The effect of gravity on liquid plug propagation in a two-dimensional channel

The effect of plug propagation speed and gravity on the quasisteady motion of a liquid plug in a two-dimensional liquid-lined channel oriented at an angle αα with respect to gravity is studied. The problem is motivated by the transport of liquid plugs instilled into pulmonary airways in medical treatments such as surfactant replacement therapy, drug delivery, and liquid ventilation. The capillary number Ca is assumed to be small, while the Bond number Bo is arbitrary. Using matched asymptotic expansions and lubrication theory, expressions are obtained for the thickness of the trailing films left behind by the plug and the pressure drop across it as functions of Ca, Bo, αα and the thickness of the precursor films. When the Bond number is small it is found that the trailing film thickness and the flow contribution to the pressure drop scale as Ca2/3Ca2∕3 at leading order with coefficients that depend on Bo and αα. The first correction to the film thickness is found to occur at O(Ca)O(Ca) compared to O(Ca4/3)O(Ca4∕3) in the Bo = 0Bo=0 case. Asymmetry in the liquid distribution is quantified by calculating the ratio of liquid volumes above and below the centerline of the channel, VṘ. VR = 1VR=1 at Bo = 0Bo=0, indicating a symmetric distribution, and decreases with Bo and Ca, but increases with the plug length LpLp. The decrease of VRVR with Ca suggests that higher propagation speeds in small airways may result in less homogenous liquid distribution, which is in contrast to the expected effect in large airways. For given values of the other parameters, a maximum capillary number CacCac is identified above which the plug will eventually rupture. When the Bond number becomes equal to an orientation-dependent critical value BocBoc, it is found that the scaling of the film thickness and pressure drop change to Ca1/2Ca1∕2 and Ca1/6Ca1∕6, respectively. It is shown that this scaling is valid for small increments of the Bond number over its critical value, Bo = Boc+BCa1/6Bo=Boc+BCa1∕6, but for higher Bond numbers the asymptotic approach breaks down.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87914/2/031507_1.pd

Stability of time-modulated electroosmotic flow

We present a linear stability analysis of parallel electroosmotic flow in a slot geometry. A spatially uniform time harmonic electric field is applied to a dilute electrolyte solution contained between two infinite parallel plates. The base state ion concentrations and electric potential are determined using the Poisson–Boltzmann equation in the Debye–Hückel approximation. The base velocity field is found to be time harmonic and parallel. It is shown that the original system can be replaced by an equivalent one consisting of an electrically neutral fluid enclosed between oscillating parallel plates, whose speed and frequency of oscillation depend on the modulated electric field. Further, the system of linearized disturbance equations can be decoupled into two stability problems: The first, called the electrokinetic problem, describes the evolution of disturbance ion concentrations and electric potential and is independent of the disturbance velocity components. The second, called the Stokes layer problem describes an oscillatory Stokes layer forced by an electrical body force. The stability of each system is determined by Floquet analysis of a dynamical system obtained from a truncated Galerkin expansion of the perturbation quantities. Our calculations show the system to be linearly stable over a wide range of parameters, with damping rates that become quite small for certain combinations of Stokes and Reynolds numbers. © 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69805/2/PHFLE6-16-7-2349-1.pd

Exploring the Effects of Bile Acid Inhibition in Cholestatic Pruritus

Ph. D. Thesis.Pruritus (itch) is an important symptom associated with cholestatic liver diseases. The aim of this work was to study cholestatic pruritus to further our understanding of the prevalence in primary biliary cholangitis (PBC) and explore the role of inhibiting circulating bile acids (BAs) in relieving cholestatic pruritus. The cross-sectional study of pruritus from over 2800 patients from the UK-PBC research cohort showed that prevalence of pruritus in PBC is high (74%) with a significant proportion of patients reporting severe itch during the course of their disease. This study also highlighted the undertreatment of itch with inadequate use of guideline recommended drugs in the UK. The impact of inhibiting circulating BAs on cholestatic pruritus was studied in two different ways- i) via nasobiliary drainage (NBD, i.e. external diversion of bile and BAs away from the ileum), and ii) via pharmacological inhibition of the ileal bile acid transporter (IBAT) that mediates enterohepatic circulation of BAs. The retrospective cohort study of NBD showed the intervention is a highly effective treatment, but only of short-term durability and associated with high complication rate. The phase 2 clinical trial of GSK2330672, a human IBAT inhibitor agent, showed that two-weeks of treatment significantly reduced pruritus severity compared to placebo. The metabonomic and microbiome studies explored the serum metabonome and gut microbiota profile of pruritus in PBC. In addition, the effects of GSK2330672 on metabonome and gut microbiome were investigated. The study demonstrated that pruritus in PBC is associated with elevated serum total and glyco-conjugated BAs but no gut bacterial dysbiosis. Also, GSK2330672 was shown to reduce all taurine and glyco- conjugated serum BAs, increase faecal BAs and alter the gut-microbial composition. Taken together, the research studies presented in this thesis suggest: i) high prevalence of pruritus and its under-treatment in PBC, ii) removal of BAs by NBD or inhibition by IBAT inhibitor drug improves cholestatic pruritus and, iii) serum BAs but not gut microbiome are altered in cholestatic pruritus and they can be modified by IBAT inhibitor treatmentNational Institute for Health Research (NIHR), Newcastle Biomedical Research Centre (BRC

