Numerical studies on columnar-to-equiaxed transition in directional solidification of binary alloys

A numerical study on columnar-to-equiaxed transition (CET) during directional solidification of binary alloys is presented using a macroscopic solidification model. The position of CET is predicted numerically using a critical cooling rate criterion reported in literature. The macroscopic solidification model takes into account movement of solid phase due to buoyancy, and drag effect on the moving solid phase because of fluid motion. The model is applied to simulate the solidification process for binary alloys (Sn-Pb) and to estimate solidification parameters such as position of the liquidus, velocity of the liquidus isotherm, temperature gradient ahead of the liquidus, and cooling rate at the liquidus. Solidification phenomena under two cooling configurations are studied: one without melt convection and the other involvin thermosolutal convection. The numerically predicted positions of CET compare well with those of experiments reported in literature. Melt convection results in higher cooling rate, higher liquidus isotherm velocities, and stimulation of occurrence of CET in comparison to the nonconvecting case. The movement of solid phase aids further the process of CET. With a fixed solid phase, the occurrence of CET based on the same critical cooling rate is delayed and it occurs at a greater distance from the chill.

Free convection heat transfer to mercury in vertical annuli

Data on free convection heat transfer to water and mercury are collected using a test rig in vertical annuli of three radii ratios, the walls of which are maintained at uniform temperatures. A theoretical analysis of the boundary layer equations has been attempted using local similarity transformation and double boundary layer approach. Correlations derived from the present theoretical analysis are compared with the analysis and the experimental data available in literature for non-metallic fluids and also with the present experimental data on water and mercury. Generalised correlations are set up for expressing the ratio of heat transferred by convection to the heat transferred by pure conduction and Nusselt's number, in terms of Grashof, Rayleigh and Prandtl numbers, based on the theoretical analysis and the present data on mercury and water. The present generalised correlations agree with the reported and present data for non-metallic fluids and liquid metals with an average deviation of 9% and maximum deviation of ± 13.7%.

Breakage of viscous and non-Newtonian drops in stirred dispersions

A model of breakage of drops in a stirred vessel has been proposed to account for the effect of rheology of the dispersed phase. The deformation of the drop is represented by a Voigt element. A realistic description of the role of interfacial tension is incorporated by treating it as a restoring force which passes through a maximum as the drop deforms and eventually reaching a zero value at the break point. It is considered that the drop will break when the strain of the drop has reached a value equal to its diameter. An expression for maximum stable drop diameter, dmax, is derived from the model and found to be applicable over a wide range of variables, as well as to data already existing in literature. The model could be naturally extended to predict observed values of dmax when the dispersed phase is a power law fluid or a Bingham plastic.

Factors affecting farmland prices in Finland

The purpose of the study was to analyse factors affecting the differences in land prices between regions. The key issue was to find out the policy effects on farmland prices. In addition to comprehensive literature review, a theoretical analysis as well as modern panel and spatial econometric techniques were utilized. The study clearly pointed out the importance of taking into account the possible spatial dependence. The data were exceptionally large, comprising more than 6 000 observations. Thus, it allowed a thorough econometric estimation including the possibility to take into account the spatial nature of the data. This study supports the view that there are many other factors that affect farmland prices besides pure agricultural returns. It was also found that the support clearly affects land prices. However, rather than assuming the discount rates for support and market returns to be similar, the rough analysis refers to the discount rate for support being a little lower. If this were true it would indicate that farmers rely more on support income than market returns. The results support the view presented in literature that land values are more responsive to government payments when these payments are perceived to be permanent. An important result of this study is that the structural differences between regions and the structural change in agriculture seemed to have a considerable role in affecting land prices. Firstly, the present structure affects the competition in the land market: the more dense farms are in the region the more there are potential buyers, and the land price increases. Secondly, the change in farm structure (especially in animal husbandry) connected to the policy changes that increase area-based support affects land prices. The effect comes from two sources. Growing farms need more land for the manure, and the proportion of retiring farmers may be lower. The introduction of the manure density variable proved to be an efficient way to aggregate the otherwise very difficult task of taking into account the environmental pressure caused by structural change in animal husbandry. Finally, infrastructure also has a very important role in determining the price level of agricultural land. If other industries are prospering in the surrounding area, agricultural viability also seems to improve. The non-farm opportunities offered to farm families make continuing and developing farming more tempting.

