Inviscid analysis of the plume created by multiple rocket engines. Part II - Description of the computer programs

Computer program for calculation of single jet and five jet interaction regimes associated with multiple rocket engine

Using FPGAs to prototype a self-timed floating point co-processor

Journal ArticleSelf- timed circuits offer advantages over their synchronously clocked counterparts in a number of situations. However, self-timed design techniques are not widely used at present for a variety of reasons. One reason for the lack of experimentation with self-timed systems is the lack of commercially available parts to support this style of design. Field programmable gate arrays (FPGAs) offer an excellent alternative for the rapid development of novel system designs provided suitable circuit structures can be implemented. This paper describes a self-timed floating point co-processor built using a combination of Actel Field Programmable Gate Arrays (FPGAs) and semi-custom CMOS chips. This co-processor implements IEEE standard single precision floating point operations on 32-bit values. The control is completely self-timed. Data moves between parts of the circuit according to local constraints only: there is no global clock or global control circuit

Dispersion of Observed Position Angles of Submillimeter Polarization in Molecular Clouds

One can estimate the characteristic magnetic field strength in GMCs by comparing submillimeter polarimetric observations of these sources with simulated polarization maps developed using a range of different values for the assumed field strength. The point of comparison is the degree of order in the distribution of polarization position angles. In a recent paper by H. Li and collaborators, such a comparison was carried out using SPARO observations of two GMCs, and employing simulations by E. Ostriker and collaborators. Here we reexamine this same question, using the same data set and the same simulations, but using an approach that differs in several respects. The most important difference is that we incorporate new, higher angular resolution observations for one of the clouds, obtained using the Hertz polarimeter. We conclude that the agreement between observations and simulations is best when the total magnetic energy (including both uniform and fluctuating field components) is at least as large as the turbulent kinetic energy.Comment: revised, accepted version; to appear in The Astrophysical Journal; 20 pages, 2 figures, 2 table

Marginal stability and predator-prey behaviour within storm tracks

A predator-prey relationship between storm track intensity and growth rate is revealed in reanalysis data for the North Atlantic and North Pacific, as well as in an idealised global circulation model with a zonally asymmetric heating dipole. Averaging in the phase space of these two quantities reveals that both quantities oscillate on approximately monthly timescales. These oscillations occur due to quasi-periodic bursts in storm track activity that reduce excess baroclinicity and bring the flow back towards a state that is marginally stable to those bursts. Many detailed properties of these oscillations are reproduced well by a two-dimensional dynamical system, especially in respect of the North Atlantic storm track which is more zonally constrained compared to the North Pacific. It is predicted and observed that on average stronger storm events occur less frequently but grow on a shorter timescale. The results suggest that nonlinearly oscillating behaviour around a state of baroclinic neutrality is a general feature of localised storm tracks, and they offer a new perspective on the study of baroclinic instability

The optimal polarizations for achieving maximum contrast in radar images

There is considerable interest in determining the optimal polarizations that maximize contrast between two scattering classes in polarimetric radar images. A systematic approach is presented for obtaining the optimal polarimetric matched filter, i.e., that filter which produces maximum contrast between two scattering classes. The maximization procedure involves solving an eigenvalue problem where the eigenvector corresponding to the maximum contrast ratio is an optimal polarimetric matched filter. To exhibit the physical significance of this filter, it is transformed into its associated transmitting and receiving polarization states, written in terms of horizontal and vertical vector components. For the special case where the transmitting polarization is fixed, the receiving polarization which maximizes the contrast ratio is also obtained. Polarimetric filtering is then applies to synthetic aperture radar images obtained from the Jet Propulsion Laboratory. It is shown, both numerically and through the use of radar imagery, that maximum image contrast can be realized when data is processed with the optimal polarimeter matched filter

Pilot climate data system: A state-of-the-art capability in scientific data management

The Pilot Climate Data System (PCDS) was developed by the Information Management Branch of NASA's Goddard Space Flight Center to manage a large collection of climate-related data of interest to the research community. The PCDS now provides uniform data catalogs, inventories, access methods, graphical displays and statistical calculations for selected NASA and non-NASA data sets. Data manipulation capabilities were developed to permit researchers to easily combine or compare data. The current capabilities of the PCDS include many tools for the statistical survey of climate data. A climate researcher can examine any data set of interest via flexible utilities to create a variety of two- and three-dimensional displays, including vector plots, scatter diagrams, histograms, contour plots, surface diagrams and pseudo-color images. The graphics and statistics subsystems employ an intermediate data storage format which is data-set independent. Outside of the graphics system there exist other utilities to select, filter, list, compress, and calculate time-averages and variances for any data of interest. The PCDS now fully supports approximately twenty different data sets and is being used on a trial basis by several different in-house research grounds

Polarimetric clutter modeling: Theory and application

The two-layer anisotropic random medium model is used to investigate fully polarimetric scattering properties of earth terrain media. The polarization covariance matrices for the untilted and tilted uniaxial random medium are evaluated using the strong fluctuation theory and distorted Born approximation. In order to account for the azimuthal randomness in the growth direction of leaves in tree and grass fields, an averaging scheme over the azimuthal direction is also applied. It is found that characteristics of terrain clutter can be identified through the analysis of each element of the covariance matrix. Theoretical results are illustrated by the comparison with experimental data provided by MIT Lincoln Laboratory for tree and grass fields

An Ultra-Wideband Millimeter-Wave Phased Array

Wideband millimeter-wave arrays are of increasing importance due to their growing use in high data rate systems, including 5G communication networks. In this paper, we present a new class of ultra-wideband millimeter wave arrays that operate from nearly 20 GHz to 90 GHz. The array is based on tightly coupled dipoles. Feeding designs and fabrication challenges are presented, and a method for suppressing feed resonances is provided