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Numerical simulations were generated using a nonlinear shallow-water model of velocity potential to study the fundamental processes of tsunami generation and amplification by atmospheric pressure waves. When an atmospheric pressure wave catches up with an existing tsunami that is propagating as a free wave over an abrupt change in water depth, the amplified tsunami propagates in the shallower water. An existing tsunami propagating as a free wave over a sloping seabed is also amplified by being passed by atmospheric pressure waves. When atmospheric pressure waves travel over an abrupt change in water depth, the water surface profile of tsunamis in the shallower water depends on both the interval of the atmospheric pressure waves and the phase of the tsunami-generation process over the change in water depth. Moreover, when atmospheric pressure waves travel over an abrupt change in water depth, the tsunami amplitude in the shallower water increases, as the water depth of the shallower area is decreased and the Proudman resonance is further reduced. When an atmospheric pressure wave train with positive pressure travels over a sloping seabed, the amplification of tsunami crests propagating as free waves is controlled by leaving the forced water waves following the atmospheric pressure waves. Conversely, the amplitudes of tsunami troughs propagating as free waves increase.

The transient pressure waves in the intake and exhaust systems directly affect the intake and exhaust processes of diesel engines, thus further affecting the combustion process and the performance of diesel engines. The variation rules of the intake and exhaust pressure waves at different engine speeds and loads in a high-pressure common-rail diesel engine were studied. Then, the effects of EGR rate and VNT nozzle opening on the intake and exhaust pressure waves were systematically studied by bench test and one-dimensional simulation analysis. The results show that at 2000 r·min-1 full-load, when the EGR rate increases from 0 to 10%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms of the intake pressure and the exhaust pressure change significantly. The fluctuation intensity of the intake pressure decreases by 58.6%, and the fluctuation intensity of the exhaust pressure increases by 77.2%. As the EGR rate increases from 10% to 30%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms are basically unchanged. The increasing magnitudes of the intake and exhaust pressure fluctuation intensities are 16.6% and 20.5%, respectively. As the VNT nozzle opening increases, the average intake pressure and the average exhaust pressure both decrease. The corresponding phases of the intake pressure wave crest and trough are delayed. The fluctuation waveforms of the intake and exhaust pressure are basically unchanged, and the fluctuation intensities do not change significantly.

During eruptions, volcanoes produce air‐pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash‐rich explosions, recording more discrete atmospheric disturbances from effusive eruptions remains a practical challenge depending on the distance to the source. At Nyiragongo volcano (D.R. Congo), towering above a 1‐million urban area, we analyzed local infrasonic records between January 2018 and April 2022. An acoustic signature from this open‐vent volcano is detected up to the volcano observatory facilities in Goma city center about 17 km from its crater. We compared infrasound signals with space‐based observations of the intra‐crater activity (SO2 emissions, thermal anomalies, crater depth/radius). We thus obtain a comprehensive picture of Nyiragongo's eruptive activity during this period, encompassing the drainage of its lava lake during its third known flank eruption on 22 May 2021. Plain Language Summary Similar to seismic waves propagating within the solid Earth, acoustic waves propagate in the atmosphere as a result of near‐surface volcanic activity. In contrast with powerful volcanic explosions, close‐range deployment of instruments around the active vent (for instance <15 km) is generally needed for continuously monitoring long‐living lava effusion or degassing as observed at open‐vent volcanoes, such as Kīlauea (Hawaii) or Nyiragongo (D.R. Congo). Nyiragongo hosted the world's largest lava lake up to 2021, which was drained during the third known flank eruption of this volcano on 22 May 2021. While watching for possible reawakening, we detected the infrasound signature of a nascent lava lake four months later, highlighting the crucial role of infrasound monitoring. Remote observations from space (ground deformation, gas emissions, thermal anomalies) can also provide essential information about the eruptive state of a volcano and were jointly analyzed with infrasound records. Knowing that Nyiragongo towers above the 1‐million inhabitant city of Goma, such an approach has significant implications for optimizing future monitoring efforts in a harsh field environment. Key Points Nyiragongo volcano (D.R. Congo) is a permanent emitter of infrasound that pauses during rare flank eruptions Intra‐crater lava eruptions (lava lake, spatter cone, lava pond) are detected up to the observatory in a dense urban area ∼17 km away Joint analysis with space‐based observations over the period 2018–2022 provides a clear picture of the persistent unrest at this volcano

Apart from peculiarities of the cerebral circulation, required to perfuse the brain with the subject erect, the principles established for function of the human systemic circulation (pulsatile flow at input and steady flow at output in capillaries) are identical to those established for other mammals. Assumption of the erect posture first as Homo erectus , then as Homo sapiens , conferred huge advantage to humans and led to command of the mammalian kingdom. But this required a circulation which could perfuse the brain securely against gravity in all positions of the body. This review covers what presently is known about the human cerebral circulation, and how such knowledge can be applied in some clinical conditions including development of dementia in older subjects, and in management of patients with elevation of intra-cranial pressure in younger subjects.

