Particle Paths Research Articles

Reversible fluxon logic: Topological particles allow ballistic gates along one-dimensional paths

As we reach the end of Moore's law, digital logic uses irreversible logic gates whose energy consumption has been scaled toward a lower limit. Reversible logic gates can provide a dramatic energy-efficient alternative, but rely on reversible dynamics. Here, we introduce a set of superconducting reversible gates that are powered alone by the inertia of the digital input states, contrasting existing adiabatic prototypes which are powered by an external adiabatic drive. The classic model of an inertia-powered reversible gate uses ballistic particles which scatter in two dimensions, where the digital state is represented by the particle path. Our ballistic gates use as the bit state the topological charge (polarity) of a fluxon moving along a long Josephson junction (LJJ) such that the particle path is confined to one dimension. The fundamental structures of our reversible fluxon logic (RFL) are one-bit gates which consist of two LJJs connected by a circuit interface that comprises three large-capacitor Josephson junctions (JJs). Numerical simulations show how a fluxon approaching the interface under its own inertia converts its energy to an oscillating evanescent field, from which in turn a new fluxon is generated in the other LJJ. We find that this resonant forward scattering of a fluxon across the interface requires large capacitances of the interface JJs because they enable a conversion between bound-evanescent and traveling fluxon states (without external power). Importantly, depending on the circuit parameters, the new fluxon may have either the original or the inverted polarity, and these two processes constitute the fundamental identity and not operations of the logic. Based on these one-bit RFL gates, we design and study a related two-bit RFL gate which shows that fluxons can exhibit conditional polarity change. Energy efficiency is accomplished because only a small fraction of the fluxon energy is transferred to modes other than the intended fluxon. Simulations show that over $97%$ of the total fluxon energy is preserved during gate operations, in contrast to irreversible gates where the entire bit energy is consumed in bit switching. To provide insight into these phenomena, we analyze the one-bit gate circuits with a collective-coordinate model which describes the field in each LJJ as a combination of fluxon and mirror antifluxon. This allows us to reduce the many-junction circuit (the three interface JJs and the many JJs approximating the LJJs, solved numerically) to that of two coupled degrees of freedom that each represent a particle. The evolution of the reduced model agrees quantitatively with the full circuit simulations and validates the use of the mirror-fluxon ansatz. Parameter tolerances are calculated for the proposed circuits and indicate that RFL gates can be manufactured and tested.

Preparing micro/nano-fibrous filters for effective PM 2.5 under low filtration resistance

An enhanced micro/nano-fibrous filter composed of microfibers and nanofiber was successfully prepared for effectively capturing particulate matter (PM). Electrospun polyacrylonitrile (PAN) nanofiber with an average diameter of 850 nm was received on PAN micro-fibrous supporting scaffold and then dispersed in PAN micro-fibrous assembly after the needle-punching process. The filtration property and structure of the PAN composite filters was controlled by adjusting the spinning time. The removal efficiency of the fabricated filters could reach to 99.99% for PM 1–2.5 with a low pressure drop below 35 Pa. In addition, the filtration mechanism of the prepared micro/nano-fibrous filter was distinctly explained by simulating the intercepted distributions and motion paths of particles using GeoDict software. These results indicated that the successful fabrication of the micro/nano-fibrous filters with a high efficiency and low air resistance was veryattractive to reduce air pollution and save energy in air filtration applications.

Fast Models of Hydrocarbon Migration Paths and Pressure Depletion Based on Complex Analysis Methods (CAM): Mini-Review and Verification

A recently developed code to model hydrocarbon migration and convective time of flight makes use of complex analysis methods (CAM) paired with Eulerian particle tracking. Because the method uses new algorithms that are uniquely developed by our research group, validation of the fast CAM solutions with independent methods is merited. Particle path solutions were compared with independent solutions methods (Eclipse). These prior and new benchmarks are briefly summarized here to further verify the results obtained with CAM codes. Pressure field solutions based on CAM are compared with independent embedded discrete fracture method (EDFM) solutions. The CAM method is particularly attractive because its grid-less nature offers fast computation times and unlimited resolution. The method is particularly well suited for solving a variety of practical field development problems. Examples are given for fast optimization of waterflood patterns. Another successful application area is the modeling of fluid withdrawal patterns in hydraulically fractured wells. Because no gridding is required, the CAM model can compute the evolution of the drained rock volume (DRV) for an unlimited (but finite) number of both hydraulic and natural fractures. Such computations of the DRV are based on the convective time of flight and show the fluid withdrawal zone in the reservoir. In contrast, pressure depletion models are based on the diffusive time of flight. In ultra-low permeability reservoirs, the pressure depletion zones do not correspond to the DRV, because the convective and diffusive displacement rates differ over an order of magnitude (diffusive time of flight being the fastest). Therefore, pressure depletion models vastly overestimate the drained volume in shale reservoirs, which is why fracture and well spacing decisions should be based on both pressure depletion and DRV models, not pressure only.

