The clustering of carbon atoms into isolated multiplets followed by their ordering into (100)α’ mono-layers leads to the B2 monoclinic multilayer structure called the extended multiplet, during the low temperature aging of Fe-C martensite. The ultimate step of the process is obtained by a lC,2Fe, lC,5Fe, lC,5Fe sequence along the [001]α′. direction giving rise to a 12 lattice parameter periodicity associated with antiphase domains, for matching the lattices of the precipitate and of the matrix. It explains the satellites observed by electron diffraction as well as the (023)α′. habit plane revealed by the diffuse scattering streaks and TEM observations. The carbon free regions between the antiphase domains correspond to the ‘C ’ or ‘к’ phase as determined from the (200)/(020) and (002) martensite peak profile X-ray analysis. The laterin situ transformation to the ordered Fe9C4 ε- or η-carbide, corresponds to an orthorhombic structure with parametersαη =3αε,bη≈ 3αε√3, andcη =cε, ifαε andcε are the initial parameters of the Fe hcp stacking,i.e., αη= 8.46 to 8.49 Å,bη = 14.04 to 14.07 Å, andcη = 4.31 to 4.32 Å for the binary Fe-C alloys. The transformation induces plate-like carbide precipitates with a (035)(gα′). predicted habit plane, which is 4.40 deg away from the approximate (012)ga′. plane observed by TEM. 相似文献
The influence of various sera and proteins on the uptake of a superparamagnetic colloid (magnetic starch microspheres (MSM); particle size, 200 nm; crystal size, 10 nm) by the isolated and perfused rat liver has been studied. It is demonstrated that the capture of MSM is slightly reduced by the addition of rat blood to the protein-free perfusion medium but highly reduced by newborn calf serum (NCS). The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis of proteins adsorbed on the nanoparticles incubated in NCS reveals major coating by albumin and IgG. The addition of bovine IgG to the perfusion fluid reduces the rate of MSM uptake in the same extent that NCS, whereas fetal calf serum that contains only traces of IgG weakly alters the MSM clearance. Finally, complemented and decomplemented NCS exhibit the same influence on the MSM hepatic extraction. It is concluded that although lectins are largely involved in the uptake of MSM administered in the absence of proteins, opsonins receptors are implicated when the perfusion medium contains relevant blood components. 相似文献
Mössbauer spectra of as-quenched and aged martensite (9.5 at. pct C) are analyzed in terms of seven Fe environments, the abundances of which evolve with aging time. Besides the atoms of the matrix (A), Fe atoms which are first nearest neighbors of an isolated interstitial can only be distinguished by their quadrupole shift depending upon whether they lie in a direction perpendicular (Ba) or parallel to thec axis (Bc); classC atoms have two carbon neighbors whileD orE belong to an ordered phase; classF atoms have three carbon neighbors. The carbon multiplet model, based on interstitials residing exclusively in octahedral sites, an elastic stability of theC-C 1/2«111” doublet and a diffusion path for carbon in (001)α' can explain all the features observed: a first step attributed to the clustering of isolated multiplets, and a second step to the coarsening into extended multiplets which leads to the emergence of a new ordered iron carbide (B2 monoclinic with parallelepiped cell of 5.73, 6.74, and 8.60 Å) which transformsin situ into ε-carbide (~Fe9C4) (η carbide as long as it is coherent with the matrix). The positions of carbon atoms in Fe9C4 are specified and a synopsis with related phenomena is drawn. 相似文献
Terrestrial Laser Scanning (TLS) systems have gained increasing popularity in the forestry domain and are today widely used for the automatic measurement of forest inventory attributes. Nevertheless, to the best of our knowledge the problem of tree species recognition from TLS data has received very little attention from the scientific community. It is in this context that we present a novel Computer-Aided Tree Species Identification method based on 3D bark texture analysis. The novelty of our approach resides in the following three key points: (1) 3D salient regions extraction using a new morphological segmentation method that we have called Burst Wind Segmentation, (2) the extraction and pre-annotation of a collection of typical 3D bark patterns, known as scars, from each of the tree species. The pre-annotated scars are stored in a dictionary that we have called ScarBook and they are used as a reference for the comparison of the 3D salient segmented regions, (3) a wide variety of advanced shape, saliency, curvature and roughness features are extracted from the 3D salient segmented regions. To study the performance of our method, an experiment has been carried out on a dataset composed of 969 patches which correspond to 30 cm long segments of the trunk at breast height. Six species among the most dominant species in European forests have been tested with patches of different diameter at breast height values so as to study the identification accuracy with respect to age. The results obtained are very encouraging and promising and they confirm the possibility of identifying tree species using TLS data. 相似文献
