Common Anabaena and Calothrix cyanobacteria and Klebsormidium green algae are shown to form intracellularly akaganeite β-FeOOH nanorods of well-controlled size and unusual morphology at room ...temperature. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy X-ray energy dispersive spectrometry (SEM-EDS) analyses are used to investigate particle structure, size, and morphology. A mechanism involving iron−siderophore complex formation is proposed and compared with iron biomineralization in magnetotactic bacteria.
A device composed of a polyacrylamide gel thin-film (18
cm high, 5
cm wide and 0.4
mm thick) and a PVC (polyvinyl chloride) film was used as a sediment probe to obtain iron and S(−II) sulfur ...dissolved species' distributions in sediment pore waters. A porous protective membrane was set on top of hydrogel layer. Probes were deployed in May 2003 for 24–48
h in the superficial sediment of Thau lagoon (France), in a shellfish farming area. The polyacrylamide gel layer was used as a DET (Diffusive Equilibration in Thin-films) device for 2D Fe(II) concentration determination, and as the diffusive layer of a DGT-like (Diffusive Gradients in Thin-films) device for sulfur species study. The accumulation layer of the DGT device consisted in a PVC film layer underneath the polyacrylamide layer. Iron determinations were performed by colorimetric methods with Ferrozine and imaging technique. Image acquisitions were performed with a flatbed scanner. Fe(II) concentrations were deducted from densitometry analysis of the magenta zones (ImageJ software). The calibration curve was obtained by densitometry analysis of polyacrylamide gel pieces which were equilibrated in known iron (II) concentration solutions. ΣFe distribution was performed but not quantified. Analysis of gray zones on the PVC layer provided a qualitative distribution of unidentified S(−II) dissolved compounds, related to H
2S zone for which information is obtained by classical methods (peeper and colorimetric measurements). EDX (X-ray energy dispersive spectrometry) and GIXR (Grazing-Incidence X-ray Diffraction) analyses of gray zone of this PVC layer provide evidence for FeS
2 catalyzed precipitation onto this film.
Dissolved Fe(II) was mainly located near the sediment–water interface (SWI), showing a nonhomogeneous layer about 10
mm thick. Small Fe rich domains appeared deeper in the sediment and likely confirm newest paradigms in the field of sediment biogeochemistry. S(−II) species are detected from 3 to 4
cm below the SWI, with a heterogeneous spatial distribution showing a burrow-like structure.
In recent times, there is a renewed and additional interest in thorium because of its interesting benefits. Thorium fuel cycle is an attractive way to produce long term nuclear energy with low ...radiotoxicity waste. In addition, the transition to thorium could be done through the incineration of weapons grade plutonium or civilian plutonium. Th-based fuel cycles have intrinsic proliferation-resistance and thorium is 3–4 times more abundant than uranium. Therefore, thorium fuels can complement uranium fuels and ensure long term sustainability of nuclear power.
In this paper, the main advantages of the use of fuel cycles based on uranium-thorium and plutonium-thorium fuel mixtures are evaluated in a hybrid system to reach the deep burn of the fuel. To reach this goal, the preliminary conceptual design of a hybrid system composed of a critical reactor and two Accelerated Driven Systems, of the type of very high temperature pebble-bed systems, moderated by graphite and cooled by gas, is analyzed.
Uranium-thorium and plutonium-thorium once-through and two stages fuel cycles are evaluated. Several parameters describing fuel behaviour and minor actinide stockpile are compared for the analyzed cycles.
•A conceptual design of a hybrid system composed by a VHTR and two ADSs is analyzed.•U + Th and Pu + Th fuel cycles are evaluated in the proposed hybrid system.•Notable reduction of the Pu isotopes and MA stockpile is obtained in the U + Th cycle.•Considering U233 recycling, the U + Th cycle in the hybrid system is advantageous.•Pu + Th cycle reaches a better performance than the U + Th cycle with the same burnup.
Studies have been demonstrating that smaller particles can lead to unexpected and diverse ecotoxicological effects when compared to those caused by the bulk material. In this study, the chemical ...composition, size and shape, state of dispersion, and surface’s charge, area and physicochemistry of micro (BT MP) and nano barium titanate (BT NP) were determined. Green algae
Chlorella vulgaris
grown in Bold’s Basal (BB) medium or Seine River water (SRW) was used as biological indicator to assess their aquatic toxicology. Responses such as growth inhibition, cell viability, superoxide dismutase (SOD) activity, adenosine-5-triphosphate (ATP) content and photosynthetic activity were evaluated. Tetragonal BT (~170 nm, 3.24 m
2
g
−1
surface area) and cubic BT (~60 nm, 16.60 m
2
g
−1
) particles were negative, poorly dispersed, and readily aggregated. BT has a statistically significant effect on
C. vulgaris
growth since the lower concentration tested (1 ppm), what seems to be mediated by induced oxidative stress caused by the particles (increased SOD activity and decreased photosynthetic efficiency and intracellular ATP content). The toxic effects were more pronounced when the algae was grown in SRW. Size does not seem to be an issue influencing the toxicity in BT particles toxicity since micro- and nano-particles produced significant effects on algae growth.
