Large Negative Pressure Research Articles

Effect of operation condition on the venting characteristics of gas/dust two-phase system explosions

This experiment focused on the study of gas and solid two-phase explosions venting characteristics. A comprehensive research of venting parameter, venting flame propagation, temperature distribution, and the influence mechanism of operation condition were revealed. Results indicate that the venting flame experienced the changes of “mushroom”, “spherical” and “strip” structures and was affected by the initial pressure (Pinit) and the film rupture pressure (Pstat). As Pstat≥0.24 MPa, the flame all exhibited a “mushroom” structure and became more prominent as the film rupture pressure increased. The velocity history was increased in the acceleration venting stage as the film rupture pressure and initial pressures enlarged, and flame exhibited an obvious oscillation during extinguishing stage and the average amplitude was also enlarged. As the film rupture pressure further increased, the secondary and third venting processes appeared. The pressure change at the venting port was more significant, even appeared a larger negative pressure and its drop extent continued to increase as the film rupture pressure and initial pressures raised. Tmax appeared in the center of “spherical” flame approach the front end and the extinguished flame still maintained a higher temperature, resulting in a larger distribution outline than the flame image.

Can Black Holes or Other Relativistic Space Objects Be a Source of Dark Energy?

We consider the hypothesis that the sources of dark energy (DE) could be black holes (BHs) or more exotic objects, such as naked singularities or gravastars. We propose a definition of the presence of DE in the Universe and a criterion for what can be considered the source of this dark energy. It is based on the idea of the accelerated expansion of the Universe, which requires antigravity caused by large negative pressure. A recently proposed hypothesis, that the mass of BHs increases with time according to the same law as the volume of the part of the Universe containing it and the population of BHs can mimic DE, is examined. We demonstrate the reasons why it cannot be accepted, even if all the assumptions on which this hypothesis is based are considered true.

LES application to wind pressure prediction for tall building on complex terrain

This study conducted numerical simulations based on the large eddy simulation (LES) model, which employs an unstructured grid system and exhibits high performance in parallel computing, to investigate the effects of a circumferential environment, such as real terrain and surrounding buildings, on the unsteady pressure fields acting on a tall building with a rectangular section. There are three numerical examples using an irregularly shaped high-rise building (aspect ratios: height/length = 7/4 and length/width = 24/11), the same building on a complex terrain, and the same building with surrounding buildings on a complex terrain. To elucidate the statistical pressure characteristics, we focused on the mean, fluctuating, and peak values on the surfaces of the target building. The pressures for the present models were validated through a comparison with experimental data obtained under the same conditions. Subsequently, the velocity and pressure fields directly influenced by the complex local terrain and surrounding buildings were studied. A concave terrain located on the leeward side of the target building could cause a large negative pressure on the side surfaces as a result of access to the deformed separating flow. In addition, the surrounding buildings led to the movement of the stagnation point to a higher location on the windward surface and intensification of the conical vortex attached to the side surface.

Synergistic Effects of Resistive Breathing on Endotoxin-Induced Lung Injury in Mice.

Resistive breathing (RB) is characterized by forceful contractions of the inspiratory muscles, mainly the diaphragm, resulting in large negative intrathoracic pressure and mechanical stress imposed on the lung. We have shown that RB induces lung injury in healthy animals. Whether RB exerts additional injurious effects when added to pulmonary or extrapulmonary lung injury is unknown. Our aim was to study the synergistic effect of RB on lipopolysaccharide (LPS)-induced lung injury. C57BL/6 mice inhaled an LPS aerosol (10mg/3mL) or received an intraperitoneal injection of LPS (10 mg/kg). Mice were then anaesthetized, the trachea was surgically exposed, and a nylon band of a specified length was sutured around the trachea, to provoke a reduction of the surface area at 50%. RB through tracheal banding was applied for 24 hours. Respiratory system mechanics were measured, BAL was performed, and lung sections were evaluated for histological features of lung injury. LPS inhalation increased BAL cellularity, mainly neutrophils (p < 0.001 to ctr), total protein and IL-6 in BAL (p < 0.001 and p < 0.001, respectively) and increased the lung injury score (p = 0.001). Lung mechanics were not altered. Adding RB to inhaled LPS further increased BAL cellularity (p < 0.001 to LPS inh.), total protein (p = 0.016), lung injury score (p = 0.001) and increased TNFa levels in BAL (p = 0.011). Intraperitoneal LPS increased BAL cellularity, mainly macrophages (p < 0.001 to ctr.), total protein levels (p = 0.017), decreased static compliance (p = 0.004) and increased lung injury score (p < 0.001). Adding RB further increased histological features of lung injury (p = 0.022 to LPS ip). Resistive breathing exerts synergistic injurious effects when combined with inhalational LPS-induced lung injury, while the additive effect on extrapulmonary lung injury is less prominent.

