Study of corrosive fatigue and life enhancement of low pressure steam turbine blade using friction dampers

The paper investigates the causes of failure of low pressure steam turbine blade of the last stage and suggests few techniques to overcome the failure causes is presented in this paper. The blade under investigation is made of chrome alloy steel. The fracture occurred at the airfoil region of the blade. The investigation included visual inspection, micro structural characterization, SEM-EDS microanalysis and spectroscopy test to identify the causes of failure. The paper also suggests the methods to reduce the blade fatigue subsequently through computation and to enhance the fatigue strength of the steam turbine blade. In order to reduce the blade fatigue susceptibility and to enhance the fatigue life of the steam turbine blade, the wedge shape friction damper is proposed.     

Mechanical and gas permeation properties of compatibilized polypropylene–layered silicate nanocomposites

Nanocomposites of polypropylene with montmorillonite modified with dimethyldioctadecylammonium ions were prepared and the effect of compatibilizers on the mechanical and permeation properties was investigated. Compatibilizers were selected on the basis of their chemical nature, molecular weight, amount of grafting and location of the polar groups. Addition of small amount of compatibilizers led to improvements in the basal spacings of clay platelets indicating enhanced exfoliation. The modulus of the composites increased as compared with the values without compatibilizer. The oxygen permeation through the composite films either increased or remained unaffected due to possible interfacial free volume enhancement owing to the incompatibility of the surface modification and the compatibilizer. Increasing the amount of compatibilizer also increased correspondingly the extent of exfoliation. The modulus reached a plateau value after which the increasing compatibilizer led to its decrease. The gas permeation through the composite films remained unchanged with increase in the amount of compatibilizer owing to a possible balance between the decrease in permeation due to path tortuity and exfoliation and increase in permeation due to interfacial incompatibility. The improving exfoliation improved the yield and break stress indicating that the absence of tactoids can hinder the premature failure owing to better stress transfer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Velocity-based time-discontinuous Galerkin space-time finite element method for elastodynamics

A velocity-based single-field Space-Time Finite Element Method (v-ST/FEM) is devised within the framework of the time-discontinuous Galerkin method for an elastodynamics problem. The new method uses finite elements for both space and time domains, and reduces the size of the resulting linear system to be solved in each time step compared to the two-field formulation. In v-ST/FEM, the trial functions for the velocity field are continuous in space and discontinuous in time, while the test functions are continuous in both space and time. The displacement and stress fields are computed in a post-processing step using the time-integration process which explicitly includes the velocity field. Accordingly, the displacement-velocity compatibility condition and the continuity of the displacement field in time are strongly imposed in the displacement-velocity-based two-field formulation. In this way, a velocity-based single-field weak formulation is derived from the two-field formulation. The present method is found to be unconditionally stable and third-order accurate. Following a review of the space–time finite element literature, the general theoretical development and formulation aspects of the present methodology are demonstrated. Several numerical examples are given to show the computational performance of the proposed scheme.     

Electronic and Optical Modeling of Solar Cell Compounds CuGaSe<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript>

We present dielectric-function-related optical properties such as absorption coefficient, refractive index, and reflectivity of the semiconducting chalcopyrites CuGaSe₂ and CuInSe₂. The optical properties were calculated in the framework of density functional theory (DFT) using linear combination of atomic orbitals (LCAO) and full-potential linearized augmented plane wave (FP-LAPW) methods. The calculated spectral dependence of complex dielectric functions is interpreted in terms of interband transitions within energy bands of both chalcopyrites; for example, the lowest energy peak in the e₂ (w) \varepsilon_{2} (\omega ) spectra for CuGaSe₂ corresponds to interband transitions from Ga/Se-4p → Ga-4s while that for CuInSe₂ emerges as due to transition between Se-4p → In-5s bands. The calculated dielectric constant, e₁ (0) \varepsilon_{1} (0) , for CuInSe₂ is higher than that of CuGaSe₂. The electronic structure of both compounds is reasonably interpreted by the LCAO (DFT) method. The optical properties computed using the FP-LAPW model (with scissor correction) are close to the spectroscopic ellipsometry data available in the literature.     

