Mechanical behaviour of aluminium-lithium alloys

Aluminium-lithium alloys hold promise of providing a breakthrough response to the crying need for lightweight alloys for use as structurals in aerospace applications. Considerable worldwide research has gone into developing a range of these alloys over the last three decades. As a result, substantial understanding has been developed of the microstructure-based micromechanisms of strengthening, of fatigue and fracture as well as of anisotropy in mechanical properties. However, these alloys have not yet greatly displaced the conventionally used denser Al alloys on account of their poorer ductility, fracture toughness and low cycle fatigue resistance. This review aims to summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations

FMEA and Fault Tree based Software Safety Analysis of a Railroad Crossing Critical System

Software for safety-critical systems must deal with the hazards identified by safety analysis in order to make the system safe, risk-free and fail-safe. Certain faults in critical systems can result in catastrophic consequences such as death, injury or environmental harm. The focus of this paper is an approach to software safety analysis based on a combination of two existing fault removal techniques. A comprehensive software safety analysis involving a combination of Failure Modes and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) is conducted on the software functions of the critical system to identify potentially hazardous software faults. A prototype safety-critical system - Railroad Crossing Control System (RCCS), incorporating a microcontroller and software to operate the train on a track circuit is described

SACRED LANDSCAPES AS REPOSITORIES OF BIODIVERSITY. A CASE STUDY FROM THE HARIYALI DEVI SACRED LANDSCAPE, UTTARAKHAND

The present study was carried out in the Hariyali Devi sacred landscape of Garhwal Himalaya in Uttarakhand State of India. The study area falls under the jurisdiction of the Forest Department, having the status of reserve forest. The land scape is dedicated to the deity “Hariyali Devi” and that plays a major role in conserving the biodiversity of this land scape. Taboos, rituals and socio-cultural practices are associated with conservation practices. The study recorded 98 plant species, representing 88 genera and 46 families with different economic values. The dominant family was Rosaceae, which recorded the highest (10) number of species. Out of 98 plant species the dominant life form contribution was of herbs (52), shrubs (26) and tree species (21). Almost 82 plants species in the landscape are of medicinal importance, 15 species are used for timber and construction purposes, 19 species with different edible plant parts, such as fruits, flowers, seeds and rhizomes. The information about the uses/economic value of different plant species was gathered directly by interviewing knowledgeable elderly local villagers (including women)

Intramolecular remote functionalisation of steroids by benzophenone- increased specificity by solvent-induced hydrophobic interactions

Proximity of reactant sites is one of the major factors that contributes to specificity and high reaction rates observed in enzyme catalysis. Enzymes achieve this proximity between the reactant sites by having high affinity for the substrate. Structural studies on enzyme-substrate complexes provide sufficient evidence in this context and indicate that weak bonding interaction are involved in formation of such complexes. We have exploited the hydrophobic interaction between cholesterol and benzophenone to carry out photoinduced remote functionalisation of cholesterol at specific sites. Thus, using polar solvents intramolecular hydrophobic interaction between cholesterol and benzophenone permitted exclusive functionalisation of ring D in cholesterol. The current study indicates that weak interactions between the reactants can be used to bring them in proximity and photochemical reactions can provide the method for functionalising even inert sites like C-H bonds

Cellular hysteresis as a principle to maximize the efficacy of antibiotic therapy

