Bounce Phenomenon Research Articles

A comprehensive analysis of cosmic evolution in f(Q,T) theory

This paper examines the bouncing cosmology in f(Q,T) theory, where Q represents non-metricity and T denotes the trace of energy-momentum tensor. The aim of this research is to study the phenomenon of a cosmic bounce, where contraction, bounce point and expansion occur at t < 0, t = 0 and t > 0, respectively. In this perspective, we consider Bianchi Type-I spacetime with perfect matter configuration to study the mysterious universe. Further, we analyze the behavior of cosmological parameters such as scale factor, Hubble parameter, deceleration parameter and equation of state parameter using three distinct functional forms of f(Q,T) theory. A comprehensive examination of energy conditions is analyzed to study the matter bounce in this modified framework. Our findings indicate that the acceleration takes place in the vicinity of the bouncing point and ensures the presence of a nonsingular bounce in this theory.

Aluminum oxide droplet collisions: Molecular dynamics study

In this work, the induced coalescence mechanism and dynamic contact behavior of alumina (Al2O3) droplets at different impact velocities were investigated for the first time from a microscopic point of view by molecular dynamics (MD) methods through the analysis of axial speed, shrinkage, neck radius ratio, contact force, temperature, kinetic energy, surface energy, and the amount of change in the internal energy of the droplets. The results show that the minimum speed at which collisional coalescence of Al2O3 droplets occurs is 30 m/s. When the speed is lower than 30 m/s, the droplets undergo bounce phenomena due to the Coulomb force. Under the high-speed impact, the inertia force of Al2O3 droplets acts less than the surface tension and viscous resistance. The droplets don’t get squashed in the whole collision process. For the different initial velocities, the magnitude of the contact force on a unilateral droplet during the collision process does not always increase with speed. When the collision speed is not higher than 400[Formula: see text]m/s, the contact force on the droplets eventually stabilizes at about 0.28[Formula: see text]Kcal/(mol⋅Å), whereas this value is about 0.36[Formula: see text]Kcal/(mol⋅Å) and about 0.5[Formula: see text]Kcal/(mol⋅Å) for the intervals from 500[Formula: see text]m/s to 700[Formula: see text]m/s and from 800[Formula: see text]m/s to 1000[Formula: see text]m/s, respectively. The increase of the droplet’s initial speed has a limited contribution to the temperature of the system after the collision, and the amount of loss of the total energy (the sum of kinetic energy, surface energy, and internal energy changes) becomes more pronounced, even up to about 20% when the speed reaches 900[Formula: see text]m/s. At the same time, we predicted the Al2O3 melting point and compared it with the standard melting point with an error of 2%, proving the accuracy of the model. This work can strengthen our understanding of the industrial processes with applications in high-energy nanomaterials, rocket propellants, rocket structure design and performance optimization.

Longitudinal Pulse-Synchronous Bouncing During Catheter Angiography—A Phenomenon Specific to Spinal Hemangioblastomas

Spinal hemangioblastomas are often evaluated with catheter angiography for both workup and treatment planning. We report a unique longitudinal pulse-synchronous bouncing phenomenon observed during their angiographic evaluation and consider the association of pulse-synchronous bouncing with syringomyelia, another pathologic feature associated with hemangioblastomas. Preoperative spinal angiograms and associated MRIs obtained over a 16-year period at a single institution were retrospectively evaluated. MRI parameters included lesion and syrinx location and size. Angiograms were evaluated for bouncing phenomena. Student's t-test and Chi square test compared characteristics between groups. Linear regression analyses evaluated maximum amplitude of dynamic motion and any associated syrinx. Nineteen hemangioblastoma patients had preoperative angiograms available for review. Eight exhibited bouncing behavior. Between the dynamic and non-dynamic cohorts, there was no difference in presence or volume of syrinxes. Lesions in the dynamic cohort trended towards a cervical location (75% versus 36.3%, p=0.10). No significant correlation was found between bouncing amplitude and syrinx size (R2 = 0.023). Dural contact may be related to this dynamic behavior since other high-flow lesions like AVMs do not demonstrate this phenomenon, and AVMs are pial-based and more likely to contact stationary dura. Here, there were fewer lesions abutting the thecal sac in the dynamic cohort (50% versus 81.8%, p=0.14). Though no significant relationship was established between this bouncing behavior and syrinx formation, noted trends included a greater range of motion for cervical lesions and limited motion in tumors abutting the thecal sac.

