A study of nonisothermal austenite formation and decomposition in Fe-C-Mn alloys

Experiments using a hot-stage confocal scanning laser microscope (CSLM) have been carried out to observe phase transformations in two steels: Si-killed resulfurized Fe-0.38 wt pct C-1.43 wt pct Mn and Al-killed Fe-0.20 wt pct C-0.87 wt pct Mn. Austenite formation during continuous heating was investigated on the surface of samples that were etched to reveal the ferrite and pearlite regions. It was found that the austenite precipitated first at the pearlite colonies and subsequently in the ferrite phase. The measured advance rates of the γ/pearlite front were roughly twice those of the γ/α front and both interfaces were found to be curved. The γ/pearlite migration rate was found to be in qualitative agreement with published rate equations for isokinetic austenite formation where diffusion is the rate-limiting step. Austenite decomposition was studied during cooling. Widmanstätten ferrite laths precipitate as distinct colonies from the existing allotriomorphic ferrite phase but then also at MnS precipitates. The electron backscatter diffraction (EBSD) analysis showed that all of the laths in a particular colony exhibit similar orientation to one another but a slightly different orientation than the parent allotriomorph, supporting a sympathetic nucleation mechanism. The growth rate of the laths was found to vary widely within a range of 1.5 to 11 μm/s. The ferrite formation is finally halted by impingement with other advancing fronts. The results are presented in a phenomological discussion, with some quantitative analysis of the transformation kinetics.     

Enhanced layered segment trees: a pragmatic data structure for real-time processing of geometric objects

The data structure that is probably most used in the pattern recognition and image processing of geometric objects is the segment tree and its optimized variant, the “layered segment tree”. In all the versions currently known, except the work of Vaishnavi and Wood described later, these data structures do not operate in real time. Even in the latter scheme, although the structure can be implemented in real time and in an on-line fashion, the operation of insertion involves the sorting of the representations of the line segments in the tree. In essence, for all the reported algorithms, there is no known strategy to insert the segments one by one, other than the trivial strategy of processing them all together as in a batched-mode. In this paper, we present a strategy in which all the operations done on the tree can be done efficiently. Indeed, by improving the bottleneck, we prove that an arbitrary horizontal segment can be inserted into this data structure without invoking an expensive sorting process. We show that while this is accomplished by maintaining the same space and query complexity of the best-known algorithm, the version presented here is applicable to on-line real-time processing of line segments. The paper thus has applications in all areas of pattern recognition and image processing involving geometric objects.     

DIFFUSION COEFFICIENT OF OXYGEN IN LIQUIDS

The laminar dispersion of a solute in a capillary tube is used to measure diffusion coefficient of oxygen in liquids. A Polarographic type oxygen microelectrode is used to detect the pulse. Such a procedure overcomes the problems of measuring dissolved gases and makes it possible to apply this well known technique to oxygen-liquid systems. The results are in agreement with literature values     

Rapid thermal annealing effects on the photoluminescence properties of molecular beam epitaxy-grown GaIn(N)As quantum wells with Ga(N)As spacers and barriers

This article describes the effects of rapid thermal annealing (RTA) on the photoluminescence (PL) emission from a series of GaIn(N)As quantum wells. Indium compositions of both 20% and 32% were examined with nominal N compositions of 1% or 2%. The N location was varied within our quantum structure, which can be divided into three regions: (1) quantum well, (2) Ga(N)As spacer layers at the barrier-to-well interface and well-to-barrier interface, and (3) barriers surrounding each quantum well. Eight combinations of samples were examined with varying In content, Ga(N)As spacer layer thickness, N content, and N location in the structure. In the best cases, the presence of these Ga(N)As spacer layers improves the PL properties, due to annealing, with a reduction in the emission wavelength blueshift by ～400 Å, a reduction of the decrease in the full-width at half-maximum (FWHM) by ～5 meV, and a threefold reduction of the increase in integrated intensity. It was also observed that relocating N from the quantum wells to the barriers produces a comparable emission wavelength both before and after annealing. Our results further show that the composition of incorporated N in the material is most influential during the stages of RTA in which relatively small amounts of thermal energy is present from our lower annealing times and temperatures. Hence, we believe a low thermal-energy anneal is responsible for the recovery of the plasma-related crystal damage that was incurred during its growth. However, the In composition in the quantum well is most influential during the latter stages of thermal annealing, at increased times and temperatures, where the wavelength blueshift was roughly independent of the amount of incorporated N. As a result, our investigations into the effects of RTA on the PL properties support other reports that suggest the wavelength blueshift is not due to N diffusion.     

Comparison of satellite and cellular architectures for downlink broadcast data transmission

Traditional voice and video‐oriented networks such as the cellular and satellite networks are being increasingly used to carry data traffic. We endeavour to compare the downlink broadcast performance of the two architectures against each other on the basis of energy consumption, end‐to‐end delay and maximum stable throughput. The architectures are modelled as systems of Geo/G/1 queues. Queuing theory arguments and then sample‐path based comparisons are used to show that the satellite architecture while being more energy‐efficient has a higher delay and a lower maximum throughput. The variation of energy and delay with the total number of receiver nodes is also studied. Copyright © 2006 John Wiley & Sons, Ltd.     

