Trellis-Coded Non-Orthogonal Multiple Access

In this letter, we propose a trellis-coded non-orthogonal multiple access (NOMA) scheme. The signals for different users are produced by trellis coded modulation (TCM) and then superimposed on different power levels. By interpreting the encoding process via the tensor product of trellises, we introduce a joint detection method based on the Viterbi algorithm. Then, we determine the optimal power allocation between the two users by maximizing the free distance of the tensor product trellis. Finally, we manifest that the trellis-coded NOMA outperforms the uncoded NOMA at high signal-to-noise ratio (SNR)

A preliminary study on the performance of indoor active noise barriers based on 2D simulations

© 2015 Elsevier Ltd. Single screen barriers are widely used in open-plan offices as a means of improving acoustical privacy. However, the insertion loss of an indoor barrier is limited in low frequency range. Active control systems have been shown to be able to enhance the insertion loss of outdoors noise barrier in low frequency range, so its feasibility for improving the performance of indoor barriers is investigated in this paper. The simulation results show that about 10 dB extra insertion loss below 500 Hz can be obtained with the active control system when the squared sound pressure inside the entire observation area is minimized. The performance of the active noise barrier deteriorated significantly due to the reflecting ceiling, and the performance is hardly improved by increasing the ceiling height or the ceiling absorption coefficient. Finally, the effects of the sensing strategy on the control performance and the impacts of the active control system on the source side are discussed

Evidence for spin-flip scattering and local moments in dilute fluorinated graphene

The issue of whether local magnetic moments can be formed by introducing adatoms into graphene is of intense research interest because it opens the window to fundamental studies of magnetism in graphene, as well as of its potential spintronics applications. To investigate this question we measure, by exploiting the well-established weak localization physics, the phase coherence length L_phi in dilute fluorinated graphene. L_phi reveals an unusual saturation below ~ 10 K, which cannot be explained by non-magnetic origins. The corresponding phase breaking rate increases with decreasing carrier density and increases with increasing fluorine density. These results provide strong evidence for spin-flip scattering and points to the existence of adatom-induced local magnetic moment in fluorinated graphene. Our results will stimulate further investigations of magnetism and spintronics applications in adatom-engineered graphene.Comment: 9 pages, 4 figures, and supplementary materials; Phys. Rev. Lett. in pres

Active control of sound transmission through a hole in a large thick wall

Holes in walls of enclosures or buildings are often the weak link in the chain of sound insulation. This paper introduces an analytical model to calculate the sound transmission from a baffled rectangular hole based on the modal expansion approach, and proposes to install an active noise control system inside the hole to improve the transmission loss of the perforated wall. Different control source and error sensing strategies are investigated, and it is found that for a 30 cm thick wall with a 6 cm by 6 cm hole, an active control system with 1 control source and 1 error sensor can achieve more than 20 dB attenuation up to 2700 Hz, while that with a compound control source consisting of 4 loudspeakers, the system can achieve similar reduction up to 3900 Hz

Multi-quark components in baryons

A brief review on some recent progresses in our understanding of multi-quark components in baryons is presented. The multi-quark components in baryons seem to be mainly in colored quark cluster configurations rather than in ``meson cloud'' configurations or in the form of a sea of quark-antiquark pairs. The colored quark cluster multi-quark picture gives a natural explanation of empirical indications for a positive strangeness magnetic moment $\mu_s$ of the proton and the longstanding mass-reverse problem of S11(1535) and $P11(1440) N* resonances. A model-prediction for the$\mu_s$ of the proton is given.Comment: Contribution to the International Conference on QCD and Hadronic Physics, June 16-20, 2005, Beijin

High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated on Epitaxial Ferroelectric Gate Oxides

The carrier mobility \mu of few-layer graphene (FLG) field-effect transistors increases ten-fold when the SiO_2 substrate is replaced by single-crystal epitaxial Pb(Zr_0.2Ti_0.8)O_3 (PZT). In the electron-only regime of the FLG, \mu reaches 7x10^4 cm^2/Vs at 300K for n = 2.4x10^12/cm^2, 70% of the intrinsic limit set by longitudinal acoustic (LA) phonons; it increases to 1.4x10^5 cm^2/Vs at low temperature. The temperature-dependent resistivity \rho(T) reveals a clear signature of LA phonon scattering, yielding a deformation potential D = 7.8+/-0.5 eV.Comment: 5 pages, 4 figure

Dynamic response of an embedded railway track subjected to a moving load

A dynamic computational model for the embedded railway track subjected to a moving load is developed in this paper. The model consists of two-layer Euler-Bernoulli beams and continuous viscoelastic elements. The lower beam, the upper beam are employed to model the concrete slab and the rail, respectively, whilst the continuous viscoelastic elements model the soil reaction and the fill material. The problem is solved by employing Newmark-β numerical integration method. The effects of the speed of the moving loads, the rail type, and the spring stiffness of rail supports are studied. Results indicate that the dynamic response of rail and slab increases with the larger moving load speeds, whilst the response of rail and slab decreases with the increase of spring stiffness and heavier rail used