Study on Relay Contact Bounce Based on the Adaptive Weight Rotation Template Matching Algorithm

In order to analyze the relay action process from an imaging perspective and further investigate the bounce phenomenon of relay contacts during the contact process, this paper utilizes a high-speed shooting platform to capture images of relay action. In light of the situation where the stationary contact in the image is inclined and continuously changing, a rotation template matching algorithm based on adaptive weight is proposed. The algorithm identifies and obtains the inclination angle of the stationary contact, enabling the study of the relay contact bounce process. By extracting contact bounce distance data from the images, a bounce process curve is plotted. Combined with the analysis of the contact bounce process, the reasons for the bounce are explored. The results indicate that the proposed rotation template matching algorithm can accurately identify stationary contacts and their angles at different angles. By analyzing the contact status and bounce process of the relay contacts in conjunction with the relay structure, parameters such as the bounce time, bounce height, and time required to reach the maximum distance can be calculated. Additionally, the main reason for contact bounce in the relay studied in this paper is the limitation imposed on the continued movement of the stationary contact by the presence of the relay brackets when the kinetic energy of the contact is too high. This phenomenon occurs during the first vibration peak in the vibration process after the moving contact contacts the stationary contact. The research results provide a reference for further studying the relay contact bounce process, optimizing relay structure, and suppressing contact bounce.

Effect of layer thickness for the bounce of a particle settling through a density transition layer.

We study numerically a spherical particle settling through a density transition layer at moderate Reynolds numbers Re_{u}=69∼259 for the upper fluid. We investigate how the transition layer thickness affects the particle's bouncing behavior as it crosses the interface. The previous intuitive understanding was that the bounce occurs when the relative thickness of the transition layer, L/D, which is characterized by the ratio of the layer thickness L to the particle diameter D, is small. Indeed, we report no bounce phenomenon for very thick interfaces, i.e., L/D>10 in the current parametric range. However, we argue that the bounce can also be inhibited when L/D is too small. Upon a fixed upper layer Reynolds number Re_{u}=207 with varying L/D, we examine the flow evolution of these cases. We propose that this inhibition is attributed to two mechanisms. First, as the interface thickness decreases, the detachment of the attached lighter fluid from the upper layer occurs more rapidly, resulting in a faster decrease in buoyancy. Second, in the case of a very thin interface (L/D=0.5-3.0), the residual light fluid accumulates and undergoes a secondary detachment, separating from the particle at an angle relative to the central axis. This secondary detachment reduces the drag force and effectively prevents the particle from experiencing a rebound motion.

PM0.1 non-bouncing impactor (NBI) for ultrafine particle mass and number measurements

This study designed and tested a 30 L/min PM0.1 non-bouncing impactor (PM0.1 NBI) for ultrafine particle (UFP) mass concentration measurement. The PM0.1 NBI uses a wetted glass fiber filter with continuous water injection to maintain a clean surface, preventing particle loading and bounce effects. Lab tests showed the 30 L/min PM0.1 NBI outperformed the PM0.1 stage of NCTU micro-orifice cascade impactor (NMCI, non-rotating) with a silicon oil-coated aluminum foil substrate in collecting solid particles, as the particle collection efficiency of the latter decreased obviously with increasing particle aerodynamic diameter for particles larger than ca. 300 nm, an apparent particle bounce phenomenon. The ambient field tests showed very close UFP mass concentrations between the PM0.1 NBI sampler (the PM0.1 NBI preceded by 3 stages with 18, 10, and 2.5 μm cutoff sizes) and the reference rotating 10-stages NMCI with the difference of ±0.5 μg/m3 only. In addition, the 3 L/min PM0.1 NBI was combined with a condensation particle counter to measure the UFP number concentrations which were shown to be very close to those of the reference with the difference of ±5% only in the laboratory tests for loaded particle mass up to 300 μg. Good agreement was also found in the field tests. Therefore, the current 3 L/min PM0.1 NBI and the future PM NBI with smaller flow rates (0.2–2.1 L/min) and larger cut-sizes (such as 0.4–0.9 μm) can be used as viable UFP classifiers for improving UFP measurement accuracy both in mass concentrations and number concentrations and reducing the maintenance needs for the UFP classifiers which are important to long-term sampling and monitoring.