Ethics and Aesthetics : Intersections in Iris Murdoch's Philosophy

The study addresses the question concerning the relationship between ethics and aesthetics in the philosophy of Iris Murdoch. The main argument is that Murdoch s philosophy cannot be accurately understood without an understanding of the relationship she sees between the aesthetic experience and morality. Reading Murdoch s philosophy with this relationship in mind shows that it must be considered as a relevant alternative to the main forms of aesthetic-ethical theories. The study consists of seven previously published articles and a summary. It shows that Murdoch belongs to a tradition of philosophers who seek to broaden the scope of ethics by reference to aesthetic value and aesthetic experience. She sees an attitude responsible for aesthetic experiences as relevant for morality. However, she does not collapse morality into aesthetic experience. The two meet on the level of the subject s attitude towards its object, but there is a distinction between the experiences that accompany the attitudes. Aesthetic experiences can function as a clue to morals in that they present in a pleasing manner moral truths which otherwise might be psychologically too difficult to face. Murdoch equates the aesthetic attitude with virtuous love characterized by unselfish attention to its object. The primary object of such love is in Murdoch s account another human individual in her particularity. She compares the recognition of the other person as a particular existence to the experience of the Kantian sublime and offers her own version of the true sublime which is the experience of awe in the face of the infinity of the task of understanding others. One of the most central claims in Murdoch s philosophy is that human consciousness is evaluatively structured. This claim challenges the distinction between facts and values which has had an immense influence on modern moral philosophy. One argument with which Murdoch supports her claim is the nature of great literature. According to her, the standard of greatness in literature is the authors awareness of the independent existence of individuals in the particularity of their evaluative consciousnesses. The analysis of the standard of greatness in literature is also Murdoch s only argument for the claim that the primary object of the loving unselfish attention is the other particular individual. She is convinced that great literature reveals a deep truth about the human condition with its capacity to capture the particular. Abstract philo¬sophical discourse cannot compete with this capacity but it should take truths revealed by literature seriously in its theorising. Recognising this as Murdoch s stand on the question of the relation between philosophy and literature as forms of human discourse settles whether she is part of what has been called philosophy s turn to literature. The answer is yes.

Analysis of human chorionic gonadotropin-monoclonal antibody interaction in BIAcore

Kinetic studies of macromolecular ligand-ligate interaction have generated ample interest since the advent of plasmon resonance based instruments like BIAcore. Most of the studies reported in literature assume a simple 1 : 1 Langmuir binding and complete reversibility of the system. However we observed that in a high affinity antigen-antibody system [human chorionic gonadotropin-monoclonal antibody (hCG-mAb)] dissociation is insignificant and the sensogram data cannot be used to measure the equilibrium and kinetic parameters. At low concentrations of mAb the complete sensogram could be fitted to a single exponential. Interestingly we found that at higher mAb concentrations, the binding data did not conform to a simple bimolecular model. Instead, the data fitted a two-step model, which may be because of surface heterogeneity of affinity sites. In this paper, we report on the global fit of the sensograms. We have developed a method by which a single two-minute sensogram can be used in high affinity systems to measure the association rate constant of the reaction and the functional capacity of the ligand (hCG) immobilized on the chip. We provide a rational explanation for the discrepancies generally observed in most of the BIAcore sensograms

Behaviour of Bi-material interface cracks in the presence of material nonlinearity of adherends

The well known features of crack face interpenetration/contact at the tip of an interface crack is re-examined using finite element analysis and assuming material nonlinear properties for the adherends. It was assumed in literature that the crack tips are fully open at all load levels in the presence of material nonlinearity of the adherends. Analysis for the case of remote tension shows that even in the presence of material nonlinearity, crack tip closes at small load levels and opens above a certain load level. Mixed-mode fracture parameters are evaluated for the situation when the crack tips are fully open. Due to the presence of nonlinearity, the mixed-mode fracture parameters are measured with the symmetric and anti-symmetric components of J-integral. The present analysis explains the sequence of events at the interface crack tip with progressively increasing remote tension load for the case of adherends with material nonlinear behaviour.

Stability of an unsupported vertical circular excavation in clays under undrained condition

By using the axisymmetric finite elements static limit analysis formulation, proposed recently by the authors, the stability numbers (gamma H/c(o)) for an unsupported vertical circular excavation in clays, whose cohesion increases with depth, have been determined under undrained condition; gamma = unit weight, H., height of the excavation and c(o) = cohesion along ground surface. The results are obtained for various values of H/b and m; where b = the radius of the excavation and m = a non-dimensional parameter which accounts for the rate of the increase of cohesion with depth. The values of the stability numbers increase continuously both with increases in H/b and m. The results obtained in this study compare well with those available in literature.(C) 2009 Elsevier Ltd. All rights reserved.

Macro fiber composite (MFC) as a delamination sensor in antisymmetric laminates

The change in extension-twist Coupling due to delamination in antisymmetric laminates is experimentally measured. Experimental results are compared with the results from analytical expression existing in literature and finite element analysis. The application of the Macro-Fiber Composite (MFC) developed at the NASA Langley Research Center for sensing the delamination in the laminates is investigated. While many applications have been reported in the literature using the MFC as an actuator, here its use as a twist sensor has been studied. The real-life application envisaged is structural health monitoring of laminated composite flexbeams taking advantage of the symmetry in the structure. Apart from the defect detection under symmetric conditions, other methods of health monitoring for the same structure are reported for further validation. Results show that MFC works well as a sensor.

