System Of Particles Research Articles

The Ulam–Hammersley problem for multiset permutations

Abstract We obtain the asymptotic behaviour of the longest increasing/non-decreasing subsequences in a random uniform multiset permutation in which each element in $\{1,\dots,n\}$ occurs k times, where k may depend on n. This generalises the famous Ulam–Hammersley problem of the case $k=1$ . The proof relies on poissonisation and on a careful non-asymptotic analysis of variants of the Hammersley–Aldous–Diaconis particle system.

Characterization of energy dissipation of particle system in high velocity compaction

Energy transmission and dissipation during HVC lead to the uneven pressing force of the powder in the die cavity, which ultimately affects the densification and mechanical properties of powder metallurgy products. This study used the discrete element method (DEM) to monitor the energy transmission and dissipation of the powder system during HVC, investigate the relationship between the dissipation of kinetic energy and the impact energy during the loading stage, and consider the relationship between the strain energy release rate and the impact energy during the unloading stage. The results show that the boundary energy (impact energy) is mainly converted into strain, frictional, and damping energy, of which the kinetic energy is only an intermediate form and its attenuation equation is also obtained. The larger the porosity of the particle system is, the larger the dissipation factor β is, and the more serious the energy dissipation is. It can be found that the release rate of the strain energy gradually decreases with increasing impact energy, and the strain energy is significantly higher than the frictional energy in the green compacts.

Reentrant phase behavior in systems with density-induced tunneling

We show that correlations in strongly interacting many-particle systems can create quantum decoherence, leading to a mechanism of dissipation that does not rely on an external source. Using analytical methods, we study a bosonic many body system in two dimensions, with extended interactions between particles. We show that, as expected, the system can be driven out of a coherent state. Surprisingly, when the interaction strength is sufficiently large, the system reenters the superfluid phase even after coherence is lost. The breakdown of quantum coherence is a certainty, but interpreting the process correctly relies on understanding and preserving the nature of the coupling between the constituents of the many particle system. The methods used provide a natural cutoff point at the critical temperature, where superfluidity breaks down.

Advancing Light Scattering Control Through the Exploration of Temperature‐Sensitive Optical Modifiers

Advancing Light Scattering Control Through the Exploration of Temperature‐Sensitive Optical Modifiers

Estimation of nuclear properties in a deuteron–lithium target using JENDL/DEU-2020 for IFMIF and similar irradiation facilities

An accelerator-based neutron source powered by deuteron–Li (d–Li) reactions is among the most promising neutron sources for fusion materials irradiation facilities, such as IFMIF, IFMIF-DONES, and A-FNS. The yield estimation of neutrons and other particles is critical to the design of these facilities. Presently, the McDelicious code is employed for the aforementioned yield estimations, although it is not an open code. Recently, a deuteron-induced reaction library, JENDL/DEU-2020, was released by the Japan Atomic Energy Agency. Thus, employing benchmark tests, such as the Particle and Heavy Ion Transport code System (PHITS) + JENDL/DEU-2020, Monte Carlo N-Particle + JENDL/DEU-2020, and McDelicious, we confirm that PHITS (or Monte Carlo N-Particle (MCNP)) + JENDL/DEU-2020 effectively reproduces the experimental data and McDelicious results. We apply PHITS + JENDL/DEU-2020 to the yield estimations of the neutron, gamma, and charged particles in a Li target and to the yield estimation of the charged particles in the target backplate for A-FNS. The estimated production rates of tritium and 7Be during the continuous operation using a deuteron beam of 40 MeV and 125 mA are 1.4 × 1016 atoms/s (2.3 g/FPY) and 5.9 × 1014 atoms/s (0.21 g/FPY), respectively, and the estimated production rates of He and H in the target backplate for A-FNS are 3.2 × 102 and 1.8 × 103 appm/FPY, respectively.

