bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of viscosity on the frozen wave instability: theory and experiment
Authors: TALIB EMMA , JALIKOP SHREYAS V. , JUEL ANNE 
Published: July 2007

We present the results of an experimental and linear stability study of the influence of viscosity on the frozen wave (FW) instability, which arises when a vessel containing stably stratified layers of immiscible liquids is oscillated horizontally. Our linear stability model consists of two superposed fluid layers of arbitrary viscosities and infinite lateral extent, subject to horizontal oscillation. The effect of the endwalls of the experimental vessel is simulated by enforcing the conservation of horizontal volume flux, so that the base flow consists of counterflowing layers.We perform experiments with four pairs of fluids, keeping the viscosity of the lower layer (ν1) constant, and increasing the viscosity of the upper layer (ν2), so that 1.02 × 102 ≤ N1 = ν2/ν1 ≤ 1.21 × 104. We find excellent quantitative agreement between theory and experiment despite the simple model geometry, for both the critical onset parameter and wavenumber of the FW. We show that the model of lyubimov:1987 (Fluid Dyn. vol. 86, 1987, p. 849), which is valid in the limit of inviscid fluids, consistently underestimates the instability threshold for fluids of equal viscosity, but generally overestimates the threshold for fluids of unequal viscosity. We extend the experimental parameter range numerically to viscosity contrasts 1 ≤ N1 ≤ 6 × 104 and identify four regions of N1 where qualitatively different dynamics occur, which are reflected in the non-monotonic dependence of the most unstable wavenumber and the critical amplitude on N1. In particular, we find that increasing the viscosity contrast between the layers leads to destabilization over a wide range of N1, 10 ≤ N1 ≤ 8 × 103. The intricate dependence of the instability on viscosity contrast is due to considerable changes in the time-averaged perturbation vorticity distribution near the interface.
Variable-density miscible displacements in a vertical Hele-Shaw cell: linear stability
Authors: GOYAL N. , PICHLER H. , MEIBURG E. 
Published: July 2007

A computational study based on the Stokes equations is conducted to investigate the effects of gravitational forces on miscible displacements in vertical Hele-Shaw cells. Nonlinear simulations provide the quasi-steady displacement fronts in the gap of the cell, whose stability to spanwise perturbations is subsequently examined by means of a linear stability analysis. The two-dimensional simulations indicate a marked thickening (thinning) and slowing down (speeding up) of the displacement front for flows stabilized (destabilized) by gravity. For the range investigated, the tip velocity is found to vary linearly with the gravity parameter. Strongly stable density stratifications lead to the emergence of flow patterns with spreading fronts, and to the emergence of a secondary needle-shaped finger, similar to earlier observations for capillary tube flows. In order to investigate the transition between viscously driven and purely gravitational instabilities, a comparison is presented between displacement flows and gravity-driven flows without net displacements.The linear stability analysis shows that both the growth rate and the dominant wavenumber depend only weakly on the Péclet number. The growth rate varies strongly with the gravity parameter, so that even a moderately stable density stratification can stabilize the displacement. Both the growth rate and the dominant wavelength increase with the viscosity ratio. For unstable density stratifications, the dominant wavelength is nearly independent of the gravity parameter, while it increases strongly for stable density stratifications. Finally, the kinematic wave theory of Lajeunesse et al. (J. Fluid Mech. vol. 398, 1999, p. 299) is seen to capture the stability limit quite accurately, while the Darcy analysis misses important aspects of the instability.
Unbalanced instabilities of rapidly rotating stratified shear flows
Authors: VANNESTE J. , YAVNEH I. 
Published: July 2007

