10,413 research outputs found
Coded Modulation Assisted Radial Basis Function Aided Turbo Equalisation for Dispersive Rayleigh Fading Channels
In this contribution a range of Coded Modulation (CM) assisted Radial Basis Function (RBF) based Turbo Equalisation (TEQ) schemes are investigated when communicating over dispersive Rayleigh fading channels. Specifically, 16QAM based Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and iteratively decoded BICM (BICM-ID) are evaluated in the context of an RBF based TEQ scheme and a reduced-complexity RBF based In-phase/Quadrature-phase (I/Q) TEQ scheme. The Least Mean Square (LMS) algorithm was employed for channel estimation, where the initial estimation step-size used was 0.05, which was reduced to 0.01 for the second and the subsequent TEQ iterations. The achievable coding gain of the various CM schemes was significantly increased, when employing the proposed RBF-TEQ or RBF-I/Q-TEQ rather than the conventional non-iterative Decision Feedback Equaliser - (DFE). Explicitly, the reduced-complexity RBF-I/Q-TEQ-CM achieved a similar performance to the full-complexity RBF-TEQ-CM, while attaining a significant complexity reduction. The best overall performer was the RBF-I/Q-TEQ-TTCM scheme, requiring only 1.88~dB higher SNR at BER=10-5, than the identical throughput 3~BPS uncoded 8PSK scheme communicating over an AWGN channel. The coding gain of the scheme was 16.78-dB
Semi-implicit and fully implicit shock-capturing methods for hyperbolic conservation laws with stiff source terms
Some numerical aspects of finite-difference algorithms for nonlinear multidimensional hyperbolic conservation laws with stiff nonhomogenous (source) terms are discussed. If the stiffness is entirely dominated by the source term, a semi-implicit shock-capturing method is proposed provided that the Jacobian of the soruce terms possesses certain properties. The proposed semi-implicit method can be viewed as a variant of the Bussing and Murman point-implicit scheme with a more appropriate numerical dissipation for the computation of strong shock waves. However, if the stiffness is not solely dominated by the source terms, a fully implicit method would be a better choice. The situation is complicated by problems that are higher than one dimension, and the presence of stiff source terms further complicates the solution procedures for alternating direction implicit (ADI) methods. Several alternatives are discussed. The primary motivation for constructing these schemes was to address thermally and chemically nonequilibrium flows in the hypersonic regime. Due to the unique structure of the eigenvalues and eigenvectors for fluid flows of this type, the computation can be simplified, thus providing a more efficient solution procedure than one might have anticipated
The Metadata Education and Research Information Commons (MERIC): A Collaborative Teaching and Research Initiative
The networked environment forced a sea change in Library and Information Science (LIS) education. Most LIS programs offer a mixed-mode of instruction that integrates online learning materials with more traditional classroom pedagogical methods and faculty are now responsible for developing content and digital learning objects. The teaching commons in a networked environment is one way to share, modify and repurpose learning objects while reducing the costs to educational institutions of developing course materials totally inhouse. It also provides a venue for sharing ideas, practices, and expertise in order to provide the best learning experience for students. Because metadata education has been impacted by rapid changes and metadata research is interdisciplinary and diffuse, the Metadata Education and Research Information Commons (MERIC) initiative aims to provide a virtual environment for sharing and collaboration within the extensive metadata community. This paper describes the development of MERIC from its origin as a simple clearinghouse proof-of-concept project to a service-oriented teaching and research commons prototype. The problems of enablers and barriers to participation and collaboration are discussed and the need for specific community building research is cited as critical for the success of MERIC within a broad metadata community
Nonlocal transistor based on pure crossed Andreev reflection in a EuO-graphene/superconductor hybrid structure
We study the interband transport in a superconducting device composed of
graphene with EuO-induced exchange interaction. We show that pure crossed
Andreev reflection can be generated exclusively without the parasitic local
Andreev reflection and elastic cotunnelling over a wide range of bias and Fermi
levels in an EuO-graphene/superconductor/EuO-graphene device. The pure
non-local conductance exhibits rapid on/off switching and oscillatory behavior
when the Fermi levels in the normal and the superconducting leads are varied.
The oscillation reflects the quasiparticle propagation in the superconducting
lead and can be used as a tool to probe the subgap quasiparticle mode in
superconducting graphene, which is inaccessible from the current-voltage
characteristics. Our results suggest that the device can be used as a highly
tunable transistor that operates purely in the non-local and spin-polarized
transport regime.Comment: 5 pages, 4 figures; To appear in Phys. Rev.
Anomaly-induced Quadrupole Moment of the Neutron in Magnetic Field
The neutrons cannot possess a quadrupole moment in the vacuum. Nevertheless,
we show that in the presence of an external magnetic field the neutrons acquire
a new type of quadrupole moment involving the
components of spin and magnetic field. This "chiral magnetic" quadrupole moment
arises from the interplay of the chiral anomaly and the magnetic field; we
estimate its value for the neutron in the static limit, and find . The detection of the quadrupole moment of the
neutron would provide a novel test of the role of the chiral anomaly in
low-energy QCD and can be possible in the presence of both magnetic and
inhomogeneous electric fields. The quadrupole moment of the neutron may affect
e.g. the properties of neutron stars and magnetars.Comment: 2 pages; extended versio
Technique for producing wind-tunnel heat-transfer models
Inexpensive thin skinned wind tunnel models with thermocouples on certain surface areas were fabricated. Thermocouples were designed for measuring aerodynamic heat transfer in wind tunnels
Baryons still trace dark matter: probing CMB lensing maps for hidden isocurvature
Compensated isocurvature perturbations (CIPs) are primordial fluctuations
that balance baryon and dark-matter isocurvature to leave the total matter
density unperturbed. The effects of CIPs on the cosmic microwave background
(CMB) anisotropies are similar to those produced by weak lensing of the CMB:
smoothing of the power spectrum, and generation of non-Gaussian features.
Previous work considered the CIP effects on the CMB power-spectrum but
neglected to include the CIP effects on estimates of the lensing potential
power spectrum (though its contribution to the non-Gaussian, connected, part of
the CMB trispectrum). Here, the CIP contribution to the standard estimator for
the lensing potential power-spectrum is derived, and along with the CIP
contributions to the CMB power-spectrum, Planck data is used to place limits on
the root-mean-square CIP fluctuations on CMB scales, . The resulting constraint of using this new technique improves on past work by a factor of
. We find that for Planck data our constraints almost reach the
sensitivity of the optimal CIP estimator. The method presented here is
currently the most sensitive probe of the amplitude of a scale-invariant CIP
power spectrum placing an upper limit of at 95% CL. Future
measurements of the large-scale CMB lensing potential power spectrum could
probe CIP amplitudes as low as ().Comment: 24 pages, 9 figures; comments welcome; v2 references correcte
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