Occupation time of a system of Brownian particles on the line with steplike initial condition

Occupation time of a system of Brownian particles on the line with steplike initial condition

Canonical vs. Grand Canonical Ensemble for Bosonic Gases under Harmonic Confinement

We analyze the general relation between canonical and grand canonical ensembles in the thermodynamic limit. We begin our discussion by deriving, with an alternative approach, some standard results first obtained by Kac and coworkers in the late 1970s. Then, motivated by the Bose–Einstein condensation (BEC) of trapped gases with a fixed number of atoms, which is well described by the canonical ensemble and by the recent groundbreaking experimental realization of BEC with photons in a dye-filled optical microcavity under genuine grand canonical conditions, we apply our formalism to a system of non-interacting Bose particles confined in a two-dimensional harmonic trap. We discuss in detail the mathematical origin of the inequivalence of ensembles observed in the condensed phase, giving place to the so-called grand canonical catastrophe of density fluctuations. We also provide explicit analytical expressions for the internal energy and specific heat and compare them with available experimental data. For these quantities, we show the equivalence of ensembles in the thermodynamic limit.

Application of stoichiometric CT number calibration method for dose calculation of tissue heterogeneous volumes in boron neutron capture therapy.

Monte Carlo simulation code is commonly used for the dose calculation of boron neutron capture therapy. In the past, dose calculation was performed assuming a homogeneous mass density and elemental composition inside the tissue, regardless of the patient's age or sex. Studies have shown that the mass density varies with patient to patient, particularly for those that have undergone surgery or radiotherapy. A method to convert computed tomography numbers into mass density and elemental weights of tissues has been developed and applied in the dose calculation process using Monte Carlo codes. A recent study has shown the variation in the computed tomography number between different scanners for low- and high-density materials. The aim of this study is to investigate the effect of the elemental composition inside each calculation voxel on the dose calculation and the application of the stoichiometric CT number calibration method for boron neutron capture therapy planning. Monte Carlo simulation package Particle and Heavy Ion Transport code System was used for the dose calculation. Firstly, a homogeneous cubic phantom with the material set to ICRU soft tissue (four component), muscle, fat, and brain was modelled and the NeuCure BNCT system accelerator-based neutron source was used. The central axis depth dose distribution was simulated and compared between the four materials. Secondly, a treatment plan of the brain and the head and neck region was simulated using a dummy patient dataset. Three models were generated; (1) a model where only the fundamental materials were considered (simple model), a model where each voxel was assigned a mass density and elemental weight using (2) the Nakao20 model, and (3) the Schneider00 model. The irradiation conditions were kept the same between the different models (irradiation time and irradiation field size) and the near maximum (D1%) and mean dose to the organs at risk were calculated and compared. A maximum percentage difference of approximately 5% was observed between the different materials for the homogeneous phantom. With the dummy patient plan, a large dose difference in the bone (greater than 12%) and region near the low-density material (mucosal membrane, 7%-11%) was found between the different models. A stoichiometric CT number calibration method using the newly developed Nakao20 model was applied to BNCT dose calculation. The results indicate the importance of calibrating the CT number to elemental composition for each individual CT scanner for the purpose of BNCT dose calculation along with the consideration of heterogeneity of the material composition inside the defined region of interest.

Towards complex dynamic physics system simulation with graph neural ordinary equations

The great learning ability of deep learning facilitates us to comprehend the real physical world, making learning to simulate complicated particle systems a promising endeavour both in academia and industry. However, the complex laws of the physical world pose significant challenges to the learning based simulations, such as the varying spatial dependencies between interacting particles and varying temporal dependencies between particle system states in different time stamps, which dominate particles’ interacting behavior and the physical systems’ evolution patterns. Existing learning based methods fail to fully account for the complexities, making them unable to yield satisfactory simulations. To better comprehend the complex physical laws, we propose a novel model – Graph Networks with Spatial–Temporal neural Ordinary Differential Equations (GNSTODE) – that characterizes the varying spatial and temporal dependencies in particle systems using a united end-to-end framework. Through training with real-world particle–particle interaction observations, GNSTODE can simulate any possible particle systems with high precisions. We empirically evaluate GNSTODE’s simulation performance on two real-world particle systems, Gravity and Coulomb, with varying levels of spatial and temporal dependencies. The results show that GNSTODE yields better simulations than state-of-the-art methods, showing that GNSTODE can serve as an effective tool for particle simulation in real-world applications. Our code is made available at https://github.com/Guangsi-Shi/AI-for-physics-GNSTODE.

Observation of liquid glass in molecular dynamics simulations.