Negative Pressure in Water for Efficient Heat Utilization and Transfer.

Thermodynamic metastable water in negative pressure provides a possible solution to elevate the upper limit of evaporative heat transfer capacity and the efficiency of low-grade heat utilization, but practical implementations are challenging due to the difficulty in generating and maintaining large negative pressure. Herein, we report a novel structure with a hydrogel film as the evaporation surface and a permeable substrate as the functional layer to suppress cavitation. Based on the structure, we achieve an evaporation-driven flow system with negative pressure as low as -1.67 MPa. Molecular dynamics simulations elucidate the importance of strong water-polymer interactions in negative pressure generation. With the large negative pressure, we demonstrate a streaming potential generator that spontaneously converts environmental energy into electricity and outputs a voltage of 1.06 V. Moreover, we propose a "negative pressure heat pipe", which achieves a high heat transfer density of 9.6 kW cm-2 with a flow length of 1 m.

The Horizontal Sonocapillary Effect in UltrasonicAssisted Soldering

In this work, the horizontal sonocapillary effect in ultrasonic-assisted soldering was investigated via numerical simulations and experiments. The numerical simulation results indicated that acoustic pressures in the liquid solder exhibited distinct sinusoidal features with negative offsets, forming a negative average acoustic pressure. When the ultrasonic vibrations were transmitted to the lower substrate in the joint clearance, the average acoustic pressures decreased from the acoustic pressure center to the filling front, forming a negative acoustic pressure gradient in the horizontal direction. As a result, the solder was sucked into the joint clearance by a large negative acoustic pressure. This sonocapillary effect was verified with experiments. In the calculation model, a high ultrasonic amplitude, a small joint clearance width, and a high base material stiffness increased the acoustic pressure and its average difference on the horizontal direction in the solder, which further improved the driving force of the sonocapillary effect. However, the wetting angle had a small influence on the sonocapillary effect.

Determination of Critical Point of Particle Migration Direction in a Confined Shear Flow of Giesekus Fluids

Migration of a particle in a confined shear flow of Giesekus fluids is investigated numerically with the method of direct forcing/fictitious domain. We focus on the migration direction for the particle with initial lateral position y0 and determination of critical point yc of a particle moving towards the center line or wall. The effect of viscosity ratio μr, shear-thinning parameter α, Weissenberg number Wi, and blocking rate β on the value yc is analyzed. The results showed that when μr ≤ 0.5, the particle will migrate towards the wall regardless of the value of y0. When μr &gt; 0.5, yc increases with increasing μr, and some particles will migrate towards the center line with the increase in μr. The particle is more likely to migrate towards the center line at small values of Wi and α but at large values of μr. The impact of Wi and β on the particle migration direction is more obvious. The particle will migrate towards the wall for β = 0.3 and is more likely to migrate towards the wall with increasing β. α and Wi have little influence on the pressure distribution in the case of the same β and μr. The particle near the wall will migrate faster because large positive pressure and negative pressure appear around the particle.

Tunable Dry Adhesion of Soft Hollow Pillars through Sidewall Buckling under Low Pressure

AbstractControlling adhesion on demand is essential for many manufacturing and assembly processes such as microtransfer printing. Among various strategies, pneumatics‐controlled switchable adhesion is efficient and robust but currently still suffers from challenges in miniaturization and high energy cost. In this paper, a novel way to achieve tunable adhesion using low pressure by inducing sidewall buckling in soft hollow pillars (SHPs) is introduced. It is shown that the dry adhesion of these SHPs can be changed by more than two orders of magnitude (up to 151×) using low activating pressure (≈−10 or ≈20 kPa). Large enough negative pressure triggers sidewall buckling while positive pressure induces sidewall bulging, both of which can significantly change stress distribution at the bottom surface to facilitate crack initiation and reduce adhesion therein. It is shown that a single SHP can be activated by a micropump to manipulate various lightweight objects with different curvatures and surface textures. Here, it is also demonstrated that an array of SHPs can realize selective pick‐and‐place of an array of objects. These demonstrations illustrate the robustness, simplicity, and versatility of these SHPs with highly tunable dry adhesion.

