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Les representations que les jeunes ont des professionnels de sante et leurs exigences en matiere de fonctionnement des services creent une problematique originale et complexe. Cette originalite implique sans doute des differences importantes d’une culture a l’autre. Pour cette raison, il a semble qu’une etude comparant les representations et les attitudes face au recours aux soins de jeunes de pays aux contextes culturels differents, aiderait a comprendre pourquoi les adolescents ont des facons si particulieres d’utiliser – ou de ne pas utiliser – les services de soins formels et auto-administres. Un questionnaire original a reponses ouvertes a ete construit et valide conjointement par une equipe francaise et chilienne. Un echantillon de convenance de 957 jeunes scolarises de 14 a 19 ans a participe a l’etude, en France et au Chili. En cas de probleme somatique, la mere est l’interlocuteur privilegie des jeunes ; en cas de probleme emotionnel/relationnel ce sont plutot les amis. Le medecin generaliste est l’interlocuteur professionnel privilegie en cas de probleme physique ; en cas de probleme emotionnel, un tiers des jeunes dit ne pas envisager une consultation. Les attentes des francais vis-a-vis des professionnels, sont plus souvent du domaine de « l’affectif » que celles des chiliens qui concernent plutot le champ « medical/technique ». Les pratiques de soins auto-administres sont qualitativement similaires mais les francais privilegient la prise de medicaments tandis que les chiliens privilegient les « petits soins domestiques ». L’utilisation des medecines naturelles est plus repandue parmi les jeunes chiliens mais les types de medecines utilisees sont similaires, notamment les tisanes et autres remedes a base de plantes et l’homeopathie. Ces resultats ont diverses implications notamment en termes de formation des professionnels de sante a la prise en charge des problemes emotionnels et relationnels. Il est souhaitable que le secteur officiel de soins considere les soins dispenses en dehors de lui comme des ressources complementaires, repondant au besoin d’autonomie des adolescents.

International audience; Assessment of recharge, paleo-recharge and groundwater residence time of aquifer systems of the Sahel is pivotal for a sustainable management of this vulnerable resource. Due to its stratified aquifer system, the Lake Chad Basin (LCB) offers the opportunity to assess recharge processes over time and to link climate and hydrology in the Sahel. Located in north-central Africa at the fringe between the Sahel and the Sahara, the lake Chad basin (LCB) is an endorheic basin of 2,5.106 km2. With a monsoon climate, the majority of the rainfall occurs in the southern one third of the basin, the Chari/Logone River system transporting about 90% of the runoff generated within the drainage basin. A complex multi-layer aquifer system is located in the central part of the LCB. The Quaternary unconfined aquifer, covering 500 000 km2, is characterized by the occurrence of poorly understood piezometric depressions. Artesian groundwaters are found in the Plio-Pleistocene lacustrine and deltaic sedimentary aquifers (early Pliocene and Continental Terminal). The present-day lake is in hydraulic contact with the Quaternary Aquifer, but during past megalake phases, most of the Quaternary aquifer was submerged and may experience major recharge events. To identify active recharge area and assess groundwater dynamics, one hundred surface and groundwater samples of all layers have been collected over the southern part of the LCB. Major and trace elements have been analyzed. Measurements of 36Cl have been carried out at CEREGE, on the French 5 MV AMS National Facility ASTER and 14C activities have been analyzed for 17 samples on the French AMS ARTEMIS. Additionally, the stable isotopic composition was measured on the artesian aquifer samples. In the Quaternary aquifer, results show a large scatter with waters having very different isotopic and geochemical signature. In its southern part and in the vicinity of the surface waters, groundwaters are predominantly Ca-Mg-HCO3 type waters with very high 36Cl/Cl ratio (>1000.10-15 at/at) very likely linked to the bomb pulse. These high 36Cl/Cl ratios are in the same order than the 36Cl/Cl signature of surface waters active modern recharge in this area. In the other part of the Quaternary Aquifer, waters are Na-HCO3-SO4-Cl type and are characterized by lower 36Cl/Cl ratios (around 200.10-15 at/at), suggesting longer residence time of the groundwaters. The 14C contents of the unconfined aquifer waters are all above 50 pmc, suggesting recent or Holocene recharge of this system. In contrast, the confined aquifer has a more homogeneous geochemical signature. The 14C contents are below all 0.5 pmc and mainly below detection level. 36Cl/Cl ratios are

