Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of Velocity

  • air velocity
  • angular velocity
  • annular velocity
  • antigen velocity
  • artery blood flow velocity
  • atrial conduction velocity
  • average path velocity
  • average velocity
  • blood cell velocity
  • blood flow velocity
  • blood velocity
  • brachial-ankle pulse wave velocity
  • bubble velocity
  • cell velocity
  • cerebral artery blood flow velocity
  • cerebral blood flow velocity
  • characteristic velocity
  • circular velocity
  • circulation velocity
  • conduction velocity
  • constant velocity
  • contraction velocity
  • coronary flow velocity
  • current velocity
  • darcy velocity
  • detonation velocity
  • diastolic flow velocity
  • diastolic velocity
  • different velocity
  • doppler velocity
  • droplet velocity
  • e velocity
  • early diastolic velocity
  • ejection velocity
  • end diastolic velocity
  • end-diastolic velocity
  • expansion velocity
  • flow propagation velocity
  • flow velocity
  • fluctuating velocity
  • fluid velocity
  • fluidization velocity
  • friction velocity
  • front velocity
  • gait velocity
  • gas superficial velocity
  • gas velocity
  • ground water velocity
  • group velocity
  • growth velocity
  • heat pulse velocity
  • height velocity
  • high gas velocity
  • high velocity
  • horizontal velocity
  • impact velocity
  • inflow velocity
  • initial velocity
  • injection velocity
  • inlet velocity
  • instantaneous velocity
  • intermediate velocity
  • interval velocity
  • jet velocity
  • linear velocity
  • liquid circulation velocity
  • liquid superficial velocity
  • liquid velocity
  • low velocity
  • lower velocity
  • maximal velocity
  • maximum blood flow velocity
  • maximum velocity
  • mean blood flow velocity
  • mean flow velocity
  • mean velocity
  • measured velocity
  • minimum fluidization velocity
  • minimum spouting velocity
  • mitral annular velocity
  • mitral inflow velocity
  • motor conduction velocity
  • motor nerve conduction velocity
  • movement velocity
  • myocardial velocity
  • nerve conduction velocity
  • normal velocity
  • outflow velocity
  • particle velocity
  • path velocity
  • peak height velocity
  • peak systolic velocity
  • peak velocity
  • phase velocity
  • pore water velocity
  • projected rotational velocity
  • propagation velocity
  • psa velocity
  • pulse velocity
  • pulse wave velocity
  • pulse-wave velocity
  • radial velocity
  • reaction velocity
  • red blood cell velocity
  • regurgitant jet velocity
  • relative velocity
  • rise velocity
  • rotation velocity
  • rotational velocity
  • s-wave velocity
  • same velocity
  • seismic velocity
  • sensory conduction velocity
  • sensory nerve conduction velocity
  • settling velocity
  • shear velocity
  • shear wave velocity
  • shear-wave velocity
  • shortening velocity
  • sliding velocity
  • slip velocity
  • solid velocity
  • sonic velocity
  • sound velocity
  • space velocity
  • sperm velocity
  • spouting velocity
  • superficial gas velocity
  • superficial liquid velocity
  • superficial velocity
  • surface velocity
  • swimming velocity
  • systolic blood flow velocity
  • systolic velocity
  • terminal velocity
  • transport velocity
  • ultrasonic velocity
  • uptake velocity
  • variable velocity
  • vertical velocity
  • water flow velocity
  • water velocity
  • wave velocity
  • wind velocity

  • Terms modified by Velocity

  • velocity analysis
  • velocity anisotropy
  • velocity anomaly
  • velocity change
  • velocity component
  • velocity control
  • velocity curve
  • velocity data
  • velocity decrease
  • velocity decreased
  • velocity difference
  • velocity dispersion
  • velocity dispersion profile
  • velocity distribution
  • velocity distribution function
  • velocity encoding
  • velocity field
  • velocity fluctuation
  • velocity gradient
  • velocity increase
  • velocity integral
  • velocity map
  • velocity measurement
  • velocity model
  • velocity models
  • velocity potential
  • velocity profile
  • velocity range
  • velocity ratio
  • velocity reserve
  • velocity response
  • velocity signal
  • velocity structure
  • velocity studies
  • velocity value
  • velocity variation
  • velocity vector
  • velocity waveform

  • Selected Abstracts


    EVOLUTION, Issue 10 2009
    Jim Mossman
    Sperm morphology (size and shape) and sperm velocity are both positively associated with fertilization success, and are expected to be under strong selection. Until recently, evidence for a link between sperm morphology and velocity was lacking, but recent comparative studies have shown that species with high levels of sperm competition have evolved long and fast sperm. It is therefore surprising that evidence for a phenotypic or genetic relationship between length and velocity within species is equivocal, even though sperm competition is played out in the intraspecific arena. Here, we first show that sperm velocity is positively phenotypically correlated with measures of sperm length in the zebra finch Taeniopygia guttata. Second, by using the quantitative genetic "animal model" on a dataset from a multigenerational-pedigreed population, we show that sperm velocity is heritable, and positively genetically correlated to a number of heritable components of sperm length. Therefore, selection for faster sperm will simultaneously lead to the evolution of longer sperm (and vice versa). Our results provide, for the first time, a clear phenotypic and genetic link between sperm length and velocity, which has broad implications for understanding how recently described macroevolutionary patterns in sperm traits have evolved. [source]


    ABSTRACT The flow velocity through the human throat and rheological properties of 0.2,0.8% agar and 0.8,2.4% gelatin were investigated. The maximum flow velocity decreased with increasing concentrations of agar and gelatin, with marked changes from 0 to 0.4% in agar, and from 0 to 1.4% in gelatin, with no further changes at concentration higher than 0.4% in agar but changes at concentration up to 2.4% in gelatin. Although the hardness and adhesiveness increased with increasing concentrations of agar and gelatin, the cohesiveness decreased. In the sensory evaluation, agar and gelatin became difficult to swallow with increasing agar and gelatin concentration. PRACTICAL APPLICATIONS This research contributes to enhance the knowledge of the investigation area of the flow velocity of bolus in a pharynx. Moreover, this research is useful in order to make the foods for person with difficulties in chewing and swallowing. In fact, the results demonstrate the importance of measuring the flow velocity of bolus in the pharynx part not only the rheological properties of food. [source]

    Is the sky falling?

