Shashank Gupta

TL;DR: Optical encoders for encoding signed, real numbers using optical fields are described in this article, where the optical fields may be detected using coherent detection, without the need for independent phase and amplitude control.

TL;DR: In this article, the effect of uniaxial tensile strain on a Ge-on-Si laser was theoretically investigated, and it was shown that approximately 3.2% tensile strength is required to achieve the anomalous threshold reduction for 1×1019 cm−3 n-type doping.

TL;DR: In this article, the authors compared the performance of the insertion gain model and the coupled periodic finite element-boundary element (FE-BE) model for underground railway vibration prediction.

Abstract: An efficient and modular numerical prediction model is presented to predict vibrations and re-radiated noise in buildings due to metro trains. The approach comprises of three weakly cou pled problems: the dynamic vehicle-track-tunnel-soil interaction problem, the dynamic soil-structure inte raction problem and the calculation of the acoustic response inside the rooms. The three-dimensional d ynamic tunnel-soil interaction problem is solved with a subdomain formulation, using a finite element formulation f or the tunnel and a boundary element method for the soil. The periodicity of the tunnel and the so il in the longitudinal direction is exploited using the Floquet transform, limiting the discretization effort to a s ingle bounded reference cell. The Craig-Bampton substructuring technique is used to efficiently incor porate a track in the tunnel. The track-tunnel-soil interaction problem is solved in the frequency-wav enumber domain and the wave field radiated into the soil is computed. This incident wave field is used to solve the dy namic soil-structure interaction problem on the receiver side and to determine the vibration levels in th e structure. The receiver side dynamic soil-structure interaction problem is solved by means of a 3D bou ndary element method for the soil coupled to a 3D finite element method for the structural. A weak coupling between the structural and acoustic vibrations is accounted for and an acoustic spectral finite ele m nt method is used to predict the acoustic response. To demonstrate the efficiency of the approach, th e Bakerloo line tunnel of London Underground has been modelled using the coupled periodic FE-BE appro ach. It is a deep bored segmented tunnel, with a cast iron lining, embedded in the London clay. The response in th free-field due to a moving vehicle on an uneven rail is predicted. Subsequently, the re-radiated no ise i a hypothetic multi-story portal frame office building is estimated. This numerical model enables to investigate the inherent physics of the generation and propagation of vibrations and re-radiated noise in building s from underground railways.