Violent Collisions Research Articles

Multiple collisions in N59 bubble: sequential cloud–cloud collisions

ABSTRACT We report that the gas components in the N59 bubble suffered from sequential multiple cloud–cloud collision (CCC) processes. The molecular gas in the N59 bubble can be decomposed into four velocity components, namely Cloud A [95, 108] km s$^{-1}$, Cloud B [86, 95] km s$^{-1}$, Cloud C [79, 86] km s$^{-1}$, and Cloud D [65, 79] km s$^{-1}$. Four CCC processes occurred among these four velocity components, i.e. Cloud A versus Cloud B, Cloud A versus Cloud C, Cloud C versus Cloud D, and Cloud A versus Cloud D. Using the near- and mid-infrared photometric point source catalogues, we identified 514 young stellar object (YSO) candidates clustered in 13 YSO groups, and most of them ($\sim 60~{{\ \rm per\ cent}}$) were located at the colliding interfaces, indicating that they were mainly triggered by these four CCC processes. We also found that these four collisions occurred in a time sequential order: the earliest and most violent collision occurred between Cloud A and Cloud D about 2 Myr ago, then Cloud B collided with Cloud A about 1 Myr ago, and finally, Cloud C collided with Clouds A and D simultaneously about 0.4 Myr ago.

Shaking table tests on transverse seismic performance of a new type of combined prefabricated utility tunnel

Due to the limitation of hoisting weight in the construction site, standard segments of prefabricated utility tunnels usually have only one or two cabins, making it difficult to carry out the multi-cabin prefabricated utility tunnel construction. To solve this problem, two rows of prefabricated utility tunnels are often combined side by side with foam board filled in between them in engineering practice, forming a new type of combined prefabricated utility tunnel. However, there is currently no study on the influence of the interaction between two rows of prefabricated utility tunnels on the seismic performance of combined tunnels. This paper conducted shaking table test of the new type of combined prefabricated utility tunnel under transverse excitation. For the purpose of comparison, shaking table test of single prefabricated utility tunnel was also conducted. To simplify the model making, the combined tunnel was combined by two rows of single-cabin tunnels. Standard segments of utility tunnels were made by microconcrete and assembled longitudinally by bolting. The soil acceleration, utility tunnel strain, and relative displacement between two cabins of the combined tunnel were measured during the tests. Numerical simulation of the test cases was conducted. The numerical results matched the test results well. The research results show that the seismic performance of the combined tunnel is superior to that of single tunnel, because the interaction between two cabins of the combined tunnel reduces the relative deformation between the top and bottom slabs of each cabin. The relative displacement between two cabins of the combined tunnel is much smaller than the initial spacing between the two cabins, and there will be no violent collision between two cabins of the combined tunnel. This study may be of a reference for seismic design of the new type of combined prefabricated utility tunnel.

Violent collisions can reveal hexadecapole deformation of nuclei

Violent collisions can reveal hexadecapole deformation of nuclei

An air-triggered contact-separation rotating triboelectric nanogenerator based on rotation-vibration-pressure conversion

Energy harvesting using triboelectric nanogenerators (TENGs) has demonstrated great potential in powering sensor network nodes and become a promising alternative for battery-free portable and wireless electronics. Unlike most existing rotational sliding-mode TENGs, an air-triggered contact-separation rotating triboelectric nanogenerator (AT-TENG) based on rotation-vibration-pressure conversion is proposed to reduce the violent collision of triboelectric materials and enhance the durability in this paper. The distinguishing feature of the AT-TENG was indirectly-excited contact separation mode along with the air-film interaction, where the rotational motion was converted into an elastic sheet vibration via the magnetic coupling and then the periodic contact or separation between the FEP film and aluminum plate was induced by the alternating air pressure. The feasibility of the presented AT-TENG was verified by theoretical analysis, fabrication and experiments. The results indicated that the distance of PVC to aluminum, radius ratio of the FEP to PVC, chamber volume (denoted by the acrylic ring height), magnet coefficient and rotational speed brought a significant effect on the output behaviors of the AT-TENG. There was an optimal PVC-aluminum distance of 0.1 mm as well as the maximum output voltage increased firstly and then decreased with the enhancement of radius ratio. Also, the output voltage was roughly enhanced with the increasing ring height except a maximum value occurred at h = 3.6 mm and demonstrated a reducing trend as the magnet coefficients was increased. In addition, the AT-TENG could achieve a maximum voltage of 367 V, maximum average power of 128.7 μW, and highest charging electricity of 14.45 mJ in the experiments. Besides, a parallel 200 LEDs could be efficiently powered by the AT-TENG. Furthermore, the AT-TENG demonstrated a long-term durability and stability through the 106444-excitation testing. It is expected that this work can offer a useful reference for further improvements of the rotational TENGs.

