Simulation is essential for embedded control systems with task jitter

Sampling or task jitter affects the performance of digital control systems but realistic simulation of this effect has not been possible to date. Our previous work has developed a novel method to simulate sampling jitter in MATLAB/Simulink simulation software where the jitter is generated randomly. What has been missing is a way to capture sampling jitter from a target platform and then feed this timing information into the simulation. This paper presents a low-cost and novel solution to these problems. The method uses an Arduino board to capture task jitter from two different hardware platforms with multiple stressing conditions. Then the recorded performance data is used to drive realistic simulations of a control system. Measurement shows that the task jitter data does not follow any specific random distribution such as Gaussian or Uniform. Furthermore, very occasional timing patterns, which may not be picked up while testing a real system, can result in extreme controller responses. This novel method allows comparisons of different platforms and reduces the effort required to choose the most appropriate platform for full implementation.

     

Modeling phosphorus in the upper Etowah River basin: identifying sources under uncertainty.

The Uniform Covering by Probabilistic Rejection (UCPR) algorithm was used, in conjunction with the Soil and Water Assessment Tool (SWAT) model, to identify P loads from point source and nonpoint source polluters in the upper Etowah River basin (UERB) in Georgia. The key findings of the research are as follows. The mean absolute error was preferred over the root mean square error as a search criterion for the UCPR algorithm when water quality observations are scarce. The undocumented P load from point sources in the UERB was consistently estimated as about 43 kg/d by the proposed method; but the method was not able to identify the broiler litter application rate to the poultry/beef operation pastures. Point sources (both documented and undocumented), poultry/beef operation pastures, and forests are the three major contributors of P. During 1992-1996, on average they accounted for 36.4, 31.7, and 17.2% of P load from the UERB, respectively.     

Electronic specific heat of overdoped Tl2Ba2CuO6+δ in a magnetic field

We have measured the magnetic field dependence of the electronic specific heat ^el (=C^el/T) of polycrystalline Tl₂Ba₂CuO₆₊ from 8 K to above T_c, for samples with T_c = 24 K to 72 K using a high resolution, differential technique. We find that in applied fields of up to 13 T the position of the specific heat jump does not shift significantly for any T_c. This is in strong disagreement with H_C2(T) inferred from magnetoresistance experiments on the same compound, where the resistive transition is shifted down considerably by similar fields. However, there is a dramatic collapse of the specific heat anomaly height in field — signifying a loss in entropy around T_c — compensated by a corresponding increase in ^el at lower temperatures. The superconducting anomaly is almost completely suppressed in 13 T for the lowest T_c sample, compared to a reduction of 65 % for the sample with T_c = 72 K. We find simple vertical scaling of ^el(T) — _n suggesting that the field forces a proportion of the superconductor into the normal state, while the remainder in the superconducting state is unaffected.     

A packet scheduling scheme for 4G wireless access systems aiming to maximize revenue for the telecom carriers

Efficient utilization of network resources is a key goal for emerging BWAS. This is a complex goal to achieve due to the heterogeneous service nature and diverse QoS requirements of various applications that BWAS support. Packet scheduling is an important activity that affects BWAS QoS outcomes. This paper proposes a new packet scheduling mechanism that improves QoS in mobile wireless networks which exploit IP as a transport technology for data transfer between BWAS base stations and mobile users at the radio transmission layer. In order to improve BWAS QoS the new packet algorithm makes changes at both the IP and the radio layers. The new algorithm exploits handoff priority scheduling principles and takes into account buffer occupancy and channel conditions. The packet scheduling mechanism also incorporates the concept of fairness. The algorithm offers an opportunity to maximize the carriers’ revenue at various traffic situations. Simulation results were compared to well-known algorithms which demonstrated the new packet scheduling algorithm is able to provide a low handoff packet drop rate, low packet forwarding rate, low packet delay, ensure fairness amongst the users of different services and generates higher revenue. Furthermore this research proposes a new and novel measure named “Satisfaction Factor” to measure the efficacy of various scheduling schemes and finally proposes four performance metrics for NodeB’s of in Next Generation Wireless Networks.     

The dispersion of life of bonded MoS2 solid lubricant coatings

Solid lubricant coatings usually fail quite suddenly and thus, for a given specimen, a well-defined life can be measured. Failure may be caused by a number of physical processes, e.g. wearing through the coating, loss of adhesion to the substrate or fatigue. Wear tests of 70 specimens with similarly loaded MoS₂ coatings are analysed. The coating life (in cycles) was in general proportional to the thickness and inversely proportional to the load and amplitude, but there was considerable scatter. The results could be expressed in terms of a specific wear rate fitting a mixed Weibull distribution.     

