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International audience; This study highlights the trace metal and metalloid (TMM) accumulation in Rosmarinus officinalis L. and its chemical responses when exposed to high levels of contamination. R. officinalis individuals growing along a gradient of mixed TMM soil pollution, resulting from past industrial activities, were analysed. Several plant secondary metabolites, known to be involved in plant tolerance to TMM or as a plant health indicator, were investigated. The levels of thiol compounds and phytochelatin precursors (cysteine and glutathione) in the shoots were measured in the laboratory, while a portable non-destructive instrument was used to determine the level of phenolic compounds and chlorophylls directly on site. The level of Pb, As, Sb and Zn contaminations within the soil and plants was also determined.The results highlighted a decrease of TMM translocation with increases of soil contamination. The concentration of TMM in the shoots followed the Mitscherlich equation and reached a plateau at 0.41, 7.9, 0.37, 51.3 mg kg−1 for As, Pb, Sb and Zn, respectively. In the shoots, the levels of thiols and phenols were correlated to concentrations of TMM. Glutathione seems to be the main thiol compounds involved in the tolerance to As, Pb and Sb. Phenols indices, using non-destructive measurements, may be considered as an easy way to establish a proxy to estimate the TMM contamination level of the R. officinalis shoots. The study highlights metabolic processes that contribute to the high potential of R. officinalis for phytostabilisation of TMM in contaminated areas in the Mediterranean.

International audience; Astragalus tragacantha is a protected plant species in France that grows even in the trace metal and metalloid (TMM) polluted soils of the Calanques National Park (PNCal). Soils are mainly contaminated by lead, copper, zinc and arsenic. An ex situ experiment was conducted, firstly to determine the molecular responses and root traits involved in the TMM tolerance of this plant species by growing individuals in a soil from the surroundings of one of the brownfields of the PNCal, known as l’Escalette, where this plant species grows spontaneously. Secondly, in order to determine the plasticity of these responses, seeds were collected from three different populations, one at l’Escalette (polluted site), one from the Frioul archipelago (non-polluted, insular site) and one from La Seyne (non-polluted, littoral site). The results of this study confirmed the capacity of A. tragacantha to germinate and grow in TMM contaminated soils. Only moderate significant variations in chlorophyll and flavonol indices, proline content and antioxidant activities were detected between polluted and control soil conditions for all populations. The main driver for A. tragacantha TMM tolerance seemed to be its ability to be associated with root symbionts i.e. arbuscular mycorrhizal fungi and dark septate endophytes, corresponding to a nutrient-uptake strategy trait. This work provides support for the challenge of A. tragacantha conservation along the littoral of the PNCal, because increasing the number of A. tragacantha individuals would both increase vegetation cover of the polluted soils to reduce the pollution transfer and reinforce the populations of this species.

International audience; The mechanical properties of materials usually depend on the size of the considered object. Silicon, for instance, undergoes between the macroscopic and nanometer scales, a brittle-to-ductile transition at room temperature. Although essential for the constantly developing Si-based nanotechnologies, the origin of this remarkable behaviour change remains undetermined for several years. The observation of the mechanisms responsible for plastic deformation in nano-objects is indeed highly challenging at the microscopic scale. One needs controlling the deformation while identifying induced individual plastic events at the smallest scale during the first stages of plasticity. This work describes nano-compression experiments on 100 nm-diameter Si nanopillars followed by post-mortem analysis of the deformed specimens through SEM and atomic resolution TEM imaging. The observed plastic deformation disrupts the usual description of low-temperature undissociated-dislocations-mediated plasticity and is comforted by molecular dynamics calculations. These results shed a new light on the transition between ductile and brittle regimes in silicon by introducing the missing link between plasticity and fracture.

International audience; Perfect dislocations have been found controlling the plasticity of silicon at high stress. Such evidence has been obtained from a number of experiments and atomistic computations. This is also consistent with the larger Peierls stresses encountered by partial dislocations as compared to perfect dislocations at low temperatures. However at very high stress and in the same temperature range partial dislocation have been reported to occur in a few experiments as well as in some atomistic computations. The aim of this paper is to discuss in what situations partial dislocations can be nucleated, what could be the nuclei responsible for their nucleation and the conditions where partial dislocations could control the plastic deformation in the place of perfect dislocations.

Physical properties of nano-objects differ from what they are in bulk materials when the size decreases down to the nanometre scale. This behavioural change, named size effect, also applies to mechanical properties and has been evidenced in various materials. For instance, at low temperature, bulk silicon is known to be a brittle material while silicon nano-objects exhibit a ductile behavior. Although mechanical properties of silicon have been intensively studied over the last decades, the origin of this remarkable brittle-to-ductile transition at small scales remains, however, undetermined. In this article, a study of the plastic behaviour of nano-pillars is reported. The main results obtained from the combination of numerical calculations and experimental compression tests followed by atomically-resolved transmission electron microscopy imaging are described. We discuss the possibility for perfect dislocations to dissociate at low temperature and the underrated role of shuffle partial dislocations in plastic deformation of silicon. The formation of unexpected extended defects in the {115} planes with increasing plastic strain, also appears as a key-factor leading to the transition between ductile and brittle regimes at small scales.

