watro, Asanteboa et Abour dans la municipalit\ue9 d\u2019Atebubu-Amantin dans la region de l\u2018 Est de Bono au Ghana ont \ue9t\ue9 examin\ue9s pour d\ue9terminer l\u2019incidence et les dommages de la gerbe d\u2019herbe sur les tubercules r\ue9colt\ue9s, pour une analyse en laboratoire des agents pathog\ue8nes en 2016 et 2017. Les tubercules ont \ue9t\ue9 tri\ue9s en quatre cat\ue9gories d\u2019igname de semence en fonction du poids. Trente ignames de semence de chacun des deux cultivars s\ue9lectionn\ue9s d\u2019igname blanche (Dente et Kpamyo) avec des tubercules perc\ue9s de rhizome de gerbe d\u2019herbe (VSRPT) et des tubercules sains perc\ue9s de rhizome non- gerbe d\u2019herbe (NSRPHT) ont \ue9t\ue9 s\ue9lectionn\ue9s au hasard et stock\ue9s dans une interdiction pour une \ue9valuation hebdomadaire de la pourriture . Les tissus pourris de la zone localis\ue9e de VPSRT ont \ue9t\ue9 soumis \ue0 des investigations pathologiques en laboratoire. L\u2019incidence des d\ue9chirures a apparemment augment\ue9 avec l\u2019augmentation du poids des tubercules. Il \ue9tait de 0% pour les \ue9chantillons <100 g et de 14% en moyenne pour les \ue9chantillons > 1 kg, quels que soient les cultivars et les emplacements. L\u2019incidence de pourriture de l\u2019\ue9chantillon NSRPHT a \ue9t\ue9 observ\ue9e 5 semaines apr\ue8s stockage (WAS) pour les deux cultivars; et 2 WAS de l\u2019\ue9chantillon VSRPT et 40% plus \ue9lev\ue9s que NSRPHT \ue0 8 WAS. Huit et six agents pathog\ue8nes de la pourriture connus ont \ue9t\ue9 isol\ue9s respectivement dans les tissus pourris du VSRPT de Dente et de Kpamyo. Les d\ue9chirures caus\ue9es par le per\ue7age du rhizome de gerbe d\u2019herbe ont consid\ue9rablement contribu\ue9 \ue0 acc\ue9l\ue9rer la pourriture des tubercules; tandis que les dommages aux tubercules augmentaient avec l\u2019augmentation de la densit\ue9 de la gerbe d\u2019herbe. Une gestion appropri\ue9e de la groseille verte est essentielle pour les producteurs commerciaux d\u2019ignames de semence afin de r\ue9duire les dommages aux tubercules qui affectent la qualit\ue9, le stockage et la commercialisation des ignames

Hydrostatic Pressure Sensing with High Birefringence Photonic Crystal Fibers

The effect of hydrostatic pressure on the waveguiding properties of high birefringence photonic crystal fibers (HiBi PCF) is evaluated both numerically and experimentally. A fiber design presenting form birefringence induced by two enlarged holes in the innermost ring defining the fiber core is investigated. Numerical results show that modal sensitivity to the applied pressure depends on the diameters of the holes, and can be tailored by independently varying the sizes of the large or small holes. Numerical and experimental results are compared showing excellent agreement. A hydrostatic pressure sensor is proposed and demonstrated using an in-fiber modal interferometer where the two orthogonally polarized modes of a HiBi PCF generate fringes over the optical spectrum of a broad band source. From the analysis of experimental results, it is concluded that, in principle, an operating limit of 92 MPa in pressure could be achieved with 0.0003% of full scale resolution

Demonstration of the temporal matter-wave Talbot effect for trapped matter waves

We demonstrate the temporal Talbot effect for trapped matter waves using ultracold atoms in an optical lattice. We investigate the phase evolution of an array of essentially non-interacting matter waves and observe matter-wave collapse and revival in the form of a Talbot interference pattern. By using long expansion times, we image momentum space with sub-recoil resolution, allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure