Worst-case response time analysis of real-time tasks under fixed-priority scheduling with deferred preemption

Fixed-priority scheduling with deferred preemption (FPDS) has been proposed in the literature as a viable alternative to fixed-priority pre-emptive scheduling (FPPS), that obviates the need for non-trivial resource access protocols and reduces the cost of arbitrary preemptions. This paper shows that existing worst-case response time analysis of hard real-time tasks under FPDS, arbitrary phasing and relative deadlines at most equal to periods is pessimistic and/or optimistic. The same problem also arises for fixed-priority non-pre-emptive scheduling (FPNS), being a special case of FPDS. This paper provides a revised analysis, resolving the problems with the existing approaches. The analysis is based on known concepts of critical instant and busy period for FPPS. To accommodate for our scheduling model for FPDS, we need to slightly modify existing definitions of these concepts. The analysis assumes a continuous scheduling model, which is based on a partitioning of the timeline in a set of non-empty, right semi-open intervals. It is shown that the critical instant, longest busy period, and worst-case response time for a task are suprema rather than maxima for all tasks, except for the lowest priority task. Hence, that instant, period, and response time cannot be assumed for any task, except for the lowest priority task. Moreover, it is shown that the analysis is not uniform for all tasks, i.e. the analysis for the lowest priority task differs from the analysis of the other tasks. These anomalies for the lowest priority task are an immediate consequence of the fact that only the lowest priority task cannot be blocked. To build on earlier work, the worst-case response time analysis for FPDS is expressed in terms of known worst-case analysis results for FPPS. The paper includes pessimistic variants of the analysis, which are uniform for all tasks, illustrates the revised analysis for an advanced model for FPDS, where tasks are structured as flow graphs of subjobs rather than sequences, and shows that our analysis is sustainable.     

Minerals controlling arsenic and lead solubility in an abandoned gold mine tailings

Numerous areas have been contaminated by heavy metals and metalloids due to industrial and mining activities. Studies investigating the behavior of such contaminants in the environment have identified speciation as a key factor controlling their mobility, availability and toxicity. Here we characterize As- and Pb-bearing phases resulting from the oxidation of sulfide-rich tailings of a former gold mine (La Petite Faye, France) in order to assess the risk for water quality. Elements were first pre-concentrated by granulometric fractionation (sedimentation in deionized water) and then investigated using X-ray diffraction and electron microprobe analyses. Two main As-Pb-bearing minerals were clearly identified: scorodite (FeAsO4 x 2H2O) and beudantite PbFe3(AsO4)(SO4)(OH)6. Minor amounts of As and Pb were dissolved in deionized water during granulometric fractionation, indicating the possible presence of other soluble Pb-sulfates which could be some of the primary metastable products of sulfide oxidation. This dissolution also provides information about the fate of these phases in the case of intensive leaching of the tailings. Scorodite may not be considered as a relevant candidate for As on-site immobilization, because its solubility largely exceeds drinking water standards whatever the pH. Since beudantite solubility has not yet been determined, an estimation of its solubility product was obtained using the Gibbs free energy of formation of plumbojarosite [Pb0.5Fe3(SO4)2(OH)6]. This estimation suggests that beudantite should efficiently maintain low Pb concentration in waters. However, Pb dissolution in deionized water during the granulometric fractionation led to Pb concentrations much higher than the French and US drinking water standards (2.4 x 10(-7) mol l(-1)), which may be due to dissolution of the suspected metastable Pb-sulfates. Accurate determination of beudantite solubility is now required to improve the Pb risk assessment on such polluted sites.     

Protective effect of the sodium/hydrogen exchange inhibitors during global low-flow ischemia

A technique for noninvasive quantitative magnetic resonance imaging of perfusion is presented. It relies on using endogenous water as a freely diffusible tracer. Tissue water proton spins are magnetically labeled by slice-selective inversion, and longitudinal relaxation within the slice is detected using a fast gradient echo magnetic resonance imaging technique. Due to blood flow, nonexcited spins are washed into the slice resulting in an acceleration of the longitudinal relaxation process. Incorporating this phenomenon into the Bloch equation yields an expression that allows quantification of perfusion on the basis of a slice-selective and a nonselective inversion recovery experiment. Based on this technique, quantitative parameter maps of the regional cerebral blood flow (rCBF) were obtained from eight rats. Evaluation of regions of interest within the cerebral hemispheres yielded an average rCBF value of 104 +/- 21 ml/min/100 g, which increased to 219 +/- 30 ml/min/100 g during hypercapnia. The measured rCBF values are in good agreement with previously reported literature values.     

