The Added Mass, Basset, and Viscous Drag Coefficients in Nondilute Bubbly Liquids Undergoing Small-Amplitude Oscillatory Motion

The motion of bubbles dispersed in a liquid when a small-amplitude oscillatory motion is imposed on the mixture is examined in the limit of small frequency and viscosity. Under these conditions, for bubbles with a stress-free surface, the motion can be described in terms of added mass and viscous force coefficients. For bubbles contaminated with surface-active impurities, the introduction of a further coeflicient to parametrize the Basset force is necessary. These coefficients are calculated numerically for random configurations of bubbles by solving the appropriate multibubble interaction problem exactly using a method of multipole expansion. Results obtained by averaging over several configurations are presented. Comparison of the results with those for periodic arrays of bubbles shows that these coefficients are, in general, relatively insensitive to the detailed spatial arrangement of the bubbles. On the basis of this observation, it is possible to estimate them via simple formulas derived analytically for dilute periodic arrays. The effect of surface tension and density of bubbles (or rigid particles in the case where the no-slip boundary condition is applicable) is also examined and found to be rather small

Determination of Particle Size Distributions from Acoustic Wave Propagation Measurements

The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley @J. Acoust. Soc. Am. 51, 1545 ~1972!# for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations

Steady Stokes flow with long-range correlations, fractal Fourier spectrum, and anomalous transport

We consider viscous two-dimensional steady flows of incompressible fluids past doubly periodic arrays of solid obstacles. In a class of such flows, the autocorrelations for the Lagrangian observables decay in accordance with the power law, and the Fourier spectrum is neither discrete nor absolutely continuous. We demonstrate that spreading of the droplet of tracers in such flows is anomalously fast. Since the flow is equivalent to the integrable Hamiltonian system with 1 degree of freedom, this provides an example of integrable dynamics with long-range correlations, fractal power spectrum, and anomalous transport properties.Comment: 4 pages, 4 figures, published in Physical Review Letter

Self-Reported Tobacco Use and Correlation with Umbilical Cord Blood Cotinine levels at Delivery among Appalachian Gravidas

The detrimental effects of cigarette use during pregnancy are well documented. Studies have shown that cigarette smoking while pregnant is associated with multiple adverse outcomes including: pre-term birth, placental abruption, placenta previa, fetal growth restriction, stillbirth, increased rate of birth defects, and increased risk of sudden infant death syndrome. Cotinine is the primary metabolite of nicotine and allows for measurement of active as well as passive exposure. Cotinine freely cross the placental barrier and maternal concentrations are closely correlated with newborn plasma levels. The aim of this study was to compare maternally reported rates of tobacco use to fetal umbilical cord blood cotinine levels at the time of delivery. A cross-sectional study was conducted on 172 patients. Patients were asked a single yes or no question in regards to their cigarette use during pregnancy. Cord blood was collected at the time of delivery and analyzed for serum concentrations of cotinine. Cotinine levels greater than 3.0 ng/mL were considered consistent with the use of tobacco or tobacco cessation products. Maternal self-reporting of tobacco use indicates a reported tobacco use rate of 27.3% and an actual use rate of 30.2%. The reported tobacco non-use rate was 72.7% and the actual non-use rate was 66.3%. The prevalence of tobacco use during pregnancy in our study was 30.2%, while the overall rate in the United States is reported to be 12.3%. Our findings indicate that self-reported smoking prevalence and verified umbilical cord blood cotinine levels at the time of delivery have excellent correlation (kappa=0.76). Compared to the national average our study group also had nearly double the rate of tobacco use. Due to the deleterious effects of cigarette use during pregnancy continued efforts to educate patients regarding cigarette cessation is of utmost importance as cessation of tobacco products will improve and promote maternal and fetal well-being

Attenuation of Sound in Concentrated Suspensions: Theory and Experiments

Ensemble-averaged equations are derived for small-amplitude acoustic wave propagation through non-dilute suspensions. The equations are closed by introducing effective properties of the suspension such as the compressibility, density, viscoelasticity, heat capacity, and conductivity. These effective properties are estimated as a function of frequency, particle volume fraction, and physical properties of the individual phases using a self-consistent, effective-medium approximation. The theory is shown to be in excellent agreement with various rigorous analytical results accounting for multiparticle interactions. The theory is also shown to agree well with the experimental data on concentrated suspensions of small polystyrene particles in water obtained by Allegra & Hawley and for glass particles in water obtained in the present study

Self-Reported Tobacco Use and Correlation with Umbilical Cord Blood Cotinine levels at Delivery among Appalachian Gravidas

The detrimental effects of cigarette use during pregnancy are well documented. Studies have shown that cigarette smoking while pregnant is associated with multiple adverse outcomes including: pre-term birth, placental abruption, placenta previa, fetal growth restriction, stillbirth, increased rate of birth defects, and increased risk of sudden infant death syndrome. Cotinine is the primary metabolite of nicotine and allows for measurement of active as well as passive exposure. Cotinine freely cross the placental barrier and maternal concentrations are closely correlated with newborn plasma levels. The aim of this study was to compare maternally reported rates of tobacco use to fetal umbilical cord blood cotinine levels at the time of delivery. A cross-sectional study was conducted on 172 patients. Patients were asked a single yes or no question in regards to their cigarette use during pregnancy. Cord blood was collected at the time of delivery and analyzed for serum concentrations of cotinine. Cotinine levels greater than 3.0 ng/mL were considered consistent with the use of tobacco or tobacco cessation products. Maternal self-reporting of tobacco use indicates a reported tobacco use rate of 27.3% and an actual use rate of 30.2%. The reported tobacco non-use rate was 72.7% and the actual non-use rate was 66.3%. The prevalence of tobacco use during pregnancy in our study was 30.2%, while the overall rate in the United States is reported to be 12.3%. Our findings indicate that self-reported smoking prevalence and verified umbilical cord blood cotinine levels at the time of delivery have excellent correlation (kappa=0.76). Compared to the national average our study group also had nearly double the rate of tobacco use. Due to the deleterious effects of cigarette use during pregnancy continued efforts to educate patients regarding cigarette cessation is of utmost importance as cessation of tobacco products will improve and promote maternal and fetal well-being

