Elastoplastic behavior of metal matrix composites based on incremental plasticity and the Mori-Tanaka averaging scheme

The applicability of the Mori-Tanaka averaging method for the prediction of the response of binary composites loaded in the plastic range is investigated. The applied loading is subdivided into small increments and the Eshelby solution for the inhomogeneity problem is used in conjunction with the Mori-Tanaka averaging scheme to obtain the load increments in the various phases. Since the Eshelby solution depends on the instantaneous matrix material properties and these are updated at the end of each load increment by using the backward difference scheme, an iterative procedure is necessary for the calculation of the correct load increments in the phases (concentration factors). The performance of the Mori-Tanaka method is compared with results obtained using the periodic hexagonal array (PHA) finite element model and experimental results for a B-Al unidirectional fibrous composite; it is also compared with numerical simulations obtained from the modified PHA model for a SiC _w -Al particulate composite.     

Effect of Y-doping on the transport and magnetic properties of La0.5Sr0.5CoO3 and La0.7Sr0.3CoO3

The temperature variation of magnetization, resistivity, and thermoelectric power of undoped and Y-doped La_0.7Sr_0.3CoO₃ and La_0.5Sr_0.5CoO₃ samples have been investigated. Y-doping decreases the magnetization possibly due to the spin-state transition of Co ions. The low temperature conduction in (La_1?y Y _y )_0.7Sr_0.3CoO₃ is consistent with the variable range hopping. With Y-doping, value of the Seebeck coefficient increases as Y-doping decreases bandwidth and increases distortion. Seebeck coefficient value also reflects that the orbital stability increases with Sr concentration.     

ISOTHERMAL FATIGUE BEHAVIOR OF SIGMA/T1METAL 21S LAMINATES,PART I: EXPERIMENTAL RESULTS

Experimental results are reported on the effect of static and cyclic loading (at 0.1 and 0.001 Hz) on the inelastic response of and damage development in (0)4, (0190), and (0/ ±45/90), SiC/Ti (Sigma/Timetal 21S) laminates, and the Timetal 21S matrix, at 650^°C and 21^°C. At the elevated temperature, viscoplastic deformation of the matrix can be observed even at relatively low applied stresses. At both temperatures, reduction of unloading elastic moduli of the laminates, which indicates onset of damage by interface decohesion, also starts after hailing to relatively low stresses. The cyclic loading rate has a significant effect on the number of cycles to failure, but not on the endurance limit of the (0/90), and (0/ ±45/90), laminates loaded by constant-amplitude tension at 650^°C. In the (0)₄ laminate, higher endurance limits were detected at 0.1 Hz than at 0.001 Hz However, regardless of loading rate and layup, the total strain at failure under both static and cyclic loading at 650^°C was measured at 1 ±0.1%. The experimental results are interpreted by micromecha-nical models in Part II [1].     

Transfer function modelling in software reliability

This paper demonstrates the applicability of transfer function model in the field of software reliability. Here a stepwise procedure for fitting a transfer function model has been described and then the prediction of remaining faults in software has been done using the built in model. Some real life data have been used for illustration purpose.     

Group III–V ternary compound semiconductor materials for unipolar conduction in tunnel field-effect transistors

A distinct materials combination is presented for tunnel field-effect transistors (TFETs): gallium arsenide phosphide (GaAsP) as a wider-bandgap material in the drain and channel regions with indium gallium arsenide (InGaAs) as a narrow-bandgap material for the source region. The introduction of this novel materials combination greatly improves the ON-state current, OFF-state current, ambipolar behavior, threshold voltage, and subthreshold slope compared with other group III–V ternary heterojunction TFETs. In GaAsP–InGaAs TFETs, the ambipolar current remains equal to the OFF-state current. This paper explores the potential of the proposed device for ultralow-power high-performance applications.     

Regulated and non-regulated emissions from in-use diesel-electric switching locomotives

Diesel-electric locomotives are vital to the operation of freight railroads in the United States, and emissions from this source category have generated interest in recent years. They are also gaining attention as an important emission source under the larger set of nonroad sources, both from a regulated emissions and health effects standpoint. The present work analyzes regulated (NOx, PM, THC, CO) and non-regulated emissions from three in-use diesel-electric switching locomotives using standardized sampling and analytical techniques. The engines tested in this work were from 1950, 1960, and 1970 and showed a range of NOx and PM emissions. In general, non-regulated gaseous emissions showed a sharp increase as engines shifted from non-idle to idle operating modes. This is interesting from an emissions perspective since activity data shows that these locomotives spend around 60% of their time idling. In terms of polycyclicaromatic hydrocarbon (PAH) contributions, the dominance of naphthalene and its derivatives over the total PAH emissions was apparent, similar to observations for on-road diesel tractors. Among nonnaphthalenic species, itwas observed that lower molecular weight PAHs and n-alkanes dominated their respective compound classes. Regulated emissions from a newer technology engine used in a back-up generator (BUG) application were also compared againstthe present engines; it was determined that use of the newer engine may lower NOx and PM emissions by up to 30%. Another area of interest to regulators is better estimation of the marine engine inventory for port operations. Toward that end, a comparison of emissions from these engines with engine manufacturer data and the newer technology BUG engine was also performed for a marine duty cycle, another application where these engines are used typically with little modifications.     

