Simplified transonic integral equations for lifting profiles and wings

Summary The basic small perturbation integral equations for steady inviscid transonic flow past a thin cambered profile at small incidence have been simplified here using Oswatitsch substitution for the velocity field in terms of that on the profile axis. The resulting equations contain only one-dimensional singular integrals. These equations represent simplification of the equations of Nixon and Hancock [3], from which the two-dimensional camber integrals have been eliminated. Also the corresponding simplified equations for a thin lifting wing have been derived, which contain only two-dimensional singular integrals.     

Diseases associated with Helicobacter pylori

As our knowledge of dental caries and periodontal diseases has increased, our perspective has changed from viewing these diseases as ubiquitous to one which sees a variety of risk profiles in a population. Now, from a perspective of assigning risk, caries and periodontitis can be thought to be more like some of our common medical conditions, i.e., certain people or subgroups of the population are at higher risk than others and that prevention and intervention involve a combination of personal behaviors and professional practices. Research into risk assessment, however, is often hampered by confusing and ambiguous use of terminology. This commentary proposes some specific definitions for terms used in risk assessment in dentistry. These terms include risk factor, risk indicator, demographic risk factor, risk predictor (risk marker), prognostic factor, risk model, and prediction model.     

Representation of motion boundaries in retinotopic human visual cortical areas

Edges are important in the interpretation of the retinal image. Although luminance edges have been studied extensively, much less is known about how or where the primate visual system detects boundaries defined by differences in surface properties such as texture, motion or binocular disparity. Here we use functional magnetic resonance imaging (fMRI) to localize human visual cortical activity related to the processing of one such higher-order edge type: motion boundaries. We describe a robust fMRI signal that is selective for motion segmentation. This boundary-specific signal is present, and retinotopically organized, within early visual areas, beginning in the primary visual cortex (area V1). Surprisingly, it is largely absent from the motion-selective area MT/V5 and far extrastriate visual areas. Changes in the surface velocity defining the motion boundaries affect the strength of the fMRI signal. In parallel psychophysical experiments, the perceptual salience of the boundaries shows a similar dependence on surface velocity. These results demonstrate that information for segmenting scenes by relative motion is represented as early as V1.     

Cationization of cotton for industrial scale salt-free reactive dyeing of garments

Reactive dyeing of cotton garments involves two stages, namely exhaustion and fixation of dyes. The exhaustion stage in reactive dyeing requires high quantity of salt. After dyeing process, the highly saline coloured effluent is discharged and the treatment of this effluent at present is not economically viable and making industries look for other alternatives for usage of salt. Cationization of cotton is one of the effective alternatives to overcome the usage of the salt. The present work focuses on the exhaust method of cationization of garments at an industrial scale using 3-chloro-2-hydroxypropyl trimethylammonium chloride as a cationic agent. Two commercially popular reactive dyes namely Navy Blue and Green dyes were chosen for dyeing the garments at 10% shade. The results of dyeing were evaluated on the basis of colour strength, dyeing levelness and colour fastness. The uniformity of dye on the fabrics was evaluated based on dyeing levelness and was found to be good for cationized cotton dyed garments. The fastness properties of dyed fabrics to washing and light were good. The dye utilization in the cationized cotton dyed garments was twice as that of the conventionally dyed cotton garments. The environmental hazard posed by the highly saline coloured effluent could be easily mitigated by the salt-free reactive dyeing process.     

Separation of phenol–water mixture by membrane pervaporation using polyimide membranes

Separation of components of aqueous waste streams containing organic pollutants is not only industrially very important but also is a challenging process. In this study, separation of a phenol–water mixture was carried out by using a membrane pervaporation technique with indigenously developed polyimide membranes. The membranes were found to permeate water selectively. The total flux as well as that of the individual components were measured. The effect of lithium chloride modification of polyimide film on total flux was investigated. The total flux obtained with 2% lithium chloride modification was about 3.6 times higher than that obtained with virgin membrane. The effects of different parameters such as feed composition and temperature on flux, and separation factor were determined. With modified membrane, a separation factor as high as 18.0 was obtained for water at 27°C and with 8.0 wt % phenol solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 822–829, 2002     

Modeling of bubble-size distribution in free rise polyurethane foams

The existing models of the foaming process in reaction injection molding are inadequate for predicting the bubble-size distribution, which influences many properties of interest. This work attempts to develop a model for the bubble-size distribution under conditions of free rise. The population balance equation for bubbles, coupled with the system of energy balance and reaction kinetics equations through the blowing agent evaporation rate expression, is solved to obtain the bubble-size distribution. A simple mass-transfer coefficient approach for expressing growth rate of bubbles is used, although various growth laws can be accommodated without affecting the solution procedure. Determining factors for the bubble size and its distribution are the foaming period and the growth law. With increase in initial blowing agent concentration, the foaming period increases and bigger bubbles are obtained. The bubble-size distribution becomes broader as the foaming period increases.     

Polyimide and nylon 6 blend film: Preparation,characterization and thermal behavior

A polyimide blend system has been prepared from a base polyimide of BTDAODA by adding ε‐caprolactam at the poly(amic acid) stage where ε‐caprolactam undergoes polymerization to form nylon 6 during the thermal cyclodehydration of poly(amic acid). The blend has been characterized by elemental analysis. IR, ¹³C CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA and DTA) shows that the stability of the blend systems is more in the lower temperature region (up to 300°C) in comparison to the control polyimide system. The isothermal study at 400°C in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400°C shows that the thermooxidative stability of the blend films (except BB 4) is higher. Also, isothermal study in air at 500°C shows more than 90% weight loss for all the films within 3 h, but in an inert atmosphere, the blend films show lower weight loss compared to the control film. Although the XRD pattern of all the blend and control films shows an amorphous character, the films developed some crystallinity when treated with boiling NMP where the blend films developed higher crystallinity.     

Distributed consensus control for multi‐agent systems using terminal sliding mode and Chebyshev neural networks

This paper investigates the problem of consensus tracking control for second‐order multi‐agent systems in the presence of uncertain dynamics and bounded external disturbances. The communication ?ow among neighbor agents is described by an undirected connected graph. A fast terminal sliding manifold based on lumped state errors that include absolute and relative state errors is proposed, and then a distributed finite‐time consensus tracking controller is developed by using terminal sliding mode and Chebyshev neural networks. In the proposed control scheme, Chebyshev neural networks are used as universal approximators to learn unknown nonlinear functions in the agent dynamics online, and a robust control term using the hyperbolic tangent function is applied to counteract neural‐network approximation errors and external disturbances, which makes the proposed controller be continuous and hence chattering‐free. Meanwhile, a smooth projection algorithm is employed to guarantee that estimated parameters remain within some known bounded sets. Furthermore, the proposed control scheme for each agent only employs the information of its neighbor agents and guarantees a group of agents to track a time‐varying reference trajectory even when the reference signals are available to only a subset of the group members. Most importantly, finite‐time stability in both the reaching phase and the sliding phase is guaranteed by a Lyapunov‐based approach. Finally, numerical simulations are presented to demonstrate the performance of the proposed controller and show that the proposed controller exceeds to a linear hyperplane‐based sliding mode controller. Copyright © 2011 John Wiley & Sons, Ltd.     

Nuclear magnetic relaxation dispersion investigations of water retention mechanism by cellulose ethers in mortars

We show how nuclear magnetic spin–lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism.