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.     

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.     

Clustering and interrelationships of coronary heart disease risk factors in schoolchildren, ages 6-19

Clustering and interrelationships of common and easily identifiable risk factors in 951 children (ages 6-19) from the Cincinnati Lipid Research Clinic's Princeton School of District Study were assessed. Several patterns of partial correlation coeffieients appeared after multiple regression analysis with adjustment for age, sex, Quetelet index, and race. Systolic blood pressure (SBP) was positively correlated with plasma cholesterol and triglyceride, and with saturated fat intake. Plasma high density lipoprotein cholesterol (C-HDL) was positively associated with occupation of the head of the household and inversely associated with cigarette smoking and sucrose intake. Using multiple regression equations, from 29-41% of the variance for SBP and diastolic blood pressure (DBP) could be explained by the measured variables, with age, skinfold thickness, Quetelet, occupation, and education of the head of the household recurrently appearing in the regression equatons. Low density lipoprotein cholesterol (C-HDL) was the variable for which the lowest amount of variance could be explained in the four race-sex groups. Discriminant function analysis allowed an assessment of interrelationships of C-LDL-C-HDL aggregate groups to other risk factor mean residuals. The variables which contributed significantly to the discrimination between lipoprotein groups were Quetelet index, skinfold thickness, and DBP. Children in the highest C-LHL-lowest C-HDL quintile group had by far the highest residual Quetelet index and skinfold thickness, along with above average SBP, while those in The lowest C-LDL-highest C-HDL quintile group had the lowest residual Quetelet index, skinfold thickness, and SBP. Common risk and anti-risk factors for coronary heart disease (CHD) in children cluster, allowing identification of groups of children putatively at relatively high and low CHD risk as adults.     

The conundrum of unmeasured confounding: Comment on: "Can some of the detrimental neurodevelopmental effects attributed to lead be due to pesticides? by Brian Gulson"

The problem described by Dr. Brian Gulson - confounding by unmeasured exposures to pesticides - is only the most recent in a series of potential confounders cited to explain the observed effect of lead on children's intellectual abilities or behavioral problems. Despite the persistent problem of unmeasured confounders, there are several lines of evidence implicating lead as a toxicant at blood lead levels <10 microg/dL. First, in striking contrast with pesticides, there is considerable evidence from numerous studies linking low-level lead exposure with cognitive deficits and behavioral problems, even after controlling for a variety of potential confounders. Second, the consistency of evidence from diverse cohorts and distinct, if not always directly measured potential confounders - enhances our confidence that the lead effect observed at blood lead levels <10 microg/dL is not attributable to unmeasured confounders. Third, in our reanalysis of the Rochester Lead Study, the inclusion of parent-reported mouthing behaviors and breastfeeding status did not attenuate the effect of lead exposure on children's intellectual function. Finally, although we can never entirely dismiss unmeasured confounding in observational studies, we can rely on experimental studies of lead-exposed animals to confirm that lead is a toxicant. Thus, while we must remain vigilant for unmeasured or poorly measured confounders, it is crucial to balance the endless search for confounders with the evidence of toxicity and the need to take action to protect public health. The alternative, to perpetually permit children to be exposed to lead and other emerging toxicants, is both absurd and unacceptable.     

Binary phase-only filtering for turbulence compensation in fiber-coupled free-space laser communication systems

Binary wavefront control in the focal plane (i.e., binary phase-only filtering) for partial compensation of atmospheric turbulence in fiber-coupled free-space laser communication systems is investigated. Numerical results from wave-optics simulations show that in an air-to-air scenario, the combination of binary phase-only filtering and centroid tracking provides mean fiber coupling efficiency close to that resulting from ideal least-squares adaptive optics, but without the requirement for direct wavefront sensing. This result suggests a simpler and less computationally demanding turbulence mitigation system that is more readily applied to tactical applications.