Superhydrophobic aluminum surfaces with nano-micro hierarchical composite structures: A novel and sustainable approach to corrosion protection

The unique properties of aluminum (Al) and its alloys make Al one of the most versatile, economical, and widely-used materials in various industries. However, the corrosion and leaching of Al can cause significant issues for the lifetimes of mechanical structures and machine components as well as environment and health problems. In the present study, a simple, eco-friendly, and rapid fabrication of superhydrophobic Al surfaces was introduced. The superhydrophobic Al surfaces with hierarchical composite structures combining microstructures prepared by laser texturing, the new formation of pseudo-boehmite nanostructures prepared by boiling water treatment, and low surface energy prepared by silicone oil heat treatment showed excellent corrosion resistance. The mechanism for wettability change and anti-corrosion were analyzed. The influence of laser parameters and surface modification procedures on the wettability and corrosion resistance of Al surfaces was also analyzed systematically through a series of surface characterization techniques, potentiodynamic polarization tests, and electrochemical impedance spectroscopy tests. The corrosion protection efficiency of the fabricated superhydrophobic Al surface has reached up to 99.40 % as compared with an untreated flat surface. Furthermore, the fabricated superhydrophobic surfaces show good stability even after prolonged exposure to air, fresh water, seawater, and high temperature environments. The performance of the non-wetting surfaces is demonstrated through self-cleaning, water jetting, and water droplet bouncing phenomena. This research provides a novel and sustainable approach for superhydrophobic metal surfaces and improved corrosion resistance for potential practical applications.

Constrictive pericarditis with massive pericardial effusion.

A 27-year-old man was admitted to our hospital for the investigation of pericardial effusion (PE) and ascites. Despite the accumulation of excessive pericardial fluid, vital signs of cardiac tamponade were not observed. He had no prior medical history except for a blunt chest trauma 10 years earlier. Echocardiography showed a tiny heart in extraordinarily retained massive PE (panel A, Supplementary data online, Video S1). Computed tomography (CT) revealed a distended overfilling pericardial cavity that remarkably compressed his heart and lung (panels B and C). Magnetic resonance imaging showed a thickened pericardium and a respiratory septal bounce phenomenon (see Supplementary data online, Video S2). Heart catheterization followed by a pericardial drainage of gigantic 6500 mL amount of exudative fluid suggested constrictive property of diastolic square root sign in left and right ventricular simultaneous pressure tracings (panel D). He was diagnosed with effusive–constrictive pericarditis. Despite the removal of pericardial fluid and the treatment with anti-inflammatory medications, the underlying pericardial constricted property continued to cause symptoms. He underwent a surgical removal of the thickened pericardium uneventfully (panel E). Further analysis of the volume of the thoracic cavity utilizing a comprehensive 3D-rendered CT revealed a significantly greater pre-operative volume of 9569 mL compared with the post-operative volume of 5903 mL (panel F, Supplementary data online, Video S3). This is the first report to suggest that the compensative and elastic ability of both the thoracic and pericardial cavities plays a role in protecting hemodynamics in effusive–constrictive pericarditis.

