Mixed convection adjacent to non-isothermal vertical surfaces

Study of laminar boundary layer in mixed convection from vertical plates is carried out. The surface temperature along the vertical plate is assumed to vary arbitrarily with vertical distance. Perturbation technique is used to solve the governing boundary layer equations. The differentials of the wall temperature are used as perturbation elements, which are functions of vertical distance, to obtain universal functions. The universal functions are valid for any type of vertical wall temperature variation. Heat transfer rates and fluid velocity inside the boundary layer can be expressed and calculated using these universal functions. Heat transfer rates are obtained for the special cases of power-law variation of the wall temperature. The effect of the governing parameter (Gr(y)/Re-y(2)) and the power index of the power-law wall temperature variation on heat transfer rates is studied. For the purpose of validation, the mixed convection results obtained by the present technique pertaining to the special cases of isothermal vertical wall are compared with those obtained by similarity analysis reported in literature, and the agreement is found to be good. (C) 2012 Elsevier Ltd. All rights reserved.

Influence of stack geometry and resonator length on the performance of thermoacoustic engine

Thermoacoustic engines convert heat energy into high amplitude sound waves, which is used to drive thermoacoustic refrigerator or pulse tube cryocoolers by replacing the mechanical pistons such as compressors. The increasing interest in thermoacoustic technology is of its potentiality of no exotic materials, low cost and high reliability compared to vapor compression refrigeration systems. The experimental setup has been built based on the linear thermoacoustic model and some simple design parameters. The engines produce acoustic energy at the temperature difference of 325-450 K imposed along the stack of the system. This work illustrates the influence of stack parameters such as plate thickness (PT) and plate spacing (PS) with resonator length on the performance of thermoacoustic engine, which are measured in terms of onset temperature difference, resonance frequency and pressure amplitude using air as a working fluid. The results obtained from the experiments are in good agreement with the theoretical results from DeltaEc. (C) 2012 Elsevier Ltd. All rights reserved.

Causality analysis of groundwater dynamics based on a Vector Autoregressive model in the semi-arid basin of Gundal (South India)

Causal relationships existing between observed levels of groundwater in a semi-arid sub-basin of the Kabini River basin (Karnataka state, India) are investigated in this study. A Vector Auto Regressive model is used for this purpose. Its structure is built on an upstream/downstream interaction network based on observed hydro-physical properties. Exogenous climatic forcing is used as an input based on cumulated rainfall departure. Optimal models are obtained thanks to a trial approach and are used as a proxy of the dynamics to derive causal networks. It appears to be an interesting tool for analysing the causal relationships existing inside the basin. The causal network reveals 3 main regions: the Northeastern part of the Gundal basin is closely coupled to the outlet dynamics. The Northwestern part is mainly controlled by the climatic forcing and only marginally linked to the outlet dynamic. Finally, the upper part of the basin plays as a forcing rather than a coupling with the lower part of the basin allowing for a separate analysis of this local behaviour. The analysis also reveals differential time scales at work inside the basin when comparing upstream oriented with downstream oriented causalities. In the upper part of the basin, time delays are close to 2 months in the upward direction and lower than 1 month in the downward direction. These time scales are likely to be good indicators of the hydraulic response time of the basin which is a parameter usually difficult to estimate practically. This suggests that, at the sub-basin scale, intra-annual time scales would be more relevant scales for analysing or modelling tropical basin dynamics in hard rock (granitic and gneissic) aquifers ubiquitous in south India. (c) 2012 Elsevier B.V. All rights reserved.

An experimental study on cracking evolution in concrete and cement mortar by the b-value analysis of acoustic emission technique

Notched three point bend (TPB) specimens made with plain concrete and cement mortar were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and simultaneously acoustic emissions (AE) released were recorded during the experiments. Amplitude distribution analysis of AE released during concrete was carried out to study the development of fracture process in concrete and mortar specimens. The slope of the log-linear frequency-amplitude distribution of AE is known as the AE based b-value. The AE based b-value was computed in terms of physical process of time varying applied load using cumulative frequency distribution (Gutenberg-Richter relationship) and discrete frequency distribution (Aki's method) of AE released during concrete fracture. AE characteristics of plain concrete and cement mortar were studied and discussed and it was observed that the AE based b-value analysis serves as a tool to identify the damage in concrete structural members. (C) 2012 Elsevier Ltd. All rights reserved.

