Carleton University

About: Carleton University is a education organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Population & Context (language use). The organization has 15852 authors who have published 39650 publications receiving 1106610 citations.

Improved progressive-edge-growth (PEG) construction of irregular LDPC codes

Abstract: Progressive-edge-growth (PEG) algorithm is known to construct low-density parity-check codes at finite block lengths with very good performance. In this letter, we propose a very simple modification to PEG construction for irregular codes, which considerably improves the performance at high signal-to-noise (SNR) ratios with no sacrifice in low-SNR performance.

An empirical study of earthquake source spectra for California earthquakes

Abstract: We generalize source, path, and site effects for California earthquakes as functions of magnitude and distance, based on regression analysis of 1000 Fourier acceleration spectra from 43 California earthquakes in the moment magnitude range from 4.4 to 7.4, recorded at rupture distances from 1 to 200 km. Empirically derived source spectra for California earthquakes are generally inconsistent with the spectral shape implied by a Brune ("omega-squared") point-source model. This is manifested by magnitude- and frequency-dependence of the Brune model parameters. For ex- ample, the Brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at M5.5 to a value near 50 bars at M7.5. At frequencies below 1 Hz, though, source spectra have much lower spectral ampli- tudes than predicted by the Brune point-source model for these values of stress; this discrepancy grows with increasing magnitude. Finite-fault simulations indicate that this is a consequence of the breakdown of the validity of the point-source approxi- mation for large ruptures. A stochastic finite-fault model, in which the fault is dis- cretized as a number of subfaults, each of which is represented by a Brune omega- squared point source, correctly matches the observed spectral shapes and amplitudes. The spectral decay parameter kappa, representing average near-surface attenuation of high-frequency motion at rock sites, increases with increasing magnitude, from values near 0.035 sec at M5.5 to 0.050 sec at M7.5. Magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical California sites subjected to strong ground motion. Comparisons of our empirical source spectra for California to corresponding spec- tra for eastern North America suggest that the spectral amplitudes are similar in the two regions for low-frequency motions (f < 2 Hz for M5.5, f < 0.5 Hz for M7.5), for equivalent crustal conditions. The eastern events appear to have enhanced high- frequency near-source amplitudes relative to the California events; this is particularly pronounced for large-magnitude earthquakes.

Assessing the development of shorebird eggs using the flotation method: species-specific and generalized regression models

Abstract: ABSTRACT We modeled the relationship between egg flotation and age of a developing embryo for 24 species of shorebirds For 21 species, we used regression analyses to estimate hatching date by modeling egg angle and float height, measured as continuous variables, against embryo age For eggs early in incubation, we used linear regression analyses to predict hatching date from logit-transformed egg angles only For late incubation, we used multiple regression analyses to predict hatching date from both egg angles and float heights In 30 of 36 cases, these equations estimated hatching date to within four days of the true hatching date for each species After controlling for incubation duration and egg size, flotation patterns did not differ between shorebirds grouped by mass (≥100 g or <100 g) or taxonomy (Scolopacidae versus Charadriidae) Flotation progressed more rapidly in species in which both adults incubate the clutch versus species in which only one adult incubates the clutch, although thi

Social Optima in Mean Field LQG Control: Centralized and Decentralized Strategies

Abstract: We study a class of linear-quadratic-Gaussian (LQG) control problems with N decision makers, where the basic objective is to minimize a social cost as the sum of N individual costs containing mean field coupling. The exact socially optimal solution (determining a particular Pareto optimum) requires centralized information for each agent and has high implementational complexity. As an alternative we subsequently exploit a mean field structure in the centralized optimal control problem to develop decentralized cooperative optimization so that each agent only uses its own state and a function which may be computed offline; the resulting set of strategies asymptotically achieves the social optimum as N → ∞. A key feature in this scheme is to let each agent optimize a new cost as the sum of its own cost and another component capturing its social impact on all other agents. We also discuss the relationship between the decentralized cooperative solution and the so-called Nash Certainty Equivalence based solution presented in previous work on mean field LQG games.