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Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 170
Author(s):  
Panayiotis Vafeas ◽  
Eleftherios Protopapas ◽  
Maria Hadjinicolaou

Modern engineering technology often involves the physical application of heat and mass transfer. These processes are associated with the creeping motion of a relatively homogeneous swarm of small particles, where the spheroidal geometry represents the shape of the embedded particles within such aggregates. Here, the steady Stokes flow of an incompressible, viscous fluid through an assemblage of particles, at low Reynolds numbers, is studied by employing a particle-in-cell model. The mathematical formulation adopts the Kuwabara-type assumption, according to which each spheroidal particle is stationary and it is surrounded by a confocal spheroid that creates a fluid envelope, in which the Newtonian fluid moves with a constant velocity of arbitrary orientation. The boundary value problem in the fluid envelope is solved by imposing non-slip conditions on the surface of the spheroid, which is also considered as non-penetrable, while zero vorticity is assumed on the fictitious spheroidal boundary along with a uniform approaching velocity. The three-dimensional flow fields are calculated analytically for the first time, in the spheroidal geometry, by virtue of the Papkovich–Neuber representation. Through this, the velocity and the total pressure fields are provided in terms of a vector and the scalar spheroidal harmonic potentials, which enables the thorough study of the relevant physical characteristics of the flow fields. The newly obtained analytical expressions generalize to any direction with the existing results holding for the asymmetrical case, which were obtained with the aid of a stream function. These can be employed for the calculation of quantities of physical or engineering interest. Numerical implementation reveals the flow behavior within the fluid envelope for different geometrical cell characteristics and for the arbitrarily-assumed velocity field, thus reflecting the different flow/porous media situations. Sample calculations show the excellent agreement of the obtained results with those available for special geometrical cases. All of these findings demonstrate the usefulness of the proposed method and the powerfulness of the obtained analytical expansions.


Author(s):  
Pierre Monmarché ◽  
Lucas Journel

We establish the convergences (with respect to the simulation time $t$; the number of particles $N$; the timestep $\gamma$) of a Moran/Fleming-Viot type particle scheme toward the quasi-stationary distribution of a diffusion on the $d$-dimensional torus, killed at a smooth rate. In these conditions, quantitative bounds are obtained that, for each parameter ($t\rightarrow \infty$, $N\rightarrow \infty$ or $\gamma\rightarrow 0$) are independent from the two others. p, li { white-space: pre-wrap; }


2021 ◽  
Vol 4 (1) ◽  
pp. 1-1
Author(s):  
Saikat Banerjee ◽  
◽  
Naveen Prasad ◽  
Sivamani Selvaraju ◽  
◽  
...  

Biogas is an alternative to gaseous biofuels and is produced by the decomposition of biomass from substances such as animal waste, sewage sludge, and industrial effluents. Biogas is composed of methane, carbon dioxide, nitrogen, hydrogen, hydrogen sulfide, and oxygen. The anaerobic production of biogas can be made cheaper by designing a high throughput reactor and operating procedures. The parameters such as substrate type, particle size, temperature, pH, carbon/nitrogen (C/N) ratio, and inoculum concentration play a major role in the design of reactors to produce biogas. Multistage systems, batch, continuous one-stage systems, and continuous two-stage systems are the types of digesters used in the industry for biogas production. A comprehensive review of reactor design for biogas production is presented in the manuscript.


2021 ◽  
pp. 739-750
Author(s):  
Muhammad Ayaz Akbar ◽  
Wai On Wong

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1094
Author(s):  
Benita Ortega-Berlanga ◽  
Lourdes Betancourt-Mendiola ◽  
César del Angel-Olarte ◽  
Luis Hernández-Adame ◽  
Sergio Rosales-Mendoza ◽  
...  

In the last decade, the publications presenting novel physical and chemical aspects of gadolinium-based oxide (Gd2O3) and oxysulfide (Gd2O2S) particles in the micro- or nano-scale have increased, mainly stimulated by the exciting applications of these materials in the biomedical field. Their optical properties, related to down and upconversion phenomena and the ability to functionalize their surface, make them attractive for developing new probes for selective targeting and emergent bioimaging techniques, either for biomolecule labeling or theranostics. Moreover, recent reports have shown interesting optical behavior of these systems influenced by the synthesis methods, dopant amount and type, particle shape and size, and surface functionality. Hence, this review presents a compilation of the latest works focused on evaluating the optical properties of Gd2O3 and Gd2O2S particles as a function of their physicochemical and morphological properties; and also on their novel applications as MRI contrast agents and drug delivery nanovehicles, discussed along with their administration routes, biodistribution, cytotoxicity, and clearance mechanisms. Perspectives for this field are also identified and discussed.


Author(s):  
José A. Carrillo ◽  
Young-Pil Choi

AbstractWe rigorously derive pressureless Euler-type equations with nonlocal dissipative terms in velocity and aggregation equations with nonlocal velocity fields from Newton-type particle descriptions of swarming models with alignment interactions. Crucially, we make use of a discrete version of a modulated kinetic energy together with the bounded Lipschitz distance for measures in order to control terms in its time derivative due to the nonlocal interactions.


Cells ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 1085
Author(s):  
Joseph Ndika ◽  
Piia Karisola ◽  
Pia Kinaret ◽  
Marit Ilves ◽  
Harri Alenius

Perturbations in cellular molecular events and their associated biological processes provide opportunities for hazard assessment based on toxicogenomic profiling. Long non-coding RNAs (lncRNAs) are transcribed from DNA but are typically not translated into full-length proteins. Via epigenetic regulation, they play important roles in organismal response to environmental stress. The effects of nanoparticles on this important part of the epigenome are understudied. In this study, we investigated changes in lncRNA associated with hazardous inhalatory exposure of mice to 16 engineered nanomaterials (ENM)–4 ENM (copper oxide, multi-walled carbon nanotubes, spherical titanium dioxide, and rod-like titanium dioxide particles) with 4 different surface chemistries (pristine, COOH, NH2, and PEG). Mice were exposed to 10 µg of ENM by oropharyngeal aspiration for 4 consecutive days, followed by cytological analyses and transcriptomic characterization of whole lung tissues. The number of significantly altered non-coding RNA transcripts, suggestive of their degrees of toxicity, was different for each ENM type. Particle surface chemistry and shape also had varying effects on lncRNA expression. NH2 and PEG caused the strongest and weakest responses, respectively. Via correlational analyses to mRNA expression from the same samples, we could deduce that significantly altered lncRNAs are potential regulators of genes involved in mitotic cell division and DNA damage response. This study sheds more light on epigenetic mechanisms of ENM toxicity and also emphasizes the importance of the lncRNA superfamily as toxicogenomic markers of adverse ENM exposure.


2021 ◽  
Author(s):  
Megha Srinivas ◽  
Preeti Sharma ◽  
Siddharth Jhunjhunwala

Particles injected intravenously are thought to be cleared by macrophages residing in the liver and spleen, but they also encounter circulating immune cells. It remains to be determined if the circulating cells can take up particles while flowing in the blood. Here, we use an in vitro peristaltic pump setup that mimics pulsatile blood flow to establish if immune cells take up particles under constant fluidic flow. Our results show that the immune cells do phagocytose under flow conditions, and the uptake depends on the cell type, particle size, and flow rate. We demonstrate that cell lines representing myeloid cells, and primary neutrophils and monocytes are similar or better at taking up sub-micrometer-sized particles under flow compared to static conditions. Experiments with whole blood show that even under the crowding effects of red blood cells, neutrophils and monocytes take up particles while flowing. These data suggest that therapeutics may be delivered to circulating immune cells using particulate delivery systems.


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