Atomic Structure of a 36.8 (210) Tilt Grain Boundary in TiO2

An understanding of the atomic structure at internal interfaces is of crucial importance for the electronic and structural properties of most advanced materials. Here, we present a detailed study of the atomic structure at a [001] tilt grain boundary of σ5(210) in Tio₂ (rutile). Z-contrast imaging is used to obtain a 2-D atomic map of the cation positions at the interface. Details of the charge state of cations and atomic structure around anion sites are then provided using electron energy loss spectroscopy. In particular, the spectroscopic data for oxygen is interpreted using multiple scattering theory to give 3-D structural information. These combined techniques allow a unique grain boundary structure to be defined.     

Constitutive activation of the TSH receptor by spontaneous mutations affecting the N-terminal extracellular domain

Activating mutations of the TSH receptor gene have been found in toxic adenomas and hereditary toxic thyroid hyperplasia. Up to now, all mutations have been located in the serpentine portion of the receptor. We now describe two additional mutations affecting Ser-281 (Ser-281-Thr and Ser-281-Asn) in the ectodomain of the receptor. After transfection in COS cells, both mutants displayed increased constitutive activity for cAMP generation despite expression at a lower level than the wild type. The mutants were responsive to TSH. The present results are compatible with a model in which the activity of the unliganded receptor is kept at a low level by an inhibitory interaction between the N-terminal domain and the serpentine portion of the receptor.     

在车身开发中应用CIMS技术

ＣＩＭ是企业面对市场竞争的发展战略，目前还没有一个普遍接受的解决方案。在东风汽车公司ＣＩＭＳ应用工程中采用了分步实施的策略，首先在车身开发一民覆盖件模具设计与制造中应用ＣＡＤ／ＣＡＰＰ／ＣＡＭ集成系统。广西分析了应用集成系统的必要性。讨论了系统集成方案，系统的结构和物理实现。     

Modification of phytohormone response by a peptide encoded by ENOD40 of legumes and a nonlegume

The gene ENOD40 is expressed during early stages of legume nodule development. A homolog was isolated from tobacco, which, as does ENOD40 from legumes, encodes an oligopeptide of about 10 amino acids. In tobacco protoplasts, these peptides change the response to auxin at concentrations as low as 10(-12) to 10(-16)M. The peptides encoded by ENOD40 appear to act as plant growth regulators.     

The abilities of a Staphylococcus epidermidis wild-type strain and its slime-negative mutant to induce endocarditis in rabbits are comparable

The abilities of a parent and mutant pair of Staphylococcus epidermidis strains, the slime-producing parent RP62A and its slime-negative mutant, to establish endocarditis in a rabbit model of aortic valve endocarditis and to accumulate and adhere to surfaces in vitro were compared. Vegetation titer and infection rate depended on the presence or absence of a catheter (P = 0.020) and on inoculum size (P < 0.001) but not on the infecting strain. The ability of the parent strain vis-à-vis its mutant to accumulate in vitro on surfaces as demonstrated in a slime test did not correlate with any enhancement in the development of endocarditis in the rabbit model. In vitro initial adherence rates were identical. Both isolates accumulated to the same reduced extent in vitro in the presence of serum, albumin, or gelatin. Adhesion was equally promoted by addition of fibronectin. These data suggest that the in vitro phenomenon of accumulation described as slime production in the absence of serum may not be an important virulence determinant in vivo.     

Morphology and composition of second phase particles in zircaloy-2

Intermetallic particles in Zircaloy-2 are analyzed for morphology (shape, size, distribution, etc.) and for crystal structure by transmission electron microscopy. Chemical composition is semi-quantitatively evaluated in a scanning transmission electron microscope. Several types of morphologically distinct particles are identified by shape, size, and substructure. All particles are found to be either nickel-bearing or chromium-bearing. Clusters containing several particles are often observed. The nickel-bearing particles are identified as a tetragonal Zr₂Ni-type phase where iron partially substitutes for some Ni giving an approximate composition of Zr₂Ni_0.4Fe_0.6. The chromium-bearing particles are found to be a hexagonal ZrCr₂-type phase where iron partially substitutes for some Cr giving an approximate composition of ZrCr_1.1Fe_0.9. Essentially all the iron is contained in these two kinds of particles, and no iron-zirconium particles are found.     

