Full numerical simulations of multifluid flows

To fully understand the behavior of multifluid systems, one must have good insight into the basic micromechanisms that govern the evolution of a single ‘‘structure’’ (e.g., a bubble or a drop) and the interactions of a few such basic entities. In addition to the usual questions about the relative magnitude of the various physical effects (inertia, viscosity, and surface tension) for multifluid systems, the effects of surface phenomena such as contaminants must be addressed. Full numerical simulations are, in principle, ideally suited to provide this information. Not only are all the quantitative data readily available, but various physical processes can be turned on and off at will. In practice, however, simulations of multifluid problems are one of the difficult areas of computational fluid dynamics. Almost all current studies of multifluid problems make a number of simplifications, such as inviscidness, Stokes flow, two‐dimensionality, or axisymmetry. Although such models capture some of the important behavior, they often put severe constraints on the problems that can be investigated.Many of the fundamental processes in multifluid flow involve fully three‐dimensional flows, where both inertia and viscous effects must be accounted for. To address these effects, we have recently developed a front‐tracking method for multifluid, incompressible flows that appears to be both accurate and robust. The method has been implemented for both two‐ as well as fully three‐dimensional situations. In this paper, we will discuss two problems that we are currently investigating using this numerical method: the Rayleigh–Taylor instability and the motion of bubbles and drops. For fluid mixing induced by unstable stratification, the Rayleigh–Taylor instability where a heavy fluid falls into a lighter underlying fluid, is the prototypical example. Indeed, for such flows its importance is similar to that of the Kelvin–Helmholtz instability for fluid mixing induced by a shear flow. For small density stratification, we show that three‐dimensionality can lead to a large amplitude vortex structure that differs considerably from what two‐dimensional simulations predict. The different vortical configuration leads to more rapid nonlinear growth for the fully three‐dimensional case, even though the linear growth rate is the same. We also show how viscosity stratification modifies the evolution. For the weakly stratified case, where inviscid calculations predict symmetric evolution with respect to the heavy and the light fluid, viscosity stratification leads to considerable asymmetry, with the more viscous fluid forming big round bubbles and the less viscous one being confined to narrow fingers. The effect of density stratification for viscous three‐dimensional motion will also be discussed. For many mixing problems, the long‐time state consists of a dispersed phase that forms drops or bubbles in another phase. We will discuss preliminary investigations of such flows. Calculations of rising bubbles for various values of surface tension and viscosity (both in two and three dimensions) appear to correlate well with experimental observations and steady‐state calculations in the literature. The interactions of bubbles with each other, density interfaces, and vortices will also be discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69841/2/PFADEB-3-5-1455-1.pd

Computations of multi-fluid flows

Full numerical simulations of three-dimensional flows of two or more immiscible fluids of different densities and viscosities separated by a sharp interface with finite surface tension are discussed. The method used is based on a finite difference approximation of the full Navier-Stokes equations and explicit tracking of the interface between the fluids. Preliminary simulations of the Rayleigh-Taylor instability and the motion of bubbles are shown.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29741/1/0000078.pd

Capture and inception of bubbles near line vortices

Motivated by the need to predict vortex cavitation inception, a study has been conducted to investigate bubble capture by a concentrated line vortex of core size rcrc and circulation Γ0Γ0 under noncavitating and cavitating conditions. Direct numerical simulations that solve simultaneously for the two phase flow field, as well as a simpler one-way coupled point-particle-tracking model (PTM) were used to investigate the capture process. The capture times were compared to experimental observations. It was found that the point-particle-tracking model can successfully predict the capture of noncavitating small nuclei by a line vortex released far from the vortex axis. The nucleus grows very slowly during capture until the late stages of the process, where bubble/vortex interaction and bubble deformation become important. Consequently, PTM can be used to study the capture of cavitating nuclei by dividing the process into the noncavitating capture of the nucleus, and then the growth of the nucleus in the low-pressure core region. Bubble growth and deformation act to speed up the capture process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87832/2/022105_1.pd

Effect of sirolimus on the regression of peritoneal sclerosis in an experimental rat model

