SPH Modeling of Solid Boundaries Through a Semi-Analytic Approach

Abstract:This paper presents a general semi-analytic approach for modeling solid boundaries in the SPH method: boundaries are here considered as a material continuum with a suitable distribution of velocity and pressure; their contributions to each term of the SPH mass and momentum equations can be expressed in terms of a suitable integral extended to the part of the sphere of influence of the particle delimited by the boundary surface. Analytical details with reference to a slightly compressible viscous Newtonian fluid in three dimensions are given. The validity of the method is checked by comparing the obtained numerical results with available experimental data in a benchmark flow case

The dissolution of monosodium urate monohydrate crystals: formulation of a biocompatible buffer solution with potential use in the treatment of gouty arthropathies

The dissolving abilities (DAs) of several aqueous media for microcrystalline monosodium urate monohydrate (MSU, NaC5N4O3H3·H2O) have been investigated using UV spectrophotometry for quantitative analytical determinations and X-ray diffraction, scanning electron microscopy and polarized light optical microscopy to assess structural aspects. High DAs were found for a buffer labeled TMT which contains tris(hydroxymethyl)aminomethane (TRIS), tris(hydroxymethyl)aminomethane hydrochloride (TRIS·HCl), D-mannitol (MAN) and taurine (TAU) and gave DA30=1298(5) mg/L for synthetic MSU after 30 min incubation at 37°C and pH 7.4, most of the dissolution taking place within the first 5-10 min. Semiempirical molecular modelling techniques (ZINDO/1) show a favorable energy balance for the formation of a TRIS-urate-TRIS adduct which might explain the high DA values. Buffers containing linear or dendrimeric polyamines gave DA values which suggest that complex formation toward sodium cations is less important. An ex vivo MSU sample was found to have a significantly lower DA value (DA30=1124(5) mg/L in TMT) as well as a lower crystallinity than its synthetic counterpart, possibly related to the presence of a non-crystalline impurity such as endogenous proteins. Cytotoxicity tests based on the MTT assay were used to check the biocompatibility of the TMT buffer and showed only moderate cell mortality after 24 h contact with the buffer solution

Rayleigh–Bénard convection of a model emulsion: anomalous heat-flux fluctuations and finite-size droplet effects

We present mesoscale numerical simulations of Rayleigh-B\'enard (RB) convection in a two-dimensional model emulsion. The systems under study are constituted of finite-size droplets, whose concentration Phi_0 is systematically varied from small (Newtonian emulsions) to large values (non-Newtonian emulsions). We focus on the characterisation of the heat transfer properties close to the transition from conductive to convective states, where it is known that a homogeneous Newtonian system exhibits a steady flow and a time-independent heat flux. In marked contrast, emulsions exhibit a non-steady dynamics with fluctuations in the heat flux. In this paper, we aim at the characterisation of such non-steady dynamics via detailed studies on the time-averaged heat flux and its fluctuations. To understand the time-averaged heat flux, we propose a side-by-side comparison between the emulsion system and a single-phase (SP) system, whose viscosity is constructed from the shear rheology of the emulsion. We show that such local closure works well only when a suitable degree of coarse-graining (at the droplet scale) is introduced in the local viscosity. To delve deeper into the fluctuations in the heat flux, we propose a side-by-side comparison between a Newtonian emulsion and a non-Newtonian emulsion, at fixed time-averaged heat flux. This comparison elucidates that finite-size droplets and the non-Newtonian rheology cooperate to trigger enhanced heat-flux fluctuations at the droplet scales. These enhanced fluctuations are rooted in the emergence of space correlations among distant droplets, which we highlight via direct measurements of the droplets displacement and the characterisation of the associated correlation function. The observed findings offer insights on heat transfer properties for confined systems possessing finite-size constituents.Comment: 15 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:2010.02139, arXiv:2010.0213

Interplay between shape and roughness in early-stage microcapillary imbibition.

