An in vitro experimental investigation of oscillatory flow in the cerebral aqueduct

This in vitro study aims at clarifying the relation between the oscillatory flow of cerebrospinal fluid (CSF) in the cerebral aqueduct, a narrow conduit connecting the third and fourth ventricles, and the corresponding interventricular pressure difference. Dimensional analysis is used in designing an anatomically correct scaled model of the aqueduct flow, with physical similarity maintained by adjusting the flow frequency and the properties of the working fluid. The time-varying pressure difference across the aqueduct corresponding to a given oscillatory flow rate is measured in parametric ranges covering the range of flow conditions commonly encountered in healthy subjects. Parametric dependences are delineated for the time-averaged pressure fluctuations and for the phase lag between the transaqueductal pressure difference and the flow rate, both having clinical relevance. The results are validated through comparisons with predictions obtained with a previously derived computational model. The parametric quantification in this study enables the derivation of a simple formula for the relation between the transaqueductal pressure and the stroke volume. This relationship can be useful in the quantification of transmantle pressure differences based on non-invasive magnetic-resonance-velocimetry measurements of aqueduct flow for investigation of CSF-related disorders.National Institutes of Health/ National Institute of Neurological Diseases and Stroke through contract # 1R01NS120343-0

On the dispersion of a drug delivered intrathecally in the spinal canal

This paper investigates the transport of a solute carried by the cerebrospinal fluid (CSF) in the spinal canal. The analysis is motivated by the need for a better understanding of drug dispersion in connection with intrathecal drug delivery (ITDD), a medical procedure used for treatment of some cancers, infections and pain, involving the delivery of the drug to the central nervous system by direct injection into the CSF via the lumbar route. The description accounts for the CSF motion in the spinal canal, described in our recent publication (Sánchez et al., J. Fluid Mech., vol. 841, 2018, pp. 203-227). The Eulerian velocity field includes an oscillatory component with angular frequency omega, equal to that of the cardiac cycle, and associated tidal volumes that are a factor epsilon 1 smaller than the total CSF volume in the spinal canal, with the small velocity corrections resulting from convective acceleration providing a steady-streaming component with characteristic residence times of order epsilon 2omega 1 omega 1 . An asymptotic analysis for epsilon 1 accounting for the two time scales omega 1 and epsilon 2omega 1 is used to investigate the prevailing drug-dispersion mechanisms and their dependence on the solute diffusivity, measured by the Schmidt number S. Convective transport driven by the time-averaged Lagrangian velocity, obtained as the sum of the Eulerian steady-streaming velocity and the Stokes-drift velocity associated with the non-uniform pulsating flow, is found to be important for all values of S. By way of contrast, shear-enhanced Taylor dispersion, which is important for values of S of order unity, is shown to be negligibly small for the large values S epsilon 2 1 corresponding to the molecular diffusivities of all ITDD drugs. Results for a model geometry indicate that a simplified equation derived in the intermediate limit 1 S epsilon 2 provides sufficient accuracy under most conditions, and therefore could constitute an attractive reduced model for future quantitative analyses of drug dispersion in the spinal canal. The results can be used to quantify dependences of the drug-dispersion rate on the frequency and amplitude of the pulsation of the intracranial pressure, the compliance and specific geometry of the spinal canal and the molecular diffusivity of the drug.C.M.-B. acknowledges the financial support provided by the Spanish MINECO (Secretaría de Estado de Investigación, Desarrollo e Innovación) through grants DPI2014-59292-C3-3 and DPI2017-88201-C3-2-R, co-financed by the European Regional Development Fund (ERDF)

Transmantle pressure computed from MR imaging measurements of aqueduct flow and dimensions

BACKGROUND AND PURPOSE: Measuring transmantle pressure, the instantaneous pressure difference between the lateral ventricles and the cranial subarachnoid space, by intracranial pressure sensors has limitations. The aim of this study was to compute transmantle pressure noninvasively with a novel nondimensional fluid mechanics model in volunteers and to identify differences related to age and aqueductal dimensions. MATERIALS AND METHODS: Brain MR images including cardiac-gated 2D phase-contrast MR imaging and fast-spoiled gradient recalled imaging were obtained in 77 volunteers ranging in age from 25-92 years of age. Transmantle pressure was computed during the cardiac cycle with a fluid mechanics model from the measured aqueductal flow rate, stroke volume, aqueductal length and cross-sectional area, and heart rate. Peak pressures during caudal and rostral aqueductal flow were tabulated. The computed transmantle pressure, aqueductal dimensions, and stroke volume were estimated, and the differences due to sex and age were calculated and tested for significance. RESULTS: Peak transmantle pressure was calculated with the nondimensional averaged 14.4 (SD, 6.5) Pa during caudal flow and 6.9 (SD, 2.8) Pa during rostral flow. It did not differ significantly between men and women or correlate significantly with heart rate. Peak transmantle pressure increased with age and correlated with aqueductal dimensions and stroke volume. CONCLUSIONS: The nondimensional fluid mechanics model for computing transmantle pressure detected changes in pressure related to age and aqueductal dimensions. This novel methodology can be easily used to investigate the clinical relevance of the transmantle pressure in normal pressure hydrocephalus, pediatric communicating hydrocephalus, and other CSF disorders

On the Timing and Nature of the Multiple Phases of Slope Instability on Eastern Rockall Bank, Northeast Atlantic

