2,951 research outputs found
User's guide to PMESH: A grid-generation program for single-rotation and counterrotation advanced turboprops
A detailed operating manual is presented for a grid generating program that produces 3-D meshes for advanced turboprops. The code uses both algebraic and elliptic partial differential equation methods to generate single rotation and counterrotation, H or C type meshes for the z - r planes and H type for the z - theta planes. The code allows easy specification of geometrical constraints (such as blade angle, location of bounding surfaces, etc.), mesh control parameters (point distribution near blades and nacelle, number of grid points desired, etc.), and it has good runtime diagnostics. An overview is provided of the mesh generation procedure, sample input dataset with detailed explanation of all input, and example meshes
Order Statistics Based List Decoding Techniques for Linear Binary Block Codes
The order statistics based list decoding techniques for linear binary block
codes of small to medium block length are investigated. The construction of the
list of the test error patterns is considered. The original order statistics
decoding is generalized by assuming segmentation of the most reliable
independent positions of the received bits. The segmentation is shown to
overcome several drawbacks of the original order statistics decoding. The
complexity of the order statistics based decoding is further reduced by
assuming a partial ordering of the received bits in order to avoid the complex
Gauss elimination. The probability of the test error patterns in the decoding
list is derived. The bit error rate performance and the decoding complexity
trade-off of the proposed decoding algorithms is studied by computer
simulations. Numerical examples show that, in some cases, the proposed decoding
schemes are superior to the original order statistics decoding in terms of both
the bit error rate performance as well as the decoding complexity.Comment: 17 pages, 2 tables, 6 figures, submitted to IEEE Transactions on
Information Theor
On predictability of rare events leveraging social media: a machine learning perspective
Information extracted from social media streams has been leveraged to
forecast the outcome of a large number of real-world events, from political
elections to stock market fluctuations. An increasing amount of studies
demonstrates how the analysis of social media conversations provides cheap
access to the wisdom of the crowd. However, extents and contexts in which such
forecasting power can be effectively leveraged are still unverified at least in
a systematic way. It is also unclear how social-media-based predictions compare
to those based on alternative information sources. To address these issues,
here we develop a machine learning framework that leverages social media
streams to automatically identify and predict the outcomes of soccer matches.
We focus in particular on matches in which at least one of the possible
outcomes is deemed as highly unlikely by professional bookmakers. We argue that
sport events offer a systematic approach for testing the predictive power of
social media, and allow to compare such power against the rigorous baselines
set by external sources. Despite such strict baselines, our framework yields
above 8% marginal profit when used to inform simple betting strategies. The
system is based on real-time sentiment analysis and exploits data collected
immediately before the games, allowing for informed bets. We discuss the
rationale behind our approach, describe the learning framework, its prediction
performance and the return it provides as compared to a set of betting
strategies. To test our framework we use both historical Twitter data from the
2014 FIFA World Cup games, and real-time Twitter data collected by monitoring
the conversations about all soccer matches of four major European tournaments
(FA Premier League, Serie A, La Liga, and Bundesliga), and the 2014 UEFA
Champions League, during the period between Oct. 25th 2014 and Nov. 26th 2014.Comment: 10 pages, 10 tables, 8 figure
Quantum Revivals in Periodically Driven Systems close to nonlinear resonance
We calculate the quantum revival time for a wave-packet initially well
localized in a one-dimensional potential in the presence of an external
periodic modulating field. The dependence of the revival time on various
parameters of the driven system is shown analytically. As an example of
application of our approach, we compare the analytically obtained values of the
revival time for various modulation strengths with the numerically computed
ones in the case of a driven gravitational cavity. We show that they are in
very good agreement.Comment: 14 pages, 1 figur
High-Rate Space-Time Coded Large MIMO Systems: Low-Complexity Detection and Channel Estimation
In this paper, we present a low-complexity algorithm for detection in
high-rate, non-orthogonal space-time block coded (STBC) large-MIMO systems that
achieve high spectral efficiencies of the order of tens of bps/Hz. We also
present a training-based iterative detection/channel estimation scheme for such
large STBC MIMO systems. Our simulation results show that excellent bit error
rate and nearness-to-capacity performance are achieved by the proposed
multistage likelihood ascent search (M-LAS) detector in conjunction with the
proposed iterative detection/channel estimation scheme at low complexities. The
fact that we could show such good results for large STBCs like 16x16 and 32x32
STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in
excess of 20 bps/Hz (even after accounting for the overheads meant for pilot
based training for channel estimation and turbo coding) establishes the
