This article describes a novel computing architecture organization based on nanoscale logic cells. We propose the use of a cluster of matrix arrangements of cells. In order to interconnect such fine-grained logic cells within a matrix, conventional techniques are not suitable due to a large interconnect overhead. Therefore, we propose the use of static and incomplete interconnect topologies to create matrices of cells. We also propose a method to map functions onto such architectures. We then explore the main parameters of the structure (size of matrices and interconnect topologies) and their impact on the main performance metrics (packing efficiency, speed, and fault tolerance). A cluster packing method also allows the evaluation of the number of matrices used by complex functions and the fill factor for various matrix sizes. The analyses show that this approach is particularly suited for matrices of 16 cells interconnected by modified omega networks. We can conclude that this architecture could improve the scalability of traditional FPGAs by a factor of 8.5.

Recently, technology advancement led to the emergence of nanodevice-based architectures. By exploiting the fine-grain dynamic reconfigurability of these logic cells, nanodevice-based architectures are expected, compared to conventional architectures, to reduce area and cost, and improve performance over a broad range of applications. In order to explore the potential of these architectures, the definition of new CAD tools is required. This paper discusses the challenges for system-level exploration for nanodevice-based architectures and proposes an approach enabling automatic application partitioning and mapping for these architectures.

In the West African Sahel, few direct measurements are currently available for the major land-use types on the extent of soil losses by wind erosion. A measurement campaign was therefore carried out in 1997 to monitor windblown sediment fluxes using Big Spring Number Eight (BSNE) sand-traps in a conventionally managed cultivated field and bush fallow in western Niger. Sediment balances were derived from the measured windblown sediment mass fluxes. Results indicate that sediment fluxes in a cultivated field increased linearly over distances up to 76 m irrespective of wind speed and duration. Sediment deposition over distances up to 47 m in an adjacent bush fallow was well described by an exponential decay function with a near constant trapping efficiency coefficient of 0.11 m−1 for incoming sediment mass fluxes between 10 and 45 kg m−1. Soil mass balances up to −17.5 and +10.5 Mg ha−1 were measured in a single storm in the field and fallow, respectively. However, 89% of the sediment deposition observed in the fallow occurred within the first 20 m. The nutrient content of windblown sediment generally declined with distance into the field and increased with distance into the bush fallow. Because of the low nutrient content of the native soil, total nutrient losses remained very low (<163 mg m−2 for any given nutrient). However, such losses were by no means negligible compared to the average nutrient uptake by a millet crop. The present measurements confirm that wind erosion can result in substantial soil losses in traditionally managed fields on the sandy soil of the Sahel. The bulk of sediment transport is, however, predominantly short range as the saltating material is efficiently trapped by the natural vegetation of fallow land.

The HAPEX-Sahel experiment was organized to investigate the impact of water, energy and CO2 fluxes at the soil-vegetation-atmosphere interface on climate processes in the Sahelian region, Measurements of the energy balance components, CO2 flux and soil moisture were conducted over a savanna area at the East Central Supersite of the one degree square during a 3 month period in 1992. The aim of this particular investigation was to understand the role of surface conditions (i.e. vegetation and moisture) in the partitioning of available energy at the surface into sensible and latent heat flux. It also aimed to improve the understanding of how water and carbon cycles are affected by vegetation functioning, soil water availability and atmospheric demand. The analysis presented in this paper showed that the relative contribution of the soil and the vegetation to latent heat flux varies intimately with the temporal rainfall distribution and the growth of the savanna grass species, which is more sensitive to the distribution of precipitation than to its amount. Finally, semi-empirical parameterizations were developed to formulate (1) the daily evapotranspiration rate of the savanna in terms of available energy at the surface and soil water content, and (2) the instantaneous carbon uptake in terms of photosynthetically active radiation received at the surface and soil water availability.

The variation in evaporative fraction and actual evaporation is examined for three sample days in the HAPEX-Sahel Intensive Observation Period (IOP), including data from all the vegetation types and sites. The trends in evaporative fraction over the IOP are also presented for eight sites. The high rate of evaporation from bare soil in the days following rainfall produces a variability in evaporation which makes differences between sites difficult to interpret on a day-to-day basis, but over the whole IOP it is shown that the millet uses a smaller proportion of the available energy for evaporation than the tiger bush or fallow savannah. The combined effect of differences in the total energy used and its partitioning into evaporation and sensible heat flux is demonstrated from the trends in cumulative total energy use and evaporation at the three southern sites, where it is shown that there is systematically less evaporation from the millet than from the savannah or tiger bush sites.

A two-layer model was developed and used to estimate sensible heat flux over a sparse millet crop from surface radiometric temperature. The millet crop was grown in farming conditions on the central site of the HAPEX-Sahel experiment in southern Niger. Surface temperature was measured with a nadir-looking radiometer. Measurements of the convective fluxes of sensible and latent heat were made simultaneously by means of the energy balance-Bowen ratio method. It is assumed that infra-red surface temperature can be represented by a weighted sum of foliage and soil surface temperatures, the weighting factors being the fractional areas of foliage and soil surface. With this assumption, the basic equations of two-layer models lead to an expression of sensible heat flux H close in form to the Ohm's law type formulation obtained from a one-layer approach, but in which the temperature difference between the surface and the air Tr − Ta has to be corrected by a factor proportional to the temperature difference δT between the foliage and the substrate. δT being not available in our experiment, it was assumed that a statistical relationship linking δT to Tr − Ta of the type δT = a(Tr − Ta)m could be used. Using one part of the data set, m and a were statistically determined by adjusting H estimated by the model to H observed by the Bowen ratio method. The best adjustment gave m = 2 and a = 0.10. For the other part of the data set (different from the one employed to calibrate this relationship) it was found that H estimated using the two-layer model with this empirical relationship compared fairly well with the values of H observed.