An Arctic Disaster and its Policy Implications

The purpose of the research reported here is to help the community in Barrow, Alaska, clarify its vulnerability to extreme weather events, and devise better-informed policies for reducing that vulnerability and adapting to climate variability and change. We examine the worst disaster on record there - a storm that struck on 3 October 1963 - from different disciplinary perspectives and in the context of other severe storms. The major policy responses to date have been a beach nourishment program, a feasibility study of additional means of erosion control, and an emergency management plan. Additional possible responses have been identified in the community's cumulative experience of these storms, but have not yet been fully explored or implemented. Meanwhile, given inherent uncertainties, it is clear that sound policies will allow for corrective action if and when expectations based on the best available knowledge and information turn out to be mistaken. It is also clear that the people of Barrow are in the best position to understand the evolving situation and to decide what to do about it.Les travaux de recherche que l'on présente ici ont pour but d'aider la collectivité de Barrow (Alaska) à définir son degré de vulnérabilité à des conditions climatiques extrêmes, et à créer des politiques plus éclairées qui réduiraient cette vulnérabilité et favoriseraient l'adaptation à la variabilité et au changement climatiques. On examine le pire désastre jamais enregistré à cet endroit, soit une tempête qui fit rage le 3 octobre 1963, et ce, sous l'angle de différentes disciplines et dans le contexte d'autres grandes tempêtes. Jusqu'à présent, les politiques majeures d'intervention se sont résumées à un programme de recharge de plage, à une étude de faisabilité portant sur des mesures supplémentaires de lutte contre l'érosion et à un plan de gestion des situations d'urgence. L'expérience cumulative de la collectivité relative à ces tempêtes a permis de dégager d'autres interventions possibles, sans qu'elles aient toutefois été explorées à fond ou concrétisées. Entre-temps, vu les incertitudes inhérentes à ce genre de choses, il est évident que des politiques bien pensées permettront l'application de mesures correctives si et quand les prédictions fondées sur les toutes dernières connaissances et informations disponibles s'avèrent erronées. Il est en outre évident que les habitants de Barrow sont les mieux placés pour comprendre comment la situation évolue et pour décider des mesures à prendre

Observing Nucleon Decay in Lead Perchlorate

Lead perchlorate, part of the OMNIS supernova neutrino detector, contains two nuclei, 208Pb and 35Cl, that might be used to study nucleon decay. Both would produce signatures that will make them especially useful for studying less-well-studied neutron decay modes, e.g., those in which only neutrinos are emitted.Comment: 6 pages, 2 figure

Complex lithium ion dynamics in simulated LiPO3 glass studied by means of multi-time correlation functions

Molecular dynamics simulations are performed to study the lithium jumps in LiPO3 glass. In particular, we calculate higher-order correlation functions that probe the positions of single lithium ions at several times. Three-time correlation functions show that the non-exponential relaxation of the lithium ions results from both correlated back-and-forth jumps and the existence of dynamical heterogeneities, i.e., the presence of a broad distribution of jump rates. A quantitative analysis yields that the contribution of the dynamical heterogeneities to the non-exponential depopulation of the lithium sites increases upon cooling. Further, correlated back-and-forth jumps between neighboring sites are observed for the fast ions of the distribution, but not for the slow ions and, hence, the back-jump probability depends on the dynamical state. Four-time correlation functions indicate that an exchange between fast and slow ions takes place on the timescale of the jumps themselves, i.e., the dynamical heterogeneities are short-lived. Hence, sites featuring fast and slow lithium dynamics, respectively, are intimately mixed. In addition, a backward correlation beyond the first neighbor shell for highly mobile ions and the presence of long-range dynamical heterogeneities suggest that fast ion migration occurs along preferential pathways in the glassy matrix. In the melt, we find no evidence for correlated back-and-forth motions and dynamical heterogeneities on the length scale of the next-neighbor distance.Comment: 12 pages, 13 figure

Backward correlations and dynamic heterogeneities: a computer study of ion dynamics

We analyse the correlated back and forth dynamics and dynamic heterogeneities, i.e. the presence of fast and slow ions, for a lithium metasilicate system via computer simulations. For this purpose we define, in analogy to previous work in the field of glass transition, appropriate three-time correlation functions. They contain information about the dynamics during two successive time intervals. First we apply them to simple model systems in order to clarify their information content. Afterwards we use this formalism to analyse the lithium trajectories. A strong back-dragging effect is observed, which also fulfills the time-temperature superposition principle. Furthermore, it turns out that the back-dragging effect is long-ranged and exceeds the nearest neighbor position. In contrast, the strength of the dynamic heterogeneities does not fulfill the time-temperature superposition principle. The lower the temperature, the stronger the mobility difference between fast and slow ions. The results are then compared with the simple model systems considered here as well as with some lattice models of ion dynamics.Comment: 12 pages, 10 figure

Tunable magnetic properties of arrays of Fe(110) nanowires grown on kinetically-grooved W(110) self-organized templates