Hydrochemical data from a total of 104 groundwater samples were used to investigate the main factors and mechanisms that control the chemistry of groundwaters in the Complexe Terminal (Cl') aquifer of Chott region in southern Tunisia. Multivariate statistical techniques combining Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were applied to the dataset of 12 physicochemical parameters (i.e. pH, T degrees, depth, Na+, K+, Ca2+, Mg2+, HCO3- NO3-, Cl-, SO42-, and TDS). The HCA using Ward's method and squared Euclidean distance classified the parameters into four clusters based on their dissimilarities. The application of PCA resulted in two factors explaining 64.25% variance. Geochemical methods combined with HCA and PCA confirm that groundwater chemistry is not controlled by the different lithological fades of the aquifer, but by the presence of evaporates randomly distributed in the basin. Although stable isotope data (H-2 and O-18) of some groundwater are consistent with a slight modern recharge, Cl' groundwaters are mostly depleted bearing witness to the recharge of the aquifer system occurred under different climatic conditions than present. The stable isotopic composition of these paleowaters which all lie to the right of the local meteoric water line also indicates more pronounced evaporation of rainfall during the recharge process than during present-day conditions.

Au Vietnam, comme dans la plupart des pays en developpement, la sante des adolescents n’est pas consideree comme prioritaire, et pourtant il existe beaucoup de grands problemes concernant ce groupe de population. Cette etude a pour objectif de decrire les representations de la sante des lyceens de Ho Chi Minh-Ville. Elle est realisee sur un echantillon representatif de 543 lyceens de 16 a 19 ans, en utilisant un instrument adapte d’un questionnaire cree et valide au Centre de Medecine Preventive de Nancy-Vandœuvre.Les adolescents interroges ont presente leurs concepts de la sante de maniere tres diverse : a la fois de facon classique – absence de maladie – mais aussi de facon globale et positive – la forme, la force, le developpement, le bonheur.La comparaison avec d’autres etudes realisees, avec le meme questionnaire en Algerie et en France, montre certaines constantes transculturelles dans les representations de la sante, et des particularites tenant a chaque societe et a chaque culture.

Ethical issues have only recently emerged as a topic of debate in health education. Until recently, health education was seen as "beneficent" by nature and as designed to improve well-being and quality of life. Traditionally, the purpose of health education was to promote behavior change. The idea of intruding into people's private lives raises the question of the objectives and methods of health education. The principles underlying ethical reflection--beneficence, non-malfeasance, autonomy and social justice--provide a basis for identifying a number of problems or abuses. Traditionally, people have tended to be seen as implicitly responsible for their own behavior, a view based on a moralistic, guilt-inducing and didactic approach to health and health behavior. The assumption is that these infringements affect the identity and dignity of persons. In addition, imposing standards and norms of behavior defined by others amounts to undermining or denying the autonomy of individuals. Finally, traditional health education approaches, and in particular communication campaigns, may contribute to the improvement of health, but it is at the cost of increased inequalities. To conclude, ethics is both a statement of values and a method or process. Ethics needs to be debated and discussed in a democratic forum. It is up to citizens, not experts, to establish the link between means and ends. Health promotion has resulted in a shift in perspective--a shift that has provided protection against ethical lapses and violations. This paper argues that health education must create the conditions of autonomy by focusing first on environmental factors and inequalities.

A questionnaire designed to measure oral health-related quality of life (OHRQOL) in adults and children was assessed for its factorial structure and reliability using data from the Second International Collaborative Study on Oral Health Outcomes in New Zealand, Poland and Germany. Principal component analysis with orthogonal and oblique rotation was applied. The three-factor structure hypothesized for the children's questionnaire (self-reported oral disease symptoms, perceived oral well-being, social and physical functioning) was confirmed in New Zealand and Poland, and two self-reported oral disease symptom dimensions emerged in Germany. Five factors instead of the three hypothesized were identified for adults: two dimensions of symptoms were identified, and social and physical functioning appeared to be independent dimensions of OHRQOL. Similarity between the factors was demonstrated in all three countries. The reliability of the questionnaire ranged from moderate to excellent depending on the dimension and the country. These findings provide preliminary evidence of the cross-cultural stability of the OHRQOL questionnaire in New Zealand, Poland and Germany, for both children and adults. Further investigations by the present authors of the properties of the instrument in other samples will focus on demonstrating the stability and replicability of the factor structure identified here.

