Identification of Defects In Ferritic/Martensitic Steels Induced by Low Dose Irradiation

The ferritic/martensitic steels which are candidates for the first wall of the future fusion reactor are investigated in TEM. While the irradiation doses expected in this reactor are in the range of 100 dpa per year, there is still a lack of knowledge on the nature of the irradiation induced defects for the low doses at which hardening is already occuring. This hardening depends strongly on the type of interaction between the moving dislocations and the defects. The early defects, which start to appear as black dots in TEM, are expected to be either three dimensional clusters of interstitials or vacancies, or dislocation loops. The nature and size of these defects is carefully studied in the F82H steel for doses ranging from about 0.5 dpa to 9 dpa and irradiation temperatures ranging from 40°C to 330°C. For that purpose, various weak beam techniques are explored at the limit of resolution of a TEM used in diffraction mode. Results are presented here for the cases of a 1.7 dpa and a 8.8 dpa irradiation.

A Comparison of the microstructure and tensile behaviour of irradiated fcc and bcc metals

As part of an on-going research program, findings are presented from a comparison of the microstructures and associated tensile properties of fcc and bcc materials after high energy proton irradiation, to fluences between 10−4 and 1 dpa, at 300-320 K. Results for this comparison between Cu, Pd, 304 and 316 stainless steel on one side and Fe and the F82H ferritic-martensitic low activation steel on the other are discussed, showing a strong difference in defect accumulation behaviour between the differing crystal structures. The overall deformation behaviour is similar, with an initial localised deformation taking place in all cases, even though the actual deformation mode itself might be different. Furthermore, a comparison is made with some of the materials that have also been irradiated with fission neutrons, showing no influence of the PKA spectra for these irradiation conditions.

Annealing Kinetics of Single Displacement Cascades in Ni: An Atomic Scale Computer Simulation

In order to describe the long term evolution of the defects produced by a displacement cascade, Molecular dynamics (MD) and Kinetic Monte Carlo (KMC) methods are employed. Using an empirical Ni interatomic potential in MD, the damage resulting from primary knock-on atom (PKA) energies up to 30 keV has been simulated. The annealing kinetics and the fraction of freely migrating defects (FMD) are determined for each single displacement cascade, by a KMC code which is based on a set of parameters extracted mainly from MD simulations. It allows an atomistic study of the evolution of the initial damage over a time scale up to lOOs and the determination of the fraction of the defects that escape the KMC box, compared to those obtained by MD, as function of temperature and PKA energy. It has been found that this fraction depends strongly on the temperature but reaches a saturation value above stage V.

Plasticity and Microstructure of Irradiated Pd

Single crystalline specimens of pure Pd have been irradiated at ambient temperature with 590 MeV protons to doses ranging between 10−4 and 10−1 dpa. Tensile deformation experiments revealed that irradiation induces hardening and embrittlement, while scanning (SEM) and transmission electron microscopy (TEM) observations showed that plastic deformation of specimens irradiated to a dose ≥ 10−2 dpa is strongly localized and yields the creation of slip bands at the macroscopic scale and of defect-free channels at the microscopic level.

Surveillance of norovirus infections in the state of Rio De Janeiro, Brazil 2005-2008

A 4-year (2005-2008) norovirus (NoV) surveillance study was conducted in the state of Rio Janeiro, Brazil, to demonstrate the role of these viruses in outbreaks and sporadic cases of acute gastroenteritis. A cohort of 1,687 fecal samples was obtained from patients with gastroenteritis; 324 were rotavirus-positive. Of the remainder 1,363 rotavirus-negative samples, 1,087 samples were tested for NoV RNA in this study. The study enrolled 267 outpatients from Municipal Public Health Centers and 820 inpatients, whose samples were obtained by active surveillance in Public Hospitals. Fecal samples were tested by reverse transcription (RT) followed by polymerase chain reaction (PCR) using the MON 431-434 set of degenerate primers for NoV GI and GII detection, and there were 35.1% (381/1,087) positive samples for NoV, consisting of 30.2% (248/820) and 49.8% (133/267) from inpatient and outpatient, respectively. Children infected by NoV had significantly more frequent mucus in feces, vomiting and fever. No seasonal pattern in NoV infections was observed in patients admitted to hospital; however, two peaks of NoV infections were observed from ambulatory cases, suggesting that there was an occurrence of outbreaks in those time periods. Molecular characterization revealed GII to be the most prevalent genogroup, totaling 96.3% (104/108) of all sequences analyzed, and GII.4 was the genotype detected most frequently (80.7%), followed by GII.6, 3, 14, 7, and 8. Two GI strains, GI.2 and GI.3, were also observed. The number of outbreaks and sporadic cases described in this study highlights the need to implement diagnosis of NoV in surveillance laboratories.

