Search results for "homogeneity"
showing 10 items of 111 documents
Relating morphology to nanoscale mechanical properties: from crystalline to mesomorphic iPP
2005
Abstract A nanoindentation technique using an atomic force microscope (AFM) was applied to characterize the mechanical behaviour of several isotactic polypropylene (iPP) samples. The samples were solidified from the melt with a CCT (continuous cooling transformation) procedure spanning a wide range of cooling rates thanks to a fast quenching apparatus developed by the authors. The influence of instrumental parameters on the nanoscale mechanical properties (indentation depth, Young's modulus) shows that for modulus determination one has to rely on simpler methods of force curve analysis based on trace curve alone. Structure homogeneity up to the scale of macroscopic samples used to evaluate …
Formation of Optical Gradient in Chemical Solution-Derived PbZr[sub 0.52]Ti[sub 0.48]O[sub 3] Thin Films: Spectroscopic Ellipsometry Investigation
2009
Investigation using a variable angle spectroscopic ellipsometer revealed the influence of sample preparation conditions on sol-gel PbZr 0.52 Ti 0.48 O 3 (PZT 52/48) thin-film homogeneity that allows identification and further optimization of thin-film performance. Separate crystallization of the layers determined the optical gradient appearance, irrespective of the chemical solvents used in this work. A more refined analysis showed that a refractive index gradient was apparent in the samples in which lattice parameters strongly changed with thickness. For these films, energy-dispersive X-ray spectroscopy analysis showed significant variation in Pb and Zr. Additionally, complex dielectric fu…
Temperature control during Spark Plasma Sintering and application to up-scaling and complex shaping
2013
International audience; The determination and the homogeneity of the sample temperature during consolidation of powders by Spark Plasma Sintering (SPS) are addressed. Densifications were carried out in three different facilities differing by their constructors and their size. A structural transformation activated in a TiAl alloy was used as a marker of the sample temperature and finite element modeling were performed to evaluate the temperature at each point of the set-up. A good agreement between experimental and simulated data is exhibited. Alloys with identical microstructures were sintered and the homogeneity of the microstructure was better in the largest machines or when the sample wa…
β-C3N4 Nanocrystals: Carbon Dots with Extraordinary Morphological, Structural, and Optical Homogeneity
2018
Carbon nanodots are known for their appealing optical properties, especially their intense fluorescence tunable in the visible range. However, they are often affected by considerable issues of optical and structural heterogeneity, which limit their optical performance and limit the practical possibility of applying these nanoparticles in several fields. Here we developed a synthesis method capable of producing a unique variety of carbon nanodots displaying an extremely high visible absorption strength (ε > 3 × 106 M(dot)−1 cm−1) and a high fluorescence quantum yield (73%). The high homogeneity of these dots reflects in many domains: morphological (narrow size distribution), structural (q…
Conoscopic Studies of Optical Homogeneity of the LiNbO3:Mg Crystals
2012
An essential modification of the method to observe large-scale conoscopic images is proposed. Divergent beam of wide-aperture radiation is formed by a diffuser placed before entrance of a lithium niobate crystal. The optical homogeneity of LiNbO3:Mg crystals is studied in a wide range of the admixture concentrations (0.01 – 5.5 mol.%). An inhomogeneous distribution of the admixture is found to increase with the admixture concentration being accompanied by growth bands, micro-defects, such as micro-domains, domain boundaries, and block structures particularly in parts of higher concentration gradients at the boundaries of the growth bands.
Electronic polarizability of small sodium clusters.
1986
Abstract : Small sodium clusters consisting of 1 to 40 atoms are described as spheres of interacting homogeneous electron gas (jellium model). The static electronic polarizability is calculated using self consistent density functional methods. An excellent agreement with recent experimental results is observed.
Stopover strategies in birds: a review of methods for estimating stopover length
1999
This study categorizes and reviews methods used to estimate stopover length in migratory birds. Stopover length is an important variable in analysing migration strategies. The analysis of the stopover pattern of migratory birds typically attempts to investigate variability in the number of stopovers and in the length of time spent at stopover sites in relation to species, age, sex and body condition. Although the number of capture-recapture studies analysing stopover length has increased substantially, most are analysed using the simple last-first capture method which gives biased estimates. The use of mathematical models to calculate stopover length is uncommon. Most researchers assume hom…
Limiting conditions of yielding for anisotropic materials
1969
The known Limiting Conditions of Yielding presuppose homogeneity andisotropy of the material. Formulas for anisotropic materials have been proposed: but they cannot be applied to all practical applications. The Limiting Condition of Yielding already proposed by the A. for isotropic materials can easily be extended to materials with different mechanical properties in different directions: the formulas obtained confirm the particular cases and the particular formulas already known for isotropic materials. The various solutions proposed by the A. for anisotropic bodies are usually represented by paraboloids whose characteristics obviously depend on the experimental parameters.
Analysis of Fiber Inhomogeneity Using Time-Resolved Acousto-Optic Interaction
2013
Workshop on Specialty Optical Fibers and their Applications 2013, Sigtuna Sweden, 28–30 August 2013
Investigation of structure, stability, phase composition and magnetic ordering in ultrathin iron/nickel films
1995
By thermal and chemical treatment of Langmuir-Blodgett (LB) films, oxidic and metallic Fe and Ni layers can be prepared. The films are characterised, where differences e.g. in the lateral homogeneity are found. The metallic Fe containing samples show a higher corrosion stability as compared with films prepared by other coating techniques. Mixed Fe/Ni oxidic and metallic layers, respectively, are prepared, where the Ni concentration in the oxidic films can be determined as a function of the ratio of initially transferred numbers of LB layers. The phase composition of the metallic Fe changes systematically with the Ni concentration.