Strain engineering of the silicon-vacancy center in diamond

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multi-qubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain suseptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator

Analyzing object categories via novel category ranking measures defined on visual feature embeddings

Visualizing 2-D/3-D embeddings of image features can help gain an intuitive understanding of the image category landscape. However, popular visualization methods of visualizing such embeddings (e.g. color-coding by category) are impractical when the number of categories is large. To address this and other shortcomings, we propose novel quantitative measures defined on image feature embeddings. Each measure produces a ranked ordering of the categories and provides an intuitive vantage point from which to view the entire set of categories. As an experimental testbed, we use deep features obtained from category-epitomes, a recently introduced minimalist visual representation, across 160 object categories. We embed the features in a visualization friendly yet similarity-preserving 2-D manifold and analyze the inter/intra-category distributions of these embeddings using the proposed measures. Our analysis demonstrates that the category ordering methods enable new insights for the domain of large-category object representations. Moreover, our ordering measure approach is general in nature and can be applied to any feature-based representation of categories

Rolling Contact Fatigue Life of Rail for Different Slip Conditions

Abstract A three-dimensional elastic-plastic finite element analysis (FEA) is carried out to estimate the rolling contact fatigue (RCF) crack initiation life for varied slip range on the rail arising from operational variations. The wheel load produces Hertzian contact pressure. Variation in engine traction induces slip variations that evolves thermal load in terms of heat flux. The aperiodic rolling of wheel on rail develops non-proportional multiaxial fatigue loading. Present study combines these effects by translating the wheel load on rail for multiple (twelve) pass in presence of thermal load, contact pressure and traction through a proposed simulation. The temperature dependent Chaboche material model with nonlinear kinematic hardening law is implemented to estimate the stresses and plastic strains governing the multiaxial fatigue condition at the interface. The location of maximum von Mises stress, found at a material point on or a layer below the rail-head, contemplates the fatigue crack initiation site. A coded search algorithm helps to identify the critical plane of crack initiation corresponding to the maximum fatigue parameter (FP). In contrast to available predictions of RCF life considering contact pressure and/or traction or frictional heat in isolation, present study combines all these loads together and provides a more realistic result by numerical simulation

Rolling Contact Fatigue Life of Rail for Different Slip Conditions

<div><p>Abstract A three-dimensional elastic-plastic finite element analysis (FEA) is carried out to estimate the rolling contact fatigue (RCF) crack initiation life for varied slip range on the rail arising from operational variations. The wheel load produces Hertzian contact pressure. Variation in engine traction induces slip variations that evolves thermal load in terms of heat flux. The aperiodic rolling of wheel on rail develops non-proportional multiaxial fatigue loading. Present study combines these effects by translating the wheel load on rail for multiple (twelve) pass in presence of thermal load, contact pressure and traction through a proposed simulation. The temperature dependent Chaboche material model with nonlinear kinematic hardening law is implemented to estimate the stresses and plastic strains governing the multiaxial fatigue condition at the interface. The location of maximum von Mises stress, found at a material point on or a layer below the rail-head, contemplates the fatigue crack initiation site. A coded search algorithm helps to identify the critical plane of crack initiation corresponding to the maximum fatigue parameter (FP). In contrast to available predictions of RCF life considering contact pressure and/or traction or frictional heat in isolation, present study combines all these loads together and provides a more realistic result by numerical simulation.</p></div