Noether current from the surface term of gravitational action, Virasoro algebra and horizon entropy

We describe a simple way of obtaining horizon entropy using the approach based on the Virasoro algebra and central charge. We show that the Virasoro algebra defined by the Noether currents corresponding to the surface term of gravitational action, for the diffeomorphisms which leave the horizon structure unaltered, has a central extension that directly leads to the horizon entropy. In this approach there are no ambiguities in the calculation of the central charge. We explain why this approach is physically well motivated and could provide greater insight into the nature of horizon entropy.Comment: v2: a comment added; accepted in PRD (Rapid Comm.

The Structure of the Gravitational Action and its relation with Horizon Thermodynamics and Emergent Gravity Paradigm

If gravity is an emergent phenomenon, as suggested by several recent results, then the structure of the action principle for gravity should encode this fact. With this motivation we study several features of the Einstein-Hilbert action and establish direct connections with horizon thermodynamics. We begin by introducing the concept of holographically conjugate variables (HCVs) in terms of which the surface term in the action has a specific relationship with the bulk term. In addition to g_{ab} and its conjugate momentum \sqrt{-g} M^{cab}, this procedure allows us to (re)discover and motivate strongly the use of f^{ab}=\sqrt{-g}g^{ab} and its conjugate momentum N^c_{ab}. The gravitational action can then be interpreted as a momentum space action for these variables. We also show that many expressions in classical gravity simplify considerably in this approach. For example, the field equations can be written in a form analogous to Hamilton's equations for a suitable Hamiltonian if we use these variables. More importantly, the variation of the surface term, evaluated on any null surface which acts a local Rindler horizon can be given a direct thermodynamic interpretation. The term involving the variation of the dynamical variable leads to T\delta S while the term involving the variation of the conjugate momentum leads to S\delta T. We have found this correspondence only for the choice of variables (g_{ab}, \sqrt{-g} M^{cab}) or (f^{ab}, N^c_{ab}). We use this result to provide a direct thermodynamical interpretation of the boundary condition in the action principle, when it is formulated in a spacetime region bounded by the null surfaces. We analyse these features from several different perspectives and provide a detailed description, which offers insights about the nature of classical gravity and emergent paradigm.Comment: 31 pages, published version with typos fixe

Noether Current, Horizon Virasoro Algebra and Entropy

We provide a simple and straightforward procedure for defining a Virasoro algebra based on the diffeomorphisms near a null surface in a spacetime and obtain the entropy density of the null surface from its central charge. We use the off-shell Noether current corresponding to the diffeomorphism invariance of a gravitational Lagrangian $L(g_{ab},R_{abcd})$ and define the Virasoro algebra from its variation. This allows us to identify the central charge and the zero mode eigenvalue using which we obtain the entropy density of the Killing horizon. Our approach works for all Lanczos-Lovelock models and reproduces the correct Wald entropy. The entire analysis is done off-shell without using the field equations and allows us to define an entropy density for any null surface which acts as a local Rindler horizon for a particular class of observers.Comment: V2: to appear in Phys. Rev.

Contact-less characterizations of encapsulated graphene p-n junctions

Accessing intrinsic properties of a graphene device can be hindered by the influence of contact electrodes. Here, we capacitively couple graphene devices to superconducting resonant circuits and observe clear changes in the resonance- frequency and -widths originating from the internal charge dynamics of graphene. This allows us to extract the density of states and charge relaxation resistance in graphene p-n junctions without the need of electrical contacts. The presented characterizations pave a fast, sensitive and non-invasive measurement of graphene nanocircuits.Comment: 4 figures, supplementary information on reques

Atomistic study on the effect of the size of diamond abrasive particle during polishing of stainless steel

Nanofinishing or polishing helps to reduce surface roughness, which further improves both the optical and chemical properties of engineering materials. During the polishing of any engineering material, the size of abrasive particles plays a significant role in efficient polishing. In this paper, stainless steel 304 (or SS304) is selected for polishing through diamond abrasives with varying particle sizes using molecular dynamics simulations (MDS). It is found that the diamond abrasive particle initially causes elastic deformation due to the attractive force between the abrasive particle and the workpiece surface. As the size of the abrasive particle increases, plastic deformation occurs by spreading the dislocations on the surface only, which helps to annihilate the dislocations after polishing. It is revealed that the smaller abrasive particles (<3 nm) get trapped due to strong chemical bonding with the surface of the workpiece, and the abrasive particles start depositing on the workpiece instead of material removal. In this paper, it is proposed that an optimum size of abrasive particles is required for a given set of polishing parameters to achieve efficient material removal and minimum surface and subsurface defects. Thus, the present study is worthwhile for efficient polishing or nanocutting of stainless steel through monocrystalline diamond