A 547 jours du troisième millénaire, le bilan social de l'humanité ne suscite pas d'enthousiasme. Et pourtant, les dernières cinquante années avaient d'abord permis l'espoir d'une prospérité durable, d'un développement économique du tiers-monde, et d'une relative égalité sociale à l'intérieur des pays et d'une nation à l'autre.

To determine the effect of occupational stress on low-back pain (LBP), a cross-sectional study has been carried out, by interviews, on workers exposed to 3 stresses: manual handling (MH, 82 women and 264 men), whole body vibrations (WBV, 274 men), and static postures (278 women). Anthropometric data, occupational stress, LBP severity and frequency, and a psychological evaluation of these groups were compared to those of a control population of 208 workers (104 men and 104 women). The results show that 30% of the population had never suffered from LBP. Age and the body mass index of the workers were the parameters most closely associated with LBP. Women involved in MH had higher frequency and severity of LBP than their reference population. Men involved in MH or exposed to WBV had higher frequency of painful episodes than their reference population. Workers exposed to one of the stresses were on sick leave for LBP more often, and for longer periods, than workers in the reference group. The results show that individual factors are often decisive in the onset of LBP. Nevertheless, in the more serious LBP cases, occupational stress is an aggravating factor for LBP and its consequences.

Information on adolescent health can be obtained from a variety of sources. Medical practitioners can offer little insight on the subject because adolescence is the period of life in which there is the least number of consultations with a doctor and the lowest rate of hospitalization. Such professionals therefore observe and record little on adolescents. Educators youth workers and some social workers with professions focused upon adolescence could offer insight into adolescent health but they are almost never consulted. Parents have hardly more occasion to say anything on the subject. To obtain a better understanding of adolescents health information must be obtained from adolescents themselves. The role of epidemiologists what is known about adolescents and their health what is being learned and what remains to be discovered are discussed.

The generator includes several tools that allows to translate the initial problem specification to a specific circuit implementation. From the rule based specification the generator produces a first computing scheme. By applying various transformations (lattice and arithmetic operation minimization, optimal register assignation, ...) the system produces the microprogram that drives the controller. For this purpose, the VHDL language is used to simulate the hardware controller, and the ES2 design kit is used to design the circuits to be integrated.

Fuzzy controllers can be implemented by standard hardware, dedicated micro controller or application specific circuits. The basic fuzzy controller architecture can use one or more arithmetic and logical units (ALU). ALUs execute the following operations: fuzzyfication, defuzzyfication, lattice and arithmetic functions. The generator includes several tools that allows to translate the initial problem specification to a specific circuit implementation. From the rule based specification the generator produces a fIrst computing scheme. By applying various transformations (lattice and arithmetic operation minimization, optimal register assignation, …) the system produces the microprogram that drives the controller. For this purpose, the VHDL language is used to simulate the hardware controller, and the ES2 design kit is used to design the circuits to be integrated.

The uranium content and 234 U/ 238 U ratios have been measured in more than thirty groundwater samples over the Tunisian part of the Continental Intercalaire (CI) aquifer. In this large artesian aquifer, uranium behavior is mainly controlled by redox front systems. The uranium concentrations vary by 5 orders of magnitude from 10-4 to 20 ppb and the ( 234 U/ 238 U) activity ratio from 1 to 10. Close to CI outcrops in the Dahar Mountains, the stepwise decrease in U concentrations combined with a significant increase of the ( 234 U/ 238 U) ratio up to 10 (“augmenting regime”) is followed, downflow by a ( 234 U/ 238 U) decrease up to 3 (“decaying regime”), clearly indicating the occurrence of a redox front. We will discuss the significance of 234 U- 238 U disequilibria in terms of water residence times and its potential to trace water-rock interaction mechanisms.