Antibacterial activity of some Lamiaceae essential oils using resazurin as an indicator of cell growth

The aim of this work was to investigate the antibacterial activity of six Lamiaceae essential oils, against pathogenic and food spoilage bacteria. The chemical profiles of essential oils were evaluated by the means of GC and GC-MS. The major constituents of the oils were 1,8-cineol (29.2%), camphor (17.2%), α-pinene (11.5%) in Rosmarinus officinalis, citronellal (20.5%), β- geraniol (17.0%), β-citronellol (11.5%) in Melissa officinalis, 1,8-cineol (27.4%), α-thujone (16.3%), β-thujone (11.2%), borneol (10.4%), camphor (7.98%) in Salvia officinalis, linalool (25.1%), linalyl acetate (22.5%) in Lavandula angustifolia, thymol (52.4%), p-cymene (17.9%) in Thymus vulgaris and Patcholene alcohol (22.7%), α-bulnesene (17.1%), α-guaine (13.8%) in Pogostemon cablin. On quantitative basis, the amounts of 1,8-cineol, citronellal, 1,8-cineol, linalool, thymol and patchouli alcohol, calculated using calibrated curve with pure standard compounds, in the respective essential oils were found to be 28.4, 19.0, 26.7, 23.3, 51.1 and 21.1 g/100 g of oil, respectively. The modified resazurin microtitre-plate assay was used to evaluate the antibacterial activity of the essential oils and their principal components. All the essential oils analyzed presented inhibitory effects on most of the strains tested. Thymus vulgaris essential oil showed the highest inhibition. It was concluded that modified resazurin assay could be effectively used for reliable assessment of antibacterial activity of the tested essential oils against several Gram positive and negative bacterial taxa. The present results also demonstrated that Lamiaceae essential oils exhibiting higher antibacterial activity were generally rich in oxygenated monoterpens.     

Seasonal variation in content,chemical composition and antimicrobial and cytotoxic activities of essential oils from four Mentha species

BACKGROUND: The aim of the present study was to appraise variation in the chemical composition, and antimicrobial and cytotoxic activities of essential oils from the leaves of four Mentha species—M. arvensis, M. piperita, M. longifolia and M. spicata—as affected by harvesting season. Disc diffusion and broth microdilution susceptibility assays were used to evaluate the antimicrobial activity of Mentha essential oils against a panel of microorganisms. The cytotoxicity of essential oils was tested on breast cancer (MCF‐7) and prostate cancer (LNCaP) cell lines using the MTT assay. RESULTS: The essential oil contents of M. arvensis, M. piperita, M. longifolia and M. spicata were 17.0, 12.2, 10.8 and 12.0 g kg^?1 from the summer and 9.20, 10.5, 7.00 and 9.50 g kg^?1 from the winter crops, respectively. Gas chromatographic–mass spectrometric analysis revealed that mostly quantitative rather than qualitative variation was observed in the oil composition of each species. The principal chemical constituents determined in M. arvensis, M. piperita, M. longifolia and M. spicata essential oils from both seasons were menthol, menthone, piperitenone oxide and carvone, respectively. The tested essential oils and their major components exhibited notable antimicrobial activity against most of the plant and human pathogens tested. The tested essential oils also exhibited good cytotoxicity potential. CONCLUSION: Of the Mentha essential oils tested, M. arvensis essential oil showed relatively better antimicrobial and cytotoxic activities. A significant variation in the content of most of the chemical components and biological activities of seasonally collected samples was documented. Copyright © 2010 Society of Chemical Industry     

Naloxone-induced withdrawal in patients with buprenorphine dependence

Naloxone-induced withdrawal was studied in seven patients currently dependent only on injecting buprenorphine, within 3 to 6 hours of their last dose. Withdrawal severity began to rise from 5 minutes and reached a peak at 60 minutes after 1.2 mg naloxone given intravenously. The mean withdrawal severity score was significantly higher at 30, 60 and 90 minutes compared to the baseline. The most frequent withdrawal signs and symptoms were mydriasis, systolic hypertension, tachypnoea, muscle pains, yawning, anxiety, restlessness and craving.