Finite element thermo-viscoplastic analysis of aerospace structures

The time-dependent thermo-viscoplastic response of aerospace structures subjected to intense aerothermal loads is predicted using the finite-element method. The finite-element analysis uses the Bodner-Partom unified viscoplastic constitutive relations to determine rate-dependent nonlinear material behavior. The methodology is verified by comparison with experimental data and other numerical results for a uniaxially-loaded bar. The method is then used (1) to predict the structural response of a rectangular plate subjected to line heating along a centerline, and (2) to predict the thermal-structural response of a convectively-cooled engine cowl leading edge subjected to aerodynamic shock-shock interference heating. Compared to linear elastic analysis, the viscoplastic analysis results in lower peak stresses and regions of plastic deformations

Thermal-structural finite element analysis using linear flux formulation

A linear flux approach is developed for a finite element thermal-structural analysis of steady state thermal and structural problems. The element fluxes are assumed to vary linearly in the same form as the element unknown variables, and the finite element matrices are evaluated in closed form. Since numerical integration is avoided, significant computational time saving is achieved. Solution accuracy and computational speed improvements are demonstrated by solving several two and three dimensional thermal-structural examples

Finite element flow-thermal-structural analysis of aerodynamically heated leading edges

Hypersonic vehicles operate in a hostile aerothermal environment which has a significant impact on their aerothermostructural performance. Significant coupling occurs between the aerodynamic flow field, structural heat transfer, and structural response creating a multidisciplinary interaction. A long term goal of the Aerothermal Loads Branch at the NASA Langley Research Center is to develop a computational capability for integrated fluid, thermal and structural analysis of aerodynamically heated structures. The integrated analysis capability includes the coupling between the fluid and the structure which occurs primarily through the thermal response of the structure, because: (1) the surface temperature affects the external flow by changing the amount of energy absorbed by the structure, and (2) the temperature gradients in the structure result in structural deformations which alter the flow field and attendant surface pressures and heating rates. In the integrated analysis, a finite element method is used to solve: (1) the Navier-Stokes equations for the flow solution, (2) the energy equation of the structure for the temperature response, and (3) the equilibrium equations of the structure for the structural deformation and stresses

Interface induced perpendicular magnetic anisotropy in Co/CoO/Co thin film structure: An in-situ MOKE investigation

Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic properties have been investigated using in-situ magneto-optic Kerr effect during growth of the sample. Magnetic anisotropy with easy axis perpendicular to the film surface has been observed in top Co layer, whereas bottom layer was found to be soft with in-plane magnetization without any influence of top layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that the growth of Co on oxidized interface takes place with preferential orientation of c-axis perpendicular to the film plane, which results in the observed perpendicular magnetic anisotropy. Texturing of the c-axis is expected to be a result of minimization of the interface energy due to hybridization between Co and oxygen at the interface.Comment: 9 pages, 3 figures, under review in IOP journa

A Scheme for Efficient Subsidisation of Kerosene in India

The distortions in price based subsidisation are very severe. The direct fiscal cost of ensuring that a rupee of value is delivered to all household users of kerosene is as high as Rs.3 and when the consideration is the benefit that finally reaches the poor “below the poverty line” consumers it is much more. This is well known. This excludes the indirect costs in the form of negative externalities imposed by adulteration, and environmental costs. Worse still are the “third order” effects of entrenched rent seeking and corruption of distribution networks and the conversion of retailing to patronage. In such situation reform and deregulation become problematic. At the core of all these failures in the “price arbitrage” that arises when price based subsidies are resorted to. The total fiscal losses on account of kerosene subsidisation are in excess of Rs. 24,000 crore far above the conventional estimates (around Rs. 8000 – 10,000 crore) which do not recognise the fiscal cost of diversion and adulteration. This paper studies the current design of the public distribution system and price based subsidisation to bring out the perversities, and argues that a complete replacement is called for. The Public Distribution System (PDS) which had value in an era of shortage and rationing has no role today. Market based distribution can bring down the direct costs since now kerosene distribution could then enjoy the synergies of oil and provisions distribution channels. There is clear evidence that a significant percentage (about 40) of kerosene is diverted out of the PDS and sold at higher prices. The commission paid to the distribution channel, in particular to the retailers of kerosene does not make the business financially viable. The rents being earned by those associated with the distribution channel for kerosene are very large. The rent extractors have become so well entrenched over time that it is plausible that other agencies in the system and even the regulatory process itself may be hostage today to their influences. The indirect losses from use of sub-optimal fuel mix, product mix and investment decisions are very large and may harm the economy significantly in the long term. The subsidy through uniform low pricing of kerosene, though intended for the poor, is in fact not reaching them as they are in no position to buy much of the kerosene allotted to them even at the low issue prices being charged by the fair price shops. It is imperative to bring into play information and communication technologies so as to break the stranglehold of the distribution channel by capturing information at the point of sale and thereby creating a permanent audit trail of all relevant transactions. Only by empowering the target segment, the BPL families, by providing them with the freedom to choose the manner in which they would like to consume the subsidy intended for them can the problem be overcome. The well-documented failure of TPDS (Targeted Public Distribution System), implemented on an experimental basis, clearly demonstrates that tinkering with the existing system would not achieve the twin goal of benefiting the really poor and not-benefiting the non-poor. The direct subsidy scheme, which is based on free market pricing of kerosene, and therefore a radical departure from the current method of uniform low pricing is the answer for achieving effectiveness of subsidization. The subsidy is to be disbursed to the poor through smart cards and the accounting of disbursal is to be done using systems similar to those used by credit card companies. The purchasing power put in the hands of the beneficiaries would allow them to use it for spending on their choice of commodities and services and thereby not only enhance the use of subsidy to the full but would also add greatly to their welfare. The proposed system would almost completely eliminate the indirect losses arising from distorted choices since the price of kerosene would be market determined and therefore not relatively cheap compared to alternate fuels. A task force (TF) must be set-up for implementation, with wide-ranging powers and full financial backing of the government of India so as to be able to function autonomously. The task force should consist of eminently qualified individuals with diverse skills and known for their integrity and appreciation for the significance of the task to be performed. The critical task of identifying the beneficiaries at micro-level should be done using all possible sources of data and information (outlined in the report) so as to minimize both, Type I and Type II errors, that is, chance of exclusion of genuine beneficiary and chance of inclusion of spurious beneficiary in the list of target beneficiaries. There are interesting ways by which private information can be brought to bear, and incentive compatibility ensured in correct identification. The disbursement of subsidy should be such that the disbursement is recorded at the point of transaction and get immediately captured in a large centralized database, thereby creating a permanent audit trail, akin to operation of credit cards (details outlined in the report). The activities associated with initial identification of beneficiaries, disbursement of subsidies and updating the list of beneficiaries is to be done by well-qualified private agencies. The operations of the system should be monitored by an SPV to be specially created for the purpose and working under the broad supervision and direction of the task force. The SPV and the TF should ensure full transparency of operation of the private vendor and the scheme by making public all relevant information on the operation of the system and opting for periodic audit of operations. The appropriate organisation design and policy framework for the same is elaborated. The immediate gain to the exchequer from the proposed system, due to market based pricing of kerosene would be an estimated inflow of Rs. 14000 crore per year by way of additional taxes. This gain from additional taxes, based on certain assumptions, is expected to rise to over Rs. 37000 crore in 2010-11, at Jan. 2006 petroleum prices. The gain to the economy and society at large from elimination of indirect losses due to sub-optimal choices of fuel-mix, product-mix, and asset mix would be immense as they would be completely eliminated in the new system. The most important gain however is that the beneficiaries would be in a position to fully utilize their entitlements and spend the same on products and services of their choice, significantly enhancing thereby the utility of their consumption. This should also make direct subsidies politically rewarding.