Purpose Immunosuppressive and anti-inflammatory agents have recently become increasingly popular in the treatment of encapsulating peritoneal sclerosis (EPS). The aim of our study was to investigate the effects of sirolimus on EPS in a rat model. Methods We separated 32 non-uremic rats into four groups: 1 control group, 2 ml isotonic saline injected IP daily for 3 weeks; 2 chlorhexidine gluconate (CG) group, 2 ml 0,1 % CG and 15 % ethanol dissolved in saline injected IP daily for 3 weeks; 3 resting group, CG (weeks 0-3) plus peritoneal rest (weeks 3-6); 4 sirolimus group, CG (weeks 0-3), plus 0.2 ml (1 mg/ml) sirolimus (weeks 3-6). Pathological samples were examined by using hematoxylin eosin (HE) and Masson's trichrome stains. Peritoneal thickness, fibrosis, vascular changes, and inflammation were evaluated by light microscopy. Finally, tissue metalloproteinase (MMP)-2 levels were measured by enzyme-linked immunoassay. Results In the CG group, there was a significant increase in peritoneal thickness, inflammatory activity, and fibrosis score compared to the control group (p<0.05). We also observed a lower fibrosis score and less peritoneal thickening in the sirolimus group compared to the resting and CG groups (p<0.05). There was no difference in histopathologic findings, except for the inflammatory activity in the sirolimus group, compared to the control group. Although the CG group had higher tissue MMP-2 levels than the control group, the tissue MMP-2 levels were not significantly different from the other groups. Conclusions Sirolimus has a beneficial effect on peritoneal fibrosis induced by CG. This suggests that sirolimus may have therapeutic value in the management of EPS. © Springer Science+Business Media, B.V. 2011

Evaluation of MUC1 and P53 expressions in noninvasive papillary urothelial neoplasms of bladder, their relationship with tumor grade and role in the differential diagnosis

Purpose: The aim of this study was to investigate the usability of MUC1 and p53 for differential diagnosis of noninvasive papillary urothelial neoplasias, especially for distinguishing papillary urothelial neoplasm of low malignant potential (PUNLMP) from low-grade papillary urothelial carcinoma (LGPUC) when the histologic signs are not obvious. Materials and Methods: Seventeen biopsy specimens of the patients with PUNLMP, 20 with LGPUC and 13 with high-grade papillary urothelial carcinoma (HGPUC) were stained for MUC1 and p53 protein by immunohistochemical methods. Histological grading was performed according to an algorithm, which allows histological parameters used in 2004 WHO/ISUP 1998. Results: We had obvious statistical difference for aberrant expression pattern of MUC1 between PUNLMP and LGPUC-HGPUC (P = 0.007). Positivity of MUC1 expression in cytoplasm of basal cells was more observed in HGPUC and LGPUC, whereas PUNLMP was more often showing apical and superficial positivity of MUC1 expression (P = 0.001 and 0.011). Nuclear p53 protein in HGPUC was obviously more frequent than that in LGPUC and PUNLMP (P < 0.001). Measures showed statistical difference among aberrant MUC1 expression, p53 overexpression, and tumor grade (P < 0.001). Conclusions: MUC1 and p53 may be helpful immunohistochemical markers for distinguishing PUNLMP from LGPUC and HGPUC, when the histologic signs are not obvious. © 2 0 1 8 I n d i a n J o u r n a l o f P a t h o l o g y a n d Mi c r o b i o l o g y | P u b l i s h e d b y Wo 510 l t e r s Kl u w e r - Me d k n o w

Fabrication of CdS nanospheres-based hybrid solar cells having increased efficiency

The impact of surface modification through diverse dyes (Eosin-Y, D205, N719 and N3) on structural, morphological, optical, and electrical properties of CdS/P3HT hybrid solar cells is studied. X-ray diffraction (XRD) pattern shows that CdS nanospheres have a hexagonal structure with a preferential orientation of (002) with respect to indium tin oxide (ITO) coated glass slide. Scanning electron microscopy (SEM) results indicate that compact and dense spherical morphologies of CdS occurred, and the P3HT layer also consisted of small spherical grains. The bandgap of CdS is found to be 2.52 eV according to Tauc's plot analysis. Absorption spectra demonstrate that interfacial modification via each dye leads to an increase in the absorption in the wavelength range of 300-1000 nm. Photoluminescence (PL) data prove that surface modification of CdS nanospheres with diverse dyes causes a decrease in the spectral intensity of PL curve, implying that efficient exciton separation is taking place upon dye loadings. Fabricated devices with and without modification show photovoltaic effects that can be seen from current density-voltage (J-V) curves obviously, and the highest power conversion efficiency (PCE) is obtained as 0.881% for N719-modified (ITO/CdS/N719/P3HT/Ag) device (almost 70-fold of pristine one) with a short-circuit current density (J(sc)) of 2.878mA/cm(2) and open-circuit voltage (V-oc) of 0.92V, respectively. This enhancement can be attributed to a better surface area between CdS and P3HT after dye modification