Brownout Simulations of Model-Rotors In Ground Effect

In this work computational fluid dynamics is used to validate experimental results for a two-bladed small rotor In Ground Effect conditions. The paper focuses on the evaluation and prediction of the rotor outwash generated in ground effect. Time-averaged outflow velocities are compared with experimental results, and the simulated flow field is used for safety studies using the PAXman model and particle tracking methods. The aircraft weights have been studied, evaluating scaling factors to define how helicopter weight can affect the outflow forces and the particle paths. Results show how the wake generated by heavier helicopters can lead to stronger forces on ground personnel and push the particles farther away from the rotor.

The origin of lift – understanding lift

In this note, an attempt at giving as simple as possible an explanation for the lift of an airfoil is proposed based on an intuitive use of Newton's law on one hand and the application of the well-established inviscid flow theory of thin airfoils on the other. A thin parabolic cambered plate is chosen as profile at zero incidence because the flow it produces minimises viscous effects and the particle paths along the plate, above and below it, have the same length, thus proving the 'equal transit' explanation to be wrong.

Simulation of Mean Free Path of Solar Energetic Particles in Three-dimensional MHD Background

太阳高能粒子（SEP）的平均自由程是研究SEP传播的重要参数，由SEP的物理性质和太阳风物理性质决定.使用MHD-SEP模型对三维MHD背景场下的平均自由程进行了探讨，利用该模型具有可提供接近物理真实的太阳风背景场的优势，对SEP的平均自由程进行了定性分析.分别对太阳活动高年和低年选取2个卡林顿周进行模拟，定性分析其空间变化，并研究平均自由程与径向太阳风速度的相关性.结果表明:该方法得到的平均自由程空间分布与以往研究得到的关于平均自由程的结论相吻合，可以用来定性确立平行平均自由程；该模型可以反映不同事件中平行平均自由程分布的不同特征；表现了平均自由程与径向太阳风速度有很好的负相关关系.结果可为未来缓变SEP平均自由程研究作参考.

Frictionless Surface Gravity Waves

A physical explanation is given for the observations that ocean surface gravity waves can travel up to half way around the world from generation in a wind storm to dissipation on shore. Inherent in these waves is an orbital fluid particle motion, known from laboratory experiments, that has no friction according to the Navier-Stokes equations. The prediction is based on application of Bernoulli’s law to all the closed orbital paths of the fluid particles and the cross-stream force balance on the particles between a pressure gradient and the centrifugal force in each orbital loop.

원심펌프 내부의 유동특성 해석

In this study, actual material manufactured and used actually in the corporation was embodied by CATIA V5, results of flow characteristics that were obtained from numerical analysis on pressure distribution and velocity distribution from inlet port to outlet port of centrifugal pump, flow phenomenon of water cut, and path of particle were compared with actual performance curve of centrifugal pump through commercial program, ADINA 9.0 and reliability of flow characteristics numerical analysis was confirmed. In addition, the comparison of numerical analysis and performance curve of centrifugal pump, outlet pressure head is nearly be a unit. In this study, biased phenomenon of impeller outlet pressure was confirmed and it prepared an opportunity to improve the phenomenon. And it should be much helpful to improve pump performance if analyzing flow characteristics of centrifugal pump used in industrial field for various purposes, grasping the reasons making an effect on pump performance and improving them.

