Collision Phenomena Research Articles

Numerical Investigation on the Transient Ignition Behavior Using CFD-DEM Approach

To consider the effects of dynamic collision during the ignition process, numerical simulations based on the CFD-DEM (computational fluid dynamic-discrete element method) approach are carried out for studying the gas-solid transient ignition behavior in guns. The motion of individual particles is modeled by DEM, tracking the dynamic collision process of particles and predicting the dynamic collision phenomena at the individual particle scale. The gas motion is described by the continuum flow, taking into account detailed grain combustion, particle-particle collisions, particle-wall collisions, interphase drag, and heat transfer between the gas and solid phases. A parameter study including particle size, particle escape, initial pressure of primer, initial particle bed height, rupture pressure of holes, and randomness on the ignition phase are investigated. The randomness of vent holes opening closely linked with the particle distribution, particle collision, and combustion process is evidently shown. There is mutual restriction between different factors and the perfect ignition performance cannot be obtained by changing one or two factors. Simulation results show a deeper understanding of ignition processes, including combustion, flame spreading, pressure wave developing, and particle collisions. A further guide for optimization of the igniter design is provided by the parameter study on ignition performance. This article puts forward a new prediction tool for the understanding and design of transient ignition process in guns.

Spin-orbit coupling and the up-down differential transverse flow in intermediate-energy heavy-ion collisions

To explore the strength, isospin dependence, and density dependence of the in-medium spin-orbit coupling that is poorly known but relevant for understanding the structure of rare isotopes, the nucleon spin up-down differential transverse flow is studied systematically by varying the beam energy and impact parameter of Au+Au collisions within a spin-isospin dependent transport model recently developed for investigating spin-related phenomena in intermediate-energy heavy-ion collisions. The optimal reaction conditions for delineating and disentangling effects of different terms in the spin-orbit coupling are discussed.

Soliton and breather solutions of the Sasa–Satsuma equation via the Darboux transformation

In this paper, we construct the general Darboux transformation on the Sasa–Satsuma equation and represent the iterated solutions in terms of the three-component Wronskian. From the once-iterated solution, we derive the breather as well as the single- and double-hump solitons. We also analyze three types of collisions: soliton–soliton, breather–breather and soliton–breather collisions. The surprising result is that the soliton–breather collision may exhibit the shape-changing phenomena, that is, one breather (or soliton) may change into a soliton (or breather) when interacting with another breather. Such novel collision phenomena may be applied in all-optical information processing, optical switching and routing of optical signals.

EIGENVALUE COLLISION FOR PT-SYMMETRIC WAVEGUIDE

We consider a model of a planar PT-symmetric waveguide and study the phenomenon of the eigenvalue collision under perturbation of the boundary conditions. This phenomenon was discovered numerically in previous works. The main result of this work is an analytic explanation of this phenomenon.

Investigation of ship collision with floating pier structures

This study investigated the collision of ships withfloating pier structures. The nature of the collision phenomenon is complex, and the understanding of it has developed through the modelling of offshore structures. ABAQUS software was used to investigate the collision phenomenon. The interaction between the ship and structural system was modelled, and the stress distribution both at thetime of collision and afterwardswasobserved and modelled. The strain energy absorption by different structural partswas calculated and comparisonswere made.

1P2-O03 カプセル型移動ロボットの運動制御 : 摩擦と衝突を考慮した動作生成アルゴリズムとその解析(特殊移動ロボット(2))

1P2-O03 カプセル型移動ロボットの運動制御 : 摩擦と衝突を考慮した動作生成アルゴリズムとその解析(特殊移動ロボット(2))

Isospin transport in84Kr+112,124Sn reactions at Fermi energies

Isospin transport phenomena in dissipative heavy ion collisions have been investigated at Fermi energies with a beam of 84Kr at 35AMeV. A comparison of the <N>/Z of light and medium products forward-emitted in the centre of mass frame when the beam impinges on a n-poor 112Sn and a n-rich 124Sn targets is presented. Data were collected by means of a three-layer telescope with very good performances in terms of mass identification (full isotopic resolution up to Z about 20 for ions punching through the first detector layer) built by the FAZIA Collaboration and located just beyond the grazing angle for both reactions. The <N>/Z of the decay products emitted when the n-rich target is used is always higher than that associated to the n-poor one. Since the detector was able to measure only fragments coming from the QuasiProjectile decay and/or neck emission, the observed behaviour can be ascribed to the isospin diffusion, driven by the isospin gradient between QuasiProjectile and QuasiTarget. Moreover, for light fragments the <N>/Z as a function of the lab velocity of the fragment increases when we move from the QuasiProjectile velocity to the centre of mass (neck zone). This effect can be interpreted as an evidence of isospin drift driven by the density gradient between the QuasiProjectile zone (at normal density) and the more diluted neck zone.

