Model-based fault diagnosis in continuous dynamic systems

Traditional fault detection and isolation methods are based on quantitative models which are sometimes difficult and costly to obtain. In this paper, qualitative bond graph (QBG) reasoning is adopted as the modeling scheme to generate a set of qualitative equations. The QBG method provides a unified approach for modeling engineering systems, in particular, mechatronic systems. An input-output qualitative equation derived from QBG formalism performs continuous system monitoring. Fault diagnosis is activated when a discrepancy is observed between measured abnormal behavior and predicted system behavior. Genetic algorithms (GA's) are then used to search for possible faulty components among a system of qualitative equations. In order to demonstrate the performance of the proposed algorithm, we have tested it on a laboratory scale servo-tank liquid process rig. Results of the proposed model-based fault detection and diagnosis algorithm for the process rig are presented and discussed.     

Formation of haloacetic acids during monochloramination

Factors that affect the formation of haloacetic acids (HAAs) during monochloramination, such as monochloramine application techniques, the initial chlorine (Cl) to ammonia-N (N) ratios, the bromide concentrations, and the wastewater quality, were studied. Aqueous humic acid solutions and undisinfected wastewater effluent samples obtained from two Hong Kong Sewage Treatment Works (STWs) were monochloraminated under various conditions. HAA formation was strongly affected by the monochloramine application techniques. The formation of trichloroacetic acid (TCAA) and total HAAs was reduced by adding preformed monochloramine. A higher initial Cl:N ratio indicated a higher chlorine demand and consequently led to higher HAA yields. Increasing the bromide concentration shifted HAAs from chlorinated species to brominated species and increased the yields of total HAAs, concurrent with decreases in the yields of dichloroacetic acid (DCAA) and TCAA but with increases in those of the other HAAs measured. Variations in the patterns of HAA formation were observed in monochloraminated wastewater effluent samples. The variations cannot be simply explained by the chlorine chemistry involving ammonia and/or bromide but are likely attributable to the combining effects of the water quality and the characteristics of the organics in the wastewater.     

A qualitative assessment methodology for road safety policy strategies

This paper proposes a qualitative assessment methodology that is comprised of a cluster analysis and an autoregression analysis that assess the effects of various road safety strategies implemented in Hong Kong over the last 10 years. The cluster analysis is first used to group over a hundred road safety projects and programs into a smaller set of meaningful road safety policy strategy clusters. These strategies, together with the trend factor, seasonal pattern, car crashworthiness and meteorological data are then used in the autoregression analysis to relate to the fatality and casualty rates of drivers, passengers, motorcyclists, and pedestrians. This method allows the evaluation of the overall effects of the road safety strategies, and the effects and relative significance of each individual strategy. The evaluation method is described, and the main findings of the study are discussed.     

Biosensor based on cellobiose dehydrogenase for detection of catecholamines

A cellobiose dehydrogenase (CDH)-modified graphite electrode was designed for amperometric detection of catecholamines in the flow injection mode, by their recycling between the graphite electrode (+300 mV vs Ag|AgCl) and the reduced FAD cofactor of adsorbed CDH, resulting in an amplified response signal. The high efficiency of the enzyme-catecholamine reaction leads to a detection limit below 1 nM and a sensitivity of 15.8 A.M(-1) x cm(-2) (approximately 1150 nA/microM) for noradrenaline, with a coverage of less than 2.5 microg of CDH adsorbed on the electrode surface (0.073 cm(2)). Working parameters such as pH, cellobiose concentration, carrier buffer, and applied potential were optimized, using hydroquinone as a model analyte. The sensitivity, linear range, and amplification factor can be modulated by the steady-state concentration of cellobiose in the flow buffer. The response of the sensor decreases only 2% when run continuously for 4 h in the flow injection mode. The response peak maximum is obtained within 6 s at a flow rate of 0.5 mL/min, representing the time of the entire sample segment to pass the electrode. CDH enzymes from Phanerochaete chrysosporium and Sclerotium rolfsii were investigated, providing different characteristics of the sensor, with sensors made with CDH from P. chrysosporium being the better ones.     

Polariscope for simultaneous measurement of the principal axis and the phase retardation by use of two phase-locked extractions

A novel polariscope with electro-optic modulation that is capable of simultaneous measurement of the principal axis and the phase retardation of an optical linear birefringent medium by means of two phase-locked extractions is described. A phase compensator is used to suppress the transmission phase-retardation effect of the beam splitter, thereby enhancing the precision of the measuring performance. The validity of the proposed design is demonstrated by measurement of the principal axis and phase retardation of a quarter-wave plate sample. There are absolute errors of 0.25 degrees on average and 0.58 degrees at maximum in the principal-axis measurement and of 0.75 degrees (0.83%) on average and 3.11 degrees at maximum in the phase-retardation measurement. Meanwhile, the retardation error lies within a 5% uncertainty range of a commercial wave plate. The root-mean-square resolutions for the principal-axis angle and phase-retardation measurements are 0.042 degrees and 0.081 degrees, respectively. Finally, the dynamic ranges of the principal-axis angle measurement and the phase-retardation measurement extend as far as 180 degrees.     