The North-Western Sahara Aquifer System (NWSAS), one of the world’s largest groundwater systems, shows an overall piezometric decline associated with increasing withdrawals. Estimating the recharge rate in such a semiarid system is challenging but crucial for sustainable water development. In this paper, the recharge of the NWSAS is estimated using a regional water budget based on GRACE terrestrial water storage monthly records, soil moisture from the GLDAS (a land data system that assimilates hydrological information), and groundwater pumping rates. A cumulated natural recharge rate of 1.40 ˙ 0.90 km3 yr–1 is estimated for the two main aquifers. Our results suggest a renewal rate of about 40% which partly contradicts the premise that recharge in this area should be very low or even null. Aquifer depletion inferred from our analysis is consistent with observed piezometric head decline in the two main aquifers in the region. Annual recharge variations were also estimated and vary between 0 and 4.40 km3 yr–1 for the period 2003–2010. These values correspond to a recharge between 0 and 6.75 mm yr–1 on the 650,000 km2 of outcropping areas of the aquifers, which is consistent with the expected weak and sporadic recharge in this semiarid environment. These variations are also in line with annual rainfall variation with a lag time of about 1 year.

Located at the transition between the Saharan and Sahelian zones, at the center of one of the largest endorheic basins, Lake Chad is ideally located to record regional environmental changes that occurred in the past. However, until now, no Holocene archive was directly cored in this lake. In this paper, we present pollen data from the first sedimentary sequence collected in Lake Chad (13° N; 14° E; Sahel region). Dated between ca. 6700 and ca. 5000 cal yr BP, this record is continuous and encompasses part of the termination of the African Humid Period (AHP). Vegetation reconstructions are based on standard analyses of pollen diagrams and are strengthened by quantitative approaches. Potential biomes are reconstructed using the biomization method and mean annual precipitation (Pann) is estimated using the modern analogues technique. Results show that, between ca. 6700 and ca. 6050 cal yr BP, a vegetation close to humid woodland or humid savanna, including elements currently found further southward, thrived in the vicinity of the Mega-Lake Chad in place of the modern dry woodland, steppe and desert vegetation. At the same time, montane forest populations extended further southward on the Adamawa Plateau. The high abundance of lowland humid pollen taxa, particularly of Uapaca, is interpreted as the result of a northward migration of the corresponding plants during the AHP. This preferential zonal occurrence of these taxa in Lake Chad Basin (LCB) (rather than extrazonal) is driven by more humid local and regional climate conditions at this latitude, as shown by mean Pann estimated values of ca. 800 (−400/+700) mm during this period. However, we cannot rule out that an increase of the Chari–Logone inputs into the Mega-Lake Chad might have also contributed to control the abundance of these taxa. Changes in the structure and floristic composition of the vegetation towards more open and drier formations occurred after ca. 6050 cal yr BP, following a decrease in mean Pann estimates to approximately 600 (−230/+600) mm. But, the constant significant presence of lowland humid taxa until ca. 5000 cal yr BP, contemporaneous with a slight increase in steppic taxa, demonstrates that at this date, the modern vegetation was not yet established in the vicinity of Lake Chad. Our data indicate that between ca. 6700 and ca. 5000 cal yr BP vegetation and climate changes must have occurred progressively, but that century-scale climate variability was superimposed on this long-term mid-Holocene drying trend as observed around ca. 6300 cal yr BP, where pollen data indicate more humid conditions.

End-of-life policies are hotly debated in many countries, with international evidence frequently used to support or oppose legal reforms. Existing reviews are limited by their focus on specific practices or selected jurisdictions. The objective is to review international time trends in end-of-life practices. We conducted a systematic review of empirical studies on medical end-of-life practices, including treatment withdrawal, the use of drugs for symptom management, and the intentional use of lethal drugs. A search strategy was conducted in MEDLINE, EMBASE, Web of Science, Sociological Abstracts, PAIS International, Worldwide Political Science Abstracts, International Bibliography of the Social Sciences and CINAHL. We included studies that described physicians’ actual practices and estimated annual frequency at the jurisdictional level. End-of-life practice frequencies were analyzed for variations over time, using logit regression. Among 8183 references, 39 jurisdiction-wide surveys conducted between 1990 and 2010 were identified. Of those, 22 surveys used sufficiently similar research methods to allow further statistical analysis. Significant differences were found across surveys in the frequency of treatment withdrawal, use of opiates or sedatives and the intentional use of lethal drugs (X 2 > 1000, p

Finite fields are used in different types of computers and digital communication systems. Two well-known examples are error-correction codes and cryptography. The traditional way of implementing the corresponding algorithms is software, running on general-purpose processors or on digital-signal processors. Nevertheless, in some cases the time constraints cannot be met with instruction-set processors, and specific hardware must be considered.

Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bolling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.

