Induced Anticlinic Ordering and Nanophase Segregation of Bow-Shaped Molecules in a Smectic Solvent

Recent experiments indicate that doping low concentrations of bent-core molecules into calamitic smectic solvents can induce anticlinic and biaxial smectic phases. We have carried out Monte Carlo (MC) simulations of mixtures of rodlike molecules (hard spherocylinders with length/breadth ratio $L_{\rm rod}/D = 5$) and bow- or banana-shaped molecules (hard spherocylinder dimers with length/breadth ratio $L_{ban}/D = 5$ or 2.5 and opening angle $\psi$) to probe the molecular-scale organization and phase behavior of rod/banana mixtures. We find that a low concentration (3%) of $L_{ban}/D = 5$ dimers induces anticlinic (SmC$_A$) ordering in an untilted smectic (SmA) phase for $100^\circ \le \psi < 150^\circ$. For smaller $\psi$, half of each bow-shaped molecule is nanophase segregated between smectic layers, and the smectic layers are untilted. For $L_{ban}/D = 2.5$, no tilted phases are induced. However, with decreasing $\psi$ we observe a sharp transition from {\sl intralamellar} nanophase segregation (bow-shaped molecules segregated within smectic layers) to {\sl interlamellar} nanophase segregation (bow-shaped molecules concentrated between smectic layers) near $\psi = 130^\circ$. These results demonstrate that purely entropic effects can lead to surprisingly complex behavior in rod/banana mixtures.Comment: 5 pages Revtex, 7 postscript figure

Aortic valve opening and closure: the clover dynamics.

Background: Systolic aortic root expansion is reported to facilitate valve opening, but the precise dynamics remain unknown. A sonometric study with a high data sampling rate (200 to 800 Hz) was conducted in an acute ovine model to better understand the timing, mechanisms, and shape of aortic valve opening and closure. Methods: Eighteen piezoelectric crystals were implanted in 8 sheep at each annular base, commissures, sinus of Valsalva, sinotubular junction, nodulus of Arantius, and ascending aorta (AA). Geometric changes were time related to pressures and flows. Results: The aortic root was hemodynamically divided into left ventricular (LV) and aortic compartments situated, respectively, below and above the leaflets. During isovolumetric contraction (IVC), aortic root expansion started in the LV compartment, most likely due to volume redistribution in the LV outflow tract below the leaflets. This expansion initiated leaflet separation prior to ejection (2.1%±0.5% of total opening area). Aortic compartment expansion was delayed toward the end of IVC, likely related to volume redistribution above the leaflets due to accelerating aortic backflow toward the aortic valve and coronary flow reduction due to myocardial contraction. Maximum valve opening during the first third of ejection acquired a truncated cone shape [leaflet free edge area smaller than annular base area (-41.5%±5.5%)]. The distal orifice became clover shaped because the leaflet free edge area is larger than the commissural area by 16.3%±2.0%. Conclusions: Aortic valve opening is initiated prior to ejection related to delicate balance between LV, aortic root, and coronary dynamics. It is clover shaped at maximum opening in systole. A better understanding of these mechanisms should stimulate more physiological surgical approaches of valve repair and replacement

Multifaceted intervention to decrease the rate of severe postpartum haemorrhage: the PITHAGORE6 cluster-randomised controlled trial.: Intervention to decrease severe postpartum haemorrhage