A study on drying of textile substrates and a new concept for the enhancement of drying rate

Gravimetric absorption test system (GATS) is used to measure the absorption capacity, absorption rate and drying rate of knit hoses, prepared from different fibres. The fibres studied are cotton, polyester and variety of modified polyesters. The study has shown that desorption or drying rate is at least two orders of magnitude lower than absorption rate. This finding implies that drying is the limiting process in moisture management. Further experiments on knit fabrics made from polyester and cotton, show that the drying rates are independent of fibre type in the constant-rate period, while the drying rates in the falling-rate period are dependent on fibre type. Subsequently, it is shown on the polyester fabric that drying rate in the falling-rate period depends on water concentration. Based on this understanding, an approach for enhancing drying rate in the falling-rate period is defined. The approach is demonstrated on knit hoses prepared from cotton and polyester yarns in alternating stripe form. The drying rate in the falling-rate period is found to be higher in the polyester-cotton stripe knit hose. A hypothesis for the observed enhancement in drying rate by wicking is put forth in terms of the internal movement of water from polyester to cotton portion. Experimentally, it is shown that 16% improvement in drying time is achieved in the case of the polyester–cotton stripe samples. Further, indications of internal water movement from polyester to cotton portion have been obtained by tracking the surface temperatures of the knit hoses during drying by infrared (IR) thermography.     

Parallel support vector architectures for taxonomy of radial pulse morphology

Application of impedance plethysmography (IP) for impedance measurement is the paradigm in assessment of central and peripheral blood flow. We propose the expediency of IP to unearth hidden patterns from Plethysmographic observations on a radial pulse. The variability analysis in one thousand control and disease subjects evolves an archetype of eight different morphological patterns. The peripheral pulse waveforms not only characterize the physiology of control subjects, but also define the morphology of patients suffering from Myocardial Infarction, cirrhosis of liver, and disorder of lungs. Diverse parallel support vector machine (pSVM) topologies are designed as an aid to the physician for multiclass pattern recognition problem. Besides a lowest confusion coefficient (0.133), the PCA-based pSVM classifier offers a comparatively higher generalized correlation coefficient and κ value of 0.6586 and 0.8407, respectively. However, the ROC characteristics and the benchmark parameters suggest that wavelet-based pSVM is the optimum classifier with a sensitivity of 85.33 %, an elevated MCC (0.69), and a least upper bound on the expected error. pSVM stands out as a model classifier as compared with identified indices such as, Fishers Ratio, Morphology Index, and Heart rate variability.     

Emulation of multipath effects on a wireless testbed and its impact on MAC layer performance

Field experiments are an important part of research in wireless networks. Since the wireless channel varies with location and time, the results vary for the same field experiment at a different place and time. Assumptions about the wireless environment can lead to biased results. It is necessary to shield wireless transmission from uncontrolled interference in order to make the experiment repeatable. This paper describes A\underline{A}dvanced wireleSS\underline{SS} E\underline{E}nvironment R\underline{R}esearch T\underline{T}estbed (ASSERT) which uses shielded co-axial cables as the communication media for radio signals to conduct reliable, scalable and accurate wireless experiments. Shielding the transmission also protects the signal from random burst of noise introduced by the environment. The paper describes how the combination of programmable attenuators and RF splitters/combiners, which are part of ASSERT, helps in emulating complex and varying environments including those in which multipath interference plays a significant role. Our experimental results indicate that (1) tweaking the MAC layer and retransmissions at the application layer neutralize, to an extent, the impact of multipath effects when the received signal strength is extremely good, and (2) when the received signal strength falls below a certain threshold multipath interference plays a significant role.     

Anticancer activity of essential oils: a review

Natural essential oil constituents play an important role in cancer prevention and treatment. Essential oil constituents from aromatic herbs and dietary plants include monoterpenes, sesquiterpenes, oxygenated monoterpenes, oxygenated sesquiterpenes and phenolics among others. Various mechanisms such antioxidant, antimutagenic and antiproliferative, enhancement of immune function and surveillance, enzyme induction and enhancing detoxification, modulation of multidrug resistance and synergistic mechanism of volatile constituents are responsible for their chemopreventive properties. This review covers the most recent literature to summarize structural categories and molecular anticancer mechanisms of constituents from aromatic herbs and dietary plants. © 2013 Society of Chemical Industry