Violent Fragmentation Research Articles

Unbounded entropy production and violent fragmentation for repulsive-to-attractive interaction quench in long-range interacting systems

Abstract We study the non-equilibrium dynamics of a one-dimensional Bose gas with long-range interactions that decay as ( 1 r α ) ( 0.5 < α < 4.0 ). We investigate exotic dynamics when the interactions are suddenly switched from strongly repulsive to strongly attractive, a procedure known to generate super-Tonks-Girardeau gases in systems with contact interactions. We find that relaxation is achieved through a complex intermediate dynamics demonstrated by violent fragmentation and chaotic delocalization. We establish that the relaxed state exhibits classical gaseous characteristics and an asymptotic state associated with unbounded entropy production. The phase diagram shows an exponential boundary between the coherent (quantum) gas and the chaotic (classical) gas. We show the universality of the dynamics by also presenting analogous results for spinless fermions. Weaker quench protocols give a certain degree of control over the relaxation process and induce a slower initial entropy growth. Our study showcases the complex relaxation behavior of tunable long-range interacting systems that could be engineered in state-of-the-art experiments, e.g. in trapped ions or Rydberg atoms.

Dynamic process of a high-level landslide blocking river event in a deep valley area based on FDEM-SPH coupling approach

This study used a three-dimensional model based on the finite-discrete element method-smoothed particle hydrodynamics (FDEM-SPH) coupling approach to reconstruct the 11 October 2018 Baige landslide that blocked the Jinsha river. The numerical model simulated the dynamic process of the landslide by FDEM, while the SPH simulated the behavior of the river water. The landslide deposit area and the water-eroded area in the FDEM-SPH simulation agree well with the results of the field investigation. According to the simulation, the main duration of the Baige landslide was 80 s. The peak average speed of the landslide was 34.4 m/s, while the local speed of the sliding mass reached a maximum velocity of 70 m/s. The tensile effect and the shear effect caused isotropic dispersive stress which caused the dynamic and violent fragmentation of the landslide. The model also simulated the variation of kinetic energy, the accumulated friction dissipation, and the fracture energy of the sliding mass with time. After the sliding mass ran into the river, the landslide triggered a wave, which rapidly dispersed due to the subsequent mass movement. The front part of the sliding mass pushed some of the river water to the opposite bank where the wave reached a height of 120 m. The results of the FDEM-SPH model, the particle flow code (PFC) model, and the depth-integrated shallow-water flow (DISWF) model are compared and analyzed concerning studying landslides that block rivers. Three types of evolution mechanisms of high-level flow-like landslide-induced waves in deep river valleys are proposed in this paper.

Who lost Ethiopia? The unmaking of an African anchor state and U.S. foreign policy

ABSTRACT In November 2020, Ethiopia descended into full-scale civil war which, owing to mass atrocities and regional intervention, metastasized into among the most acute humanitarian emergencies in the world. The violent fragmentation of state authority tarnished Ethiopia’s internationally sanctioned role as regional peacekeeper and developmental leader—an “anchor state” of the Pax Americana in the Horn of Africa. While acknowledging the complex, multi-dimensional origins of the conflict, this article examines how efforts by the U.S. government to reinvent the strategic relationship during the 2018–2020 political transition in Addis Ababa helped pave the road to war. We argue that U.S. policymakers provided largely unconditional support to Ethiopia’s new Prime Minister Abiy Ahmed, creating problems of moral hazard that encouraged confrontation between rival political forces. The story of U.S. engagement in Ethiopia in this period illustrates the perils of Washington’s efforts to rebalance fraught relations with its most important regional anchors.

Droplet aerobreakup under the shear-induced entrainment regime using a multiscale two-fluid approach

A droplet exposed to a high-speed gas flow is subject to a violent fragmentation, dominated by a widespread mist of multiscale structures that introduce significant complexities in numerical studies. The present work focuses on capturing all stages of the aerodynamic breakup of a waterlike droplet under the shear-induced entrainment regime. The numerical investigation is conducted within a physically consistent multiscale framework, which provides insight into the mist dynamics and the distribution of the produced secondary droplets under different postshock conditions.

Synergistic Antimicrobial Titanium Carbide (MXene) Conjugated with Gold Nanoclusters.

