Search

A novel general-purpose online measurement system for the resonant piezoelectric bulk-acoustic-wave sensors is presented. The system supports the various sensor types for the different physical measurands, such as the temperature, humidity, the viscosity, density, and speed of sound of liquids, and the film thickness. The measurement principle is based on the determination of the locus of the admittance curves of the respective sensors for one or several resonances (fundamental and/or overtones). The measurement results are calculated from the measured resonance frequencies or quality factors by applying the appropriate sensor function or calibration data for each sensor. The system covers sensors with resonance frequencies ranging from 30 kHz to 30 MHz. Special electronics have been developed to transform the sensor-admittance values (real and imaginary parts) to voltage signals that are acquired by the computer system. The disturbing effects caused by the capacitance of the sensor connecting cable are minimized by a special electronic circuitry. System performance was tested successfully in combination with two different types of temperature sensors (30-MHz quartz crystal and 6-MHz GaPO4 crystal) and two different types of viscosity sensors (56-kHz torsional mode and 2.8-MHz thickness-shear-mode quartz crystals) [ABSTRACT FROM PUBLISHER]

A technique of using an adaptive pulse repetition frequency (PRF) to operate an ultrasonic contrapropagation transit-time gas flowmeter (UFM) is introduced. This adaptive PRF technique allows transient measurements of hot (up to 450 degC) and pulsating (up to 1.5 kHz) gas flows. Such conditions occur in the exhaust gas of a combustion engine. Here, a UFM with the widely used fixed PRF technique is not applicable, because the large gas temperature variations would prevent a reliable detection of ultrasonic pulse arrival times. Coherently reflected waves are generated within the gas because of the unavoidable acoustic impedance mismatch between the gas and the transducers, and, depending on the gas temperatures, these echoes overlap with the main signal. The adaptive PRF technique overcomes this problem and allows correct pulse detection over the whole temperature range required. The UFM utilizes special high-temperature-resistant capacitance ultrasonic transducers (CUTs) to meet the requirements in terms of operating temperature range and dynamic response. Results, which are obtained with a preliminary laboratory prototype, are presented for the exhaust gas mass flow rate in a otimes 50-mm pipe measured at gas temperatures of up to 450 degC and at PRFs of up to 5.5 kHz, which is an increase in frequency response of one order of magnitude in comparison to existing measurement systems [ABSTRACT FROM PUBLISHER]

Deals with a study which examined the renal loss of leptin in patients with nephrotic syndrome. Methodology; Results; Conclusion.

Introduction: Appetite and eating behavior are frequently altered in psychiatric patients. The newly discovered gut-derived neuropeptide ghrelin simulates hunger and weight gain. Therefore, it might be involved in appetite regulation during psychiatric disorders., Methods: In 83 depressed, 42 schizophrenic patients and 46 healthy controls plasma ghrelin levels were measured, and the psychometric scores on the Three-Factor Eating Questionnaire (TFEQ) were assessed., Results: Neither ghrelin levels nor TFEQ scores differed between both patient groups and healthy subjects. However, TFEQ subscale 2 (disinhibition) was predicted by BMI-corrected ghrelin levels, while age, sex, smoking, and medication did not show any influence., Discussion: Ghrelin correlates with factors of eating behavior, specifically with subscale 2 on the TFEQ. Ghrelin might be involved in appetite-regulating pathways during psychiatric disorders. However, its influence is not likely to be displayed as a difference between diagnostic groups. Rather, ghrelin is associated with eating behavior in psychiatric patients meaning susceptibility to eating problems., (Copyright 2008 S. Karger AG, Basel.)