Effect of oil viscosity on transformer loading capability at lowambient temperatures

The applicability of the ANSI loading guide for power transformers is limited to ambient temperatures above 0°C because the thermal model does not account for variations in the oil viscosity and winding resistance. A practical calculation method based on the bottom-oil temperature and the surface temperature at the top of the cooling duct has been developed. Results indicate that the proposed thermal model could provide a sound basis for calculating the overload capacity for ambient temperatures below 0°C or for severe overloads of short duration     

ARIANEXPERT: A knowledge based system to analyze ARIANE's mission data

The ARIANE launcher post mission analysis is done at ARIANESPACE. This activity is called the ‘level 0 post flight analysis’ (PFA) and is carried out after each launch by about 60 engineers who are working together under the leadership of ARIANESPACE.

The PFA is one of the most critical of ARIANE operations, for several reasons:

• - The launch rate (8 a year for ARIANE 4) leaves a very short time to carry out all the verification work. Moreover, the PFA is a mandatory step before authorizing the next launch.

• - The complexity of the ARIANE launcher results in a very high demand on the PFA engineers. Moreover, there are problems of availability of people with relevant expert knowledge (characterized by a substantial staff turn-over during the 10 year life duration of ARIANE 4) which could potentially result in errors or omissions.

It is very important to be able to take into account the experience of the preceding flights and to record the results and the knowledge accumulated for each launch.

• - The quality and the reliability of the PFA mainly depends on the accessibility of data and on the used methodology.

Because the PFA is still largely done manually, and does not benefit from improved methodologies and advanced technologies providing computerized support for data processing and diagnosis, ARIANESPACE has sponsored MATRA ESPACE for the development of a knowledge based system, called ARIANEXPERT, for supporting the PFA activity. This system combines AI techniques and numerical analysis techniques, together with advanced graphical capabilities.

A prototype has been delivered in April 1990 and has been used since 6 months by ARIANESPACE during real PFAs. Several lessons have been drawn from this operational experience and are described in this paper. They concern:

• - The utility and justification of the use of AI techniques mostly coming from the explanation capabilities and the stress put on capturing the expert knowledge.

• - The difficulties associated with the integration of such systems in the exploitation of ARIANE due to the introduction of very new tasks.

• - The user point of view which evolved from reluctant to convinced.

     

Optimal data gathering paths and energy-balance mechanisms in wireless networks

This paper studies the data gathering problem in wireless networks, where data generated at the nodes has to be collected at a single sink. We investigate the relationship between routing optimality and fair resource management. In particular, we prove that for energy-balanced data propagation, Pareto optimal routing and flow maximization are equivalent, and also prove that flow maximization is equivalent to maximizing the network lifetime. We algebraically characterize the network structures in which energy-balanced data flows are maximal. Moreover, we algebraically characterize communication links which are not used by an optimal flow. This leads to the characterization of minimal network structures supporting the maximal flows.We note that energy-balance, although implying global optimality, is a local property that can be computed efficiently and in a distributed manner. We suggest online distributed algorithms for energy-balance in different optimal network structures and numerically show their stability in particular setting. We remark that although the results obtained in this paper have a direct consequence in energy saving for wireless networks they do not limit themselves to this type of networks neither to energy as a resource. As a matter of fact, the results are much more general and can be used for any type of network and different types of resources.     

Exhaust ventilation in attached garages improves residential indoor air quality

Previous research has shown that indoor benzene levels in homes with attached garages are higher than homes without attached garages. Exhaust ventilation in attached garages is one possible intervention to reduce these concentrations. To evaluate the effectiveness of this intervention, a randomized crossover study was conducted in 33 Ottawa homes in winter 2014. VOCs including benzene, toluene, ethylbenzene, and xylenes, nitrogen dioxide, carbon monoxide, and air exchange rates were measured over four 48‐hour periods when a garage exhaust fan was turned on or off. A blower door test conducted in each garage was used to determine the required exhaust fan flow rate to provide a depressurization of 5 Pa in each garage relative to the home. When corrected for ambient concentrations, the fan decreased geometric mean indoor benzene concentrations from 1.04 to 0.40 μg/m³, or by 62% (P<.05). The garage exhaust fan also significantly reduced outdoor‐corrected geometric mean indoor concentrations of other pollutants, including toluene (53%), ethylbenzene (47%), m,p‐xylene (45%), o‐xylene (43%), and carbon monoxide (23%) (P<.05) while having no impact on the home air exchange rate. This study provides evidence that mechanical exhaust ventilation in attached garages can reduce indoor concentrations of pollutants originating from within attached garages.     

