Formation of miarolitic-class, segregation-type pegmatites in the Taishanmiao batholith, China: The role of pressure fluctuations and volatile exsolution during pegmatite formation in a closed, isochoric system

2021 ◽  
Keyword(s):  
Pressure Fluctuations ◽  
Volatile Exsolution

Cardiac baroreflex dysfunction in patients with pulmonary arterial hypertension at rest and during orthostatic stress: Role of the peripheral chemoreflex

2021 ◽  
Author(s):  
Marcelle Paula-Ribeiro ◽  
Indyanara C. Ribeiro ◽  
Liliane C. Aranda ◽  
Talita M. Silva ◽  
Camila M. Costa ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Pulmonary Arterial Hypertension ◽  
Arterial Hypertension ◽  
Early Stage ◽  
Pressure Fluctuations ◽  
Sit To Stand ◽  
Peak Aerobic Capacity ◽  
Pulmonary Arterial ◽  
Peripheral Chemoreflex

The baroreflex integrity in early-stage pulmonary arterial hypertension (PAH) remains uninvestigated. A potential baroreflex impairment could be functionally relevant and possibly mediated by enhanced peripheral chemoreflex activity. Thus, we investigated 1) the cardiac baroreflex in non-hypoxemic PAH; 2) the association between baroreflex indexes and peak aerobic capacity (i.e., V̇O2peak); and 3) the peripheral chemoreflex contribution to the cardiac baroreflex. Nineteen patients and 13 age- and sex-matched healthy adults (HA) randomly inhaled either 100% O2 (peripheral chemoreceptors inhibition) or 21% O2 (control session), while at rest and during a repeated sit-to-stand maneuver. Beat-by-beat analysis of R-R intervals and systolic blood pressure provided indexes of cardiac baroreflex sensitivity (cBRS) and effectiveness (cBEI). The PAH group had lower cBEIALL at rest (mean ± SD: PAH = 0.5 ± 0.2 vs HA = 0.7 ± 0.1 a.u., P = 0.02) and lower cBRSALL (PAH = 6.8 ± 7.0 vs HA = 9.7 ± 5.0 ms mmHg-1, P < 0.01) and cBEIALL (PAH = 0.4 ± 0.2 vs HA= 0.6 ± 0.1 a.u., P < 0.01) during the sit-to-stand maneuver versus the HA group. The cBEI during the sit-to-stand maneuver was independently correlated to V̇O2peak (partial r = 0.45, P < 0.01). Hyperoxia increased cBRS and cBEI similarly in both groups at rest and during the sit-to-stand maneuver. Therefore, cardiac baroreflex dysfunction was observed under spontaneous and, most notably, provoked blood pressure fluctuations in non-hypoxemic PAH, was not influenced by the peripheral chemoreflex, and was associated with lower V̇O2peak suggesting it could be functionally relevant.

Unconventional relaxation of hydrodynamic modes in anharmonic chains under strong pressure fluctuations

2021 ◽  
Author(s):  
Da Ke ◽  
Wei Zhong ◽  
Sergey V Dmitriev ◽  
Daxing Xiong
Keyword(s):  
Thermal Transport ◽  
Numerical Scheme ◽  
Pressure Fluctuations ◽  
Hydrodynamic Theory ◽  
Hydrodynamic Modes ◽  
Large Pressure

Abstract We develop an effective numerical scheme to capture hydrodynamic modes in general classical anharmonic chains. This scheme is based on the hydrodynamic theory suggested by Ernst-Hauge-van Leeuwen, which takes full role of pressure fluctuations into account. With this scheme we show that the traditional pictures given by the current nonlinear fluctuating hydrodynamic theory are valid only when the system's pressure is zero and the pressure fluctuations are weak. For nonvanishing pressure, the hydrodynamic modes can, however, respond to small and large pressure fluctuations and relax in some distinct manners. Our results shed new light on understanding thermal transport from the perspective of hydrodynamic theory.

