Mechanical Failure of a Small and Confined Solid

Starting from a commensurate triangular thin solid strip, confined within two hard structureless walls, a stretch along its length introduces a rectangular distortion. Beyond a critical strain the solid fails through nucleation of "smectic"-like bands. We show using computer simulations and simple density functional based arguments, how a solid-smectic transition mediates the failure. Further, we show that the critical strain introducing failure is {\em inversely} proportional to the channel width i.e. thinner strips are stronger!Comment: 6 pages, 7 figures, to be published in Indian Journal of Physics (in press) as a Conference proceeding of CMDAYS-0

Anomalous structural and mechanical properties of solids confined in quasi one dimensional strips

We show using computer simulations and mean field theory that a system of particles in two dimensions, when confined laterally by a pair of parallel hard walls within a quasi one dimensional channel, possesses several anomalous structural and mechanical properties not observed in the bulk. Depending on the density $\rho$ and the distance between the walls $L_y$, the system shows structural characteristics analogous to a weakly modulated liquid, a strongly modulated smectic, a triangular solid or a buckled phase. At fixed $\rho$, a change in $L_y$ leads to many reentrant discontinuous transitions involving changes in the number of layers parallel to the confining walls depending crucially on the commensurability of inter-layer spacing with $L_y$. The solid shows resistance to elongation but not to shear. When strained beyond the elastic limit it fails undergoing plastic deformation but surprisingly, as the strain is reversed, the material recovers completely and returns to its original undeformed state. We obtain the phase diagram from mean field theory and finite size simulations and discuss the effect of fluctuations.Comment: 14 pages, 13 figures; revised version, accepted in J. Chem. Phy

Do Oil Shocks Affect Financial Stress? Evidence from Oil-Exporting and -Importing Countries

In recent years, there is increasing attention to examining the relationship between oil prices, financial markets, and the economy. Relatively little is known about the dynamic relationship between structural oil shocks and financial market stress of countries, which are majorly dependent on oil price fluctuations. This paper examines the impact of structural oil shocks (oil supply shocks, global aggregate demand shocks, speculative shocks, and other oil shocks) on the financial stress of major oil-exporting and-importing economies. In this study, we construct a financial stress index and using a structural vector autoregression model, we investigate the effects of oil price shocks on the financial stress of major oil-exporting and importing economies. We find evidence that global demand shocks, followed by speculative demand shocks, have significant impacts on financial stress. Furthermore, the US subprime crisis has a significant bearing on the response of the financial stress index to structural oil shocks. The magnitude of oil price shocks on financial stress has subdued during the post-crisis period

A numerical renormalization group study of laser induced freezing

We study the phenomenon of laser induced freezing, within a numerical renormalization scheme which allows explicit comparison with a recent defect mediated melting theory. Precise values for the `bare' dislocation fugacities and elastic moduli of the 2-d hard disk system are obtained from a constrained Monte Carlo simulation sampling only configurations {\em without} dislocations. These are used as inputs to appropriate renormalization flow equations to obtain the equilibrium phase diagram which shows excellent agreement with earlier simulation results. We show that the flow equations need to be correct at least up to third order in defect fugacity to reproduce meaningful results.Comment: Minor Corrections; Combined version of Europhys. Lett. 67 (2004) p. 814 and Europhys. Lett. 68 (2004) p. 16

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C-S cross-coupling reaction

The present work demonstrates the C-S cross-coupling reaction between aryl halides and thiols using nickel nanoparticles (Ni NPs) supported on reduced graphene oxide (Ni/RGO) as a heterogeneous catalyst. It is observed that the uniformly dispersed Ni NPs supported on RGO could exhibit excellent catalytic activity in C-S cross-coupling reactions and the catalytic application is generalized with diverse coupling partners. Although the electron-rich planar RGO surface helps in stabilizing the agglomeration-free Ni NPs, the catalytic process is found to occur involving Ni(II) species and the recovered catalyst containing both Ni(0)/Ni(II) species is equally efficient in recycle runs. A correlation of loading of Ni species, size of NPs and the intermediate Ni-related heterostructures formed during the catalytic process has been established for the first time, and found to be best in the C-S cross-coupling reaction for Ni(0) and Ni(II) NPs of the average sizes 11-12 nm and 4 nm, respectively

Direct test of defect mediated laser induced melting theory for two dimensional solids

We investigate by direct numerical solution of appropriate renormalization flow equations, the validity of a recent dislocation unbinding theory for laser induced freezing/melting in two dimensions. The bare elastic moduli and dislocation fugacities which are inputs to the flow equations are obtained for three different 2-d systems (hard disk, inverse $12^{th}$ power and the Derjaguin-Landau-Verwey-Overbeek potentials) from a restricted Monte Carlo simulation sampling only configurations {\em without} dislocations. We conclude that (a) the flow equations need to be correct at least up to third order in defect fugacity to reproduce meaningful results, (b) there is excellent quantitative agreement between our results and earlier conventional Monte Carlo simulations for the hard disk system and (c) while the qualitative form of the phase diagram is reproduced for systems with soft potentials there is some quantitative discrepancy which we explain.Comment: 11 pages, 14 figures, submitted to Phys. Rev.

Power system small signal stability analysis and control

Power System Small Signal Stability Analysis and Control presents a detailed analysis of the problem of severe outages due to the sustained growth of small signal oscillations in modern interconnected power systems. The ever-expanding nature of power systems and the rapid upgrade to smart grid technologies call for the implementation of robust and optimal controls. Power systems that are forced to operate close to their stability limit have resulted in the use of control devices by utility companies to improve the performance of the transmission system against commonly occurring power syste