Molecular anisotropy plays an important role in the glass transition of a liquid. Recently, a novel bulk glass state has been discovered by optical microscopy experiments on suspensions of ellipsoidal colloids. "Liquid glass" is a disordered analog of a nematic liquid crystal, in which rotation motion is hindered but particles diffuse freely. Global nematic order is suppressed as clusters of aligned particles intertwine. We perform Brownian dynamics simulations to test the structure and dynamics of a dense system of soft ellipsoidal particles. As seen in the experiments and in accordance with predictions from the mode coupling theory, on the time scale of our simulations, rotation motion is frozen but translation motion persists in liquid glass. Analyses of the dynamic structure functions for translation and rotation corroborates the presence of two separate glass transitions for rotation and translation, respectively. Even though the equilibrium state should be nematic, aligned structures remain small and orientational order rapidly decays with increasing size. Long-wavelength fluctuations are remnants of the isotropic-nematic transition.

Cosmic-ray exposure assessment using particle and heavy ion transport code system: case study Douala-Cameroon.

According to UNSCEAR, cosmic radiation contributes to ~16% (0.39mSv/y) of the total dose received by the public at sea level. The exposure to cosmic rays at a specific location is therefore a non-negligible parameter that contributes to the assessment of the overall public exposure to radiation. In this study, simulations were conducted with the Particle and Heavy Ion Transport code System, a Monte Carlo code, to determine the fluxes and effective dose due to cosmic rays received by the population of Douala. In minimum solar activity, the total effective dose considering the contribution of neutron, muon+, muon-, electron, positron and photon, was found to be 0.31±0.02mSv/y at the ground level. For maximum solar activity, it was found to be 0.27±0.02mSv/y at ground level. During maximum solar activity, galactic cosmic rays are reduced by solar flares and winds, resulting in an increase in the solar cosmic-ray component and a decrease in the galactic cosmic-ray component on Earth. This ultimately leads to a decrease in the total cosmic radiation on Earth. These results were found to be smaller than the UNSCEAR values, thus suggesting a good estimation for the population of Douala city located near the equatorial line. In fact, the cosmic radiation is more deflected at the equator than near the pole. Muons+ were found to be the main contributors to human exposure to cosmic radiation at ground level, with ~38% of the total effective dose due to cosmic exposure. However, electrons and positrons were found to be the less contributors to cosmic radiation exposure. As regards the obtained results, the population of Douala is not significantly exposed to cosmic radiation.

Study on Explosion Characteristics and Mechanism of Electrostatic Spray Powder.

In order to fully understand the explosion risk of electrostatic spraying powder, corresponding preventive measures are put forward. The explosion characteristics, ignition sensitivity, and flame propagation of three typical electrostatic spraying powders were tested using a 20 L spherical explosion test device, a G-G furnace test device, and a Hartmann tube test device, and the explosion process and mechanism of electrostatic spraying powders were discussed. The results show that the maximum explosion pressure and the maximum explosion pressure rise rate increase first and then decrease with the increase in mass concentration. The maximum explosion pressure and the maximum explosion pressure rise rate of acrylic powder coating are the largest, which are 0.75 and 85.4 MPa/s, respectively. The shortest burning time is 97.5 ms, and the highest explosion danger level is 23.46 MPa·m/s. The flame propagation of electrostatic spraying powder develops slowly; the flame front spreads linearly and the average flame velocity increases first and then decreases. The explosive development process of powder coating particles is concentrated in the three-phase system of solid particles, molten particles, and pyrolytic gasification combustible gas, which goes through the kinetic process of particle heating melting, cross-linking curing, pyrolytic gasification, combustion, and extinction.

Consensus-based optimisation with truncated noise

Abstract Consensus-based optimisation (CBO) is a versatile multi-particle metaheuristic optimisation method suitable for performing non-convex and non-smooth global optimisations in high dimensions. It has proven effective in various applications while at the same time being amenable to a theoretical convergence analysis. In this paper, we explore a variant of CBO, which incorporates truncated noise in order to enhance the well-behavedness of the statistics of the law of the dynamics. By introducing this additional truncation in the noise term of the CBO dynamics, we achieve that, in contrast to the original version, higher moments of the law of the particle system can be effectively bounded. As a result, our proposed variant exhibits enhanced convergence performance, allowing in particular for wider flexibility in choosing the noise parameter of the method as we confirm experimentally. By analysing the time evolution of the Wasserstein- $2$ distance between the empirical measure of the interacting particle system and the global minimiser of the objective function, we rigorously prove convergence in expectation of the proposed CBO variant requiring only minimal assumptions on the objective function and on the initialisation. Numerical evidences demonstrate the benefit of truncating the noise in CBO.