The photosensitivity of a ZrTiO4 sample (33 m2/g) prepared by a sol-gel method has been assessed in the presence of O2 by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures
< ca. 13.3 Pa, the steady-state photoconductance of ZrTiO4 was unaffected by
, which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, varied as the reciprocal of
, which was consistent with the fact that the electronic equilibrium was then governed by O2 + e– O
2–
. OIE over ZrTiO4 occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO4 sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples. 相似文献
Silica and alumina supported tantalum and tungsten hydrides were tested in alkane metathesis, for comparison of their catalytic
properties. In propane metathesis [W]–H/Al2O3 proves to be twice more efficient than the usual [Ta]–H/SiO2 catalyst which is still better than [Ta]–H/Al2O3 and [W]–H/SiO2. Tungsten based catalysts lead to a narrower distribution in the products selectivity and to a higher amount of linear products
than [Ta]–H/SiO2. [W]–H/Al2O3 is also a better catalyst than [Ta]–H/SiO2 for butane metathesis but is less efficient with ethane. Whereas the results in the case of propane or butane can involve
the higher initial activity and a lower deactivation of the tungsten catalyst, in the case of ethane, mechanistic or kinetic
aspects can be envisaged in particular concerning the difficulty to dehydrogenate ethane into ethylene. 相似文献
The oxidation of liquid cyclohexane by O2 over UV-illuminated TiO2 at room temperature has been studied in a static slurry reactor. From the effects of the mass of catalyst, the temperature, the radiant flux, the concentration of C6H12 (using acetonitrile as a solvent), it is concluded that the reaction is photocatalytic. Using mainly the 365 nm-ray of a mercury-lamp, an initial quantum yield of 0.1 is found for pure cyclohexane and radiant fluxes < ca.5mWcm–2 (6×1015 photons s–1 cm–2). A high selectivity to cyclohexanone is observed (83%), the other products being cyclohexanol (5%) and CO2 (12%). The low amount of cyclohexanol is explained by the higher rate of oxidation of this alcohol compared to that of cyclohexane. Smaller oxidation rates are observed when TiO2 is loaded with 0.5 to 10 wt%Pt and the cyclohexanone/cyclohexanol ratio decreases to ca. 4. Finally, the C6H12 oxidation has been employed as a test reaction to confirm the detrimental effect of the doping with several tri or pentavalent cations upon the photocatalytic activity of TiO2. 相似文献
In order to better asses the influence of organic matter on the bioavailability of hydrophobic organic contaminants, the effect of algae and POM of bacterial origin on the bioaccumulation of benzo[a]pyrene in Daphnia magna was evaluated. The bioaccumulation was monitored with increasing concentrations of particulate organic matter (POM) and dissolved organic matter (DOM). In all experiments, the presence of POM greatly reduced the bioaccumulation of benzo[a]pyrene. The reduction was more pronounced in the presence of algae, for which we observed a 99%-reduction effect in the presence of 6 x10 (5) cell/mL (equivalent to 5.3 mg C/L). The bioaccumulation of benzo[a]pyrene was decreased by 49% by organic matter of bacterial origin at 4.7 mg C/L. Assuming that benzo[a]pyrene was partitioned between water, DOM and POM and supposing that D. magna accumulated free benzo[a]pyrene via respiration and POM-bond benzo[a]pyrene via ingestion, bioaccumulation data allowed to estimate the dietary uptake rate of benzo[a]pyrene as well as partitioning coefficients K(POC) and K(DOC). Despite the ingestion of contaminated particles, we could not observe any dietary uptake of benzo[a]pyrene in daphnids. We verified, as usually supposed, that the bioaccumulation of benzo[a]pyrene to D. magna occurs mainly via direct contact. Very high partitioning coefficients (log K(POC) between 5.2 and 6.2) were estimated. This study pointed out the great influence of biogenic organic matter on the fate and the bioavailability of benzo[a]pyrene in aquatic ecosystems. 相似文献
Over the years, different approaches to identify temporal and spatial conflicts in hypermedia applications has been proposed. Most of them are based on formal verification techniques and impose to the designers to follow a formal model or language to ensure application’s functional correctness. Furthermore, the error diagnose is hard to be interpreted by a non-specialist in this domain. In this paper, we present an approach which supports formal verification for documents written in markup languages. We proposed a method and built a verification toolchain that helps designers to verify time and spatial constraints in hypermedia applications. The input language is the designer language. Its translation towards the input of toolchain is automatic and transparent for the application designer. The errors scenarios provided by the verification tool are presented in a timeline way, easily understandable by the designer. The method and toolchain support different markup languages translated in the same intermediary language in order to facilitate the use of different verification tools in the same environment.