Memory-processor co-scheduling in fixed priority systems

A major obstacle towards the adoption of multi-core platforms for real-time systems is given by the difficulties in characterizing the interference due to memory contention. The simple fact that multiple cores may simultaneously access shared memory and communication resources introduces a significant pessimism in the timing and schedulability analysis. To counter this problem, predictable execution models have been proposed splitting task executions into two consecutive phases: a memory phase in which the required instruction and data are pre-fetched to local memory (M-phase), and an execution phase in which the task is executed with no memory contention (C-phase). Decoupling memory and execution phases not only simplifies the timing analysis, but it also allows a more efficient (and predictable) pipelining of memory and execution phases through proper co-scheduling algorithms. In this paper, we take a further step towards the design of smart co-scheduling algorithms for sporadic real-time tasks complying with the M/C (memory-computation) model. We provide a theoretical framework that aims at tightly characterizing the schedulability improvement obtainable with the adopted M/C task model on a single-core systems. We identify a tight critical instant for M/C tasks scheduled with fixed priority, providing an exact response-time analysis with pseudo-polynomial complexity. We show in our experiments that a significant schedulability improvement may be obtained with respect to classic execution models, placing an important building block towards the design of more efficient partitioned multi-core systems

Response-Time Analysis of Conditional DAG Tasks in Multiprocessor Systems

Different task models have been proposed to represent the parallel structure of real-time tasks executing on manycore platforms: fork/join, synchronous parallel, DAG-based, etc. Despite different schedulability tests and resource augmentation bounds are available for these task systems, we experience difficulties in applying such results to real application scenarios, where the execution flow of parallel tasks is characterized by multiple (and nested) conditional structures. When a conditional branch drives the number and size of sub-jobs to spawn, it is hard to decide which execution path to select for modeling the worst-case scenario. To circumvent this problem, we integrate control flow information in the task model, considering conditional parallel tasks (cp-tasks) represented by DAGs composed of both precedence and conditional edges. For this task model, we identify meaningful parameters that characterize the schedulability of the system, and derive efficient algorithms to compute them. A response time analysis based on these parameters is then presented for different scheduling policies. A set of simulations shows that the proposed approach allows efficiently checking the schedulability of the addressed systems, and that it significantly tightens the schedulability analysis of non-conditional (e.g., Classic DAG) tasks over existing approaches

Temporal variation of soil sorptivity under conventional and no-till systems determined by a simple laboratory method

Soil water sorptivity (S) is an important property that measures the soil capacity to take water rapidly under capillary forces. Usually S is not included in soil laboratory routine experiments because there is not a widely accepted methodology for its determination. The objectives of this work were: i) to propose a modification on the Leeds-Harrison et al. (1994) method (LH) to determine S in undisturbed soil samples; and ii) to determine the temporal variation of S and saturated hydraulic conductivity (K0) in a soil under conventional tillage (CT) and no-tillage (NT) treatments. Additionally, the influence of soil pore size distribution (PoSD) on S was analyzed. Undisturbed soil samples (5 cm height, 5 cm diameter) were collected from the upper 10 depth cm of each plot, from each treatment at four different times during a maize growing season (before seeding (BS), 6 leaf stage (V6), physiological maturity (R5) and after harvest (AH)). PoSD was determined in a sand box apparatus. After that, S was determined in the same samples using a modified Leeds-Harrison approach. For the proposed modification the difference between initial and final water content was actually gravimetrically measured in each sample, rather than considering it equal to the total porosity (TP). The proposed improvement was validated comparing the obtained S values with those calculated using standard one-dimension horizontal infiltration in sieved soil (0.098 vs 0.079 cm s-1/2, respectively) and in calibrated sand (0.041 vs 0.040 cm s-1/2, respectively). These differences were not significant. Both S and K0 were significantly affected by the sampling time in both treatments (mean values ranged between 0.022 and 0.077 cm s-1/2 and 1.57 and 3.75 cm s-1 respectively). We did not find a significant dependence of S with three pore size ranges analyzed. The proposed improvement of the Leeds-Harrison method allowed determining the temporal variation of S in representative undisturbed soil samples.Facultad de Ciencias Agrarias y Forestale