A review of droplet bouncing behaviors on superhydrophobic surfaces: Theory, methods, and applications

The phenomenon of droplet bouncing on superhydrophobic surfaces has received extensive attention in the academic and industrial fields, as it is critical for various engineering applications, such as anti-icing, spray cooling, and metal quenching. In this review, the research of droplet bouncing behaviors is comprehensively introduced from the bouncing mechanism, research methods, and potential applications. The bouncing mechanism is related to three aspects: droplet properties, surface characteristics, and ambient conditions. Among them, droplet size, impact velocity, gas film, surface morphology, surface temperature, and applied electric field are frequently concerned. Surface wettability is critical for droplet bouncing behaviors, which affects the droplet movement on the surface. Momentum and mass distribution are essential to reduce contact time, which can be achieved through the surface morphology design. The manipulation of solid–liquid contact lines and surface tension can achieve directional droplet transportation. In addition, typical droplet bouncing experiments are presented, and experimental studies of single and successive droplets in recent decades are collated. Volume of fluid, the lattice Boltzmann method, and molecular dynamics are described, which are typical simulation methods for droplet bouncing dynamics at different scales. Potential engineering applications such as surface self-cleaning, digital microfluidics, and enhanced heat transfer have been developed through theoretical foundations and research methods. Finally, the conclusions and the possible future research directions are outlined. The durability of superhydrophobic surfaces becomes a bottleneck for engineering applications. The life cycle research perspective may be applied to future studies.

Lubricant Droplets Can Bounce on Wetted Cylinders

In this work, the droplet bounce phenomenon of polyalphaolefin, olive oil, silicone oil, and paraffin oil on wetted cylinders was reported. With a uniform oil film with a thickness of 0.06 mm formed on the cylinder, typical categories of spread, maximum, retract, deposit, and bounce existed. The ratio of the maximum spreading diameter and the initial diameter was negatively corrected with the viscosity due to the viscous resistance. The effect of tangential velocity from 0 m/s to 0.75 m/s on the spreading was investigated, which shows a strong promotion for it. The force analysis explained the mechanism of bouncing caused by the compressed air film, and oil droplets would bounce if the support force was larger than the combined force of gravity and inertia force. The findings in the work provide a basic understanding of droplets impact on wetted and rotating surfaces and design concepts for applications in modern industry.

Understanding the impact dynamics of droplets on superhydrophobic surface

The dynamics of droplets impacting superhydrophobic surfaces is investigated using experiments and numerical simulations. The superhydrophobic surface is fabricated by growing the carbon nanotube forest on stainless steel mesh in order to perform experiments. To numerically model the surface, Kistler dynamic contact angle model is used. Depending on different physical properties such as drop Weber number, the inclination of the surface and Ohnesorge number, the impact outcomes are categorized into symmetric bouncing, asymmetric bouncing, breakup, and tail impingement. It is observed that with the increase in the inclination angle of the surface, the contact time of droplets on the surface decreases drastically. The energy budget of impacting drops is analyzed for the entire evolution cycle to delineate the process of drop deformation and its bouncing. It is observed that the droplets bouncing off the inclined surface carried more kinetic energy compared to those of their counterparts on horizontal surfaces. To address the bouncing phenomena, co-efficient of restitution of the drop is also explored. The inclination of the substrate is found to increase the co-efficient of restitution of the drop, which is directly related to the energy budget of the bouncing drop. Furthermore, the force exerted by a drop on such surfaces is also analyzed, showing two peaks, making superhydrophobic surfaces more prone to damage in comparison to hydrophilic surfaces, which showed only a single peak. It is observed that the magnitudes of the peak forces are smaller for oblique impact as compared to horizontal impact.

The bouncing cosmic behavior with logarithmic law [formula omitted] model

In this paper, we study the bouncing behavior of our universe under f(G,T) theory, by taking Friedmann–Lemaître–Robertson–Walker metric, which is assumed to be coupled with an ideal fluid distribution. Here G is the Gauss–Bonnet scalar and T is the trace of stress energy tensor. The corresponding field equations are explored after assuming two specific forms of Hubble parameter in the presence of f(G,T)=G(log(ςG))+2λT correction terms. The energy bounds are examined analytically to provide necessary explanations for the theoretical phenomenon of cosmic bounce. The equation of state parameter, deceleration parameter, jerk and snap are also evaluated, accompanied by the associated dynamical parameters. With constraints-based model parameters, the modified geometrical action is configured to work for the removal of initial singularity.