Numerical-Study of Large-Liquid Rocket Plume-Flow-Field

Aiming at the complexity of plume field structure caused by plume collision in the rising section of multi-nozzle parallel rocket, this paper establishes an analytical model of the rising section of a nine-nozzle configuration rocket. The plume field phenomenon is studied at different heights through numerical simulation. The reliability of the numerical method is verified based on the comparison of simulation and wind tunnel test data. The analytical results. Show that violent collision occurs between the jets in the ascent section of the multi-nozzles rocket, and many phenomena such as circulating vortex, gas reflux, reflux back splash and so on occur at different altitudes. When the altitude is less than 25km, gas reflux and circulation vortex appear in the rocket base. With the increasing of altitude, the jet collision impacts the base. After the altitude reaches 45km, back splash appears in some areas of the rocket base. There is an obvious flow diversion phenomenon on the side wall surface. The higher the altitude, the greater the expansion angle of the jet after the gas exits the nozzle.

Light curves and spectra for theoretical models of high-velocity red-giant star collisions

High-velocity stellar collisions driven by a supermassive black hole (BH) or BH-driven disruptive collisions in dense, nuclear clusters can rival the energetics of supergiant star explosions following the gravitational collapse of their iron core. Starting from a sample of red-giant star collisions simulated with the hydrodynamics code AREPO, we generated photometric and spectroscopic observables using the nonlocal thermodynamic equilibrium time-dependent radiative transfer code CMFGEN. Collisions from more extended giants or more violent collisions (with higher velocities or smaller impact parameters) yield bolometric luminosities on the order of 1043 erg s−1 at 1 d, evolving on a timescale of a week to a bright plateau at ∼1041 erg s−1 before plunging precipitously after 20–40 d at the end of the optically thick phase. This luminosity falls primarily in the UV in the first few days, thus when it is at its maximum, and shifts to the optical thereafter. Collisions at lower velocities or from less extended stars produce ejecta that are fainter but can remain optically thick for up to 40 d if they have a low expansion rate. This collision debris shows a similar spectral evolution as that observed or modeled for Type II supernovae from blue-supergiant star explosions, differing only in the more rapid transition to the nebular phase. Such BH-driven disruptive collisions should be detectable by high-cadence surveys in the UV such as ULTRASAT.

The Transfer and Change of Paints in a Hit-and-run Motor Vehicle Accident

Abstract This work investigated transfer and change of paint evidences in a case of hit-and-run. Two kinds of attachments were found on the clothes of the victim and they were initially considered paint fragments from the vehicle causing the accident. Infrared spectroscopy (IR), scanning electron microscope–energy dispersive spectrometer, and Microspectrophotometry were applied for examination of paints and clothing fibers. Polyester was detected in one of the attachments and in the clothing fibers of the victim by IR. A traffic accident simulation experiment was designed and conducted to research whether the polyester attachments come from suspected vehicle paints or victim’s clothing fibers. The results showed that a melt mixture of transferred paints and clothing fiber was formed after a violent collision. Because the amount of transferred paints was too low to be detectable in the mixture, the components detected by IR were mainly from clothing fibers. Thereby, we inferred that only one kind of attachment and paint fragments existed on the clothes of the victim, and the polyester attachments cannot be used to indicate the composition of suspected vehicle paint. Clothing fibers and paints are both common trace evidence in traffic accident cases, and more attention should be paid to the examination of transferred paints on clothing fibers.

