Direct Solution of the Inverse Stochastic Problem through Elementary Markov State Disaggregation

Existing methods to find the eigenvalue spectrum (or a reasonable approximation to it) of square matrices can be extended to Stochastic Matrices (SM). The matter is more delicate for the Inverse Eigenvalue Problem (IEP), which consists in the reconstruction of a matrix from a given eigenvalue spectrum. In this work, we present a simple method to solve a real-valued IEP for SM by constructing step-by-step the solution matrix through an elementary Markov state disaggregation method named state splitting, and based on a matrix operator. After showing some results on how the splitting operator influences the steady-state distribution of the Markov chain associated with the SM, we demonstrate that the state splitting operator has a fundamental property: when applied to a SM A of size n-by-n, it yields a SM of size (n+1)-by-(n+1), whose eigenvalue spectrum is equal to that of A, plus an additional eigenvalue belonging to a bounded interval. We use a constructive method to prove that for any spectrum made of real and positive eigenvalues, one can build up an infinite number of SM sharing this spectrum. Finally, we present a new sufficient condition to test if a given set of real values can be the spectrum of a SM constructed by the proposed method

Operational Dust Prediction

Over the last few years, numerical prediction of dust aerosol concentration has become prominent at several research and operational weather centres due to growing interest from diverse stakeholders, such as solar energy plant managers, health professionals, aviation and military authorities and policymakers. Dust prediction in numerical weather prediction-type models faces a number of challenges owing to the complexity of the system. At the centre of the problem is the vast range of scales required to fully account for all of the physical processes related to dust. Another limiting factor is the paucity of suitable dust observations available for model, evaluation and assimilation. This chapter discusses in detail numerical prediction of dust with examples from systems that are currently providing dust forecasts in near real-time or are part of international efforts to establish daily provision of dust forecasts based on multi-model ensembles. The various models are introduced and described along with an overview on the importance of dust prediction activities and a historical perspective. Assimilation and evaluation aspects in dust prediction are also discussed

Contribution of Saharan dust on radionuclides aerosol activity levels in Europe ? The 21-22 february 2004 case study

International audienceIn February 2004, a spectacular dust event was observed in the south of France. Associated with huge particulate matter deposition, unusual 137Cs concentrations were found in samples. Using the transport model CHIMERE-DUST, we first show that these dust aerosols came from North Africa. More precisely, the question is whether this sudden increase of measured 137Cs concentrations was due to a huge amount of dust over a large region (with an usual radionuclide content) or due to an import of more concentrated air masses over a limited area. This question is connected to the open debate about the contribution of 137Cs concentrations in Europe from "Gerboise" sites, where former French nuclear tests in the 1960s were performed. With the model in scenario mode, this study attempts to track down 137Cs concentrations recorded in the south of France. To quantify the origin and percentage of dust originating from North Africa to the south of France, three simulations are performed: (1) with the complete dust emissions inventory of Africa, (2) with only emissions in the eastern Maghreb, and (3) only considering the Gerboise sites. It is showed that the majority (80%) of the dust was coming from eastern Maghreb, but only 0.7% of the African emissions were from Gerboise, leading to 1-5% of the concentrations recorded in the south of France for the day of the peak

Alkali Uranyl Borates: Bond Length, Equatorial Coordination and 5f States

Three uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states have been probed using High Energy Resolved Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) at the uranium M4-edge and L3-edge respectively. We demonstrate that the 5f splitting is increased by the decrease of the uranyl U-Oax distance, which in turn correlates with an increased bond covalency. This is correlated to the equatorial coordination change of the uranium. The role of the alkalis as charge compensating the axial oxygen of the uranyl is discussed

Alkali uranyl borates: bond length, equatorial coordination and 5f states

International audienceThree uranyl borates, UO2B2O4, LiUO2BO3 and NaUO2BO3, have been prepared by solid state syntheses. The influence of the crystallographic structure on the splitting of the empty 5f and 6d states have been probed using High Energy Resolved Fluorescence Detected X-ray Absorption Spectroscopy (HERFD-XAS) at the uranium M4-edge and L3-edge respectively. We demonstrate that the 5f splitting is increased by the decrease of the uranyl U-Oax distance, which in turn correlates with an increased bond covalency. This is correlated to the equatorial coordination change of the uranium. The role of the alkalis as charge compensating the axial oxygen of the uranyl is discussed

