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Ejection Velocity (ejection + velocity)

Distribution by Scientific Domains
Medical Sciences33%

Selected Abstracts

Meteoroid ejection velocities deduced from a study of the April Lyrid meteor shower

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002
T.R. Arter
The use of meteor shower observations to determine the probable ejection velocity of the stream meteoroids from the parent body depends on the identification of some characteristic of the shower that is very sensitive to the ejection velocity. The April Lyrid meteor shower occasionally produces spectacular displays with rates exceeding 600 meteors per hour, as opposed to the usual rate of no more than meteors per hour. These outbursts occur with an apparent 12-yr periodicity. Arter & Williams have postulated that this is caused by an interplay between the ejection velocity (which determines the initial orbit) and gravitational perturbations from Jupiter. This produces a structure for the stream as a whole that can be described as a hollow tube with a cross-section on to the ecliptic in the form of an elliptical ring. Individual meteoroids follow a single strand along the surface of this tube and arrive at the ecliptic at slightly different times, there being a periodicity of 12 yr in the arrival times. Generation of this pattern is very sensitive to ejection velocity, and this paper investigates the range of ejection velocities over which this behaviour exists and thus, by inference, deduces the ejection velocity of the meteoroids. [source]

Grading Functional Mitral Regurgitation by Tissue Doppler,Derived Isovolumic Acceleration Parameters in Patients with Nonischemic Dilated Cardiomyopathy

ECHOCARDIOGRAPHY, Issue 7 2010
Tansu Karaahmet M.D.
Functional mitral regurgitation (FMR) is relatively common in heart failure and it is associated with adverse prognosis. The severity of FMR is usually assessed by echocardiography. Tissue Doppler echocardiography is used to acquire signals to determine the myocardial systolic functional parameters, including systolic ejection velocity and the systolic isovolumic acceleration (IVAs) rate. We investigated the utility of isovolumic acceleration parameters to grade the severity of FMR in nonischemic dilated cardiomyopathy (DC) patients. We analyzed the left ventricular systolic IVA rate, systolic isovolumic contraction (IVCs) velocity, and IVA duration (IVAd) values in 73 patients with DC. Patients were subgrouped according to FMR grade (Group I = mitral regurgitation mild and moderate; Group II = mitral regurgitation severe). IVAs was similar between two groups; however IVCs and IVAd were significantly higher in Group II than Group I. The IVCs cutoff value to predict severe FMR was 1.2 cm/sec (sensitivity 75% and specificity 70%). The IVAd cutoff value to predict severe FMR was 33 ms (sensitivity 77% and specificity 77%). Patients with IVCs , 1.2 cm/sec and IVAd , 33 ms had significantly higher FMR volume than the other subgroups. IVCs and IVAd values are useful to determine FMR severity in patients with DC. (Echocardiography 2010;27:815-822) [source]

Meteoroid ejection velocities deduced from a study of the April Lyrid meteor shower

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002
T.R. Arter
The use of meteor shower observations to determine the probable ejection velocity of the stream meteoroids from the parent body depends on the identification of some characteristic of the shower that is very sensitive to the ejection velocity. The April Lyrid meteor shower occasionally produces spectacular displays with rates exceeding 600 meteors per hour, as opposed to the usual rate of no more than meteors per hour. These outbursts occur with an apparent 12-yr periodicity. Arter & Williams have postulated that this is caused by an interplay between the ejection velocity (which determines the initial orbit) and gravitational perturbations from Jupiter. This produces a structure for the stream as a whole that can be described as a hollow tube with a cross-section on to the ecliptic in the form of an elliptical ring. Individual meteoroids follow a single strand along the surface of this tube and arrive at the ecliptic at slightly different times, there being a periodicity of 12 yr in the arrival times. Generation of this pattern is very sensitive to ejection velocity, and this paper investigates the range of ejection velocities over which this behaviour exists and thus, by inference, deduces the ejection velocity of the meteoroids. [source]

The effect of transient balloon occlusion of the mitral valve on left atrial appendage blood flow velocity and spontaneous echo contrast

CLINICAL CARDIOLOGY, Issue 7 2000
Jianan Wang M.D.
Abstract Background: Spontaneous echo contrast (SEC) is a phenomenon that is commonly seen in areas of blood stasis. It is a slowly moving, cloud-like swirling pattern of "smoke" or increased echogenicity recorded on echocardiography. SEC is commonly seen in the left atrium of patients with mitral stenosis or atrial fibrillation. The prescence of SEC has been shown to be a marker of increased thromboembolic risk. Hypothesis: By using transesophageal echocardiography during percutaneous balloon mitral valvotomy (PBMV), the study investigated the relationship between SEC and varying left atrial appendage (LAA) blood flow velocity in the human heart. Methods: Thirty,five patients with rheumatic mitral stenosis underwent percutaneous balloon mitral valvotomy with intraoperative transesophageal echocardiography monitoring. We alternatively measured LAA velocities and observed the left atrium for various grades of SEC (0 = none to 4 = severe) before and after each balloon inflation. Results: Left atrial appendage maximal ejection velocity was reduced from 35 ± 14 to 6 ± 2 mm/s at peak balloon inflation and increased to 40 ± 16 mm/s after balloon deflation. In comparison with the values before balloon inflation and after balloon deflation, LAA velocities were significantly lower (p < 0.001). New or increased SEC grade was observed during 54 of 61 (88%) inflations and unchanged in 7 (12%) inflations at peak balloon inflation. Spontaneous echo contrast became lower in grade after 55 balloon deflations (90%), completely disappeared after 18 deflations (30%), and remained unchanged after 6 deflations (10%). The mean time to achieve maximal SEC grade (2.5 ± 1.2 s) coincided with the mean time to trough LAA velocities (2.3 ±1.1 s) after balloon inflation. Upon deflation, the mean time to lowest SEC grade (2.9 ± 1.8 s) coincided with mean time to achieve maximal LAA velocities (2.7 ± 1.6s). Conclusion: During balloon inflation, the severity of SEC was enhanced with corresponding reduction in LAA flow velocity. Upon balloon deflation, SEC lightens or disappears with increase in LAA flow velocity. [source]