56,383 research outputs found
Real-time combiner loss
Telemetry signals from several channels are aligned in time and combined by the Real-Time Combiner (RTC) in order to increase the strength of the total signal. In this article, the impact of the timing jitter in the RTC on the bit/symbol error rate is investigated. Equations are derived for the timing jitter loss associated with the coded and uncoded channels. Included are curves that depict the bit-symbol error rate vs. E sub b/N sub 0 and E sub s/N sub 0 for some typical telemetry conditions. The losses are typically below 0.1 dB
Performance analysis of the DSN baseband assembly (Bba) Real-Time Combiner (RTC)
The operation of the BBA Real Time Combiner (RTC) is discussed and its performance investigated in detail. It is shown that each channel of the RTC can be modelled by a simple block diagram in the z-transform domain from which all pertinent transient and steady state behavioral characteristics can be determined. In particular, the characteristic equation of the tracking loop and its equivalent noise bandwidth are found and used to evaluate the closed loop transient response and steady-state mean squared timing jitter. The impact of the totality of these loop jitter contributions on the combiner output SNR is evaluated and illustrated numerically. These results show that for parameters of interest to various space missions, the RTC is capable of providing significant SNR improvement relative to a single receiving antenna
cuIBM -- A GPU-accelerated Immersed Boundary Method
A projection-based immersed boundary method is dominated by sparse linear
algebra routines. Using the open-source Cusp library, we observe a speedup
(with respect to a single CPU core) which reflects the constraints of a
bandwidth-dominated problem on the GPU. Nevertheless, GPUs offer the capacity
to solve large problems on commodity hardware. This work includes validation
and a convergence study of the GPU-accelerated IBM, and various optimizations.Comment: Extended paper post-conference, presented at the 23rd International
Conference on Parallel Computational Fluid Dynamics (http://www.parcfd.org),
ParCFD 2011, Barcelona (unpublished
Explicit Representations for the T-Matrix on Unphysical Energy Sheets and Resonances in Two- and Three-Body Systems
We discuss the structure of the two- and three-body T-matrices, scattering
matrices, and resolvents continued to the unphysical energy sheets. Our
conclusions arise due to the representations that have been found for
analytically continued momentum-space kernels of the T-operators. These
representations are explicitly written only in terms of the physical-sheet
kernels of the T-matrix itself. One of advantages of the representations in the
three-body case is that they show which portions of the physical-sheet
three-body scattering matrix are ``responsible'' for the resonances associated
with a particular unphysical sheet. A resonance appears to be the energy where
the correspondingly truncated scattering matrix (taken on the physical sheet)
has eigenvalue zero. We also mention applications of this approach to some
specific three-body systems, based on the Faddeev differential equations.Comment: Based on a lecture given at the International Workshop ``Critical
Stability of Few-Body Quantum Systems'' (Dresden, October 17--22, 2005
Polaron Coherence as Origin of the Pseudogap Phase in High Temperature Superconducting Cuprates
Within a two component approach to high Tc copper oxides including polaronic
couplings, we identify the pseudogap phase as the onset of polaron ordering.
This ordering persists in the superconducting phase. A huge isotope effect on
the pseudogap onset temperature is predicted and in agreement with experimental
data. The anomalous temperature dependence of the mean square copper oxygen ion
displacement observed above, at and below Tc stems from an s-wave
superconducting component of the order parameter, whereas a pure d-wave order
parameter alone can be excluded.Comment: 7 pages, 2 figure
The 3D Spin Geometry of the Quantum Two-Sphere
We study a three-dimensional differential calculus on the standard Podles
quantum two-sphere S^2_q, coming from the Woronowicz 4D+ differential calculus
on the quantum group SU_q(2). We use a frame bundle approach to give an
explicit description of the space of forms on S^2_q and its associated spin
geometry in terms of a natural spectral triple over S^2_q. We equip this
spectral triple with a real structure for which the commutant property and the
first order condition are satisfied up to infinitesimals of arbitrary order.Comment: v2: 25 pages; minor change
Quantum criticality in a double quantum-dot system
We discuss the realization of the quantum-critical non-Fermi liquid state,
originally discovered within the two-impurity Kondo model, in double
quantum-dot systems. Contrary to the common belief, the corresponding fixed
point is robust against particle-hole and various other asymmetries, and is
only unstable to charge transfer between the two dots. We propose an
experimental set-up where such charge transfer processes are suppressed,
allowing a controlled approach to the quantum critical state. We also discuss
transport and scaling properties in the vicinity of the critical point.Comment: 4 pages, 3 figs; (v2) final version as publishe
Discriminative Tandem Features for HMM-based EEG Classification
Abstract—We investigate the use of discriminative feature extractors in tandem configuration with generative EEG classification system. Existing studies on dynamic EEG classification typically use hidden Markov models (HMMs) which lack discriminative capability. In this paper, a linear and a non-linear classifier are discriminatively trained to produce complementary input features to the conventional HMM system. Two sets of tandem features are derived from linear discriminant analysis (LDA) projection output and multilayer perceptron (MLP) class-posterior probability, before appended to the standard autoregressive (AR) features. Evaluation on a two-class motor-imagery classification task shows that both the proposed tandem features yield consistent gains over the AR baseline, resulting in significant relative improvement of 6.2% and 11.2 % for the LDA and MLP features respectively. We also explore portability of these features across different subjects. Index Terms- Artificial neural network-hidden Markov models, EEG classification, brain-computer-interface (BCI)
Helicopter roll control effectiveness criteria program summary
A study of helicopter roll control effectiveness is summarized for the purpose of defining military helicopter handling qualities requirements. The study is based on an analysis of pilot-in-the-loop task performance of several basic maneuvers. This is extended by a series of piloted simulations using the NASA Ames Vertical Motion Simulator and selected flight data. The main results cover roll control power and short-term response characteristics. In general the handling qualities requirements recommended are set in conjunction with desired levels of flight task and maneuver response which can be directly observed in actual flight. An important aspect of this, however, is that vehicle handling qualities need to be set with regard to some quantitative aspect of mission performance. Specific examples of how this can be accomplished include a lateral unmask/remask maneuver in the presence of a threat and an air tracking maneuver which recognizes the kill probability enhancement connected with decreasing the range to the target. Conclusions and recommendations address not only the handling qualities recommendations, but also the general use of flight simulators and the dependence of mission performance on handling qualities
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