Report on the Examination of I Stage Compressor Blades

The damages suffered by I stage compressor blades of three aeroengines have been studied at the request of Indian Air Force

Exotic matter on singular divisors in F-theory

We analyze exotic matter representations that arise on singular seven-brane configurations in F-theory. We develop a general framework for analyzing such representations, and work out explicit descriptions for models with matter in the 2-index and 3-index symmetric representations of SU($N$) and SU(2) respectively, associated with double and triple point singularities in the seven-brane locus. These matter representations are associated with Weierstrass models whose discriminants vanish to high order thanks to nontrivial cancellations possible only in the presence of a non-UFD algebraic structure. This structure can be described using the normalization of the ring of intrinsic local functions on a singular divisor. We consider the connection between geometric constraints on singular curves and corresponding constraints on the low-energy spectrum of 6D theories, identifying some new examples of apparent "swampland" theories that cannot be realized in F-theory but have no apparent low-energy inconsistency.Comment: 71 page

Mechanical and Frictional Behavior of Textured and non-Textured Surfaces

Tribology is the study of surfaces where two objects are sliding against another. Significant energy is lost due to friction between the sliding surfaces. Therefore, developing or designing surfaces to minimize friction is critical for the durability and reliability of the mechanical components. Several researchers have identified that surface texturing at the nanoscale (nanotexture) would reduce the friction between the contacting surfaces. The nanotextured surfaces have several applications in microelectromechanical systems and nanoelectromechanical systems. This dissertation employs molecular dynamics simulations to investigate the frictional and mechanical response of nanotextured aluminum (Al) and Al/amorphous silicon (a-Si) composite surfaces. This study determines the effective geometry (spherical or cylindrical) for texturing an Al surface that lowers the coefficient of friction of the nanotextured surface compared to a smooth surface. The results suggest that as the counter surface radius increases, the coefficient of friction decreases. For the lower counter surface radius, the coefficient of friction of the textured surface is higher than the smooth surface. But, after a specific increase in the radius of the counter surface, the coefficient of friction of the textured surface is lower than the smooth surface. The nanotextured surface consisting of Al has lower mechanical strength, which results in permanent failure even at low contact forces. Thus, a nanotextured hemispherical Al core surface is coated by an a-Si to protect the nanotextured surface from plastic deformation, and they are named as core-shell nanostructures (CSNs). The CSNs has previously shown remarkable deformation recovery to compression loading beyond the elastic limit. This study finds an optimum coating thickness that would protect the core from plastic deformation. i.e., the ratio of core radius to shell thickness should be between 0.5 and 2.0 to have deformation resistant CSNs. Additionally, this research investigates the core (single crystal and grain boundary) and substrate (crystalline and amorphous) material that affect the mechanical behavior of the CSNs subject to indentation. The results from this study conclude that CSNs with a single crystal core and crystalline substrate are more reliable for deformation-resistant behavior than those that contain grain boundary core and amorphous substrate. From our previous studies, it is clear that not all textured surfaces will have a lower coefficient of friction. The coefficient of friction also depends on the indenter or counter surface radius. Therefore, we investigate the relationship between surface texture (r, L) and counter surface (R) variables. The results from this study suggest that the counter surface radius should be greater than the difference between twice the pitch length and radius of the asperity (R \u3e (2L -r)) in order to have lower COF for the textured surface compared to a smooth surface. The relationship found between the textured surface and indenter surface variables is also confirmed for CSNs. Further, the relationship established in this study is also verified using experiments. This work provides the groundwork in designing the textured surfaces as well as deformation-resistant core-shell nanostructures that has both lower COF and deformation-resistant behavior. Additionally, this research finds the mechanisms behind the deformation-resistant behavior of the CSNs

Ca2+ sensor proteins in dendritic spines: a race for Ca2+

Dendritic spines are believed to be micro-compartments of Ca2+ regulation. In a recent study, it was suggested that the ubiquitous and evolutionarily conserved Ca2+ sensor, calmodulin (CaM), is the first to intercept Ca2+ entering the spine and might be responsible for the fast decay of Ca2+ transients in spines. Neuronal calcium sensor (NCS) and neuronal calcium-binding protein (nCaBP) families consist of Ca2+ sensors with largely unknown synaptic functions despite an increasing number of interaction partners. Particularly how these sensors operate in spines in the presence of CaM has not been discussed in detail before. The limited Ca2+ resources and the existence of common targets create a highly competitive environment where Ca2+ sensors compete with each other for Ca2+ and target binding. In this review, we take a simple numerical approach to put forth possible scenarios and their impact on signaling via Ca2+ sensors of the NCS and nCaBP families. We also discuss the ways in which spine geometry and properties of ion channels, their kinetics and distribution, alter the spatio-temporal aspects of Ca2+ transients in dendritic spines, whose interplay with Ca2+ sensors in turn influences the race for Ca2+

Investigation of aileron control cable failure of a Pushpak aircraft

This is an investigation on the failure of aileron control cable in a Pushpak aircraft carried out at the request of the Deputy Director General of Civil Aviation. The nature of failure is analysed

Focal Epithelial Hyperplasia: A Rare Case Report

Focal epithelial hyperplasia is a rare entity of oral mucosa induced by Human Papilloma virus type 13 and 32. It was described by Estrada in 1956 within a group of Colombian Caramanda Indians. In Latin America it is called Multifocal Papilloma virus induced epithelial hyperplasia. It is common in younger age groups. Generally it is very rare in Asia. Here we report a case of 32 year old male who came with a complaint of burning sensation for past 6 months. The lesion was diagnosed as Focal epithelial hyperplasia according to clinical and Histopathological features. Dental clinicians should be aware of these lesions with a careful clinical and Histopathological observation under definitive diagnosis