Analyses of robot systems using fault and event trees: case studies

Safety in the use of robotics outside factories or processing plants has become a matter of great international concern. Domestic robots and those intended to assist nurses and surgeons in hospitals are examples of cases where safety and reliability are considered critical. The safe performance of robot systems depends on many factors, including the integrity of the robot's hardware and software, the way it communicates with sensory and other production equipment, the reliable function of the safety features present and the way the robot interacts with its environment. The use of systematic techniques such as Fault and Event Tree analysis to examine the safety and reliability of a given robotic system is presented. Considerable knowledge is needed before the application of such analysis techniques can be translated into safety specifications or indeed ‘fail-safe’ design features of robotic systems. The skill and understanding required for the formulation of such specifications is demonstrated here based on a number of case studies.     

A statistical analysis on the mechanical properties of nanocomposite modified asphalt mixtures

This study aimed to characterize the rate of change that takes place in the mechanical properties of polymer-nanocomposite asphalt (PNMA) mixtures due to altering asphalt binder grade and styrene-butadiene-styrene (SBS) type. Laboratory testing program included Marshall stability, resilient modulus, and wheel-tracking tests. Test results were compared and analyzed statistically by means of two-way analysis of variance and Tukey test. Variance analysis indicated the significant effect of both binder type and SBS grade on mechanical properties of asphalt mixtures. Interaction between binder type and SBS grade is also meaningful in all the experiments. The results also show that the binder type is the primary affecting factor, followed by the SBS grade.     

Prevalence and antimicrobial resistance of Campylobacter isolated from retail raw chicken and beef meat, Tehran, Iran

Campylobacter spp. is a leading cause of human diarrhea. The common source of infection is contaminated food, particularly poultry. The veterinary use of antimicrobial drugs has been suggested to be largely responsible for resistance in human isolates of this zoonotic pathogen. From April to October 2004, 241 samples of chicken and beef meat for sale in retail outlets in Tehran (Iran) were analyzed for the presence of Campylobacter. Totally, 88 (36.5%) Campylobacter strains were isolated. Campylobacter was isolated from a significantly larger number of chicken (63%) than beef (10%) meat (P < 0.0001). Susceptibilities of 72 strains were determined for eight antimicrobial drugs using the disk diffusion assay. Resistance to nalidixic acid was the most common finding (75%), followed by resistance to ciprofloxacin (69.4%), tetracycline (45.8%), amoxicillin (11.1%), streptomycin (4.2%), chloramphenicol (2.8%) and gentamicin (1.4%). None of the isolates was resistant to erythromycin. Multidrug resistance was seen in 75% of the Campylobacter strains.     

Study of Subsonic Flow Over a TOW 2B Missile

The objective of this investigation is to study the subsonic flow over a missile. In this paper, a model of TOW 2B missile is studied. Two computational approaches are being explored, namely solutions based on the Reynolds-averaged compressible Navier-Stokes equations and solutions based on the inviscid flow (small disturbance theory). The simulations are performed at the Mach number of 0.6, 0.7, 0.8, 0.9 and 1.0 at four angles of attack of 2, 4, 6 and 8 degree. Results obtained from analytical simulation are compared with numerical data. It is found that lift and drag coefficients would go up by increasing of the angle of attack and the Mach number. Trend of changes of the results that obtained from the small disturbance theory is roughly as same as the numeric solution.     

PERFORMANCE AND PROPERTIES OF KUSP1-BORIC ACID GEL SYSTEM FOR PERMEABILITY MODIFICATION PURPOSES

Blocking high permeability zones of reservoirs by hydrogels, and diverting the injected fluid towards the unswept zones of the reservoir is a promising method for improving the overall oil recovery in waterflooding and carbon dioxide flooding processes. A polymer gel treatment typically involves the injection of a solution of a medium to high molecular weight polymer and crosslinking agents into the high permeability zones or fractures. The polymer reacts with the crosslinker to form a three-dimensional gel network. KUSP1 biopolymer in sodium hydroxide solution produces a delayed gel system with orthoboric acid. The gelation time varies depending on the concentration of the orthoboric acid and temperature. Syneresis of this gel was studied in bottle tests as well as in the porous media. Samples of KUSP1-boric acid gel lost more than 80% of their initial volume in bottle tests after 250 h. Also, it was observed that this gel, when placed in a sandpack, lost up to about 50% of its initial volume. However, the high values of syneresis did not have a severe effect on the performance of the gel in porous media. KUSP1-boric acid gel was tested for reducing permeability to carbon dioxide and water in a series of tests conducted in a Berea sandstone core. It reduced the carbon dioxide permeability from 164 to 26 md and brine permeability from 420 to 90 md.     

IN SITU COMBUSTION IN ENHANCED OIL RECOVERY (EOR): A REVIEW

Enhanced oil recovery (EOR) refers to the technologies developed to increase extraction of crude oil from reservoirs after primary production. In situ combustion (ISC) is one of the methods developed for EOR. This review examines studies done by researchers worldwide to improve our understanding of the mechanism of oil cracking kinetics, which is one of the fundamental mechanisms of in situ combustion. Good agreement between the laboratory and field results has encouraged further research in this field. Extensive research at the laboratory scale to understand the pyrolysis and oxidation behavior of coke formed from medium and light oil and also to propose more realistic models to mimic the true behavior of in situ combustion has been undertaken in recent years. Apart from the classical Arrhenius model, researchers have come up with other models (two-step oxidation model) based on the type of combustion activity observed from their samples, thus modeling the process more accurately. Research work showing optimization of the parameters of ISC and improving the economic viability of the entire process is been one of the main focuses of this article. The review also explains the nature of the various experiments, sheds light on some of the concepts that remain unexplained, and opens the way for fresh thinking in those areas. It also highlights the possibility of developing global solutions for numerical simulation of this EOR process.     

Simultaneous Determination of Nitrite and Nitrate in Milk Samples by Ion Chromatography Method and Estimation of Dietary Intake

The presence of nitrate and nitrite in foods may be considered hazardous after ingestion in the gastrointestinal tract due to their reaction with naturally occurred secondary amines to form potentially carcinogenic nitrosamines. Due to this fact, a new method was developed in this study for the simultaneous determination of nitrite and nitrate in milk samples using by ion chromatography. Proposed mobile phase composed of sodium hydrogen carbonate and sodium carbonate (1.0 and 3.2 mmol/L) with a flow rate of 0.7 ml/min. The average recoveries for nitrate and nitrite were higher than 86 and 88%, respectively. The limit of detection for nitrate and nitrite were 0.24 and 0.09 mg/L, respectively. The results of 102 real milk samples showed nitrate was found in all of the samples (100%) with a mean of 34 ± 11 mg/L, while nitrite was found in none of the samples. The mean intake of nitrate in all age groups was lower than World Health Organization guideline. The present assessment concludes that the maximum contaminant level was equal to 82.8 mg/L nitrate. This method was fast, sensitive and accurate and is capable of being an alternative method in food control laboratories for investigation of nitrite and nitrate content. This is the first study of the determination and survey of nitrite and nitrate and exposure assessment of the Iranian population to nitrite and nitrate level in milk, which was widely used in infants and adolescents as one of the basic food components.