The dynamics of turbulence near a wall according to a linear model

1967 ◽  
Vol 29 (1) ◽  
pp. 113-135 ◽  
Author(s):  
Gerald Schubert ◽  
G. M. Corcos
Keyword(s):  
Boundary Layer ◽  
Amplitude Ratio ◽  
Equations Of Motion ◽  
Pressure Fluctuations ◽  
Homogeneous System ◽  
Viscous Sublayer ◽  
Spanwise Direction ◽  
Mean Velocity ◽  
Normal Fluctuations

The dynamics of turbulent velocity fluctuations in and somewhat outside the viscous sublayer are examined by linearizing the equations of motion around the known mean velocity profile. The rest of the boundary layer is assumed to drive the motion in the layer by means of a fluctuating pressure which is independent of distance from the wall. The equations, which are boundary-layer approximations to the Orr-Sommerfeld equations, are thus treated as a non-homogeneous system and solved by convergent power series. The solutions which exhibit the strong role of viscosity throughout the layer considered provide a model endowed with many of the known features of turbulence near a wall. In particular, the phase angle between streamwise and normal fluctuations is found to be in plausible agreement with experiments. An important role is ascribed by the solutions to the displacement of the mean velocity by the normal fluctuations. The impedance of the layer is found to be anisotropic in that it favours fluctuations with a much larger scale in the streamwise than in the spanwise direction. For such disturbances, the ratio of turbulent intensity to the intensity of the pressure fluctuations approximates the experimental ratio. According to the solutions it is primarily the spanwise component of the pressure gradient which is responsible for the intense level of turbulence very near the wall. The model apparently underestimates the amplitude ratio of normal to streamwise components of the velocity.

Compressible turbulent channel and pipe flow: similarities and differences

2010 ◽  
Vol 648 ◽  
pp. 155-181 ◽  
Author(s):  
SOMNATH GHOSH ◽  
HOLGER FOYSI ◽  
RAINER FRIEDRICH
Keyword(s):  
Pipe Flow ◽  
Pressure Fluctuations ◽  
Plane Channel ◽  
Reynolds Numbers ◽  
Mean Flow ◽  
Specific Heats ◽  
Pipe Radius ◽  
Turbulent Plane ◽  
Similarities And Differences

Direct numerical simulation (DNS) is used to explore similarities and differences between fully developed supersonic turbulent plane channel and axisymmetric non-swirling pipe flow bounded by isothermal walls. The comparison is based on equal friction Mach number, friction Reynolds number, Prandtl number, ratio of specific heats and viscosity exponent. The channel half-width and pipe radius are chosen to define the Reynolds numbers. To what extent and why mean flow quantities, second-order turbulence statistics and terms in the Reynolds stress equations coincide or diverge in both flows are investigated. The role of the fluctuating pressure in causing characteristic differences among correlations involving pressure fluctuations is identified via a Green-function-based analysis of the pressure field.

Respiratory fluctuations in pupil size

1975 ◽  
Vol 228 (4) ◽  
pp. 1094-1102 ◽  
Author(s):  
P Borgdorff
Keyword(s):  
Pupil Size ◽  
Respiratory Activity ◽  
Sympathetic Innervation ◽  
Pressure Fluctuations ◽  
Pertinent Literature ◽  
Mechanical Factor ◽  
Central Respiratory Activity ◽  
Per Se ◽  
Stimulation Of

Regular fluctuations in pupil size of the cat were measured and the properties, nervous pathways, and origin of these oscillations were investigated. The rhythm of pupil movements under control conditions appeared to be either locked to the central respiratory cycle or to the artificial ventilatory cycle. These movements were only seen in lightly anesthetized or tranquilized cats, but not in alert or deeply anesthetized cats (ether, halothane or pentobarbital). The fluctuations proved to be independent of sympathetic innervation but related to variations in parasympathetic outflow. At least two sources for pupil oscillations appeared to be involved: central respiratory activity and respiratory blood pressure fluctuations that modulated pupil width via sinoaortic baroreceptors. Lung movements per se, as a third possible factor, did not modulate pupil width, whereas electrical stimulation of the afferent lung vagi did; therefore the role of this mechanical factor is not clear. A review of the pertinent literature shows that in the organism there are many phenomena exhibiting respiratory oscillations. It seems likely that these oscillations have the same origin as the respiratory pupil fluctuations.

Role of Nitric Oxide in Buffering Short-Term Blood Pressure Fluctuations

Physiology ◽  
2000 ◽  
Vol 15 (5) ◽  
pp. 229-233 ◽  
Author(s):  
Harald M. Stauss ◽  
Pontus B. Persson
Keyword(s):  
Nitric Oxide ◽  
Blood Pressure ◽  
Shear Stress ◽  
Pressure Fluctuations ◽  
Initial Increase ◽  
Short Term ◽  
Nitric Oxide Release ◽  
Arterial Blood ◽  
Endothelial Shear Stress

Blood pressure instability may promote cardiovascular morbidity. Recent data suggest a role of nitric oxide in stabilizing arterial blood pressure. A rise in blood pressure enhances endothelial shear stress and nitric oxide release. The resulting vasodilation antagonizes the initial increase in blood pressure. This system can respond within 2–10 seconds.

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