Mobility of Power-law and Carreau Fluids through Fibrous Media

The flow of generalized Newtonian fluids with a rate-dependent viscosity through fibrous media is studied with a focus on developing relationships for evaluating the effective fluid mobility. Three different methods have been used here: i) a numerical solution of the Cauchy momentum equation with the Carreau or power-law constitutive equations for pressure-driven flow in a fiber bed consisting of a periodic array of cylindrical fibers, ii) an analytical solution for a unit cell model representing the flow characteristics of a periodic fibrous medium, and iii) a scaling analysis of characteristic bulk parameters such as the effective shear rate, the effective viscosity, geometrical parameters of the system, and the fluid rheology. Our scaling analysis yields simple expressions for evaluating the transverse mobility functions for each model, which can be used for a wide range of medium porosity and fluid rheological parameters. While the dimensionless mobility is, in general, a function of the Carreau number and the medium porosity, our results show that for porosities less than $\varepsilon\simeq0.65$, the dimensionless mobility becomes independent of the Carreau number and the mobility function exhibits power-law characteristics as a result of high shear rates at the pore scale. We derive a suitable criterion for determining the flow regime and the transition from a constant viscosity Newtonian response to a power-law regime in terms of a new Carreau number rescaled with a dimensionless function which incorporates the medium porosity and the arrangement of fibers

In vitro Cortical Network Firing is Homeostatically Regulated: A Model for Sleep Regulation.

Prolonged wakefulness leads to a homeostatic response manifested in increased amplitude and number of electroencephalogram (EEG) slow waves during recovery sleep. Cortical networks show a slow oscillation when the excitatory inputs are reduced (during slow wave sleep, anesthesia), or absent (in vitro preparations). It was recently shown that a homeostatic response to electrical stimulation can be induced in cortical cultures. Here we used cortical cultures grown on microelectrode arrays and stimulated them with a cocktail of waking neuromodulators. We found that recovery from stimulation resulted in a dose-dependent homeostatic response. Specifically, the inter-burst intervals decreased, the burst duration increased, the network showed higher cross-correlation and strong phasic synchronized burst activity. Spectral power below <1.75 Hz significantly increased and the increase was related to steeper slopes of bursts. Computer simulation suggested that a small number of clustered neurons could potently drive the behavior of the network both at baseline and during recovery. Thus, this in vitro model appears valuable for dissecting network mechanisms of sleep homeostasis

Infant Serum and Maternal Milk Vitamin B-12 Are Positively Correlated in Kenyan Infant-Mother Dyads at 1-6 Months Postpartum, Irrespective of Infant Feeding Practice.

BackgroundVitamin B-12 is an essential nutrient required for many functions including DNA synthesis, erythropoiesis, and brain development. If maternal milk vitamin B-12 concentrations are low, infants may face elevated risks of deficiency when exclusively breastfed.ObjectiveWe evaluated cross-sectional associations between infant serum vitamin B-12 concentrations and maternal milk vitamin B-12 concentrations at 1-6 mo postpartum among an unsupplemented population in rural western Kenya, and assessed biological demographic, and dietary characteristics associated with adequate infant serum vitamin B-12.MethodsWe modeled 1) infant serum vitamin B-12 using maternal milk vitamin B-12 concentration with linear regression; and 2) adequate (>220 pmol/L) infant serum vitamin B-12 using hypothesized biological, demographic, and dietary predictors with logistic regression. In both models, we used generalized estimating equations to account for correlated observations at the cluster-level.ResultsThe median (quartile 1, quartile 3) infant serum vitamin B-12 concentration was 276 pmol/L (193, 399 pmol/L) and approximately one-third of infants had serum vitamin B-12 ≤220 pmol/L, indicating that they were vitamin B-12 depleted or deficient. There was a positive correlation between maternal milk and infant serum vitamin B-12 (r = 0.36, P < 0.001) and in multivariable analyses, maternal milk vitamin B-12 concentration was significantly associated with infant serum vitamin B-12 adequacy (P-trend = 0.03).ConclusionsDespite a high prevalence (90%) of maternal milk vitamin B-12 concentrations below the level used to establish the Adequate Intake (<310 pmol/L), there was a low prevalence of infant vitamin B-12 deficiency. We found few factors that were associated with infant vitamin B-12 adequacy in this population, including infant feeding practices, although maternal vitamin B-12 status was not measured. The contribution of maternal milk to infant vitamin B-12 status remains important to quantify across populations, given that maternal milk vitamin B-12 concentration is modifiable with supplementation. This trial was registered at clinicaltrials.gov as NCT01704105

Frequency and antimicrobial susceptibility of Shigella species isolated in Children Medical Center Hospital, Tehran, Iran, 2001-2006

AbstractAppropriate antimicrobial treatment of shigellosis depends on identifying its changing resistance pattern over time. We evaluated 15,255 stool culture submitted from July 2001 to June 2006 to the Laboratory of Children Medical Center Hospital. Specimen culture, bacterial identification, and disk diffusion susceptibility testing were performed according to National Committee for Clinical Laboratory Standards guidelines. From 15,255 stool samples, 682 (4.5%) were positive for Shigella species. The most common species of Shigella were S. flexneri (48%) and S. sonnei (45%); other results were S. dysenteriae (5%) and S. boydii (2%). The rate of Sensitivity to ceftriaxone (95%), ceftizoxime (94%), and nalidixic acid (84%) were among our isolates. Resistance to co-trimoxazole and ampicillin was 87% and 86%, respectively. S. flexneri was more multiresistant than other species (47.9%). Our isolates are overall most sensitive to ceftriaxone, ceftazidime, and nalidixic acid (> 84%). They were most resistant to co-trimoxazole and ampicillin (> 86%). Because resistance varies according to specific location, continuous local monitoring of resistance patterns is necessary for the appropriate selection of empirical antimicrobial therapy

Adequate vitamin B12 and folate status of Norwegian vegans and vegetarians

Plant-based diets may increase the risk of vitamin B12 deficiency due to limited intake of animal-source foods, while dietary folate increases when adhering to plant-based diets. In this cross-sectional study, we evaluated the B12 and folate status of Norwegian vegans and vegetarians using dietary B12 intake, B12- and folic acid supplement use, and biomarkers (serum B12 [B12], plasma total-homocysteine [tHcy], plasma-methylmalonic acid [MMA], and serum-folate). Vegans (n=115) and vegetarians (n=90) completed a 24-hour dietary recall and a food-frequency questionnaire and provided a non-fasting blood sample. cB12, a combined indicator for evaluation of B12 status, was calculated. B12 status were adequate in both vegans and vegetarians according to the cB12 indicator, however 4% had elevated B12. Serum B12, tHcy, MMA concentrations and the cB12 indicator (overall median: 357pmol/L, 9.0µmol/L, 0.18µmol/L, 1.30 (cB12)) did not differ between vegans and vegetarians, unlike for folate (vegans: 25.8nmol/L, vegetarians: 21.6nmol/L, p=0.027). Serum B12 concentration <221pmol/L, was found in 14% of all participants. Vegetarians revealed the highest proportion of participants below the RDI of 2 µg/day including supplements (40 vs. 18%, p<0.001). Predictors of higher serum B12 concentrations were average daily supplement use and older age. Folate deficiency (<10 nmol/L) was uncommon overall (<2.5%). The combined indicator cB12 suggested that none of the participants was B12 depleted, however low serum B12 concentration was found in 14% of the participants. Folate concentrations were adequate, indicating adequate folate intake in Norwegian vegans and vegetarians.publishedVersionPaid open acces