International audience; The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why. Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for in situ analysis of phytoliths in leaves via X-ray imaging. PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%. Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.

Different core structures have been evidenced in silicon which control, respectively, low and high temperature deformation. Indeed perfect shuffle dislocations have been found to build deformation microstructures in the temperature range and stress where silicon is usually brittle. In contrast, the plastic regime is controlled by dissociated glide set dislocations. This paper aims at relating the plastic properties of silicon to the core structure of dislocations and in particular to the existence and the properties of these two core structures.

Silicon micropillars obtained by FIB from Floating Zone silicon single crystal have been deformed in situ in a SEM between room temperature and 400 °C. Pillars with axis were studied in order to promote single slip deformation. Mechanical data as a function of pillar diameter and surface deformation microstructures observed by SEM are reported. Yield stresses as a function of temperature are compared with those resulting from high-pressure tests (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The aim of this study was to investigate the properties of cultivated urban soils and metal concentrations in these soils and in roots and leaves of the crops Amaranthus cruentus (amaranth) and Hibiscus sabdariffa(roselle). The soil physicochemical properties showed a poor fertility rate of cultivated soils. The metal concentrations in soils were in the range of concentrations for uncontaminated agricultural soils. The ranges of concentrations of metals were as follows: Aluminium (Al), 239-1222 mg/kg; cadmium (Cd), Al > Mn > Zn > Cu >Pb; in roots, Al > Fe > Zn > Mn > Cu > Pb. Al and Fe were weakly bioaccumulated but their concentrations were high. Cu and Mn were more accumulated in leaves than roots for amaranth and roselle. The leaves of amaranth were found to accumulate soil Cu and Zn more efficiently than other tissues of both vegetables. The translocation factor was in the order: Mn > Cu > Fe > Zn > Al, and when this value was compared between amaranth and roselle, it was observed to be higher in amaranth than in roselle. The concentrations of the essential elements Cu and Mn in roselle, and Cu, Fe, Mn and Zn in amaranth indicate that these leafy vegetable are a good nutrient sources. Key words: Soil, edible vegetables, metals, bioconcentration factor (BCF), translocation factor (TF).

4H-SiC intrinsic homoepitaxied single crystals have been nano indented at room temperature using a spherical indentor and the related deformation microstructures have been analyzed by Transmission Electron Microscopy. Dislocations are lying in the basal plane but have been found to be perfect, in contrast with observations made at higher temperature. Although such a change in deformation mechanism has been observed in other semiconductors such as Silicon and Indium Antimonide, it was unexpected in a very low stacking fault material such as SiC.

Indium antimonide (InSb) has been plastically deformed over a wide temperature range, from 400 down to −176 °C (see the companion paper: Kedjar B, Thilly L, Demenet JL, Rabier J. Acta Mater 2009) and transmission electron microscopy was used to characterize the deformation microstructures. In the ductile regime, i.e. T > T tr1 ≈ 150 °C, the crystal deforms via the nucleation and motion of perfect dislocations belonging to the glide set. In the brittle domain, i.e. for T T tr1 ≈ 150 °C, two regimes are observed: for T tr2 ≈ 20 °C T T tr1 ≈ 150 °C, the crystal deformation takes place via the nucleation and glide of dissociated perfect dislocations or only leading partials, while for T T tr2 ≈ 20 °C, the crystal deformation proceeds via the nucleation and motion of perfect dislocations belonging to the shuffle set. In view of these observations, the brittle-to-ductile transition (at T tr1 ) is confirmed to correspond to a change in the dislocation nature in the glide set, from partial-mediated plasticity at low temperature to perfect-mediated plasticity at high temperature. Another transition is observed at T tr2 and corresponds to the glide-to-shuffle transition which is observed experimentally for the first time in a III–V compound semiconductor.