An approach to multi-temporal MODIS image analysis using image classification and segmentation

This paper discusses an approach for river mapping and flood evaluation based on multi-temporal time series analysis of satellite images utilizing pixel spectral information for image classification and region-based segmentation for extracting water-covered regions. Analysis of MODIS satellite images is applied in three stages: before flood, during flood and after flood. Water regions are extracted from the MODIS images using image classification (based on spectral information) and image segmentation (based on spatial information). Multi-temporal MODIS images from ``normal'' (non-flood) and flood time-periods are processed in two steps. In the first step, image classifiers such as Support Vector Machines (SVMs) and Artificial Neural Networks (ANNs) separate the image pixels into water and non-water groups based on their spectral features. The classified image is then segmented using spatial features of the water pixels to remove the misclassified water. From the results obtained, we evaluate the performance of the method and conclude that the use of image classification (SVM and ANN) and region-based image segmentation is an accurate and reliable approach for the extraction of water-covered regions. (c) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

Nonstoichiometry, defects and thermodynamic properties of YFeO3, YFe2O4 and Y3Fe5O12

Oxygen nonstoichiometry of three ternary oxides. YFeO3-delta, YFe2O4-alpha and Y3Fe5O12-theta. in the system Y-Fe-O was investigated as a function of oxygen partial pressure by thermogravimetry at high temperature. The defects responsible for nonstoichiometry were identified as oxygen vacancies for YFeO3-delta and YFe2O4-alpha although the manner of variation of nonstoichiometric parameter with oxygen partial pressure for these two oxides is quite different. Cation interstitials are the predominant defects in Y3Fe5O12-theta. Gibbs energies of formation of the three nonstoichiometric oxides were determined using solid-state electrochemical cells in the temperature range from 975 to 1475 K. YFe2O4-alpha was found to be stable only above 1391 K. Gibbs energies of formation of the three stoichiometric compounds from their component binary oxides were obtained by combining information from solid state cells with results of thermogravimetric analysis using the Gibbs-Duhem relation. The results can be summarized as: (1/2)Y2O3 + (1/2)Fe2O3 -> YFeO3;Delta G(f(ox))(O)(+/- 250)(J/mol) = 17, 126-8.263T (1/2)Y2O3 + FeO + (1/2)Fe2O3 -> YFe2O4;Delta G(f(ox))(O)(+/- 260)(J/mol) = -10,352-13.24T (3/2)Y2O3 + (5/2)Fe2O3 -> Y3Fe5O12;Delta G(f(ox))(O)(+/- 780)(J/mol) = -56, 647-31.091T. (C) 2012 Elsevier B.V. All rights reserved.

Premixed flame response to equivalence ratio fluctuations: Comparison between reduced order modeling and detailed computations

Combustion instability events in lean premixed combustion systems can cause spatio-temporal variations in unburnt mixture fuel/air ratio. This provides a driving mechanism for heat-release oscillations when they interact with the flame. Several Reduced Order Modelling (ROM) approaches to predict the characteristics of these oscillations have been developed in the past. The present paper compares results for flame describing function characteristics determined from a ROM approach based on the level-set method, with corresponding results from detailed, fully compressible reacting flow computations for the same two dimensional slot flame configuration. The comparison between these results is seen to be sensitive to small geometric differences in the shape of the nominally steady flame used in the two computations. When the results are corrected to account for these differences, describing function magnitudes are well predicted for frequencies lesser than and greater than a lower and upper cutoff respectively due to amplification of flame surface wrinkling by the convective Darrieus-Landau (DL) instability. However, good agreement in describing function phase predictions is seen as the ROM captures the transit time of wrinkles through the flame correctly. Also, good agreement is seen for both magnitude and phase of the flame response, for large forcing amplitudes, at frequencies where the DL instability has a minimal influence. Thus, the present ROM can predict flame response as long as the DL instability, caused by gas expansion at the flame front, does not significantly alter flame front perturbation amplitudes as they traverse the flame. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Comparison of rhodamine B degradation under UV irradiation by two phases of titania nano-photocatalyst

