Flow of particulate solids through tumbling mills

The transport behavior of particulate solids flowing through tumbling mills depends strongly on the mill operating conditions. This paper presents the results of a detailed study to delineate the effect of the important operating variables on the hold-up, mean residence time and residence time distribution of particulate solids flowing through ball mills and rod mills. The effects of feed rate, media load, and mill speed on these transport parameters are discussed, emphasizing the fundamental differences between particulate transport in ball mills and rod mills. Under identical dimensionless operating conditions over the range of the investigation, the material hold-up and the Peclet number of the flow regime in the rod mill were always higher than those in the ball mill. Mechanistic interpretations of the observed transport phenomena are presented, and their implications in the context of tumbling mill analysis and design pointed out.     

Characteristics of Metal Droplets in Slag Tapped from the Blast Furnace

Slag samples, hot‐metal samples and hot‐metal temperatures were obtained during tapping of two blast furnaces. Sampling was carried out at different time points during tapping of three separate heats. The size distribution and composition of metal droplets found in the slag were determined using scanning electron microscopy. Only metal droplets above 0.75 μm could be counted and analysed. All droplets were below 8 μm in diameter and the great majority of these droplets were found to be between 0.75 and 2 μm. The size distribution did not differ significantly for different slag samples. Iron was the main droplet component. Electron probe microanalysis showed that the droplets contained small amounts of carbon. The percentage of the area in a studied cross‐section that was covered with metal droplets varied between 0.01 and 0.07%. Calculations based on Stoke's law showed that the distance droplets travel in the slag is in the micron range. Slag samples taken in the beginning of slag tapping contained more droplets than those taken in the middle of slag tapping, an indication that most droplets can be found in the area near the furnace wall. Some droplets were determined to have magnesium enrichment at the external surface.     

Variation in the volatile terpenoids of two industrially important basil (Ocimum basilicum L.) cultivars during plant ontogeny in two different cropping seasons from India

BACKGROUND: Two Ocimum basilicum cultivars, ‘Vikarsudha’ and ‘CIM‐Saumya’, grown in the Kumaon region of western Himalaya were evaluated for their essential oil yield and composition at different stages of plant growth during two distinct cropping seasons (spring–summer and rain–autumn). RESULTS: The highest yield of essential oil was obtained at full bloom stage in both cultivars in both cropping seasons. The essential oils obtained from different stages in two cropping seasons were analysed by capillary gas chromatography with flame ionisation detection, and gas chromatography–mass spectrometry. The major component of cultivar ‘Vikarsudha’ was methyl chavicol (84.3–94.3%), while for cultivar ‘CIM‐Saumya’ the main components were methyl chavicol (62.5–77.6%) and linalool (14.4–34.1%). CONCLUSION: This study clearly indicated that cultivar, cropping season, plant ontogeny and plant part had significant effects on the yield and quality of the essential oil of O. basilicum. Further, the amount of methyl chavicol in the cultivars grown in this region was higher than in cultivars from other parts of India. Copyright © 2011 Society of Chemical Industry     

Limitations of employing undirected information flow graphs for the maintenance of rigid formations for heterogeneous vehicles

In this paper, we consider the problem of decentralized control of a collection of heterogeneous vehicles trying to maintain a rigid formation. In a rigid formation of vehicles, the separation distance between any pair of vehicles does not change throughout their motion and equals a pre-specified value that defines the formation. In each formation, there is a set of reference vehicles and a set of following vehicles. A reference vehicle may not be influenced by the motion of the following vehicle, but the motion of the following vehicle is influenced by the motion of the reference vehicle. Since we will be primarily dealing with translational maneuvers of the formation, we will consider formations where there is only one reference vehicle whose motion specifies the desired motion for all the vehicles in the formation. Each following vehicle attempts to maintain a specified constant safe distance from its adjacent vehicles in the collection. We call a vehicle B adjacent to a vehicle A if the relative position of vehicle B is known to vehicle A either by communication or by sensing. We only consider information flow graphs that are undirected when restricted to the set of following vehicles, i.e., graphs where a following vehicle A is adjacent to a following vehicle B if and only if the following vehicle B is adjacent to the following vehicle A. We model each vehicle as a point mass of one unit with two types of forces act on each vehicle - a controlled force, which is the output of an actuation system and a disturbing force over which there is no control. The actuation system is assumed to be linear and time invariant, and may be representable by a rational and strictly proper transfer function. The input to the control system of a vehicle in the formation is based on the error in maintaining the desired separation from its adjacent vehicles and the output of the control system is a command to the actuator.An earlier result showed that spacing errors due to disturbances amplify in a collection of identical vehicles with identically structured linear controllers if the reference vehicle information is not available to Ω(n) (A function f(n) is Ω(g(n)) if there is a constant c > 0 and a N > 0 such that ∣f(n)∣ > c∣g(n)∣ for all n > N.) vehicles, n being the size of the collection [1]. From the viewpoint of tolerance to communication failures, it is therefore necessary that there be at least two vehicles in the formation that are adjacent to Ω(n) vehicles in the formation. In this paper, we consider a broad class of heterogeneously structured controllers defined by a pre-specified bound, say B_c > 0 as follows: the allowable controller in conjunction with the actuation systems on-board any vehicle will produce a force no greater than B_c in response to a constant input to the control system. If this class of controllers were to be employed with the aforesaid undirected information flow graphs, we show that there is a critical size of the formation beyond which the motion of the vehicles in the formation will be unstable. This result shows the inability to scale such controllers for maintenance of rigid formations in conjunction with undirected information flow graphs.     