Bacterial resistance toward antibiotics is a world-wide problem, and one potential solution to fight against the resistance is to develop multi-mechanism antimicrobial agents to achieve synergistic performance. Titanium carbide (MXene) is an emerging 2D nanomaterial with antimicrobial ability to physically damage bacterial membrane and chemically induce oxidative stress, and it can be further conjugated with nanomaterials to improve its antibacterial performance. Herein, a synergistic antimicrobial agent is developed through conjugation of the ultra-small gold nanoclusters (AuNCs) on MXene nanosheets. The conjugated AuNCs are effectively delivered into bacteria after bacterial membrane damage caused by MXene, generating localized reactive oxygen species (ROS) of high concentration to effectively oxidize bacterial membrane lipid for enhanced membrane broken, as well as bacterial DNA for violent fragmentation. Thus, the synergistic physical (via MXene) and chemical (via MXene and AuNCs) antimicrobial mechanisms lead to eventual bacterial death of both Gram-positive and Gram-negative bacteria, with low IC50 values of 11.7µg mL-1 of MXene and 0.04µm of AuNCs. Moreover, the crumpled MXene-AuNCs structure is constructed to inhibit biofilm formation, which hold synergistic antibacterial ability of MXene-AuNCs conjugation, hydrophobic surface to prevent bacterial attachment, and large surface area containing higher density of bactericides.

Desectarianization: Looking Beyond the Sectarianization of Middle Eastern Politics

Violent fragmentation in the Middle East has often been reduced to a consequence of “ancient hatreds” that pit Sunni against Shi’a. One of the more compelling arguments to understand the emergence of sectarian violence was proposed by Nader Hashemi and Danny Postel who suggest that the politics of the Middle East has undergone a process of sectarianization. This article builds upon the work of Hashemi and Postel to consider potential mechanisms to challenge this process of sectarianization, to work towards desectarianization. Drawing on interviews conducted across the Middle East and on a number of different disciplines, the article proposes a four-stage framework to facilitate desectarianization.

Numerical simulation for the air entrainment of aerated flow with an improved multiphase SPH model

ABSTRACTAerated flow is a complex hydraulic phenomenon that exists widely in the field of environmental hydraulics. It is generally characterised by large deformation and violent fragmentation of the free surface. Compared to Euler methods (volume of fluid (VOF) method or rigid-lid hypothesis method), the existing single-phase Smooth Particle Hydrodynamics (SPH) method has performed well for solving particle motion. A lack of research on interphase interaction and air concentration, however, has affected the application of SPH model. In our study, an improved multiphase SPH model is presented to simulate aeration flows. A drag force was included in the momentum equation to ensure accuracy of the air particle slip velocity. Furthermore, a calculation method for air concentration is developed to analyse the air entrainment characteristics. Two studies were used to simulate the hydraulic and air entrainment characteristics. And, compared with the experimental results, the simulation results agree with the experimental results well.

1968/2008: Reflections on Social Movements in an Age of Permanent War

1968 represents a crossroads of sorts, whose alternative political trajectories continue to influence the present in often confusing and contradictory ways. We have an increasingly exhaustive historical narrative detailing the long Black freedom struggle against white supremacist monopolizations of power and resources in the era before the Montgomery bus boycott. From the heroic mobilizations of Reconstruction-era Black politics in the face of white terror, through two great migrations, the mobilizations of Black labor, a new Black urbanism, and forms of worldly engagement in an era of global wars and decolonization struggles, the Black freedom movement simultaneously carried and deepened a demand for racial democracy. It is ironic, however, that even as aspects of this past become clarified, the more immediate history and political meaning of this long struggle have grown murky. I am specifically thinking about the foreclosure of Black freedom imperatives in the United States, particularly in the late 1960s and early 1970s, for which the year 1968 retains an iconic significance. Here the story often bifurcates, becoming a tale either of teleological fulfillment and narrative closure, or of violent fragmentation and ragged endings. These different trajectories lead us in turn to starkly different eventualities: the election of Barack Obama and the symbolic validation of the promise of Black politics, or the increasingly global US war-prison complex, where the tattered ends of our social contract once again meet the unforgiving cut of racialized governance. In this context, the searching question asked by Martin Luther King in his fateful final year—“Where Do We Go from Here?”—remains as relevant as ever.