A novel MEMS inertial switch with frictional electrode

This paper presents a frictional MEMS inertial switch with aiming to solve the problems of short contact time and bounce. According to contact principle in MEMS inertial switch, a new enhanced contact method by friction is proposed and a frictional switch is designed. To compare the frictional switch with common rigid switch and flexible switch, three switches were fabricated by micro electroforming technology and tested by a standard dropping hammer system. The tested results show that the contact time of rigid switch, flexible switch and frictional switch is 13 μs, 85 μs and 620 μs, respectively. Both rigid switch and flexible switch have bounce problem, while frictional switch is closed stably without bounce phenomenon. Frictional MEMS inertial switch has great advantages in enhancing contact.

Scheme for Generating True Random Numbers using Electro-mechanical Switches

This paper proposes a novel method for generating True Random Numbers (TRNs) using electromechanical switches. The proposed generator is implemented using an FPGA board. The system utilizes the phenomenon of electromechanical switch bounce to produce a randomly fluctuated signal that is used to trigger a counter to generate a binary random number. Compared to other true random number generation methods, the proposed approach features a high degree of randomness using a simple circuit that can be easily built using off-the-shelf components. The proposed system is implemented using a commercial relay circuit connected to an FPGA board that is used to process and record the generated random sequences. Applying statistical testing on the experimentally generated sequences revealed a high degree of randomness, which proves its viability to modern applications, such as cryptography and communication system simulation and modeling.

Reversing Behavior of Planetary Gear Train Influenced by Support Stiffness of Driving Shaft

Planetary gear trains (PGTs) are widely used in many machines and are one of the most important mechanisms in hybrid and electric vehicles. Previous research, based on empirical knowledge gained from the automobile industry, indicates that high carrier-support stiffness and low ring-gear support stiffness are required to reduce ring-gear errors. Therefore, here, we evaluate the vibration characteristics of a PGT as a function of the support stiffness, which is varied by inserting urethane rubber into the driving shaft. We conducted experiments using a 2K-HV-type tester, which contains a coaxially rotating and revolving planet gear shaft based on a universal joint. This mechanism allows the observation of the inner workings of the mechanism with the use of a transparent acrylic carrier. We were able to detect the so-called “bounce” phenomenon consisting of a swaying motion when the rotation of the ring gear is reversed, and this result was confirmed by our internal observations of the mechanism. It is evident that the index of vibration increases due to the bounce phenomenon because the reversal of the ring gear causes a larger vibration than that of the carrier because the ring gear can vibrate without restraint, unlike the planet gear that is sandwiched between the sun and ring gears. Furthermore, the influence of the radial support stiffness of the driving shaft, load torque to the output shaft, and acceleration time of the reversing gear on the “bounce” phenomenon were evaluated. We found that a larger load torque corresponds to a greater difference depending on the acceleration conditions of the sun gear. During reversal, at the moment when the rotation speed is zero and rotation recommences, the ring gear exerts the maximum force, and the larger is the load torque, the greater is the effect of the difference in acceleration.

Theoretical and Numerical Analysis of Coupled Axial-Torsional Nonlinear Vibration of Drill Strings

Based on a lumped parameter model with two degrees of freedom, the periodic response of the coupled axial-torsional nonlinear vibration of drill strings is studied by HB-AFT (harmonic balance and alternating frequency/time domain) method and numerical simulations. The amplitude-frequency characteristic curves of axial relative displacement and torsional relative angular velocity are given to reveal the mechanism of bit bounce and stick-slip motion. The stability of periodic response is analyzed by Floquet theory, and the boundary conditions of bifurcation of periodic response are given when parameters such as nominal drilling pressure, angular velocity of turntable, and formation stiffness are varied. The results show that the amplitude of the periodic response of the system precipitates a spontaneous jump and Hopf bifurcation may occur when the angular velocity of the turntable is varied. The variation of parameters may lead to the complex dynamic behavior of the system, such as period-doubling motion, quasiperiodic motion, and chaos. Bit bounce and stick-slip phenomenon can be effectively suppressed by varying the angular velocity of turntable and nominal drilling pressure.