There are many data processing applications (e.g. image and voice processing), which use a large range of values and that need a relatively high precision. In such cases, instead of encoding the information in the form of integers or fixed-point numbers, an alternative solution is a floating-point representation. In the first section of this chapter, the IEEE standard for floating point is described. The next section is devoted to the algorithms for executing the basic arithmetic operations. The two following sections define the main rounding methods and introduce the concept of guard digit. Finally, the last few sections propose basic implementations of the arithmetic operations, namely addition and subtraction, multiplication, division and square root.

This chapter describes the classical architecture of many digital circuits and presents, by means of several examples, the conventional techniques that digital circuit designers can use to translate an initial algorithmic description to an actual circuit. The main topics are the decomposition of a circuit into Data Path and Control Unit and the solution of two related problems, namely scheduling and resource assignment.

This chapter is devoted to those electronics aspects important for digital circuit design. The digital devices are built with analog components, and then some considerations should be taken into account in order to obtain good and reliable designs.

Embedded systems are computers designed and programmed to meet the requirements of a specific application. Applications may not require an OS (Operating System) or may rely on a customized OS. The system architecture is usually composed of a low-cost microprocessor, memory and peripherals interconnected through busses. It may also include a coprocessor to speed-up a specific computation.

This chapter introduces the main concepts related to the implementation of embedded systems on FPGA devices. Many of these concepts will appear during the case studies that are exposed in the next chapter.

Partial Reconfiguration (PR) is the ability to change a portion (the reconfigurable partition) of the device without disturbing the normal operation of the rest (the static partition). A typical PR application is a reconfigurable coprocessor which switches the configuration of the reconfigurable partition at run-time when required by the application. The main advantage is the ability to map different coprocessor configurations in the reconfigurable partition in a time-multiplexed way, reducing the required area.

The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between similar to 18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.

Several important implementation techniques are presented in this chapter. The first one is pipelining, a very commonly used method in systems that process great volumes of data. Self-timing is the topic of the second section. To some extent it can be considered as an extension of the pipelining concept and is especially attractive in the case of very big circuits.

Modern Electronic Design Automation tools have the capacity to synthesize the control unit from a finite state machine description, or even to extract and synthesize the control unit from a functional description of the complete circuit (Chap. 5). Nevertheless, in some cases the digital circuit designer can himself be interested in performing part of the control unit synthesis.

Solid state detectors operating in Geiger mode such as the silicon photomultiplier (SiPM) are poised to replace currently used photomultiplier tubes in many applications due to their robustness, dimension and magnetic insensibility. A next generation SiPM well suited for near UV photons with low dark count rate has been developed. 1 mm, 3 mm and 5 mm devices with 25, 50 and 100 µm micro-cells and geometrical efficiencies ranging from 29% to 74% have been produced. A probability of detection of 58% in photon counting mode at 440 nm has been reached. The photon detection efficiency (PDE) thus ranges from 42% to 17% depending on the geometrical efficiency of the chip. The dark count rate varied between the different designs (25 µm to 100 µm micro-cells, 1 mm to 5 mm chips) and was in the region of 300 kcps per mm2 at room temperature and at an operating voltage maximizing the PDE. Characteristics from this novel low dark count SiPM design will be presented and compared, further developments and improvements will also be discussed.

CT imaging is currently the standard modality to provide anatomical reference in PET molecular imaging. Since both PET and CT rely on detecting radiation to generate images, it would make sense to use the same detection system for data acquisition. Merging PET and CT hardware imposes stringent requirements on detectors, including wide dynamic range with high signal-to-noise ratio for good energy resolution in both modalities, high pixellisation for high spatial resolution, and very high count rate capabilities. The APD-based LabPET II module is proposed as the building block for a truly combined PET/CT scanner. The module is made of two 4 × 8 APD pixel monolithic arrays mounted side by side unto a custom ceramic holder, with each element having an active area of 1.1 × 1.1 mm2 at a 1.2 mm pitch, coupled to a 12-mm high LYSO scintillator block array. While a previous version of the module was made of pyramidal shaped crystals (1.35 × 1.35 / 1.2 × 1.2 mm2, top/bottom), a recent version was designed with a simpler rectangular geometry (1.2 × 1.2 mm2), better reflective material optimizing the shift of refractive index at crystal interface, and enhanced APD quantum efficiency to improve intrinsic detector performance. Mean energy resolution was improved to 20 ± 1% (formerly 24 ± 1%) at 511 keV and to 41 ± 4% (formerly 48 ± 3%) at 60 keV. These intrinsic detector performance characteristics make the LabPET II module suitable for counting CT imaging with efficient energy discrimination. Initial phantom images obtained from a CT test bench demonstrated excellent contrast linearity as a function of material density and spatial resolution of 0.61 mm FWHM / 1.1 mm FWTM, corresponding to 1.3 lp/mm at MTF 10% / 0.73 lp/mm at MTF 50% , which allowed 0.75 mm air holes in an Ultra Micro resolution phantom to be clearly distinguished.