Simulating Three-Dimensional Hydrodynamics on a Cellular-Automata Machine

We demonstrate how three-dimensional fluid flow simulations can be carried out on the Cellular Automata Machine 8 (CAM-8), a special-purpose computer for cellular-automata computations. The principal algorithmic innovation is the use of a lattice-gas model with a 16-bit collision operator that is specially adapted to the machine architecture. It is shown how the collision rules can be optimized to obtain a low viscosity of the fluid. Predictions of the viscosity based on a Boltzmann approximation agree well with measurements of the viscosity made on CAM-8. Several test simulations of flows in simple geometries -- channels, pipes, and a cubic array of spheres -- are carried out. Measurements of average flux in these geometries compare well with theoretical predictions.Comment: 19 pages, REVTeX and epsf macros require

Free energy of colloidal particles at the surface of sessile drops

The influence of finite system size on the free energy of a spherical particle floating at the surface of a sessile droplet is studied both analytically and numerically. In the special case that the contact angle at the substrate equals $\pi/2$ a capillary analogue of the method of images is applied in order to calculate small deformations of the droplet shape if an external force is applied to the particle. The type of boundary conditions for the droplet shape at the substrate determines the sign of the capillary monopole associated with the image particle. Therefore, the free energy of the particle, which is proportional to the interaction energy of the original particle with its image, can be of either sign, too. The analytic solutions, given by the Green's function of the capillary equation, are constructed such that the condition of the forces acting on the droplet being balanced and of the volume constraint are fulfilled. Besides the known phenomena of attraction of a particle to a free contact line and repulsion from a pinned one, we observe a local free energy minimum for the particle being located at the drop apex or at an intermediate angle, respectively. This peculiarity can be traced back to a non-monotonic behavior of the Green's function, which reflects the interplay between the deformations of the droplet shape and the volume constraint.Comment: 24 pages, 19 figure

Dynamic Analysis of Unidirectional Pressure Infiltration of Porous Preforms by Pure Metals

Unidirectional pressure infiltration of porous preforms by molten metals is investigated numerically. A phenomenological model to describe fluid flow and transport phenomena during infiltration of fibrous preforms by a metal is formulated. The model describes the dynamics of the infiltration process, the temperature distribution, and solid fraction distribution. The numerical results are compared against classical asymptotic analyses and experimental results. This comparison shows that end effects may become important and render asymptotic results unreliable for realistic samples. Fiber volume fraction and initial temperature appear as the factors most strongly influencing infiltration. Metal superheating affects not only the length of the two-phase zone but also the solid fraction distribution in the two-phase zone. The effect of constant applied pressure, although significant on the infiltration velocity, is almost negligible on the two-phase zone length and on solid fraction distribution. When the initial preform temperature is below the metal melting point, and constant pressure is applied under adiabatic conditions, the flow ceases when sufficient solidification occurs to obstruct it. A comparison with literature experiments proves the model to be an efficient predictive tool in the analysis of infiltration processes for different preform/melt systems

Meta-analysis Reveals Genome-Wide Significance at 15q13 for Nonsyndromic Clefting of Both the Lip and the Palate, and Functional Analyses Implicate GREM1 As a Plausible Causative Gene

Nonsyndromic orofacial clefts are common birth defects with multifactorial etiology. The most common type is cleft lip, which occurs with or without cleft palate (nsCLP and nsCLO, respectively). Although genetic components play an important role in nsCLP, the genetic factors that predispose to palate involvement are largely unknown. In this study, we carried out a meta-analysis on genetic and clinical data from three large cohorts and identified strong association between a region on chromosome 15q13 and nsCLP (P = 8.13×10−14 for rs1258763; relative risk (RR): 1.46, 95% confidence interval (CI): 1.32–1.61)) but not nsCLO (P = 0.27; RR: 1.09 (0.94–1.27)). The 5 kb region of strongest association maps downstream of Gremlin-1 (GREM1), which encodes a secreted antagonist of the BMP4 pathway. We show during mouse embryogenesis, Grem1 is expressed in the developing lip and soft palate but not in the hard palate. This is consistent with genotype-phenotype correlations between rs1258763 and a specific nsCLP subphenotype, since a more than two-fold increase in risk was observed in patients displaying clefts of both the lip and soft palate but who had an intact hard palate (RR: 3.76, CI: 1.47–9.61, Pdiff<0.05). While we did not find lip or palate defects in Grem1-deficient mice, wild type embryonic palatal shelves developed divergent shapes when cultured in the presence of ectopic Grem1 protein (P = 0.0014). The present study identified a non-coding region at 15q13 as the second, genome-wide significant locus specific for nsCLP, after 13q31. Moreover, our data suggest that the closely located GREM1 gene contributes to a rare clinical nsCLP entity. This entity specifically involves abnormalities of the lip and soft palate, which develop at different time-points and in separate anatomical regions.Clefts of the lip and palate are common birth defects, and require long-term multidisciplinary management. Their etiology involves genetic factors and environmental influences and/or a combination of both, however, these interactions are poorly defined. Moreover, although clefts of the lip may or may not involve the palate, the determinants predisposing to specific subphenotypes are largely unknown. Here we demonstrate that variations in the non-coding region near the GREM1 gene show a highly significant association with a particular phenotype in which cleft lip and cleft palate co-occ