1,789 research outputs found

    Quantum Isometries of the finite noncommutative geometry of the Standard Model

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    We compute the quantum isometry group of the finite noncommutative geometry F describing the internal degrees of freedom in the Standard Model of particle physics. We show that this provides genuine quantum symmetries of the spectral triple corresponding to M x F where M is a compact spin manifold. We also prove that the bosonic and fermionic part of the spectral action are preserved by these symmetries.Comment: 29 pages, no figures v3: minor change

    Sensory organ like response determines the magnetism of zigzag-edged honeycomb nanoribbons

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    We present an analytical theory for the magnetic phase diagram for zigzag edge terminated honeycomb nanoribbons described by a Hubbard model with an interaction parameter U . We show that the edge magnetic moment varies as ln U and uncover its dependence on the width W of the ribbon. The physics of this owes its origin to the sensory organ like response of the nanoribbons, demonstrating that considerations beyond the usual Stoner-Landau theory are necessary to understand the magnetism of these systems. A first order magnetic transition from an anti-parallel orientation of the moments on opposite edges to a parallel orientation occurs upon doping with holes or electrons. The critical doping for this transition is shown to depend inversely on the width of the ribbon. Using variational Monte-Carlo calculations, we show that magnetism is robust to fluctuations. Additionally, we show that the magnetic phase diagram is generic to zigzag edge terminated nanostructures such as nanodots. Furthermore, we perform first principles modeling to show how such magnetic transitions can be realized in substituted graphene nanoribbons.Comment: 5 pages, 5 figure

    Lag synchronization and scaling of chaotic attractor in coupled system

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    We report a design of delay coupling for lag synchronization in two unidirectionally coupled chaotic oscillators. A delay term is introduced in the definition of the coupling to target any desired lag between the driver and the response. The stability of the lag synchronization is ensured by using the Hurwitz matrix stability. We are able to scale up or down the size of a driver attractor at a response system in presence of a lag. This allows compensating the attenuation of the amplitude of a signal during transmission through a delay line. The delay coupling is illustrated with numerical examples of 3D systems, the Hindmarsh-Rose neuron model, the R\"ossler system and a Sprott system and, a 4D system. We implemented the coupling in electronic circuit to realize any desired lag synchronization in chaotic oscillators and scaling of attractors.Comment: 10 pages, 7 figure

    Symmetry-dependent phonon renormalization in monolayer MoS2 transistor

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    Strong electron-phonon interaction which limits electronic mobility of semiconductors can also have significant effects on phonon frequencies. The latter is the key to the use of Raman spectroscopy for nondestructive characterization of doping in graphene-based devices. Using in-situ Raman scattering from single layer MoS2_2 electrochemically top-gated field effect transistor (FET), we show softening and broadening of A1g_{1g} phonon with electron doping whereas the other Raman active E2g1_{2g}^{1} mode remains essentially inert. Confirming these results with first-principles density functional theory based calculations, we use group theoretical arguments to explain why A1g_{1g} mode specifically exhibits a strong sensitivity to electron doping. Our work opens up the use of Raman spectroscopy in probing the level of doping in single layer MoS2_2-based FETs, which have a high on-off ratio and are of enormous technological significance.Comment: 5 pages, 3 figure

    Intrinsic photoluminescence stokes shift in thin-film cadmium sulfide

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    Exciting a semiconductor through light absorption produces photoluminescence (PL). In general, the emitted energy is lower than the energy absorbed. The phenomenon, first discovered in the nineteenth century, is known as Stokes shift energy [1]. The change in energy (AS t o k e s), crucial for the information about the phonon relaxation in the material and with importance in light emitting devices, has not been investigated experimentally very systematically [2]. In this project, we present the observation of the intrinsic photoluminescence Stokes shift in a semiconductor

    Effect of twist level and twist direction of core (double) yarn on dref-3 spun yarn

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    In this study, an attempt has been made to understand the behaviour of friction spun yarn by introducing doubled yarns as core with diversity in twist level and direction. ‘Z’ twisted 15tex (40s Ne) parent yarn has been used for doubling purposes. To examine the effect of doubling, three twist levels are chosen, viz. 50, 60 and 70 % of the parent yarn twist for both the directions viz. S and Z. Thus, six samples of doubled yarns are prepared. These samples are tested for the count, twist, breaking force and elongation. These yarns are introduced as core into DREF-3 friction spinning system; keeping the sheath fibre constant viz. combed cotton sliver of 0.15 hank for all the samples. The twist direction of the doubled yarn used as core is found to be the influential factor for the breaking force and elongation of the friction spun yar
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