Inhalable FN-binding liposomes or liposome-exosome hybrid bionic vesicles encapsulated microparticles for enhanced pulmonary fibrosis therapy

Pulmonary fibrosis (PF) is a chronic, progressive and irreversible interstitial lung disease that seriously threatens human life and health. Our previous study demonstrated the unique superiority of traditional Chinese medicine cryptotanshinone (CTS) combined with sustained pulmonary drug delivery for treating PF. In this study, we aimed to enhance the selectivity, targeting efficiency and sustained-release capability based on this delivery system. To this end, we developed and evaluated CTS-loaded modified liposomes-chitosan (CS) microspheres SM(CT-lipo) and liposome-exosome hybrid bionic vesicles-CS microspheres SM(LE). The prepared nano-in-micro particles system integrates the advantages of the carriers and complements each other. SM(CT-lipo) and SM(LE) achieved lung myofibroblast-specific targeting through CREKA peptide binding specifically to fibronectin (FN) and the homing effect of exosomes on parent cells, respectively, facilitating efficient delivery of anti-fibrosis drugs to lung lesions. Furthermore, compared with daily administration of conventional microspheres SM(NC) and positive control drug pirfenidone (PFD), inhaled administration of SM(CT-lipo) and SM(LE) every two days still attained similar efficacy, exhibiting excellent sustained drug release ability. In summary, our findings suggest that the developed SM(CT-lipo) and SM(LE) delivery strategies could achieve more accurate, efficient and safe therapy, providing novel insights into the treatment of chronic PF.

Radiation levels outside a patient undergoing 177Lu-PSMA radioligand therapy

Understanding the spatial distribution of radiation levels outside of a patient undergoing 177Lu radioligand therapy is not only helpful for conducting correct tests for patient release, but also useful for estimation of its potential exposure to healthcare workers, caregivers, family members, and the general public. In this study, by mimicking the 177Lu-labeled prostate-specific membrane antigen radioligand therapy for prostate cancers in an adult male, the spatial distribution of radiation levels outside of the phantom was simulated based on the Monte Carlo software of Particle and Heavy Ion Transport System, and verified by a series of measurements. Moreover, the normalized dose rates were further formulized on the three transverse planes representing the heights of pelvis, abdomen and chest. The results showed that the distributions of radiation levels were quite complex. Multi-directional and multi-height measurements are needed to ensure the external dose rate to meet the release criteria. In general, the radiation level was higher at the horizontal plane where the source was located, and the levels in front and behind of the body were higher than those of the left and right sides at the same height. The ratio of simulated dose rates to measured ones ranged from 0.82 to 1.19 within 1 m away from the body surface in all directions. Based on the established functions, the relative root mean square deviation between the calculated and simulated values were 0.21, 0.25 and 0.23 within a radius of 1 m on the pelvis, abdomen and chest transverse planes, respectively. It is expected that the results of this study would be helpful for guiding the test of extracorporeal radiation to determine the patient’s release, and of benefit to estimate the radiation exposure to others.

Validation study on a coarse-grained DEM-CFD simulation in a bead mill

A bead mill is often employed in powder processes. In the bead mill, the bead-particles move rapidly under high shear rate due to the moving structures. The discrete element method (DEM) coupled with the computational fluid dynamics (CFD) has been applied to simulate the bead-particle behavior for the optimization of the bead mill design and operating conditions. However, the existing DEM-CFD method faces essential problems regarding the substantial limit of the number of computational particles, stable calculations, and modeling of rapidly moving structures. To solve these problems, we newly investigate a numerical model combining the coarse-grained DEM-CFD, an implicit algorithm for the drag force term, and a scalar field-based wall boundary in the calculation of a bead mill commonly employed in industrial powder processes. In this study, our proposed model is shown to successfully simulate the macroscopic behavior of the bead-particles through the validation test of the coarse-grained DEM-CFD simulation in the bead mill system. Specifically, the macroscopic characteristics such as the particle location, the particle velocity, and total kinetic energy, are shown to agree well between the original particle system and coarse-grained particle systems. Consequently, this study illustrates the combination of the coarse-grained DEM-CFD, an implicit algorithm for the drag force term, and the scalar field-based wall boundary is essential for simulating the typically industrial bead mill, where an enormous number of bead-particles should be calculated in liquid under high shear rate.