    RAVE surveys, Searching for stellar streams in the local Milky Way disc in the CORAVEL
    ABSTRACT We have searched for in-falling stellar streams on to the local Milky Way disc in the CORrelation RAdial VELocities (CORAVEL) and RAdial Velocity Experiment (RAVE) surveys. The CORAVEL survey consists of local dwarf stars (Nördstrom et al. Geneva,Copenhagen survey) and local Famaey et al. giant stars. We select RAVE stars with radial velocities that are sensitive to the Galactic vertical space velocity (Galactic latitude b < ,45°). Kuiper statistics have been employed to test the symmetry of the Galactic vertical velocity distribution functions in these samples for evidence of a net vertical flow that could be associated with a (tidal?) stream of stars with vertically coherent kinematics. In contrast to the ,Field of Streams' found in the outer halo, we find that the local volumes of the solar neighbourhood sampled by the CORAVEL dwarfs (complete within ,3 × 10,4 kpc3), CORAVEL giants (complete within ,5 × 10,2 kpc3) and RAVE (5,15 per cent complete within ,8 kpc3) are devoid of any vertically coherent streams containing hundreds of stars. This is sufficiently sensitive to allow our RAVE sample to rule out the passing of the tidal stream of the disrupting Sagittarius (Sgr) dwarf galaxy through the solar neighbourhood. This agrees with the most-recent determinations of its orbit and dissociates it from the Helmi et al. halo stream. Our constraints on the absence of the Sgr stream near the Sun could prove a useful tool for discriminating between Galactic potential models. The lack of a net vertical flow through the solar neighbourhood in the CORAVEL giants and RAVE samples argues against the Virgo overdensity crossing the disc near the Sun. There are no vertical streams in the CORAVEL giants and RAVE samples with stellar densities ,1.6 × 104 and 1.5 × 103 stars kpc,3, respectively, and therefore no evidence for locally enhanced dark matter. [source]

    Correlation of Tricuspid Annular Velocities With Invasive Hemodynamics in Pulmonary Hypertension

    Navin Rajagopalan
    The authors performed tissue Doppler imaging of the tricuspid annulus in patients with pulmonary hypertension to assess its correlation with invasive indices of right ventricular function. The study population consisted of 32 patients with suspected pulmonary hypertension who underwent pulsed tissue Doppler imaging of the tricuspid annulus and right heart catheterization. Peak systolic (Sa), early diastolic (Ea), and late diastolic (Aa) velocities of the lateral tricuspid annulus were measured and correlated with hemodynamic variables. Peak Sa demonstrated excellent correlation with hemodynamic variables, including cardiac index (r=0.78; P<.001), pulmonary vascular resistance (r=,0.79; P<.001), and transpulmonary gradient (r=,0.72; P<.001). Peak Sa <10 cm/s predicted cardiac index <2.0 L/min/m2 with 89% sensitivity and 87% specificity. In conclusion, tissue Doppler imaging of the tricuspid annulus is a complementary method to assess right ventricular function in pulmonary hypertensive patients. [source]

    Slope dynamics of Lake Albano (Rome, Italy): insights from high resolution bathymetry

    Francesca Bozzano
    Abstract New detailed data about the morphology of the submerged slopes of Lake Albano (Rome, Italy) have been collected by a sonar multibeam survey financed by the Italian Department of Civil Protection. These data allow for investigation of the subaqueous slope dynamics of the lake, which partially fills a volcanic depression, and the elucidation of the relationships between subaqueous and subaerial slope processes. Subaerial, submerged and combined subaerial/submerged landslide-related morphologies were detected around the inner slopes of the lake. In the submerged slopes, several gravity-induced landforms were recognized: landslide scar areas, landslide accumulations, erosional chutes and channels, block fields, isolated blocks, scarps and slope breaks. An attempt to evaluate the state of activity of the submerged slopes was carried out by taking into consideration the relative freshness of some selected landforms. Interpretation of bathymetric data, as well as direct surveys of the subaerial slopes, was used to assess the morphometric features and interpret the type of movement of the landslides. We propose a comprehensive classification based on the landslide's size and type of movement. We recognized rock fall/topples, debris flows, rock slides and slump, complex rock slides/channelled flows and debris slide and slump. The volume of the main landslides ranged between 101 and 103 m3, while a few rock and debris slides have volumes ranging between 103 and 105 m3. Two large palaeo-landslides with volumes on the order of 106 m3 were identified in the southern and northern part of the lake, respectively. Velocities of the recognized landslides range from rapid to extremely rapid. Two main landslide hazard scenarios have been depicted from the results of the integrated analysis of both subaerial and submerged gravity-induced landforms. The most hazardous scenario involves extremely rapid large volume events (>106 m3) that could, if they interacted with water, induce catastrophic tsunamis. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Aortic Valve Closure: Relation to Tissue Velocities by Doppler and Speckle Tracking in Patients with Infarction and at High Heart Rates

