Strain components of nuclear-reactor-type concretes during first heat cycle

Strains of three advanced-gas-cooled-reactor-type nuclear reactor concretes were measured during the first heat cycle and their relative thermal stability determined. It was possible to isolate for the first time the shrinkage component for the period during heating. Predictions of the residual strains for the loaded specimens can be made by simple superposition of creep and shrinkage components up to a certain critical temperature, which for basalt concrete is about 500 °C and for limestone concrete is about 200–300 °C. Above the critical temperature, an expansive “cracking” strain component is present. It is shown that the strain behaviour of concrete provides a sensitive indication of its thermal stability during heating and subsequent cooling.     

Nouvelle approche pour concevoir des inductances actives flottantes positives et négatives en technologie MMIC

An original method for the determination of all possible inductive circuits as a function of the number of fets used in this paper. The method is of general use in monolithic microwave integrated circuits. Circuits with large inductance, either positive or negative in value, can be obtained along with low loss or even negative resistance.     

A CMOS modem analog processor for V.22 bis modems

A mixed analog/digital chip that forms the core of a medium-speed modem for use on the public switched telephone network is described. It meets CCITT and AT&T requirements for data transmission at 2400 and 1200 b/s, and the AT&T requirement for 300-b/s operation. The chip is implemented in a 1.75-μm analog CMOS process and occupies 32.4 mm ². The device is powered by a single +5-V supply and consumes less than 115 mW. The architecture and circuit implementation are described, and experimental results are given     

The implementation of digital echo cancellation in codecs

The architecture of a codec in which the echo cancellation is done in two stages, an analog hybrid to reduce the echo level at the input of the A/D converter and a programmable digital balance filter, is presented. The design problems connected with this architecture, such as the signal-to-noise performance of the A/D converter and the limiting effects of the variation of the analog components on the echo cancellation performance of the device and on the structure of the digital balance filters, are discussed. These results were used in the design of a single-power-supply CMOS device implemented in 1.5-μm technology using ΣΔ modulation techniques for A/D and D/A conversion. Its echo cancellation performance is sufficiently high that only one set of coefficients per national standard is necessary     

Mineralogical and engineering properties of problematic expansive clayey beds causing landslides

Many landslides have occurred at slope cuts-embankments adjacent to the Amman-Na'ur-Dead Sea and Irbid-Jerash-Amman highways in Jordan, especially during the last four years that were characterized by exceptional raifall during winter. Clayey beds found in the foundations of the failing areas were responsible for the occurrence of these landslides. This paper presents the results of research evaluating the chemical and engineering properties of the clayey beds in the Kurnub Sandstone Unit and the Ajlun Group of the Upper Cretaceous at twenty four landslîde locations along the Amman-Na'ur-Dead Sea and Irbid-Jerash Amman highways. The clay minerals associated with the clayey beds were characterized and correlated with their engineering properties. The relationship between clay minerals, chemical and engineering properties of clayey beds and the foundation failures were also identified. The study included field visits to twenty four landslides sites to identify the problem, collect samples from the foundation along the slip surface, draw profiles and columnar sections. Chemical analysis was carried out for the whole rock sample and for clay samples. Tests were also conducted to evaluate the physical and engineering properties of the samples. Results showed that most of the landslides occurred within the upper part of the Kurnub Sandstone and the Na'ur formation. Quartz, calcite and dolomite are the non-clay minerals and Mixed-Layer (I/S) and kaolinite are the clay minerals identified for samples obtained from the studied areas. The jointed rocks allowed water to penetrate through the joints and reach the clayey beds. The ability of the mixed-layer (I/S) clays to expand in the presence of water resulted in the reduction of shear strength during rainfall, thus initiating the sliding process. The double-layer effect was noticed in samples with higher (I/S) content which gave the highest swelling potential, highest Liquid and Plastic Limits, and the lowest angle of friction.     

Rotavirus-specific intestinal immune response in mice assessed by enzyme-linked immunospot assay and intestinal fragment culture

Primate rotavirus strain RRV and bovine strain WC3 or reassortants made between these animal viruses and human rotaviruses have been administered to infants as candidate vaccines. We compared RRV and WC3 in a murine model of oral infection. We determined the relative capacities of these viruses to induce a virus-specific humoral immune response by intestinal lymphocytes as tested by enzyme-linked immunospot assay, intestinal fragment culture, and enzyme-linked immunosorbent assay of intestinal contents. We found that inoculation of mice with RRV induced higher frequencies of virus-specific immunoglobulin A (IgA)-secreting cells in the lamina propria, greater quantities of virus-specific IgA in intestinal fragment cultures, and greater quantities of virus-specific IgA in intestinal secretions than did inoculation with WC3 or inactivated RRV (iRRV). The induction of an IgA response in serum was predictive of an IgA response among intestinal lymphocytes after inoculation with RRV but not WC3. In addition, large quantities of IgG, IgA, and IgM not specific for rotavirus were produced in fragment cultures from mice inoculated with RRV but not in cultures from mice inoculated with WC3 or iRRV. Possible mechanisms of RRV-induced polyclonal stimulation of intestinal B cells are discussed.     