Optical implementation of the hopfield neural network with matrix gratings

We propose a new method for the optical implementation of the Hopfield neural network with a universal tool. The tool is a matrix grating constituted with a group of element gratings. The algorithms for designing a matrix grating are proposed, and a matrix grating is created to execute recognition experiments by use of the Hopfield neural network. The experimental results demonstrate that the proposed method performs well. The stability of the light efficiencies of different optical components used in optical networks is also considered.     

Statistical intensity of amplitude scintillations on Earth-space X-band link

Amplitude fluctuation measurements made on a 30° of elevation earth-space link at 11.6 GHz using the Orbital Test Satellite transmissions are described. Results on the intensity and cumulative distribution of the scintillations between 0.01 Hz and 14 Hz are presented and show that for percentages of time less than 20% the peak amplitude deviations from the mean exceed the values derived using a log-normal distribution and the average r.m.s. value. For greater time percentages the agreement with a log-normal distribution is good.     

Rate of evolution of the specific surface area of surface snow layers

The snowpack can impact atmospheric chemistry by exchanging adsorbed or dissolved gases with the atmosphere. Modeling this impact requires the knowledge of the specific surface area (SSA) of snow and its variations with time. We have therefore measured the evolution of the SSA of eight recent surface snow layers in the Arctic and the French Alps, using CH4 adsorption at liquid nitrogen temperature (77 K). The SSA of fresh snow layers was found to decrease with time, from initial values in the range 613-1540 cm2/g to values as low as 257 cm2/g after 6 days. This is explained by snow metamorphism, which causes modifications in crystal shapes, here essentially crystal rounding and the disappearance of microstructures. A parametrization of the rate of SSA decrease is proposed. We fit the SSA decrease to an exponential law and find that the time constant alpha(exp) (day(-1)) depends on temperature according to alpha(exp) = 76.6 exp (-1708/7), with Tin kelvin. Our parametrization predicts that the SSA of a snow layer evolving at -40 degrees C will decrease by a factor of 2 after 14 days, while a similar decrease at -1 degrees C will only require 5 days. Wind was found to increase the rate of SSA decrease, but insufficient data did not allow a parametrization of this effect.     

Snow metamorphism as revealed by scanning electron microscopy

Current theories of snow metamorphism indicate that sublimating snow crystals have rounded shapes, while growing crystals have shapes that depend on growth rates. At slow growth rates, crystals are rounded. At moderate rates, they have flat faces with rounded edges. At fast growth rates, crystals have flat faces with sharp edges, and they have hollow faces at very fast growth rates. The main growth/sublimation mechanism is thought to be by the homogeneous nucleation of new layers at or near crystal edges. It was also suggested that the equilibrium shape of snow crystals would be temperature dependent: rounded above -10.5 degrees C, and faceted below. To test these paradigms, we have performed SEM investigations of snow samples having undergone metamorphism under natural conditions, and of snow samples subjected to isothermal metamorphism at -4 degrees and -15 degrees C in the laboratory. In general, current theories predicting crystal shapes as a function of growth rates, and of whether crystals are growing or sublimating, are verified. However, the transition in equilibrium shapes from rounded to faceted at -10.5 degrees C is not observed in our isothermal experiments that reveal a predominance of rounded shapes after more than a month of metamorphism at -4 and -15 degrees C. Some small crystals with flat faces that also have sharp angles at -15 degrees C, are observed in our isothermal experiments. These faces are newly formed, and contradict current theory. Several hypotheses are proposed to explain their occurrence. One is that they are due to sublimation at emerging dislocations.     

A framework for efficient regression tests on database applications

Regression testing is an important software maintenance activity to ensure the integrity of a software after modification. However, most methods and tools developed for software testing today do not work well for database applications; these tools only work well if applications are stateless or tests can be designed in such a way that they do not alter the state. To execute tests for database applications efficiently, the challenge is to control the state of the database during testing and to order the test runs such that expensive database reset operations that bring the database into the right state need to be executed as seldom as possible. This work devises a regression testing framework for database applications so that test runs can be executed in parallel. The goal is to achieve linear speed-up and/or exploit the available resources as well as possible. This problem is challenging because parallel testing needs to consider both load balancing and controlling the state of the database. Experimental results show that test run execution can achieve linear speed-up by using the proposed framework.