Inhibitory activity of Indian spice plant Cinnamomum zeylanicum extracts against Alternaria solani and Curvularia lunata, the pathogenic dematiaceous moulds

<p>Abstract</p> <p>Background</p> <p>Dematiaceous moulds are pathogenic microorganisms and act as etiological agents of mycoses with different degrees of severity in humans and animals. These moulds also cause loss of food crops and storage food products. The information regarding antimicrobial efficacy of the plant preparations on these moulds is scanty. The present study reveals phytochemical characterization and the effect of bark and leaf extracts of Indian spice plant, <it>Cinnamomum zeylanicum </it>(Cz), against the growth of two species of dematiaceous moulds, <it>Alternaria solani </it>and <it>Curvularia lunata</it>.</p> <p>Methods</p> <p>Cz bark and leaf samples were sequentially extracted in different solvents using Soxhlet apparatus. Phytochemical analyses of extracts were done as per standard protocols. The antifungal bioassay of extracts was done by hanging drop technique. The inhibition of fungal spore germination was monitored under influence of three different concentrations of extracts.</p> <p>Results</p> <p>The lowest test concentration (50 μg/ml) of extracts of Cz bark prepared into acetone and that of Cz leaf into petroleum ether and ethanol exhibited complete inhibition (100%) of spore germination in both the moulds. At 100 μg/ml concentration all the extracts showed about 50 to 100% inhibition. However, the treatment of the spores of the two fungal species with highest concentration (500 μg/ml) of bark and leaf extracts in all the solvents showed 100% fungicidal activity as it completely arrested the germination of spores. Relatively lower activity of aqueous extracts at 50 and 100 μg/ml concentrations suggests that the antifungal ingredients present in Cz bark and leaf are more soluble in organic solvents than water.</p> <p>Conclusion</p> <p>The results demonstrated that the Cz bark and leaves contain certain fungicidal constituents exhibiting potential antimould activity against <it>A. solani </it>and <it>C. lunata</it>.</p

Estimation of leakage power and delay in CMOS circuits using parametric variation

SummaryWith the advent of deep-submicron technologies, leakage power dissipation is a major concern for scaling down portable devices that have burst-mode type integrated circuits. In this paper leakage reduction technique HTLCT (High Threshold Leakage Control Transistor) is discussed. Using high threshold transistors at the place of low threshold leakage control transistors, result in more leakage power reduction as compared to LCT (leakage control transistor) technique but at the scarifies of area and delay. Further, analysis of effect of parametric variation on leakage current and propagation delay in CMOS circuits is performed. It is found that the leakage power dissipation increases with increasing temperature, supply voltage and aspect ratio. However, opposite pattern is noticed for the propagation delay. Leakage power dissipation for LCT NAND gate increases up to 14.32%, 6.43% and 36.21% and delay decreases by 22.5%, 42% and 9% for variation of temperature, supply voltage and aspect ratio. Maximum peak of equivalent output noise is obtained as 127.531nV/Sqrt(Hz) at 400mHz