174 research outputs found

    Etude par simulations de dynamique des dislocations des effets d'irradiation sur la ferrite à haute température

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    This study is a contribution to the multi-scale modeling of hardening and embrittlement of the vessel steel in Pressurized Water Reactors (PWR) under irradiation conditions. Dislocation Dynamics simulations (DD) were conducted to describe the plasticity of irradiated iron at grain scale. Quantitative information about the pinning strength of radiation-induced loops was extracted and can be transferred at crystal plasticity scale. Elementary interactions between an edge dislocation and different types of loops were first analyzed. A new model of DD was identified and validated, both qualitatively in terms of interaction mechanisms and quantitatively in terms of critical stress, using Molecular Dynamics results available in the literature. The influence of the size of the loops and of the strain rate was particularly studied. Elementary simulations involving a screw dislocation and the same radiation-induced defects were conducted and carefully compared to available MD results, extending the range of validity of our model. Finally, a set of massive simulations involving an edge dislocation and a large number of loops was performed and allowed a first estimation of the obstacle strength for this type of defects (α≈0.26). This value is in a good agreement with previous experimental and numerical studies, and gives us confidence in future work based on this new DD model.Cette Ă©tude s’insĂšre dans le cadre d’une modĂ©lisation multi-Ă©chelles du durcissement et de la fragilisation par irradiation de l’acier de cuve des RĂ©acteurs nuclĂ©aires Ă  Eau PressurisĂ©e (REP). Des simulations en Dynamique des Dislocations (DD) ont Ă©tĂ© menĂ©es pour dĂ©crire la plasticitĂ© du fer pur irradiĂ© Ă  l’échelle du grain et fournir aux Ă©chelles supĂ©rieures des informations quantitatives telles que la force d’épinglage des dislocations par les boucles induites par l’irradiation. Nous avons dĂ©butĂ© notre Ă©tude par l’analyse des interactions Ă©lĂ©mentaires entre une dislocation coin et diffĂ©rents types de boucles. Un nouveau modĂšle de DD a Ă©tĂ© identifiĂ© puis validĂ©, que ce soit d’un point de vue qualitatif (mĂ©canismes d’interaction) ou quantitatif (contrainte critique), en comparant ces rĂ©sultats Ă  ceux obtenus en Dynamique MolĂ©culaire dans la littĂ©rature. L’influence de la taille des boucles et de la vitesse de dĂ©formation a Ă©tĂ© particuliĂšrement Ă©tudiĂ©e.Des simulations Ă©lĂ©mentaires impliquant cette fois-ci une dislocation vis et les mĂȘmes dĂ©fauts d’irradiation ont permis d’étendre le domaine de validitĂ© du modĂšle de DD, en se comparant toujours aux rĂ©sultats de DM de la littĂ©rature. Enfin, un premier jeu de simulations massives entre une dislocation coin et diffĂ©rents types de boucles a permis d’obtenir une premiĂšre estimation de la valeur de la force d’obstacle pour ce type de dĂ©fauts, α≈0,26. Cette valeur est en accord avec diffĂ©rents travaux prĂ©cĂ©dents, expĂ©rimentaux ou numĂ©riques, et permet d’envisager avec confiance de futurs travaux s’appuyant sur ce nouveau modĂšle de DD

    Ultrahigh-sensitivity label-free singlemode- tapered no core-singlemode fiber immunosensor for Listeria monocytogenes detection

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    A challenge for optical fiber biosensor is to achieve ultrahigh sensitivity with narrow full width at half maximum (FWHM) of the spectrum. To address this challenge, an ultrahigh-sensitivity microfiber interferometer fiber ring laser (FRL) biosensor is proposed and investigated for Listeria monocytogenes (L. monocytogenes) detection. The fiber biosensor is composed of a singlemode- tapered no core-singlemode (STNS) fiber configuration, which is functionalized with the anti-L. monocytogenes antibodies. An Erbium Doped Fiber Amplifier is applied to the sensor to excite laser and thus reduce the FWHM of the spectrum, which significantly improved the limit of detection (LoD). The proposed STNS FRL biosensor has excellent reproducibility, specificity and sensitivity for L. monocytogenes. The developed STNS FRL biosensor can directly detect L. monocytogenes cells with LoD as low as 1.0 cell/mL, indicating the capability for detecting single cell of L. monocytogenes. Real lettuce and milk samples have been tested and test result in lettuce and milk samples has deviations within ±30% from that of Phosphate-buffered saline (PBS) for L. monocytogenes concentrations vary from 101 to 103 cells/mL(g). The developed STNS FRL biosensor has ultrahigh sensitivity, good stability, reproducibility, and specificity, which has potential applications in diseases/medical diagnostics

    Polymorphisms in thymidylate synthase gene and susceptibility to breast cancer in a Chinese population: a case-control analysis

