Search results for " Pressure"
showing 10 items of 3868 documents
A fully manipulable damped driven harmonic oscillator using optical levitation
2020
We implement an experimental system based on optical levitation of a silicone oil droplet to demonstrate a damped driven harmonic oscillator. The apparatus allows us to control all the parameters present in the differential equation that theoretically describes such motion. The damping coefficient and driving force can be manipulated in situ by changing the pressure in the apparatus and by applying a variable electric field. We present two different experimental procedures. First, a transition from the overdamped to underdamped regimes is demonstrated by gradually lowering the air pressure. The characteristic resonance associated with an underdamped driven harmonic oscillator is observed by…
Experimental investigation of holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound lev…
2011
Abstract This paper experimentally investigates the holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels. The theoretical formulations are based on a semi-empirical approach and the use of Fok’s function to model the acoustic surface impedance. For the high sound level regime, an empirical power law involving three coefficients is adapted. It is shown theoretically and experimentally that these coefficients can lead to optimized absorption performance and particularly, a formula relating the critical Reynolds number (Reynolds number value after which the absorption coefficient decreases with the increase of sound level) a…
H�modynamische Untersuchungen zur blutdrucksteigernden Wirkung von Mineralocorticoiden
1979
Bei 6 gesunden freiwilligen Probanden wurde der Einflus einer langerfristigen hochdosierten Mineralocorticoid-Applikation auf die Hamodynamik untersucht. Die Versuchspersonen erhielten das synthetische Mineralocorticoid 9α-Fluorhydrocortison in einer Dosierung von 0,8 mg p.o. taglich. Vor der Gabe des Steroids sowie nach 1- und 6wochiger Steroidbehandlung wurden der zentrale Venendruck und der arterielle Blutdruck direkt gemessen, das Herzzeitvolumen wurde mittels Farbstoffverdunnungsmethode bestimmt.
Right Heart Dysfunction and Readmission Risk Across Left Ventricular Ejection Fraction Status in Patients With Acute Heart Failure.
2021
BACKGROUND: Right heart dysfunction (RHD) parameters are increasingly important in heart failure (HF). This study aimed to evaluate the association of advanced RHD with the risk of recurrent admissions across the spectrum of left ventricular ejection fraction (LVEF). METHODS AND RESULTS: We included 3383 consecutive patients discharged for acute HF. Of them, in 1435 patients (42.4%), the pulmonary artery systolic pressure could not be measured accurately, leaving a final sample size of 1948 patients. Advanced RHD was defined as the combination of a ratio of tricuspid annular plane systolic excursion/pulmonary artery systolic pressure of less than 0.36 and significant tricuspid regurgitation…
Identification of 5,6,7,8-tetrahydropterin and 5,6,7,8-tetrahydrobiopterin in Drosophila melanogaster.
1988
Summary Using reversed-phase high-performance liquid chromatography with electrochemical detection we have demonstrated the occurrence of 5,6,7,8-tetrahydropterin and 5,6,7,8-tetrahydrobiopterin in Drosophila melanogaster . The former is the first time that has been detected in vivo . The identification has been based on the retention times, hydrodinamic voltagrams and the differential concentration in three strains of Drosophila melanogaster . Compared to the wild type, the Punch 2 mutant has diminished levels of both pteridines, whereas Henna-recessive 3 lacks completely tetrahydropterin and has increased levels of tetrahydrobiopterin, as expected according to their biochemical lesions.
Hemodynamic Parameters Change Earlier Than Tissue Oxygen Tension in Hemorrhage
2010
BACKGROUND: Untreated hypovolemia results in impaired outcome. This study tests our hypothesis whether general hemodynamic parameters detect acute blood loss earlier than monitoring parameters of regional tissue beds. MATERIALS AND METHODS: Eight pigs (23-25 kg) were anesthetized and mechanically ventilated. A pulmonary artery catheter and an arterial catheter were inserted. Tissue oxygen tension was measured with Clark-type electrodes in the jejunal and colonic wall, in the liver, and subcutaneously. Jejunal microcirculation was assessed by laser Doppler flowmetry (LDF). Intravascular volume was optimized using difference in pulse pressure (dPP) to keep dPP below 13%. Sixty minutes after p…
Hemodynamic and ventilatory changes during implant surgery with intravenous conscious sedation
2010
Purpose: This study was conducted to determine the hemodynamic and ventilatory changes during implant surgery with intravenous conscious sedation, and whether preoperative anxiety, gender or age influence these parameters. Patients and Methods: A prospective study carried out between May 2004 and February 2007, on 102 patients treated with dental implants under local anesthesia and conscious intravenous sedation. Patients completed a questionnaire prior to surgery to evaluate preoperative dental anxiety using Corah's scale. The hemodynamic and ventilatory changes were evaluated by monitoring systolic pressure (SP), diastolic pressure (DP), heart rate (HR) and oxygen saturation (SaO2). These…
Stimulatory and inhibitory effects of ethanol on hippocampal acetylcholine release
1998
Using the microdialysis technique and sensitive HPLC procedures for the determination of acetylcholine (ACh) and ethanol, we investigated the release of ACh in rat hippocampus after acute ethanol administration. Systemic administration of ethanol (0.8 and 2.4 g/kg i.p.) led to peak ethanol concentrations of 21 and 42 mM in the hippocampus, respectively. The high dose caused a long-lasting inhibition of basal ACh release by up to 33%. Local infusion of scopolamine (1 microM) enhanced hippocampal ACh release up to eightfold in the presence of neostigmine (10 microM), and this stimulated release was also inhibited after systemic ethanol administration (by up to 45%). The low dose of ethanol (0…
Current L2 self-concept of Finnish comprehensive school students : The role of grades, parents, peers, and society
2021
L2 (second/foreign language) motivation research in Finland has been scarce. Furthermore, international motivational research has focused more on ideal and ought-to selves, leaving the current L2 self-concept in the background. In the present study, we attempted to address this gap, exploring what shapes L1 (mother tongue) Finnish students' understanding of themselves as users and learners of L2s. Using structural equation modelling, we studied the relationships between students' (n = 1206) current L2 self-concept and parental encouragement, peer pressure, societal expectations, and grades. We further studied which of these factors are the best predictors of students' current L2 self-concep…
Studying hypertension in ocular fundus images using Hausdorff dispersion ordering.
2010
Retinal arterial and vein diameters are altered in individuals at risk of cardiovascular events mainly due to high blood pressure. The measurement of retinal vessel diameters has been proved to reflect individuals' vascular health. Dispersion of such measures which are obtained by means of ocular fundus images is a major factor not usually considered in clinical research. In this paper, a method to evaluate if different levels of clinically relevant covariables induce greater dispersion in retinal arterial and vein diameters is proposed. A multivariate dispersion ordering, the Hausdorff dispersion order, is used to compare the level of dispersion in such diameters for different groups of pa…