Particle Theory Research Articles

Boosting unstable particles

In relativity, there is no absolute notion of simultaneity, because two clocks that are in different places can always be desynchronized by a Lorentz boost. Here, we explore the implications of this effect for the quantum theory of unstable particles. We show that, when a wavefunction is boosted, its tails travel one to the past and the other to the future. As a consequence, in the new frame of reference, the particle is in a quantum superposition "decayed + non decayed", where the property "decayed-ness" is entangled with the position. Since a particle cannot be localised in a region smaller than the Compton wavelength, there is a non-zero lower bound on this effect, which is fundamental in nature. The surprising implication is that, in a quantum world, decay probabilities can never be Lorentz-invariant. We show that this insight was the missing ingredient to reconcile the seemingly conflicting views about time dilation in relativistic quantum mechanics and quantum field theory.

Mechanisms of Anisotropic Particle Deposition: Prolate Spheroid Layers on Mica

Anisotropic particle deposition was investigated using the streaming potential method complemented with the atomic force microscopy (AFM) determination of the absolute particle coverage. The polymer particles were synthesized using the stretching procedure with consecutive oxidation of surface hydroxyl groups and coupling of polyethyleneimine. The bulk particle physicochemical properties were characterized by scanning electron microscopy (SEM), dynamic light scattering, and laser Doppler velocimetry. The particles were positively charged in the pH range of 3–10, exhibiting a prolate spheroid shape with an axis ratio of five. Thorough AFM and in situ optical microscopy measurements yielded the adsorption kinetics of particles under the diffusion-controlled regime. The experimental data were adequately interpreted in terms of the random sequential adsorption model with the surface blocking function derived from the scaled particle theory. The root-mean-square (rms) parameter of the layers for a broad range of particle coverage was also determined and interpreted using the topographical model developed in this work. The experiments were complemented by the measurements of the streaming potential of particle layers under various ionic strengths and pHs. The ζ (zeta)-potential data acquired in this way enabled to determine the universal hydrodynamic function describing the dependence of the streaming potential on the particle coverage. The function was used to express the ζ-potential of surfaces covered by particles in terms of substrate rms. It was argued that the acquired results, in addition to being significanct to basic science, can be exploited as useful reference systems for quantitative interpretation of bioparticle deposition on abiotic surfaces.

Interacting Loop Ensembles and Bose Gases

We study interacting Bose gases in thermal equilibrium on a lattice. We establish convergence of the grand-canonical Gibbs states of such gases to their mean-field (classical field) and large-mass (classical particle) limits. The former is a classical field theory for a complex scalar field with quartic self-interaction. The latter is a classical theory of point particles with two-body interactions. Our analysis is based on representations in terms of ensembles of interacting random loops, the Ginibre loop ensemble for Bose gases and the Symanzik loop ensemble for classical scalar field theories. For small enough interactions, our results also hold in infinite volume. The results of this paper were previously sketched in Fröhlich et al. (J Stat Phys 180(1–6):810–831, 2020).

Enhancing flotation separation of fine copper oxide from silica by microbubble assisted hydrophobic aggregation

One of the main challenges facing the flotation of base metal oxide minerals is their fine sizes of particles as a result of fine grinding to achieve a desired degree of liberation for low-grade and finely disseminated complex ores. This study aims at studying hydrophobic aggregation and in situ gas nucleation of fine copper oxides with sodium dodecyl sulfate (SDS) as a selective collector to enhance CuO recovery. Experimental results by in situ and real time particle size measurement using focused beam reflectance measurement (FBRM) coupled with particle vision measurement (PVM) showed an enhanced aggregation of fine CuO by SDS adsorption. Particle aggregation assisted by gas nuclei which were generated in situ on CuO by high intensity agitation (HIA) was visualized by total internal reflection fluorescence microscopy (TIRFM). It is the enhanced aggregation with nanobubbles as bridges that improved its recovery from fine silica. Coupled with the calculation using the extended DLVO theory, contact angle and zeta potential of fine particles were measured to understand the critical role of hydrophobic forces in aggregation of fine CuO particles. The copper ions dissolved from the fine copper oxide were found to inadvertently activate fine silica flotation which could be effectively depressed by ethylene diamine tetraacetic acid (EDTA). A combination of SDS with EDTA was proposed and demonstrated to achieve selective recovery of fine copper oxide from fine silica gangue. The results from this study provide directions for enhancing copper recovery from low grade and finely disseminated copper oxidize ores, in particular from tenorite ores.