An analysis of the morphology of the extended defects revealed behind dislocation in the slip plane of silicon is presented. These extended defects show an electrical activity contradictorily to dislocations themselves; this is confirmed by Electron Induced Surface Potential (EISP) measurements. It is shown, that the generation of these extended defects is a common phenomenon for diamond lattice materials. The defects generation which has to be elucidated is considered to be relevant to a dynamical dislocation core structure during the plastic deformation of semiconductor materials with covalent lattice. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The possibility to oxygenate the YBa2Cu3O7−δ(Y123) structure to 7−δ ≈ 6.9 atoms (which ensures the highest temperature of transition into the superconductive state of this compound) at high temperature (800°C) and relatively low pressure (16 MPa) of oxygen has been first shown. This fact differs from the generally accepted notions of the equilibrium in the given system. It has been found that the MT-YBCO oxygenation at enhanced pressures and high temperatures decreases the oxygenation time and the amount of cracks and increases the twin density in the material, which positively affects the critical current density and mechanical characteristics of the ceramics. The experiments have shown that twins are largely responsible for high density of the critical currents j c and irreversibility fields in the MT-YBCO ceramics. In the case of high dislocation density (1012 cm−2) and low twin density (0–1 μm−1) in the Y123 structure, the critical current turned out to be an order of magnitude lower than in the case of high twin density (22 μm−1) and absence of dislocations and stacking faults. The density of twins and microcracks (parallel to the ab plane) in the structure of the YBa2Cu3O7−δ phase has been found to depend on the size of the Y2BaCuO5 inclusions and the pattern of their distribution, which in turn is defined by the initial materials. A process has been developed of the oxygenation of the thin-wall (cellular) MT-YBCO ceramics under the conditions of the controllable oxygen pressure from 0.5 kPa to 16 MPa and temperatures from 900 to 800°C. The process allows one to attain record high j c values and double the trapped magnetic field as compared to both the bulk MT-YBCO ceramics oxygenated under the same conditions and thin-wall MT-YBCO ceramics oxygenated at atmospheric pressure and optimal temperature.

The relevant pinning centers of Abrikosov vortices in MgB$_{2}$–based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgB$_{x}$ (x>4) phases. The high critical current densities, j$_{c}$, of 10$^{6}$ and 10$^{3}$A/cm$^{2}$ at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB$_{2}$ structure in small amounts (MgB$_{1.5}$O$_{0.5}$), which is supported by Auger studies and calculations of the DOS and the binding energy. The j$_{c}$ of melt textured YBa$_{2}$Cu$_{3}$O$_{7-δ }$ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y$_{2}$BaCuO$_{5}$ (Y211) inclusions in Y123. At 77 K j$_{c}$=8⋅10$^{4}$ A/cm$^{2}$ in self-field and j$_{c}$=10$^{3}$ A/cm$^{2}$ at 10 Т were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per μm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB$_{2}$ to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.

The recent observation of perfect dislocations at high stress and low temperature in silicon [J. Rabier, P. Cordier, J. L. Demenet, and H. Garem, Mater. Sci. Eng. A 309/310, 74 (2001)] in accordance with the calculations of Duesbery and Joos [M. S. Duesbery and B. Joos, Philos. Mag. A 74, 253 (1996)] has solved the apparent paradox regarding the nature of mobile dislocations in silicon under usual deformation conditions. However, although several experiments and calculations are consistent with those perfect dislocations being located in the shuffle set, little is known about the actual core structure of those dislocations which lie along unusual Peierls valleys: (112)/30°, /41°. This paper aims to review and discuss recent results related to high-stress plasticity and dislocation core structure in silicon.

Mineral Physics Institute, Stony Brooks University, Stony Brooks, NY 11794-2100, USA Received 17 September 2006, revised 18 December 2006, accepted 18 December 2006 Published online 24 May 2007 PACS 61.66.Bi, 61.72.Bb, 61.72.Lk, 62.20.-e, 62.50.+p Mechanical data have been obtained on silicon single crystal under hydrostatic pressure between room temperature and 450 °C. This temperature domain corresponds to the regime where perfect dislocations control plastic deformation. This was achieved using a D-DIA apparatus in the synchrotron beam of NSLS. Stress strain curves were deduced from X Ray diffraction and sample imaging under 5 GPa and a strain rate of 2.5 10

International audience; Atractylis serratuloides is an abundant native spiny species that grows in the surroundings of superphosphate factories in Tunisia. This plant species is adapted to arid environments and tolerates a high level of fluoride pollution in soils. The aim of this study was to better understand the physiological mechanisms of fluoride tolerance of this species, comparing the fluoride-contaminated sites of Gabes and Skhira with the reference site of Smara. Results demonstrated the involvement of leaf element and phytometabolite balances in the in situ response of A. serrulatoides to fluoride. Calcium, sulphur and magnesium were differently distributed between the sites of Gabes and Smara in all plant organs. No specific tissue fluorine accumulation in root, stem and leaf, even in the most contaminated site at Gabes, was detected by EDAX mapping. Lower anthocyan and flavonol levels but enhanced nitrogen balance index were found in A. serrulatoides leaves from Gabes compared to the two other sites. A. serratuloides appeared as a fluoride excluder and its tolerance involved calcium interactions with fluoride. Moreover, an occurrence of dark septate endophytes and arbuscular mycorhizal fungi in root systems of A. serratuloides was reported for the first time, and these symbioses were present but low at all sites. We suggest the use of this plant species for fluoride-polluted soil stabilization.