Role of range of interaction potential on structure and dynamics of a one-component system of particles interacting via Mie potential

Role of range of interaction potential on structure and dynamics of a one-component system of particles interacting via Mie potential

Particle surface oxidation modification and particle gradation strategy for the preparation of high-strength SiC ceramics via vat photopolymerization

The high refractive index, high absorbance, and low sintering activity of SiC powders pose challenges in achieving sufficient curing depth of SiC slurries and achieving densification of SiC ceramics. Hence, the preparation of high-strength SiC ceramics by vat photopolymerization is a challenge. This study proposes a strategy of particle surface oxidation modification and particle gradation to address this difficulty. Specifically, the surface of micron and submicron SiC particles is oxidatively modified to enhance the curing depth of SiC slurry, and the gradation of these particles is optimized to improve the sintering activity of the SiC particle system. The percentage of oxidized micron and submicron SiC particles is carefully adjusted to meet the requirements of both vat photopolymerization preparation and sintering. It found that increasing the percentage of sub-micron particles in the particle grade system had a negative impact on the rheological and curing properties of the slurry but contributed to the stability of the slurry and the performance of the sintered ceramic parts. Ensuring that the percentage of sub-micron particles reaches 50% or higher and reducing direct contact between micron particles to form sintered necks are two key conditions for the preparation of high-strength SiC ceramics. Additionally, it found that interlayer bonding location is the pore defects concentrated in the sintered ceramic parts, providing direction for further optimization of ceramic properties. By implementing the oxidation modification and particle gradation optimization strategy, the densification and three-point flexural strength of SiC ceramic parts were improved significantly. The relative density and three-point flexural strength of SiC increased from 65.7 ± 5.3% to 86.8 ± 3.7% and from 75.0 ± 2.1–170.9 ± 11.6 MPa, respectively. This approach provides a simple and effective method to prepare high-strength SiC ceramics by vat photopolymerization.

Food vs packaging: Dynamics of oil migration from particle systems into fibrous material

Paper packaging for compacted or tabletted foods is seen as a key sustainable packaging of the future. Yet its fibrous structure is susceptible to absorb oils, fats, greases and other small molecules from the contacting food. Underlying phenomena associated with oil release from compacted food on fibre-based packaging, such as viscous liquid flow, capillarity, and gravity from compacted particle systems into fibre networks are not fully understood yet. As such, oil stain mitigation on packaging remains a challenge. Using model food tablets of 95% 500 and 50 μm particle size with 5% sunflower oil as the liquid phase, this work employed for the first-time quantitative Raman spectroscopic chemical imaging (RCI) coupled with automated image quantification for comparison of oil flow dynamics between food compacts and contacting paper packaging. The extent of de-oiling from the compact and imbibed into paper showed similar exponential decay with time for both porous systems. For the first time, oil migration dynamics on the food compact surface was 2D visualised via Raman spectroscopy and showed markedly different trends with varying environment climatic conditions and compact microstructure. The larger particle system leaked up to 50% of oil into paper, whereas the 50 μm system retained 100% of its oil, creating an effective internal oil barrier. This novel technique opens the way for further understanding liquid transfer between porous food media and harnessing microstructure engineering to increase food and packaging performance.

Classical stochastic approach to quantum mechanics and quantum thermodynamics

We derive the equations of quantum mechanics and quantum thermodynamics from the assumption that a quantum system can be described by an underlying classical system of particles. Each component φ j of the wave vector is understood as a stochastic complex variable whose real and imaginary parts are proportional to the coordinate and momentum associated with a degree of freedom of the underlying classical system. From the classical stochastic equations of motion, we derive a general equation for the covariance matrix of the wave vector, which turns out to be of the Lindblad type. When the noise changes only the phase of φ j , the Schrödinger and the quantum Liouville equations are obtained. The component ψ j of the wave vector obeying the Schrödinger equation is related to the stochastic wave vector by |ψj|2=⟨|ϕj|2⟩ .