International audienceOBJECTIVE: Decreasing the prevalence of severe postpartum haemorrhages (PPH) is a major obstetrical challenge. These are often considered to be associated with substandard initial care. Strategies to increase the appropriateness of early management of PPH must be assessed. We tested the hypothesis that a multifaceted intervention aimed at increasing the translation into practice of a protocol for early management of PPH, would reduce the incidence of severe PPH. DESIGN: Cluster-randomised trial. POPULATION: 106 maternity units in six French regions. METHODS: Maternity units were randomly assigned to receive the intervention, or to have the protocol passively disseminated. The intervention combined outreach visits to discuss the protocol in each local context, reminders, and peer reviews of severe incidents, and was implemented in each maternity hospital by a team pairing an obstetrician and a midwife. MAIN OUTCOME MEASURES: The primary outcome was the incidence of severe PPH, defined as a composite of one or more of: transfusion, embolisation, surgical procedure, transfer to intensive care, peripartum haemoglobin decrease of 4 g/dl or more, death. The main secondary outcomes were PPH management practices. RESULTS: The mean rate of severe PPH was 1.64% (SD 0.80) in the intervention units and 1.65% (SD 0.96) in control units; difference not significant. Some elements of PPH management were applied more frequently in intervention units-help from senior staff (P = 0.005), or tended to - second-line pharmacological treatment (P = 0.06), timely blood test (P = 0.09). CONCLUSION: This educational intervention did not affect the rate of severe PPH as compared with control units, although it improved some practices

Semen cryopreservation, utilisation and reproductive outcome in men treated for Hodgkin's disease

Between 1978 and 1990, 122 men underwent semen analysis before starting sterilising chemotherapy for Hodgkin's disease. Eighty-one (66%) had semen quality within the normal range, 25 were oligospermic (<20×106 sperm per ml) and five were azoospermic (no sperm in the ejaculate). Semen from 115 men was cryopreserved and after a median follow-up time of 10.1 years, 33 men have utilised stored semen (actuarial rate 27%) and nine partners have become pregnant resulting in 11 live births and one termination for foetal malformation. Actuarial 10 year rates of destruction of semen before death or utilisation and death before utilisation are 19% and 13% respectively. This retrospective cohort study demonstrates that approximately one-quarter of men utilising cryopreserved semen after treatment for Hodgkin's disease obtain a live birth. The high non-utilisation rate is intriguing and warrants further investigation

Immersed boundary-finite element model of fluid-structure interaction in the aortic root

It has long been recognized that aortic root elasticity helps to ensure efficient aortic valve closure, but our understanding of the functional importance of the elasticity and geometry of the aortic root continues to evolve as increasingly detailed in vivo imaging data become available. Herein, we describe fluid-structure interaction models of the aortic root, including the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the sinotubular junction, that employ a version of Peskin's immersed boundary (IB) method with a finite element (FE) description of the structural elasticity. We develop both an idealized model of the root with three-fold symmetry of the aortic sinuses and valve leaflets, and a more realistic model that accounts for the differences in the sizes of the left, right, and noncoronary sinuses and corresponding valve cusps. As in earlier work, we use fiber-based models of the valve leaflets, but this study extends earlier IB models of the aortic root by employing incompressible hyperelastic models of the mechanics of the sinuses and ascending aorta using a constitutive law fit to experimental data from human aortic root tissue. In vivo pressure loading is accounted for by a backwards displacement method that determines the unloaded configurations of the root models. Our models yield realistic cardiac output at physiological pressures, with low transvalvular pressure differences during forward flow, minimal regurgitation during valve closure, and realistic pressure loads when the valve is closed during diastole. Further, results from high-resolution computations demonstrate that IB models of the aortic valve are able to produce essentially grid-converged dynamics at practical grid spacings for the high-Reynolds number flows of the aortic root

A project for future life—Swedish women's thoughts on childbearing lacking experience of giving birth and parenthood

A lifeworld hermeneutic approach was used in order to understand Swedish women's thoughts on childbearing. Nine women were interviewed, and they ranged in age from 22 to 28 years and represented diverse socioeconomic, educational, sexual, and fertility backgrounds. All women were similar in that they lacked experience of giving birth and parenthood. The analysis showed that childbearing includes dimensions of both immanence and transcendence. Immanence, as childbearing is seen as stagnant to women's freedom in present life. Transcendence, as childbearing is thought of as a project for future life, a part of female identity, and a conscious standpoint for which the woman wants to be prepared and for which she wants to create the best conditions