Simulation of U-box test for fresh self-compacting concrete based on lattice Boltzmann method

• The 3-D model of the U-box test is successfully established based on H-B model and LBM with an average error of 7%. • The yield stress is the key rheological parameter that determines the passing performance of fresh SCC. • The increase of rheological parameters all reduce the flow ability of fresh SCC. • The rheological features made a greater impact on the average surface pressure of the steel bars at the start of U-box test. • The speed of pulling up the partition gate only had an influence on the early period of U-box test. In this research, the numerical model of fresh self-compacting concrete (SCC) U-box test was established by combining lattice Boltzmann method (LBM) and Herschel-Bulkley (H–B) model. The flow behavior of fresh SCC in U-box was studied and its rheological mechanism was analyzed. The test results showed that the simulation model established based on U-box test had high simulation accuracy, and the average error was about 7 %. The effects of rheological parameters (power-law index n , consistency index k and yield stress σ 0 ) on the U-box test were explored. The numerical results demonstrated that σ 0 was the crucial rheological parameter that determined the passing ability of fresh SCC, and its increase resulted in weaker passing ability . n and k had less effect on the passing ability. At the early stage of U-box test ( t < 1.0 s), the increase of n , k and σ 0 all reduced the velocity of flow and the pressure exerted on the fresh SCC, with n bringing the most significant effect. The peak velocity and pressure of shear-thinning ( n = 0.6) SCC could reach 0.74 m/s and 4200 Pa at t = 0.1 s. The peak velocity of shear-thickening ( n = 1.4) SCC was less than half of the former, and a larger negative pressure appeared, up to about −1600 Pa. The speed of pulling up the partition gate ( u g ) only had an effect, which gradually diminished with the increase of u g , on the initial phase of U-box test ( t < 5.0 s). The cross-sectional area corresponding to the obstacles that could be passed by the SCC was the main factor affecting the early velocity and pressure of the concrete.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps.

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1kHz) decreased monotonically as the pressure became more negative except for a dip (about 500Pa wide) that occurred between - 700 and - 1800Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

Bianchi Type V Tsallis Holographic Dark Energy Model with Hybrid Expansion Law

A number of recent cosmological observations have provided increasing evidence that currently the universe is undergoing a phase of accelerated expansion, the root cause of which is supposed to be due to an exotic component of the universe with large negative pressure, dubbed dark energy. Out of the various candidates of dark energy proposed in the literature, the holographic dark energy emerged from the Holographic Principle is drawing much attention in the research field. In this paper, we investigate a spatially homogeneous and anisotropic Bianchi Type V space-time filled with non-interacting Tsallis holographic dark energy (THDE) with Hubble horizon as the IR cutoff and pressureless cold dark matter within the framework of General Relativity. Exact solutions of the Einstein field equations are obtained by considering the average scale factor to be a combination of a power law and an exponential law, the so called hybrid expansion law first proposed by Akarsu et al. (2014). We study the cosmological dynamics of various models for different values of the non-additive parameter that appeared in the Tsallis entropy and that for that appeared in the exponential function of the hybrid expansion law. We find that our model exhibits present cosmological scenario.

Laser-induced shock-wave-expanded nanobubbles in spherical geometry

The secondary cavitation generation following laser-induced breakdown in aqueous media in spherical geometry, mimicking the geometry of the frontal part of the human eye, was studied. A numerical simulation of the shock wave propagation was performed, yielding peak-pressure maps, correctly predicting the location of the secondary cavitation onset for different shock wave source positions. The comparison between the simulation results and the experiments, performed with a high-precision, multiple-illumination technique, supports the suggested description of the nature of the secondary cavitation onset. It is shown that large transient negative pressures are created at the location of the acoustic image of the shock wave source, which is different from the optical focus. After the passage of the shock wave, abundant secondary cavitation is generated there. Additionally, the existence of an important contributing factor to the reduction of the secondary cavitation threshold is supported by the experimental results, namely the pre-illumination of the water by the breakdown-generating laser pulse, playing a crucial role in conditioning the medium. There is strong experimental evidence of the existence of another mechanism of pre-conditioning the water for the secondary cavitation onset, namely in the form of repetitive negative pressure pulse passage through the same volume, an indication of a possible two- or multiple-stage process.