Background, Aim and Scope Most studies of sewage sludge disposal effects on plants have focused on high metal loadings. Less attention has been paid to plant responses to trace metal loadings below the recommended limit values. Materials and Methods: Here, a lysimetric experiment was conducted to assess the uptake, distribution and binding of trace metals by metal-induced, sulfhydryl-rich peptides (phytochelatins) in colza (Brassica napus, v. Jaguar) grown on a clayey, silty soil amended with a sewage sludge compost containing trace metal contents far below the recommended limit values established by French legislation. Chemical fractionation of unamended and sludge-amended soils was performed using a sequential extraction technique. Results: Copper concentrations in plant tissues were not affected by compost disposal. Its application at a single rate equivalent to 30 t/ha stimulated the growth of plants. Lead was not detectable in the plant material (< 1 mg g-1 dry wt.). Plants grown on the amended soil accumulated significantly more zinc than control plants. These phytochelatin complexes detected in leaves had a lower molecular weight than those extracted from roots. Those extracted from roots were composed of one type of phytochelatins (PCs) such as in leaves or a mixture of glutathione, PC2 and PC4. In comparison with control plants, sewage sludge compost application caused the synthesis of longer chain PCs in roots and in leaves. Furthermore, in comparison with control roots, glutathione and phytochelatin mixtures of higher molecular weight were detected in roots produced on the amended soil, whereas no significant increase in \total\ Cu and Zn content was observed in these organs after sludge application. Discussion: Compost application induces a significant increase in the proportion of the most labile forms of zinc and especially its pH 4.7 acid-soluble forms and, as a consequence, a higher accumulation of zinc in plants. Effects of copper are limited due to its strong affinity for humic substances and lead does not seem to be transported in any organ of plants. The presence of phytochelatins, even in plants grown on the unamended soil, proved the ability of colza to synthesize them in the presence of zinc and copper. Conclusions: These primary results seem to prove, on one hand, ability of colza (Brassica napus, v. Jaguar) to synthesize phytochelatins as well as in roots, in leaves and, on the other hand, the sensitivity of the PC induction as suggested by their identification in plants grown on the control soil. Synthesis of longer chain PCs in roots and in leaves, and formation of glutathione and phytochelatin mixtures in roots, are plant responses to sewage sludge compost application. Recommendations and Perspectives: Phytochelatin analysis is thus supposedly able to be one of the bioindicators that may be used as an ecotoxicological risk assessment of wastes. Due to its ability to synthesize phytochelatins, colza could be chosen as a plant test. Phytochelatin analysis could also be limited to roots (more sensitive than leaves). However, further experiments are needed. Quantitative analysis of phytochelatins had not been carried out due to insufficient amounts of pure phytochelatin standards, that had allow us to better study relationships between trace metal amounts to vegetal response.

Numerous original alkaloids are present in tubers of Arisarum vulgare Targ. a species belonging to the Araceae family known in Morocco for its toxicity. Some previous works deal with the activity of these natural compounds as R-irniine. As the enantioselective total synthesis of irniine has been realised, the R- and S-forms were obtained and this last one could be tested. Thus, a study of the cytotoxicity and the electrophysiological activity of S-irniine was carried out on human MRC-5 fibroblasts. A cytotoxic effect of S-irniine at 40 microg/mL was detected on MRC-5 fibroblasts. An electrophysiological study was also carried out on the MRC-5 cells by using the patch-clamp technique and no effect of this compound at this concentration on the outward potassium current of MRC-5 fibroblasts was observed. Thus, this study showed, as it was for R-irniine, that the cytotoxicity of S-irniine was not explained by an effect on the potassium currents.

Intergrowths, stacking faults and dislocations have been investigated by transmission electron microscopy in (Hg, Re)Ba2Ca2Cu3O8+δ and HgBa2CaCu2O6+δ bulk superconductors. The stacking fault vectors and the Burgers vectors of partial edge dislocations associated with the nucleation or the annihilation of [Ca–CuO2] bilayers in the unit cells of both compounds are derived by different methods. We discuss the influence of uniaxial stresses on intergrowth propagation and also mechanisms yielding strain relaxation around intergrowths. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations in silicon are nucleated under high stresses as perfect ones in the shuffle set. It is shown that the same nucleation mechanism operates in hexagonal 4H-polytype SiC but, in contrast to silicon, perfect-shuffle configurations are unstable and transform by cross-slip into glide set dislocations.

The essential oil of the aerial parts of Triumfetta rhomboidea was analysed by GC and GC-MS and assayed for its antibacterial and antifungal activities. The main constituents identified were trans-β-caryophyllene (22.4%),kessane (14%) and caryophyllene oxide (13%). The antimicrobial tests showed a mild activity against Escherichia coli and Enterococcus hirae.

The article [1] describes specific features of positron trapping in silicon plastically deformed at room temperature. The results are related to the dislocation core structure and the inhomogeneous deformation. The picture shows the probability density function of a positron localized in a vacancy in silicon. The calculation was performed with the superimposed-atom model. The degree of localization and consequently the defect-related positron lifetime vary for different open-volume defects, such as vacancies, voids, and dislocations. The first author, Hartmut S. Leipner, is CEO of the Center of Materials Science of the University Halle–Wittenberg. His research activities are focused on the characterization of extended defects in semiconductors.

