Lead-vanadate sorbents for iodine trapping and their conversion into an iodoapatite-based conditioning matrix

New lead-vanadate based sorbents were synthesized with the aim to entrap and confine gaseous iodine in off-gas streams coming from reprocessing facilities of spent nuclear fuel. Their synthesis relies on the shaping of a lead-vanadate, lead sulfide and alginic acid mix as millimetric beads. These beads were calcined between 220°C and 500°C to remove organic alginic compounds template. However, according to the calcination temperature, lead sulfide could be partially oxidized, limiting iodine loading capacity. A compromise temperature between 290°C and 350°C was found to remove most of the alginic acid template and avoiding lead sulfide oxidation. These sorbents were tested for iodine trapping in static conditions at 60°C. They performed well with a sorption capacity up to 155 mg.g^-1 by forming PbI₂. Furthermore, these iodine-loaded sorbents could be easily converted into an iodine-containing lead-vanadate apatite matrix by spark plasma sintering. A dense sample was produced for a sintering temperature of 500°C under 70 MPa. Such a material could be suitable for radioactive iodine conditioning in deep geological disposal. Finally, lead-vanadate sorbents could provide an easy way to entrap and confine radioactive iodine from off-gas streams into a durable material within a few steps.

Controlled imbibition in a porous medium from a soft wet material (poultice)

We provide a first approach of the mechanisms of liquid imbibition in a porous medium from a wet paste in contact with this substrate. Through Magnetic Resonance Imaging (MRI) we first show that, in contrast with intuition, the liquid can invade the substrate even if it has a larger pore size than the paste, which induces a lower capillary pressure in the substrate. This phenomenon happens because the paste can easily shrink. We then show that the imbibition stops when the capillary pressure in the substrate balances the stress needed to further contract the paste. The dynamics of the process then mainly results from the competition of these two effects plus the pressure gradient associated with the liquid flow through the paste. This in particular shows that the liquid penetration in a porous medium, from a poultice in contact with this medium, may be controlled by adjusting the poultice characteristics.

Convective drying of a porous medium with a paste cover

The convective drying of a composite system made of a porous medium covered with a paste is a situation often encountered with soils, roads, building and cultural heritage materials. Here we discuss the basic mechanisms at work during the drying of a model composite system made of a homogeneous paste covering a simple granular packing. We start by reviewing the rather well-known case of the convective drying of a simple granular packing (i.e. without paste cover), which serves as a reference for physical interpretations. We show that a simple model assuming homogeneous desaturation followed by a progressive development of a dry front from the sample free surface is in agreement with observations of the internal liquid distribution variations in time. In particular, this model is able to reproduce the saturation vs. time curves of various simple granular systems, which supports our understanding of physical mechanisms at work. Then we show the detailed characteristics of drying of initially saturated model composite systems (with kaolin or cellulose paste) with the help of MRI measurements providing the liquid distribution in the sample at different times during the process up to the very last stages of drying. It appears that the granular medium is unaffected (i.e. remains saturated) during an initial period during which the paste shrinks and finally forms a sufficiently rigid porous structure which will not any more shrink later on. Then the drying process is governed by capillary effects down to very low saturation. Over a wide range of saturations both media desaturate homogeneously (within each medium) at different rates which depend on the specific porous structure of the media, so as to maintain capillary equilibrium throughout the sample. During these different stages the drying rate of the whole system remains constant. For sufficiently low saturation in the paste a dry front can develop, both in the paste and the porous medium below, and the drying rate now decreases. These results show that in a drying composite system liquid extraction can occur more or less simultaneously in the different parts of the material up to the very last stages of drying. The corresponding evolution of the distributions of liquid in the different parts of the sample also provides key information for the prediction of ion or particle transport and accumulation in the different parts of a composite system.

Phonon localization in heat conduction

Nondiffusive phonon thermal transport, extensively observed in nanostructures, has largely been attributed to classical size effects, ignoring the wave nature of phonons. We report localization behavior in phonon heat conduction due to multiple scattering and interference events of broadband phonons, by measuring the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interfaces. With an increasing number of superlattice periods, the measured thermal conductivities near room temperature increased and eventually saturated, indicating a transition from ballistic to diffusive transport. In contrast, at cryogenic temperatures the thermal conductivities first increased but then decreased, signaling phonon wave localization, as supported by atomistic Greenșs function simulations. The discovery of phonon localization suggests a new path forward for engineering phonon thermal transport.

Purification of a single-photon nonlinearity

Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes. In practice, however, the finite quantum dot lifetime and cavity-quantum dot coupling lead to reduced fidelity. Here we show that, with a nearly polarization degenerate microcavity in the weak coupling regime, polarization pre- and postselection can be used to restore high fidelity. The two orthogonally polarized transmission amplitudes interfere at the output polarizer; for special polarization angles, which depend only on the device cooperativity, this enables cancellation of light that did not interact with the quantum dot. With this, we can transform incident coherent light into a stream of strongly correlated photons with a second-order correlation value up to 40, larger than previous experimental results, even in the strong-coupling regime. This purification technique might also be useful to improve the fidelity of quantum dot based logic gates.

Single-photon optical nonlinearity is possible using an optical cavity to create strong coupling between a cavity mode and a two-level quantum system. Here, the authors demonstrate it is also possible in the weak-coupling regime by using quantum interference in a polarization-degenerate cavity.

Ursodeoxycholic acid or clofibrate in the treatment of non-alcohol-induced steatohepatitis: a pilot study

Non-alcohol-induced steatohepatitis (NASH) is characterized by elevated serum aminotransferase activities with hepatic steatosis, inflammation, and occasionally fibrosis that may progress to cirrhosis. No established treatment exists for this potentially serious disorder. Our aim was to conduct a pilot study to evaluate the safety and estimate the efficacy of ursodeoxycholic acid (UDCA) and clofibrate in the treatment of NASH. Forty patients were diagnosed with NASH based on a compatible liver biopsy with other causes of liver disease, including alcohol abuse, excluded by history, serum tests, and use of ultrasound. Twenty-four patients received 13 to 15 mg/kg/d of UDCA for 12 months. Sixteen patients with hypertriglyceridemia were placed on clofibrate, 2 g/day for 12 months. Twenty-five women and 15 men entered the study. Six of 40 patients (15%) withdrew because of side effects. Four additional patients were withdrawn because of noncompliance; one of them later required liver transplantation. In the UDCA group, the decreases in mean serum levels of alkaline phosphatase, alanine transaminase (ALT), and gamma-glutamyl transpeptidase (GGT) as well as histological grade of steatosis were significant. Among the patients treated with clofibrate, no change from baseline was found in mean ALT, aspartate transaminase (AST), GGT, bilirubin, triglycerides, and cholesterol, or in histological grade of steatosis, inflammation, or fibrosis after 12 months of treatment as compared with entry. Alkaline phosphatase activities decreased significantly from baseline. Despite the known lipid-lowering effects of clofibrate, it did not appear to be of clinical benefit in the treatment of NASH in this 1-year pilot study. However, treatment of NASH with UDCA for 12 months resulted in significant improvement in alkaline phosphatase, ALT, GGT, and hepatic steatosis. The possible benefit of UDCA therapy should be further investigated in the context of a randomized, controlled trial.