Can we avoid high coupling?

It is considered good software design practice to organize source code into modules and to favour within-module connections (cohesion) over between-module connections (coupling), leading to the oft-repeated maxim "low coupling/high cohesion". Prior research into network theory and its application to software systems has found evidence that many important properties in real software systems exhibit approximately scale-free structure, including coupling; researchers have claimed that such scale-free structures are ubiquitous. This implies that high coupling must be unavoidable, statistically speaking, apparently contradicting standard ideas about software structure. We present a model that leads to the simple predictions that approximately scale-free structures ought to arise both for between-module connectivity and overall connectivity, and not as the result of poor design or optimization shortcuts. These predictions are borne out by our large-scale empirical study. Hence we conclude that high coupling is not avoidable--and that this is in fact quite reasonable

The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described

Proceedings

1 fig. 3 tab. 22 ref. Sum. (En)Itchgrass (Rottboellia cochinchinensis) is a serious and persistent weed problem in many tropical agricultural and conservation areas. In Central America it is one of the most noxious and serious weeds in several upland crops, causing severe yield losses. Experimentally, pre-emergence control with herbicides, weed elimination during the fallow period and zero tillage reduced itchgrass populations in comparison to conventional practices used growers (no fallow management, soil preparation by disc harrowing and limited use of in-crop herbicides. Additional improvement in itchgrass management is brought about by inter-sowing legume cover crops. Of several legumes evaluated, mucuna (Mucuna deeringiana) and Canavalia ensiformis controlled the weed better and covered the soil, especially if planted simultaneously with maize. Itchgrass suppression by mucuna usually corresponded with increased grain yields but competition by the cover crop could reduce yields a good compromise is to delay mucuna planting by two weeks in relation to maize. Integrated tactics to control itchgrass were evaluated in on-farm validation plots. Pendimethalin controlled itchgrass at the onset of validation plots and facilitated the establishment of the cover crop. Itchgrass densities were lower in validation plots than in grower's fields while infestation levels and the soil seed bank decreased over three years with integrated management. In general, corn yields were also higher in validation plots. Integrated itchgrass management also proved economically feasible for smallholders. A promising alternative is biological control with the itchgrass smut, Sporisorium ophiuru, which prevents seed set and its host specifi