Kinematic modeling for the assessment of wheelchair user'sstability

A computer kinematic model was developed to simulate the lateral and transverse stabilities of wheelchair users in order to compare the effect of different backrests. This model is composed of ellipsoids and parallelepipeds representing the main components of the human body, the seating devices and the wheelchair. A fifteen-segment three-dimensional (3-D) model linked by spherical and revolute joints was created using the ADAMS software (Mechanical Dynamics, Inc.). Torsional springs and dampers are used at the joints to represent four sets of articulation stiffness. Seating devices are represented with 45 rectangular surface patches. The interface between human body and seating devices is modeled by contact elements, which included the specification of stiffness, damping, and deformation of cushions and buttocks. Simulations of a user and his wheelchair moving at 1.4 m/s on a tilted pathway were performed. Different indexes [trunk lateral tilt (TLT) and trunk transverse rotation (TTR)] were measured and compared to those of a similar experimental study on four subjects. The effect of joint stiffness was quantified and a sensitivity study showed the importance of the hip, neck, lumbar, and thoracic joint stiffness on model response (between 16% and 68%). Two backrests (standard and highly contoured) were tested with the kinematic model and their stability compared. Overall, the coherence between the simulations and the experiments shows that this approach is appropriate to compare various seating devices (maximal difference of 1.3° between the simulated and experimental curves for the intermediate joint stiffness sets). The smallest rotations of the highly contoured backrest (6.3° versus 8.9° for TLT and 3.9° versus 6.7° for TTR) suggest that the contouring of the mid torso is more efficient than the lower torso to provide stability to the wheelchair user. This model is an adequate tool to test and improve the design of seating aids     

Impulse differential inclusions: a viability approach to hybridsystems

Impulse differential inclusions are introduced as a framework for modeling hybrid phenomena. Connections to standard problems in the area of hybrid systems are discussed. Conditions are derived that allow one to determine whether a set of states is viable or invariant under the action of an impulse differential inclusion. For sets that violate these conditions, methods are developed for approximating their viability and invariance kernels, that is the largest subset that is viable or invariant under the action of the impulse differential inclusion. The results are demonstrated on examples     

Joint influence of alcohol, tobacco, and coffee on biological markers of heavy drinking in alcoholics

BACKGROUND: Recent reports suggest that gamma-glutamyl transferase (GGT) decreases with coffee intake. The aim of this study was to examine the joint influence of alcohol, tobacco, cotinine, coffee, and caffeine on biological markers of heavy drinking in an alcoholic population. METHODS: Subjects were 160 alcohol-dependent inpatients. Biological assessments, performed at admission, were plasma levels of GGT, apolipoprotein AI, aspartate aminotransferase, and mean corpuscular volume (MCV), and urine cotinine and caffeine indexes. Years of alcohol abuse and of smoking, alcohol and coffee intake, and smoking rate were estimated in a semistructured interview, and Fagerstr?m Tolerance Questionnaire was completed by inpatients. RESULTS: Coffee intake, but not caffeine, correlated negatively with biological markers of heavy drinking, after controlling for alcohol and tobacco intake. Years of smoking correlated positively to MCV, after controlling for alcohol and coffee intake. CONCLUSIONS: Concerning the effect of coffee, the most likely hypothesis is that noncaffeine coffee fractions have a protective effect on liver cells. Concerning the effect of smoking, one can propose that the increase of MCV with smoking could be a consequence of carbon monoxide inhalation, leading to hypoxemia, or of folate deficiency.     

Fiber optic applications of multiple quantum well electroabsorption modulators

Electroabsorption modulators (eam) have proved to be very attractive both as optical sources (monolithically integrated NRZ transmitters andrz pulse generators) as well as for very fast signal processing (demultiplexing, regeneration, wavelength conversion,...). Their design criteria, technology and implementation in future networks are reviewed, and the main issues are discussed.     

Andreev Bound-State Tunneling and ESR Spectroscopy of High-Temperature Superconductors and Observations of Broken Time-Reversal Symmetry

An emphasis on reliable materials growth and development of new fabrication techniques has allowed us to investigate the electronic structure of high-temperature superconductors by planar quasiparticle tunneling and electron paramagnetic resonance (EPR) spectroscopies. The quasiparticle (QP) density of states (DoS) is investigated by tunneling into oriented thin films of Y₁Ba₂Cu₃O₇ (YBCO) and single crystals of Ba₂Sr₂Ca₁Cu₂O₈ (BSCCO). Data are obtained as a function of crystallographic orientation, temperature, doping, damage, and applied magnetic field. These data demonstrate that the observed zero-bias conductance peak (ZBCP) is composed of Andreev bound states (ABS) which intrinsically form at a symmetry-breaking interface of an unconventional superconductor, for example, a (110)-surface of d-wave YBCO. Tunneling into doped or ion-damaged YBCO provides a measure of the QP scattering rate below T _c. An applied field causes Doppler shift of the ABS, arising from the scalar product between the QP velocity and the superfluid momentum, v _F·P _s, observed as a splitting in the ZBCP. Magnetic hysteresis of the splitting is consistent with the effects of strong vortex pinning near the interface. The directional field dependence shows that the ABS is highly anisotropic in its transport. These results, plus in-plane crystallographic orientational dependence on single-crystal BSCCO, demonstrate the d-wave symmetry of this superconductor. Below 8 K and in zero applied field, the ZBCP splits, indicating a transition into a superconducting state with spontaneously broken time-reversal symmetry (BTRS). EPR experiments are used to detect directly the spontaneous formation of the magnetic moments in the BTRS state.