Construction Design of the Floater Considering the Free-Falling Impact of the Floatplane on Calm Water

The floatplane-type aircraft is very suitable to be developed as a means of transportation connecting the scattered islands in Indonesia, as it has floats under the fuselage to make landings and operate on the water surface. In bad weather, a floatplane can lose lift, resulting in a free fall from an abnormal height and a violent collision between the floatplane structure and the water surface. Meanwhile, regulations require that the strength of the structure be able to withstand the impact load due to an emergency landing. This paper proposes a floater construction design for the N219 floatplane with three scantling variations of 5083 H321 aluminium material that considers the total payload and take-off weight. The magnitude of the impact load on the bottom of the float with the water surface in the case of free fall at 0.5 m and 1 m height is predicted by the Wegner equation model at each cross section along the float. The magnitude of stress in each floater construction design is evaluated by the principle of the finite element method using commercial software. The simulation results show that all models have a maximum stress less than permissible stress and also maximum deformation is unsignificant.

Nonmonotonic dependence of adhesion between liquid aluminum and silicon surface on the temperature of the surface

In this paper, the effect of temperature on the adhesion properties between liquid aluminum (Al) and solid silicon (Si) in the presence and absence of vacancy defects is elucidated. Firstly, the perfect defect-free and vacancy defect models consist of crystalline Al probe and Si substrate are established by classical molecular dynamics simulation method. Then, the melting and adhesion process of probe Al are simulated, and the adhesion performance and microscopic permeation evolution of liquid Al/solid Si are analyzed. The results show that the adhesion force changes nonmonotonically with increasing substrate temperature T without vacancy defects. Specifically, when the substrate temperature varies at relatively low values smaller than the melting point of Al, that is, 100 K < T < 933 K, the thermal excitation provides more energy to the substrate Si atoms, which intensifies the aggregation of the substrate atoms, makes the interfacial atoms more dense and the number of atoms permeating into the substrate decreases, resulting in a decrease in adhesion force. On the contrary, when 933 K < T < 1500 K, due to the thermal effect, higher temperatures intensify the thermal vibration of the substrate atoms, resulting in violent collisions between the interfacial atoms, and the space for free movement increases, thus making the distance between the atoms larger. And the number of Al atoms permeating into the substrate Si increases, leading to an increase in interfacial adhesion. Furthermore, the adhesion force shows an upward trend with the elevated temperature in the presence of vacancy defects at low temperatures, this is attributed to the fact that more atoms are broken away from the equilibrium lattice structure, and the number of permeating atoms increases by increasing temperature. In particular, the interfacial adhesion is the largest when the vacancy defects of the substrate are the most serious.

Discussion of the unique “eclogitic” clast reported from Northwest Africa 801 (CR2) and the possibility of ejection of foundered crust from deep in a molten Moon‐sized projectile

AbstractA unique 2 mm‐wide clast of fine‐grained garnet–omphacite peridotite with chondritic chemistry was reported from the CR2 chondrite Northwest Africa 801 by Hiyagon et al. (2016, Geochimica et Cosmochimica Acta, 186, 32–48). Those authors described the clast as eclogitic and inferred from its mineral compositions that the rock formed quickly, during perhaps 100–1000 years of burial, deep within a Moon‐sized body at about 3 GPa (30 kbar) pressure and 1000°C. Such conditions are unprecedented among meteorites and invite scrutiny. Here, we discuss the clast and its origin. The inferred conditions appear justified, but the published idea of burial during a protoplanetary merger and, soon after, exhumation in a violent collision seems improbable and contrary to the clast's low shock levels. We find that exhumation is better explained by pull‐apart of a projectile in a low velocity hit‐and‐run collision. We try inconclusively to explain near‐simultaneous burial and exhumation in a hit‐and‐run return scenario. Taking a different approach, and to conclude, we speculate that an approximately lunar‐mass body was molten beneath a thin dense chondritic crust, of which fragments foundered and sank deep into the magma ocean as an ongoing process. Fragments that were changing to garnet–omphacite peridotite were exhumed when the molten body was pulled apart in a hit‐and‐run collision with a larger body.