Rapid evolution is central to the current antibiotic crisis. Sustainable treatments must thus take account of the bacteria’s potential for adaptation. We identified cellular hysteresis as a principle to constrain bacterial evolution. Cellular hysteresis is a persistent change in bacterial physiology, reminiscent of cellular memory, which is induced by one antibiotic and enhances susceptibility toward another antibiotic. Cellular hysteresis increases bacterial extinction in fast sequential treatments and reduces selection of resistance by favoring responses specific to the induced physiological effects. Fast changes between antibiotics are key, because they create the continuously high selection conditions that are difficult to counter by bacteria. Our study highlights how an understanding of evolutionary processes can help to outsmart human pathogens.Antibiotic resistance has become one of the most dramatic threats to global health. While novel treatment options are urgently required, most attempts focus on finding new antibiotic substances. However, their development is costly, and their efficacy is often compromised within short time periods due to the enormous potential of microorganisms for rapid adaptation. Here, we developed a strategy that uses the currently available antibiotics. Our strategy exploits cellular hysteresis, which is the long-lasting, transgenerational change in cellular physiology that is induced by one antibiotic and sensitizes bacteria to another subsequently administered antibiotic. Using evolution experiments, mathematical modeling, genomics, and functional genetic analysis, we demonstrate that sequential treatment protocols with high levels of cellular hysteresis constrain the evolving bacteria by (i) increasing extinction frequencies, (ii) reducing adaptation rates, and (iii) limiting emergence of multidrug resistance. Cellular hysteresis is most effective in fast sequential protocols, in which antibiotics are changed within 12 h or 24 h, in contrast to the less frequent changes in cycling protocols commonly implemented in hospitals. We found that cellular hysteresis imposes specific selective pressure on the bacteria that disfavors resistance mutations. Instead, if bacterial populations survive, hysteresis is countered in two distinct ways, either through a process related to antibiotic tolerance or a mechanism controlled by the previously uncharacterized two-component regulator CpxS. We conclude that cellular hysteresis can be harnessed to optimize antibiotic therapy, to achieve both enhanced bacterial elimination and reduced resistance evolution

Stochastic slowdown in evolutionary processes

We examine birth--death processes with state dependent transition probabilities and at least one absorbing boundary. In evolution, this describes selection acting on two different types in a finite population where reproductive events occur successively. If the two types have equal fitness the system performs a random walk. If one type has a fitness advantage it is favored by selection, which introduces a bias (asymmetry) in the transition probabilities. How long does it take until advantageous mutants have invaded and taken over? Surprisingly, we find that the average time of such a process can increase, even if the mutant type always has a fitness advantage. We discuss this finding for the Moran process and develop a simplified model which allows a more intuitive understanding. We show that this effect can occur for weak but non--vanishing bias (selection) in the state dependent transition rates and infer the scaling with system size. We also address the Wright-Fisher model commonly used in population genetics, which shows that this stochastic slowdown is not restricted to birth-death processes.Comment: 8 pages, 3 figures, accepted for publicatio

Spin Motion in Electron Transmission through Ultrathin Ferromagnetic Films Accessed by Photoelectron Spectroscopy

Ab initio and model calculations demonstrate that the spin motion of electrons transmitted through ferromagnetic films can be analyzed in detail by means of angle- and spin-resolved core-level photoelectron spectroscopy. The spin motion appears as precession of the photoelectron spin polarization around and as relaxation towards the magnetization direction. In a systematic study for ultrathin Fe films on Pd(001) we elucidate its dependence on the Fe film thickness and on the Fe electronic structure. In addition to elastic and inelastic scattering, the effect of band gaps on the spin motion is addressed in particular.Comment: 4 pages, 5 figure

On the interpretation of spin-polarized electron energy loss spectra

We study the origin of the structure in the spin-polarized electron energy loss spectroscopy (SPEELS) spectra of ferromagnetic crystals. Our study is based on a 3d tight-binding Fe model, with constant onsite Coulomb repulsion U between electrons of opposite spin. We find it is not the total density of Stoner states as a function of energy loss which determines the response of the system in the Stoner region, as usually thought, but the densities of Stoner states for only a few interband transitions. Which transitions are important depends ultimately on how strongly umklapp processes couple the corresponding bands. This allows us to show, in particular, that the Stoner peak in SPEELS spectra does not necessarily indicate the value of the exchange splitting energy. Thus, the common assumption that this peak allows us to estimate the magnetic moment through its correlation with exchange splitting should be reconsidered, both in bulk and surface studies. Furthermore, we are able to show that the above mechanism is one of the main causes for the typical broadness of experimental spectra. Finally, our model predicts that optical spin waves should be excited in SPEELS experiments.Comment: 11 pages, 7 eps figures, REVTeX fil