    ECHOCARDIOGRAPHY, Issue 4 2010
    Ph.D., Svein A. Aase M.Sc.
    Aim: To resolve the event in tissue Doppler (TDI)- and speckle tracking-based velocity/time curves that most accurately represent aortic valve closure (AVC) in infarcted ventricles and at high heart rates. Methods: We studied the timing of AVC in 13 patients with myocardial infarction and in 8 patients at peak dobutamine stress echo. An acquisition setup for recording alternating B-mode and TDI image frames was used to achieve the same frame rate in both cases (mean 136.7 frames per second [FPS] for infarcted ventricles, mean 136.9 FPS for high heart rates). The reference method was visual assessment of AVC in the high frame rate narrow sector B-mode images of the aortic valve. Results: The initial negative velocities after ejection in the velocity/time curves occurred before AVC, 44.9 ± 21.0 msec before the reference in the high heart rate material, and 25.2 ± 15.2 msec before the reference in the infarction material. Using this time point as a marker for AVC may cause inaccuracies when estimating end-systolic strain. A more accurate but still a practical marker for AVC was the time point of zero crossing after the initial negative velocities after ejection, 5.4 ± 15.3 msec before the reference in high heart rates and 8.2 ± 12.9 msec after the reference in the infarction material. Conclusion: The suggested marker of AVC at high heart rate and in infarcted ventricles was the time point of zero crossing after the initial negative velocities after ejection in velocity/time curves. (Echocardiography 2010;27:363-369) [source]

    Comparison of Tissue Doppler Velocities Obtained by Different Types of Echocardiography Systems: Are They Compatible?

    ECHOCARDIOGRAPHY, Issue 3 2010
    Mónika Dénes M.D.
    Background: Both systolic and diastolic tissue Doppler (TD) velocities have an important diagnostic and prognostic role in cardiology. We aimed to compare TD velocities between two different echocardiography systems. Patients: Thirty-one consecutive patients (mean age: 65.2 ± 17.5 years; 12 males) were enrolled. Methods: Systolic (Sa), early (Ea), and late (Aa) diastolic velocities were measured by TD at the lateral mitral annulus by a Sonos 2000 (Hewlett-Packard, Andover, MA, USA) and a Philips iE33 system. The E/Ea ratio was calculated. Results: Ea, Aa, and Sa velocities were higher when measured by the Sonos system (Ea: 13.2 ± 4.1 cm/s vs. 8.3 ± 3.6 cm/s; Aa: 14.8 ± 3.8 cm/s vs. 9.3 ± 2.3 cm/s; Sa: 15.2 ± 3.6 cm/s vs. 8.4 ± 2.0 cm/s; P < 0.0001 all). A significant correlation was found in Ea and in Ea/Aa (r = 0.84 and r = 0.85 resp; P < 0.0001 for both), and a weaker in Aa (r = 0.43; P = 0.02) between the machines. The Bland-Altman analysis showed broad limits of agreement between the measurements for Ea, Aa, and Sa (mean difference: 4.95 cm/s; 5.52 cm/s; 6.73 cm/s, respectively; limits: 0.64,9.25 cm/s; ,1.39,12.39 cm/s; ,0.37,13.83 cm/s, respectively). An E/Ea ratio >5.6 by the Sonos system showed 75% sensitivity and 79% specificity for elevated left ventricular filling pressure, defined as E/Ea >10 by the reference Philips system. Conclusions: Although diastolic TD velocities had excellent correlations between the two machines, there was a systematic overestimation by the Sonos system. Since the limits of agreement do not allow replacing the measurements, we suggest using the same echocardiographic equipment at patient follow-up. (Echocardiography 2010;27:230-235) [source]

    Isolated Nonrespiratory Alternans in Doppler Tissue Imaging Velocities in a Patient with Ischemic Heart Disease

    ECHOCARDIOGRAPHY, Issue 8 2009
    Sitaram Mittal D.M.Article first published online: 2 SEP 200
    No abstract is available for this article. [source]

    Relationship between Slow Coronary Flow and Left Atrial Appendage Blood Flow Velocities

    ECHOCARDIOGRAPHY, Issue 1 2007
    Recep Demirbag M.D.
    Aims: This study was undertaken to assess whether slow coronary flow (SCF)is related to low left atrial appendage (LAA) blood flow velocities. Methods: Study subjects consist of 44 patients with SCF and 11 volunteer subjects with normal coronary angiogram. The diagnosis of SCF was made using the TIMI frame count method. The blood flow velocities were obtained by placing a pulsed-wave Doppler sample volume inside the proximal third of the LAA. Results: The mean LAA emptying velocities (MEV)were significantly lower in patients than control subjects (34.5 ± 9.9 cm/sec vs 84.0 ± 12.1 cm/sec; P < 0.001). In bivariate analysis, significant correlation was found between MEV, and systolic pulmonary venous flow, mean TIMI frame count, deceleration time, and isovolumetric relaxation time (P < 0.05). By multiple linear regression analysis, mean TIMI frame count (ß=,0.865, P < 0.001) was identified as independent predictors of MEV. Conclusion: This study indicates that SCF phenomenon may be related to low LAA blood flows. [source]

    Comparison of Coronary Flow Velocities Between Patients with Obstructive and Nonobstructive Type Hypertrophic Cardiomyopathy: Noninvasive Assessment by Transthoracic Doppler Echocardiography

