Dilute gelling systems: copolymers of styrene and glycol dimethacrylates

Gelation properties of the copolymers of styrene with various proportions of ¹⁴C labelled ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and polyethylene glycol (MW = 400) dimethacrylate have been studied. The thermal copolymerizations were carried out in 15% (v/v) solution in toluene. The rates of polymerization were found to increase with larger proportions of dimethacrylate cross-linking agents. The conversion at the gel point was surprisingly constant over a wide range of crosslinker concentration. The fraction of crosslinker saturated at both ends was found to increase in the order ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and polyethylene glycol 400 dimethacrylate. The proportion of completely reacted crosslinker increased only slowly with conversion. At very high concentrations of crosslinker, the onset of inhomogeneity was observed as described previously by Storey³ and Dusek¹⁸.     

The effect of microstructure on the fracture toughness of 300 and 350 grade maraging steels

The fracture toughness of 300 and 350 grade maraging steel that has been given simple heat treatments has been studied. By heating into the austenite region at well-controlled rates and holding for short times, the toughness can be increased significantly above that which is obtained for the standard treatment. It is shown that the toughness increase is due to plastic deformation of the austenite for single-cycled material. When multiple cycles are used, the 300 grade steel undergoes a strain-induced transformation at the crack tip that contributes significantly to the toughness. When singly cycled, 300 grade material is tested at −196°C, its properties approach those obtained for conventionally treated material at room temperature. Models for the toughness improvements are developed that take crack tip phenomena into account, and they are in good agreement with experiment.     

A recursive quadratic programming method with active set strategy for optimal design

Recursive quadratic programming methods have become popular in the field of mathematical programming owing to their excellent convergence characteristics. There are two recursive quadratic programming methods that have been published in the literature. One is by Han and the other is by Pshenichny, published in 1977 and 1970, respectively. The algorithm of Pshenichny had been undiscovered until now, and is examined here for the first time. It is found that the proof of global convergence by Han requires computing sensitivity coefficients (derivatives) of all constraint functions of the problem at every iteration. This is prohibitively expensive for large-scale applications in optimal design. In contrast, Pshenichny has proved global convergence of his algorithm using only an active-set strategy. This is clearly preferable for large-scale applications. The method of Pshenichny has been coded into a FORTRAN program. Applications of this method to four example problems are presented. The method is found to be very reliable. However, the method is found to be very sensitive to local minima, i.e. it converges to a local minimum nearest to the starting design. Thus, for optimal design problems (which usually possess multiple local minima) it is suggested that Pshenichny's method be used as part of a hybrid method.     

Theoretical analysis of some configurations of double exposure solar air heaters

We present a theoretical analysis of three different configurations of double exposure solar air heaters. The heat-balance equations are written in each case and are solved explicitly. The periodic responses have been studied for different combinations of parameters. Measured values of solar radiation in the plane of the collector and the ambient temperature are used in the analysis. The effects of collector length, reflectance and flow rate have been studied.The outlet air temperature increases with an increase in plate length but the instantaneous and average efficiency decrease. The outlet air temperature is approximately the same, for a given model and combinations of parameters, when the ratio of the length of the air heater to the mass flow rate is constant. A double exposure solar air heater performs better than a single exposure air heater if the reflectance for solar radiation is greater than 10%.     

Addition polyimides. I

Crosslinking of 4,4′(bismaleimido)diphenyl ether (BM) was investigated in presence of bis(m-aminophenyl)methylphosphine oxide (BAP), tris(m-aminophenyl)phosphine oxide (TAP), diaminodiphenyl ether (E) and 3,3-bis(p-aminophenyl)phthalide (AP). These crosslinked resins were examined for thermal stability by thermogravimetric analysis. A slight decrease in initial decomposition temperature, the temperature of maximum rate of weight loss, was observed, though the char yield in nitrogen atmosphere at 800°C did not change appreciably. Glass-cloth-reinforced laminates were fabricated from BM and amine mixtures. An improvement in mechanical properties was observed in the presence of phosphorus-containing di- and triamines.     