Assessment of norovirus contamination in environmental samples from Florianópolis City, Southern Brazil

AIMS

To assess norovirus (NoV) contamination in aquatic ecosystems in the city of Florianópolis, in Southern Brazil, to provide epidemiological data that can support actions for environmental contamination control.

METHODS AND RESULTS

An adsorption-elution method, followed by ultrafiltration, was performed to concentrate the viruses. NoV were detected using semi-nested PCR and quantified by real-time PCR. From June 2007 to May 2008, NoV were detected in 23% (22/94) of the samples analysed, including seawater, drinking water, superficial water (creek and brackish lagoon) and treated sewage. The mean viral loads for genogroups (G)I and GII in treated sewage samples were 297 and 440 genomic copies (gc) l(-1) , respectively, whereas creek water samples contained 2603 and 1361 gc l(-1) , respectively. Six samples were sequenced: two samples were GII.4, two were GII.2 and two were GI.3.

CONCLUSIONS

NoV were detected in all water types analysed, demonstrating the widespread contamination of this geographical area with several cocirculating strains belonging to GI and GII.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the environmental spread of NoV in environmental waters and highlights the potential hazard for human health following the consumption of or contact with these waters, which could result in waterborne or foodborne acute gastroenteritis.

Comparative analysis of different secondary optical elements for aspheric primary lenses

The performance of different reflexive and refractive secondaries optimized for the same primary lens is studied by using ray-tracing simulation. Different solutions are approached according to materials and manufacturing processes currently available in the market, which can be potentially cost-effective for concentrator photovoltaic (CPV) modules. They are compared in terms of system optical efficiency and acceptance angle. In addition, irradiance distribution over the cell is also studied.

Environmental dissemination of group A rotavirus: P-type, G-type and subgroup characterization

Rotaviruses A (RV-A) infection is the most common cause of acute diarrheal diseases in infants and the dissemination of these viruses in the environment represents a public health hazard. The present study aims to evaluate reverse transcription-polymerase chain reaction (RT-PCR) based protocols for the detection of RV-A genes in different types of environmental samples. RV-A were concentrated by the adsorption-elution method using negatively charged membranes associated with a Centriprep Concentrator 50. The RV-A VP4, VP7 and VP6 genes were detected using RT-PCR in river water from the Amazon Hydrographic basin (Northern region) and from wastewater in a sewage treatment plant in Rio de Janeiro (Southeast region), Brazil. RV-A were successfully detected in water environmental samples by the methods used. The detection of the VP6 gene by RT-PCR was the most sensitive for detecting RV-A in environmental samples (44.0%), when compared to the detection of the VP4 (33.3%) and VP7 (25.3%) genes. Based on nucleotide sequence and phylogenetic analysis of the partial VP6 gene, 22 environmental samples were determined to be subgroup II (Wa-like). These results indicate that analysis of environmental samples could possibly make a valuable contribution to studies on the epidemiology of RV-A.

Magnetic and structural properties of FeCr alloys

Synergistic synchrotron x-ray absorption experiments using imaging magnetic microspectroscopy, x-ray magnetic circular dichroism, and ab initio calculations on FeCr alloys reveal that the Cr content strongly influences the ferromagnetic microstructure and the Fe magnetic moments. The Cr local structure resolved by extended x-ray absorption fine structure (EXAFS) is also found to be affected by the alloy's composition. Both EXAFS and ab initio calculations show a change in the Cr local atomic structure above 10 at.% Cr content from the distance contraction of the first two coordination shells around the Cr absorbing atom. These results indicate the strong dependence of magnetic and structural properties of these alloys on Cr concentration.

Computer simulation of displacement cascades in nanocrystalline ni

Large-scale molecular dynamics of cascade production of the primary damage state are performed in fcc nanocrystalline Ni of average grain diameters of 5 and 12 nm. Primary knock-on atom kinetic energies of 5-30 keV are simulated. During the thermal spike phase, significant atomic motion towards the surrounding grain boundary structure is observed, characterized by many replacement-collision sequences. Upon resolidification, the excess volume condenses to form vacancy dominated defects with a complex partial dislocation network forming at higher energies.