Birefringence analysis of multilayer leaky cladding optical fibre

We analyse a multilayer leaky cladding (MLC) fibre using the finite element method and study the effect of the MLC on the bending loss and birefringence of two types of structures: (i) a circular core large-mode-area structure and (ii) an elliptical-small-core structure. In a large-mode-area structure, we verify that the multilayer leaky cladding strongly discriminates against higher order modes to achieve single-mode operation, the fibre shows negligible birefringence, and the bending loss of the fibre is low for bending radii larger than 10 cm. In the elliptical-small-core structure we show that the MLC reduces the birefringence of the fibre. This prevents the structure from becoming birefringent in case of any departures from circular geometry. The study should be useful in the designs of MLC fibres for various applications including high power amplifiers, gain flattening of fibre amplifiers and dispersion compensation.Comment: 18 page

Spoof detection using time-delay shallow neural network and feature switching

Detecting spoofed utterances is a fundamental problem in voice-based biometrics. Spoofing can be performed either by logical accesses like speech synthesis, voice conversion or by physical accesses such as replaying the pre-recorded utterance. Inspired by the state-of-the-art \emph{x}-vector based speaker verification approach, this paper proposes a time-delay shallow neural network (TD-SNN) for spoof detection for both logical and physical access. The novelty of the proposed TD-SNN system vis-a-vis conventional DNN systems is that it can handle variable length utterances during testing. Performance of the proposed TD-SNN systems and the baseline Gaussian mixture models (GMMs) is analyzed on the ASV-spoof-2019 dataset. The performance of the systems is measured in terms of the minimum normalized tandem detection cost function (min-t-DCF). When studied with individual features, the TD-SNN system consistently outperforms the GMM system for physical access. For logical access, GMM surpasses TD-SNN systems for certain individual features. When combined with the decision-level feature switching (DLFS) paradigm, the best TD-SNN system outperforms the best baseline GMM system on evaluation data with a relative improvement of 48.03\% and 49.47\% for both logical and physical access, respectively

Noncommutative BTZ Black Hole and Discrete Time

We search for all Poisson brackets for the BTZ black hole which are consistent with the geometry of the commutative solution and are of lowest order in the embedding coordinates. For arbitrary values for the angular momentum we obtain two two-parameter families of contact structures. We obtain the symplectic leaves, which characterize the irreducible representations of the noncommutative theory. The requirement that they be invariant under the action of the isometry group restricts to $R\times S^1$ symplectic leaves, where $R$ is associated with the Schwarzschild time. Quantization may then lead to a discrete spectrum for the time operator.Comment: 10 page

Ultrafast switching of photonic entanglement

To deploy and operate a quantum network which utilizes existing telecommunications infrastructure, it is necessary to be able to route entangled photons at high speeds, with minimal loss and signal-band noise, and---most importantly---without disturbing the photons' quantum state. Here we present a switch which fulfills these requirements and characterize its performance at the single photon level; it exhibits a 200-ps switching window, a 120:1 contrast ratio, 1.5 dB loss, and induces no measurable degradation in the switched photons' entangled-state fidelity (< 0.002). Furthermore, because this type of switch couples the temporal and spatial degrees of freedom, it provides an important new tool with which to encode multiple-qubit states in a single photon. As a proof-of-principle demonstration of this capability, we demultiplex a single quantum channel from a dual-channel, time-division-multiplexed entangled photon stream, effectively performing a controlled-bit-flip on a two-qubit subspace of a five-qubit, two-photon state

The late-time development of the Richtmyer–Meshkov instability

Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness delta of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for delta at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, ddelta/dt[proportional]t–p (i.e., delta[proportional]t1–p), where 0.67<~p<~0.74 and that a small dependence on the initial wavelength lambda0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed

Biodiesel: Freedom from Dependence on Fossil Fuels?

In view of the depleting oil reserves and exponential rise in petroleum prices, the search for alternative sources of fuel is very timely and important. The present paper addresses the underlying issues in biodiesel production from biomaterials and sustainable production and supply of first-generation biofuels, especially the one from jatropha. The agencies and research institutions involved in the production of biofuels and the national and international efforts made in this regard are discussed here. There is also a dire need of a step towards large-scale production and supply of second-generation biofuels, although in infant stage, to strengthen the world economy in general and Indian economy in particular. However, the production of biofuels are likely to have serious socio-economic implications especially to the lesser developed societies. This needs serious attention from policy makers and public at large