Study of Female Character Images in Stendhal's Novels

Human nature is even more complicated, drifting between the black and white world. The image of Julien created by "The Red and the Black" has left a deep imprint on readers' hearts. Stendhal expressed his profound understanding of ethical issues by depicting the relationship between Mrs. De Reinal and different characters. In order to create the image of Mrs. De Reinal, the author used a lot of pen and ink to show the ethical dilemma she faced and her ethical redemption, which has rich ethical connotation. In Stendhal's works, the violent shock caused by the violent storm and the violent collision of thoughts and feelings in the hero's heart, and the torment of cooking and baking in the soul are lingering. "The Red and the Black" is a classic work by Stendhal, a French critical realist. This book has created a very moving female image of Mrs. De Reinal. This paper tries to analyze the female characters in Stendhal's works by taking Mrs. De Reinal as an example.

Impact Analysis of Off-State Avalanche-Breakdown Stress on 650 V-Class Superjunction MOSFET

In this work, the reliability degradation of a 650 V-class superjunction (SJ) MOSFET under continuous violent OFF-state avalanche-breakdown stress is studied. Decreased threshold voltage and increasing saturation current have been observed which are attributed to the injection of hot holes below the trench bottom into the gate oxide layer. High-energy electrons and holes are generated under OFF-state avalanche stress leading to accelerated and violent collision ionization. The body diode suffers from severe avalanche breakdown leading to heat generation by collision ionization. In addition, the injection of hot holes is further enhanced with the assistance of the electrical field at the bottom of the gate. These phenomena are further analyzed by experimental characterizations and theoretical simulation using TCAD tools. Our comprehensive study on the reliability degradation behaviors of SJ devices under OFF-state avalanche-breakdown stress can be instructive in future device optimization and failure analysis.

A method for calculating the void fraction of two-phase leakage ports of storage tanks

The problem of leakage of superheated liquids such as LPG, LNG, LCG and AML is widely valued in the process industry. The key to superheated liquid storage and transportation is to prevent cracks due to unexpected situations such as tank overpressure, pipe corrosion and violent collisions. When the tank wall ruptures, the air pressure inside the tank drops sharply and a violent phase change occurs in the degraded liquid inside the tank to maintain energy balance. The liquid instantly evaporates into a gas, releasing a huge amount of energy to form a flash, and this leakage can lead to violent phase changes and two-phase flash jets containing large amounts of liquid droplets and steam, and further lead to major safety accidents such as fires, explosions and the spread of toxic substances. In this work, the pressure drop in the tank during a leak and the phase change at the leak caused by the pressure change at the orifice are investigated through theoretical analysis and experiments. Based on the ideal gas equation of state, mass conservation, gas-liquid non-slip and thermodynamic equilibrium, the pressure drop inside the tank and the phase change at the orifice during the whole leakage process are modelled and validated, and the results show that the model is in good agreement.

Numerical simulations of hypervelocity impacts to defend against small bodies

<p indent="0mm">Millions of small bodies have been observed in the solar system, with frequent and violent collisions during their formations and evolutions. Small bodies entering the earth’s neighborhood are recognized as Near Earth Objects, which are likely to impact the earth and cause disaster to humans. A kinetic impactor could be one of the most effective and feasible solutions to defend against such threats. Therefore, understanding the hypervelocity impacts on small bodies is of great importance. In this paper, a new hydrocode THU-SPHSOL has been developed, based on the Smoothed Particle Hydrodynamics method. With numerical simulations, the effects of material properties and structures on asteroid disruptions have been investigated, as well as the ejecta distribution from a cratering impact. The results should provide guidance for the future asteroid defense mission of China.