The linear stability of a rotating stratified inviscid horizontal plane Couette flow in a channel is studied in the limit of strong rotation and stratification. Two dimensionless parameters characterize the flow: the Rossby number ε, defined as the ratio of the shear to the Coriolis frequency and assumed small, and the ratio s of the Coriolis frequency to the buoyancy frequency, assumed to satisfy s ≤ 1. An energy argument is used to show that unstable perturbations must have large, O(ε−1), wavenumbers. This motivates the use of a WKB-approach which, in the first instance, provides an approximation for the dispersion relation of the various waves that can propagate in the flow. These are Kelvin waves, trapped near the channel walls, and inertia–gravity waves with or without turning points.Although the waves have real phase speeds to all algebraic orders in ε, we establish that the flow is unconditionally unstable. This is the result of linear resonances between waves with oppositely signed wave momenta. Three modes of instabilities are identified, corresponding to the resonance between (i) a pair of Kelvin waves, (ii) a Kelvin wave and an inertia–gravity wave, and (iii) a pair of inertia–gravity waves. Whilst all three modes of instability are active when the Couette flow is anticyclonic, mode (iii) is the only possible instability mechanism when the flow is cyclonic.We derive asymptotic estimates for the instability growth rates. These are exponentially small in ε, i.e. of the form Im ω = a exp(-Ψ/ε) for some positive constants a and Ψ. For the Kelvin-wave instabilities (i), we obtain analytic expressions for a and Ψ; the maximum growth rate, in particular, corresponds to Ψ = 2. For the other types of instabilities, we make the simplifying assumption s ≪ 1 and find that the maximum growth rates correspond to Ψ=2.80 for (ii) and Ψ= π for (iii). The asymptotic results are confirmed by numerical computations. These reveal, in particular, that the instabilities (iii) have much smaller growth rates in cyclonic flows than in anticyclonic flows, even though Ψ = π in both cases.Our results highlight the limitations of the so-called balanced models, widely used in geophysical fluid dynamics, which filter out Kelvin and inertia–gravity waves and hence predict the stability of Couette flow. They are also relevant to the stability of Taylor–Couette flows and of astrophysical accretion disks.
Mixing at the interface between two fluids in porous media: a boundary-layer solution
Authors: PASTER AMIR , DAGAN GEDEON 
Published: July 2007

A lighter fluid (fresh water) flows steadily above a body of a standing heavier one (sea water) in a porous medium. If mixing by transverse pore-scale dispersion is neglected, a sharp interface separates the two fluids. Solutions for interface problems have been derived in the past, particularly for the case of interest here: sea-water intrusion in coastal aquifers. The Péclet number characterizing mixing, Pe = b′/αT where b′ is the aquifer thickness and αT is transverse dispersivity, is generally much larger than unity. Mixing is nevertheless important in a few applications, particularly in the development of a transition layer near the interface and in entrainment of sea water within this layer. The equations of flow and transport in the mixing zone comprise the unknown flux, pressure and concentration fields, which cannot be separated owing to the presence of density in the gravity term. They are nonlinear because of the advective term and the dependence of the dispersion coefficients on flux, the latter making the problem different from that of mixing between streams in laminar viscous flow.The aim of the study is to solve the mixing-layer problem for sea-water intrusion by using a boundary-layer approximation, which was used in the past for the case of uniform flow of the upper fluid, whereas here the two-dimensional flux field is non-uniform. The boundary-layer solution is obtained in a few steps: (i) analytical potential flow solution of the upper fluid above a sharp interface is adopted; (ii) the equations are reformulated with the potential and streamfunction of this flow serving as independent variables; (iii) boundary-layer approximate equations are formulated in terms of these variables; and (iv) simple analytical solutions are obtained by the von Káarmán integral method. The agreement with an existing boundary-layer solution for uniform flow is excellent, and similarly for a solution of a particular case of sea-water intrusion with a variable-density code. The present solution may serve for estimating the thickness of the mixing layer and the rate of sea-water entrainment in applications, as well as a benchmark for more complex problems.
Cost-effective species conservation: an application to Huemul (Hippocamelus bisulcus) in Chile
Authors: ISAZA CARLOS ADRIÁN SALDARRIAGA , BOFILL WALTER GÓMEZ , CABRERA HUGO SALGADO 
Published: July 2007

