Declining labor force participation of older men throughout the 20th century and recent increases in participation have generated substantial interest in understanding the effect of public pensions on retirement. The National Bureau of Economic Research's International Social Security (ISS) Project, a long-term collaboration among researchers in a dozen developed countries, has explored this and related questions. The project employs a harmonized approach to conduct within-country analyses that are combined for meaningful cross-country comparisons. The key lesson is that the choices of policy makers affect the incentive to work at older ages and these incentives have important effects on retirement behavior.

Understanding variations in body size is essential for deciphering the response of an organism to its surrounding environmental conditions and its ecological adaptations. In modern environments, large marine animals are mostly found in cold waters. However, numerous parameters can influence body-size variations other than temperatures, such as oxygenation, nutrient availability, predation or physical disturbances by storms. Here, we investigate trilobite size variations in the Lower Ordovician Fezouata Shale deposited in a cold-water environment. Trilobite assemblages dominated by small- to normal-sized specimens that are a few centimetres in length are found in proximal and intermediate settings, while those comprising larger taxa more than 20 cm in length are found in the most distal environment of the Fezouata Shale. Drill core material from distal settings shows that sedimentary rocks hosting large trilobites preserved in situ are extensively bioturbated with a high diversity of trace fossils, indicating that oxygen and nutrients were available in this environment. In intermediate and shallow settings, bioturbation is less extensive and shallower in depth. The rarity of storm events (minimal physical disturbance) and the lack of predators in deep environments in comparison to shallower settings would also have helped trilobites attain larger body sizes. This highly resolved spatial study investigating the effects of numerous biotic and abiotic parameters on body size has wider implications for the understanding of size fluctuations over geological time.

The development of power electronics in the field of transportations (automotive, aeronautics) requires the use of power semiconductor devices providing protection and diagnostic functions. In the case of series protections power semiconductor devices which provide protection may operate in shortcircuit and act as a current limiting device. This mode of operations is very constraining due to the large dissipation of power. In these particular conditions of operation, electro-thermal models of power semiconductor devices are of key importance in order to optimize their thermal design and increase their reliability. The development of such an electro-thermal model for power MOSFET transistors based on the coupling between two computation softwares (Matlab and Cast3M) is described in this paper. The 2D electro-thermal model is able to predict (i) the temperature distribution on chip surface well as in the volume under short-circuit operations, (ii) the effect of the temperature on the distribution of the current flowing within the die and (iii) the effects of the ageing of the metallization layer on the current density and the temperature. In this paper, the electrical and thermal models are described as well as the implemented coupling scheme.

Early attempts to find how solar activity can influence the Earth's climate involved comparison of many physical processes, such as dynamo mechanism, magnetic reconnection and eruptive activity, irradiance, open flux and particles variations, global atmospheric chemistry and dynamics.. . . However, such direct links seem to be weak even if the solar effects has been found to be stronger during extended maxima or minima of solar activity. Thus, temporal scales ranging from days to thousand of years must be investigated. A description of the most recent results on solar variability and its possible influence on the Earth's climate and atmosphere will be here addressed, with a particular emphasize on modulations of about 120 years (and harmonics). The extrapolation indicates a significant negative decrease of the solar signal, and consequently a decrease of the global Earth's temperature in the forthcoming years. Such a modulation is also testifying by other means, such as spectral observations of temperature sensitive lines indicating a decline of solar activity around 2015 (up to a new prolonged minimum). Prediction of global effects from the Sun's influence over the climate is thus planted in a new way.

We present an on-line linear time and space algorithmto check if an integer array f is the border array of at least one string w built on a boundedor unbounded size alphabet Σ. First of all, we show a bijection between the border array of a string w and the skeleton of the DFA recognizing Σ*ω, called a string matching automaton (SMA).Different strings can have the same border array but the originality of the presented method is that the correspondence between a border array anda skeleton of SMA is independent from the underlying strings. This enables to design algorithms for validating and generating border arrays that outperform existing ones.The validating algorithm lowers the delay (maximal number of comparisons onone element of the array) from O(|w|) to 1 + min{|Σ|,1 + log2|ω|}compared to existing algorithms.We then give results on the numbers of distinct border arrays depending on the alphabet size.We also present an algorithm that checks if a given directed unlabeled graph G is the skeleton of aSMA on an alphabet of size s in linear time.Along the process the algorithm can build one string w for which G is the SMA skeleton.

