Relaxation processes in a glassy polymer containing methanol molecules

The interaction of small guest molecules with the molecular degrees of freedom of a glassy polymer matrix is investigated, i.e. (i) the dynamics of these guest molecules and (ii) their effect on the secondary ‘β’ and main ‘’ relaxations of the host polymeric matrix. The system considered here is the glassy poly(methyl metacrylate) modified by introduction and desorption of methanol. The dynamics of the system is observed by means of low-frequency mechanical and wide band dielectric spectroscopies. The presence of small molecules in the PMMA glassy matrix induces several effects, namely (i) a strong relaxation peak develops at low temperature (near 120 K at 1 Hz and called _m in the following), (ii) the strength of the β relaxation is increased while the temperature of the maximum shifts towards the low temperatures, (iii) a sharp peak appears superimposed on the β peak, and finally (iv) the relaxation shifts towards the low temperatures. Dielectric and mechanical spectroscopies results are in agreement and make it possible to capture the dynamical behavior in a wide frequency range (eight decades). The experimental results are explained on the basis of physical concepts recently introduced in the physics of glassy matter: cooperativity and nanoheterogeneity. In particular, the low-temperature relaxation process _m is attributed to cooperative motions in methanol clusters which form in the nanoheterogeneous polymeric matrix, in agreement with small angle X-rays scattering and low-frequency Raman scattering observations recently reported.     

Improving the reliability of transformer gas-in-oil diagnosis

Dissolved gas analysis (DGA) is widely used to detect incipient faults in oil-filled electrical equipment. There is always some degree of inaccuracy in laboratory dissolved-gas measurements, especially at low gas concentrations, which affects gas ratios and other diagnostic calculations. This paper examines the measurement inaccuracy problem in detail using recent CIGRE data. It shows how proper allowance for this inaccuracy can improve transformer condition assessment and diagnosis by DGA.     

Computerized transcutaneous control of a multichannel implantableurinary prosthesis

In the present paper we describe a personal computer interface of a multichannel implantable urinary prosthesis. This system is composed of two main parts: the first one is internal and consists of an implant using a 4-microns CMOS gate array chip controlling a wide variety of waveforms via eight monopolar channels. The second, an external controller featuring a versatile software, a PCB card plugged in a portable microcomputer, and a radiofrequency-coupled technique. This device is used to transmit the power, the data and the synchronization clock to the implant by a simple binary signal modulating a 20 MHz carrier. We also report the features of implant encapsulation and electrode design and fabrication. In the experimental phase, we studied the effect of early electric stimulation of the bladder during the spinal shock phase in the dog. We present the operative techniques that enabled us to perform chronic electrostimulation of the sacral roots and discuss the results.     

Dissolved gas analysis: It can save your transformer

The use of dissolved gas analysis (DGA) to monitor the in-service behavior of transformers is discussed. Sampling techniques are briefly considered, and two commercial hydrogen-in-oil detectors are described. The first allows the hydrogen concentration to be measured at intervals of a few hours by a portable gas collector that can be connected to semipermeable tubes. Continuous remote monitoring from the substation is possible with the second model, which uses a fuel-cell-type detector. The use of DGA for fault diagnosis is examined, and acceptable gas levels are indicated. The use of expert systems to facilitate decision making on the basis of DGA results is discussed, as is international cooperation in sharing data and experience and reaching agreement on methods of analysis and interpretation. Further applications of DGA are indicated     

A review of faults detectable by gas-in-oil analysis intransformers

IEC Publication 60599 provides a coded list of faults detectable by dissolved gas analysis (DGA): PD = partial discharges; D1 = discharges of low energy; D2 = discharges of high energy; T1 = thermal faults of temperature < 300°C; T2 = thermal faults of temperature 300°C < T < 700°C; T3 = thermal faults of temperature > 700°C. The IEC TC10 databases of DGA results corresponding to faults identified by visual inspection of faulty transformers in service have been presented in a previous paper (see IEEE Elec. Insulation Mag., vol. 17, no. 2, p.31-41, 2001). The present paper reviews these DGA results in a more user-friendly graphical form. It also reviews the DGA results of laboratory models attempting to simulate these faults, as published in the scientific literature or technical reports. The specific case of on-load tap changers (OLTC) is reviewed much more extensively, and separately, since DGA interpretation in this case must take into account the large background of residual gases resulting from the normal current-breaking operation of the OLTC. Particular attention is also given to DGA results related to PDs and low-temperature thermal faults     

Efficacy of the plant phototoxinα-terthienyl againstAedes intrudens and effects on nontarget organisms

The botanical phototoxin, -terthienyl (-T) was spray applied to natural or artificial pools containing mosquito (Aedes intrudens) larvae and nontarget invertebrates (caddisfly, damselfly, midge, shrimp,Daphnia, snail) and one vertebrate (trout) at concentrations varying from 0.01 to 1 kg/hectare, under field and laboratory conditions. All field-treated nontarget invertebrates survived -T treatment better thanA. intrudens which can be controlled at doses as low as 0.01 kg/hectare within one week. Under laboratory conditions, snails and trout survived -T and UV treatments up to 10 kg/ hectare. These results compare favorably with organophosphates and pyrethroid insecticides currently used for mosquito control. The results confirm that -T is a highly effective larvicide with acceptable nontarget effects.     

Clonal relationships among high-level penicillin-resistant Streptococcus pneumoniae in the United States

Emu antibody responses to avian influenza virus (AIV) infection were evaluated by the competitive enzyme-linked immunosorbent assay (C-ELISA), agar gel immunodiffusion (AGID) and hemagglutination inhibition (HI) tests. All birds infected with AIV H5N1, H5N3, or H7N7 developed antinucleoprotein (NP) antibodies as early as 7 days postinfection as detected by the C-ELISA. The responses lasted 49 days for the emus receiving H5N3 and at least 56 days for emus receiving the other two viruses. By evaluating 50 emu field serum samples, the C-ELISA was found more sensitive than the AGID test for the detection of anti-NP antibodies. This study indicates that emus experimentally infected with AIV developed antibody responses that can be detected by C-ELISA, AGID, and HI tests. The results from this and our previous studies demonstrate the use of the C-ELISA as a substitute for the AGID test in a routine serodiagnostic screening for detection of antibodies to AIV infection in multiple avian species.     

Periodes et repetitions des mots du monoide libre

We study the relationship between the global periodicity of a word and its (local) repetitions, that is to say its successive equal factors.Our main result generalizes the theorem of Cesari Vincent according to which the period of a word is the maximum of the minimal repetitions. Our generalization is twofold, it does not take account of any sides to define repetitions (the above result does) and calculates the maximum only on a special set of points. It allows a sharpened version of the solution to a problem settled by Schützenberger in which the theorem of Cesari Vincent originates.