Black carbon health impacts in the Indo-Gangetic plain: Exposures, risks, and mitigation

A large discrepancy between simulated and observed black carbon (BC) surface concentrations over the densely populated Indo-Gangetic plain (IGP) has so far limited our ability to assess the magnitude of BC health impacts in terms of population exposure, morbidity, and mortality. We evaluate these impacts using an integrated modeling framework, including successfully predicted BC concentrations. Population exposure to BC is notable, with more than 60 million people identified as living in hotspots of BC concentration (wintertime mean, >20 μg m −3 ). The attributable fraction of the total cardiovascular disease mortality (CVM) burden to BC exposures is 62% for the megacity. The semiurban area comprised about 49% of the total BC-attributable CVM burden over the IGP. More than 400,000 lives can potentially be saved from CVM annually by implementing prioritized emission reduction from the combustion of domestic biofuel in the semiurban area, diesel oil in transportation, and coal in thermal power plant and brick kiln industries in megacities

Revisiting the optical interferometry observations of HR 4049

International audienceAims: We present high spatial resolution observations in the mid-infrared of the dusty core of the binary system HR 4049. Methods: We used the mid-infrared interferometer MIDI/VLTI with 40 m projected baselines. These observations provided two spectrally dispersed visibility curves at a spatial resolution of ~10 mas. Acquisition images and spectra are in addition obtained with a single telescope spatial resolution of ~250 mas. Results: The MIDI spectra show features due to emission lines (7.9, 8.6 and 11.3 micron) attributed to PAHs. The comparison between ISO and MIDI spectra and dispersed visibility curves allows us to investigate the budget of continuum and PAH emission from distant regions to the inner regions of the compact dusty structure. The flux balance between these different PAH features is different to the one seen in the large beam ISO spectrum, suggesting different contributions at varying locations from the central star for the different PAH species. These features are over-resolved (i.e. their correlated flux is close to zero), placing the bulk of their line forming region at least at 50-70 mas from the central star. The continuum extension is estimated to range between 23 and 27 mas using a Gaussian model, and is very close to the K-band sizes measured with VINCI/VLTI, implying that the emitting regions of the near and mid-IR are similar. The visibilities from the two different baselines do not allow us to constrain the shape of the continuum emitting region but noticeable differences between them suggest that the N band dusty environment is flattened in a direction that coincides with the one suggested by previous polarimetric observations

Size and structure of hexanuclear plutonium oxo-hydroxo clusters in aqueous solution from synchrotron analysis

International audienceThe size and shape of a water-soluble hexanuclear plutonium cluster wereprobed by combining synchrotron small-angle X-ray scattering (SAXS) andextended X-ray absorption fine structure (EXAFS). A specific setup couplingboth techniques and dedicated to radioactive samples on the MARS beamlineendstation at Synchrotron SOLEIL is described. The plutonium hexanuclearcores are well stabilized by the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaceticacid ligands and this allows a good evaluation of the setup to probe thevery small plutonium core. The results show that, in spite of the constrainedconditions required to avoid any risk of sample dispersion, the flux and thesample environment are optimized to obtain a very good signal-to-noise ratio,allowing the detection of small plutonium aggregates in an aqueous phase. Thestructure of the well defined hexanuclear cluster has been confirmed by EXAFSmeasurements in solution and correlated with SAXS data processing andmodelling. An iterative comparison of classical fit models (Guinier or sphereform factor) with the experimental results allowed a better interpretation ofthe SAXS signal that will be relevant for future work under environmentallyrelevant conditions

First observation of [Pu6(OH)4O4 ]12+ cluster during the hydrolytic formation of PuO2 nanoparticles using H/D kinetic isotope effect

International audienceNew insights are provided about the formation mechanism of PuO2 nanoparticles (NPs) by investigating an unprecedented kinetic isotope effect observed during their hydrolytic synthesis in H2O or D2O media