Effects of SEBS-g-MA copolymer on non-isothermal crystallization kinetics of polypropylene

The non-isothermal crystallization kinetics of pure PP and PP/SEBS-g-MA blends up to volume fraction, Φ _d (0–0.50) was studied by differential scanning calorimetry at four different cooling rates. Crystallization parameters were analyzed by Ozawa and Liu models. The Ozawa model fits in the PP/SEBS-g-MA blends and indicates the effect of SEBS-g-MA copolymer on the crystallization process of polypropylene. Augis–Bennet model has been used to calculate activation energy, ?E, during non-isothermal crystallization process. The value of ?E decreased with SEBS-g-MA due to flexibility of SEBS-g-MA by which movements of chains of PP become easier.     

Additive Manufacturing of Ceramics Enabled by Flash Pyrolysis of Polymer Precursors with Nanoscale Layers

We show that a polymer‐based route to ceramics can be implemented into additive manufacturing by reducing the time for pyrolysis to about a second, which we call flash pyrolysis. Repetitive deposition of nanometer scale coatings of the ceramic, in this way, is employed to create defect‐free infiltrations of carbon fiber composites. The mechanical strength of the fibers is retained in the composite. Excellent wetting properties of the polymer precursor permits three‐dimensional, conformal coating through the three stages of infiltration: nanoscale coating of the single fibers, filling of interstitial spaces between the fibers, and a buildup of the coating over the entire composite. The flash pyrolysis method will enable a new genre of polymer‐derived ceramics made into net shape by this unusual method of additive manufacturing.     

The Change of X‐ray Diffraction Peak Width During in situ Conventional Sintering of Nanoscale Powders

Diffraction peaks of nanoscale particles of 3 mol% yttria‐stabilized zirconia become sharper as the powder sinters. The reduction in the peak width is correlated with the increase in density. The sharpening of the peak agrees reasonably well with the remaining free surface area as the sample sinters. Therefore, high curvature of the free surface of the pores is assumed to lead to peak broadening (the grain boundaries that grow at the expense of the free surfaces of the pores do not have this curvature). The change in the grain size during sintering does not make a significant contribution to peak width.     

达芬奇效应:简便的数字视频

数字视频将引发人们与电子产品交互方式的变革。实现数字视频不但复杂,而且费时费钱。而这一切难题在达芬奇技术面前全部烟消云散。     

Solid Yttria-Stabilized Zirconia Films by Pulsed Chemical Vapor Deposition from Metal-organic Precursors

A pulsed chemical vapor deposition from metal-organic precursors (MOCVD) system was used to produce solid zirconia, and yttria-stabilized zirconia (YSZ) films. A total of six candidate metal-organic precursors for zirconia and three for yttria were investigated. Three precursor solutions for YSZ proved suitable for pulsed-MOCVD processing. Layers were deposited on metal, alumina, and porous nickel cermet substrates. Under optimal deposition conditions, precursor conversion efficiency of 90% was achieved using a solution of 3.74 vol% zirconium 2-methyl-2-butoxide + 0.42% yttium methoxyethoxide in toluene. The film growth rate was 7.5 μm·h⁻¹ at 525°C deposition temperature. Two alkoxide precursors produced YSZ layers with material costs under $0.50/(μm·cm²).     

On the predictability of the water-table variation in a ditch-drainage system

The irrigation in regions of brackish groundwater in many parts of the world results in the rise of the water-table very close to the groundsurface. The salinity of the productive soils is therefore increased. A proper layout of the ditch-drainage system and the prediction of the spatio-temporal variation of the water table under such conditions are of crucial importance in order to control the undesirable growth of the water-table. In this paper, an approximate solution of the nonlinear Boussinesq equation has been derived to describe the water-table variations in a ditch-drainage system with a random initial condition and transient recharge. The applications of the solution is discussed with the help of a synthetic example.Notations a lower value of the random variable representing the initial water-table height at the groundwater divide - a+b upper value of the random variable representing the initial water-table height at the groundwater divide - h variable water-table height measured from the base of the aquifer - K hydraulic conductivity - L half width between ditches - m ₀ initial water-table height at the groundwater divide - N(t) rate of transient recharge at time t - N ₀ initial rate of transient recharge - P N ₀/K - S Specific yield - t time of observation - t ₀ logarithmic decrement of the recharge function - T Kt/SL - x distance measured from the ditch boundary - X x/L - Y h/L - Y mean of Y - Y Variance of Y     