Mercury’s formation within the early instability scenario

The inner solar system’s modern orbital architecture provides inferences into the epoch of terrestrial planet formation; a ∼100 Myr time period of planet growth via collisions with planetesimals and other proto-planets. While classic numerical simulations of this scenario adequately reproduced the correct number of terrestrial worlds, their semi-major axes and approximate formation timescales, they struggled to replicate the Earth–Mars and Venus–Mercury mass ratios (∼9 and 15, respectively). In a series of past independent investigations, we demonstrated that Mars’ mass is possibly the result of Jupiter and Saturn’s early orbital evolution, while Mercury’s diminutive size might be the consequence of a primordial mass deficit in the region (potentially the result of the growing Earth’s early outward migration). Here, we combine these ideas in a single modeled scenario designed to simultaneously reproduce the formation of all four terrestrial planets and the modern orbits of the giant planets in broad strokes. By evaluating our Mercury analogs’ core mass fractions, masses, and orbital offsets from Venus, we favor a scenario where Mercury forms through a series of violent erosive collisions between a number of ∼Mercury-mass embryos in the inner part of the terrestrial disk. We also compare cases where the gas giants begin the simulation locked in a compact 3:2 resonant configuration to a more relaxed 2:1 orientation and find the former to be more successful. In 2:1 cases, the entire Mercury-forming region is often depleted due to strong sweeping secular resonances that also tend to overly excite the orbits of Earth and Venus as they grow. While our model is quite successful at replicating Mercury’s massive core and dynamically isolated orbit, the planets’ low mass remains extremely challenging to match. Indeed, the majority of our Mercury analogs have masses that are 2–4 times that of the real planet. Finally, we discuss the merits and drawbacks of alternative evolutionary scenarios and initial disk conditions (specifically a narrow annulus of material between 0.7-1.0 au). We argue that the results of our N-body accretion models are not sufficient to break degeneracies between these different models, and implore future studies to apply further cosmochemical and dynamical constraints on terrestrial planet formation models.

Dementia in Sport: Causation, Management and Prevention

Dementia in sport emerged as a problem at the beginning of the 20th century, when "punch drunk syndrome" was diagnosed in boxers. This diagnosis was soon refined to dementia pugilistica and later to chronic traumatic encephalopathy. Since then dementia has appeared in other sports, particularly those involving violent collisions and/or head injuries. The problem continues in boxing, but during the 21st century dementia has become a significant problem in American Football, football in the United Kingdom (soccer) and rugby. For example, a recent study from Boston found evidence of chronic traumatic encephalopathy in &gt;90% of former American Football players, and a controlled study of &gt;7,000 soccer players found that the former footballers were 3.5 times more likely to die from dementia or other neuro-degenerative diseases than the controls, the increased risk being related to playing position and length of playing career, thus establishing a dose-response relationship. The emerging consensus is that dementia in sport is caused by repetitive subconcussive head injuries occurring over a long-playing career. The author asserts that the brain’s vulnerability to repeated minor blows to the head is due to its inherent fragility and evidence is provided to support this view. For effective prevention and management three steps are outlined. The first is recognition and acceptance of the brain’s vulnerability and fragility and mounting a public health initiative to educate the public and the sporting world. Second, all players at risk should have baseline cognitive tests which must be repeated regularly; if this show deterioration early retirement from the sport must be considered. The third recommendation is that all the sports regulatory bodies must explore with urgency how brain injuries in their specific field can be reduced and eliminated.

Highly water-dispersed composite of cellulose nanofibers and boron nitride nanosheets

In this work, a composite of cellulose nanofibers (CNFs) and boron nitride nanosheets (BNNSs) with high dispersity in water is prepared via the combination of ball-milling and high-pressure homogenization, which is then transformed into paper-like film by vacuum assisted filtering and drying. The obtained CNF/BNNS dispersions can stably exist over 30 days without the observation of sediments. CNFs as a medium of ball-milling can protect the exfoliated BNNSs from being reaggregation and severely destroyed in violent collisions, and the BNNSs and CNFs can promote their exfoliation with each other. The hydrophilicity and electrostatic repulsion of CNFs, as well as the strong interfacial interactions and stereo-hindrance effects between one-dimensional (1D) CNFs and two-dimensional (2D) BNNSs are the reasons for the high dispersity of the composite in water, which in turn results in the favorable mechanical properties of the formed films. Although the introduction of BNNSs lowers the stress, strain, and toughness of the neat CNF films, but increases their modulus due to the stiffness of BNNSs. However, the thermal conductivities of the homogenized samples are inferior to the unhomogenized ones, as the decreased lateral sizes and excellent dispersibility of BNNSs are unfavorable to the formation of connective path of thermal conduction.Graphical abstract

