On-Line Global Energy Optimization in Multi-Core Systems Using Principles of Analog Computation

This work presents the design and the silicon implementation of an on-line energy optimizer unit based on novel analog computation approaches, which is capable of dynamically adjusting power supply voltages and operating frequencies of multiple processing elements on-chip. The optimized voltage/frequency assignments are tailored to the instantaneous workload information on multiple tasks and fully adaptive to variations in process and temperature. The optimizer unit has a response time of less than 50 us, occupies a silicon area of 0.021 sqmm and dissipates 2 mW/task

Plant community diversity in the Chobe Enclave, Botswana: Insights for functional habitat heterogeneity for herbivores

Precise vegetation descriptions and maps are essential tools for the management of natural areas, as well as for understanding animal habitat use. The Chobe Enclave (CE), adjacent to the Chobe National Park and the Chobe Forest Reserve, forms a critical dry season range for many large herbivores. As a tool for future management and studies about wildlife habitat use and migration, this study proposed to describe the plant communities in the CE and to study their relationships with microtopography and soils. Plant species were inventoried in 82 sampling plots (40 x 20 m), covering the vegetation diversity recognised by an unsupervised classification (Landsat images, 30-m resolution). A hierarchical clustering classified the inventories in eight plant communities, mapped with a supervised classification. This study was conducted in parallel with a soil study. Soil variations and degree of flooding largely determine community composition. Floodplains along the Linyanti River and dambos (concentrating local run off from rainfall) provide reliable green forage for wildlife during the dry season. Adjacent to floodplains, riverine forests also maintain green browse and grazing well into the dry season. In drylands, vegetation is largely determined by soil texture. Forests dominated by Baikiaea plurijuga occupy the acidic, red sands in the east, while sandveld vegetation grows on deep sands in paleo-river channels. These habitats support dominant grasses, which provide important forage for grazers during the wet season. Finally, woodlands dominated by Colophospermum mopane, characterised by sodium-rich and alkaline soils, enable herbivores to meet their mineral requirements during reproduction. Conservation implications: Our soil and vegetation studies provide important insights into factors determining plant communities. Their diversity and close vicinity play a critical role in enabling herbivores to adapt to seasonal variations in forage quantity and quality. Results will enable researchers to gain insights into animal habitat seasonal use in the Chobe Enclave

Ultra low power subthreshold current-mode logic utilizing a novel PMOS load device

A novel approach for implementing MOS current-mode logic (MCML) circuits that can operate with ultra low bias currents is introduced. Measurements of test structures fabricated in 0.18 μm CMOS technology show that the proposed PMOS load device concept can be utilized successfully for bias currents as low as 1 nA, achieving sufficiently high gain (>3) over a wide frequency range

Subthreshold Source-Coupled Logic Circuits for Ultra Low Power Applications

This article presents a novel approach for implementing ultra-low power digital components and systems using source-coupled logic (SCL) circuit topology, operating in weak inversion (sub-threshold) regime. PMOS transistors with shorted drain-substrate contacts are used as gate- controlled, very high resistivity load devices. Based on the proposed approach, the power consumption and the operation frequency of logic circuits can be scaled down linearly by changing the tail bias current of SCL gates over a very wide range spanning several orders of magnitude, which is not achievable in sub-threshold CMOS circuits. Measurements in conventional 0.18um CMOS technology show that the tail bias current of each gate can be set as low as 10pA, with a supply voltage of 300mV. Fundamental circuits such as ring oscillators and frequency dividers, as well as more complex digital blocks such as parallel multipliers designed by using the STSCL topology have been experimentally characterized

Ultra Low Power Subthreshold MOS Current Mode Logic Circuits Using a Novel Load Device Concept

This article presents a novel and robust approach for implementing ultra-low power MOS current mode logic (MCML) circuits. To operate at very low bias currents, a simple and compact high resistance load device has been introduced. Operating in subthreshold regime, the circuit can be used in a very wide frequency range by adjusting the bias current without any need for resizing the devices. Measurements in 0.18 μm CMOS technology show that the proposed MCML circuit can be operated reliably with bias currents as low as 1 nA offering a significant improvement of the power-delay product compared to conventional CMOS gates. Simulations show that the proposed circuit exhibits faster response compared to the conventional MCML circuits with triode-mode PMOS load devices at low bias currents

Soil diversity and major soil processes in the Kalahari basin, Botswana

The study area of the Chobe Enclave (northern Botswana) is defined as mostly covered by Arenosols in available maps. However, recent explorations of the area showed that soils are more diverse than expected. This is because of complex interactions between current alluvial deposition processes, paleo-environmental effects (ancient alluvial deposition, ancient wind-blown sand deposits) and ongoing hydrological effects and colluvial effects on topographic gradients. An in-depth exploration of both soils and vegetation in the area was conducted with the aim (i) to survey the soil diversity at the Chobe Enclave, (ii) to study soil dynamics and identify the key factors of this diversity, and (iii) to create a soil map based on the analysis of the soil-vegetation relationship. For this purpose, thirty-six soil profiles were extensively described according to the World Reference Base for soil resources. In order to better classify these soils, physicochemical parameters, such as pHH2O, exchangeable cations, and particle size distributions, were measured for a specific set of soils (n = 16), representative of their diversity. To assess Soil Organic Matter (SOM) dynamics, samples were studied using Rock Eval pyrolysis. Results show a high soil diversity and heterogeneity with the presence of (i) Arenosols, as expected, but also of (ii) organic-rich soils, such as Chernozems, Phaeozems, and Kastanozems, (iii) salty/sodic soils, such as Solonchaks and Solonetz, and finally (iv) calcium-rich soils, such as Calcisols. Analyses of the different actors driving the soil diversity emphasized the importance of the surficial geology, composed of different sand deposits (red sands/white sands), carbonate and diatomite beds, as well as ancient salt deposits, in which high proportions of exchangeable Na+ were found, associated with high pHH2O (up to 11.3). In addition, as a parameter, the topography creates a complex hydrological system in the Chobe Enclave and therefore, induces a notable soil moisture gradient. Moreover, this study stressed the key role of termites: not only do they modify physicochemical patterns of soils, but they also decay and incorporate large quantities of fresh plant materials into soils. Finally, the analysis of Organic Matter (OM) showed that the Soil Organic Carbon (SOC) is composed essentially by recalcitrant Organic Carbon (OC) substances, such as charcoal, a common carbon type of tropical soils