Titania (TiO2) nano-photocatalysts, with different phases, prepared using a modified sol-gel process were employed in the degradation of rhodamine at 10 mg L-1 concentration. The degradation efficiency of these nano-photocatalysts was compared to that of commercial Degussa P25 titania. It was found that the nanocatalysts calcined at 450 degrees C and the Degussa P25 titania had similar photoreactivity profiles. The commercial Degussa P25 nanocatalysts had an overall high apparent rate constant of (K-app) of 0.023 min(-1). The other nanocatalyst had the following rate constants: 0.017, 0.0089, 0.003 and 0.0024 min(-1) for 450, 500, 550 and 600 degrees C calcined catalysts, respectively. This could be attributed to the phase of the titania as the anatase phase is highly photoactive than the other phases. Furthermore, characterisation by differential scanning calorimetry showed the transformation of titania from amorphous to anatase and finally to rutile phase. SEM and TEM characterisations were used to study the surface morphology and internal structure of the nanoparticles. BET results show that as the temperature of calcinations was raised, the surface area reduced marginally. X-ray diffraction was used to confirm the different phases of titania. This study has led to a conclusion that the anatase phase of the titania is the most photoactive nanocatalyst. It also had the highest apparent rate constant of 0.017 min(-1), which is similar to that of the commercial titania.

An EQCM investigation of capacitance of MnO2 in electrolytes containing multivalent cations

MnO2 is electrochemically deposited on Au coated quartz crystal to study the electrochemical capacitance properties and to monitor the mass variations that accompany reversible adsorption/desorption of Na+, Mg2+ and La3+ ions during discharge/charge cycling. There is an increase in the values of specific capacitance of MnO2 with increase in charge of the cation in the electrolyte. Also, there is an increase in mass during discharge due to adsorption of cations from the electrolyte resulting from reduction of MnO2. Mass decreases during charging process due to desorption of cations. The magnitude of mass variation is approximately proportional to the atomic weight of the cationic element. (C) 2012 Elsevier B.V. All rights reserved.

Efficient external memory structures for range-aggregate queries

We present external memory data structures for efficiently answering range-aggregate queries. The range-aggregate problem is defined as follows: Given a set of weighted points in R-d, compute the aggregate of the weights of the points that lie inside a d-dimensional orthogonal query rectangle. The aggregates we consider in this paper include COUNT, sum, and MAX. First, we develop a structure for answering two-dimensional range-COUNT queries that uses O(N/B) disk blocks and answers a query in O(log(B) N) I/Os, where N is the number of input points and B is the disk block size. The structure can be extended to obtain a near-linear-size structure for answering range-sum queries using O(log(B) N) I/Os, and a linear-size structure for answering range-MAX queries in O(log(B)(2) N) I/Os. Our structures can be made dynamic and extended to higher dimensions. (C) 2012 Elsevier B.V. All rights reserved.

Catalytic activity of Peptidase N is required for adaptation of Escherichia coli to nutritional downshift and high temperature stress

Peptidase N (PepN), the sole M1 family member in Escherichia coli, displays broad substrate specificity and modulates stress responses: it lowers resistance to sodium salicylate (NaSal)-induced stress but is required during nutritional downshift and high temperature (NDHT) stress. The expression of PepN does not significantly change during different growth phases in LB or NaSal-induced stress; however, PepN amounts are lower during NDHT stress. To gain mechanistic insights on the roles of catalytic activity of PepN in modulating these two stress responses, alanine mutants of PepN replacing E264 (GAMEN motif) and E298 (HEXXH motif) were generated. There are no major structural changes between purified wild type (WT) and mutant proteins, which are catalytically inactive. Importantly, growth profiles of Delta pepN upon expression of WT or mutant proteins demonstrated the importance of catalytic activity during NDHT but not NaSal-induced stress. Further fluorescamine reactivity studies demonstrated that the catalytic activity of PepN is required to generate higher intracellular amounts of free N-terminal amino acids; consequently, the lower growth of Delta pepN during NDHT stress increases with high amounts of casamino acids. Together, this study sheds insights on the expression and functional roles of the catalytic activity of PepN during adaptation to NDHT stress. (C) 2012 Elsevier GmbH. All rights reserved.