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    BACKGROUND: Accumulative evidence suggests that low folate intake is associated with increased risk of breast cancer. Polymorphisms in genes involved in folate metabolism may influence DNA methylation, nucleotide synthesis, and thus individual susceptibility to cancer. Thymidylate synthase (TYMS) is a key enzyme that participates in folate metabolism and catalyzes the conversion of dUMP to dTMP in the process of DNA synthesis. Two potentially functional polymorphisms [a 28-bp tandem repeat in the TYMS 5'-untranslated enhanced region (TSER) and a 6-bp deletion/insertion in the TYMS 3'-untranslated region (TS 3'-UTR)] were suggested to be correlated with alteration of thymidylate synthase expression and associated with cancer risk. METHODS: To test the hypothesis that polymorphisms of the TYMS gene are associated with risk of breast cancer, we genotyped these two polymorphisms in a case-control study of 432 incident cases with invasive breast cancer and 473 cancer-free controls in a Chinese population. RESULTS: We found that the distribution of TS3'-UTR (1494del6) genotype frequencies were significantly different between the cases and controls (P = 0.026). Compared with the TS3'-UTR del6/del6 wild-type genotype, a significantly reduced risk was associated with the ins6/ins6 homozygous variant genotype (adjusted OR = 0.58, 95% CI = 0.35–0.97) but not the del6/ins6 genotype (OR = 1.09, 95% CI = 0.82–1.46). Furthermore, breast cancer risks associated with the TS3'-UTR del6/del6 genotype were more evident in older women, postmenopausal subjects, individuals with a younger age at first-live birth and individuals with an older age at menarche. However, there was no evidence for an association between the TSER polymorphism and breast cancer risks. CONCLUSION: These findings suggest that the TS3'-UTR del6 polymorphism may play a role in the etiology of breast cancer. Further larger population-based studies as well as functional evaluation of the variants are warranted to confirm our findings

    Solar Ring Mission: Building a Panorama of the Sun and Inner-heliosphere

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    Solar Ring (SOR) is a proposed space science mission to monitor and study the Sun and inner heliosphere from a full 360{\deg} perspective in the ecliptic plane. It will deploy three 120{\deg}-separated spacecraft on the 1-AU orbit. The first spacecraft, S1, locates 30{\deg} upstream of the Earth, the second, S2, 90{\deg} downstream, and the third, S3, completes the configuration. This design with necessary science instruments, e.g., the Doppler-velocity and vector magnetic field imager, wide-angle coronagraph, and in-situ instruments, will allow us to establish many unprecedented capabilities: (1) provide simultaneous Doppler-velocity observations of the whole solar surface to understand the deep interior, (2) provide vector magnetograms of the whole photosphere - the inner boundary of the solar atmosphere and heliosphere, (3) provide the information of the whole lifetime evolution of solar featured structures, and (4) provide the whole view of solar transients and space weather in the inner heliosphere. With these capabilities, Solar Ring mission aims to address outstanding questions about the origin of solar cycle, the origin of solar eruptions and the origin of extreme space weather events. The successful accomplishment of the mission will construct a panorama of the Sun and inner-heliosphere, and therefore advance our understanding of the star and the space environment that holds our life.Comment: 41 pages, 6 figures, 1 table, to be published in Advances in Space Researc

    Cerebrospinal fluid oligoclonal bands in Chinese patients with multiple sclerosis: the prevalence and its association with clinical features

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    BackgroundCerebrospinal fluid oligoclonal band (CSF-OCB) is an established biomarker in diagnosing multiple sclerosis (MS), however, there are no nationwide data on CSF-OCB prevalence and its diagnostic performance in Chinese MS patients, especially in the virtue of common standard operation procedure (SOP).MethodsWith a consensus SOP and the same isoelectric focusing system, we conducted a nationwide multi-center study on OCB status in consecutively, and recruited 483 MS patients and 880 non-MS patients, including neuro-inflammatory diseases (NID, n = 595) and non-inflammatory neurological diseases (NIND, n=285). Using a standardized case report form (CRF) to collect the clinical, radiological, immunological, and CSF data, we explored the association of CSF-OCB positivity with patient characters and the diagnostic performance of CSF-OCB in Chinese MS patients. Prospective source data collection, and retrospective data acquisition and statistical data analysis were used.Findings369 (76.4%) MS patients were OCB-positive, while 109 NID patients (18.3%) and 6 NIND patients (2.1%) were OCB-positive, respectively. Time from symptom onset to diagnosis was significantly shorter in OCB-positive than that in OCB-negative MS patients (13.2 vs 23.7 months, P=0.020). The prevalence of CSF-OCB in Chinese MS patients was significantly higher in high-latitude regions (41°-50°N)(P=0.016), and at high altitudes (>1000m)(P=0.025). The diagnostic performance of CSF-OCB differentiating MS from non-MS patients yielded a sensitivity of 76%, a specificity of 87%.InterpretationThe nationwide prevalence of CSF-OCB was 76.4% in Chinese MS patients, and demonstrated a good diagnostic performance in differentiating MS from other CNS diseases. The CSF-OCB prevalence showed a correlation with high latitude and altitude in Chinese MS patients
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