In this paper we study the cost-effective allocation of the land in the Cordilleran Protection Area (CPA), Region VIII, Chile, for the conservation of a highly threatened species: the Huemul (Hippocamelus bisulcus). Using a production possibilities frontier (PPF) approach, a linear programming optimization model for a ten-year time period is proposed. Our model takes into account both the preferences of the species for different habitats and the opportunity cost of the land. We evaluate different possibilities of land allocation and identify cost-effective alternatives in the provision of both conservation and income.The results confirm the hypothesis that both the population of Huemul and income from economic activities can be increased compared with current levels. Therefore the current allocation of the land in the CPA is not cost-effective.
Elective caesarean section and respiratory morbidity in the term and near‐term neonate
Authors: HANSEN ANNE KIRKEBY , WISBORG KIRSTEN , ULDBJERG NIELS , HENRIKSEN TINE BRINK 
Published: July 2007

AbstractAim. The aim of this review was to assess the relationship between delivery by elective caesarean section and respiratory morbidity in the term and near‐term neonate. Methods. Searches were made in the MEDLINE database, EMBASE, Cochrane database and Web of Science to identify peer‐reviewed studies in English on elective caesarean section and respiratory morbidity in the newborn. We included studies that compared elective caesarean section to vaginal or intended vaginal delivery, with clear definition of outcome measures and information about gestational age. Results. Nine eligible studies were identified. All studies found that delivery by elective caesarean section increased the risk of various respiratory morbidities in the newborn near term compared with vaginal delivery, although the findings were not statistically significant in all studies. It was inappropriate to carry out a meta‐analysis with a pooled risk estimate because of a variety of methodological differences between the studies. The overall risk for respiratory morbidity, however, seemed to increase about 2 to 3 times, though some studies presented much higher risk estimates. A decreasing risk with increasing gestational age was shown in 2 studies. Conclusion. Delivery by elective caesarean section was shown to increase the risk of respiratory morbidity in all studies eligible for inclusion. The magnitude of this relative risk seemed to depend on gestational age even in deliveries after 37 completed weeks of gestation.
Pre‐symptomatic increase in urine‐orosomucoid excretion in pre‐eclamptic women
Authors: KRONBORG CAMILLA S. , ALLEN JIM , VITTINGHUS ERIK , KNUDSEN ULLA BRETH 
Published: July 2007

AbstractBackground. Although the pre‐eclamptic pathogenesis begins at least around the 18th week of pregnancy, clinically evident disease often does not appear until the third trimester. This long pre‐symptomatic latency period has led to intensive research for early markers of evolving disease. We evaluated urine excretion and plasma levels of orosomucoid and albumin longitudinally in healthy and pre‐eclamptic pregnancies. Orosomucoid is an acute phase protein involved in inflammation and protection of the endothelium. Methods. From a prospective, longitudinal cohort study consisting of 1,631 women, 32 women developed pre‐eclampsia, and 5 controls for every case of pre‐eclampsia were found. Blood samples were collected 4 times and urine samples 6 times from the 18/19th week and throughout pregnancy. Orosomucoid and albumin in plasma were analysed by standard methods, and in urine by sandwich ELISA. Results. Orosomucoid/creatinin excretion ratio was significantly higher early in pre‐eclamptic pregnancies (from the 20th week of pregnancy, p = 0.0053) compared with healthy pregnancies, the difference increased throughout pregnancy. Albumin/creatinin ratio increased subsequent to the increase in orosomucoid. In the plasma samples, orosomucoid was significantly higher late in pre‐eclamptic pregnancies (≥36th week, p = 0.0275). Conclusions. Pre‐eclampsia is associated with a pre‐symptomatic increase in the urine excretion of orosomucoid, and orosomucoid excretion precedes that of albumin. Orosomucoid excretion can probably be used as a prognostic tool in combination with other screening methods, and seems to be a more sensitive marker for evolving pre‐eclampsia than albumin. Plasma orosomucoid is significantly increased late in pre‐eclampsia. Thus, the increased excretion of orosomucoid must primarily originate from altered renal processing of orosomucoid.
Women's experiences and attitudes towards expectant management and induction of labor for post‐term pregnancy
Authors: HEIMSTAD RUNA , ROMUNDSTAD PÅL R. , HYETT JON , MATTSSON LARS‐ÅKE , SALVESEN KJELL Å. 
Published: July 2007