The Lax-Friedrichs scheme for interaction between the inviscid Burgers equation and multiple particles

We propose a finite difference method based on the Lax-Friedrichs scheme for a model of interaction between multiple solid particles and an inviscid fluid. The single-particle version has been studied extensively during the past decade. The model studied here consists of the inviscid Burgers equation with multiple nonconservative moving source terms that are singular and account for drag force interaction between the fluid and the particles. Each particle trajectory satisfies a differential equation that ensures conservation of momentum of the entire system. To deal with the singular source terms we discretize a model that associates with each particle an advection PDE whose solution is a shifted Heaviside function. This alternative model is well known but has not previously been used in numerical methods. We propose a definition of entropy solution which directly generalizes the previously defined single-particle notion of entropy solution. We prove convergence (along a subsequence) of the Lax-Friedrichs approximations, and also prove that if the set of times where the particle paths intersect has Lebesgue measure zero, then the limit is an entropy solution. We also propose a higher resolution version of the scheme, based on MUSCL processing, and present the results of numerical experiments.

Simulation of Coulomb particles collisions and calculation of Lyapunov exponent for bound orbits

The computer simulation from the first principles allows us to obtain results for systems consisting ofmany particles and interacting according to the Coulomb law (plasma, star clusters and astrophysicalobjects). In this work, the methodology of simulation for Coulomb systems is investigated. The influenceof rounding errors, integration errors of reversible Newton equations is studied on the characteristics ofCoulomb collisions on the basis of the consideration of several model problems. The trajectories of twoparticles attracted to the positively charged force center are got for various initial coordinates andvelocities and also their energetic natures are researched. It is shown that the symmetries are broken andthe particle paths are destroyed due to rounding errors and calculation errors. The degree of deviationfrom symmetry is described by the value of the Lyapunov exponent, which characterizes the chaos andturbulence in plasmas for the system. The results can be also extended to the system of gravitatingmasses.

Evaluation of the performance of a hydraulic barrier by the Null space Monte Carlo method

A gasoline leak caused the contamination of a shallow alluvial aquifer in an urbanized area in Northern Italy. A rapid intervention was conceived to stop the spreading of contamination: a hydraulic barrier has been placed downstream of the source to collect both the floating oil and the contaminated groundwater. A numerical model has been built to assess the performance of the existing barrier, and to design a new configuration of the hydraulic barrier aimed at stopping the hydrocarbon plume already dispersed downstream. A preliminary model was built and calibrated against groundwater levels measured in 41 monitoring wells. Hydraulic conductivities in pilot points, recharge zones and constant head BCs were calibrated. The non-uniqueness of the calibrated parameters led to identify 283 alternative parameter sets, all able to represent the observed heads within an absolute average error of 10 cm. These sets, generated with the Null space Monte Carlo method, served to build 283 models, used to simulate the dispersion of solved contamination through forward particle tracking. A further step was the censoring of all simulations resulting in particle paths at a distance closer than 5 meters from monitoring wells where contamination was never found since the spilled occurred. Analysis was performed of the particle paths generated with the 187 models that were retained. Overall, the barrier captures 89% of all particles. Moreover, in 74% of all realizations, at least a particle escapes, with a mean and median of 7 particles in each realization where it happens. Two main contamination paths are identified: while one is confirmed by the monitoring wells already present, another one would require the placement of new wells to assess the actual presence of contamination. Thus, the validity of the stochastic simulation would be assessed together with the need to improve the performance of the hydraulic barrier.

Liver Radioembolization: a New Chapter in Russian Oncology

Recent years have seen an increase in the number of patients with malignant tumours of the liver. In this context, new treatment methods are being actively introduced into practice, one of which is liver radioembolization utilizing microspheres embedded with yttrium-90 (90Y).Aim. To review literature data on the history of radioembolization and its application for liver tumours.Key findings. Annually, over 200 thousand patients with inoperable primary liver cancer and over 270 thousand patients with inoperable metastatic liver cancer are registered globally, for whom radioembolization is considered as the most suitable treatment method. 90Y is a pure beta emitter without its own gamma line, which is characterized by a small average particle path in the tissue of 2.5 mm (the maximum level is 11 mm), a maximum beta particle energy of 2.27 MeV (average energy of 0.937 MeV) and a half-life of 64.1 hours. Clinical research into microspheres containing 90Y has been actively conducted since 1977 all over the world. However, it was only in 2004 that the US FDA authorized the clinical use of glass microspheres containing 90Y for the treatment of hepatocellular cancer and liver colorectal cancer metastases. Until recently, radioembolization has not been applied in Russia. In 2018, the joint efforts of the A. Tsyb Medical Radiological Research Centre (MRRC) — branch of the National Medical Research Radiological Centre and BEBIG LLC resulted in the production of Russian microspheres containing yttrium-90, which were subsequently introduced into routine clinical practice. The first liver embolization in Russia using microspheres containing domestic yttrium-90 (BEBIG LLC) to a patient with hepatocellular cancer was carried out by V.V. Kucherov and A.P. Petrosyan at the A. Tsyb RMMC on April, 25 in 2019.Conclusion. The production of microspheres containing 90Y in Russia, as well as a technical improvement of the procedure, will facilitate the introduction of liver radioembolization into the routine management of patients with malignant liver tumours.

