Continuum Of Particles Research Articles

Oncolytic viruses alter the biogenesis of tumor extracellular vesicles and influence their immunogenicity

Extracellular vesicles (EVs) are mediators of intercellular communication in the tumor microenvironment. Tumor EVs are commonly associated with metastasis, immunosuppression or drug resistance. Viral infections usually increase EV secretion, but little is known about the effect of oncolytic viruses (OVs) on tumor EVs. Here, we investigated the impact of oncolytic vesicular stomatitis virus (VSV) and vaccinia virus (VACV) on EVs secreted by human melanoma and thoracic cancer cells. We found that OV infection increases the production of EVs by tumor cells. These EVs contain proteins of viral origin, such as VSV-G, thus creating a continuum of particles sharing markers of both canonical EVs and viruses. As such, the presence of VSV-G on EVs improves the transfer of their protein content to cell types commonly found in the tumor microenvironment. A proteomic analysis also revealed that EVs-OV secreted during VSV infection are enriched in immunity-related proteins. Finally, CD8+ T cells incubated with EVs-OV from infected cells display slightly enhanced cytotoxic functions. Taken together, these data suggest that OVs enhance the communication mediated by tumor EVs, which could participate to the therapeutic efficacy of OVs. These results also provide rationale for engineering OVs to exploit EVs and disseminate therapeutic proteins within the tumor microenvironment.

A method to assess the cloud-aerosol transition zone from ceilometer measurements

Cloud and aerosol contribution to the Earth's radiative budget constitutes one of the most significant uncertainties in future climate projections. To distinguish between clouds and cloud-free air, atmospheric scientists have been using a wide range of instruments, techniques, and algorithms with various detection thresholds. However, since the change from a cloudy to a cloud-free atmosphere may be gradual and, in some cases, far from obvious, recent research is questioning where the threshold between both phases should be established. These considerations lead to contemplate a transition zone (TZ) between cloud and cloud-free conditions. In the present study, backscatter profiles obtained by a Vaisala CL31 ceilometer were processed to assess the transition zone. First, two widely used cloud detection algorithms were applied and compared: the method provided by the ceilometer manufacturer (Vaisala) and Cloudnetpy, the algorithm from ACTRIS Cloudnet, a project devoted to aerosol, clouds, and trace gases research. Second, a sensitivity analysis was applied to the backscatter and signal-to-noise ratio thresholds used for cloud detection in Cloudnetpy. This methodology has allowed us to assess the vertical distribution of clouds, aerosols, the TZ, and its frequency of occurrence. Results indicate a gradual transition in backscatter retrievals from cloud to cloud-free, where particles detected near cloud boundaries induced higher backscatter values than those found further away. Depending on the thresholds used, we observed a 9.3% (with an estimated range of uncertainty of 5.420%) variation in cloud occurrence which can be attributed to TZ conditions. Analysing the whole backscatter profile, we found as many TZ conditions as cloudy values, which emphasises the importance of studying the vertical distribution of the TZ. Moreover, the analysis of TZ occurrence in height and time revealed that such conditions concentrate below 800m during night periods, although annual height-hour distributions involve a remarkable variability among seasons. These findings highlight the importance of either including an additional phase between ‘pure clouds’ and ‘pure aerosols’ or treating them as a continuum of suspended particles in the atmosphere.

Toxicity assessment of environmental MPs and NPs and polystyrene NPs on the bivalve Corbicula fluminea using a multi-marker approach

Small plastic particles, microplastics (MPs) and nanoplastics (NPs) represent a major threat in aquatic environments. Freshwater organisms are exposed to MPs and NPs, particularly in industrial and urban areas. The present study aimed to compare the toxicity between polystyrene NPs (PS NPs) and environmental microplastics (ENV MPs) and nanoplastics (ENV NPs) generated from macro-sized debris collected in the Garonne River on the freshwater bivalve C. fluminea. The organisms were exposed to the different plastic particles at three environmentally relevant concentrations: 0.008, 10, and 100 μg L−1 for 21 days. The biological responses of organisms were assessed using a multi-biomarker approach from the sub-individual to the individual level. The results demonstrated that: i) ENV NPs triggered more effects on detoxification processes and immune response, confirming that using manufactured NPs for laboratory exposure can lead to misleading conclusions on the risks posed by plastic particles; ii) effects of ENV MPs were less marked than ENV NPs, emphasizing the importance of testing a size continuum of plastic particles from NPs to MPs; iii) some effects were only observed for the low and/or intermediate concentrations tested, underlining the importance of using environmentally relevant concentrations. In light of these results, laboratory studies should be continued by exposing aquatic species to environmental MPs and NPs. The properties of these particles have to be characterized for a better risk assessment of environmental plastic particles.

