A discussion on the interpretation of the Darcy equation in case of open-cell metal foam based on numerical simulations

It is long known that for high-velocity fluid flow in porous media, the relation between the pressure drop and the superficial velocity is not linear. Indeed, the classical Darcy law for shear stress dominated flow needs to be extended with a quadratic term, resulting in the empirical Darcy–Forchheimer model. Another approach is to simulate the foam numerically through the volume averaging technique. This leads to a natural separation of the total drag force into the contribution of the shear forces and the contribution of the pressure forces. Both representations of the total drag lead to the same result. The physical correspondence between both approaches is investigated in this work. The contribution of the viscous and pressure forces on the total drag is investigated using direct numerical simulations. Special attention is paid to the dependency on the velocity of these forces. The separation of the drag into its constituent terms on experimental grounds and for the volume average approach is unified. It is shown that the common approach to identify the linear term with the viscous forces and the quadratic term with the pressure forces is not correct

Model kontakta s efektima podmazivanja za simulacije postupka hladnog valjanja

U ovome radu prikazan je numerički model za proračun kontaktnog tlaka i trenja u simulacijama hladnog valjanja metala uz podmazivanje. Efekti trenja i podmazivanja su važni čimbenici u postupcima obrade metala, budući da neoptimalne vrijednosti parametara trenja mogu uzrokovati nižu učinkovitost samoga postupka te smanjiti kvalitetu površine proizvoda. Kako bi se kvalitetno prikazale fizikalne pojave kontakta u postupku valjanja metala potrebno je uzeti u obzir interakciju između površinske hrapavosti i strujanja lubrikanta. Zbog promjene debljine sloja lubrikanta tijekom samog proizvodnog postupka, lubrikant struji u tri različita režima: hidrodinamičkom, mješovitom i graničnom režimu. Sposobnost proračuna sva tri režima je nužna u realnoj industrijskoj primjeni. Model uzima u obzir utjecaje površinske hrapavosti, režima podmazivanja i promjene svojstava lubrikanta. Za proračun kontaktnog tlaka i sila trenja lubrikanta koristi se osrednjena Reynoldsova jednadžba, koja je diskretizirana pomoću metode kontrolnih površina (eng. „Finite Area Method“). Model implementiran u paketu otvorenog koda OpenFOAM koristi se kao rubni uvjet kontakta prilikom proračuna deformacije tijela pomoću numeričkog modela za visokonapregnute elastoplastične deformacije. Rezultati modela su prikazani na slučajevima valjanja metalne trake

Estimation of ontogeny functions for renal transporters using a combined population pharmacokinetic and physiology-based pharmacokinetic approach : application to OAT1,3

To date, information on the ontogeny of renal transporters is limited. Here, we propose to estimate the in vivo functional ontogeny of transporters using a combined population pharmacokinetic (popPK) and physiology-based pharmacokinetic (PBPK) modeling approach called popPBPK. Clavulanic acid and amoxicillin were used as probes for glomerular filtration, combined glomerular filtration, and active secretion through OAT1,3, respectively. The predictive value of the estimated OAT1,3 ontogeny function was assessed by PBPK predictions of renal clearance (CLR) of other OAT1,3 substrates: cefazolin and piperacillin. Individual CL(R)post-hoc values, obtained from a published popPK model on the concomitant use of clavulanic acid and amoxicillin in critically ill children between 1 month and 15 years, were used as dependent variables in the popPBPK analysis. CLR was re-parameterized according to PBPK principles, resulting in the estimation of OAT1,3-mediated intrinsic clearance (CLint,OAT1,3,invivo) and its ontogeny. CLint,OAT1,3,invivo ontogeny was described by a sigmoidal function, reaching half of adult level around 7 months of age, comparable to findings based on renal transporter-specific protein expression data. PBPK-based CLR predictions including this ontogeny function were reasonably accurate for piperacillin in a similar age range (2.5 months-15 years) as well as for cefazolin in neonates as compared to published data (%RMSPE of 21.2 and 22.8%, respectively and %PE within +/- 50%). Using this novel approach, we estimated an in vivo functional ontogeny profile for CLint,OAT1,3,invivo that yields accurate CLR predictions for different OAT1,3 substrates across different ages. This approach deserves further study on functional ontogeny of other transporters

Anomalous Transport in Conical Granular Piles

Experiments on 2+1-dimensional piles of elongated particles are performed. Comparison with previous experiments in 1+1 dimensions shows that the addition of one extra dimension to the dynamics changes completely the avalanche properties, appearing a characteristic avalanche size. Nevertheless, the time single grains need to cross the whole pile varies smoothly between several orders of magnitude, from a few seconds to more than 100 hours. This behavior is described by a power-law distribution, signaling the existence of scale invariance in the transport process.Comment: Accepted in PR

Functional magnetic resonance imaging : cerebral function alterations in subthreshold and suprathreshold spinal cord stimulation

Peer reviewedPublisher PD

Spontaneous Stratification in Granular Mixtures

Granular materials size segregate when exposed to external periodic perturbations such as vibrations. Moreover, mixtures of grains of different sizes spontaneously segregate in the absence of external perturbations: when a mixture is simply poured onto a pile, the large grains are more likely to be found near the base, while the small grains are more likely to be near the top. Here, we report a spontaneous phenomenon arising when we pour a mixture between two vertical plates: the mixture spontaneously stratifies into alternating layers of small and large grains whenever the large grains are rougher than the small grains. In contrast, we find only spontaneous segregation when the large grains are more rounded than the small grains. The stratification is related to the occurrence of avalanches; during each avalanche the grains comprising the avalanche spontaneously stratify into a pair of layers through a "kink" mechanism, with the small grains forming a sublayer underneath the layer of large grains.Comment: 4 pages, 6 figures, http://polymer.bu.edu/~hmakse/Home.htm