Software correlators as testbeds for RFI algorithms

In-correlator techniques offer the possibility of identifying and/or excising radio frequency interference (RFI) from interferometric observations at much higher time and/or frequency resolution than is generally possible with the final visibility dataset. Due to the considerable computational requirements of the correlation procedure, cross-correlators have most commonly been implemented using high-speed digital signal processing boards, which typically require long development times and are difficult to alter once complete. "Software" correlators, on the other hand, make use of commodity server machines and a correlation algorithm coded in a high-level language. They are inherently much more flexible and can be developed - and modified - much more rapidly than purpose-built "hardware" correlators. Software correlators are thus a natural choice for testing new RFI detection and mitigation techniques for interferometers. The ease with which software correlators can be adapted to test RFI detection algorithms is demonstrated by the addition of kurtosis detection and plotting to the widely used DiFX software correlator, which highlights previously unknown short -duration RFI at the Hancock VLBA station.Comment: 6 pages, 1 figure, accepted for publication in Proceedings of Science [PoS(RFI2010)035]. Presented at RFI2010, the Third Workshop on RFI Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland

Large Farms and Small Businesses: The difficult path toward development in rural China

The "Chinese Economic Miracle" of sustained growth since the 1970s has been thoroughly explored by many economists. So, too, has the obvious dichotomy between China's urban industrial sector and its rural agrarian economy. What has kept China's industrial development from migrating outward from its cities and into its countryside? When will the industrial revolution in Chinese agriculture begin? This paper examines a series of obstacles to the development of an industrial agricultural system in selected communities in China, contrasting government's goals for development with a realistic assessment of the economic characteristics of China's rural areas. The first section of this paper addresses the development of China's modern agricultural system, and the systems of land trading utilized by rural Chinese. The second section examines the impact of formal and informal financing on the development of rural businesses, as well as the development of a microfinance market in China's rural areas. Together, analysis of these issues demonstrates that China's government must address issues of property rights, access to capital, and social welfare if agricultural industrialization is to be encouraged

Slurry infiltration tests for slurry shield tunnelling in saturated sand

Tunnelling in saturated sand will cause excess pore pressures in the sand. This was the case during the construction of all tunnels in the Netherlands. This excess pore pressure influences the stability of the tunnel face. Therefore the magnitude of the excess pore pressure is of importance. Furthermore, it requires more information on the penetration process of the bentonite slurry as it will occur at the front of the tunnel face. This paper deals with preliminary infiltration tests to investigate some aspects of the infiltration. Results will be compared with theory

The Schwinger Mass in the Massive Schwinger Model

We derive a systematic procedure to compute Green functions for the massive Schwinger model via a perturbation expansion in the fermion mass. The known exact solution of the massless Schwinger model is used as a starting point. We compute the corrections to the Schwinger mass up to second order.Comment: Latex, 7 pages, no figure

pony - The occam-pi Network Environment

Although concurrency is generally perceived to be a `hard' subject, it can in fact be very simple --- provided that the underlying model is simple. The occam-pi parallel processing language provides such a simple yet powerful concurrency model that is based on CSP and the pi-calculus. This paper presents pony, the occam-pi Network Environment. occam-pi and pony provide a new, unified, concurrency model that bridges inter- and intra-processor concurrency. This enables the development of distributed applications in a transparent, dynamic and highly scalable way. The first part of this paper discusses the philosophy behind pony, explains how it is used, and gives a brief overview of its implementation. The second part evaluates pony's performance by presenting a number of benchmarks