    ECHOCARDIOGRAPHY, Issue 1 2005
    Seden Celik M.D.
    Background: We aimed to compare coronary flow velocity (CFV) measurements of patients with nonobstructive (NHCM) and obstructive hypertrophic cardiomyopathy (HOCM) by using transthoracic Doppler echocardiography (TTDE). Methods and Results: In 11 patients with NHCM and 26 with HOCM, CFV in the distal left anterior descending (LAD) coronary was measured by TTDE (3.5 MHz) under the guidance of color Doppler flow mapping in addition to standard 2D and Doppler echocardiography. The results were compared with 24 normal participants who had no evidence of cardiac disease. Peak diastolic velocity of LAD was also higher in NHCM and HOCM than controls (52 ± 14 cm/sec and 54 ± 20 cm/sec vs 41 ± 11 cm/sec, respectively, P < 0.01). The analysis of systolic velocities revealed abnormal flow patterns in 16 (61%) patients with HOCM (12 systolic-reversal flow and 4 no systolic flow) and 6 (54%) (5 reversal flow and 1 zero flow) patients with NHCM (,11 ± 30 cm/sec and ,13 ± 38 cm/sec, vs 24 ± 9 cm/sec, respectively, P < 0.001). Linear regression analysis demonstrated no correlation between intraventricular pressure gradient and coronary flow velocities in HOCM patients. However, there were significant positive and negative correlations between septal thickness and diastolic and systolic velocities, respectively (r = 0.50, P < 0.002, and r =,0.43, P < 0.005). Conclusion: We conclude that the coronary flow velocity abnormalities are independent from the type of hypertrophic cardiomyopathy. [source]

    Noninvasive Assessment of Influence of Resistant Respiration on Blood Flow Velocities Across the Cardiac Valves in Humans,A Quantification Study by Echocardiography

    ECHOCARDIOGRAPHY, Issue 5 2004
    Lijun Yuan M.D.
    The aim of our study is to quantitatively investigate influence of the intrathoracic pressure change on the four cardiac valves' velocities and further verify a new proposal of the mechanism of respiratory influence on hemodynamics. Methods: Thirty healthy volunteers with no cardiopulmonary diseases were included. The intrathoracic pressure changes were measured with self-designed device. The velocity across the four cardiac valves during spontaneous respiration and with the intrathoracic pressure change at ,4, ,8, and ,12 mmHg, respectively, were recorded simultaneously with the electrocardiogram and respiratory curve. The respiratory variation indices (RVIs) were calculated. The average RVIs of mitral, aortic, tricuspid, and pulmonary valves were 12.54%, 13.19%; 6.23%, 8.27%; 20.27%, 24.36%; and 6.45%, 7.69% with intrathoracic pressure change at ,8 mmHg and ,12 mmHg, respectively. All the above parameters have a significant difference from those during spontaneous respiration (P < 0.01 or P < 0.001). We concluded that it might be the respiratory intrathoracic pressure change that causes the change of the velocity across the valves. (ECHOCARDIOGRAPHY, Volume 21, July 2004) [source]

    Effect of Angular Error on Tissue Doppler Velocities and Strain

    ECHOCARDIOGRAPHY, Issue 7 2003
    Camilla Storaa M.S.
    One of the major criticisms of ultrasound Doppler is its angle dependency, that is its ability to measure velocity components directly to or from the transducer only. The present article aims to investigate the impact of this angular error in a clinical setting. Apical two- and four-chamber views were recorded in 43 individuals, and the myocardium was marked by hand in each image. We assume that the main direction of the myocardial velocities is longitudinal and correct for the angular error by backprojecting measured velocities onto the longitudinal direction drawn. Strain was calculated from both corrected and uncorrected velocities in 12 segments for each individual. The results indicate that the difference between strain values calculated from corrected and uncorrected velocities is insignificant in 5 segments and within a decimal range in 11 segments. The biggest difference between measured and corrected strain values was found in the apical segments. Strain is also found to be more robust against angular error than velocities because the difference between corrected and uncorrected values is smaller for strain. Considering that there are multiple sources of noise in ultrasound Doppler measurements, the authors conclude that the angular error has so little impact on longitudinal strain that correction for this error can safely be omitted. (ECHOCARDIOGRAPHY, Volume 20, October 2003) [source]

    The sedimentary structure of the Lomonosov Ridge between 88°N and 80°N

    Wilfried Jokat
    SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87°36,N and 80°N perpendicular to and along the LR show a sediment starved continental margin with a variety of geological structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities <3.0 km s,1 are considered to represent Cenozoic sediments deposited after the ridge subsided below sea level. Velocities >4.0 km s,1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155°E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81°N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85°N the seismic data indicate the presence of a bottom simulating reflector along all lines. [source]

    BARGEN continuous GPS data across the eastern Basin and Range province, and implications for fault system dynamics

    Nathan A. Niemi
    SUMMARY We collected data from a transect of continuous Global Positioning System (GPS) sites across the eastern Basin and Range province at latitude 39°N from 1997,2000. Intersite velocities define a region ,350 km wide of broadly distributed strain accumulation at ,10 nstr yr,1. On the western margin of the region, site EGAN, ,10 km north of Ely, Nevada, moved at a rate of 3.9 ± 0.2 mm yr,1 to the west relative to site CAST, which is on the Colorado Plateau. Velocities of most sites to the west of Ely moved at an average rate of ,3 mm yr,1 relative to CAST, defining an area across central Nevada that does not appear to be extending significantly. The late Quaternary geological velocity field, derived using seismic reflection and neotectonic data, indicates a maximum velocity of EGAN with respect to the Colorado Plateau of ,4 mm yr,1, also distributed relatively evenly across the region. The geodetic and late Quaternary geological velocity fields, therefore, are consistent, but strain release on the Sevier Desert detachment and the Wasatch fault appears to have been anomalously high in the Holocene. Previous models suggesting horizontal displacement rates in the eastern Basin and Range near 3 mm yr,1, which focused mainly along the Wasatch zone and Intermountain seismic belt, may overestimate the Holocene Wasatch rate by at least 50 per cent and the Quaternary rate by nearly an order of magnitude, while ignoring potentially major seismogenic faults further to the west. [source]