Economics of producing hydrogen as transportation fuel using offshore wind energy systems

Over the past few years, hydrogen has been recognized as a suitable substitute for present vehicular fuels. This paper covers the economic analysis of one of the most promising hydrogen production methods—using wind energy for producing hydrogen through electrolysis of seawater—with a concentration on the Indian transport sector. The analysis provides insights about several questions such as the advantages of offshore plants over coastal installations, economics of large wind-machine clusters, and comparison of cost of producing hydrogen with competing gasoline. Robustness of results has been checked by developing several scenarios such as fast/slow learning rates for wind systems for determining future trends. Results of this analysis show that use of hydrogen for transportation is not likely to be attractive before 2012, and that too with considerable learning in wind, electrolyzer and hydrogen storage technology.     

Spectrum of mutations in the RPGR gene that are identified in 20% of families with X-linked retinitis pigmentosa

The RPGR (retinitis pigmentosa GTPase regulator) gene for RP3, the most frequent genetic subtype of X-linked retinitis pigmentosa (XLRP), has been shown to be mutated in 10%-15% of European XLRP patients. We have examined the RPGR gene for mutations in a cohort of 80 affected males from apparently unrelated XLRP families, by direct sequencing of the PCR-amplified products from the genomic DNA. Fifteen different putative disease-causing mutations were identified in 17 of the 80 families; these include four nonsense mutations, one missense mutation, six microdeletions, and four intronic-sequence substitutions resulting in splice defects. Most of the mutations were detected in the conserved N-terminal region of the RPGR protein, containing tandem repeats homologous to those present in the RCC-1 protein (a guanine nucleotide-exchange factor for Ran-GTPase). Our results indicate that mutations either in as yet uncharacterized sequences of the RPGR gene or in another gene located in its vicinity may be a more frequent cause of XLRP. The reported studies will be beneficial in establishing genotype-phenotype correlations and should lead to further investigations seeking to understand the mechanism of disease pathogenesis.     

A method for estimating the proportion of nonresponsive traffic at a router

In this paper, a scheme for estimating the proportion of the incoming traffic that is not responsive to congestion at a router is presented. The idea of the proposed scheme is that if the observed queue length and packet drop probability do not match the predictions from a model of responsive (TCP) traffic, then the error must come from nonresponsive traffic; it can then be used for estimating the proportion of nonresponsive traffic. The proposed scheme is based on the queue length history, packet drop history, and expected TCP and queue dynamics. The effectiveness of the proposed scheme over a wide range of traffic scenarios is corroborated using ns-2-based simulations. Potential applications of the proposed algorithms in traffic engineering and control are discussed.     

A carboxy-terminal truncation of 99 amino acids resulting from a novel mutation (Arg555-->stop) in the CHM gene leads to choroideremia

The gene content of the MHC class I telomerically adjacent region, in linkage disequilibrium with hereditary hemochromatosis, has not been well characterized yet. In the present work, we established three bacterial clone contigs, including mainly P1-derived artificial chromosomes. These contigs cover 89% of the 1.2-Mb 6p-subtelomeric region encompassing locus D6S105. Terminal exon trapping was applied to selected clones from these contigs. Forty-six independent terminal exons were identified and mapped within the region, 2 of which matched perfectly to expressed sequence tags. These 3' exons are all expressed in human fetal brain but differentially expressed in four tissues and two cell lines. The high number of exons identified indicates that the high gene density observed in the MHC class I region extends to this telomerically adjacent region.     

cDNA libraries from human tissues and cell lines

We report the construction of 34 cDNA libraries from human tissues and cell lines in lambda phage vectors (Charon BS, lambda gt11, lambda SHK, or lambda zapII). The cDNA was synthesized from poly A+ RNA, using oligo-dT as a primer, and size-selected before ligation to vector arms. High-complexity cDNA libraries from human tissues and cell lines should be a valuable resource for genome mapping studies and identification of disease genes.     

Charge density and bare surface barrier height in GaN/AlGaN/GaN heterostructures: A modeling and simulation study

In this article, we present a physics‐based model to explain the effect of the GaN cap layers on the 2D electron gas density and the bare surface barrier height in AlGaN/GaN heterostructures. We consider that the 2DEG originates from the surface donor states present on the GaN cap top surface. The influence of a 2D hole gas, formed when the valence band crosses the Fermi energy level, has also been considered. This model agrees well with the published experimental results and TCAD simulations, and can easily be incorporated into the modeling of GaN/AlGaN/GaN‐based HEMT devices.