Spin 2 Particle with Anomalous Magnetic Moment in Riemann Space−Time: A Massless Case with the Gauge Symmetry

The most of studies in the theory of spin 2 field were performed with the use of the 2-nd order equations. The spin 2 particle theory proposed by F.I. Fedorov is based on the first order equations requires a 30-component set of tensors. Besides, by him and coauthors was elaborated a more general theory, which is based on 50-component set of tensors. In the present paper, we consider this more general theory in presence of arbitrary electromagnetic fields and Riemannian space-time backgrounds. First we study the 50-component theory for a massive particle. In this case, there arises the non-minimal interaction with the curved space-time background through the Ricci and Riemann tensors. It is important that the theory under consideration allows for a new massless limit for the spin 2 field. This fact is of special interest, because the conventional Pauli - Fierz theory for the massless field does not possess gauge symmetry in the curved space-time, in particular, in models with the vanishing Ricci tensor. We show that the generalized theory possesses such a gauge symmetry in all space-time models for which the Ricci tensor vanishes.

Augmented scaled particle theory for a hard disk fluid

The success of scaled particle theory (SPT) can be certainly ascribed to the appealing physical idea embedded in it, i.e., accounting for the work needed to insert a particle into a liquid by a bulk contribution and a surface contribution. So, it can describe bulk and surface thermodynamic properties in the same framework. The surface tension term in SPT involves one flat-surface contribution and two additional contributions due to surface curvatures. High-order curvature terms (also called non-Hadwiger terms) were evidenced. Recently, we have developed an augmented scaled particle theory (ASPT) by adding one high-order curvature term for a hard sphere fluid. Here, we extend ASPT to a two-dimensional hard disk fluid. As for the 3D case, our 2D ASPT allows for improving both bulk and surface thermodynamic properties of a hard disk fluid with respect to the original SPT.

LEGIONNAIRES DISEASE: A CASE WITH SEVERE NEUROLOGIC AND RENAL INVOLVEMENT

LEGIONNAIRES DISEASE: A CASE WITH SEVERE NEUROLOGIC AND RENAL INVOLVEMENT

Active particles driven by competing spatially dependent self-propulsion and external force

We investigate how the competing presence of a nonuniform motility landscape and an external confining field affects the properties of active particles. We employ the active Ornstein-Uhlenbeck particle (AOUP) model with a periodic swim-velocity profile to derive analytical approximations for the steady-state probability distribution of position and velocity, encompassing both the Unified Colored Noise Approximation and the theory of potential-free active particles with spatially dependent swim velocity recently developed. We test the theory by confining an active particle in a harmonic trap, which gives rise to interesting properties, such as a transition from a unimodal to a bimodal (and, eventually multimodal) spatial density, induced by decreasing the spatial period of the self propulsion. Correspondingly, the velocity distribution shows pronounced deviations from the Gaussian shape, even displaying a bimodal profile in the high-motility regions. We thus show that the interplay of two relatively simple physical fields can be employed to generate complex emerging behavior.

The fundamentality of fields

There is debate as to whether quantum field theory is, at bottom, a quantum theory of fields or particles. One can take a field approach to the theory, using wave functionals over field configurations, or a particle approach, using wave functions over particle configurations. This article argues for a field approach, presenting three advantages over a particle approach: (1) particle wave functions are not available for photons, (2) a classical field model of the electron gives a superior account of both spin and self-interaction as compared to a classical particle model, and (3) the space of field wave functionals appears to be larger than the space of particle wave functions. The article also describes two important tasks facing proponents of a field approach: (1) legitimize or excise the use of Grassmann numbers for fermionic field values and in wave functional amplitudes, and (2) describe how quantum fields give rise to particle-like behavior.

Effect of combined roundness and polydispersity on the phase behavior of hard-rectangle fluids.

We introduce a model for a fluid of polydisperse rounded hard rectangles where the length and width of the rectangular core are fixed, while the roundness is taken into account by the convex envelope of a disk displaced along the perimeter of the core. The diameter of the disk has a continuous polydispersity described by a Schulz distribution function. We implemented the scaled particle theory for this model with the aim of studying: (i) the effect of roundness on the phase behavior of the one-component hard-rectangle fluid and (ii) how polydispersity affects phase transitions between isotropic, nematic, and tetratic phases. We found that roundness greatly affects the tetratic phase, whose region of stability in the phase diagram strongly decreases as the roundness parameter is increased. Also, the interval of aspect ratios where the tetratic-nematic and isotropic-nematic phase transitions are of first order considerably reduces with roundness, both transitions becoming weaker. Polydispersity induces strong fractionation between the coexisting phases, with the nematic phase enriched in particles of lower roundness. Finally, for high enough polydispersity and certain mean aspect ratios, the isotropic-to-nematic transition can change from second (for the one-component fluid) to first order. We also found a packing-fraction inversion phenomenon for large polydispersities: the coexisting isotropic phase has a higher packing fraction than the nematic.