Flows in microcapillaries and associated imbibition phenomena play a major role across a wide spectrum of practical applications, from oil recovery to inkjet printing and from absorption in porous materials and water transport in trees to biofluidic phenomena in biomedical devices. Early investigations of spontaneous imbibition in capillaries led to the observation of a universal scaling behavior, known as the Lucas-Washburn (LW) law. The LW allows abstraction of many real-life effects, such as the inertia of the fluid, irregularities in the wall geometry, and the finite density of the vacuum phase (gas or vapor) within the channel. Such simplifying assumptions set a constraint on the design of modern microfluidic devices, operating at ever-decreasing space and time scales, where the aforementioned simplifications go under serious question. Here, through a combined use of leading-edge experimental and simulation techniques, we unravel a novel interplay between global shape and nanoscopic roughness. This interplay significantly affects the early-stage energy budget, controlling front propagation in corrugated microchannels. We find that such a budget is governed by a two-scale phenomenon: The global geometry sets the conditions for small-scale structures to develop and propagate ahead of the main front. These small-scale structures probe the fine-scale details of the wall geometry (nanocorrugations), and the additional friction they experience slows the entire front. We speculate that such a two-scale mechanism may provide a fairly general scenario to account for extra dissipative phenomena occurring in capillary flows with nanocorrugated walls

Abundance and biodiversity of soil arthropods in one conventional and two organic fields of maize in stockless arable systems

Soil arthropod community was evaluated, in three different farming systems in Central Italy, in the context of a long-term experimental stockless arable system (MOLTE). The soil arthropodofauna was recorded in two organic agrosystems of different age (16-year old organic, named OldO; 6-year young organic, named YngO) and in one conventional (Co), at a fixed time on maize. Arthropods, extracted by Berlese-Tullgren funnels, were counted and identified at order or suborder taxonomic level. In the three maize fields, the farming system affected both abundance and biodiversity of arthropods. The arthropod density ranged from about 20,000 individuals/m2 in OldO to about 45,000 in YngO. The number of oribatid mites was higher in Co than in OldO, while YngO showed the highest density of collembolans. The mite/collembolan ratio was the highest in Co (6.43), the lowest in YngO (1.95). Both biodiversity indices adopted – V, synthetic index of degree of diversity change of ecological systems and QBS, index of biological soil quality – showed the highest values for YngO. On the whole, differences in the arthropod community were higher in the YngO-OldO comparison than in OldO-Co. The soil arthropod community tended to be characterized by lower density of specimens and lower number of taxa in the OldO organic system than in the YngO

Doline Fills - Case Study of the Faverghera Plateau (Venetian Pre-Alps, Italy)

The sedimentary fills of two dolines in the Faverghera plateau in the Venetian Pre-Alps, south of Belluno, have been investigated. This small plateau is a sub-horizontal surface about 0.5 km2 wide, located on the northeastern slope of Mt. Faverghera (1640 m a.s.l.) hosting nearly 40 karst dolines partially filled by periglacial slope deposits. Topographic survey, electric resistivity tomography (ERT), soil and pollen analyses have been carried on. The structure of the dolines and the characters of the filling deposits indicate that the evolution of these forms has been controlled by the alternation of different climatic and environmental conditions during the Pleistocene. The results indicate that the dolines are “filters” for the sediments, more than good traps, archiving only some of the climatic and environmental changes

Oxygen Radical Scavenger Activity, EPR, NMR, Molecular Mechanics and Extended-Hückel Molecular Orbital Investigation of the Bis(Piroxicam)Copper(II) Complex