Specific surface area versus porosity from digital images: High-porosity granular samples

We micro-CT-scanned several granular packs, including glass beads of two different particle sizes and their mixtures, a natural dune sand, as well as two sieved samples of this sand and their mixtures. After segmenting these digital volumes into grains and pores, we computed their porosity (φ) and specific surface area (S). Moreover, we subsampled these segmented volumes and computed the respective φ and S of the subvolumes as well. The resulting data pairs exhibited fairly tight S versus φ trends. These trends, as observed among different samples, present a somewhat inconsistent picture. In some granular digital samples, S increases with increasing φ, while in others the opposite behavior is observed. To explain these behaviors, we analytically model the evolution of the pore-space geometry as that of a binary mixture of large and small particles. Where the small particles gradually fill the pores of an undisturbed large-particle frame, S becomes larger as φ reduces. The opposite behavior takes place where the disparate large particles are embedded into the continuum of the small particles. The smaller the number of the large particles the higher the porosity and the larger the specific surface area. Where the particles in a pack are of uniform size, S reduces with increasing φ. This theory quantitatively supports the observed experimental relations. The observed consistency between the experiment and theory means that the behaviors observed on microscopic samples are applicable at a much larger spatial scale.

Influence of trace level As or Ni on pyrite formation kinetics at low temperature

Pyrite formation at low temperature during early diagenesis in (sub-)surface sediments is an essential step of Fe and S biogeochemical cycles and the presence of this ubiquitous mineral of surface environments is often used as an indicator of paleo-redox conditions. Pathways of pyrite formation are usually discussed in environmental settings by involving a variety of nanosized Fe-S mineralogical precursors as a function of the local geochemical conditions. However, the influence of trace element impurities such as Ni and As in the solution at the time of pyrite formation has been poorly studied, whereas specific chemical signatures of trace elements are commonly observed in sedimentary pyrites. A better understanding of the impact of Ni and As incorporation at trace levels on pyrite formation is essential to help refining the use of these elements as paleo-redox indicators and to evaluate the role of pyrite as a sink regulating the biogeochemical cycle of potentially toxic trace elements. In this study, we have performed syntheses of pyrite at low temperature via the polysulfide pathway using aqueous Fe(III) and H2S in the presence of trace amounts of Ni(II) (0.001 mol%Fe) and As(III) (0.001 mol%Fe). Analysis of the solids collected at different time steps over the course of the experiments using X-Ray absorption spectroscopy at both the Fe and S K-edges shows that pyrite starts to precipitate within 5 days in presence of Ni(II) and within 32 days in presence of As(III), while the control experiment showed an intermediate precipitation rate of 14 days. Shell-by-shell analysis of Fe K-edge EXAFS data shows that the initial mineralogical precursors are the same in all the experiments and correspond to poorly-crystalline FeS (3.0 ± 0.1 Fe-S@2.25 Å; 1.7 ± 0.2 Fe-Fe@2.67 Å). In addition, XANES qualitative analysis suggests the incorporation of small amounts of Fe(III) within these FeS precursors. Synchrotron-based XRD and WAXS-PDF analysis of the starting solids show that in addition to S(0), the FeS precursors correspond to a continuum of FeS particles that ranges from tetragonal nanocrystalline FeS (a = 3.70(2) Å, c = 5.24(7) Å, MCDab = 41 ± 4 Å MCDc = 21 ± 2 Å) to cluster-type FeS (MCDabc < 8.4 ± 4.3 Å). We propose that Ni(II) and As(III) have a different type of interaction with these FeS precursors, resulting respectively in an increase and a decrease in the rate of pyrite nucleation. While Ni(II) would incorporate within the structure of the FeS precursors, As would interact with (poly)sulfides in solution to form thio-As, possibly binding or precipitating onto FeS surfaces and thus slowing FeS transformation to FeS2. Given that both Ni and As were introduced at trace levels in our experiments, these results suggest that the occurrence of trace amounts of impurities could have a strong influence on pyrite precipitation kinetics in natural settings such as pore-scale microenvironments. In addition to emphasizing the importance of trace elements such as Ni or As on the persistence of mobile colloidal FeS species in anoxic conditions, the results of the present study also point to the importance of considering the actual nature of the impurities when using pyrite composition for ancient environments and past climates reconstruction.

