Effect of surface pinning on magnetic nanostuctures

Magnetic nanostructures are often considered as highly functional materials because they exhibit unusual magnetic properties under different external conditions. We study the effect of surface pinning on the core-shell magnetic nanostuctures of different shapes and sizes considering the spin-interaction to be Ising-like. We explore the hysteresis properties and find that the exchange bias, even under zero field cooled conditions, increases with increase of, the pinning density and the fraction of up-spins among the pinned ones. We explain these behavior analytically by introducing a simple model of the surface. The asymmetry in hysteresis is found to be more prominent in a inverse core-shell structure, where spin interaction in the core is antiferromagnetic and that in the shell is ferromagnetic. These studied of inverse core-shell structure are extended to different shapes, sizes, and different spin interactions, namely Ising, XY- and Heisenberg models in three dimension. We also briefly discuss the pinning effects on magnetic heterostructures.Comment: 12 pages, 12 figure

Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles

We studied the magnetic properties of self-assembled aggregates of BiFeO3 nanoparticles (~ 20-40 nm). The aggregates formed two different structures - one with limited and another with massive cross-linking - via `drying-mediated self-assembly' process following dispersion of the nanoparticles within different organic solvents. They exhibit large coercivity H_C (>1000 Oe) and exchange bias field H_E (~ 350-900 Oe) in comparison to what is observed in isolated nanoparticles (H_C ~ 250 Oe; H_E ~ 0). The H_E turns out to be switching from negative to positive depending on the structure of the aggregates with |H_E| being larger. The magnetic force microscopy reveals the magnetic domains (extending across 7-10 nanoparticles) as well as the domain switching characteristics and corroborate the results of magnetic measurements. Numerical simulation of the `drying-mediated-self-assembly' process shows that the nanoparticle-solvent interaction plays an important role in forming the `nanoparticle aggregate structures' observed experimentally. Numerical simulation of the magnetic hysteresis loops, on the other hand, points out the importance of spin pinning at the surface of nanoparticles as a result of surface functionalization of the particles in different suspension media. Depending on the concentration of pinned spins at the surface pointing preferably along the easy-axis direction - from greater than 50\% to less than 50% - H_E switches from negative to positive. Quite aside from bulk sample and isolated nanoparticle, nanoparticle aggregates - resulting from surface functionalization - therefore, offer remarkable tunability of properties depending on structures.Comment: 14 pages, 33 pdf figures. Contact authors for the supplementary data and movie

Implications of Banking Regulations on Online Payment Failures

This paper explores the `latent economy' of online transaction failure that prevails in the digital payment system. A two-variant model of profit, with a different cost function in each variant, has been proposed to examine the profit of commercial banks. The model considers that when an online transaction fails, banks use the money held in the Unified Payment System to earn revenue in the form of interest income by investing the same. The theoretical exposition of the model has been corroborated by simulation by assuming feasible parametric restrictions and exogenous values. The paper finds that commercial banks make profit by using the held amount at the existing cost. As the proportion of the held money used by the banks increases, their profits increase and the commercial banks incur losses when an `alternative cost' with stricter penalties is imposed

Implications of Banking Regulations on Online Payment Failures

This paper explores the `latent economy' of online transaction failure that prevails in the digital payment system. A two-variant model of profit, with a different cost function in each variant, has been proposed to examine the profit of commercial banks. The model considers that when an online transaction fails, banks use the money held in the Unified Payment System to earn revenue in the form of interest income by investing the same. The theoretical exposition of the model has been corroborated by simulation by assuming feasible parametric restrictions and exogenous values. The paper finds that commercial banks make profit by using the held amount at the existing cost. As the proportion of the held money used by the banks increases, their profits increase and the commercial banks incur losses when an `alternative cost' with stricter penalties is imposed

A situation analysis of care and support for rape survivors at first point of contact in India and Bangladesh

A situation analysis of post-rape care services available at the first point of contact was conducted in three cities in India and four cities in Bangladesh. The aim of this investigation was to gather information that could be used in the development of a comprehensive care and support system for the rape survivor. Secondarily, the study field-tested sensitive and practical tools that could be used in the future for large-scale situation analyses of the rape survivor services. The results demonstrated that there is no uniform service provision protocol to follow for managing rape survivors at health facilities in India or Bangladesh. Despite small sample sizes, the study findings provide a good lead for a full-scale situation analysis of the police stations and health facilities that may potentially provide services to these women in need. The tools in this study were developed, revised, and tested, and in general, were found to be efficient and may be applicable for use in a number of diverse settings

Increased toll-like receptor-2 expression on nonclassic CD16⁺monocytes from patients with inflammatory stage of eales' disease

Purpose.: To identify the distribution, differential Toll-like receptor (TLR) expression, and functional contribution of monocyte subpopulations in the inflammatory stage of Eales' disease (ED). Methods.: Peripheral blood mononuclear cells were isolated from nine patients during the inflammatory stage of ED and nine age- and sex-matched healthy controls. The expression of CD14, CD16, TLR-2, and TLR-4 on monocytes was measured by flow cytometry. The CD14+, CD16−, and CD16+ monocyte populations were sorted on the basis of magnetic-activated cell-sorting methodology, and levels of cytokines were measured by ELISA. Results.: In ED patients, the number of circulating monocytes was significantly expanded compared with that in controls (P = 0.01), with a marked increase in the nonclassic CD16+ subset, which showed an activated phenotype in patients that correlated with levels of serum proinflammatory cytokines and clinical progression. A higher expression of cell surface TLR-2 (P = 0.02), but not TLR-4, was found in monocytes of patients with ED. Furthermore, TLR-2 was expressed at higher levels on CD16+ monocytes than on CD16− monocytes in patients, whereas no significant variation was found in TLR-4 expression on different monocyte subsets. Peptidoglycan-induced TNF-α expression correlated with TLR-2 expression in monocytes isolated from controls (r = 0.85, P = 0.0061), but not in monocytes isolated from ED patients (r = 0.553, P = 0.1328). Conclusions.: These results indicate that in the pathogenesis of ED, TLR activation and increased numbers of nonclassic CD16+ monocytes are crucial regulators, along with the secretion of proinflammatory cytokines that perpetuate the inflammatory process in the retina