Gas permeation properties of polyamide membrane prepared by interfacial polymerization

Interfacial polymerization technique has been widely employed to prepare reverse osmosis (RO) and nanofiltration (NF) membranes. The present study explores the possibility of preparing a polyamide membrane by interfacial polymerization and its utilization for the separation of CO₂ and H₂S from CH₄. A novel ultraporous substrate of polysulfone (PSF) was prepared by phase inversion technique from a solution containing 18% PSF and 4% propionic acid in dimethyl formamide (DMF) solvent. Thin film composite (TFC) polyamide membrane was synthesized on PSF substrate from the reaction between meta-phenylene diamine in an aqueous media and isophthaloyl chloride in hexane. The membrane prepared was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) to study intermolecular interactions, crystallinity, thermal stability and surface morphology, respectively. Gas permeabilities of pure CO₂, H₂S, CH₄, O₂, and N₂ gases were measured using the indigenously built permeation cell incorporated into a high-pressure gas separation manifold. At the feed pressure of 1 MPa, the membrane exhibited permeances of 15.2 GPU for CO₂ and 51.6 GPU for H₂S with selectivities of 14.4 and 49.1 for CO₂/CH₄ and H₂S/CH₄ systems, respectively. The observed N₂ permeance of 0.95 GPU was close to that of CH_4. The corresponding O₂ permeance was 5.13 GPU with a reasonably high O₂/N₂ selectivity of 5.4. The effect of feed pressure on polyamide membrane performance was examined. Further, molecular dynamics (MD) simulations were employed to compute the cohesive energy density (CED), solubility parameter (δ) and sorption of CO₂, H₂S, CH₄, O₂, and N₂ gases in polyamide membrane to corroborate theoretical study with experimentally determined gas transport properties.     

W/W型PAM-MMT乳液的制备及性能研究

为了提高以明胶为稳定剂分散聚合制备的聚丙烯酰胺“水包水”（W/W型PAM）乳液的絮凝性能，首先，采用阳离子单体甲基丙烯酰氧乙基三甲基氯化铵（methacrylatoethyl trimethyl ammonium chloride, DMC）对钠基蒙脱土（sodium-montmorillonite, Na-MMT）进行插层改性制备有机蒙脱土（organic montmorillonite, OMMT），通过X射线衍射（X-ray diffraction, XRD）测试得到插层改性后蒙脱土的层间距由1.25 nm增加至1.43 nm，说明DMC单体已经成功插层进入蒙脱土片层。然后，将OMMT引入以明胶为稳定剂的W/W型PAM乳液的体系中，以制备W/W型PAM-MMT乳液。通过透射电镜（transmission electron microscope, TEM）乳液微观形貌进行观察，得到乳液结构是由以蒙脱土颗粒为“交联点”的聚丙烯酰胺高分子网络和W/W型PAM乳液的混合体。研究了OMMT用量、明胶浓度、体系pH值以及阳离子单体DMC添加比例对合成W/W型PAM-MMT乳液性能的影响规律。结果显示：在适宜条件下合成的乳液均具有较好的储存稳定性和在水中的再分散性。乳液的表观黏度和絮凝性能都与OMMT和明胶用量呈正相关性；当pH值在明胶等电点（isoelectric point，IEP）时，得到的乳液的表观黏度最低，絮凝效果最好；随着DMC单体用量比例增大，乳液表观黏度减小，高岭土悬浮液的絮凝效果先增大后减小。     

Soil line transformation based relative radiometric normalization

Relative radiometric normalization is a prerequisite for multi‐temporal remotely sensed data analysis. Dark object subtraction (DOS) and pseudo‐invariant feature (PIF) methods are two commonly employed scene‐based methods for relative radiometric normalization. Both these methods have known limitations. The authors describe a soil line transformation method for multi‐date relative radiometric normalization, which circumvents the limitations of the DOS and PIF methods.     

Optimization of the continuously extruded unleavened flat bread (chapati) process

Processing variables such as size of die openings, production rate and initial moisture content on the discharge temperature and power input used in the continuous production of Indian unleavened flat bread (chapati) were studied. The extruder was a specially designed continuous chapati making system. The net specific energy (NSE) decreased with increasing size of die openings and moisture content. The total power efficiency increased with increasing production rate while NSE values remain unchanged. The discharge temperature decreased with increased moisture content of the dough and increased die opening size. The process variables were optimized for the continuous production of chapati, based on minimum specific energy and maximum puffing index. The optimum conditions were found to be a rate of 40 kg/h, a die opening of 1.4 mm height쐘 mm width and moisture contents of 60% and 75% (w.b.) for Resultant Atta and Atta, respectively. Sensory analysis showed that chapatis produced under the above conditions compared well with traditionally made chapatis in quality.     

Equations for nucleation of hydrogen gas pores during solidification of aluminium seven weight percent silicon alloy

A statistical prediction model has been applied to the nucleation rate as a function of temperature for an Al7Si alloy based upon observations of pore formation during solidification in an XTGS. A normalised Gaussian function was developed ((1), (2), (3) and (4)) which may be used to describe pore nucleation in mathematical simulations of porosity formation during solidification.