    Distribution and temporal variability of 500 hPa cyclone characteristics in the Southern Hemisphere

    Murray Keable
    Abstract A 40 year period (1958,97) of US National Centers for Environmental Prediction reanalysis data has been used to diagnose the behaviour and variability of 500 hPa extratropical cyclones for the Southern Hemisphere using a Lagrangian perspective. The ,finding' and ,tracking' of these systems were performed using a fully automated scheme. Seasonal distributions of system density, cyclone formation (cyclogenesis), decay (cyclolysis), cyclone centre velocity and intensity/strength are presented. System density is shown to exhibit a maximum in the surface circumpolar trough region and over the Antarctic continent. A broad band of enhanced cyclone system density was evident across the South Pacific from southeast Australia to South America in all seasons, most markedly in winter. As this feature appears also at the surface level, strong vertical consistency of these cyclones in the low and middle troposphere is indicated. Velocities of cyclone centres were found to peak in the latitudes 50,55 °S, and 500 hPa systems appeared to move on average in a much more zonal (easterly) direction than their sea-level counterparts. The mean number of midlatitude cyclones per analysis has exhibited a significant downward trend over the record, with particularly low values observed in the early 1980s. Offsetting this trend have been increases in three measures of mean cyclone vigour. Three orographic features, in particular, are seen to influence the behaviour of 500 hPa cyclones: the mountains of New Zealand, the Antarctic Peninsula and the southern Andes. Over most of Antarctica the rate of cyclogenesis exceeds that of cyclolysis, indicating that many of the cyclones being formed in the vortex are actually exported out (i.e. to the north) of the continent. In the subtropics, considerable numbers of systems are formed in the Mozambique Sea region, but these tend to be quasi-stationary features. Copyright © 2002 Royal Meteorological Society. [source]

    Characterization of the Electroanatomical Substrate in Human Atrial Fibrillation: The Relationship between Changes in Atrial Volume, Refractoriness, Wavefront Propagation Velocities, and AF Burden

    Introduction: Progressive remodeling occurs in experimental models of AF whereby slowing of conduction, shortening of refractoriness, and atrial dilatation are associated with an increased vulnerability to atrial fibrillation (AF). This study investigates the relative changes in atrial geometry and electrophysiology with increasing AF burden in humans. Methods and Results: Patients undergoing ablation of AF or left-sided accessory pathways were recruited. Atrial volumes were determined by echocardiography. Wavefront propagation velocities (WPV), specifically in the direction of activation, were calculated from pre-ablation activation (CartoÔ) maps of both atria. Dispersion, adaptation of, and effective refractoriness (ERP) were measured at 3 sites. A composite arrhythmogenic index (Atrial Volume/WPV × ERP) was derived to compare the degree of electroanatomical remodeling with AF burden. Fifty-nine patients (22 paroxysmal AF, 19 recurrent persistent AF, and 18 controls) were recruited. AF subjects had slower right atrial WPV (P = 0.01), but no difference in left atrial WPV compared with controls. ERP was reduced globally (P < 0.05), with increased dispersion (P < 0.05). WPV and ERP did not distinguish between patients with paroxysmal or persistent AF. Biatrial volumes were greater only in patients with persistent AF (P < 0.01). There was a stepwise increase in the AI with increasing AF burden (P < 0.0001). Conclusion: An arrhythmogenic substrate exists in human AF, characterized by globally decreased refractoriness with greater dispersion, slower right atrial conduction, and atrial dilatation. Persistence of AF is not accompanied by any further electrical remodeling, but only atrial dilatation. The degree of electroanatomical remodeling is associated with the clinical pattern of AF. [source]

    Estimating Projectile Perpendicular Impact Velocity on Metal Sheet Targets from the Shape of the Target Hole

    Tsadok Tsach M.Sc.
    Abstract:, The correlation between bullet hole shapes in metal and projectile impact velocity was examined. A series of shots were fired from an M-16A1 assault rifle of 5.56 mm caliber toward a 1-mm thick metal target. All shots were fired at a perpendicular angle to the metal sheets, and the velocity was measured just before the projectile hit the target. Velocities ranged between 400 and 900 m/sec. From the replica of the shooting hole, a perpendicular plane was created, showing the symmetrical properties of the hole. The best mathematical equation describing the shape of the entrance hole was the exponential function in the form: The empirical equation of the hole defined using the regression method is: This equation describes the general shape of shooting holes created by velocities ranging from 440 to 750 m/sec. From this equation, one can estimate the bullet velocity when it hits the target. [source]

    Interaction of metamorphism, deformation and exhumation in large convergent orogens

    R. A. Jamieson
    Abstract Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (, 450 km) at 1 cm yr,1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties , the upper crust (0,20 km) follows a wet quartzite flow law, with heat production of 2.0 ,W m,3, and the lower crust (20,35 km) follows a modified dry diabase flow law, with heat production of 0.75 ,W m,3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T,600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ,ductile extrusion' of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ,inverted' metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P,T,t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen. [source]

    Quantitative Assessment of Regional Right Ventricular Myocardial Velocities in Awake Dogs by Doppler Tissue Imaging: Repeatability, Reproducibility, Effect of Body Weight and Breed, and Comparison with Left Ventricular Myocardial Velocities