Some Intensive and Extensive Quantities in High-Energy Collisions

We review the evolution of some statistical and thermodynamical quantities measured in difference sizes of high-energy collisions at different energies. We differentiate between intensive and extensive quantities and discuss the importance of their distinguishability in characterizing possible critical phenomena of nuclear collisions at various energies with different initial conditions.

Overview of Flow and Hydrodynamic Modeling of Nuclear Collisions

I give a brief overview of flow phenomena in relativistic heavy-ion collisions and the hydrodynamic models used to simulate these systems, aimed at new and young researchers, such as those attending the Hot Quarks 2012 conference.

SPARC experiments at the high-energy storage ring

The physics program of the SPARC collaboration at the Facility for Antiproton and Ion Research (FAIR) focuses on the study of collision phenomena in strong and even extreme electromagnetic fields and on the fundamental interactions between electrons and heavy nuclei up to bare uranium. Here we give a short overview on the challenging physics opportunities of the high-energy storage ring at FAIR for future experiments with heavy-ion beams at relativistic energies with particular emphasis on the basic beam properties to be expected.

Detecting Bifurcation Types and Characterizing Stability in DC–DC Switching Converters by Duplicate Symbolic Sequence and Weight Complexity

Based on the characteristics of dc-dc switching converters and the logical arithmetic method of computer that changes to decimal system from binary system, the main switching block is presented to distinguish the switching behaviors and the degree of the converter's complexity during one switching period. The main symbolic sequence is established to clearly show how the switching modes change in one switching period. Adopting the coarse-grained symbolic sequence method, the secondary switching block and secondary symbolic sequence are established in terms of main switching block too. Hence, the duplicate symbolic sequence is put forward to detect bifurcation types in dc-dc switching converters. Based on the duplicate symbolic sequence, the concept of weight complexity is first defined and utilized to analyze border collision and bifurcation phenomena qualitatively along with Lempel-Ziv (L-Z) complexity. The presented weight complexity and the L-Z complexity are combined to introduce the stability index for guiding circuit design of power electronics. Finally, voltage-mode-controlled flyback converter is used as an example to illustrate the applications of the proposed duplicate symbolic sequence and complexity to detect bifurcation behaviors of the switching system.

Effects of droplet collision phenomena on the development of pressure swirl sprays

In this work, the sprays generated by a pressure swirl atomizer were examined for different liquid injection pressures and particularly, the effects of the droplet collision phenomena on the axial evolution of the droplet size distribution were carefully studied. Sizes and droplet velocities were measured by means a phase Doppler particle analyzer and number concentrations and liquid volume fluxes for different droplet classes, were evaluated using a full data post-processing based on the droplet transit time inside the probe volume. The collision rates between droplet classes were calculated and some collision outcomes as coalescence and separation were investigated.In all the sprays studied, the highest collision rates were obtained in the region where both high number concentration and elevated relative velocity between droplets were measured. A progressive increase of the droplet mean diameter was produced along the sprays due to the coalescing collisions. As injection pressure increased, higher droplet collision rates and higher inertia collisions were found. The separation with formation of satellite droplets was a more frequent collision outcome. In addition, bigger axial mean free paths were calculated and hence, a more moderated axial increase of the droplet mean diameter was obtained.

Soliton collision in a general coupled nonlinear Schrödinger system via symbolic computation

A general coupled nonlinear Schrödinger system with the self-phase modulation, cross-phase modulation and four-wave mixing terms is investigated. The system is still integrable with the variable coefficients. Through the Hirota bilinear method, one- and two-soliton solutions are derived via symbolic computation. With the asymptotic analysis, it is found that the two-soliton solutions admit the inelastic and elastic collisions depending on the choice of solitonic parameters. A new inelastic collision phenomenon occurring in this system is that both the amplitudes of two components of each soliton get suppressed or enhanced after the collision, which might provide us with a different approach of signal amplification.