To evaluate phytoremediation potentialities by metal accumulation in tolerant plants, trials are carried out using in vitro cultures. Organic compounds influence on metal accumulation is studied with metals supplemented media. The tested compounds on zinc and lead absorption by Brassica juncea, are chelating agents (EDTA, citric acid) and soluble organic fractions of compost. EDTA seems to enhance the transfer of lead in plant but it is the opposite in the case of zinc. Citric acid stimulates root absorption for both zinc and lead. For the aqueous extracts of compost, variable effects are obtained according to the origin of compost (green wastes and food wastes). In all tested conditions of cultures, zinc is mainly exported towards shoot while lead is stored in root.

We have examined the various possible configurations for an undissociated screw dislocation in group IV materials (Ge, Si, 3C-SiC, diamond) by means of semi-empirical atomistic calculations. A complete structural characterization and a determination of the relative stability are performed. We found that, in contrast to the case for Ge and Si, a geometry with the presence of sp 2 atoms in th ec ore is the most stable structure for 3C-SiC and diamond. This yields a stable screw dislocation configuration i nt he ‘shuffle’ set for Si and Ge, and in th e‘ glide’ set for 3C-SiC and diamond.

The evolution of the microstructure of melt-textured YBa2Cu3O7−Y2BaCuO5 (123–211) composites in O2 at 100 bar and 600°C has been characterized by transmission electron microscopy (TEM). Under these conditions the 123 phase is brought out of its stability field, within a region of the phase diagram where the weakly superconducting YBa2Cu4O8 (124) polytype is stable against a CuO + 123 mixture. The nucleation of 1/6 (301) stacking faults is not restricted to the 211–123 interfaces, as found in samples processed at 350 and 450°C but is strongly enhanced in the bulk matrix. Simultaneously, matrix decomposition into a Ba-Cu oxide, 211 and presumably CuO occurs at 211 interfaces, which is accompanied by an exaggerated growth of the stacking faults. After 12 h at PO2 = 100 bar and 600°C, the whole volume imaged by TEM appears to be covered by large stacking faults overlapping along the c axis. It is found that, when the 211 interfaces become saturated by stacking faults, new stacking faults have to nucl...

International audience; Elements uptake, histological distributions as well as mycorrhizal and physiological statuses of Atriplex halimus were determined on trace metal and metalloid polluted soils from the surrounding spray zones of a former lead smelter in the South-East coast of Marseille (France). Analyses of heavy metal and arsenic distribution in soil and plant organs showed that A. halimus tolerance is largely due to exclusion mechanisms. No specific heavy metal concentration in leaf or root tissues was observed. However, accumulation of salts (NaCl, KCl, Mg and Ca salts) on leaf bladders and peripheral tissues of roots was observed and may compete with metal element absorption. Occurrence of endomycorrhizal structures was detected in roots and may contribute to lower element transfer from root into the aerial parts of plants. The non-destructive measurements of leaf epidermal chlorophylls, flavonols and phenols showed a healthy state of the A. halimus population on the metal and metalloid polluted sites. Considering the low metal bioaccumulation and translocation factors along with a reduced metal stress diagnosis, A. halimus appeared as a good candidate for phytostabilization of trace metals and metalloids and notably arsenic in contaminated soils of the Mediterranean spray zone. However, its invasive potential has to be determined before an intensive in situ use.

Dislocation configurations resulting from high stress low temperature deformation in silicon are found non-dissociated and elongated along different Peierls valleys as compared to usual results from the literature. Experiments on pre-deformed samples are reported and discussed in the context of a possible transition in the core structure at high stresses between dissociated glide and perfect shuffle configurations.

Dislocation microstructures induced by room-temperature microhardness tests have been investigated in silicon nitride. Surface analysis of the residual indent by atomic force microscopy reveals intragranular slip bands and demonstrates that room-temperature plastic deformation involves dislocation motion as well as cross-slip events. Cross-slip events have been found to occur between {1010} prismatic planes. Transmission electron microscopy shows that dislocations have a Burgers vector b = [0001] and are located along the screw direction. Based on these observations, specific dislocation core configurations are discussed.

Macroscopic plastic deformation of silicon single crystals has been achieved at RT and 150°C under a confining pressure of 5 GPa in a multi-anvil apparatus. TEM observations of a sample deformed at 150°C show that the deformation microstructure is built with dislocations with 1 2 a 1 1 0 Burgers vector in (1 1 1) planes which are undissociated. They appear as mainly aligned along the screw orientation and 〈1 1 2〉 orientations at 30° from the Burgers vector. Those features are analysed in the light of perfect dislocation generation in the shuffle set.

Intragranular plasticity induced by indentation is studied in β Silicon Nitride between room temperature and 700°C by Transmission Electron Microscopy (TEM). It is shown that all the dislocations resulting unambiguously from plastic deformation have a Burgers vector b = [0001] and a dominant screw character. This can account for a large Peierls stress along the [0001] direction and a larger mobility of edge dislocation segments as compared to screw ones. Dislocations bowing out of screw direction are found to glide in [1010] prismatic planes. Cross-slip is evidenced from the dislocation microstructure observations. It is found to occur between {1010} prismatic planes at 20°C whereas {1120} is found to be a new deviation plane at 700°C. Those observations are discussed in relation with the possible core structure of [0001] screw dislocations.