    Valérie Chetboul
    Right ventricular myocardial (RVM) motion is poorly documented. The objective of this study was to determine the variability of RVM velocities by tissue Doppler imaging (TDI) in healthy dogs (study 1), to analyze RVM motion in a large healthy canine population (study 2), and to compare the results with those obtained for the left ventricular free wall. Six healthy Beagle Dogs were monitored in study 1, and 64 healthy dogs of 14 different breeds were monitored in study 2. Velocities were recorded in 2 segments (basal and apical) of the right and left myocardial walls. In study 1, 36 TDI examinations were performed for 4 days, whereas a single TDI examination was performed on each dog in study 2. All velocity profiles included 1 positive systolic wave and 2 negative diastolic waves. The lowest intraday and interday coefficient of variation values of the right TDI variables were observed at the base (3.5,16.1%). The variability of the right apical velocities was much higher, with most coefficient of variation values >15%. RVM velocities were higher in the basal than in the apical segments (P < .001) and were higher than the left velocities of the corresponding segment (P < .01). Body weight and breed had an effect on only a few right and left TDI variables. TDI provides a repeatable and reproducible method for evaluating basal RV function in the dog. These data also demonstrate the heterogeneity of the myocardial velocities between the left and the right ventricles and between the base and the apex. [source]

    Volumetric flow mapping for microvascular networks by bimodality imaging with light microscope and laser doppler imager

    Ying Sun
    Abstract A method was developed to produce a composite image of microvascular networks with grayscales proportional to volumetric flows. Velocities in arterioles and venules were assessed with a high-resolution laser Doppler imager (LDI). The vascular structures were quantified from the micrograph with a computerized vessel detection algorithm. After registering the detected vascular network with the LDI scan, volumetric flows were calculated along the centerlines of the vessels. In vivo data were obtained from the hamster cheek pouch in 6 studies. Flow continuity of the flow map was evaluated by comparing the main flow (Q) with the sum of branch flows (Qs), averaging over the respective vessel segments incident to each bifurcation. The method was reproducible across the 6 studies with the correlation coefficient (r) between Qs and Q ranging from 0.913 to 0.986. In all, over 20,000 flow estimates from 360 vessel segments (24,160 ,m in diameter) at 166 bifurcations were analyzed. With flow normalized between 0 and 1, the linear regression yielded: Qs = 1.03 Q + 0.006; r = 0.952, n = 166, P < 0.0005. The bimodality imaging method exploits a large amount of velocity and diameter data, and therefore should be useful for studying heterogeneous flows in the microvasculature. Microsc. Res. Tech. 65:130,138, 2004. © 2004 Wiley-Liss, Inc. [source]

    Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT-NO3)

    Janna Geith
    Abstract The enthalpies of combustion (,combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT-NO3) were determined experimentally using oxygen bomb calorimetry: ,combH(DNB)=5195±200,kJ kg,1, ,combH(HDAT-NO3)=7900±300,kJ kg,1. The standard enthalpies of formation (,fH°) of DNB and HDAT-NO3 were obtained on the basis of quantum chemical computations at the electron-correlated ab initio MP2 (second order Møller-Plesset perturbation theory) level of theory using a correlation consistent double-zeta basis set (cc-pVTZ): ,fH°(DNB)=,353,kJ mol,1, ,1,829,kJ kg,1; ,fH°(HDAT-NO3)=+254,kJ mol,1, +1,558,kJ kg,1. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT-NO3 were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66,mm,,s,1, P(DNB)=33.9,GPa, D(HDAT-NO3)=8.77,mm,,s,1, P(HDAT-NO3)=33.3,GPa. [source]

    Determination of Minimum Spouting Velocities in Conical Spouted Beds

    Zhiguo Wang
    Abstract Minimum spouting velocities in conical spouted beds have been obtained from pressure drops versus the superficial gas velocity curves, based on both increasing and decreasing the superficial gas velocity. It has been shown that the minimum spouting velocity from decreasing the superficial gas velocity is lower than from increasing the superficial gas velocity in most cases. This phenomenon is similar to that in conventional spouted beds and different from the early works. The experimental results also showed that there isn't significant difference in the pressure drop and Ums under identical operating conditions between semi-circular and circular conical spouted beds, and the same Ums can be obtained from absolute pressure drops at any position above the gas inlet. The Ums is found to increase with increasing the cone angle and static bed height, as well as the gas inlet diameter to a less extent. Des vitesses de jaillissement minimales dans des lits jaillissants coniques ont été obtenues à partir des pertes de charge en fonction des courbes de vitesse de gaz superficielles pour des vitesses de gaz superficielles croissantes ou décroissantes. On montre que la vitesse de jaillissement minimale lorsqu'on diminue la vitesse de gaz superficielle est inférieure à celle que l'on obtient lorsqu'on augmente la vitesse de gaz superficielle dans la plupart des cas. Ce phénomène est semblable à celui observé dans les lits jaillissants classiques et est différent des observations antérieures. Les résultats expérimentaux montrent également qu'il n'y pas de grande différence dans la perte de charge et dans la valeur de Ums pour des conditions opératoires identiques entre des lits jaillissants coniques semi-circulaires et circulaires, et le même Ums peut être obtenu à partir des pertes de charge absolues à n'importe quelle position au-dessus de l'entrée du gaz. On a trouvé que Ums augmentait avec l'angle du cône et la hauteur de lit statique, ainsi qu'avec le diamètre de l'orifice d'entrée du gaz mais dans une moindre mesure. [source]

    Measurement and Correlation of Critical Gas and Liquid Velocities for Complete Circulation of Solid Particles in External Loop Airlift Bubble Columns

