Search results for "Pressure"

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…

1976

The phenomenon of “true cosolvency”, which has only recently been observed in the system acetone/diethyl ether/polystyrene (AC/DEE/PS), is investigated with regard to its pressure dependence and compared with the thermodynamic behaviour of the corresponding binary sub-systems. For the determination of the limits of complete solubility, a pressure apparatus was used which had been constructed, in order to measure the turbidity of fluids in the temperature range of −70 to +500°Cand in the pressure range of 1 to 4000 bar (105 to 4·108 Nm−2). The critical line observed for the system DEE/PS (MPS=20400) looks similar to that reported for AC/PS in the literature, i.e. the upper critical solution …

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…

Impacts of Varying Concentrations of Cloud Condensation Nuclei on Deep Convective Cloud Updrafts—A Multimodel Assessment

2021

AbstractThis study presents results from a model intercomparison project, focusing on the range of responses in deep convective cloud updrafts to varying cloud condensation nuclei (CCN) concentrations among seven state-of-the-art cloud-resolving models. Simulations of scattered convective clouds near Houston, Texas, are conducted, after being initialized with both relatively low and high CCN concentrations. Deep convective updrafts are identified, and trends in the updraft intensity and frequency are assessed. The factors contributing to the vertical velocity tendencies are examined to identify the physical processes associated with the CCN-induced updraft changes. The models show several c…

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…