The deformation microstructures of Si single crystals have been studied by transmission electron microscopy (TEM) in the temperature range of deformation where “dislocation trails” are evidenced. The main features of the deformation microstructures are characterized by dislocations dipoles and their debris. These microscopic observations are discussed in relation with the mesoscopic properties of dislocation trails as well as the possible transformation between two different core structures of dislocations in silicon.

The problem of transient primary or secondary metabolism remaining a persisting problem in plant cell cultures is discussed. Since secondary metabolites occurred mainly in differentiated tissues, an effort was made to mimic the cell-to-cell contact of multicellular organisms. Sucrose metabolism and indoleglucosinolate production from immobilized cells of Armoracia rusticanawere investigated. Immobilization acted by reducing the assimilation of the hexoses released into the culture medium. Although sucrose hydrolysis occurred prior to uptake, the decrease of acid invertase activity in immobilized cells was accompanied by an increased yield (2–3-fold) of the intracellular sucrose. Glucosinolates accumulated as indolic forms only during the stationary stage of cell growth. Their amount in immobilized cells may be increased 2-fold compared to the control cultures. On the other hand intracellular sucrose concentration declined whilst the cleavage activity of sucrose synthase increased simultaneously with production of indole-3-methyl- and 4-hydroxy-indole-3-methyl-glucosinolates. Thus, the role of cell immobilization in the biosynthesis of indoleglucosinolates is discussed.

Partial dislocation nucleation and multiplication in III–V semiconductor compounds are usually ascribed to the difference in mobility between α and β partials. These differences in mobility increase when the temperature decreases, so that the contribution of twinning to the deformation mechanisms becomes important for high stresses and low temperatures. Starting from transmission electron microscopic observations of plastically deformed InSb under high stresses and hydrostatic pressure at room temperature, showing the multiplication of α as well as β partial dislocations, a model for the partial dislocation multiplication is proposed. This model does not rely on the difference in α and β partial dislocation mobilities but on the formation of Lomer-Cottrell sessile dislocations issued from dislocation dipoles. Les phenomenes de nucleation et de multiplication de dislocations partielles dans les semi-conducteurs III–V sont habituellement attribues a la difference de mobilite entre les partielles α et β. Cette difference de mobilite augmente lorsque la temperature diminue, de sorte que la contribution du maclage dans les mecanismes de deformation devient importante pour les fortes contraintes et les basses temperatures. A partir d'observations en microscopie electronique en transmission de InSb deforme a temperature ambiante sous fortes contraintes et sous pression hydrostatique, mettant en evidence la multiplication de dislocations partielles α et β, nous proposons un modele de multiplication des dislocations partielles. Ce modele ne fait pas appel a la difference de mobilite entre les dislocations partielles α et β, mais il fait intervenir la formation de dislocations sessiles de Lomer-Cottrell a partir de dipoles de dislocations.

From observations of extended dislocation nodes in β silicon nitride, possible stacking fault structures in the basal plane of this compound have been investigated. It has been found that stacking fault structure is locally analogous to α silicon nitride. A phase transformation α to β or β to α can also be achieved by cooperative shear of partial dislocations with Burgers vectors.

This paper considers the plasticity of InSn under high stress, at low temperatures. The studies cover the plasticity of InSh in the temperature range between 20 and 200°C and under stress which is applied by superimposing uniaxial pressure on a confining hydrostatic pressure. The analysis of the deformed substructures by transmission electron microscopy revealed the existence of different deformation mechanisms at different temperatures, and consequently. stress regimes At temperatures T ≥ 50°C the dominant deformation mechanism is the glide of perfect dislocations, while at room temperature the deformation can be attributed to partial dislocations. At lower temperatures. screw dislocalions become dominant, a fact that demonstrates the small mobility of these dislocations. Extended stacking faults introduced by the dissociation of β-type segments demonstrate the higher mobility of the 90 β partial dislocations conspired to the mobility of the 30 β ones. In contrast, the absence or extended dissociation for the 60 α-type dislocations suggests that the 90 α and the 30 α partial dislocations have the sortie mobility An additional interesting issue arises from the observations showing a small difference in mobility between the 30 α and the 30 β partial dislocations The significance of these observations is discussed and the results are correlated to similar observations in other III-V compounds.

Dislocations substructures in aluminium nitride (AIN) ceramics have been studied by transmission electron microscopy for samples plastically deformed under a high stress in the temperature range 20–800°C. The activation of basal slip ⅓ 〈1120〉(0001) as well as of the first-kind prismatic slip ⅓ 〈1120〉{1100} have been observed. In the basal plane, dislocations configurations attest to the role of the Peierls forces along the screw orientation. It is easier for a dislocation to cross-slip in the prismatic plane than to lie in the basal plane along an orientation other than the screw direction. In the basal plane as well as in the prismatic plane, no dissociation of dislocations has been resolved under weak-beam imaging conditions. Cross-slip is favoured by numerous pinning points on screw dislocations, giving rise to dipole dragging. From 20 to 500°C, AIN deformation proceeds by dislocation glide in the basal and the prismatic planes and frequent corss-slip between these two planes. At higher temper...