    Katsumi Nakao
    Abstract The external loop airlift bubble column provides an easy way of good contacting among gas, liquid and solid phases due to a relatively high recirculating liquid velocity UL. The critical gas and liquid velocities for complete circulation of solid particles, UG,C and UL,C, were measured in two different scales of columns with air, tap water and aqueous CMC solutions, and ion exchange resin and glass beads (155,3834 µm) were employed. The UG,C was determined as the inflection point on the plot of the pressure drop due to the suspended solid particles in the downcomer as a function of the gas velocity UG. The critical liquid velocity UL,C corresponding to the UG,C was obtained from the measured relationship between UL and UG. As a result, a unified dimensionless empirical correlation of UL,C was obtained within an error of ±20% and a dimensionless empirical relationship between UL and UG was developed within an error of ±15%. La colonne à bulles de type airlift à boucle externe offre un moyen facile pour le contact entre les phases gazeuse, liquide et solide grâce à la vitesse de liquide en recirculation UL relativement élevée. Les vitesses de gaz et de liquide critiques pour la circulation complète des particules solides, UG,C et UL,C, ont été mesurées dans deux colonnes d'échelle différente avec de l'air, de l'eau du robinet et des solutions aqueuses de CMC, et des billes de verre et de résine échandeuse d'ions (155,3834 µm) ont été employées. La vitesse UG,C est déterminée comme étant le point d'inflexion sur la courbe de la perte de chgarge causée par les particules solides suspendues dans le déversoir en fonction de la vitesse de gaz UG. La vitesse de liquide critique UL.C correspondant à la vitesse UG.C est obtenue à partir de la relation mesurée entre UL et UG. Ainsi, on obtient une corrélation empirique adimensionnelle unifiée de UL.C avec une erreur de ± 20% et une relation empirique adimensionnelle entre UL et UG est établie avec une erreur de ±15%. [source]

    Adding Velocities without Exceeding the Velocity of Light: Wilhelm Wien's Algorithm (1904) and Albert Einstein's Light Postulate (1905)

    CENTAURUS, Issue 2 2006
    Giora Hon
    Abstract We propose a likely path to Einstein's postulate of the constancy of the velocity of light as part of his theory of relativity in 1905. Our principal claim is that the issue of adding velocities played a crucial role in pointing the way to positing a second postulate, for Einstein realized that the principle of relativity is not sufficient to provide the basis for the new theory. We suggest that Wilhelm Wien's novel algorithm for adding velocities, published in 1904 in Annalen der Physik, stimulated Einstein's thinking, which led to the light postulate. [source]

    Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

    S. Al Rabadi
    Abstract Two-dimensional phase Doppler anemometer measurements of droplet size and velocity conducted under several nozzle conditions and a systematic variation of the air mass flow quality and liquid phase viscosity show that the air entrainment process is enhanced when keeping all test conditions constant except for increasing the Newtonian liquid viscosity above of that of water. A two-zone entrainment model based on a variable two-phase entrainment coefficient is proposed with the normalized axial distance allowing for a change in the jet angle. Thus, the jet perimeter is lower and the breakup length is longer in the case of air/relatively higher viscosity liquid phase. It provides the most accurate reproduction of the experimental droplet velocity in comparison with that of other models in the literature and, hence, is recommended for the prediction of the droplet velocity in the case of two-phase air/liquid phase free jet flow in stagnant ambient air. A model for predicting the droplet rain out, considering the droplet trajectories in the free jet flow, allows also for an adequate reproduction of the experimental data. [source]

    Gas-Liquid Mass Transfer in a Slurry Bubble Column at High Slurry Concentrations and High Gas Velocities

    C. O. Vandu
    Abstract The volumetric mass transfer coefficient kLa in a 0.1,m-diameter bubble column was studied for an air-slurry system. A C9 -C11n -paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n -paraffin oil had properties similar to those of the liquid phase in a commercial Fischer-Tropsch reactor under reaction conditions. The superficial gas velocity UG was varied in the range of 0.01 to 0.8,m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration ,S ranged from 0 to 0.5. The experimental results obtained show that the gas hold-up ,G decreases with an increase in slurry concentration, with this decrease being most significant when ,S < 0.2. kLa/,G was found to be practically independent of the superficial gas velocity when UG > 0.1,m/s is taking on values predominantly between 0.4 and 0.6,s,1 when ,S = 0.1 to 0.4, and 0.29,s,1, when ,S = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient kLa in an industrial-size bubble column slurry reactor, with a particular focus on the Fischer-Tropsch process as well as high gas velocities and high slurry concentrations. [source]

    The Relation between the Color M-Mode Propagation Velocity of the Descending Aorta and Coronary and Carotid Atherosclerosis and Flow-Mediated Dilatation

    ECHOCARDIOGRAPHY, Issue 3 2010
    Yilmaz Gunes M.D.
    Background: To improve clinical outcomes, noninvasive imaging modalities have been proposed to measure and monitor atherosclerosis. Common carotid intima-media thickness (CIMT) and brachial artery flow-mediated dilatation (FMD) have correlated with coronary atherosclerosis. Recently, the color M-mode-derived propagation velocity of descending thoracic aorta (AVP) was shown to be associated with coronary artery disease (CAD). Methods: CIMT, FMD, and AVP were measured in 92 patients with CAD and 70 patients having normal coronary arteries (NCA) detected by coronary angiography. Patients with acute myocardial infarction, renal failure or hepatic failure, aneurysm of aorta, severe valvular heart disease, left ventricular ejection fraction <40%, atrial fibrillation, frequent premature beats, left bundle branch block, and inadequate echocardiographic image quality were excluded. Results: Compared to patients with normal coronary arteries, patients having CAD had significantly lower AVP (29.9 ± 8.1 vs. 47.5 ± 16.8 cm/sec, P < 0.001) and FMD (5.3 ± 1.9 vs. 11.4 ± 5.8%, P < 0.001) and higher CIMT (0.94 ± 0.05 vs. 0.83 ± 0.14 mm, P < 0.001) measurements. There were significant correlations between AVP and CIMT (r =,0.691, P < 0.001), AVP and FMD (r = 0.514, P < 0.001) and FMD and CIMT (r =,0.530, P < 0.001). Conclusions: The transthoracic echocardiographic determination of the color M-mode propagation velocity of the descending aorta is a simple practical method and correlates well with the presence of carotid and coronary atherosclerosis and brachial endothelial function. (Echocardiography 2010;27:300-305) [source]