Optimization and Experiment of a Disturbance-Assisted Seed Filling High-Speed Vacuum Seed-Metering Device Based on DEM-CFD

In disturbance-assisted seed filling vacuum seed-metering devices, the suction hole causes difficulty in quickly and stably sucking seeds when used for high-speed seeding and the large working negative pressure demand is used. To address this difficulty, this study’s authors designed a seed disk hole with a variable cross-section structure, and the groove depth, which has the function of assisting seed filling, was optimized. Using the combined method of Fluent numerical analysis and an orthogonal experiment, the influence of the shape, inlet diameter, and length of the seed disk hole on the pressure difference of the seed disk hole was analyzed. The working process of the vacuum seed meter was simulated and analyzed by the Discrete Element Method and Computational Fluid Dynamics coupling method. It was found that with the increase of the diameter of the seed disk hole, the pressure difference decreased, and the length of the seed disk hole had little effect on the pressure difference. The best diameter of the seed disk hole was 5.4 mm, and the length was 5 mm. It was found that the pressurization effect of the arc-shaped seed disk hole is better. With the increase of groove depth, the leakage rate shows a trend of first decreasing and then increasing, which was determined to be 1.5 mm. The verification experiment proved that the working performance of the optimized seed metering device is better than that of the original one. The results show that when the working negative pressure was 4 kPa and the working speeds were 8~14 km·h−1, the qualified rate was not less than 95.0%, and the seed filling performance was relatively stable. The optimized vacuum seed metering device can be applied to high-speed seeders, while ensuring the requirements of high-speed sowing operations.

Wind loads on multi-span roof buildings

This paper examines wind loads acting on multi-span roofs of low-rise buildings by performing wind tunnel tests with models whose parameters are roof shape (sawtooth, gable), roof slope (5°, 10°, 20°, 30°, 45°) and the number of spans (1–5). Large suctions can occur at either a high corner/edge or a low corner of sawtooth roofs, depending on roof slope and the location of roof span. Low corners of multi-span gable roofs experience large negative pressures on edge roofs of low-pitch roof slopes and on middle roofs of steeper roof slopes. Relatively large positive pressures on both sawtooth and multi-span gable roofs can occur at roof troughs of low-pitch roof slopes and their magnitude becomes larger as roof slope increases. For steeper roof slopes, large positive pressures are also observed at roof ridges of both roof shapes although their magnitude and the location of the roof span depend on roof shape. Both the size and the magnitude of suctions on walls between spans of sawtooth roofs increase with roof slope. Comparisons with ASCE7-16 design values were performed and the results imply that ASCE7-16 underestimates both positive and negative wind loads on most roof zones of multi-span roofs.

Clathrate Adhesion Induced by Quasi-Liquid Layer.

The adhesive force of clathrates to surfaces is a century-old problem of pipeline blockage for the energy industry. Here, we provide new physical insight into the origin of this force by accounting for the existence of a quasi-liquid layer (QLL) on clathrate surfaces. To gain this insight, we measure the adhesive force between a tetrahydrofuran clathrate and a solid sphere. We detect a strong adhesion, which originates from a capillary bridge that is formed from a nanometer-thick QLL on the clathrate surface. The curvature of this capillary bridge is nanoscaled, causes a large negative Laplace pressure, and leads to a strong capillary attraction. The microscopic capillary bridge expands and consolidates over time. This dynamic behavior explains the time-dependent increase of measured capillary forces. The adhesive force decreases greatly upon increasing the roughness and the hydrophobicity of the sphere, which founds the fundamental basics for reducing clathrate adhesion by using surface coating.

Manduca sexta experience high parasitoid pressures in the field but minor fitness costs of consuming plant secondary compounds.