Constants of motion in the theory of energetic particles propagating through magnetic turbulence

Constants of motion in the theory of energetic particles propagating through magnetic turbulence

Virus models in complex frameworks: Towards modeling space patterns of SARS-CoV-2 epidemics

This paper deals with the micro–macro-derivation of virus models coupled with a reaction–diffusion system that generates the dynamics in space of the virus particles. The first part of the presentation focuses, starting from [N. Bellomo, K. Painter, Y. Tao and M. Winkler, Occurrence versus absence of taxis-driven instabilities in a May–Nowak model for virus infection, SIAM J. Appl. Math. 79 (2019) 1990–2010; N. Bellomo and Y. Tao, Stabilization in a chemotaxis model for virus infection, Discrete Contin. Dyn. Syst. S 13 (2020) 105–117], on a survey and a critical analysis of some phenomenological models known in the literature. The second part shows how a Hilbert type can be developed to derive models at the macro-scale from the underlying description delivered by the kinetic theory of active particles. The third part deals with the derivation of macroscopic models of various virus models coupled with the reaction–diffusion systems. Then, a forward look to research perspectives is proposed.

An experimental investigation on the magnetoviscous effect and shear rate-dependent viscosity of a magnetic suspension under longitudinal and transverse magnetic fields

In the present investigation, we report experimental evidence that the magnetoviscous effect of a ferrofluid can be described by a suspension of ellipsoidal particles. The studies are carried out in shear and pipe flows, and comparison with theory for non-spherical particle is made. Flows of this type appear in many applications where magnetic fluids are used as lubricants or magnetic seals. The chain-like aggregates present in the magnetic fluid are modeled as equivalent prolate spheroids. A power-law correlation accounts for the breakup of aggregates due to the shear flow. The viscosity of a real ferrofluid is measured in a parallel disk rheometer with an applied magnetic field parallel to velocity gradient and in a capillary viscometer with a field in the velocity direction. An asymptotic solution for the low Péclet number limit presents an excellent agreement with the experimental results in this regime, while the numerical results provide a good agreement up to moderate values of Péclet. In addition, the numerical results for the non-dimensional viscosity of the fluid and the magnetic increment viscosity are verified by comparing results with the experimental measurements of the same quantities for moderate values of the Péclet number. The relative importance of the mean stresslet and rotlet contributions for the non-dimensional magnetic suspension viscosity is also examined in a regime of low Péclet number. The results also were important to verify our previous theoretical work presented recently in a companion paper Sinzato and Cunha [Phys. Fluids 33, 102006 (2021)] for the regime of Pe < 1.

Effect of choline lactate ionic liquid as entrainer on the thermodynamic properties of alcohols + water azeotropic mixtures

Ionic liquids could be used as entrainer in the azeotropic mixture separation process efficiently. Accordingly, the thermodynamic properties of ionic liquid choline lactate ([Ch][Lac]) as a potential entrainer have been studied in different azeotropic mixtures. In this respect, the density and speed of sound for binary systems containing (water + [Ch][Lac]) (ethanol/ 1-propanol/ 2-propanol) + [Ch][Lac])] and also ternary systems with different mass percent from alcohol-containing (water + alcohol + [Ch][Lac]) have been measured under a pressure 871 hPa at different temperatures T = (288.15 to 318.15) K. These data are used to calculate standard partial molar volume (Vφ0), and the limiting apparent molar compressibility (κφ0) using the Redlich-Mayer model besides the intermolecular free length (Lf) and relative association (RA) to interpret the existing interaction in the azeotropic mixture of the studied alcohols. Also, the scaled particle theory is used as a microscopic approach. All of the properties have been analyzed to interpret the interactions between the components of the mixture and 2-propanol has stronger interactions with the [Ch][Lac] in the azeotrope composition. The results suggest that the [Ch][Lac] could be used as an entrainer to separate 2-propanol more efficiently rather than the other studied alcohols.

Classical Limits of Light Quanta

It is argued that from a formal point of view, the classical limit of light quanta or photons is not that of a point-like particle but that of a geometric ray. According to this view, standard particle-wave dualism, which is often used in schools to describe the quantum behavior of massive objects, could be replaced by a ray-wave dualism (or even a particle-ray-wave trialism), which seems to be more appropriate for massless quantum objects such as photons. We compare the limits leading from quantum electrodynamics to a classical (Hamiltonian) theory of particles for electrons with those leading from photons via Maxwell’s equations to geometric ray optics. We also discuss the question to which extent Maxwell’s theory for electromagnetic waves should be considered as being on the same formal level as Schrödinger’s or Dirac’s theory.