On the Implementation of a regional X-bandweather radar network

In the last few years, the number of worldwide operational X-band weather radars has rapidly been growing, thanks to an established technology that offers reliability, high performance, and reduced efforts and costs for installation and maintenance, with respect to the more widespread C- and S-band systems. X-band radars are particularly suitable for nowcasting activities, as those operated by the LaMMA (Laboratory of Monitoring and Environmental Modelling for the sustainable development) Consortium in the framework of its institutional duties of operational meteorological surveillance. In fact, they have the capability to monitor precipitation, resolving very local scales, with good spatial and temporal details, although with a reduced scanning range. The Consortium has recently installed a small network of X-band weather radars that partially overlaps and completes the existing national radar network over the north Tyrrhenian area. This paper describes the implementation of this regional network, detailing the aspects related with the radar signal processing chain that provides the final reflectivity composite, starting from the acquisition of the signal power data. The network performances are then qualitatively assessed for three case studies characterised by different precipitation regimes and different seasons. Results are satisfactory especially during intense precipitations, particularly regarding what concerns their spatial and temporal characterisation

The Potential of Smartlnb Networks for Rainfall Estimation

NEFOCAST is a research project that aims at retrieving rainfall fields from channel attenuation measurements on satellite links. Rainfall estimation algorithms rely on the deviation of the measured Es/N0 from the clear-sky conditions. Unfortunately, clear-sky measurements exhibit signal fluctuations (due to a variety of causes) which could generate false rain detections and reduce estimation accuracy. In this paper we first review the main causes of random amplitude fluctuations in the received Es/N0, and then we present an adaptive tracking algorithm based on two Kalman filters: one that tracks slow changes in Es/N0 due to external causes and another which tracks fast Es/N0 variations due to rain. A comparison of the outputs of the two filters confirms the reliability of the rainfall rate estimate

Mídias Digitais e suas potencialidades nos tempos contemporâneos: estudo de caso “Mídia Ninja”

Este texto traz aproximação preliminar em relação a indagações e questionamentos sobre as possibilidades oportunizadas pelas redes sociais digitais e o jornalismo móvel. A partir de algumas exemplificações como o caso do “Mídia Ninja”, mídia digital alternativa com visibilidade potencializada nas manifestações do Movimento “Vem Pra Rua”, mostra-se a necessidade de compreender esses fenômenos midiáticos, principalmente na sociedade contemporânea, sob a ótica da juventude e da cidadania, assim como suas potencialidades na construção do conhecimento colaborativo e compartilhamento de informações e opiniões. A análise envolveu pesquisa exploratória, bibliográfica, estudo de caso e análise de imagem.

Memory-Processor Co-Scheduling in Fixed Priority Systems

ABSTRACT A major obstacle towards the adoption of multi-core platforms for real-time systems is given by the difficulties in characterizing the interference due to memory contention. The simple fact that multiple cores may simultaneously access shared memory and communication resources introduces a significant pessimism in the timing and schedulability analysis. To counter this problem, predictable execution models have been proposed splitting task executions into two consecutive phases: a memory phase in which the required instruction and data are pre-fetched to local memory (Mphase), and an execution phase in which the task is executed with no memory contention (C-phase). Decoupling memory and execution phases not only simplifies the timing analysis, but it also allows a more efficient (and predictable) pipelining of memory and execution phases through proper co-scheduling algorithms. In this paper, we take a further step towards the design of smart co-scheduling algorithms for sporadic real-time tasks complying with the M/C (memory-computation) model. We provide a theoretical framework that aims at tightly characterizing the schedulability improvement obtainable with the adopted M/C task model on a single-core systems. We identify a tight critical instant for M/C tasks scheduled with fixed priority, providing an exact response-time analysis with pseudo-polynomial complexity. We show in our experiments that a significant schedulability improvement may be obtained with respect to classic execution models, placing an important building block towards the design of more efficient partitioned multi-core systems

Temporal Variation of Soil Physical Quality under Conventional and No-Till Systems