AbstractBackground. Clinical guidelines for post‐term management differ, and studies on women's attitudes are lacking. We aimed to assess the experiences and attitudes among women managed with serial antenatal monitoring or induction of labor, and the effects of post‐term pregnancy on self‐reports of quality of life. Methods. Women were randomized at 41weeks to immediate induction of labor or antenatal fetal surveillance every third day. At inclusion women answered a questionnaire about their attitudes towards post‐term pregnancy and health‐related quality of life. This was repeated in a follow‐up phone interview 6months later, including questions about their experiences of labor and perspective on future deliveries. Results. A total of 508women entered the study. At 41weeks 74% of all women preferred to be induced. Women reported good general and mental health, but physical health and vitality scores were low. In the induction group, 74% of women said they would prefer the same management in future pregnancies; only 38% of women who had serial antenatal monitoring would prefer this option again (p<0.001). In the induction group, contractions were reported as more intense (n = 157 versus n = 118, p<0.01) and frequent (n = 116 versus n = 87, p<0.01) compared to the monitored group. The majority (84%) reported a positive labor induction experience. Conclusion. Women preferred induction of labor to serial antenatal monitoring beyond 41weeks. Labors were shorter and contractions were reported to be more frequent and intense in the induction group compared with the monitored group. However, their experience with labor induction was positive.
N‐terminal parathyroid hormone‐related protein levels in human intrauterine growth restricted pregnancies
Authors: BRIANA DESPINA D. , BOUTSIKOU MARIA , BAKA STAVROULA , HASSIAKOS DEMETRIOS , GOURGIOTIS DEMETRIOS , MARMARINOS ANTONIOS , IACOVIDOU NICOLETTA , MALAMITSI‐PUCHNER ARIADNE 
Published: July 2007

AbstractBackground. N‐terminal parathyroid hormone‐related protein has a vital role in regulating cell growth and differentiation, uteroplacental vasodilatation, uterine muscle relaxation, and placental transport. These functions are compromised in intrauterine growth restriction. We aimed to investigate N‐terminal parathyroid hormone‐related protein concentrations in maternal, fetal, and neonatal plasma of intrauterine‐growth‐restricted and appropriate for gestational age pregnancies. Methods. Plasma N‐terminal parathyroid hormone‐related protein levels were determined in 40 mothers and their 20 intrauterine‐growth‐restricted and 20 appropriate for gestational age singleton full‐term fetuses and neonates on postnatal days 1 and 4. Results. Fetal N‐terminal parathyroid hormone‐related protein levels were significantly lower in the intrauterine growth restriction group (b = 1.166, 95%CI: 0.430–1.902, p = 0.003) and correlated with the customized centiles of the infants (r = 0.407, p = 0.009). In the appropriate for gestational age group, neonatal day 1 N‐terminal parathyroid hormone‐related protein levels were significantly lower compared to maternal (p<0.001) and fetal (p = 0.022) ones. Fetal and neonatal day 1 levels were significantly lower in males (b = −1.303, 95%CI: −2.508 to −0.097, p = 0.036, and b = −0.802, 95%CI: −1.5 to −0.105, p = 0.027, respectively). In the intrauterine growth restriction group, maternal N‐terminal parathyroid hormone‐related protein levels were significantly increased compared to fetal (p<0.001) and neonatal day 1 (p = 0.001) levels. Conclusions. The reduced fetal N‐terminal parathyroid hormone‐related protein concentrations in intrauterine growth restriction may reflect compromised placental function and impaired fetal growth, suggesting that N‐terminal parathyroid hormone‐related protein may be involved in the pathogenesis of intrauterine growth restriction.
Erythropoietin and intravenous iron therapy in postpartum anaemia
Authors: WÅGSTRÖM ELLE , ÅKESSON AGNETA , VAN ROOIJEN MARIANNE , LARSON BARBRO , BREMME KATARINA 
Published: July 2007

