High Electrical and Thermal Conductivity Cast Al-Fe-Mg-Si Alloys with Ni Additions

Metallurgical and Materials Transactions A - Aluminum alloys with transition metals Fe and Ni show potential to form the basis for castable alloys with high electrical and thermal conductivity for...     

Effect of polymer composition on performance properties of maleate-vinyl ether donor-acceptor UV-curable systems

The effect of unsaturated polyester backbone composition on the properties of donor-acceptor-UV-cured coatings was explored. The polyesters were designed with similar molecular weights and levels of unsaturation, but with otherwise widely varying backbone compositions. UV-curable coatings were formulated with stoichiometric levels of triethylenglycol divinyl ether and a photoinitiator. The resulting coatings had a broad range of properties, which were found to correlate with the properties and compositions of the polyester backbone polymers. A relatively flexible backbone resulted in lower glass transition temperatures (T_g). The polymer T_g was found to influence the conversion of double bonds achieved during UV curing. Reaction kinetics were evaluated for the coating systems and the results confirmed that the T_g of the systems influenced the double bond conversion. Thermal stability and König pendulum hardness were also found to vary with the backbone composition of the constituent polyester.     

Synthesis and properties of poly ether nitrile sulfone copolymers with pendant methyl groups

Poly ether nitrile and poly ether nitrile sulfone copolymers with pendant methyl groups were prepared by the nucleophilic substitution reaction of 2,6′‐dichlorobenzonitrile with methyl hydroquinone and with varying mole proportions of methyl hydroquinone and 4,4′dihydroxydiphenylsulfone using N‐methyl pyrrolidone as solvent in the presence of anhydrous K₂CO₃. The polymers were characterized by different physicochemical techniques. Copolymer composition was determined using FTIR technique. Thermogravimetric data reveals that all the polymers were stable up to 420°C with a char yield above 40% at 900°C in N₂ atmosphere. The glass transition temperature was found to increase and the activation energy and inherent viscosities were found to decrease with increase in concentration of the 4,4′‐dihydroxydiphenylsulfone units in the polymer. Trimerization reactions are found to be favorable with increase in concentration of methyl hydroquinone units in the polymer. Crystallinity of the polymer was also studied using wide angle X‐ray diffraction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1303–1309, 2006     

New powellite type oxides in Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi)—Their synthesis, structure and dielectric properties

New complex oxides having powellite (CaMoO₄) type structure in the Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi) were prepared employing the method of solid state reaction between the component oxides at high temperature (1000–1100 °C). The new compounds, CaRNbMoO₈ (R = Y, La, Nd, Sm, Bi) are colorless and electrical insulators. The dielectric constants (K at 1 MHz) of these compounds are in the range 14–33 and K shows very little variation in the temperature range 30–100 °C. Their temperature coefficient of dielectric constant (TCK) is negative, which varies from − 21 to − 220 ppm/°C.     

Theoretical investigations on low energy surfaces and nanowires of MgH(2)

The phase stability, chemical bonding, and electronic structure of MgH(2) nanowires and possible low energy surfaces of α-MgH(2) thin films have been investigated using the ab initio projected augmented plane-wave method. Structural optimizations based on total energy calculations predicted that, for the α-MgH(2) phase, the (101) surface is more stable among the possible low energy surfaces. The electronic structure study reveals that the nanowires also have nonmetallic character similar to that of the bulk and thin film phases. Bonding analysis shows that the character of chemical bonding in nanowires has been considerably changed compared with that in bulk phases. Similarly, the bond distances in the surfaces of nanowires are found to be higher than in the bulk material, suggesting that it is possible to remove hydrogen from the nanowires considerably more easily than from bulk crystals.     

Attractor selection in a modulated laser and in the Lorenz circuit

By tuning a control parameter, a chaotic system can either display two or more attractors (generalized multistability) or exhibit an interior crisis, whereby a chaotic attractor suddenly expands to include the region of an unstable orbit (bursting regime).Recently, control of multistability and bursting have been experimentally proved in a modulated class B laser by means of a feedback method. In a bistable regime, the method relies on the knowledge of the frequency components of the two attractors. Near an interior crisis, the method requires retrieval of the unstable orbit colliding with the chaotic attractor.We also show that a suitable parameter modulation is able to control bistability in the Lorenz system. We observe that, for every given modulation frequency, the chaotic attractor is destroyed under a boundary crisis. The threshold control amplitude depends on the control frequency and the location of the operating point in the bistable regime. Beyond the boundary crisis, the system remains in the steady state even if the control is switched off, demonstrating control of bistability.     

Phytosterols in Seaweeds: An Overview on Biosynthesis to Biomedical Applications

Seaweed extracts are considered effective therapeutic alternatives to synthetic anticancer, antioxidant, and antimicrobial agents, owing to their availability, low cost, greater efficacy, eco-friendliness, and non-toxic nature. Since the bioactive constituents of seaweed, in particular, phytosterols, possess plenty of medicinal benefits over other conventional pharmaceutical agents, they have been extensively evaluated for many years. Fortunately, recent advances in phytosterol-based research have begun to unravel the evidence concerning these important processes and to endow the field with the understanding and identification of the potential contributions of seaweed-steroidal molecules that can be used as chemotherapeutic drugs. Despite the myriad of research interests in phytosterols, there is an immense need to fill the void with an up-to-date literature survey elucidating their biosynthesis, pharmacological effects, and other biomedical applications. Hence, in the present review, we summarize studies dealing with several types of seaweed to provide a comprehensive overview of the structural determination of several phytosterol molecules, their properties, biosynthetic pathways, and mechanisms of action, along with their health benefits, which could significantly contribute to the development of novel drugs and functional foods.     

Spectroscopic studies on DLC/TM (Cr,Ag, Ti,Ni) multilayers

The hydrogen-free diamond-like carbon (DLC) films with transition metal (TM = Cr, Ag, Ti, Ni) interlayer (bilayer and multilayer) were deposited on to stainless steel and silicon substrates using pulsed laser deposition technique. Secondary ion mass spectroscopy (SIMS) confirmed that the films were hydrogen free. Incorporation of chromium inter layer reduced the stress value by about 3 GPa as determined by micro Raman spectroscopy. Incorporation of the TM inter layer enhanced the photoluminescence (PL) intensity as compared to the monolithic DLC films. The optical band gap determined by spectroscopic ellipsometry for DLC/TM films was found to be in the range of 1.56–1.67 eV.     

Mart Algorithms for Circular and Helical Cone-Beam Tomography

The present work is concerned with the evaluation of the performance and the efficient implementation of multiplicative algebraic reconstruction technique (MART) to reconstruct three-dimensional (3D) objects for two different source/detector trajectories. Three types of MART algorithms are tested on a numerical phantom (Defrise), and they are implemented on a 3D X-ray system of Vikram Sarabhai Space Centre (VSSC). Circular and helical cone-beam trajectories are used. The results are compared with convolution backprojection (CBP) algorithm for each trajectory. It is found that iterative algorithms perform better than their counterpart, the transform-based CBP algorithm, whenever tomography systems are ill-conditioned due to limited views and/or noisy projection data.     

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.