Observations of dislocation substructures have shown that the basal and first-kind prismatic planes are easily activated in plastically deformed aluminium nitride between room temperature and 800°C as shown in the companion paper, part I. In this paper, several analyses are performed to determine the ability of dislocations to glide in one plane relative to others. According to the closest-packed criterion, the first-kind prismatic plane appears to be favoured. Line energy calculations under anisotropic elasticity do not allow one to conclude the preferential activation of one of the glide planes. The crystallographic structures of basal and first-kind prismatic planes, core structures of dislocations and dissociation reactions are investigated and stacking-fault configurations in prismatic planes are proposed.

Some preliminary results of dislocation analysis and associated glide systems in as-grown as well as in superplastically deformed β silicon nitride are presented. Transmission electron microscopy observations using the weak-beam technique, are reported. [0 0 0 1] {1 0 1 0} and 1/3〈1 2 1 0〉 {1 0 1 1} glide systems have been characterized. In the basal plane, a superposition of two hexagonal networks built with screw dipoles has been observed. Both a sequence extended node–constricted node and partial dislocations have been identified in these networks which clearly evinces dislocation dissociation in β-silicon nitride following the reaction 1/3〈2 1 1 0〉→1/3 〈1 0 1 0〉+1/3 〈1 1 0 0〉.

International audience; This study aimed at estimating exposition risks to wild rosemary used as herbs in the contaminated area of the former smelting factory of L'Escalette (South of Marseille, France). Metals and metalloids i.e. Pb, As, Sb, Zn, and Cu concentrations were analyzed in soils and in rosemary aerial parts (stems and leaves) on two sites: one heavily contaminated and the other far away from the pollution source, considered as reference, The metal and metalloid transfer into water during the brewing process of herbal tea was also determined. A mixed contamination by the above-cited contaminants was demonstrated in soils of the factory site, with average concentrations of 9253, 1127, 309, 2698 and 32 mg/kg for Pb, As, Sb, Zn and Cu, respectively. However, metals and metalloids' transfer in rosemary aerial parts was limited, as bioaccumulation factors were under 1. Thus, Pb, As and Cu concentrations in leaves were below international regulation limits concerning ingestion of medicinal herbs (no regulation values available for Sb and Zn). This study highlighted that, if contaminated rosemary leaves were ingested, health risks may be limited since acceptable daily intake (ADI) for Pb, As, Sb and Cu (no ADI value available for Zn) will only be reached if very high quantities are consumed. Furthermore, we aimed to establish if this mixed contamination could alter rosemary's essential oil quality, and thereby the compositions of essential oils obtained from individuals on the heavily contaminated soil were compared to those obtained from the reference population. An increased biosynthesis of antioxidant compounds was favored in essential oils from rosemary individuals growing in contaminated site. Although the health risk of a long-term exposition of low level of the mixed contamination by rosemary ingestion is not easy to elucidate, the use of rosemary essential oils from contaminated site appears as safe. (C) 2013 Elsevier B.V. All rights reserved.

Discrepancies exist in the literature about the formation and atomic structure of intercalated CuO layers in YBa2Cu3O7−δ, the so-called ⅙[031] stacking faults. In this paper the fault structures are re-analysed depending OR whether the additional CuO layer has expanded into a tetragonal matrix or an orthorhombic matrix. Of particular interest are the interaction features of such a fault with mirror twin boundaries.

International audience; This study was aimed at assessing the impact of urban agriculture on physicochemical properties of the soil and the metal uptake by some leafy vegetables cultivated in urban soils of Libreville, Gabon. Cultivated and uncultivated topsoil and vegetable samples were collected from two urban garden sites, and analyzed. The results showed that there was strong acidification and a decrease in the concentrations of nutrients and metals in soils due of agricultural practices. The metal transfer to plants was important, with the exception of iron. The non-essential metals cadmium and lead were not detectable in the plant tissues. Amaranth accumulated more metals than other vegetables. Amaranth and Roselle were vegetables that preferentially concentrated metals in their leaves and could, therefore, be used for metal supplementation in the food chain.

A Comment on the Letter by V. L. R. Jacques et al., Phys. Rev. Lett. 106, 065502 (2011). The authors of the Letter offer a Reply.

This chapter is devoted to the structure and properties of dislocations obtained at high stress in silicon, which have been shown to have different core structures from the ones observed at low stress and high temperature. TEM observations of high-stress deformation microstructures revealing the existence of a specific type of dislocations, which exhibit a non-dissociated core and are expected to lie in the shuffle set, are reported together with relevant atomistic computations. The results of experiments and computations are confronted in order to obtain a comprehensive view of the high-stress deformation regime. The transition between the two deformation regimes is also discussed.

