Solar 5-min Oscillation Amplitude Anisotropy and Doppler Velocity Systematics

1988 ◽  
pp. 63-65
Author(s):  
J. R. Kuhn ◽  
C. M. O’Neill ◽  
L. B. Gilliam
Keyword(s):  
Oscillation Amplitude ◽  
Doppler Velocity ◽  
Amplitude Anisotropy

scholarly journals Solar 5-min Oscillation Amplitude Anisotropy and Doppler Velocity Systematics

1988 ◽  
Vol 123 ◽  
pp. 63-65
Author(s):  
J.R. Kuhn ◽  
C.M. O'Neill ◽  
L.B. Gilliam
Keyword(s):  
Spatial Resolution ◽  
Oscillation Amplitude ◽  
Level Line ◽  
Line Center ◽  
Doppler Velocity ◽  
Systematic Effect ◽  
Conflicting Information ◽  
Doppler Shifts ◽  
Line Asymmetry ◽  
Observing Techniques

Several measurements of 5-min velocity amplitudes have yielded confusing and conflicting information on the l and m dependence of the modal excitation (Kuhn and O'hanlon, 1983 – henceforth KO; Deubner, 1985; and Hill et al. 1985). We have obtained considerably more data than was described in KO using similar observing techniques. Additional analysis has illuminated a systematic effect related to the finite spatial resolution, and line asymmetry of the data that can lead to errors in inferred velocity amplitudes. Even though Doppler shifts are calculated from the Fraunhofer line center positions the effect can lead to 5-min oscillation amplitude errors at the 10 percent or greater level. Line wing observations should be more susceptible, and comparable resolution 2-dimensional data may be less sensitive to this systematic.

Nonlinear dynamics of a shell encapsulated microbubble near solid boundary in an ultrasonic field

2020 ◽  
Vol 14 (3) ◽  
pp. 7235-7243
Author(s):  
N.M. Ali ◽  
F. Dzaharudin ◽  
E.A. Alias
Keyword(s):  
Oscillation Amplitude ◽  
Ultrasonic Field ◽  
Dynamical Behaviour ◽  
Ultrasound Contrast Agents ◽  
Chaotic Behaviour ◽  
Solid Boundary ◽  
Driving Frequency ◽  
Pressure Amplitude ◽  
Radial Expansion ◽  
Therapeutic Delivery

Microbubbles have the potential to be used for diagnostic imaging and therapeutic delivery. However, the transition from microbubbles currently being used as ultrasound contrast agents to achieve its’ potentials in the biomedical field requires more in depth understanding. Of particular importance is the influence of microbubble encapsulation of a microbubble near a vessel wall on the dynamical behaviour as it stabilizes the bubble. However, many bubble studies do not consider shell encapsulation in their studies. In this work, the dynamics of an encapsulated microbubble near a boundary was studied by numerically solving the governing equations for microbubble oscillation. In order to elucidate the effects of a boundary to the non-linear microbubble oscillation the separation distances between microbubble will be varied along with the acoustic driving. The complex nonlinear vibration response was studied in terms of bifurcation diagrams and the maximum radial expansion. It was found that the increase in distance between the boundary and the encapsulated bubble will increase the oscillation amplitude. When the value of pressure amplitude increased the single bubble is more likely to exhibit the chaotic behaviour and maximum radius also increase as the inter wall-bubble distance is gradually increased. While, with higher driving frequency the maximum radial expansion decreases and suppress the chaotic behaviour.

Catalytic Resonance Theory: Parallel Reaction Pathway Control

2019 ◽  
Author(s):  
M. Alexander Ardagh ◽  
Manish Shetty ◽  
Anatoliy Kuznetsov ◽  
Qi Zhang ◽  
Phillip Christopher ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Active Site ◽  
Active Sites ◽  
Reaction Pathway ◽  
Control Strategies ◽  
Oscillation Amplitude ◽  
Catalytic Performance ◽  
Parallel Reaction ◽  
Resonance Theory ◽  
Static Conditions

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10<sup>-6</sup> < f < 10<sup>4</sup> Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

scholarly journals The role of sildenafil citrate in the treatment of fetal growth restriction: a randomized controlled trial

2019 ◽  
Vol 8 (5) ◽  
pp. 1840
Author(s):  
Ahmed Abdelshafy ◽  
Khaled Ibrahim Abdullah ◽  
Sherif Ashoush ◽  
Heba E. Hosni
Keyword(s):  
Middle Cerebral Artery ◽  
Fetal Growth ◽  
Cerebral Artery ◽  
Fetal Growth Restriction ◽  
Umbilical Artery ◽  
Controlled Trial ◽  
Maternity Hospital ◽  
Growth Restriction ◽  
Sildenafil Citrate ◽  
Doppler Velocity

Background: This study was aimed to evaluate the effect of sildenafil citrate on Doppler velocity indices in patients with fetal growth restriction (FGR) associated with impaired placental circulation.Methods: A double-blinded, parallel group randomized clinical trial (clinicaltrials.gov NCT02590536) was conducted in Ain Shams Maternity Hospital, in the period between October 2015 and June 2017. Ninety pregnant women with documented intrauterine growth retardation at 24-37 weeks of gestation were randomized to either sildenafil citrate 25 mg orally every 8 hours or placebo visually-identical placebo tablets with the same regimen. The primary outcome of the study was the change in umbilical artery and fetal middle cerebral artery indices.Results: There was a significant improvement in umbilical and middle cerebral artery indices after sildenafil administration p<0.001. Present study observed that, sildenafil group, in comparison to placebo, has a significantly higher mean neonatal birth weight. 1783±241g vs 1570±455g (p<0.001). There was a significantly higher mean gestational age at delivery in women in sildenafil group 35.3±1.67 weeks, whereas it was lower in the placebo group 33.5±1.7 weeks. The side effects as headache, palpitation and facial flushing were significantly higher in sildenafil group compared to placebo group.Conclusions: The use sildenafil citrate in pregnancies with fetal growth restriction (FGR) improved the feto-placental Doppler indices (pulsatility index of umbilical artery and middle cerebral artery) and improved neonatal outcomes.

scholarly journals A computational model-based approach for atlas construction of aortic Doppler velocity profiles for segmentation purposes

2018 ◽  
Vol 40 ◽  
pp. 23-32 ◽  
Author(s):  
Vedrana Baličević ◽  
Hrvoje Kalinić ◽  
Sven Lončarić ◽  
Maja Čikeš ◽  
Bart Bijnens
Keyword(s):  
Computational Model ◽  
Velocity Profiles ◽  
Doppler Velocity ◽  
Model Based ◽  
Atlas Construction
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