Porous metallic scaffolds have recently gained recognition as a promising avenue toward the regeneration of damaged bone structures. Interest in these materials resides in their ability to guide bone growth by presenting a favorable structure for cellular adhesion and three-dimensional proliferation. A powder metallurgy process to fabricate titanium foams with favorable microstructural parameters for applications in bone engineering has recently been developed. This study assesses the potential of this novel material for applications as an osteoconductive scaffold through in vitro characterization of early cellular interactions with titanium foams having pore sizes ranging from 167 to 500 µm. The foams exhibit no cytotoxic effects on J774 mouse macrophages while favoring adhesion and proliferation of MC3T3-E1 pre-osteoblasts. Three-dimensional morphology assumed by these cells on porous titanium suggests that the microstructure of the foams is biomimetic.

Given an ordered alphabet and a permutation, according to the lexicographic order, on the set of suffixes of a word w, we present in this article a linear time and space method to determine whether a word w' has the same permutation on its suffixes. Using this method, we are then also able to build the class of all the words having the same permutation on their suffixes, first of all the smallest one. Finally, we note that this work can lead to a method for generating a Lyndon word randomly in linear time or for computing the set of Lyndon words of length n .

GaN/sapphire layers have been grown by Metal Organic Vapour Phase Epitaxy (MOVPE). An amorphous silicon nitride layer is deposited using a SiH4/NH3 mixture prior to the growth of the low temperature GaN buffer layer. Such a process induces a 3D nucleation at the early beginning of the growth, resulting in a kind of maskless ELO process with random opening sizes. This produces a significant decrease of the threading dislocation (TD) density compared to the best GaN/sapphire templates. Ultra Low Dislocation density (ULD) GaN layers were obtained with TD density as low as 7×107cm−2 as measured by atomic force microscopy (AFM), cathodoluminescence and transmission electron microscopy (TEM). Time-resolved photoluminescence experiments show that the lifetime of the A free exciton is principally limited by capture onto residual donors, similar to the situation for nearly dislocation-free homoepitaxial layers.

Recombination dynamics in a variety of InGaN/GaN quantum systems has been studied by time resolved photoluminescence (PL). We have discovered that the time-decay of PL exhibits a scaling law: the nonexponential shape of this decay is preserved for quantum wells and quantum boxes of various sizes while their decay time varies over several orders of magnitude. To explain these results, we propose an original model for electron-hole pair recombination in these systems, combining the effects of internal electric fields and of carrier localization on a nanometer-scale. These two intricate effects imply a separate localization of electrons and holes. Such a microscopic description accounts very well for both the decays shape and the scaling law.

Insulin sensitivity of kininogen-deficient rats was compared with that of normal rats using euglycaemic hyperinsulinaemic glucose clamping. Anaesthetized animals were infused with 2-50 mU kg-1 min-1 of insulin and the glucose infusion rates needed to maintain euglycaemia were determined. Maximum glucose uptake, insulin sensitivity index and insulin clearance were reduced in kininogen-deficient rats. Captopril increased the amount of glucose needed to maintain euglycaemia during infusion of 2 and 10 mU kg-1 min-1 of insulin in normal rats, but had no effect in kininogen-deficient rats. Anaesthetized rats of both strains were given an intraperitoneal injection of glucose and the evolution of blood glucose was followed for 120 min. The peak increase was higher in kininogen-deficient rats. Similar larger increases in blood glucose were observed after glucose injection in normal rats previously treated with HOE 140, a bradykinin B2 receptor antagonist. After glucose injection, plasma insulin increased in both groups of rats but reached lower levels in kininogen-deficient animals. These results suggest that bradykinin is involved not only in the clearance of glucose and insulin by the tissues during insulin infusion but also that bradykinin can affect the release of insulin after a glucose load.