    Aortic Upper Wall Tissue Doppler Image Velocity: Relation to Aortic Elasticity and Left Ventricular Diastolic Function

    ECHOCARDIOGRAPHY, Issue 9 2009
    Soon Yong Suh M.D.
    Background: Aortic stiffening contributes to the left ventricular (LV) afterload, hypertrophy, and substrate for diastolic dysfunction. It is also known that aortic elastic properties could be investigated with color tissue Doppler imaging (TDI) in aortic upper wall. The purpose of this study is to evaluate the relation of aortic upper wall TDI and aortic stiffness and other parameters of LV diastolic function. Methods: We examined aortic upper wall by TDI at the 3 cm above the aortic valves because of patient's chest discomfort or dyspnea. We excluded the patient with arterial hypertension or reduced left ventricular ejection fraction (LVEF) or significant valvular heart disease. So a total of 126 (mean age 53.8 ± 13.9 years, male 49.2%) patients were enrolled in this study and divided normal LV filling group (N = 31) and abnormal LV filling group (N = 95). Results: Aortic upper wall early systolic velocity and late diastolic velocity were not different between the two groups. Only aortic upper wall early diastolic velocity (AWEDV) was related to aortic stiffness index (r =,0.25, P = 0.008), distensibility (r = 0.28, P = 0.003), early diastolic (Em) (r = 0.45, P = 0.001), E/Em (r =,0.26, P = 0.003), and significantly reduced in abnormal LV filling group (6.19 ± 2.50 vs 8.18 ± 2.87, P = 0.001). Conclusions: AWEDV is decreased significantly in abnormal LV filling patients. It is statistically related to aortic stiffness, distensibility and parameters of abnormal LV filling, Em, E/Em. TDI velocity of the aortic upper wall can be a helpful tool for evaluating aortic stiffness, distensibility, and diastolic function. [source]

    Correlation between NT-pro BNP Levels and Early Mitral Annulus Velocity (E,) in Patients with Non,ST-Segment Elevation Acute Coronary Syndrome

    ECHOCARDIOGRAPHY, Issue 4 2008
    Marcia M. Barbosa M.D., Ph.D.
    Acute coronary syndromes in the absence of ST-segment elevation (NSTE-ACS) are a heterogeneous entity in which early risk stratification is essential. Diastolic dysfunction is precocious and associated with poor prognosis. BNP has been recognized as a biochemical marker of ventricular dysfunction and ischemia. Objective: To investigate if there is correlation of NT pro-BNP levels with diastolic dysfunction in patients with NSTE-ACS. Methods: Fifty-two patients with NSTE-ACS admitted to the coronary unit were included. NT-pro brain natriuretic hormone (BNP) levels and a Doppler echocardiogram were obtained in all and systolic and diastolic functions were analyzed. Their Doppler indexes were compared with those of 53 age- and sex-matched controls, without heart failure symptoms and with normal ejection fraction (EF) and normal NT-pro BNP levels. Results: Twenty-four patients (46%) with unstable angina and 28 patients (54%) with acute myocardial infarction (AMI) were included. Mean EF was 55.9 ± 10.7% and mean NT-pro BNP level was 835 ± 989 pg/ml. No mitral or pulmonary venous flow parameters of diastolic function correlated with NT-pro BNP levels. E,/A, correlated with NT-pro BNP level in univariate analysis but, in a multivariate analysis, only the EF and the E, showed negative correlation with the peptide level (r =,0.33, P = 0.024 and r =,0.29, P = 0.045, respectively). Thirteen patients presented with stage II diastolic dysfunction but the NT-pro BNP level in these patients did not differ from the level in stage I patients. Conclusion: NT-pro BNP levels are elevated in acute coronary syndromes, even in the absence of significant necrosis. Of all echocardiographic parameters investigated, only E, and the EF correlated with the levels of NT-pro BNP in this group of patients. [source]

    Color M-Mode Regurgitant Flow Propagation Velocity: A New Echocardiographic Method for Grading of Mitral Regurgitation

    ECHOCARDIOGRAPHY, Issue 9 2005
    Ramazan Akdemir M.D.
    Purpose: The aim of this study was to evaluate the reliability of mitral regurgitation color M-mode regurgitant flow propagation velocity (RFPV) in grading mitral regurgitation (MR).Methods: We prospectively examined 52 consecutive patients with grades of MR mild in 10 patients, moderate in 19 patients, and severe in 23 patients with quantitative pulse Doppler echocardiography. MR was evaluated by vena contracta diameter (VCD), regurgitant jet area (RJA), and RFPV. These qualitative and quantitative methods were compared with the pulsed Doppler quantitative flow measurements and concordance of these three methods was determined.Results: The mean RFPV for mild, moderate, and severe MR were 26.4 ± 7 cm/sec, 43.3 ± 7 cm/sec, and 60.3 ± 7.3 respectively (P < 0.001). RFPV is highly sensitive and moderately specific in differentiating mild and severe MR from other subgroups. Sensitivity and specificity were 92.1%,64.3% for mild and 100%,68.5% for severe MR, respectively. Significant correlation was observed between pulse Doppler quantitative grades, RFPV, VC, and RJA (P < 0.0001, r = 0.87; P < 0.0001, r =,0.84; P < 0.0001, r = 0.76, respectively).Conclusion: This results show that RFPV is a reliable and simple semiquantitative new method that can be used for determining severity of MR. [source]