Dynamic Evolution of Inclusions in Ti‐Bearing Al‐Deoxidized Molten Irons at 1873 K

AbstractTo study the evolution of inclusions in Ti‐bearing Al‐deoxidized steel, four types of molten irons with different Al and Ti contents were prepared. Subsequently, scanning electron microscope (SEM) and high‐temperature confocal scanning laser microscope (CSLM) were used to investigate the dynamic process of inclusions in the samples. The CSLM showed that Al2O3 inclusions strongly attracted each other and agglomerated easily. In high‐Al and high‐Ti melt, although inclusion clusters were frequently observed, its number and size were small. The Al–Ti–O cluster appeared much denser, unlike the Al2O3 cluster, which had loose structure. In high‐Al and low‐Ti melt, the number of inclusions was large, whereas their size was small. Collision among small inclusions was not observed, possibly because the trace of Ti addition accelerated the dispersion of inclusions. In low‐Al and high‐Ti melt, typical inclusions of Al–Ti–N–O were observed, and they always had irregular or bar‐like shapes or form a cluster. The bar‐like inclusion was found to adhere easily to a cluster via bridging or packing. In low‐Al and low‐Ti melt, only small amount of inclusions were observed. The inclusions presented nearly spherical in shape, and few cluster could be seen. In addition, the phenomenon of collision and agglomeration among the inclusions was never observed.

Modeling of Interior Ballistic Gas-Solid Flow Using a Coupled Computational Fluid Dynamics-Discrete Element Method.

In conventional models for two-phase reactive flow of interior ballistic, the dynamic collision phenomenon of particles is neglected or empirically simplified. However, the particle collision between particles may play an important role in dilute two-phase flow because the distribution of particles is extremely nonuniform. The collision force may be one of the key factors to influence the particle movement. This paper presents the CFD-DEM approach for simulation of interior ballistic two-phase flow considering the dynamic collision process. The gas phase is treated as a Eulerian continuum and described by a computational fluid dynamic method (CFD). The solid phase is modeled by discrete element method (DEM) using a soft sphere approach for the particle collision dynamic. The model takes into account grain combustion, particle-particle collisions, particle-wall collisions, interphase drag and heat transfer between gas and solid phases. The continuous gas phase equations are discretized in finite volume form and solved by the AUSM+-up scheme with the higher order accurate reconstruction method. Translational and rotational motions of discrete particles are solved by explicit time integrations. The direct mapping contact detection algorithm is used. The multigrid method is applied in the void fraction calculation, the contact detection procedure, and CFD solving procedure. Several verification tests demonstrate the accuracy and reliability of this approach. The simulation of an experimental igniter device in open air shows good agreement between the model and experimental measurements. This paper has implications for improving the ability to capture the complex physics phenomena of two-phase flow during the interior ballistic cycle and to predict dynamic collision phenomena at the individual particle scale.

Ion-neutral chemistry at ultralow energies: dynamics of reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap †

Cold chemical reactions between laser-cooled Ca+ ions and Rb atoms were studied in an ion-atom hybrid trap. Reaction rate constants were determined in the range of collision energies ⟨E coll⟩/k B=20 mK-20 K. The lowest energies were achieved in experiments using single localised Ca+ ions. Product branching ratios were studied using resonant-excitation mass spectrometry. The dynamics of the reactive processes in this system (non-radiative and radiative charge transfer as well as radiative association leading to the formation of CaRb+ molecular ions) have been analysed using high-level quantum-chemical calculations of the potential energy curves of CaRb+ and quantum-scattering calculations for the radiative channels. For the present low-energy scattering experiments, it is shown that the energy dependence of the reaction rate constants is governed by long-range interactions in line with the classical Langevin model, but their magnitude is determined by short-range non-adiabatic and radiative couplings which only weakly depend on the asymptotic energy. The quantum character of the collisions is predicted to manifest itself in the occurrence of narrow shape resonances at well-defined collision energies. The present results highlight both universal and system-specific phenomena in cold ion-neutral reactive collisions.