Extracellular Vesicles in Viral Infections: Two Sides of the Same Coin?

Extracellular vesicles are small membrane structures containing proteins and nucleic acids that are gaining a lot of attention lately. They are produced by most cells and can be detected in several body fluids, having a huge potential in therapeutic and diagnostic approaches. EVs produced by infected cells usually have a molecular signature that is very distinct from healthy cells. For intracellular pathogens like viruses, EVs can have an even more complex function, since the viral biogenesis pathway can overlap with EV pathways in several ways, generating a continuum of particles, like naked virions, EVs containing infective viral genomes and quasi-enveloped viruses, besides the classical complete viral particles that are secreted to the extracellular space. Those particles can act in recipient cells in different ways. Besides being directly infective, they also can prime neighbor cells rendering them more susceptible to infection, block antiviral responses and deliver isolated viral molecules. On the other hand, they can trigger antiviral responses and cytokine secretion even in uninfected cells near the infection site, helping to fight the infection and protect other cells from the virus. This protective response can also backfire, when a massive inflammation facilitated by those EVs can be responsible for bad clinical outcomes. EVs can help or harm the antiviral response, and sometimes both mechanisms are observed in infections by the same virus. Since those pathways are intrinsically interlinked, understand the role of EVs during viral infections is crucial to comprehend viral mechanisms and respond better to emerging viral diseases.

Calculation of Finely Dispersed Powder Mixing Process

An entropy approach-based model of kinetics of absorbing wall bounded continuum of particles of a suspension under treatment is proposed. Based on the model, calculation of the mixing process is substantiated, and analytical relationships are proposed for calculating the efficiency of finely dispersed powder mixing. Numerical experiment is conducted to check if the results of the quantitative analysis of the mixing process conform to the physical interpretation of the studied phenomenon.

Micropolar theory with production of rotational inertia: A farewell to material description

This paper takes a new look at micropolar media. Initially the necessary theoretical framework for a micropolar continuum is presented. To this end the standard macroscopic equations for mass, linear and angular momentum are complemented by a recently proposed kinetic equation for the moment of inertia tensor containing a production term. The main purpose of this paper is to study possible forms of this production term and its effects. For this reason two examples are investigated. In the first example we study a continuum of hollow particles subjected to an external pressure and gravity, such that the number of particles does not change. In the second example a continuous stream of matter through a crusher is considered so that the total number of particles will change. In context with these examples it will also become clear that the traditional Lagrangian way of describing the motion of solids is no longer adequate and should be superseded by an Eulerian approach.

Extended Galilean symmetries of non-relativistic strings

We consider two non-relativistic strings and their Galilean symmetries. These strings are obtained as the two possible non-relativistic (NR) limits of a relativistic string. One of them is non-vibrating and represents a continuum of non-relativistic massless particles, and the other one is a non-relativistic vibrating string. For both cases we write the generator of the most general point transformation and impose the condition of Noether symmetry. As a result we obtain two sets of non-relativistic Killing equations for the vector fields that generate the symmetry transformations. Solving these equations shows that NR strings exhibit two extended, infinite dimensional space-time symmetries which contain, as a subset, the Galilean symmetries. For each case, we compute the associated conserved charges and discuss the existence of non-central extensions.

Steady States of Rotating Stars and Galaxies

A rotating continuum of particles attracted to each other by gravity may be modeled by the Euler--Poisson system. The existence of solutions is a very classical problem. Here it is proven that a cu...