Modelling heavy-ion energy deposition in extended media

We present recent developments of the Monte Carlo model for heavy-ion therapy (MCHIT), which is currently based on the Geant4 toolkit of version 9.2. The major advancement of the model concerns the modelling of violent fragmentation reactions by means of the Fermi break-up model, which is used to simulate decays of hot fragments created after the first stage of nucleus-nucleus collisions. By means of MCHIT we study the dose distributions from therapeutic beams of carbon nuclei in tissue-like materials, like water and PMMA. The contributions to the total dose from primary beam nuclei and from charged secondary fragments produced in nuclear fragmentation reactions are calculated. The build-up of secondary fragments along the beam axis is calculated and compared with available experimental data. Finally, we demonstrate the impact of violent multifragment decays on energy distributions of secondary neutrons produced by carbon nuclei in water.

An investigation of the thermal decomposition of gold acetate

The thermal decomposition characteristics of gold acetate to produce gold nanoparticles were investigated. A rapid and violent fragmentation of the gold acetate particles was observed at approximately 103±20°C when a rapid heating rate of 25°C min−1 was used, leading to formation of nanosized spherical and partially coalesced gold particles. Particle size analysis was used to investigate possible relationships between the gold acetate crystallite size and the gold nanoparticles produced by thermal decomposition. The results indicate rapid (<0.14 ms) coalescence of the gold particles occurs for fragments in close proximity.

The formation of the first galaxies and the transition to low-mass star formation

AbstractThe formation of the first galaxies at redshifts z ~ 10−15 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding their assembly process with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. In this context we emphasize the importance and influence of selecting appropriate initial conditions for the star formation process. We revisit the notion of a critical metallicity resulting in the transition from primordial to present-day initial mass functions and highlight its dependence on additional cooling mechanisms and the exact initial conditions. We also review recent work on the ability of dust cooling to provide the transition to present-day low-mass star formation. In particular, we highlight the extreme conditions under which this transition mechanism occurs, with violent fragmentation in dense gas resulting in tightly packed clusters.

Anisotropic bulletlike emission of terminal ethynyl fragment ions: Ionization of ethynylbenzene-d under intense femtosecond laser fields

The authors investigated Coulomb explosions of ethynylbenzenes under intense femtosecond laser fields. Deuteration on the edge of the triple bond gave information about specific fragment emissions and the contribution of hydrogen migration. Some fragments not resulting from migration were emitted in the direction of laser polarization. These were ethynyl fragment ions (D(+), CD(+), C(2)D(+), and C(3)D(+)). Although two bonds have to be cleaved to produce C(3)D(+), the rigid character of the triple bond was maintained in the Coulomb explosion process. In contrast, fragment ions, which are formed after single or double hydrogen migration, showed isotropic emissions with distinct kinetic energies. The character of the substituents has been found to hold even under strong laser light fields where violent fragmentation took place. The ethynyl parts were emitted like bullets from the molecular frame of ethynylbenzene despite the explosion into pieces of the main body of benzene ring.