The oxygen radical scavenger activity (ORSA) of [CuII(Pir)2] (HPir = Piroxicam = 4-hydroxy -2- methyl -N-2- pyridyl -2H- 1,2-benzothiazine -3- carboxamide 1,1-dioxide) was determined by chemiluminescence of samples obtained by mixing human neutrophils (from healthy subjects) and [CuII(Pir)2(DMF)2] (DMF = N,N -dimethylformammide) in DMSO/GLY/PBS (2:1:2, v/v) solution (DMSO = dimethylsulfoxide, GLY = 1,2,3-propantriol, PBS = Dulbecco’s buffer salt solution). The ratio of the residual radicals, for the HPir (1.02·10−4M) and [CuII(Pir)2(DMF)2] (1.08·10−5M)/HPir (8.01·10−−5M) systems was higher than 12 (not stimulated) [excess of piroxicam was added (Cu/Pir molar ratio ≈1:10) in order to have most of the metal complexed as bischelate]. In contrast, the ratio of residual radicals for the CuCl2 (1.00·10−5M) and [CuII(Pir)2(DMF)2] (1.08·10−5M)/Hpir (8.01·10−5M)system was 5. The [CuII(Pir)2] compound is therefore a stronger radical scavenger than either HPir or CuCl2. A molecular mechanics (MM) analysis of the gas phase structures of neutral HPir, its zwitterionic (HPir+-) and anionic (Pir-) forms, and some CuII-piroxicam complexes based on X-ray structures allowed calculation of force constants. The most stable structure for HPir has a ZZZ conformation similar to that found in the CuII (and CdII complexes) in the solid state as well as in the gas phase. The structure is stabilized by a strong H bond which involves the N(amide)-H and O(enolic) groups. The MM simulation for the [CuII(Pir)2(DMF)2] complex showed that two high repulsive intramolecular contacts exist between a pyridyl hydrogen atom of one Pir- molecule with the O donor of the other ligand. These interactions activate a transition toward a pseudo-tetrahedral geometry, in the case the apical ligands are removed. On refluxing a suspension of [CuII(Pir)2(DMF)2] in acetone a brown microcystalline solid with the Cu(Pir)2·0.5DMF stoichiometry was in fact prepared. 13C spin-lattice relaxation rates of neutral, zwitterionic and anionic piroxicam, in DMSO solution are explained by the thermal equilibrium between the three most stable structures of the three forms, thus confirming the high quality of the force field. The EPR spectrum of [CuII(Pir)2(DMF)2] (DMSO/GLY, 2:1, v/v, 298 and 110 K) agrees with a N2O2+O2 pseudo-octahedral coordination geometry. The EPR spectrum of [CuII(Pir)2·0.5DMF agrees with a pseudo-tetrahedral coordination geometry. The parameters extracted from the room temperature spectra of the solution phases are in agreement with the data reported for powder and frozen solutions. The extended-Hückel calculations on minimum energy structures of [CuII(Pir)2(DMF)2] and [CuII(Pir)2] (square planar) revealed that the HOMOs have a relevant character of dx2−y2. On the other hand the HOMO of a computer generated structure for [CuII(Pir)2] (pseudo-tetrahedral) has a relevant character of dxy atomic orbital. A dxy orbital is better suited to allow a dπ-pπ interaction to the O2- anion. Therefore this work shows that the anti-inflammatory activity of piroxicam could be due in part to the formation of [CuII(Pir)2] chelates, which can exert a SOD-like activity

Terpene arms race in the Seiridium cardinale - Cupressus sempervirens pathosystem

The canker-causing fungus Seiridium cardinale is the major threat to Cupressus sempervirens worldwide. We investigated the production of terpenes by canker-resistant and susceptible cypresses inoculated with S. cardinale, the effect of these terpenes on fungal growth, and the defensive biotransformation of the terpenes conducted by the fungus. All infected trees produced de novo terpenes and strongly induced terpenic responses, but the responses were stronger in the cankerresistant than the susceptible trees. In vitro tests for the inhibition of fungal growth indicated that the terpene concentrations of resistant trees were more inhibitory than those of susceptible trees. The highly induced and de novo terpenes exhibited substantial inhibition (more than a fungicide reference) and had a high concentration-dependent inhibition, whereas the most abundant terpenes had a low concentration-dependent inhibition. S. cardinale biotransformed three terpenes and was capable of detoxifying them even outside the fungal mycelium, in its immediate surrounding environment. Our results thus indicated that terpenes were key defences efficiently used by C. sempervirens, but also that S. cardinale is ready for the battle

Mesoscopic lattice Boltzmann modeling of flowing soft systems

A mesoscopic multi-component lattice Boltzmann model with short-range repulsion between different species and short/mid-ranged attractive/repulsive interactions between like-molecules is introduced. The interplay between these composite interactions gives rise to a rich configurational dynamics of the density field, exhibiting many features of disordered liquid dispersions (micro-emulsions) and soft-glassy materials, such as long-time relaxation due to caging effects, anomalous enhanced viscosity, ageing effects under moderate shear and flow above a critical shear rate.Comment: 4 pages, 4 figure