Instabilities in a self-gravitating granular gas

A kinetic and hydrodynamic descriptions are developed in order to analyze the instabilities in a self-gravitating granular gas. In the kinetic description the Boltzmann equation is coupled with the Poisson equation, while in the hydrodynamic description the Poisson equation is coupled with the balance equations of mass density, hydrodynamic velocity and temperature for an Eulerian fluid. In the background solution for both descriptions the fluid is at rest with constant mass density and gravitational potential while the temperature depends on time through Haff’s law. In the kinetic description the perturbed distribution function and gravitational potential in the Fourier space are related to time dependent small amplitudes. In the hydrodynamic description the perturbed mass density, hydrodynamic velocity and temperature in the Fourier space are functions of time dependent small amplitudes. From the analysis of the system of coupled differential equations for the amplitudes for the two descriptions the time evolution of the density contrast – a parameter that indicate where there are local enhancements in the matter density – is determined. The solutions depend on two parameters, one is the mean free path of the gas particles and another Jeans’ wavelength, which is a function of the gravitational constant, mass density and speed of sound of the gas. It is shown that instabilities due to the inelastic collisions occur when the Jeans and the perturbation wavelengths are larger than the mean free path, while Jeans’ instabilities due to the gravitational field happen when the mean free path and the perturbation wavelength are larger than Jeans’ wavelength.

Searches for exotica and dark matter with neutrino telescopes.

Neutrino telescopes are designed to search for neutrino sources in the Universe, exploiting the Cherenkov light emitted along the path of the charged particles produced in interactions occurring close to the detector volume. Their huge size and the shield offered by large water or ice overburden make them excellent tools to search for exotic and rare particles in the cosmic radiation. In particular, they are sensitive to particles not predicted by the Standard Model that could be messenger of new physics. An overview of the experimental scenario and the relevant results obtained looking for magnetic monopoles, dark matter candidates and other exotic relic particles with neutrino telescopes is given, together with the description of possible new perspectives. This article is part of a discussion meeting issue 'Topological avatars of new physics'.

Efficacy of Electric Field Models in Reproducing Observed Ring Current Ion Spectra During Two Geomagnetic Storms

AbstractWe use the UNH‐IMEF, Weimer 1996, https://doi.org/10.1029/96GL02255 and Volland‐Stern electric field models along with a dipole magnetic field to calculate drift paths for particles that reach the Van Allen Probes' orbit for two inbound passes during two large geomagnetic storms. We compare the particle access in the models with the observed particle access using both realistic and enhanced solar wind model parameters. To test the accuracy of the drift paths, we estimate the H+ charge exchange loss along these drift paths. While increasing the strength of the model electric field drives particles further inward, improving agreement, energy‐dependent cutoffs in the spectra do not agree, indicating that potential patterns for highly disturbed times are inaccurate. While none of the models were able to reproduce the observed features of the more dawnward pass during the 17 March 2013 storm, the UNH‐IMEF model with enhanced inputs was able to adequately reproduce the access, charge exchange loss, and H+ particle pressure during the 17 March 2015 storm.