Involuntary Vulnerability and the Felix Culpa in Toni Morrison's Jazz

Given that jazz is interplay of voices improvising on basic themes or motifs (Jones 200) and Toni Morrison's Jazz is often considered a textualized piece of jazz, characters' involuntary vulnerability to harsh outside circumstances is fundamentally reiterated and varied throughout novel. The recurrent tunes of motif are intricately intertwined with a variety of other thematic elements--such as the mystery of that involves jealousy and forgiveness (Jazz 5), history of southern blacks' migration to northern cities, and their quest for identity by seeking their parents. The narrative of Jazz thus weaves motif of turn-of-the-century African American characters' involuntary vulnerability and its improvised variations, synchronizing distinct levels of structure and textuality with jazz-like flexibility and fluidity. On superficial level, narrator interweaves both negative and positive natures of characters. The reader may easily find characters' disordered aspects--carnal desire, jealousy, lack of morality, injury, murder, and like; yet, with a bit more care, their affirmative aspects also become clear. Instead of giving a moral assessment of their binary behaviors, however, Jazz turns its attention toward a deeper level, starting to seriously examine question of shot whom (6). The narrator now traces concealed forces that govern and victimize characters' psyches stealthily but dominantly. She indicates existence of manipulating external circumstances, which make them crack involuntarily in terms of morality, as Richard Hardack observes: The implicit connection between transcendental/Modernist fragmentation, violence, and site of involuntary has been recently reinforced and rendered explicit in Morrison's Jazz. Morrison asserts that violent fragmentation of American character--in Melville's Pierre, who loses control of his body, and in Billy Budd, who kills without intention, in Norris' McTeague or De Lillo's Axton in The Names, or in any of a plethora of American characters who are defined by what is in some context an act of involuntary or unconscious violence--is foremost a projected attribute of American blackness. (452) The deviant conduct of characters in Jazz is involuntary and, perhaps, inevitable. They are inevitably fragmented by outer forces such as seducing City and its music, unreliable narrator, as well as social, political,and economic conditions. Morrison, therefore, does not assert that these involuntarily victimized, pathetic characters are to blame for their extraordinary behaviors; rather, she gives them a chance to redeem themselves, exhorting them to forgive and love each other and to be careful in order not to be trapped by manipulating circumstances. Sth (3), novel's opening word, serves to elicit attention from listener/reader and may well launch this exploration of text with an emphasis on main characters--Joe Trace, Violet, Dorcas Manfred, and Golden Gray. Throughout novel, characters exhibit duplicity of human mind: while they display aberrant behaviors such as murder, injury, and misunderstanding, they are also neighborly and kind. The narrative begins with their extraordinary transgressions, which might make reader consider characters as morally/mentally corrupt. Above all, Joe is a dreamer desirous to take a bite of forbidden apple--that is, Dorcas. Although knew wrong wasn't right, his vain impulse to taste apple keeps growing intense (74). And he appears to have fulfilled this desire in sense that he could date young Dorcas, but affair ends up with his shooting Dorcas because of unsatisfied desire to possess her as his own. Even after her death, Joe's aspiration for Dorcas is still operating: dreaming of Dorcas, he quits his job and pays little attention to his wife. …

Excimer and Isomer Mediated Reactions in Ionized van der Waals Clusters

Electron impact ionization of rare gas clusters Rn (Nen, Arn) has been found to result via multiple collisions of the incoming/outgoing electrons in the production of cluster ions R containing R excimers. Radiative decay of these excimers leads to violent fragmentation of the respective cluster ions. Energetics, kinetics and dynamics of these reactions will be discussed. Moreover, a new technique – cluster autoscavenging spectroscopy – based on the excitation of neutral electronic states in the production process of mixed cluster anions (e.g. (XeSF6)−, (ArO4)−, (ArO3)−) will be introduced. Finally, a novel metastable decay reaction – observed for ionized hydrocarbon clusters of propane and butane – originating from an isomerization reaction of a single ion constituent within the cluster (e.g. C3H7+ and C4H7+ respectively) will be presented.

Combustion of metal droplets ignited by flash heating

The use of single, intense pulses of light from a capacitor discharge lamp to form and ignite submillimeter droplets of metals in a glass oxidation chamber is described. The droplets were photographed in free fall, or were quenched in liquid argon at various stages of combustion and analyzed conventionally. It has been possible to investigate burning droplets of Zr, Ta, Ti, Mo, W, Pu, Sm, Re, and Al by this technique. The combustion of Zr is emphasized here. The violent fragmentation or explosion of zirconium droplets that occurs a short time after ignition has been shown to be related to the presence of nitrogen and possibly other gas-related impurities in the combustion system. Zirconium droplets that do not explode when burning in pure oxygen may be induced to fragmenteither by dissolving a small amount of nitrogen in the metal before ignition or by adding a few per cent of gaseous nitrogen to the oxygen. A similar effect can be produced by coating the metal thinly with a heavy hydrocarbon wax prior to ignition. In the explosion-free combustion of zirconium droplets, it has been possible to observe spearpointing—the abrupt brightening of a droplet near the end of combustion—by photographic techniques. This has been ascribed to the sudden freezing of the droplet and is probably due to nucleation of the droplet after appreciable supercooling. This phenomenon should provide a calibration point for the determination of burning temperatures of certain metal droplets. Direct microweighing of droplets quenched in liquid argon at various stages of combustion has provided preliminary information on the kinetics of oxygen uptake by molten zirconium. In pure oxygen near atmospherie pressure, a 525-μ droplet reacts with less than 3% of the oxygen molecules that strike its surface during combustion, an indication that mass-transfer processes within the droplet limit the rate of oxidation.