Measurement and correlation of quaternary solubilities of dihydroxybenzene isomers in supercritical carbon dioxide

The equilibrium quaternary solubilities of dihydroxybenzene (resorcinol + pyrocatechol + hydroquinone + SCCO2) isomers were experimentally determined at 308, 318 and 328K over a pressure range of 9.8-15.7 MPa by using a saturation method. The effects of temperature, pressure and the components on each other have been thoroughly investigated. The selectivity of SCCO2 for ternary (resorcinol + pyrocatechol + SCCO2) and quaternary systems was discussed. A new model equation for quaternary solubilities of solids has been developed by accounting for non-idealities by combining the solution model with Wilson activity coefficient model. The model equation has five adjustable parameters and correlates the quaternary solubilities of current data along with two other quaternary data reported in the literature. (C) 2012 Elsevier B.V. All rights reserved.

Threshold voltage model for accumulation mode polycrystalline SOI MOSFETs and comparisons with experimental results

In this paper, a simple but accurate semi analytical charge sheet model is presented for threshold voltage of accumulation mode polycrystalline silicon on insulator (PSOI) MOSFETs. In this model, we define the threshold voltage (V-T) of the polysilicon accumulation mode MOSFET as the gate voltage required to raise the surface potential (phi(s)) to a value phi(sT) necessary to overcome the charge trapping in the grain boundary and to create channel accumulation charge that is equal to the channel accumulation charge available in the case of single crystal silicon accumulation mode MOSFET at that phi(sT). The correctness of the model is demonstrated by comparing the theoretically estimated values of threshold voltage with the experimentally measured threshold voltages on the accumulation mode PSOI MOSFETs fabricated in the laboratory using LPCVD polysilicon layers doped with boron to achieve dopant densities in the range 3.3 x 10(-15)-5 x 10(17)/cm(3). Further, it is shown that the threshold voltage values of accumulation mode PSOI MOSFETs predicted by the present model match very closely with the experimental results, better than those obtained with the models previously reported in the literature. (C) 2012 Elsevier B.V. All rights reserved.

Mesostructured-aluminosilicate-Nafion hybrid membranes for direct methanol fuel cells

Organic-inorganic hybrid membranes are prepared from Nafion and acid functionalized aluminosilicate with varying structures and surface areas. Acid-functionalized mesostructured aluminosilicate with cellular foam framework (Al-MSU-F type) of surface area 463 m(2) g(-1), acid-functionalized aluminosilicate molecular sieves (Al-HMS type) of surface area 651 m(2) g(-1) and acid-functionalized mesostructured aluminosilicate with hexagonal network (Al-MCM-41 type) of surface area 799 m(2) g(-1) have been employed as potential filler materials to form hybrid membranes with Nafion. The structural behavior, water uptake, ion-exchange capacity, proton conductivity and methanol permeability of the hybrid membranes are extensively investigated. Direct methanol fuel cells (DMFCs) with Al-HMS-Nafion and Al-MCM-41-Nafion hybrid membranes deliver respective peak power-densities of 170 mW cm(-2) and 246 mW cm(-2), while a peak power-density of only 48 mW cm(-2) is obtained for the DMFC employing pristine recast-Nafion membrane under identical operating conditions. The unique properties associated with hybrid membranes could be exclusively attributed to the presence of pendant sulfonic-acid groups in the filler materials, which provide proton-conducting pathways between the filler and matrix in the hybrid membranes, and facilitate proton transport with adequate balance between proton conductivity and methanol permeability. (C) 2012 Elsevier Ltd. All rights reserved.

Surface modification and paclitaxel drug delivery of folic acid modified polyethylene glycol functionalized hydroxyapatite nanoparticles

Nanoparticles are used for a number of biomedical applications. In this work we report the synthesis of folic acid (FA) modified polyethylene glycol (PEG) functionalized hydroxyapatite (HAp) nanoparticles. The anticancer drug, paclitaxel, is attached to the folic acid modified polyethylene glycol functionalized hydroxyapatite nanoparticles and the in vitro drug release is analyzed. The surface modification and functionalization is confirmed by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA) and UV spectroscopy. The importance of the paper is the investigation of the release behavior of paclitaxel conjugated folic acid modified polyethylene glycol functionalized hydroxyapatite nanoparticles. The results show an initial rapid release and then a sustained release. (C) 2012 Elsevier B.V. All rights reserved.