effectiveness of the proposed detector and channel estimator. We decode perfect
codes of large dimensions using the proposed detector. With the feasibility of
such a low-complexity detection/channel estimation scheme, large-MIMO systems
with tens of antennas operating at several tens of bps/Hz spectral efficiencies
can become practical, enabling interesting high data rate wireless
applications.Comment: v3: Performance/complexity comparison of the proposed scheme with
other large-MIMO architectures/detectors has been added (Sec. IV-D). The
paper has been accepted for publication in IEEE Journal of Selected Topics in
Signal Processing (JSTSP): Spl. Iss. on Managing Complexity in Multiuser MIMO
Systems. v2: Section V on Channel Estimation is update
Entanglement Capacity of Nonlocal Hamiltonians : A Geometric Approach
We develop a geometric approach to quantify the capability of creating
entanglement for a general physical interaction acting on two qubits. We use
the entanglement measure proposed by us for -qubit pure states (PRA
\textbf{77}, 062334 (2008)). Our procedure reproduces the earlier results (PRL
\textbf{87}, 137901 (2001)). The geometric method has the distinct advantage
that it gives an experimental way to monitor the process of optimizing
entanglement production.Comment: 8 pages, 1 figure
Tight lower bound to the geometric measure of quantum discord
Dakic, Vedral and Brukner [Physical Review Letters \tf{105},190502 (2010)]
gave a geometric measure of quantum discord in a bipartite quantum state as the
distance of the state from the closest classical quantum (or zero discord)
state and derived an explicit formula for a two qubit state. Further, S.Luo and
S.Fu [Physical Review A \tf{82}, 034302 (2010)] obtained a generic form of this
geometric measure for a general bipartite state and established a lower bound.
In this brief report we obtain a rigorous lower bound to the geometric measure
of quantum discord in a general bipartite state which dominates that obtained
by S.Luo and S.Fu.Comment: 10 pages,2 figures. In the previous versions, a constraint was
ignored while optimizing the second term in Eq.(5), in which case, only a
lower bound on the geometric discord can be obtained. The title is also
consequently changed. Accepted in Phys.Rev.
Polarization Dynamics in Nonlinear Photonic Resonators
The global market demand for higher-bandwidth communication is increasing exponentially. Although optical networks provide high transmission speed using light to transmit signals, a bottleneck-inducing conversion is often needed to perform the processing of optical signals in the electrical domain. Such processing imposes a major barrier that would limit the high transmission speed of fiber-optic communications. This bottleneck conversion may be mitigated by extending signal-processing capabilities directly into the optical domain itself. Thus, I have studied the dynamics of optical polarization in a nonlinear photonic resonator to understand a new optical physical behavior to enhance the capabilities of optical signal processing. I present a theoretical model and experimental investigation to study the simultaneous occurrence of two optical nonlinear processes---nonlinear polarization rotation (NPR) and dispersive optical bistability. These two optical nonlinear processes within a nonlinear photonic resonator produce an optical signal exhibiting hysteresis curves in its state of polarization (SOP). Bistable action accompanied with simultaneous NPR is a significant departure from traditional optical memory, where the optical signal only exhibits hysteresis curves in the output power. Bistable polarization rotation (BPR) term is used to refer to the new physical process of bistable action accompanied by simultaneous NPR. I have leveraged this new physical process of the bistable polarization rotation to realize a hysteresis-shape transformation and optimization. A diversity of hysteresis shapes are demonstrated in optical power including the canonical counter-clockwise (CCW) shape (S-shape), the clockwise (CW) shape (inverted S-shape), and butterfly shapes. The control of the shape is performed downstream of the nonlinear photonic resonator within which the bistable signal is generated. I have derived a mathematical model to study this transformation process. Critical to our model, a generalized Malus\u27 law of a non-ideal linear polarizer and an elliptical input polarization. Since all hysteresis shapes originate from the same bistable signal, all shapes exhibit the same switching input powers. Moreover, the shape-control process is used to enhance the bistable switching contrast to surpass 20 dB for the CCW and CW shapes. Additionally, the new technique of hysteresis shape control enables the ability of simultaneous distribution of the bistable signal into multiple paths. In each path, the optical signal can be independently controlled to produce a hysteresis shape. For example, CCW and CW shapes can be configured in two locations using the same BPR signal. The theoretical and experimental work reported here is carried out for the case of a Fabry-Perot semiconductor optical amplifier as the nonlinear photonic resonator. Both the new physical process and the new control capability presented here are extendable to other nonlinear media (such as Kerr media) and other photonic resonators (such as ring and distributed feedback resonators). The dissertation outcomes detail processes and techniques to enhance the performance of all-optical combinational gates, such as photonic AND and XOR gates, as well as all-optical sequential devices, such as photonic flip-flops
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