Simulation of a hydrocarbon fueled scramjet exhaust

Exhaust nozzle flow fields for a fully integrated, hydrocarbon burning scramjet were calculated for flight conditions of M (undisturbed free stream) = 4 at 6.1 km altitude and M (undisturbed free stream) = 6 at 30.5 km altitude. Equilibrium flow, frozen flow, and finite rate chemistry effects are considered. All flow fields were calculated by method of characteristics. Finite rate chemistry results were evaluated by a one dimensional code (Bittker) using streamtube area distributions extracted from the equilibrium flow field, and compared to very slow artificial rate cases for the same streamtube area distribution. Several candidate substitute gas mixtures, designed to simulate the gas dynamics of the real engine exhaust flow, were examined. Two mixtures are found to give excellent simulations of the specified exhaust flow fields when evaluated by the same method of characteristics computer code

Constant beamwidth generalised sidelobe canceller

In this paper, we proposed a constant beamwidth discrete Fourier transform (DFT) beamformer based on the generalised sidelobe canceller (GSC). Broadband signals are decomposed into frequency bins which are grouped into octaves and tapered individually. The resulting beampattern possesses constant beamwidth across the entire operating spectrum, thus ensuring uniform spatial resolution. Further incorporation of the GSC allows adaptive nulling of interference to coincide with uniform resolution, enhancing the beamformer’s performance. However, modification to the constraint equation of the standard GSC is required to account for the frequency-dependent weighting of sensors

Commercial conflict and regulation in the discourse of trade in seventeenth-century England

This article seeks to re-examine the intellectual context of commercial policy and regulation in seventeenth-century England. It questions a common assumption about so-called ‘mercantilist’ writers: that they saw trade as in some way finite and therefore won by one nation at the expense of another. Instead, it proposes that the often belligerent attitude of the ‘mercantilists’ towards trade was rooted in an understanding of the nature of international commerce as both communication and competition. Although writers acknowledged the mutual aspect of trade, they did not see this exchange as automatically equal, but saw it as possible for one party to exploit the other. This situation demanded state action to protect national trading interests in the disputed area of commerce, and thus this ‘discourse of trade’ was linked to political and juridical discourses about international relations. The article shows how this understanding of trade influenced debates about commercial governance in the critical middle decades of the seventeenth century, culminating in the attempt to create a national monopoly through the navigation acts, ‘securing sovereignty’ over the nation's trade. The second half of this article examines this in more detail with reference to the ideas of a prominent defender of the 1651 Navigation Act: Benjamin Worsley

Asymptotics in directed exponential random graph models with an increasing bi-degree sequence

Although asymptotic analyses of undirected network models based on degree sequences have started to appear in recent literature, it remains an open problem to study statistical properties of directed network models. In this paper, we provide for the first time a rigorous analysis of directed exponential random graph models using the in-degrees and out-degrees as sufficient statistics with binary as well as continuous weighted edges. We establish the uniform consistency and the asymptotic normality for the maximum likelihood estimate, when the number of parameters grows and only one realized observation of the graph is available. One key technique in the proofs is to approximate the inverse of the Fisher information matrix using a simple matrix with high accuracy. Numerical studies confirm our theoretical findings.Comment: Published at http://dx.doi.org/10.1214/15-AOS1343 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org