A cell culture model for alveolar epithelial transport

Abstract 10 Backgroun

Wettability Gradients on Soft Surfaces

Properties, behaviors, and applications of soft materials depend decisively on the characteristics of their surfaces. Physical features and chemical functionality of the soft surfaces control their interactions with the surroundings thereby deciding their responses to various physical and chemical phenomena. A gradient of such surface features i.e, a gradual change in a chemical or physical characteristic across a surface will result in a gradual change in the response of the surface to its surroundings in the same direction. Chemical as well as physical (morphological) gradients on soft surface enable useful properties pertinent to a variety of fields such as microfluidics, surface coatings, sensing, optics, and biology. Numerous methods have been used for the preparation of chemical as well as morphological gradients. Practical applications of soft surface gradients require stable large-scale surfaces with precisely controlled directionality and resolution of the gradients. Wettability gradients are one of the prominent classes of gradients created on soft surfaces. These gradients are constituted by gradual increase or decrease of hydrophobicity/hydrophilicity across a surface. One-dimensional (1D) as well as two-dimensional (2D) wettability gradients are fabricated with different patterns. This short review will summarize the advancements in the preparation, properties, and applications of wettability gradients on soft surfaces. Qualitative description of the fabrication processes, properties, and practical applications of the gradients are included along with our comments about the future prospects of these systems.&nbsp

Peristaltic flow in the glymphatic system.

The flow inside the perivascular space (PVS) is modeled using a first-principles approach in order to investigate how the cerebrospinal fluid (CSF) enters the brain through a permeable layer of glial cells. Lubrication theory is employed to deal with the flow in the thin annular gap of the perivascular space between an impermeable artery and the brain tissue. The artery has an imposed peristaltic deformation and the deformable brain tissue is modeled by means of an elastic Hooke\u27s law. The perivascular flow model is solved numerically, discovering that the peristaltic wave induces a steady streaming to/from the brain which strongly depends on the rigidity and the permeability of the brain tissue. A detailed quantification of the through flow across the glial boundary is obtained for a large parameter space of physiologically relevant conditions. The parameters include the elasticity and permeability of the brain, the curvature of the artery, its length and the amplitude of the peristaltic wave. A steady streaming component of the through flow due to the peristaltic wave is characterized by an in-depth physical analysis and the velocity across the glial layer is found to flow from and to the PVS, depending on the elasticity and permeability of the brain. The through CSF flow velocity is quantified to be of the order of micrometers per seconds

Computational Modeling of Glucose Uptake in the Enterocyte

Absorption of glucose across the epithelial cells of the small intestine is a key process in human nutrition and initiates signaling cascades that regulate metabolic homeostasis. Validated and predictive mathematical models of glucose transport in intestinal epithelial cells are essential for interpreting experimental data, generating hypotheses, and understanding the contributions of and interactions between transport pathways. Here we report on the development of such a model that, in contrast to existing models, incorporates mechanistic descriptions of all relevant transport proteins and is implemented in the CellML framework. The model is validated against experimental and simulation data from the literature. It is then used to elucidate the relative contributions of the sodium-glucose cotransporter (SGLT1) and the glucose transporter type 2 (GLUT2) proteins in published measurements of glucose absorption from human intestinal epithelial cell lines. The model predicts that the contribution of SGLT1 dominates at low extracellular glucose concentrations (<20 mM) and short exposure times (<60 s) while the GLUT2 contribution is more significant at high glucose concentrations and long durations. Implementation in CellML permitted a modular structure in which the model was composed by reusing existing models of the individual transporters. The final structure also permits transparent changes of the model components and parameter values in order to facilitate model reuse, extension, and customization (for example, to simplify, or add complexity to specific transporter/pathway models, or reuse the model as a component of a larger framework) and carry out parameter sensitivity studies

Investigation on Tribological Characteristics of Al 7075 MMNC: Behavior of Micro- and Nano-Sized Composites

This study investigates the mechanical properties and the wear behavior of Al 7075/Al2O3/SiCNP composites. The hybrid composites are manufactured using the stir casting technique. In this work, the Al 7075 alloy is reinforced with five different weight fractions of Al2O3 and a constant SiCNp, with an average particle size of 50 nm. The aluminum metal matrix composites are examined through surface morphology and X-ray diffraction (XRD) patterns to identify the material behavior. The material characteristics and the wear behavior of the metal composites are examined using a pin-on-disk test. Wear measurements are performed by varying loads, sliding speeds, and sliding distances. The results reveal that the composites reinforced with 4% of Al2O3 particulates exhibit superior properties. The wear rate and the coefficient of friction (COF) decrease with the increase in the reinforcement content

Effective Image Clustering with Differential Evolution Technique

The paper presents a novel approach of clustering image datasets with differential evolution (DE) technique. The differential evolution is a parallel direct search population based optimization method. From our simulations it is found that DE is able to optimize the quality measures of clusters of image datasets. To claim the superiority of DE based clustering we have compared the outcomes of DE with the classical K-means and popular Particle Swarm Optimization (PSO) algorithms for the same datasets. The comparisons results reveal the suitability of DE for image clustering in all image datasets