This study aims to characterize nanoparticles with different compositions and structures as well as seeing their evolutions over time in a natural environment such as Seine river water (Paris, ...France). Face centered cubic (fcc) and hexagonal (hcp) CdS as well as hexagonal (hcp) ZnO nanoparticles were synthesized by the Polyol method. CdS nanoparticles (i) cfc structure: are agglomerated, present 100 nm length with heterogeneous diameter and 10 m2 g(-1) specific surface area (S(g)) from Brunauer Emett and Teller (BET) measurements; (ii) hcp structure: 20 nm and S(g) = 67 m2 g(-1). ZnO hcp nanoparticles presents 50 nm length and 15 nm diameter and S(g) = 54 m2 g(-1). These results are in agreement with X-ray diffraction (XRD), and small angle X-ray scattering (SAXs). After 48 h interaction with Seine river water, cryo-TEM analysis showed that ZnO nanoparticles form spherical agglomerates with 300 nm diameter; CdS nanoparticles (fcc) are agglomerated presenting large diameters (> 500 nm); and CdS nanoparticles (hcp) are not agglomerated and present the same characteristics of the starting material. After 168h of contact with Seine river water, CdS (fcc) presents only 14% of dissolution, CdS (hcp) presents both 60% dissolution and 30% reprecipitation in a cadmium carbonate form and finally almost 90% of ZnO nanoparticles are dissolved.
The purpose of this study is to evaluate in vitro the cervical microleakage of two bonding systems (Group 1: Scotchbond Multi-Purpose—3M; Group 2: Clearfil Mega Bond—Kuraray) in occluso-proximal ...composite restorations of primary molars.
Two occluso-proximal standard cavities preparations (vertical slots) were made in each one of the 11 primary molars. The cavities were filled using adhesive systems (one for each cavity) and hybrid composite (Filtek Z250—3M) by incremental technique. The first increment was inserted horizontally at the cervical wall and light-cured with 100
mW/cm
2 intensity for 60
s (VIP™-Bisco). Other two increments were inserted diagonally on the buccal and lingual portion and each one light-cured with 200
mW/cm
2 intensity for 60
s. The restorations were finished and polished, and then partially sealed and embedded in 0.5% methylene blue solution for 24
h. The specimens were sectioned mesio-distally and the dye penetration was evaluated (score from 0 to 3) under a stereomicroscope.
The statistical analysis (Qui square and Mann–Whitney non-parametric test) revealed no statistical difference (
p=0.193) between the two adhesive systems tested.
Both bonding systems provided small early cervical microleakage in occluso-proximal restorations of primary molars.
Compression of Synthesized Textures Brayner, F.; Walter, M.
2010 23rd SIBGRAPI Conference on Graphics, Patterns and Images,
2010-Aug.
Conference Proceeding
In spite of graphics hardware advancements, graphics memory is still a scarce resource for usual applications. Besides, for most raster-based applications, the available bandwidth is one important ...limiting factor for increasing performance in the system. Texture compression addresses both of these problems. We introduce a new technique for compression of textures synthesized from samples. The compressed texture stores the sample plus encoded data, gathered during synthesis, which enables real-time decompression of large textures. With this scheme we are able to achieve high compression rates. Our solution explores a spectrum of textures where general texture compression schemes achieve less than optimal compression rates. These are usually textures with repeating patterns, regular or near-regular ones, and stochastic ones, the exactly types of textures where texture synthesis algorithms perform well. We also present analytical formulae for our compression scheme that allows an exact computation of compression rates achieved.
The technique of sensibility analysis studies the behavior of the ratio between the variation of output results and the variation of input parameters in general. This study performed in the reactor ...pressurizer, which is a component responsible for controlling of the pressure inside the vessel, has the fundamental importance in designing the security of any concept of an advanced reactor. In fact, for its feature of passive action of the pressurizer (there is no spray), this analysis becomes a necessary step for safety and performance of the plant. The direct method through code MODPRESS, which represents the pressurizer model of the International Reactor Innovative and Secure (IRIS), has required a huge computational effort. To solve this problem, artificial neural networks (ANNs), beyond faster, has been used to replace the MODPRESS in this article. The ANNs do not require linear behavior of the system and can use both, simulated or experimental data for their training and learning. In order this, we adopted a classical non-supervised training ANN for mapping and forecasting of the pressurized using initially simulated data. In next future, we will incorporate the experimental data from the operation of the CRCN-NE reduced-scale test facility mapping. Moreover, based on the results obtained in this study, one can conclude that the artificial neural networks are presented as an alternative to MODPRESS code, and artificial neural networks are actually a great tool to calculate the sensitivity coefficient.
•This article presents a sensibility analysis applied to Innovative Nuclear Reactor Concept.•This study has the fundamental importance in designing of any concept of an advanced compact reactor.•Artificial neural network has been used to simulate IRIS Reactor Pressurizer behavior.
PDF