Determination of soil physical quality (SPQ) is very important because it is related to many important soil processes. However, it is not clear which indicators should be considered in this evaluation, and information about temporal variation of SPQ under different soil tillage systems is scarce. The aim of this study was to determine the effects of no tillage (NT) and conventional tillage (CT) on temporal variation of capacity SPQ indicators [bulk density (BD), macroporosity (Pmac), air capacity (AC), plant available water capacity (PAWC), relative field capacity (RFC), Dexter's (S), and structural stability index (SSI)], and dynamic SPQ indicators [field saturated hydraulic conductivity (K0), water-conducting macroporosity (εma), and mesoporosity (εme); and pore continuity indexes based on water flux of total porosity (CWTP), of macroporosity (CWmac), and of mesoporosity (Cwmes)]. Additionally, the effect of the soil management system on corn yield was evaluated. Measurements and determinations were made at four different moments/cropping stages in the corn growing season (BS: before seeding; V6: six leaf stage; R5: physiological maturity; and AH: after harvest). Capacity SPQ indicators were derived from the soil water retention curve determined using sand box and pressure chambers, and dynamic SPQ indicators were derived from field infiltration data measured using a tension disc infiltrometer. Most capacity SPQ indicators were affected by the moment/cropping stage in which samples were taken, but followed similar trends and had similar values under both treatments, particularly in the AH stage. Dynamic SPQ indicators varied differently during the growing season depending on the management system. Under NT, most dynamic indicators increase from BS to V6 and decrease again at AH, whereas under CT, they follow a different trend, decreasing from BS to V6, remaining constant until R5, and increasing at AH. Corn yield was lower under CT (NT: 10,939 kg ha-1; CT: 8,265 kg ha-1). These results emphasize the need to include dynamic SPQ indicators, and their temporal variation when evaluating cropping systems with the aim of modeling crop yields. The capacity SPQ indicators were not able to distinguish between treatments.Facultad de Ciencias Agrarias y Forestale

Therapeutic effects of strategic supplementation with copper in breeding calves

Debido a que las menores ganancias diarias de peso (GDP) son una seria consecuencia de la carencia de Cu en los sistemas de cría bovina, en una zona con incidencia endémica de hipocuprosis se evaluó el efecto terapéutico de la suplementación de las madres al final de su gestación y de sus terneros a los tres meses de edad. Este grupo de suplementación estratégica (GSE) fue comparado con otros dos grupos: uno suplementado (GS) que mantuvo durante el ensayo un estatus normal de Cu y un grupo no suplementado (GNS) que reflejó la carencia. Los terneros de cada grupo nacieron sin diferencia de peso en agosto. Las GDP fueron similares para los grupos GS y GSE hasta diciembre, cuando comenzó a disminuir la performance del GNS. En febrero el GS se diferenció claramente del GNS, mientras que el GSE perdió performance y acompañó al GNS. Las cupremias reflejaron claramente el comportamiento de la GDP, aunque las menores GDP en el GSE al final del ensayo se presentaron con hipocupremias moderadas, superiores a las consideradas de riesgo. Se concluye que bajo las condiciones de este ensayo, la suplementación estratégica de las madres en el último tercio de la gestación y de los terneros cuando promedian los tres meses de edad es útil para evitar menores GDP, pero deja un lapso previo al destete que origina pérdidas de performance.Considering that low average daily gain (ADG) is a serious consequence of Cu deficiency in breeding cattle, the therapeutic effects of Cu supplementation was evaluated in third-trimester pregnant cows and their three-months old calves in an endemic area of hypocuprosis. This strategic supplementation group (SSG) was compared with other two groups: one Cu-supplemented (SG) which maintained normal Cu status, and the other non-supplemented (NSG) which expressed Cu deficiency. The calves of each group were born in August without body weight differences. The AVG was similar for both SG and SSG groups until December when NSG performance began to reduce. In February the SG was clearly different from NSG, while SSG decreased its performance and remained similar to the NSG. The cupremia clearly reflected the AVG differences, although the lower ADG in the SSG at the end of the trial occurred in the presence of moderate hypocupremia, and this Cu concentration was higher than that considered risky. It is concluded that, under the conditions of this study, the strategic supplementation of cows during the last trimester of pregnancy and calves at the age of three months old was useful to avoid low ADG, although there was a period of time before weaning with performance loss.Facultad de Ciencias Veterinaria