AbstractBackground. We assessed whether recombinant human erythropoietin (rhEPO) enhances a rise in haemoglobin concentration in postpartum anaemia compared to intravenous iron alone. Design. Some 60 patients with haemoglobin values≤80 g/l were randomized within 72 h after parturition into 3 different treatment groups. All 3 groups were given a total dose of 450 mg intravenous iron sucrose. In addition, 2 groups were given 20,000 or 40,000 U of total rhEPO. All treatments were given on 2 occasions with an interval of 3 days (day 0 and 3). Results. Haemoglobin increased significantly in all 3 groups over time (p<0.001), and there were no differences between the different treatment groups on any day of evaluation (p = 0.59). The total mean increment in haemoglobin in all subjects was 18 g/l after 1 week, and 28 g/l after 2 weeks. Conclusion. In comparison to intravenous iron alone, the addition of rhEPO did not further increase haemoglobin concentration in women with postpartum anaemia.
Tight junction formation in epithelial ovarian adenocarcinoma
Authors: ZHU YIHONG , SUNDFELDT KARIN 
Published: July 2007

AbstractBackground. Epithelial cells are characterised by their ability to form polarised cell sheets with barriers between two tissue compartments. Epithelial tightness and apical/basolateral orientation are maintained through adherens and tight junctions (TJs). Alterations in junction formation and function could promote tumorigenesis via increased access to growth factors and cytokines. The etiology and development of epithelial ovarian cancer (EOC) are far from understood. The ovarian surface epithelium (OSE), regarded as progenitor cells of EOC, form weak functional TJs in culture without expressing typical junction proteins. However, these integral membrane epithelial proteins, E‐cadherin, claudin‐3 and claudin‐4, are often found in EOC. Methods. To clarify whether EOC can form functional TJs, 4 different ovarian cancer cell lines of various histology were analysed for their expression of TJ (claudin‐1, claudin‐3, claudin‐4 and zonola occludens‐1 (ZO‐1)) and adherens junction (AJ) (E‐cadherin and N‐cadherin) proteins, and the ability to build up trans‐epithelial resistance (TER) in culture was measured. Results. We found expression for all cell‐junction proteins with a typical honeycomb‐staining pattern in the serous adenocarcinomas indicating proper junction formation. Clear‐cell and endometrioid adenocarcinomas showed a different expression pattern. By measuring TER, including Ca2+ switch experiments, functional TJs were shown to build up only in serous adenocarcinomas. Conclusion. Serous adenocarcinomas formed functional TJs in vitro. The presence of claudin‐4 might be essential for the function of TJs in ovarian cancer.
Undergraduate Teaching of Child and Adolescent Psychiatry in Australia: Survey of Current Practice
Authors: Sawyer Michael , Giesen Femke 
Published: July 2007

Objective: To identify the goals, content, and time allocated for undergraduate child psychiatry teaching programmes in Australian medical schools. Method: A structured questionnaire designed specifically for the present study was used to identify the goals, content, and time allocated to child psychiatry teaching for undergraduate medical students. Staff responsible for child psychiatry teaching programmes at all 15 medical schools in Australia were contacted and those in 12 schools (80%) agreed to participate. Results: All 12 medical schools provided some teaching relevant to child psychiatry. Teaching was commonly provided as part of general psychiatry and/or paediatric teaching programmes. Between 4 and 12 h were allocated for child psychiatry teaching, with the exception of one school, which assigned 46 h. Ten schools (83%) offered clinical placements in child psychiatry to some or all students, with placements ranging in length from 0.5 days to 8 weeks. However, only four schools (33%) offered clinical placements to all students. Two schools (17%) offered no clinical placements or electives in child psychiatry. The skills required to assess children and families, and knowledge about normal child development were identified as key teaching goals. Barriers to teaching child psychiatry included the lack of academic child psychiatrists in Australia, and the limited time allocated for this teaching in medical school curricula. Conclusions: The amount of time allocated for teaching child psychiatry in Australian medical schools is relatively small and not consistent with the size of the public health problem posed by child and adolescent mental disorders. Staff responsible for teaching child psychiatry need to coordinate their activities more effectively at a national level to identify teaching goals, design curricula, and advocate for high-quality child psychiatry teaching programmes in medical schools.