Data converters for communication systems

Data converters are playing an ever increasingly important role in digital communication channels. As VLSI technologies scale, more of the signal processing is performed in the digital domain, making superior converter design critical. Attributes of various modern analog-to-digital converters such as flash and ΣΔ are described     

Post-laparoscopic vomiting in females versus males: comparison of prophylactic antiemetic action of ondansetron versus metoclopramide

PURPOSE: To evaluate the clinical usefulness of the continuous intra-arterial blood gas (CIABG) monitoring system, Paratrend 7, during differential lung ventilation (DLV) in 12 patients undergoing oesophagectomy. METHODS: Anaesthesia was induced with propofol and was maintained with isoflurane, oxygen and air, supplemented by an epidural infusion of mepivacaine. Arterial samples for estimation of blood gases (ABG) were taken just before and 5, 10, 20, 30, 60, and 90 min after the pleura was opened. The pH, PO2, and PCO2 values displayed by the CIABG monitor, which were recorded prior to the arterial blood sampling, were compared with the results of ABG analysis. RESULTS: Eighty-four blood samples were obtained and the ranges for the measured variables were PCO2 24.8-57.4 mmHg, PO2 47-449 mmHg, and pH 7.30-7.49. The correlation between CIABG and ABG measurements was strong and significant (r values: PCO2 0.80, PO2 0.93, pH 0.94). The overall bias +/- precision between the two methods was PCO2 0.9 +/- 3.1 mmHg, PO2 -1 +/- 40 mmHg, %PO2 0.8 +/- 21.6%, pH 0.00 +/- 0.02. For PO2 values < 150 mmHg, the biases +/- precision were PO2 -5 +/- 17 mmHg, %PO2 -2.1 +/- 20.7%. CONCLUSION: The agreement between CIABG and ABG measurements was better for PCO2 and pH than for PO2. Although the CIABG system is clinically useful for monitoring trends in blood gas changes, the accuracy of the PO2 value may be unacceptable during DLV because the error is theoretically < 34 mmHg with 95% reliability in the clinically important range of PO2, < 150 mmHg.     

Quantitative determination of the monoclinic crystalline phase content in polyethylene by 13C n.m.r.

Solid-state ¹³C n.m.r. spectroscopy involving the techniques of cross-polarization (CP), magic angle spinning (MAS), and high power proton decoupling, has been used to determine quantitatively the ratio of monoclinic to orthorhombic crystalline phases in compression moalded ultra-high molecular weight polyethylene (UHMWPE) sheet which had been stretched uniaxially. Criteria for expecting quantitative relative intensities in ¹³C CP-MAS spectra are discussed. Attenuation of the non-crystalline (NC) signals relative to crystalline signals was observed. Experiments were therefore carried out to ascertain whether measurable relative intensity distortions exist between the monoclinic crystalline phase (MCP) and the orthorhombic crystalline phase (OCP) resonances due to possible differences in proton ‘spin diffusion’ between the NC and the two crystalline phases during cross-polarization. No relative intensity distortions were detected. This result, coupled with experiments in which spin diffusion was monitored at times longer than those used for cross-polarization, suggests that the average distance from the protons in a given crystalline phase to the nearest protons in the NC regions is the same for the MCP and the OCP. Finally, non-spinning ¹³C spectra of the deformed polyethylene were recorded to determine the orientation of the chains in the crystalline and NC regions. The Hermans orientation function, F_c, was determined independently for the crystalline (combined OCP and MCP) and NC regions, and found to be 0.66 + 0.06 and 0.23 + 0.04 respectively. The occurrence of orientation in the NC regions may be evidence for internal stresses, which, it is suggested, also stabilize the metastable MCP in the stretched sample.     

Crystal growth kinetics and the lateral habits of polyethylene crystals

The lateral growth habits of lamellar crystals of polyethylene grown from solution can be typified in terms of the aspect ratio, r, which is the ratio of the dimension of the crystals in the b-axis direction to that in the a-axis direction. The aspect ratio depends on crystallization temperature, undercooling, solvent, polymer concentration and molecular weight. At steady state growth, r can be expressed in terms of the ratio of growth rates normal to the {110} and (200) faces. Expressing the growth rates in terms of the kinetic theory of polymer crystal growth yields an expression which is used to analyse experimental results on the effect of temperature and concentration on the lateral growth habits of crystals grown from xylene. Using as two adjustable parameters the ratio of end surface free energies for the two growth surfaces and the ratio of the lateral surface free energies to fit the rversusΔT data permits the determination of these ratios with high sensitivity. The actual values obtained are dependent upon concentration, the assumed growth regime, and, most importantly, ?, the parameter in the growth rate equations apportioning the bulk free energy change to the forward and backward steps in the stem deposition process.