Microprocessor-based digital correlator

We describe the design, construction, and operation of a low-cost, microprocessor-based digital correlator. The device has 128 channels, operates in either the single clipping or single scaling mode, and allows selection of the sample interval with 2-digit precision over the range 100 ns to 9.9 s. The device can be operated in the autocorrelate or cross-correlate mode and may easily be expanded to more than 128 correlation channels

Automatic infrasound signal detection using the Hough transform

The Hough transform is a mathematical device that allows the retrieval of parametric curve information from binary-pixelated data in the presence of noise. This slope-intercept transform maps each point in the image space S into a straight line in parameter space P and has the very useful property that all points in S that lie along the same straight-line map to the same number of straight lines in P with a common intersection point. Thus with a suitable counting procedure, the problem of extended straight-line detection in noisy pixelated data becomes one of local peak finding, a problem that may be substantially more tractable. In this study, an algorithm that utilizes the Hough transform for the detection of signals in International Monitoring System style infrasonic array data by seeking periods of constant backazimuth that are associated with coherent acoustic signals is described. A system of synthetic signal implants is used to assess the performance of the detection algorithm by generating a set of pseudo Receiver Operator Characteristic curves. A feature of the detection algorithm is the ability to accommodate full three-dimensional array geometry

On the development of a meshless method to study multibody systems using computational fluid dynamics

Multibody systems, which consist of several separate or interconnected, rigid or flexible bodies, occur frequently in problems of aerospace engineering. Such problems can be difficult to solve using conventional finite volume methods in computational fluid dynamics. This is particularly so if the bodies are required to undergo translational or rotational displacements during time-dependent simulations, which occur, for example, with cases involving store release or control surface deflection. These problems are generally limited to those when the movements are small or known a-priori. This thesis investigates the use of the meshless method to solve these difficult multibody systems using computational fluid dynamics, with the aim of performing moving-body simulations involving large scale motions, with no restrictions on the movement. An implicit meshless scheme is developed to solve the Euler, laminar and Reynolds-Averaged Navier-Stokes equations. Spatial derivatives are approximated using a least squares method on clouds of points. The resultant system of equations is linearised and solved implicitly using approximate, analytical Jacobian matrices and a preconditioned Krylov subspace iterative method. The details of the spatial discretisation, linear solver and construction of the Jacobian matrix are discussed, and results which demonstrate the performance of the scheme are presented for steady and unsteady flows in two and three-dimensions. The selection of the stencils over the computational domain for the meshless solver is vital for the method to be used to solve problems involving multibody systems accurately and efficiently. The computational domain is obtained using overlapping point distributions associated with each body in the system. Stencil selection is relatively straight forward if the point distributions are isotropic in nature; however, this is rarely the case in computations that solve the Navier-Stokes equations. A fully automatic method of selecting the stencils is outlined, in which the original connectivity and the concept of a resolving direction are used to help construct good quality stencils with limited user input. The methodology is described, and results, that are solutions to the Navier-Stokes equations in two-dimensions and the Euler equations in three-dimensions, are presented for various systems

Discovery of circularly polarised radio emission from SS 433

We report the discovery of circularly polarised radio emission from the radio-jet X-ray binary SS 433 with the Australia Telescope Compact Array. The flux density spectrum of the circular polarization, clearly detected at four frequencies between 1 - 9 GHz, has a spectral index of (-0.9 +/- 0.1). Multiple components in the source and a lack of very high spatial resolution do not allow a unique determination of the origin of the circular polarization, nor of the spectrum of fractional polarization. However, we argue that the emission is likely to arise in the inner regions of the binary, possibly via propagation-induced conversion of linear to circular polarization, and the fractional circular polarization of these regions may be as high as 10%. Observations such as these have the potential to investigate the composition, whether pairs or baryonic, of the ejecta from X-ray binaries.Comment: Accepted for publication in ApJ Letter

Sea surface temperature changes in the southern California borderlands during the last glacial-interglacial cycle

A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal δ18O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°-10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus, both of which are currently restricted to subpolar regions of the North Pacific. The glacial-interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial

William Vickrey's Legacy: Innovative Policies for Social Concerns

William Vickrey, who won the Nobel Prize in Economics in 1996, was a moral and brilliant man. His major contributions to economics came from his desire to advance ways to decrease waste through creative pricing. The economic areas where he had the most impact are congestion pricing, tax reform and auctions. At the end of his life the unemployment issue dominated his research. Vickrey saw macroeconomics turning increasingly from full employment to stable prices as the dominant policy goal. Vickrey was deeply concerned that economists and politicians believed that price stability was a more laudable goal than full employment.Economics; Morals

The elastic constants of MgSiO3 perovskite at pressures and temperatures of the Earth's mantle

The temperature anomalies in the Earth's mantle associated with thermal convection1 can be inferred from seismic tomography, provided that the elastic properties of mantle minerals are known as a function of temperature at mantle pressures. At present, however, such information is difficult to obtain directly through laboratory experiments. We have therefore taken advantage of recent advances in computer technology, and have performed finite-temperature ab initio molecular dynamics simulations of the elastic properties of MgSiO3 perovskite, the major mineral of the lower mantle, at relevant thermodynamic conditions. When combined with the results from tomographic images of the mantle, our results indicate that the lower mantle is either significantly anelastic or compositionally heterogeneous on large scales. We found the temperature contrast between the coldest and hottest regions of the mantle, at a given depth, to be about 800K at 1000 km, 1500K at 2000 km, and possibly over 2000K at the core-mantle boundary.Comment: Published in: Nature 411, 934-937 (2001

Paleogene calcite compensation depth in the eastern subtropical Pacific: Answers and questions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95436/1/palo1183.pd

Application specific compression : final report.

With the continuing development of more capable data gathering sensors, comes an increased demand on the bandwidth for transmitting larger quantities of data. To help counteract that trend, a study was undertaken to determine appropriate lossy data compression strategies for minimizing their impact on target detection and characterization. The survey of current compression techniques led us to the conclusion that wavelet compression was well suited for this purpose. Wavelet analysis essentially applies a low-pass and high-pass filter to the data, converting the data into the related coefficients that maintain spatial information as well as frequency information. Wavelet compression is achieved by zeroing the coefficients that pertain to the noise in the signal, i.e. the high frequency, low amplitude portion. This approach is well suited for our goal because it reduces the noise in the signal with only minimal impact on the larger, lower frequency target signatures. The resulting coefficients can then be encoded using lossless techniques with higher compression levels because of the lower entropy and significant number of zeros. No significant signal degradation or difficulties in target characterization or detection were observed or measured when wavelet compression was applied to simulated and real data, even when over 80% of the coefficients were zeroed. While the exact level of compression will be data set dependent, for the data sets we studied, compression factors over 10 were found to be satisfactory where conventional lossless techniques achieved levels of less than 3