Grevillea exul var exul (Proteaceae), a tree species native to serpentine soils in New Caledonia, is a reported manganese accumulator. Since the metal tolerance of this species remains unknown, its growth and metal accumulation were studied for seven heavy metals under controlled conditions. Brassica juncea, a popular species for metal phytoremediation, was used as a reference. G. exul seedlings were more tolerant to Cr, Zn, Ni, and Cu than B. juncea. There were no differences in Hg, and Cd tolerance between both species. B. juncea seedlings concentrated more Cd, Hg, and Cr in their shoot than G. exul seedlings, while Ni, Zn, and Mn levels were similar for both species. Comparison then focused on tolerance at toxic doses of Ni and Mn using older individuals of both species. No growth inhibition for G. exul plants was observed, whereas the growth of B. juncea was significantly inhibited at the higher metal concentrations. Shoot Mn and Ni concentrations were again lower in G. exul plants as compared to B. juncea, suggesting a mechanism of partial Ni and Mn exclusion in G. exul. In a subsequent study, 1-year-old G. exul plants favored Ni accumulation in roots while Mn accumulated preferentially in shoots.

The possibility to saturate MT-YBCO with oxygen up to about 7 oxygen atoms per one unit cell of YBa2Cu3O7-δ at 800 °C under controllable oxygen pressure (from 0.5 kPa to 16 MPa) has been established. On condition that the material heating to high temperatures occurs in the nitrogen atmosphere with gradual substitution of it for oxygen and further increase of the oxygen pressure, the saturation of MT-YBCO by oxygen takes place practically without the macrocrack formation and results in the decrease of microcrack density parallel to ab-planes, that leads to the increase of critical current density and mechanical characteristics. It has been shown that in the case of a higher twin density, the material demonstrates higher critical currents, jc. Bulk and thin-walled MT-YBCO oxygenated at high controllable pressure and 800 °C contained a large amount of twins (4-11 and 20-22 μm-1, respectively) and were practically free from dislocations and stacking faults, but demonstrated very high values of jc at 77 K: jc higher than 10 kA/cm2 was observed in the fields up to 5T in ab-planes and up to 2 T in the direction of the c-axis. Specially detwinned MT-YBCO containing a large amount of dislocations (up to 1012 cm-2) demonstrated critical currents lower by about one order of magnitude, which gives us ground to conclude that the presence of twins is extremely important for attaining high critical currents in MT-YBCO. The high-pressure oxygenation allows one to essentially reduce the duration of the oxygenation process as compared to that under atmospheric pressure.

The aim of the study was the sintering of aluminium nitride at rather low temperatures (≤1650°C). Various sintering aids were studied, in particular AlSi- and Ca-based oxides. CaCO3 and 3CaO-3SiO2-Al2O3 are the most efficient additives, because quantities as low as 0·5 wt% are enough to yield sintered AlN substrates with no open porosity. TEM observations showed that low concentrations of CaCO3 or CaSiO3 lead to location of the secondary phases at the triple points, whereas high concentrations lead to wetting of the grains. Thermal diffusivity of sintered materials was determined by a laser flash method. The highest conductivity (70 W m−1 K−1) is obtained with CaCO3 additions. These additions promote liquid formation, which cleans the surface of the AlN grains from oxygen and thereby prevents oxygen from entering the AlN lattice. The CaAl2O4 compound exhibits a lower thermal conductivity than the CaAl4O7 and Ca3Al10O18 compounds. The Ca2SiAl2O7 compound and the 27R AlN polytype have a strong negative influence on the thermal conductivity of sintered materials.

Grevillea exul var. exul, an endemic serpentinic Proteaceae of New Caledonia, was chosen to study the spatial distribution of Ni because this species supports strong content of metals, which can allow important absorptions thus detectable by microanalysis. Fine transversal sections of axenic G. exul var. exul plants grown during 15 days on nickel sulphate medium were examined by EDXS microanalysis. It showed that in Ni treated plants, Ni was concentrated mostly in the phloem compared to the xylem and the epidermis, either in roots or in the basal part of the stems and was mostly in the epidermis in the upper part of the stems and not detectable in the leaves. This metal took the place of P and K in the treated plants whereas the localization of these macroelements was quite uniform in control sections. We assume that a mechanism of phloem loading is implicated to restrict Ni accumulation in G. exul var. exul.

International audience; The stability of the perfect screw dislocation in silicon has been investigated using both classical potentials and first-principles calculations. Although a recent study by Koizumi et al . stated that the stable screw dislocation was located in both the 'shuffle' and the 'glide' sets of {111} planes, it is shown that this result depends on the classical potential used, and that the most stable configuration belongs to the 'shuffle' set only, in the centre of one hexagon. We also investigated the stability of an sp 2 hybridization in the core of the dislocation, obtained for one metastable configuration in the 'glide' set. The core structures are characterized in several ways, with a description of the three-dimensional structure, differential displacement maps and derivatives of the disregistry.