The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain-heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes. We implemented a fast non-gated two-dimensional MRI pulse sequence based on echo-planar imaging (EPI) with ultra-short repetition time (approx. 30-50 ms), which stepped through slices every approximately 20 s. We constrained the solution of the Bloch equations for spins moving faster than a critical speed to produce an endogenous contrast primarily dependent on spin volume changes, and an approximately sixfold signal gain compared with Ernst angle acquisitions achieved by the use of a 90° flip angle. Using cardiac and respiratory peaks detected on physiological recordings, average cardiac and respiratory MRI pulse waveforms in several brain compartments were obtained at 7 Tesla, and used to derive a compliance indicator, the pulsatility volume index (pVI). The pVI, evaluated in larger cerebral arteries, displayed significant variation within and across vessels. Multi-echo EPI showed the presence of significant pulsatility effects in both S0 and signals, compatible with blood volume changes. Lastly, the pVI dynamically varied during breath-holding compared with normal breathing, as expected for a compliance indicator. In summary, we characterized and performed an initial validation of a novel MRI indicator of cerebrovascular compliance, which might prove useful to investigate brain-heart interactions in cerebrovascular disease and other disorders.

Background Pressure contour analysis is commonly used to estimate cardiac performance for patients suffering from cardiovascular dysfunction in the intensive care unit. However, the existing techniques for continuous estimation of stroke volume (SV) from pressure measurement can be unreliable during hemodynamic instability, which is inevitable for patients requiring significant treatment. For this reason, pressure contour methods must be improved to capture changes in vascular properties and thus provide accurate conversion from pressure to flow. Methods This paper presents a novel pressure contour method utilizing pulse wave velocity (PWV) measurement to capture vascular properties. A three-element Windkessel model combined with the reservoir–wave concept are used to decompose the pressure contour into components related to storage and flow. The model parameters are identified beat-to-beat from the water-hammer equation using measured PWV, wave component of the pressure, and an estimate of subject-specific aortic dimension. SV is then calculated by converting pressure to flow using identified model parameters. The accuracy of this novel method is investigated using data from porcine experiments (N = 4 Pietrain pigs, 20–24.5 kg), where hemodynamic properties were significantly altered using dobutamine, fluid administration, and mechanical ventilation. In the experiment, left ventricular volume was measured using admittance catheter, and aortic pressure waveforms were measured at two locations, the aortic arch and abdominal aorta. Results Bland–Altman analysis comparing gold-standard SV measured by the admittance catheter and estimated SV from the novel method showed average limits of agreement of ±26% across significant hemodynamic alterations. This result shows the method is capable of estimating clinically acceptable absolute SV values according to Critchely and Critchely. Conclusion The novel pressure contour method presented can accurately estimate and track SV even when hemodynamic properties are significantly altered. Integrating PWV measurements into pressure contour analysis improves identification of beat-to-beat changes in Windkessel model parameters, and thus, provides accurate estimate of blood flow from measured pressure contour. The method has great potential for overcoming weaknesses associated with current pressure contour methods for estimating SV.

In this study, the impact of the number of bubbles on the velocity of laser-induced microjet is numerically investigated, focusing on the pressure wave propagation generated by multiple laser-induced bubbles. First, we show that the microjet velocity increases with the increasing impulse of the pressure wave propagating to the meniscus direction. This result indicates that it is possible to study the structure of the pressure field generated from bubbles to investigate the effect on microjet generation. In addition, it is found that the microjet is weakened with the increase in the number of bubbles. Next, we show that the propagation of the pressure waves has two types. The first type is propagating from a bubble to a meniscus. The second type is propagating round trip between nearby bubbles or by the bubble itself. Finally, we explain the reason for the decrease in the microjet velocity with the increasing number of bubbles by an expansion history of the bubbles, which depends on their interaction with the pressure waves. These results could help to design not only laser-induced microjet generation but also devices that use laser-induced bubbles generated in a microchannel.

In a piping system, water hammer occurs when pressure rapidly varies. As a result of these conditions, undesirable and damaging outcomes can occur, such as noise, excessive wear and fatigue, and collapse of the piping system and valves. This paper provides a review and mathematically analysis of the water hammering in check valves. The purpose of this paper is to review and mathematically analyze water hammering in check valves. Various approaches to selecting the best check valve or to modifying the design of the check valve are discussed in this paper. In addition, various equations and mathematical models are presented to evaluate and analyze water hammering in piping and check valves. There are also case studies of water hammering analysis of swing and dual plate check valves. These case studies provide examples of how water hammering can be calculated and analyzed for swing and dual plate check valves in the oil and gas industry.

Small-scale physical experiments were conducted to investigate the application of the Goda wave pressure formulae modified to predict the horizontal wave loads on elevated structures considering non-breaking, broken, and impulsive breaking waves. The air gap defined as the vertical distance from the still water level to the base of the structure played a key role in the reduction of wave impact forces. Physical model results using random waves confirmed that the modified application of the Goda wave pressure formulae provided a good estimate of the horizontal forces on elevated structures for both broken and impulsive breaking waves. As the air gap was increased, the resulting forces decreased, and the estimated values became increasingly conservative. When the ratio of the air gap to water depth, a / h ′, increased from −1.0 to 1.5, the reduction in force was approximately 75% when the wave height to breaking water depth ratio, H / h b , was equal to unity.