Calculating jetvnand the event plane in the presence of a jet

Advances in measurements of jets and collective phenomena in ultrarelativistic heavy ion collisions have led to further understanding of the properties of the medium created in such collisions. Measurements of the correlations between the axes of reconstructed jets and the reaction plane or second-order participant plane of the bulk medium (defined as jet ${v}_{2}$), as well as the higher-order participant planes (jet ${v}_{n}$), provide information on medium-induced parton energy loss. Additionally, knowledge of jet ${v}_{n}$ as well as the ability to reconstruct the event plane in the presence of a jet are necessary in analyses of jet-triggered particle correlations, which are used to study medium-induced jet shape modification. However, the presence of a jet can bias the event plane calculation, leading to an overestimation of jet ${v}_{2}$. This paper proposes a method for calculating jet ${v}_{2}$ (and by extension, the higher jet ${v}_{n}$ harmonics) and the event plane in an unbiased way, using knowledge of the azimuthal angle of the jet axis from full jet reconstruction.

Modeling Calcium Wave Based on Anomalous Subdiffusion of Calcium Sparks in Cardiac Myocytes

sparks and waves play important roles in calcium release and calcium propagation during the excitation-contraction (EC) coupling process in cardiac myocytes. Although the classical Fick’s law is widely used to model sparks and waves in cardiac myocytes, it fails to reasonably explain the full-width at half maximum(FWHM) paradox. However, the anomalous subdiffusion model successfully reproduces sparks of experimental results. In this paper, in the light of anomalous subdiffusion of sparks, we develop a mathematical model of calcium wave in cardiac myocytes by using stochastic release of release units (CRUs). Our model successfully reproduces calcium waves with physiological parameters. The results reveal how concentration waves propagate from an initial firing of one CRU at a corner or in the middle of considered region, answer how large in magnitude of an anomalous spark can induce a wave. With physiological currents (2pA) through CRUs, it is shown that an initial firing of four adjacent CRUs can form a wave. Furthermore, the phenomenon of calcium waves collision is also investigated.

Design of a multi-hop dynamic consensus algorithm over wireless sensor networks

In the last few years great attention has been concentrated on the consensus algorithm in a network of agents. A consensus problem in which the agreement value is a distributed estimation of some non-constant quantity of interest is referred to as a dynamic consensus. In practical applications an effective network architecture to support sensing and communication between agents is based on a Wireless Sensor Network (WSN). This paper deals with the design of a fast dynamic consensus algorithm when it is implemented over the WSN. A sufficient stability condition of the dynamic consensus algorithm in the presence of heterogeneous time delays affecting communication through the multi hops of the WSN is introduced and used for consensus algorithm gain design. Moreover, the algorithm implementation by the standard AODV routing protocol is discussed and the best parameter setting to reduce the effect of packet collision phenomena on the performance of the consensus algorithm is indicated. Several trade-offs between network parameter setting, sensor node technology selection and application performance have to be taken into account by the designer in the implementation of the dynamic consensus algorithm. A representative simulation based design procedure is presented to validate through realistic simulation experiments the proposed design approach.

Pigmented solar (actinic) keratosis: An underrecognized collision lesion

The lack of well-established diagnostic criteria for pigmented solar (actinic) keratosis (PSK) along with its poorly understood etiopathogenesis has contributed to underrecognition. The clinical, dermatoscopic, and histopathologic features of PSK and the cause of the pigmentation are elucidated. In all, 167 histologic specimens, 22 clinical images, and 17 dermatoscopic images of PSK were reviewed. In 38 cases, Melan-A-stained sections were available for analysis. The majority of the lesions were located on the head and neck (84%). A separate pigmented lesion was adjacent to or admixed within PSK in 138 (83%) of the cases indicating that PSK represents a collision between a nonpigmented solar keratosis and a pigmented lesion. Solar lentigo (72%) was the most commonly associated pigmented lesion followed by seborrheic keratosis and melanoma. PSK was suspected clinically in 17% of the cases. There were no significant differences in the quality and quantity of the melanocytes between pigmented and nonpigmented solar keratosis. This was a single-center retrospective study. The sample sizes were small for the clinical and dermatoscopic images and Melan-A stains. In the majority of the cases, a collision between a nonpigmented solar keratosis and a separate coexistent pigmented lesion, primarily a solar lentigo, accounts for the pigmentation in PSK rather than from any fundamental changes in the quantity or quality of the melanocytes. The collision phenomenon accounts for the spectrum of the clinical and dermatoscopic features observed in PSK and its underrecognition.