Three-dimensional simulation of silted-up dam-break flow striking a rigid structure

Different from the clear water dam-break flow, flow patterns and multiphase interactions of the silted-up dam-break flow are always more complicated, hence it may lead to more potential hazards. In this paper, three-dimensional numerical simulations of the silted-up dam-break flow striking a rigid structure are carried out by using a proposed Eulerian-Eulerian multiphase model, coupling kinetic particle theory (KPT) and computational fluid dynamics (CFD). The coupled level set and volume of fluid (CLSVOF) method and an advection-diffusion equation are employed to capture the air-water interface and sediment transport, respectively. Modified momentum equations suitable to the two-fluid method are solved by OpenFOAM, an open-source package based on fixed unstructured mesh. Furthermore, rheology-based constitutive equations of sediment are also taken into account for the simulation of scouring and deposition. The results of the benchmark case agree well with those in published papers, which demonstrates that the proposed model can effectively simulate gravity-dominated collapse flow while considering the multi-interface capturing problems. Subsequently, the Eulerian-Eulerian multiphase model is used to reproduce the problems of three-dimensional silted-up dam-break flow striking a rigid structure, mainly focusing on the aspects of front propagation, violent free surface deformation, sediment movement, dynamic pressure loads and sediment deposition. Four scenarios in the downstream are considered: dry bed, a tailwater sill, a short obstacle, and a vertical cylinder. In addition, the effects of the height of the silted-up sediment on dam-break flow are investigated numerically.

Inside and out: Surface thermodynamics from positive to negative curvature.

To explore the curvature dependence of solid-fluid interfacial thermodynamics, we calculate, using Grand Canonical Monte Carlo simulation, the surface free energy for a 2d hard-disk fluid confined in a circular hard container of radius R as a function of the bulk packing fraction η and wall curvature C̄=-1/R. (The curvature is negative because the surface is concave.) Combining this with our previous data [Martin et al., J. Phys. Chem. B 124, 7938-7947 (2020)] for the positive curvature case (a hard-disk fluid at a circular wall, C̄=+1/R), we obtain a complete picture of surface thermodynamics in this system over the full range of positive and negative wall curvatures. Our results show that γ is linear in C̄ with a slope that is the same for both positive and negative wall curvatures, with deviations seen only at high negative curvatures (strong confinement) and high density. This observation indicates that the surface thermodynamics of this system is consistent with the predictions of so-called morphometric thermodynamics at both positive and negative curvatures. In addition, we show that classical density functional theory and a generalized scaled particle theory can be constructed that give excellent agreement with the simulation data over most of the range of curvatures and densities. For extremely high curvatures, where only one or two disks can occupy the container at maximum packing, it is possible to calculate γ exactly. In this limit, the simulations and density functional theory calculations are in remarkable agreement with the exact results.

A kinetic modeling of crowd evacuation with several groups in complex venues

The evacuation of human crowds consisting of several groups in complex venues is studied, in this paper, by the kinetic theory of active particles. We consider a complex venue that consists of several chambers which are separated by interior walls and doors, for which the geometrical effects may come from the walls both on the boundary and inside the domain, the exits, and the doors connecting the chambers. The geometrical properties are incorporated in the geometrical preferred direction, which is specified such that an individual can avoid the wall and approach the exit through the evacuation vector. The notion of group is corresponding to the concept of functional subsystem in the mathematical theory of active particles. In the present framework of several groups, the rules of interactions can be specified for both the interactions among the same group and the interactions between different groups. Furthermore, the motility is assigned for each group, which serves as the average activity of a group. Some interesting features and phenomena are shown in the numerical tests of the evacuation of a crowd with one, two or three groups.

On the relationship between volume fluctuations in liquids and the Gibbs free energy of cavity formation

Microscopic volume fluctuations in liquids are a reflection of their structure and intermolecular energy. Microscopic volume fluctuations in liquids are associated with cavity formation. The latter is considered of fundamental importance for the solvation process. The relationship between volume fluctuations and cavity formation is investigated in the present study. Scaled particle theory calculations provide a relationship between the Gibbs free energy of cavity formation and the average density fluctuations in volume at 298 K. The already foreseen correlation between the Gibbs free energy of cavity formation and the isothermal compressibility is confirmed and adjusted using no less than 200 liquids, covering a large category of organic compounds, plus water.

Volume properties of tetramethylenediethylenetetramine (pharmaceutical teotropine) in aqueous solutions between 278.15 and 318.15 K

The densities of aqueous solutions of tetramethylenediethylenetetramine (the teotropine pharmaceutical) with the solute molality from (0.01 to 0.12) mol·(kg water)−1 were measured at T = (278.15, 288.15, 298.15, 308.15, and 318.15) K and p = 0.1 MPa. The uncertainty in density measured using the Anton Paar DMA 5000 M densimeter (equipped with an oscillating U-tube) was estimated to be 0.03 kg m−3 or lower. The standard (apparent at infinite dilution) molar volumes and expansibilities of teotropine were computed. Based on the analysis of contributions to the standard molar volume in terms of the Scaled Particle Theory was confirmed that a bulkier molecule of teotropine interacts with water stronger than it does a molecule of urotropine or hexamethylenetetramine – the related aminal (cage-like) compound.