Cooperative adaptive sampling of random fields with partially known covariance

This paper considers autonomous robotic sensor networks taking measurements of a physical process for predictive purposes. The physical process is modeled as a spatiotemporal random field. The network objective is to take samples at locations that maximize the information content of the data. The combination of information‐based optimization and distributed control presents difficult technical challenges as standard measures of information are not distributed in nature. Moreover, the lack of prior knowledge on the statistical structure of the field can make the problem arbitrarily difficult. Assuming the mean of the field is an unknown linear combination of known functions and its covariance structure is determined by a function known up to an unknown parameter, we provide a novel distributed method for performing sequential optimal design by a network comprised static and mobile devices. We characterize the correctness of the proposed algorithm and examine in detail the time, communication, and space complexities required for its implementation. Copyright © 2011 John Wiley & Sons, Ltd.     

Electric Fields Obviate Constrained Sintering

The phenomenon of constrained sintering, where large rigid inclusions of alumina have been shown to significantly reduce the rate of sintering of titania [Bordia and Raj (1988) J. Am. Ceram. Soc. 71, 302–310], is shown to subside nearly completely during flash sintering carried out under modest electrical fields. The result is explained by a different mechanism for volumetric and shear deformation under electric fields. It is proposed that vacancy and interstitials generated within the grains migrate to grain boundaries and pores to produce both volumetric and shear strain at equal rates, since, in this way, the diffusion distance for both modes of deformation becomes the same. In conventional sintering, where transport occurs from one interface to another, the diffusion distance for shear is twice as far as for densification, which retards sintering should it become controlled by shear deformation, as seen in constrained sintering.     

Limits to the Stability of the Amorphous Nature of Polymer‐Derived HfSiCNO Compounds

Substituting silicon by transition metals in polymer‐derived ceramics (PDCs) holds the potential for a new class of polymer‐derived ceramics for ultrahigh‐temperature structural applications. We present experiments that show that the solid solubility of HfO₂ extends to Hf/Si ratio of <0.22. The materials are synthesized from (miscible) organic precursors. Similar to silicon‐based materials they remain amorphous after pyrolysis at 1000°C. Small‐angle X‐ray scattering and Raman spectra remain essentially unaltered. It is postulated that Hf, like Si, forms mixed‐bond tetrahedra with C, O, and N. The difference in the enthalpy of Hf‐based, and Si‐centered tetrahedra is calculated using single‐bond energies, reinforcing the feasibility of substituting Si with Hf or with Zr atoms. Such polymer‐based HfSiCNO compounds made directly from liquid organics, by a simple manufacturing process, may also be relevant to nanoscale dielectrics with low leakage electric charge in microelectronics applications.     

Remote sensing technique for mapping salt affected soils

The salt affected soils of Etah, Aligarh, Mainpuri and Mathura districts have been mapped into S1: < 10 per cent of the area covered by salts, S2: 10–30 per cent, S3: 30–50 per cent, S4: 50–75 per cent and S5: > 75 per cent using an integrated approach of image interpretation. The dull white tone of salt affected and sandy soils have posed problems in their discrimination, on TM false colour composite, however, the problem of spectral similarity was solved through integration of interpretation of thermal data (10.4–12.5μm) with TM FCC (bands 2, 3, 4) interpretation. The discrimination of salt affected soils was significantly better on data between March and first week of April because of maximum contrast. Out of l-75m ha of the total geographical area, the salt affected soils account for 11–8 per cent. Another 16–2 per cent is likely to be affected with this problem if similar degraded conditions prevail there. The values of pH: 8–7 and ECe: 1–3 dsm^-1 of S1 soils group them into non saline and mildly alkali class. Similarly low ECe: 4–4dSm^-1 and high pH: 9–8 for S3 soils and high ECe: 24–0 dsm^-1 and very high pH: 10–7 of S4/S5 soils, placed the soils into alkali and sodic classes respectively. The gypsum requirement based on pH values varies from 1 to 15 tha^-1.