On an exponential server with general cyclic arrivals

Summary A E ⁿ¦ M ¦ 1 queue is defined as a single server queue with exponential service time and general cyclic arrival distributions of cycle length n. The waiting time distribution for such a queue is proved to be a sum of n exponential terms; this is a generalization of G ¦ M ¦ 1 queue results. Based on this a method for obtaining the steady-state waiting time distributions for E ⁿ¦ M ¦ 1 queues is introduced. An example is presented to show an application of E ⁿ¦ M ¦ 1 queues in deterministic routing.The work was supported in part by the U.S. Air Force Office of Scientific Research under grant AFOSR 78-3654 A to the Department of Computer Science     

A New Technique for Coating Silicon Carbide Onto Carbon Nanotubes Using a Polycarbosilane Precursor

Multiwalled carbon nanotubes (MWCNTs) have been coated with silicon carbide (SiC) using polycarbosilane as precursor in order to improve their thermo oxidative stability. The polycarbosilane coated MWCNTs were heated to ~1300°C under an inert atmosphere to generate the SiC coating. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have confirmed the formation of SiC on the MWCNTs. The retention of the tubular structure of the MWCNTs has been confirmed by transmission electron microscopy. Thermogravimetric analysis has been performed to evaluate the thermo oxidative stabilities of coated and virgin MWCNTs. Sonication studies have shown that the mechanical strength of the MWCNTs was increased after coating with SiC.     

Genome-Wide Identification and Characterization of PIN-FORMED (PIN) Gene Family Reveals Role in Developmental and Various Stress Conditions in Triticum aestivum L.

PIN-FORMED (PIN) genes play a crucial role in regulating polar auxin distribution in diverse developmental processes, including tropic responses, embryogenesis, tissue differentiation, and organogenesis. However, the role of PIN-mediated auxin transport in various plant species is poorly understood. Currently, no information is available about this gene family in wheat (Triticum aestivum L.). In the present investigation, we identified the PIN gene family in wheat to understand the evolution of PIN-mediated auxin transport and its role in various developmental processes and under different biotic and abiotic stress conditions. In this study, we performed genome-wide analysis of the PIN gene family in common wheat and identified 44 TaPIN genes through a homology search, further characterizing them to understand their structure, function, and distribution across various tissues. Phylogenetic analyses led to the classification of TaPIN genes into seven different groups, providing evidence of an evolutionary relationship with Arabidopsis thaliana and Oryza sativa. A gene exon/intron structure analysis showed a distinct evolutionary path and predicted the possible gene duplication events. Further, the physical and biochemical properties, conserved motifs, chromosomal, subcellular localization, transmembrane domains, and three-dimensional (3D) structure were also examined using various computational approaches. Cis-elements analysis of TaPIN genes showed that TaPIN promoters consist of phytohormone, plant growth and development, and stress-related cis-elements. In addition, expression profile analysis also revealed that the expression patterns of the TaPIN genes were different in different tissues and developmental stages. Several members of the TaPIN family were induced during biotic and abiotic stress. Moreover, the expression patterns of TaPIN genes were verified by qRT-PCR. The qRT-PCR results also show a similar expression with slight variation. Therefore, the outcome of this study provides basic genomic information on the expression of the TaPIN gene family and will pave the way for dissecting the precise role of TaPINs in plant developmental processes and different stress conditions.     

Synthesis and characterisation of rubber seed oil trans-esterified biodiesel using cement clinker catalysts

The synthesis of biodiesel using rubber seed oil by a transesterification reaction using cement clinker catalysts was studied. The mineral composition and morphology of both the catalysts were analysed using X-ray diffraction and scanning electron microscopy. The gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy and nuclear magnetic resonance studies were used to find the Fatty acid methyl ester content and various compounds of esters in the synthesised biodiesel, which showed an efficient conversion of rubber seed oil to biodiesel. The highest yield of 80% was obtained from calcium oxide catalyst (1.5?g) activated at 50°C with a methanol-to-oil ratio of 6:1. The highest yield of 70% biodiesel was obtained using a cement clinker catalyst (0.5?g) activated at 50°C with a methanol-to-oil ratio of 6:1. The significant physical properties of biodiesel flash point, acid value and saponification value were found, and the results are within the American standard test method (ASTM D6751) limits.