Plant‐herbivore coevolutionary interactions have led to a range of plant defenses that minimize insect damage and a suite of counter adaptations that allow herbivores to feed on defended plants. Consuming plant secondary compounds results in herbivore growth and developmental costs but can have beneficial effects such as deterrence or harm of parasitoid enemies. Therefore, the role of secondary compounds on herbivore fitness must be considered in the context of the abundance and level of harm from natural enemies and the costs herbivores incur feeding on plant secondary compounds.In this study, I combined field measurements of Cotesia congregata wasp parasitism pressure with detailed measurements of the costs of plant secondary compounds across developmental stages in the herbivore host, Manduca sexta.I show that C. congregata parasitoids exert large negative selective pressures, killing 31%–57% of M. sexta larvae in the field. Manduca sexta developed fastest during instars most at risk for parasitoid oviposition but growth was slowed by consumption of plant secondary compounds. The negative effects of consuming plant secondary compounds as larvae influenced adult size traits but there were no immune, survival, or fecundity costs.These results suggest that developmental costs experienced by M. sexta herbivores consuming defensive compounds are minor in comparison to the strong negative survival pressures from abundant parasitoid enemies.

Modeling the Physics of Bubble Nucleation in Histotripsy.

This work aims to establish a theoretical framework for the modeling of bubble nucleation in histotripsy. A phenomenological version of the classical nucleation theory was parametrized with histotripsy experimental data, fitting a temperature-dependent activity factor that harmonizes theoretical predictions and experimental data for bubble nucleation at both high and low temperatures. Simulations of histotripsy pressure and temperature fields are then used in order to understand spatial and temporal properties of bubble nucleation at varying sonication conditions. This modeling framework offers a thermodynamic understanding on the role of the ultrasound frequency, waveforms, peak focal pressures, and duty cycle on patterns of ultrasound-induced bubble nucleation. It was found that at temperatures lower than 50 °C, nucleation rates are more appreciable at very large negative pressures such as -30 MPa. For focal peak-negative pressures of -15 MPa, characteristic of boiling histotripsy, nucleation rates grow by 20 orders of magnitude in the temperature interval 60 °C-100 °C.

Elevated tanks effect on transient pressures: case study

Abstract Elevated tanks are an integral part of the water supply networks. This paper highlights the effect of elevated tanks' location and size on the transient pressures resulting from the sudden failure of pumps. A comparison between the impact of elevated tanks and air vessels on the water hammer was also performed. The Bentley HAMMER model was first validated then applied to analyze the unsteady flow within an actual distribution network. The results display that the elevated tanks have a considerable effect on the surge pressures, where they improve the extreme pressures effectively at and around them, but they cannot fully protect the system from the water hammer risks, as there are still relatively large negative pressures at some distant junctions. Besides, as the tank capacity increases, the surge pressures increase slightly. In our case study, the best location of the elevated tank is at the network extremity and then at the pumping stations, since the minimum pressures improve by 67 and 54%, respectively. Although the present case study may differ from other supply systems, the obtained results can provide an indication of the elevated tanks' role in alleviating undesirable water hammer effects.

Developments in multiple-valve water-hammer control

This paper investigates multiple-valve closures in a simple reservoir-valve-pipeline-valve system. Multiple closing (or opening) of valves may induce large positive or low negative pressure waves due to wave interference (superposition of the waves). The effect of multiple-valve closure can be either beneficial or detrimental, with the outcome being entirely dependent on the position of the valves and the sequence and delay of the closures. Valves are incorporated as boundary conditions in the method of characteristics model. The staggered (diamond) grid with consideration of unsteady skin friction is applied. Experimental investigations of multiple-valve induced water-hammer have been performed in the University of Montenegro laboratory pipeline apparatus. The apparatus consists of an upstream end high-pressurized tank, horizontal steel pipeline (length 55.37 m, inner diameter 18 mm), four valve units positioned along the pipeline including the end points, and a downstream end tank. The transient event is initiated first by rapid closure of the downstream-end valve followed by the delayed closure of the upstream-end valve. Calculated and measured results are compared and discussed in the light of the effects of pressure wave interference.

Edema polmonare da pressione negativa dopo settoplastica in un adolescente

Negative pressure pulmonary edema (NPPE) is a danger-ous and potentially fatal condition with a multifactorial pathogenesis. NPPE is frequently a manifestation of upper airway obstruction, indeed the large negative intrathoracic pressure generated by forced inspiration against an obstructed airway is thought to be the main mechanism involved. The early detection of the signs of this syndrome is vital to the treatment and to patient outcome. The paper presents a case of NPPE due to post-extubation laryngospasm in a 14-year-old patient.