40,088 research outputs found

    Klein tunneling through an oblique barrier in graphene ribbons

    Full text link
    We study a transmission coefficient of graphene nanoribbons with a top gate which acts as an oblique barrier. Using a Green function method based on the Dirac-like equation, scattering among transverse modes due to the oblique barrier is taken into account numerically. In contrast to the 2-dimensional graphene sheet, we find that the pattern of transmission in graphene ribbons depends strongly on the electronic structure in the region of the barrier. Consequently, irregular structures in the transmission coefficient are predicted while perfect transmission is still calculated in the case of metallic graphene independently of angle and length of the oblique barrier

    Systems analysis of the space shuttle

    Get PDF
    Developments in communications systems, computer systems, and power distribution systems for the space shuttle are described. The use of high speed delta modulation for bit rate compression in the transmission of television signals is discussed. Simultaneous Multiprocessor Organization, an approach to computer organization, is presented. Methods of computer simulation and automatic malfunction detection for the shuttle power distribution system are also described

    Higgs bosons of a supersymmetric U(1)U(1)' model at the ILC

    Full text link
    We study the scalar Higgs sector of the next-to-minimal supersymmetric standard model with an extra U(1), which has two Higgs doublets and a Higgs singlet, in the light leptophobic ZZ' scenario where the extra neutral gauge boson ZZ' does not couple to charged leptons. In this model, we find that the sum of the squared coupling coefficients of the three neutral scalar Higgs bosons to ZZZZ, normalized by the corresponding SM coupling coefficient is noticeably smaller than unity, due to the effect of the extra U(1), for a reasonable parameter space of the model, whereas it is unity in the next-to-minimal supersymmetric standard model. Thus, these two models may be distinguished if the coupling coefficients of neutral scalar Higgs bosons to ZZZZ are measured at the future International Linear Collider by producing them via the Higgs-strahlung, ZZZZ fusion, and WWWW fusion processes.Comment: 12 pages, 2 figures, 1 table, PR

    Testing tripartite Mermin inequalities by spectral joint-measurements of qubits

    Full text link
    It is well known that Bell inequality supporting the local realism can be violated in quantum mechanics. Numerous tests of such a violation have been demonstrated with bipartite entanglements. Using spectral jointmeasurements of the qubits, we here propose a scheme to test the tripartite Mermin inequality (a three-qubit Bell-type inequality) with three qubits dispersively-coupled to a driven cavity. First, we show how to generate a three-qubit Greenberger-Horne-Zeilinger (GHZ) state by only one-step quantum operation. Then, spectral joint-measurements are introduced to directly confirm such a tripartite entanglement. Assisted by a series of single-qubit operations, these measurements are further utilized to test the Mermin inequality. The feasibility of the proposal is robustly demonstrated by the present numerical experiments.Comment: 7pages,3figure

    Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures

    Full text link
    We show that large amplitude, coherent acoustic phonon wavepackets can be generated and detected in Inx_xGa1x_{1-x}N/GaN epilayers and heterostructures in femtosecond pump-probe differential reflectivity experiments. The amplitude of the coherent phonon increases with increasing Indium fraction xx and unlike other coherent phonon oscillations, both \textit{amplitude} and \textit{period} are strong functions of the laser probe energy. The amplitude of the oscillation is substantially and almost instantaneously reduced when the wavepacket reaches a GaN-sapphire interface below the surface indicating that the phonon wavepackets are useful for imaging below the surface. A theoretical model is proposed which fits the experiments well and helps to deduce the strength of the phonon wavepackets. Our model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refraction, primarily through the Franz-Keldysh effect, and as a result, modulate the reflectivity of the probe beam. Our model correctly predicts the experimental dependence on probe-wavelength as well as epilayer thickness.Comment: 11 pages, 14 figure

    Synchronization transition of heterogeneously coupled oscillators on scale-free networks

    Full text link
    We investigate the synchronization transition of the modified Kuramoto model where the oscillators form a scale-free network with degree exponent λ\lambda. An oscillator of degree kik_i is coupled to its neighboring oscillators with asymmetric and degree-dependent coupling in the form of \couplingcoeff k_i^{\eta-1}. By invoking the mean-field approach, we determine the synchronization transition point JcJ_c, which is zero (finite) when η>λ2\eta > \lambda-2 (η<λ2\eta < \lambda-2). We find eight different synchronization transition behaviors depending on the values of η\eta and λ\lambda, and derive the critical exponents associated with the order parameter and the finite-size scaling in each case. The synchronization transition is also studied from the perspective of cluster formation of synchronized vertices. The cluster-size distribution and the largest cluster size as a function of the system size are derived for each case using the generating function technique. Our analytic results are confirmed by numerical simulations.Comment: 11 pages, 3 figures and two table
    corecore