Heat transfer to newtonian fluids in coiled pipes in laminar flow

Data on pressure drop and heat transfer to aqueous solutions of glycerol flowing in different types of coiled pipes are presented for laminar flow in the range of NRe from 80 to 6000. An empirical correlation is set up which can account the present data as well as the data available in literature within ±10 per cent deviation. Conventional momentum and heat transfer analogy equation is used to analyse the present data.

Transcriptional switching in Escherichia coli during stress and starvation by modulation of Sigma 70 activity

During active growth of Escherichia coli, majority of the transcriptional activity is carried out by the housekeeping sigma factor (Sigma 70), whose association with core RNAP is generally favoured because of its higher intracellular level and higher affinity to core RNAP. In order to facilitate transcription by alternative sigma factors during nutrient starvation, the bacterial cell uses multiple strategies by which the transcriptional ability of Sigma 70 is diminished in a reversible manner. The facilitators of shifting the balance in favour of alternative sigma factors happen to be as diverse as a small molecule (p)ppGpp (represents ppGpp or pppGpp), proteins (DksA, Rsd) and a species of RNA (6S RNA). Although 6S RNA and (p)ppGpp were known in literature for a long time, their role in transcriptional switching has been understood only in recent years. With themelucidation of function of DksA, a new dimension has been added to the phenomenon of stringent response. As the final outcome of actions of (p)ppGpp, DksA, 6S RNA and Rsd is similar, there is a need to analyse hese mechanisms in a collective manner. We review the recent trends in understanding the regulation of Sigma 70 by (p)ppGpp, DksA, Rsd and 6S RNA and present a case for evolving a unified model of RNAP redistribution during starvation by modulation of Sigma 70 activity in E. coli.

Total risk rating and stability analysis of embankment dams in the Kachchh Region, Gujarat, India

A method for total risk analysis of embankment dams under earthquake conditions is discussed and applied to the selected embankment dams, i.e., Chang, Tapar, Rudramata, and Kaswati located in the Kachchh region of Gujarat, India, to obtain the seismic hazard rating of the dam site and the risk rating of the structures. Based on the results of the total risk analysis of the dams, coupled non-linear dynamic numerical analyses of the dam sections are performed using acceleration time history record of the Bhuj (India) earthquake as well as five other major earthquakes recorded worldwide. The objective of doing so is to perform the numerical analysis of the dams for the range of amplitude, frequency content and time duration of input motions. The deformations calculated from the numerical analyses are also compared with other approaches available in literature, viz, Makdisi and Seed (1978) approach, Jansen's approach (1990), Swaisgood's method (1995), Bureau's method (1997). Singh et al. approach (2007), and Saygili and Rathje approach (2008) and the results are utilized to foresee the stability of dams in future earthquake scenario. (C) 2010 Elsevier B.V. All rights reserved.

On determining the elastic modulus of a cylindrical sample subjected to flexural excitation in a resonant column apparatus

For resonant column tests conducted in the flexure mode of excitation, a new methodology has been proposed to find the elastic modulus and associated axial strain of a cylindrical sample. The proposed method is an improvement over the existing one, and it does not require the assumption of either the mode shape or zero bending moment condition at the top of the sample. A stepwise procedure is given to perform the necessary calculations. From a number of resonant column experiments on aluminum bars and dry sand samples, it has been observed that the present method as compared with the one available in literature provides approximately (i) 5.9%-7.3% higher values of the elastic modulus and (ii) 6.5%-7.3% higher values of the associated axial strains.

A multi-stage model for drop breakage in stirred vessels

Existing models for dmax predict that, in the limit of μd → ∞, dmax increases with 3/4 power of μd. Further, at low values of interfacial tension, dmax becomes independent of σ even at moderate values of μd. However, experiments contradict both the predictions show that dmax dependence on μd is much weaker, and that, even at very low values of σ,dmax does not become independent of it. A model is proposed to explain these results. The model assumes that a drop circulates in a stirred vessel along with the bulk fluid and repeatedly passes through a deformation zone followed by a relaxation zone. In the deformation zone, the turbulent inertial stress tends to deform the drop, while the viscous stress generated in the drop and the interfacial stress resist deformation. The relaxation zone is characterized by absence of turbulent stress and hence the drop tends to relax back to undeformed state. It is shown that a circulating drop, starting with some initial deformation, either reaches a steady state or breaks in one or several cycles. dmax is defined as the maximum size of a drop which, starting with an undeformed initial state for the first cycle, passes through deformation zone infinite number of times without breaking. The model predictions reduce to that of Lagisetty. (1986) for moderate values of μd and σ. The model successfully predicts the reduced dependence of dmax on μd at high values of μd as well as the dependence of dmax on σ at low values of σ. The data available in literature on dmax could be predicted to a greater accuracy by the model in comparison with existing models and correlations.