Control of heat transfer and growth uniformity of solidifying copper shells through substrate temperature

To determine the optimal roll temperature in a twin-roll copper-strip caster, copper blocks preheated between 25 °C and 350 °C were immersed in a bath of molten copper for 0.5 seconds. A significant increase in the contact heat-transfer coefficient at the substrate-shell interface was obtained when the substrates were heated above 200 °C and the gain in the solidified shell thickness was 20 pct. The shell growth was also approximately 35 pct more uniform at a high substrate temperature, and micrographic examination showed the dendritic structure to be finer. The contact heat-transfer coefficient was decomposed into two constituents, one for the substrate and the other for the shell. The former was found to be the limiting factor in heat transfer.     

Anisotropy of segregation at grain boundaries and surfaces

The purpose of this article is to review analytical models of the anisotropy of segregation to grain boundaries (GBs) and surfaces, and to evaluate their predictions. A summary of Gibbsian interfacial thermodynamics is provided as an introduction to the topic. This is followed by a historical overview of previous analytical models. A recently developed model of the dependence of GB segregation on the five macroscopic parameters of GB orientation is outlined, and illustration of how this formulation reduces to the particular cases of segregation to simpler types of interfaces is provided. In addition, some specific aspects of interfacial segregation, which have either been problematic or have lacked satisfactory explanation, are addressed. These include (a) the relationship between the compositions on the two sides of a given GB; (b) the difficulty of meaningful definitions of segregation-free energy (and related thermodynamic quantities such as enthalpy and entropy); (c) the so-called compensation temperature, at which the anisotropy of interfacial segregation seems to vanish; (d) the relationship between surface and GB segregation; and finally (e) an attempt to determine whether segregation increases or decreases interfacial energy anisotropy, and the consequences thereof on the equilibrium crystal shape of alloys. Where possible, comparisons are made with the results of experiments or computer simulations.     

Highly ordered orthorhombic mesoporous silica films

Mesoporous silica films are made by the spin-coating technique using an ethylene oxide––propylene oxide––ethylene oxide triblock copolymer (Pluronic PE6800) as template. After optimization of the polymer concentration in the silica sol, films are textured and organized over all the thickness. They exhibit an orthorhombic symmetry (a=16.0 nm, b=10.2 nm, c=23.0 nm) with the b-axis perpendicular to the substrate. This results from a body-centered cubic (bcc) micellar structure which is deformed along the [0 1 1]_bcc cubic axis, i.e. perpendicular to the film plane.     

Average functionalities of macromolecules in stepwise polyfunctional polymerization

General expressions are derived for the average functionalities of macromolecules in stepwise polyfunctional polymerization, in particular for systems composed of monomers endowed with both A and B coreactive functional groups. Knowing the molecular distribution functions the weight average functionalities are calculated directly, on the basis of a new method using the propagation expectation.     

Stabilization and tracking control for an extended Heisenberg system with a drift

In this paper, we present sliding mode control algorithms, that are designed to practically stabilize (which means that the system state is stabilized to an neighborhood of the origin) the perturbed multidimensional Heisenberg system (therefore, with a drift) with additional two multidimensional integrators in the control inputs path. This result is then used to solve a tracking problem for the class of system which unperturbed model fails Brockett's necessary condition for the existence of a continuous, time independent feedback law.     

Gastropod communities, vegetation dynamics and landscape changes along an old-field succession in Provence, France

Studies about the relationships between land snail communities and landscape are scarce. The abandonment of many cultivated lands in Provence since the end of the last century gives us the opportunity of an analysis of the organisation pattern of gastropod communities in relation to the recent history and the present day structure of a Mediterranean landscape. The dynamics of a 40 ha landscape, mapped on a raster mode, was studied using cadaster data for seven periods between 1890 and 1990. These data were computed using MCA and PCA. Both floristic and malacological relevés were made at a scale of one grid cell. At the stand level, the patterns of gastropod communities are strongly correlated with the vegetation structure and composition. At the landscape level, the analysis of gastropod communities permits a very good perception of the present day landscape structure, as well as insight into the recent landscape history. However, even if the fits obtained are good, they should be improved in order to take into account scale dependences of snail communities.     

Determination of refractive index, thickness, and the optical losses of thin films from prism-film coupling measurements

We present a method of analysis of prism-film coupler spectroscopy based on the use of transfer matrix and genetic algorithm, which allows the simultaneous determination of refractive index, thickness, and optical losses of the measured layer.     

Attenuated total reflection infrared spectroscopy: an efficient technique to quantitatively determine the orientation and conformation of proteins in single silk fibers

Polarized attenuated total reflection (ATR) infrared spectroscopy is an efficient technique to determine the orientation and conformation of a large variety of samples, but it is more difficult to apply to very small specimens such as silk fibers. The Golden Gate single-reflection ATR accessory that uses diamond as an ATR element and a focalized beam turns out to be highly efficient to study quantitatively the orientation and conformation of a single silk fibroin filament of the silkworm Bombyx mori that is about 10 mum in diameter. For orientation measurements, rotating the sample instead of the electric field greatly simplifies the theoretical analysis and keeps the penetration depth of the infrared radiation constant. A sample holder that can be fitted on the ATR accessory has thus been developed to allow accurate rotation of the sample and to obtain spectra with a low, non-damaging, and reproducible pressure on the fiber. To validate the method, spectra have been recorded as a function of the angle theta between the fiber axis and the polarization of the incident radiation. The data have been fitted following the cosine square dependency of the absorbance with respect to the angle theta. The procedure has been applied to the spectral components of the amide I bands, as determined from spectral decomposition. Multiple angle measurements turn out to be quite useful to correct systematic angle errors and validate the accuracy of the curve-fitting parameters of the band decomposition. By using the calculated dichroic ratio, a parameter of -0.46 +/- 0.01 has been calculated for the antiparallel beta-sheets and -0.04 +/- 0.02 for the remaining structures. From the orientation-insensitive spectrum A(0), the amount of beta-sheets has been estimated to 49 +/- 3%. The results obtained from only two measurements with the electric field of the incident radiation parallel and perpendicular to the fiber axis has demonstrated that ATR spectroscopy can be used routinely in quantitative studies of the molecular orientation and conformation of macromolecules.     

Accuracy of Raman lidar water vapor calibration and its applicability to long-term measurements

A Raman lidar calibration method adapted to the long-term monitoring of atmospheric water vapor is proposed. The accuracy of Raman lidar water vapor profiles is limited by that of the calibration process. Typically, calibration using in situ balloon-borne measurements suffers from the nonsimultaneity and noncollocation of the lidar and in situ measurements, while calibration from passive remote sensors suffers from the lower accuracy of the retrievals and incomplete sampling of the water vapor column observed by lidar. We propose a new hybrid calibration method using a combination of absolute calibration from radiosonde campaigns and routine-basis (off-campaign) partial calibration using a standard lamp. This new method takes advantage of the stability of traceable calibrated lamps as reliable sources of known spectral irradiance combined with the best available in situ measurements. An integrated approach is formulated, which can be used for the future long-term monitoring of water vapor by Raman lidars within the international Network for the Detection of Atmospheric Composition Change and other networks.