Response to therapy in demyelinating motor neuropathy

We reviewed results of immunotherapy in patients with demyelinating motor neuropathy (DMN), and found that patients over 50 years of age at onset responded poorly, and younger patients responded variably to intervention. We suggest that patients with DMN be given a guarded prognosis, particularly if >50 years of age at onset.     

Multiple-Fiber and Multiple-Wavelength Confocal Sensing With Diffractive Optical Elements

Adding a diffractive element to the imaging optics of a fiber-based confocal sensor greatly enhances the chromatic dispersion of the optics. This can be exploited to enhance the sensing range and resolution of the sensor. Several examples are given using one and two fibers with simultaneous dual wavelength illumination to probe the displacement of a target object.     

Improved Message Forwarding for Multi-Hop HaRTES Real-Time Ethernet Networks

Nowadays, switched Ethernet networks are used in complex systems that encompass tens to hundreds of nodes and thousands of signals. Such scenarios require multi-switch architectures where communications frequently occur in multiple hops. In this paper we investigate techniques to allow efficient multi-hop communication using HaRTES switches. These are modified Ethernet switches that provide real-time traffic scheduling, dynamic bandwidth management and temporal isolation between real-time and non-real-time traffic. This paper addresses the problem of forwarding traffic in HaRTES networks. Two methods have been recently proposed, namely Distributed Global Scheduling (DGS) that buffers traffic between switches, and Reduced Buffering Scheme (RBS), that uses immediate forwarding. In this paper, we discuss the design and implementation of RBS within HaRTES and we carry out an experimental validation with a prototype implementation. Then, we carry out a comparison between RBS and DGS using worst-case response time analysis and simulation. The comparison clearly establishes the superiority of RBS concerning end-to-end response times. In fact, with sample message sets, we achieved reductions in end-to-end delay that were as high as 80 %.     

Parameterization of aerosol and cirrus cloud effects on reflected sunlight spectra measured from space: application of the equivalence theorem

An original methodology to account for aerosol and cirrus cloud contributions to reflected sunlight is described. This method can be applied to the problem of retrieving greenhouse gases from satellite-observed data and is based on the equivalence theorem with further parameterization of the photon path-length probability density function (PPDF). Monte Carlo simulation was used to validate this parameterization for a vertically nonhomogeneous atmosphere including an aerosol layer and cirrus clouds. Initial approximation suggests that the PPDF depends on four parameters that can be interpreted as the effective cloud height, cloud relative reflectance, and two additional factors to account for photon path-length distribution under the cloud. We demonstrate that these parameters can be efficiently retrieved from the nadir radiance measured in the oxygen A-band and from the H(2)O-saturated area of the CO(2) 2.0 microm spectral band.     

Improving seismic chimney detection using directional attributes

The chimney cube is a seismic body detection technique to facilitate the interpretation of seismic chimneys. The method uses multi-attributes and a supervised neural network to produce a chimney cube, i.e. a three-dimensional (3D) volume of the chimney probability. In the original method, single and multi-trace attributes are extracted in three vertically aligned windows. Within each window the energy and several trace-to-trace similarities are computed. Similarities are computed without correcting for structural dip. Here we discuss improvements made to the original algorithm by taking local dip and azimuth information into account. The similarity attributes are now calculated by following the local direction (dip and azimuth) from trace to trace. A technique we call “phase-locking” fine-tunes the calculated times at which trace segments are extracted for similarity calculations. The new network with these similarities and a new attribute called dip-variance yields a lower misclassification and a significantly higher resolution chimney cube as compared to the original algorithm.     

Influence of turbulence on the thermal radiation transfer in diffusion hydrogen flames

The effect of the turbulent fluctuations of the temperature and concentrations in a diffusion hydrogen flame on its thermal radiation has been quantitatively estimated. The numerical investigations were carried out using the data on the laser probing of this flame. The coefficients of the radiation-transfer equation were determined by averaging instantaneous temperatures and concentrations, which made it possible to eliminate the errors introduced by model distribution functions. It is shown that the effect of the turbulence of a flame on its radiation determines, to a large extent, the formation of the thermal radiation fields of the flame.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 77, No. 6, pp. 146–151, November–December, 2004.     

Red-black trees with relative node keys

This paper addresses the problem of storing an ordered list using a red-black tree, where node keys can only be expressed relative to each other. The insert and delete operations in a red-black tree are extended to maintain the relative key values. The extensions rely only on relative keys of neighboring nodes, adding constant overhead and thus preserving the logarithmic time complexity of the original operations.