The role of surface profilometry in failure diagnosis

Many machine failures are initiated at surfaces, often where two components interact, and before any realistic modification or remedial action can be pursued it is necessary to establish what initiated failure. Wear, plastic deformation, corrosion and adhesion/pick-up/transfer may be present in isolation or together and their positive identification can make large contributions to failure diagnosis. In such studies the role of surface topography is frequently significant, particularly where component size or the presence of ionizing radiation means that only surface replicas can be examined.This paper describes the use of profilometry as an aid to failure diagnosis in a number of applications including the following: a flow control valve where plastic deformation enabled the cause of malfunction to be positively identified; a static seal failure which was attributed to plastic deformation; positive identification of indentation arising under centrifugal loading; wear assessments to predict component life; the prediction of rolling element bearing life or reliability based on quantitative assessments of wear and oxide.     

An experimental study of a fixed bed chlor-alkali reactor

A 100 A continuous ‘flow-by’ chlor-alkali membrane reactor was constructed with both anode and cathode consisting of fixed beds of 0.6 to 1 mm diameter graphite particles. The reactor was operated over a range of conditions with and without co-current flow of air or oxygen to the cathode. With an anolyte of 5 M NaCl and catholyte 1.4–3 M NaOH the reactor produced sodium hydroxide and chlorine with ≥80% efficiency at temperatures 28–100°C, absolute pressure 270–970 kPa and superficial current density up to 3.3 kA m^?2. For operation at 100°C and an average pressure of 870 kPa with no gas delivered to the cathode, the cell voltage increased linearly from 2.5V at 0.3 kA m^?2 (10 A) to 4.0 V at 3.3 kA m^?2 (100 A). When oxygen was delivered to the cathode at 1 litre min^?1 under 870 kPa average pressure, the corresonding cell voltages were 1.6 V at 0.3 kA m^?2 to 3.4 V at 3.3 kA m^?2. In operation with air under the same conditions the cell voltage rose from 1.6 V at 0.3 kA m^?2 to 3.1 V at 1.6 kA m^?2. The performance of the oxygen cathode deteriorated with lower pressure and temperature due to mass transfer constraints on the oxygen reaction in the fixed bed electrode.     

Solute transport at the pedon and polypedon scales

Soil solute transport parameters are usually measured at the pedon scale, but predictions of transport at the polypedon scale are often required. Our objectives were to compare pedon- and polypedon-scale convection dispersion equation (CDE) transport parameters measured in a field leaching experiment and to compare deterministic and stochastic predictions of polypedon-scale transport. The study was conducted near Watkinsville, Ga. on a 12.5 by 30.5 m plot. Time domain reflectometry (TDR) waveguides (30 and 60 cm in length) were installed vertically at 80 locations to measure water content and impedance. The plot was irrigated and a Cl pulse was used as a tracer. We found very good agreement between the average CDE parameters measured at the pedon scale and those estimated at the polypedon scale in the 0–30 and 0–60 cm depth intervals. Although the variability in average pore velocities between pedons was large, the variability in velocities within a pedon caused by hydrodynamic dispersion was greater. As a result, a deterministic approach based on the CDE more accurately predicted the estimated polypedon scale breakthrough curve (BTC) at 30 and 60 cm depths than a stochastic approach based on the convective lognormal transfer function (CLT). This indicates that the pedon serves as a representative elementary volume (REV) for solute transport in this soil.     

The yeast PRS3 gene is required for cell integrity, cell cycle arrest upon nutrient deprivation, ion homeostasis and the proper organization of the actin cytoskeleton.

PRS3 is one of a family of five genes encoding phosphoribosylpyrophosphate synthetase, an enzyme which catalyses the first step in a variety of biosynthetic pathways, including purine and pyrimidine biosynthesis. We report here that prs3Delta mutants have a number of phenotypes that suggest an unexpected role for PRS3 in linking nutrient availability to cell cycle progression, cell integrity and the actin cytoskeleton. Upon nutrient limitation, prs3Delta mutants fail to arrest in G(1)-cells remain budded and a significant fraction have a G(2) DNA content. Furthermore, in such conditions, prs3Delta mutants have a disorganized actin cytoskeleton: actin accumulates in one or two intensely staining clumps per cell. Prs3Delta mutants also show defects in ion homeostasis and cell integrity. They fail to grow on medium containing 1.0 M NaCl, 5 mM caffeine or when incubated at 37 degrees C. The caffeine and temperature sensitivity are rescued by supplementing the growth medium with 1.0 M sorbitol. These phenotypes resemble those of whi2Delta mutations and indeed, a prs3 allele was recovered in a colony-sectoring screen for mutations that are co-lethal with whi2Delta. However, further investigation showed that the prs3Delta whi2Delta double mutant was viable, with no obvious growth defect compared to either single mutant. In the same colony-sectoring assay, an mpk1 allele was also recovered. Multicopy PRS3 rescued the caffeine sensitivity of this mpk1 allele.