Particle counting and tracking: Zooming on deposition and flow paths during initial stages of cake formation in forward osmosis with spacers

Deposition and flow paths of particles (live and inert) often control the first stages of “cake” (fouling) formation in membrane systems. Developments in crossflow cell design such as three-dimensional (3D) printing and state of the art imaging techniques enable real-time and in situ tracking of initial cake formation. In this work, high-resolution large-field fluorescent microscopy was used to concomitantly study and compare the deposition and flow paths of inert beads and Bacillus subtilis as biofilm forming bacteria. The membrane surface was imaged continuously (30 s intervals) during the initial stages of cake formation (< 4 h) in a 3D printed forward osmosis (FO) cell containing diamond-shaped spacers. Deposition patterns were analyzed using particle detection and counting for quantitative comparison. Flow paths and velocities (< 17 μm s−1) of beads were similar to those of B. subtilis, thus providing a reliable approximation for bacteria passing through the feed channel. However, spatiotemporal deposition of beads and bacteria were markedly different: Final bacteria deposition was 20 times lower than that of beads when normalized to the initial foulant concentration in the feed solution, although beads had a linear deposition increase, while bacteria deposition rose exponentially. Additionally, deposition of beads was homogeneously distributed within the spacer element compared to bacteria, which were mostly captured around the spacer filaments obstructing the flow. Our results provide a novel approach to quantify cake formation in membrane systems as well as new insights on the impact of inert and living particles on the deposition patterns and flow paths during the first stages of cake formation. These insights could be applicable to design new membrane surfaces and spacer shapes that minimize and delay fouling development.

Erosion of oval elbows in turbulent particulate natural gas flow with different aspect ratio of cross-sections

In this study, the erosion of the oval elbow duct pipe due to the natural gas–solid particles in the turbulent flow (k-epsilon) by (CFD) is investigated with specific consideration to the effect of the oval aspect ratio. The natural gas–solid particle turbulent flow is simulated by utilizing the two-way coupling, Eulerian–Lagrangian approach; while an enhanced wall treatment method is used because the flow has unique behavior when is close to the walls. Effects of most important erosion variable like channel geometry change, natural gas rate, and velocity on the erosion rate in all geometries were evaluated and discussed. Simulation results were verified with existing experimental results of the circular duct. Our results show that the geometry change has a severe effect on the erosion rate, and also the pipe aspect ratio has a considerable effect on the Dean Flow, the particle path line, and finally, the erosion rate of the elbow channel. Particle trajectory shows that the particles have an intense focus on inside the convex wall of the high-aspect-ratio cross-sections. Our result shows that the erosion will be decreased by reducing the aspect ratio to 0.4.

Alignment of Nonspherical Active Particles in Chaotic Flows.

We study the orientation statistics of spheroidal, axisymmetric microswimmers, with shapes ranging from disks to rods, swimming in chaotic, moderately turbulent flows. Numerical simulations show that rodlike active particles preferentially align with the flow velocity. To explain the underlying mechanism, we solve a statistical model via the perturbation theory. We show that such an alignment is caused by correlations of fluid velocity and its gradients along particle paths combined with fore-aft symmetry breaking due to both swimming and particle nonsphericity. Remarkably, the discovered alignment is found to be a robust kinematical effect, independent of the underlying flow evolution. We discuss its possible relevance for aquatic ecology.

Coupled shallow-water fluid sloshing in an upright annular vessel

The coupled motion of shallow-water sloshing in a horizontally translating upright annular vessel is considered. The vessel’s motion is restricted to a single space dimension, such as for Tuned Liquid Damper systems. For particular parameters, the system is shown to support an internal 1 : 1 resonance, where the frequency of coupled sloshing mode which generates the vessel’s motion is equal to the frequency of a sloshing mode which occurs in a static vessel. Using a Lagrangian Particle Path formation, the fully nonlinear motion of the system is simulated using an efficient numerical symplectic integration scheme. The scheme is based on the implicit-midpoint rule which conserves energy and preserves the energy partition between the fluid and the vessel over many time-steps. Linear and nonlinear results are presented, including those showing the system transitioning to higher-frequency eigenmodes as the fluid depth is reduced.

Solids flow pattern in cold flow mockup of fluidized bed gasifier

We report solids flow pattern in a laboratory-scale fluidized bed of coal and ash mixtures. Suitable tracers were designed and deployed to determine the solids flow path of a typical particle through Radioactive Particle Tracking (RPT). Experiments were conducted in a cylindrical bed of 0.1 m in i.d. with two inventory compositions, namely, 70% Coal + 30% Bottom Ash (Composition I) and 20% Coal + 80% Bottom Ash (Composition II). Comparative analysis of RPT measurements yielded overall bed behavior, which was quantified in terms of time-averaged mean velocity, solids flux, RMS velocity, and kinetic energy per unit volume of the coal – bottom ash mixture. The mean axial velocity and solids flux profile indicated the influence of strong slugs on the solids flow patterns.