AlGaN/GaN quantum well (QWs) were grown on (0001) sapphire substrates by molecular beam epitaxy (MBE) using ammonia as nitrogen precursor. The Al composition in the barriers was varied between 8 and 27 % and the well thickness from 4 to 17 monolayers (MLs, 1ML = 2.59Å). X-ray diffraction (XRD) experiments are used to investigate the strain state of both the well and the barriers. The QW transition energy are measured by low temperature photoluminescence (PL). A large quantum confined Stark effect is observed leading to QW luminescence much lower than the emission line of the GaN buffer layer for well width above a certain critical thickness. The built-in electric field responsible for such a phenomenon is deduced from fit of the PL data. Its magnitude is of several hundred kV/cm and increases linearly with the Al composition.

We analyze the low-temperature photoluminescence decay times, for a series of MBE-grown samples embedding GaN-AlGaN quantum wells. We investigate a variety of configurations in terms of well widths, barrier widths and overall strain states. We find that not only the wells but also the barriers are submitted to large built-in electric fields. In the case of narrow barriers (5 nm), these fields favor the nonradiative escape of carriers from narrow wells into wider wells. When all wells have the same width, the field in such narrow barriers allow us to observe the recombination of long-lived “inter-well” excitons at energies close to those of the short-lived “intra-well” excitons. Our results also prove that the energies and the dynamics of excitonic recombinations depend on the parameters of the heterostructures in a complicated way, due to the interplay of piezoelectric and spontaneous polarizations.

We analyze the low-temperature photoluminescence decay times, for a series of MBE-grown samples embedding GaN-AlGaN quantum wells. We investigate a variety of configurations in terms of well widths, barrier widths and overall strain states. We find that not only the wells but also the barriers are submitted to large built-in electric fields. In the case of narrow barriers (5 um), these fields favor the nonradiative escape of carriers from narrow wells into wider wells. When all wells have the same width, the field in such narrow barriers allow us to observe the recombination of long-lived “inter-well” excitons at energies close to those of the short-lived “intra-well” excitons. Our results also prove that the energies and the dynamics of excitonic recombinations depend on the parameters of the heterostructures in a complicated way, due to the interplay of piezoelectric and spontaneous polarizations.

AIGaN/GaN quantum well (QWs) were grown on (0001) sapphire substrates by molecular beam epitaxy (MBE) using ammonia as nitrogen precursor. The Al composition in the barriers was varied between 8 and 27 % and the well thickness from 4 to 17 monolayers (MLs, 1ML = 2.59Å). X-ray diffraction (XRD) experiments are used to investigate the strain state of both the well and the barriers. The QW transition energy are measured by low temperature photoluminescence (PL). A large quantum confined Stark effect is observed leading to QW luminescence much lower than the emission line of the GaN buffer layer for well width above a certain critical thickness. The built-in electric field responsible for such a phenomenon is deduced from fit of the PL data. Its magnitude is of several hundred kV/cm and increases linearly with the Al composition.

Time-resolved photoluminescence spectra have been recorded on three GaN epitaxial layers of thickness 2.5 μm, 7 μm and 16 μm, at various temperatures ranging from 8K to 300K. The layers were deposited by MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve good homogeneities, the growth was in-situ monitored by laser reflectometry. All GaN layers showed sharp excitonic peaks in cw PL and three excitonic contributions were seen by reflectivity. The recombination dynamics of excitons depends strongly upon the layer thickness. For the thinnest layer, exponential decays with τ ~ 35 ps have been measured for both XA and XB free excitons. For the thickest layer, the decay becomes biexponential with τ1 ~ 80 ps and τ2 ~ 250 ps. These values are preserved up to room temperature. By solving coupled rate equations in a four-level model, this evolution is interpreted in terms of the reduction of density of both shallow impurities and deep traps, versus layer thickness, roughly following a L−1 law.