International audience; Authigenic 10Be/9Be ratiomeasurementswere performed at high resolution along a Portuguese Margin deep-sea core (37°48 N; 10°09W) spanning the 20–50 ka time interval, in order to reconstruct variations in atmospheric cosmogenic 10Be production rates and derive the related geomagnetic dipole moment modulation. A complementary approach consisting in 230Thxs-normalized 10Be deposition rate determination on selected samples confirmed the reliability of the authigenic 10Be/9Be record. This study constitutes the first successful comparison of the two widely-used normalization techniques of 10Be concentrations. For both methods, the presented results herein evidence a factor of ~2 cosmogenic nuclide overproduction linked to a minimum dipole moment associated with the Laschamp Excursion. The latter is stratigraphically constrained beneath Heinrich Event 4. Its age is estimated at ~41 ka on the basis of direct correlation between the series of rapid paleoclimatic events recorded inthe Portuguese Margin sediments and in the Greenland ice sheet, and is confirmed by calibrated radiocarbon dating carried out on the same sediments. The remarkable agreement between the authigenic 10Be/9Be and the Greenland Ice cores 10Be deposition rate records attests to their global significance. This new authigenic 10Be/9Be record has been combined with that previously obtained at the same site to produce a stacked record that is calibrated using absolute values of Virtual Dipole Moment determined on lava flows. This provides a reconstruction of dipole geomagnetic moment variations over the 20–50 ka interval, independent frompaleomagnetically-constrainedmethods, that documents the Laschamp dipole low but fails to express any dipole low related to t e Mono Lake Excursion. This high resolution record responds to the necessity of supplementing the knowledge of the atmospheric Δ14C variations in the 30–45 ka interval during which the 14C calibration curve suffers from a lack of accurate data, and during which a discrepancy of about 5500 yr between the 14C and U–Th ages is due to the Laschamp geomagnetic dipole low. Such new high resolution datasets from records obtained from different latitudes will be required to make significant advances in understanding the causes of atmospheric Δ14C variations.

The widespread occurrence of microbialites in the last deglacial reef frameworks (16–6 Ka BP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes. The present study is based on the sedimentological and chronological analysis (14C AMS dating) of drill cores obtained during the IODP Expedition #310 “Tahiti Sea Level” on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise. The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6 m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the “reefal microbialites” which developed a few hundred years after coralgal communities in shallow-water environments, whereas the “slope microbialites” grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities. The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (> 50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~ 30%) and could not host a significant microbialite expansion.

The scintillator is one of the key building blocks that critically determine the physical performance of PET detectors. The quest for scintillation crystals with improved characteristics has been crucial in designing scanners with superior imaging performance. Recently, it was shown that the decay time constant of high lutetium content Lu 1.8 Gd 0.2 SiO 5 :Ce (LGSO) scintillators can be adjusted between 30 ns and 48 ns by varying the cerium concentration from 0.025 mol% to 0.75 mol%, thus providing interesting characteristics for phoswich detectors. The large light output (90–120% NaI), the better spectral match and the high initial photoelectron rate (∼200 phe−/ns) of these scintillators with avalanche photodiode (APD) readout promise to provide superior energy and timing resolution. Moreover, their improved mechanical properties as compared to conventional LGSO (Lu 0.2 Gd 1.8 SiO 5 :Ce) make block array manufacturing readily feasible. To verify these assumptions, new phoswich block arrays made of LGSO-90%Lu with low and high mol% Ce concentrations were fabricated and assembled into LabPET modules. Typical crystal decay time constants were 32 ns and 48 ns, respectively. We therefore report on the initial evaluation of this modified version of the LabPET detector module. Phoswich crystal identification performed using a non-optimized digital pulse shape discrimination algorithm yielded an average 10% error. At 511 keV, energy resolution of 20 ± 2% and 15 ± 1% were obtained, while coincidence timing resolution between 4.9 ± 0.3 ns and 4.1 ± 0.1 ns were achieved. The improved characteristics of this new LGSO-based phoswich detector module are expected to enhance the LabPET scanner performance, first by improving sensitivity due to the overall higher stopping power of the detector module, and second by narrowing the coincidence time window, thus minimizing the random event rate. Altogether these two improvements will significantly enhance the noise equivalent count rate performance of an all LGSO-based LabPET scanner.