We report a detailed magnetic study of a new type of self-organized nanowires disclosed briefly previously [B. Borca et al., Appl. Phys. Lett. 90, 142507 (2007)]. The templates, prepared on sapphire wafers in a kinetically-limited regime, consist of uniaxially-grooved W(110) surfaces, with a lateral period here tuned to 15nm. Fe deposition leads to the formation of (110) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coeffcients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50K to 200 K

Rumen physiology constrains diet niche: linking digestive physiology and food selection across wild ruminant species

We propose a hypothesis for digestive constraints on the browsing and grazing options available to ruminants: that the diet-niche range (maximum and minimum grass intake) of a species is dependent upon its predisposition to stratified rumen contents, based on observations that this characteristic is a critical step towards enhanced fibre digestion and greater fluid throughput. We compare a physiological (heterogeneity of ingesta fluid content) and an anatomical (the intraruminal papillation pattern) measure with dietary evidence for a range of African and temperate species. Both measures are strongly related to the mean percentage of grass in species’ natural diets, as well as to the maximum and minimum levels of grass intake, respectively. The nature of these effects implies a stratification-level threshold, below which a species will not use a grass-based diet, but above which grass consumption can increase exponentially. However, above this threshold, a minimum percentage of grass in the diet is a prerequisite for optimal performance. We argue that this second constraint is crucial, as it depicts how a greater fluid throughput reduces potential for detoxification of plant secondary compounds, and therefore limits the maximum amount of browse a stratifying species will consume

Strong-correlation effects in Born effective charges

Large values of Born effective charges are generally considered as reliable indicators of the genuine tendency of an insulator towards ferroelectric instability. However, these quantities can be very much influenced by strong electron correlation and metallic behavior, which are not exclusive properties of ferroelectric materials. In this paper we compare the Born effective charges of some prototypical ferroelectrics with those of magnetic, non-ferroelectric compounds using a novel, self-interaction free methodology that improves on the local-density approximation description of the electronic properties. We show that the inclusion of strong-correlation effects systermatically reduces the size of the Born effective charges and the electron localization lengths. Furthermore we give an interpretation of the Born effective charges in terms of band energy structure and orbital occupations which can be used as a guideline to rationalize their values in the general case.Comment: 10 pages, 4 postscript figure

Quantum Bayes rule

We state a quantum version of Bayes's rule for statistical inference and give a simple general derivation within the framework of generalized measurements. The rule can be applied to measurements on N copies of a system if the initial state of the N copies is exchangeable. As an illustration, we apply the rule to N qubits. Finally, we show that quantum state estimates derived via the principle of maximum entropy are fundamentally different from those obtained via the quantum Bayes rule.Comment: REVTEX, 9 page

The angular distribution of the reaction νˉe+p→e++n\bar{\nu}_e + p \to e^+ + n

The reaction $\bar{\nu}_e + p \to e^+ + n$ is very important for low-energy ($E_\nu \lesssim 60$ MeV) antineutrino experiments. In this paper we calculate the positron angular distribution, which at low energies is slightly backward. We show that weak magnetism and recoil corrections have a large effect on the angular distribution, making it isotropic at about 15 MeV and slightly forward at higher energies. We also show that the behavior of the cross section and the angular distribution can be well-understood analytically for $E_\nu \lesssim 60$ MeV by calculating to ${\cal O}(1/M)$, where $M$ is the nucleon mass. The correct angular distribution is useful for separating $\bar{\nu}_e + p \to e^+ + n$ events from other reactions and detector backgrounds, as well as for possible localization of the source (e.g., a supernova) direction. We comment on how similar corrections appear for the lepton angular distributions in the deuteron breakup reactions $\bar{\nu}_e + d \to e^+ + n + n$ and $\nu_e + d \to e^- + p + p$. Finally, in the reaction $\bar{\nu}_e + p \to e^+ + n$, the angular distribution of the outgoing neutrons is strongly forward-peaked, leading to a measurable separation in positron and neutron detection points, also potentially useful for rejecting backgrounds or locating the source direction.Comment: 10 pages, including 5 figure

User-Based Solutions for Increasing Level of Service in Bike-Sharing Transportation Systems

International audienceBike-sharing transportation systems have been well studied from a top-down viewpoint, either for an optimal conception of the system , or for a better statistical understanding of their working mechanisms in the aim of the optimization of the management strategy. Yet bottom-up approaches that could include behavior of users have not been well studied so far. We propose an agent-based model for the short time evolution of a bike-sharing system, with a focus on two strategical parameters that are the role of the quantity of information users have on the all system and the propensity of user to walk after having dropped their bike. We implement the model in a general way so it is applicable to every system as soon as data are available in a certain format. The model of simulation is parametrized and calibrated on processed real time-series of bike movements for the system of Paris. After showing the robustness of the simulations by validating internally and externally the model, we are able to test different user-based strategies for an increase of the level of service. In particular, we show that an increase of user information can have significant impact on the homogeneity of repartition of bikes in docking stations, and, what is important for a future implementation of the strategy, that an action on only 30% of regular users is enough to obtain most of the possible amelioration