РЕГУЛЯРНЫЕ КОНТИНУАЛЬНЫЕ СИСТЕМЫ ТОЧЕЧНЫХ ЧАСТИЦ. I: СИСТЕМЫ БЕЗ ВЗАИМОДЕЙСТВИЯ

Normally in mathematics and physics only point particle systems, which are either finite or countable, are studied. We introduce new formal mathematical object called regular continuum system of point particles (with continuum number of particles). Initially each particle is characterized by the pair: (initial coordinate, initial velocity) in \(R^{2d}\). Moreover, all initial coordinates are different and fill up some domain in \(R^{d}\). Each particle moves via normal newtonian dynamics under influence of sone external force, but there is no interaction between particles. If the external force is bounded then trajectories of any two particles in the phase space do not intersect. More exactly, at any time moment any two particles have either different coordinates or different velocities. The system is called regular if there are no particle collisions in the coordinate space. The regularity condition is necessary for the velocity of the particle, situated at a given time at a given space point, were uniquely defined. Then the classical Euler equation for the field of velocities has rigorous meaning. Though the continuum of particles is in fact a continuum medium, the crucial notion of regularity was not studied in mathematical literature. It appeared that the seeming simplicity of the object (absence of interaction) is delusive. Even for simple external forces we could not find simple necessary and sufficient regularity conditions. However, we found a rich list of examples, one dimensional and many dimensional, where we get regularity conditions on different time intervals. In conclusion we formulate many perspective problems for regular systems with interaction.

Dark matter from spacetime nonlocality

We propose that dark matter is not yet another new particle in nature, but that it is a remnant of quantum gravitational effects on known fields. We arrive at this possibility in an indirect and surprising manner: by considering retarded, nonlocal, and Lorentzian evolution for quantum fields. This is inspired by recent developments in causal set theory, where such an evolution shows up as the continuum limit of scalar field propagation on a background causal set. Concretely, we study the quantum theory of a massless scalar field whose evolution is given not by the the d'Alembertian $\ensuremath{\square}$, but by an operator $\stackrel{\texttildelow{}}{\ensuremath{\square}}$ which is Lorentz invariant, reduces to $\ensuremath{\square}$ at low energies, and defines an explicitly retarded evolution: $(\stackrel{\texttildelow{}}{\ensuremath{\square}}\ensuremath{\phi})(x)$ only depends on $\ensuremath{\phi}(y)$, where $y$ is in the causal past of $x$. This modification results in the existence of a continuum of massive particles, in addition to the usual massless ones, in the free theory. When interactions are introduced, these massive or off-shell quanta can be produced by the scattering of massless particles, but once produced, they no longer interact, which makes them a natural candidate for dark matter.

Velocity Reversal Criterion of a Body Immersed in a Sea of Particles

We consider a rigid body colliding with a continuum of particles. We assume that the body is moving at a velocity close to an equilibrium velocity V_{\infty} and that the particles colliding with the body reflect diffusely, that is, probabilistically with some probablility distribution K. We find a condition that is sufficient and almost necessary that the collective force of the colliding particles reverses the relative velocity V(t) of the body, that is, changes the sign of V(t)-V_{\infty}, before the body approaches equilibrium. Examples of both reversal and irreversal are given. This is in strong contrast with the pure specular reflection case in which only reversal happens.

Convergence to Equilibrium of a Body Moving in a Kinetic Sea

We consider a continuum of particles that are acted upon by an external force $\mathbf{G}(t,\mathbf{x})$ and that collide with a rigid body. The body itself is subject to a constant force $E$ as well as to the collective force of interaction with the particles. We assume that the particles that collide with the body reflect probabilistically with some probablility distribution $K(v,u)$. Under certain conditions on $\mathbf{G}(t,\mathbf{x})$ and $K(v,u)$, we identify an equilibrium velocity $V_{\infty }$ of the body and we prove that this equilibrium is asymptotically stable.