The properties of avalanche photodiodes and associated electronics required for photon counting in the Geiger and the sub-Geiger modes are reviewed. When the Geiger mode is used, there are significant improvements reported in overall photon detection efficiencies (approaching 70% at 633 nm), and a timing jitter (under 200 ps) is achieved with passive quenching at high overvoltages (20-30 V). The results obtained by using an active-mode fast quench circuit capable of switching overvoltages as high as 15 V (giving photon detection efficiencies in the 50% range) with a dead time of less than 50 ns are reported. Larger diodes (up to 1 mm in diameter) that are usable in the Geiger mode and that have quantum efficiencies over 80% in the 500-800-nm range are also reported.

International audience; The concentrations of atmospheric cosmogenic 10Be normalized to the solubilized fraction of its stable isotope 9Be have been measured in the authigenic phase leached from silicated continental sediments deposited since the upper Miocene in the northern Chad Basin. This method is validated by the systematic congruence with the biochronological estimations based on the fossil mammal evolutive degree of faunal assemblages. The fifty-five authigenic 10Be/9Be ages obtained along 12 logs distributed along two West-East cross sections that encompass best representative Mio-Pliocene outcrops including paleontological sites show a systematic stratigraphic decrease when considering all studied sedimentary facies extending from the Pleistocene up to 8 Ma and allow performing geologic correlations otherwise impossible in the studied area. The resulting global sequence evidences and temporally specifies the succession of the main paleoenvironments that have developed in this region since the Miocene. Under the special conditions encountered in the northern Chad Basin, this study demonstrates that the authigenic 10Be/9Be ratio may be used as a dating tool of continental sedimentary deposits from 1 to 8 Ma. The half-life of 10Be theoretically allowing dating up to 14 Ma, it may have fundamental implications on important field research such as paleoclimatology and, through the dating of fossiliferous deposits in paleontology and paleoanthropology.

This paper first presents a study on the classical BCD adders from which a carry-chain type adder is redesigned to fit within the Xilinx FPGA's platforms. Some new concepts are presented to compute the P and G functions for carry-chain optimization purposes. Several alternative designs are presented. Then, attention is given to FPGA implementations of add/subtract algorithms for 10's complement BCD numbers. Carry-chain type circuits have been designed on 4-input LUTs (Virtex-4, Spartan-3) and 6-input LUTs (Virtex-5) Xilinx FPGA platforms. All designs are presented with the corresponding time performance and area consumption figures. Results have been compared to straight implementations of a decimal ripple-carry adder and an FPGA 2's complement binary adder-subtractor using the dedicated carry logic, both carried out on the same platform. Better time delays have been registered for decimal numbers within the same range of operands., This work is supported by the Universities FASTA, Mar del Plata, Argentina, UNCPBA Tandil, Argentina, UAM ,Madrid, Spain, and URV, Tarragona, Spain; it has been partially granted by the CICYT of Spain under contract TEC2007- 68074-C02-02/MIC.

The work reported in this paper is devoted to the FPGA implementation of decimal dividers. Two types of dividers are described. The first one implements a decimal non-restoring like algorithm and uses ripple-carry operators. For medium size operators it gives a good compromise between cost and latency. The second one implements an SRT-like algorithm and uses carry-free operators. Their latencies are close to that of a binary radix-16 divider with the same range, implemented in the same FPGA.

This paper presents FPGA implementations of add/subtract algorithms for 10´s complement BCD numbers. Carry-chain type circuits have been designed on 6-input LUT´s Xilinx Virtex-5 FPGA technologies. Some new concepts are reviewed to compute the P and G functions for carry-chain optimization purposes. Designs are presented with the corresponding time performances and area consumption figures. Results have been compared with 2´s complement binary implementations carried out on the same platform. Better time delays have been registered for decimal number within same range of operands.