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Velocity Difference (velocity + difference)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Clinical Value of the Tissue Doppler S Wave to Characterize Left Ventricular Hypertrophy as Defined by Echocardiography

ECHOCARDIOGRAPHY, Issue 4 2010
Demian Chejtman M.D.
Left ventricular hypertrophy (LVH) may be a physiological finding and may also be associated with different disease entities and hence, with different outcomes. Regional myocardial function can be assessed with color Doppler tissue imaging, specifically by the waveform of the isovolumic contraction (IC) period and the regional systolic wave ("s"). Methods and Results: We studied five groups (G): healthy, sedentary young volunteers (G1, n:10); healthy sedentary adult volunteers (G2, n:8); and subjects with LVH (left ventricular mass index >125 g/m2) including: high performance athletes (G3, n:21), subjects with hypertension (G4, n:21), subjects with hypertrophic cardiomyopathy (HCM) (G5, n:18). We measured peak "s" wave velocity (cm/sec) at the basal and mid septum, the IC/s ratio, and basal to mid-septal velocity difference (BMVD) of the "s" wave. Regional "s" wave values (cm/sec) were G1 = 5.6 ± 1; G2 = 5.4 ± 0.8; G3 = 5.7 ± 0.6; G4 = 5.3 ± 1.1; G5 = 4.2 ± 1.1 (P < 0.0001). The IC/s ratio was G1 = 0.28 ± 0.18; G2 = 0.39 ± 0.21; G3 = 0.23 ± 0.10; G4 = 0.42 ± 0.15; G5 = 0.64 ± 0.15 (P < 0.0001). The BMVD (cm/sec) was G1 = 2 ± 0.51; G2 = 1.71 ± 0.29; G3 = 1.78 ± 0.44; G4 = 1.26 ± 0.96; G5 = 0.45 ± 0.4 (P < 0.0001). IC/s < 0.38 discriminated physiological from pathological forms of hypertrophy (sensitivity 90%; specificity 88%). Peak "s" wave velocity discriminated HCM from other causes of hypertrophy, with a cutoff value of 4.46 cm/sec (sensitivity 72%; specificity 90%). BMVD <0.98 cm/sec detected HCM with 89% sensitivity and 86% specificity. Conclusions: Peak "s" wave velocity and two indices: IC/s and BMDV are novel parameters that may allow to discriminate physiological from pathological forms of hypertrophy as well as different subtypes of hypertrophy. (ECHOCARDIOGRAPHY 2010;27:370-377) [source]

Star formation in close pairs selected from the Sloan Digital Sky Survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
B. Nikolic
ABSTRACT The effect of galaxy interactions on star formation has been investigated using Data Release One of the Sloan Digital Sky Survey (SDSS). Both the imaging and spectroscopy data products have been used to construct a catalogue of nearest companions to a volume-limited (0.03 < z < 0.1) sample of galaxies drawn from the main galaxy sample of SDSS. Of the 13 973 galaxies in the volume-limited sample, we have identified 12 492 systems with companions at projected separations less than 300 kpc. Star formation rates for the volume-limited sample have been calculated from extinction and aperture corrected H, luminosities and, where available, IRAS data. Specific star formation rates were calculated by estimating galaxy masses from z -band luminosities, and r -band concentration indices were used as an indicator of morphological class. The mean specific star formation rate is significantly enhanced for projected separations less than 30 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star formation rate is observed to decrease with increasing recessional velocity difference, but the magnitude of this effect is small compared to that associated with the projected separation. We also observe a tight relationship between the concentration index and pair separation; the mean concentration index is largest for pairs with separations of approximately 75 kpc and declines rapidly for separations smaller than this. This is interpreted as being due to the presence of tidally triggered nuclear starbursts in close pairs. Further, we find no dependence of star formation enhancement on the morphological type or mass of the companion galaxy. [source]

High relative velocity central dumbbells in poor clusters,

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
H. Quintana
Abstract We propose that some high relative velocity dumbbell galaxies are the centers of poor clusters or groups that are coming into a merging process. The components of these galaxies closely follow the incoming velocity of the merging groups, as revealed by the bimodality of the velocity histograms. Only mergers in a direction with a small angle to the line of sight can show the large velocity difference of the components and the velocity separation of incoming subgroups in the histograms. In this case the simple interpretation would be that the dumbbells components are also in an early phase of their merger, as they still keep the information of the incoming orbits, but analysis of a numerous sample is needed to prove this suggestion (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Galaxy-galaxy interactions as triggers of star formation

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
N.A. Popescu
Abstract Galaxy-galaxy interactions represent the main physical processes that trigger substantial star formation in galaxies. In order to study the galaxy interactions effects on color and morphology of the galaxies in the fields of two radio galaxies at z , 1, we combined optical-NIR photometry and HST/WFPC2 morphology data from the Stanford et al. (2002) catalog, with HST/WFPC2 archival images. Using a strong pair isolation criterion in terms of the apparent angular separation and rest-frame line-of-sight velocity difference, we obtained a sample of galaxy pairs in the studied fields. The fact that close interactions and mergers induce star-forming episodes is confirmed by the presence of morphological disturbances and bluer optical-NIR colors at many analyzed galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]