Mechanism of surface modification on monocrystalline silicon during diamond polishing at nanometric scale

The demand for polished silicon wafers has increased significantly in recent years to cater to the development of the semiconductor industry. For example, polished silicon wafer has direct applications in integrated circuits, radio frequency amplifiers, micro-processors, micro-electromechanical systems, etc. To carry out mechanical polishing, lapping, grinding, or single-point diamond turning of silicon, diamond abrasives were extensively used before the implementation of chemo-mechanical polishing. During the diamond-based polishing, a few problems have already been identified, such as the formation of an amorphous phase, heat-affected zones, low material removal, etc. Some research work has also reported that nano-structured abrasives lead to a thin layer of the amorphous phase and a better material removal rate. In the same direction, a molecular dynamics simulation is carried out in this paper to investigate the mechanism of material removal from monocrystalline silicon during the diamond-abrasive-based polishing process. The present work is mainly focused on the dynamics of material removal phenomena near the abrasive particles at the nanometric scale by considering stress, lattice, cohesive energy, etc. This reveals that a higher value of indentation force results in surface buckling, which creates a zone of both compressive and tensile stresses, which increases the coordination number and forms β-silicon just ahead of the abrasive particle. This mechanism happens by developing a β-silicon phase on the surface with a thickness beyond a certain value of indentation force on the zone of compression. Buckling on this phase happens due to stress localisation in compression, as the flow stress of this phase is less than that of diamond cubic lattices. To avoid the mechanism of surface buckling and process silicon material on the surface, the indentation force needs to be maintained below a critical value. In the present case, it was found that the indentation force of less than or equal to 190 nN for the abrasive size of ϕ8 nm does the material removal by surface processing only without surface buckling. It was also found that surface processing helps to reduce the depth of the amorphous layer significantly without compromising the material removal rate or the generation of a wavy surface. Thus, the present mechanism will help in the polishing of silicon with minimum defects and reduce processing time for the final stage of polishing towards manufacturing ultra-smooth and planer surfaces

Literature Review Report on-“Work-Life Balance of Loco-Pilots (Railway Drivers) in India”

The railway driver is exposed to a demanding psychosocial work environment, which includes solitary work, limited opportunities for social contact and a heavy responsibility for operating the train (in terms of both safety and adhering to the timetable). The railway driver’s job, i.e. to operate the train, is largely governed by timetables and technical conditions (e.g. type of train, track area), which restricts the driver’s ability to decide for himself how the job is to be done. Railway drivers struggle to fulfill work and family responsibilities. This struggle is due to long hours, irregular and inflexible work schedules, and heavy workloads. Thus, work–family conflict can be a common work stressor for railway drivers. This paper deals with the quality of work life of Indian railways’ drivers and the factors that lead to an imbalance, causing high probability of accident. This paper discusses the working conditions and quality of life to the Indian railway drivers. This paper also briefly reviews concepts relevant to defining work-life balance. This  review of literature deals with the Work-Life balance of an Indian railways’ drivers to determine the working conditions and level of their work life balance which is having very high importance on their total wellbeing and hence their productivity and entire growth of an Indian railway. Keywords: Railway driver, Working conditions, Stress and Work-life balanc

Literature Review Report on -“An Analytical Study on Working Conditions of Loco-Pilots (Railway Drivers) in India”

The work of Indian railways’ drivers is considered as extremely stressful. It is working in an environment over which they have no control whatsoever and is an atmosphere that wrecks their schedules, disrupts their home life, makes social activities and regular breaks very hard to plan. This paper deals with the working conditions of Indian railways’ drivers and the factors that lead to a fatigue and stress, causing high probability of accident. This review of literature deals with the working conditions of an Indian railways’ drivers which is having very high importance on their total wellbeing and hence their productivity and entire growth and safety of an Indian railway. Keywords: Railway driver, working conditions, fatigue and stress