On the Leidenfrost effect of water droplet impacting on superalloy plate surface

The boiling of liquid water on the superalloy surface is important in applications such as steam and gas turbines, for which it is necessary to explore the mechanisms of the Leidenfrost phenomenon. The molecular dynamics simulation method provides an effective way to study this phenomenon at the nanoscale. Previous studies, however, have not revealed the Leidenfrost effect of liquid molecules on a superalloy surface. This work investigated the effects of surface temperature and impact velocity on the nanoscale Leidenfrost phenomenon of water droplet over the Fe-Cr superalloy plate. When the surface temperature is higher than 798 K, the Leidenfrost phenomenon occurs on the superalloy surface with apparent temperature, stress, and pressure differences. The results indicate that the Leidenfrost phenomenon is related to the high surface temperature, rather than its impacting velocity. Furthermore, it is found that the Leidenfrost phenomenon is the combined results from the temperature and pressure differences exist in the vapor film, as enough kinetic energy can be generated by the thermal motion to cause the bounce phenomenon of droplet. The revealed mechanisms are critical for the design of a gas turbine, in which vapor film could be dominant in determining the film cooling effectiveness of gas/vapor on the blade surface.

Dip-coating of Superhydrophobic Surface on Irregular Substrates for Dropwise Condensation

Herein, self-assembled superhydrophobic composite coatings were successfully prepared using a one-step dip-coating method on different irregular parts. The fluorinated nano-SiO2 particles spread into a uniform layer owing to the viscosity of the composite resin. After the optimization of the process, the fabricated nanoporous-structured coating has low adhesion properties with chemical and high thermal stabilities. After baking at 250 °C for 2 h or soaking in a solution of pH = 1 or pH = 13 for 10 days, the coating could maintain its good superhydrophobicity. The self-ejecting effects of the condensed dewdrops and droplet bounce phenomenon indicate that the coatings can be well-distributed on components of different structures, and they have significant application prospects in irregular parts and industrial production in the near future.

A one-step method to fabricate bio-friendly patterned superhydrophobic surface by atmospheric pressure cold plasma

Superhydrophobic surfaces have special restrictions and manipulation capabilities on liquids, and have great potential applications in fields of biological analysis. However, the preparation of bio-friendly superhydrophobic surfaces by high efficiency methods remains a challenge. In this work, a new one-step preparation method to fabricate bio-friendly superhydrophobic surface based on atmospheric pressure cold plasma is proposed. Using argon as the working gas and HMDSN as the monomer, the superhydrophobic surface can be prepared in one step by APCP whether on the surface of conductive metal, the surface of a flexible paper, or the surface of hard and brittle glass. The plasma characteristics, surface wettability, surface morphology, chemical composition, adhesion performance and bounce phenomenon have been systematically studied, which proves the excellent performance of the prepared superhydrophobic surface. Finally, the bio-friendly properties were verified by the cultivation of Hela cell, Escherichia coli, the seeds of bacopa monnieri and clover on the prepared superhydrophobic surface. This work shows great potential in applications for biological system cultivation and analysis.

Rock Breaking Mechanism and Drilling Performance of Harmonic Vibro-Impact Drilling

An improved model of displacement response of rock considering damping is proposed and the energy response model is further presented. Then, the rock breaking mechanism under harmonic vibro-impact is investigated based on the displacement response and energy response. Furthermore, the numerical simulations are conducted to analyze the principal stress of rock and drilling characteristics in axial and torsional directions under harmonic vibro-impact. Finally, the performance of the harmonic vibro-impact drilling technology is verified by the field application. Based on the analysis undertaken, it can be concluded that the periodic harmonic impact force makes the rock subjected to more tensile stress and continuous damage accumulation, which causes the efficient rock breakage. What’s more, the harmonic vibro-impact can also alleviate the stick-slip effect and bounce phenomenon of drill bit to a certain extent. Our investigations confirm that the harmonic vibro-impact can achieve the purpose of rate of penetration (ROP) improvement.