A transmission electron microscopy study of the mechanisms of strengthening in heat-treated Co-Cr-Mo-C alloys

Microstructures produced in the Co-Cr-Mo-C alloy H.S.21 were observed by transmission electron microscopy in cast specimens following solutionizing at 1230°C and aging at 650°C and in low-carbon wrought specimens following solutionizing and aging at 650°C and 750°C. In all cases, aging was found to promote the formation of fcc stacking faults and to cause an initial martensitic transformation from the fcc phase to a heavily faulted hep structure. Precipitate formation was observed in hcp areas of the cast material after 20 h at 650°C and in hcp areas of wrought material after 20 h at 750°C. Prolonged aging at 750°C produced a transformation in the hcp structure of wrought specimens, with a relatively fault-free structure replacing the heavily faulted martensitic form. Interruption of fcc slip by both fcc stacking faults and bands of hcp phase was found to be the principal strengthening mechanism activated by aging. Precipitate formation in the hcp plays an increasingly significant role as aging time is increased. This microstructural information is used to explain the observed tensile properties of these alloys after the heat treatments mentioned.     

A formulation development strategy for multivariate kinetic responses

The purpose of this paper was to evaluate a multivariate strategy for handling time-dependent kinetic data during formulation development. Dissolution profiles were evaluated by the Weibull equation, multiple linear regression (MLR), principal component analysis (PCA), alone and in combination. In addition a soft independent modeling of class analogy (SIMCA) was performed. Employing a typical kinetic model for solid formulations (here Weibull) showed difficulties with the model adaptation, resulting in increased model standard deviation and thereby failure in identifying significant variables. In general, the selection of a kinetic model is crucial for finding the significant formulation variables. Describing the dissolution profile based on MLR models of individual time points described the dissolution rates as a function of formulation variables with good precision. Establishing prediction models made it easy to evaluate effects on the entire dissolution profile. The use of PCA/MLR (PCR) reduced the influence of noise from single measurements in a kinetic profile, since they develop statistical parameters representing the profile without being dependent on a physicochemically-modeled profile. The use of PCA reduced the eight time-point variables to two latent variables (principal components), simplifying the classification of formulations and new samples as well as avoiding unwanted effects of model non-linearities between the factors and responses (model error). The group membership of new samples was demonstrated by SIMCA.     

Spinodal decomposition during aging of Fe-Ni-C martensites

A collaborative study of the aging of virgin Fe-Ni-C martensites has combined the techniques of transmission electron microscopy (TEM), atom-probe field-ion microscopy (APFIM), and electrical resistometry. Aging at room temperature leads to the rapid development of a finescale structural modulation along 〈203 〉 lattice directions. Atom-probe analysis of Fe-15Ni-lC martensite reveals the formation of carbon-rich regions whose carbon concentration increases with time and approaches 11 at. pct C on prolonged aging. The early stage kinetics of this process are composition-dependent and are consistent with carbon-diffusion control. The morphological features of the aging reaction are explained by elastic strain-energy considerations. In accordance with previous thermodynamic models, it is concluded that virgin Fe-C martensites are unstable and that phase separation occurs by a spinodal mechanism. The martensitic substructure does not appear to exert any substantial influence on this decomposition behavior. Due to tetragonality of the martensites in this paper, it should be noted that the third Miller index (representing the c-axis) is not interchangeable with the other two indices when obtaining equivalent variants. K.A. Taylor, formerly with the Massachusetts Institute of Technology L. Chang, formerly with the University of Oxford G.B. Olson, formerly with the Massachusetts Institute of Technology