Quantum Potential Energy as Concealed Motion

It is known that the Schroedinger equation may be derived from a hydrodynamic model in which the Lagrangian position coordinates of a continuum of particles represent the quantum state. Using Routh\s method of ignorable coordinates it is shown that the quantum potential energy of particle interaction that represents quantum effects in this model may be regarded as the kinetic energy of additional concealed freedoms. The method brings an alternative perspective to Planck\s constant, which plays the role of a hidden variable, and to the canonical quantization procedure, since what is termed kinetic energy in quantum mechanics may be regarded literally as energy due to motion.

A new model of a micropolar continuum and some electromagnetic analogies

A new model of micropolar continuum composed of two-spin particles is considered. In fact, this continuum represents a two-component continuum. The first component possesses the translational and rotational degrees of freedom, whereas the second component has only the rotational degrees of freedom. The main characteristic feature of the suggested model is that both the components are not infinitesimal rigid bodies. They are the body-points of a general type, which differ from infinitesimal rigid bodies by additional inertia parameters. A continuum, composed of such particles, has some additional properties compared with a conventional material. We suggest to use the continuum of two-spin particles as a mechanical model (or, in other words, a mechanical analogy) of the electromagnetic field in matter. This model does not pretend to be an explanation of the physical nature of electromagnetic phenomena. The interpretations of the electric charge, the electric field vector, the magnetic induction vector, and other physical quantities, which are given in accordance with the suggested model, are no more than the mechanical analogies. We show that the mathematical description of our model contains two special cases. Under one simplifying assumption, the suggested equations are reduced to the equations similar to Maxwell’s equations. Under another simplifying assumption, an analogue of the Lorentz force is obtained. We believe that in some cases the exact equations describing our mechanical model can be of interest for applications in electrodynamics.

Approach to Equilibrium of a Body Colliding Specularly and Diffusely with a Sea of Particles

We consider a rigid body acted upon by two forces, a constant force and the collective force of interaction with a continuum of particles. We assume that some of the particles that collide with the body reflect elastically (specularly), while others reflect probabilistically with some probablility distribution K. We find that the rate of approach of the body to equilibrium is O(t^{-3-p}) in three dimensions where p can take any value from 0 to 2, depending on K.

The continuum limit of gl(M|N) spin chains

We study the spectrum of an integrable antiferromagnetic Hamiltonian of the gl(M|N) spin chain of alternating fundamental and dual representations. After extensive numerical analysis, we identify the vacuum and low lying excitations and with this knowledge perform the continuum limit, while keeping a finite gap. All gl(n+N|N) spin chains with n,N>0 are shown to possess in the continuum limit 2n-2 multiplets of massive particles which scatter with gl(n) Gross-Neveu like S-matrices, namely their eigenvalues do not depend on N. We argue that the continuum theory is the gl(M|N) Gross-Neveu model. We then look for remaining particles in the gl(2m|1) chains. The results suggest there is a continuum of such particles, which in order to be fully understood require finite volume calculations.

Algebraic and exponential instabilities in a sheared micropolar granular fluid

Based on a micropolar continuum of rough granular particles that takes into account the balance equations for the spin (/rotational) velocity and the spin granular temperature, the linear stability characteristics of an unbounded shear flow (.

Continuum model of abrasive layer in an abrasive wear test

In order to find out the relationship between driving torque and thickness of abrasive layer of a three-body abrasive wear system, a continuum model of abrasive layer was proposed. The model is based on the assumption of continuum of abrasive particles and a continuous contact pressure distribution was obtained. A sand crushing test was designed to get compressive behavior of the abrasive layer. The test was used to understand the loading–unloading–reloading behavior and the constitutive relationship between compressive displacement and compressive loading. The macro-contact pressure distribution of the abrasive wear between the cylinder–cylinder and cylinder–plane was obtained based on the sand compressive behavior. With the sand compressive behavior, an FEA model has been built for ring-on-ring abrasive wear test machine to simulate the normal contact pressure distribution and friction force. To verify the model, a set of experiments was conducted. Quartz sands were used as abrasives in the analysis and test. The measurement of torque accorded well with model prediction. With this model, only a simple sand crushing test is needed to obtain the relationship between driving torque and thickness of abrasive layer which is important for wear prediction of a three-body abrasive wear system.