Effect of solvent swelling with different enhancement methods on the microstructure and pyrolysis performance of Hefeng subbituminous coal

Hefeng subbituminous coal (HSBC) was swelled with different enhancement method, including mechanical activation (THSBC2), ultrasonic radiation (THSBC3) and microwave radiation (THSBC4), with isometric N-methylpyrrolidone (NMP) and 1-ethyl-3-methylimidazole acetate (IL) mixture as the solvent (the un-enhancement coal was marked as THSBC1). Pore structure and pyrolysis performance of each sample were discussed. Results showed that the five samples presented abundant micropores, mesopores and some macropores from N2 adsorption-desorption profiles. In lower P/P0 range, the pore type was mainly semi-open pore closed at one end that did not affect the hysteresis loop of the samples; in higher P/P0 range, the pore types were mainly open pore (including cylindrical pore with two open ends and parallel plate pore with four open sides), ink-bottle pore and semi-open pore closed at one end. Hysteresis loops of THSBC3 and THSBC4 were similar to THSBC1, and the pore types were similar to some extent. The hysteresis loop in higher P/P0 range of THSBC2 was not obvious, indicating that there were more semi-open pores closed at one end (with no ink-bottle pore). Pore structure and pyrolysis kinetics of each sample were investigated, and fractal dimension and kinetic parameter were calculated by Frenkel-Halsey-Hill model and Coats-Redfern model, respectively. Results demonstrated that the fractal dimensions D1 (related to surface roughness) and D2 (related to complexity of inner pore structure) were closely related to the pore structure. Compared to THSBC1, the value of D1 is larger for THSBC2, presenting more obvious surface roughness. While the complexity of the pore structure of the five samples is little different, showing very close D2. In addition, the change of pyrolysis activation energy was more obvious for the sample of THSBC2 (29.027 kJ∙mol−1), 4.75% less than THSBC1 (30.482 kJ∙mol−1), which might be attributed to the violent collision process caused by mechanical activation. HSBC presents higher solid yield during pyrolysis, up to 64%, and the solid yield of others samples is around 60%. Compared with HSBC, the gas yields of other four samples have little change, while the liquid yields are increased, indicating that the swelling treatment can promote the formation of tar.

Bernard Bailyn's Barbarous Modernity

Bernard Bailyn's Barbarous Modernity

Numerical study of three-dimensional flow and aerodynamic characteristics of a cylindrical cavity in rarefied hypersonic flows

Cylindrical cavity configuration frequently appears on the surface of an aerospace vehicle while flow physics of rarefied hypersonic flows over it are not clear yet. This work presents a comprehensive numerical study to reveal flow structures inside the cavity and aerodynamic surface quantities, including the pressure on and heat flux to the surfaces of three-dimensional cylindrical cavities using the DSMC method. The results showed that the traditional cavity flow types based on the classical categorization are not suitable for characterizing rarefied hypersonic flows over cylindrical cavities due to more diverse flow patterns induced by the curved cylindrical sidewall, especially for the cylindrical cavity with a shallow depth. Both the pressure on and heat flux to the striped area near the top lip of downstream curved sidewall are always the strongest due to the violent airflow collision there, which is a depth range of about 0.4 y/H away from the top lip, but those for the cavity floor are usually quite weak because the gas over it moves slowly. With the increase of cavity depth, the weaker pressure on and heat flux to the cavity floor appear because the rising curved sidewall makes it more difficult for freestream to permeate into the cavity, whereas the maximum pressure on and peak heat flux to the downstream curved sidewall seem to be unchanged. The severe rarefaction effect at 90 km make the flow pattern and temperature distribution inside the cavity different from those for 50, 60, and 70 km. As the freestream Mach number is increased from 13.4 to 33.5, the streamline patterns and velocity contours around and inside the cavity only change slightly, consequently leading to similar numerical trends of both the pressure on and heat flow to the cavity surfaces.