One of the most challenging tasks when studying large submarine landslides is determining whether the landslide was initiated as a single large event, a chain of events closely spaced in time or multiple events separated by long periods of time as all have implications in risk assessments. In this study we combine new multichannel seismic profiles and new sediment cores with bathymetric data to test whether the Rockall Bank Slide Complex, offshore western Ireland, is the composite of multiple slope collapse events and, if so, to differentiate them. We conclude that there have been at least three voluminous episodes of slope collapse separated by long periods of slope stability, a fourth, less voluminous event, and possibly a fifth more localized event. The oldest event, Slide A (200 km3), is estimated to be several hundred thousand years old. The second event, Slide B (125 km3), took place at the same location as slide A, reactivating the same scar, nearly 200 ka ago, possibly through retrogression of the scarp. Slide C (400 km3) took place 22 ka ago and occurred further north from the other slides. Slide D was a much smaller event that happened 10 ka ago, while the most recent event, albeit very small scale, took place within the last 1,000 years. This study highlights the need to thoroughly investigate large slide complexes to evaluate event sequencing, as seismic studies may hide multiple small‐scale events. This work also reveals that the same slide scarps can be reactivated and generate slides with different flow behaviors

‘Sons of athelings given to the earth’: Infant Mortality within Anglo-Saxon Mortuary Geography

FOR 20 OR MORE YEARS early Anglo-Saxon archaeologists have believed children are underrepresented in the cemetery evidence. They conclude that excavation misses small bones, that previous attitudes to reporting overlook the very young, or that infants and children were buried elsewhere. This is all well and good, but we must be careful of oversimplifying compound social and cultural responses to childhood and infant mortality. Previous approaches have offered methodological quandaries in the face of this under-representation. However, proportionally more infants were placed in large cemeteries and sometimes in specific zones. This trend is statistically significant and is therefore unlikely to result entirely from preservation or excavation problems. Early medieval cemeteries were part of regional mortuary geographies and provided places to stage events that promoted social cohesion across kinship systems extending over tribal territories. This paper argues that patterns in early Anglo-Saxon infant burial were the result of female mobility. Many women probably travelled locally to marry in a union which reinforced existing social networks. For an expectant mother, however, the safest place to give birth was with experience women in her maternal home. Infant identities were affected by personal and legal association with their mother’s parental kindred, so when an infant died in childbirth or months and years later, it was their mother’s identity which dictated burial location. As a result, cemeteries central to tribal identities became places to bury the sons and daughters of a regional tribal aristocracy

EXPLORING THE ROLE OF OSPREYS IN EDUCATION

Recent research in childhood education has demonstrated that experiences in nature are important in shaping early environmental consciousness (Hinds and Sparks 2008, Hussar and Horvath 2011, Cheng and Monroe 2012) and ultimately the expression of pro-environmental attitudes and behaviors during adulthood (Wells and Lekies 2006, Chawla and Cushing 2007, Collado et al. 2013). Increasingly, those experiences happen via written and electronic media (e.g., textbooks, computer screens) or in very anthropogenic environments (e.g., in parks and zoos) and less through direct contact with nature, a concept Louv (2005) referred to as ‘‘nature deficit disorder.’’ Even in schools where environmental education is prioritized, the extent of access to outdoor classroom activities or experiential learning opportunities can limit the degree to which children can observe, explore, and directly experience the natural world (Hudson 2001, Louv 2005, Ernst 2009). Interestingly, the same information technologies that might serve to limit contact with nature also have the potential to enhance and encourage interest and concern for the natural world (Blewitt 2011, Pearson et al. 2011). We believe this is an important paradox that warrants much further exploration and evaluation within educational and scientific communities

Ethnopolitics Across Central and Eastern Europe in a State of Flux: Time for Updating and Upgrading?

This chapter illustrates why and how the existing theoretical models in the study of ethnopolitics need to be updated in light of the latest developments and the increasing impact of new catalysts. These are, namely, anti-immigration and the rise of the populist and radical right across Central and Eastern Europe. This chapter hints that the more systematic cooperation between academic experts in nationalism and academic experts in the populist and radical right will enable: (a) the former to assess more accurately the degree to which new variables such as Euroscepticism and anti-immigrant trends can reshape ethnopolitics, both as a living reality and a field of study, across Central and Eastern Europe; (b) the latter to formulate new interpretative models about how (right-wing) populist and Eurosceptic actors embed their agendas inside the pre-existing political cultures of nationalism and particularistic identity and memory politics. This chapter introduces and outlines the ethnosymbolic approach as well as the triadic and quadratic configurations of ethnopolitics. Then, it proceeds into a more empirical assessment of the applicability of these theoretical approaches in a series of case studies during the 1990s, as well as the more recent emergence of new catalysts and the ensuing necessity to update and upgrade the existing theoretical models

Networking Our Way to Better Ecosystem Service Provision.

The ecosystem services (EcoS) concept is being used increasingly to attach values to natural systems and the multiple benefits they provide to human societies. Ecosystem processes or functions only become EcoS if they are shown to have social and/or economic value. This should assure an explicit connection between the natural and social sciences, but EcoS approaches have been criticized for retaining little natural science. Preserving the natural, ecological science context within EcoS research is challenging because the multiple disciplines involved have very different traditions and vocabularies (common-language challenge) and span many organizational levels and temporal and spatial scales (scale challenge) that define the relevant interacting entities (interaction challenge). We propose a network-based approach to transcend these discipline challenges and place the natural science context at the heart of EcoS research.The QUINTESSENCE Consortium gratefully acknowledges the support of Départment SPE and Métaprogramme ECOSERV of INRA, and the French ANR projects PEERLESS (ANR-12-AGRO-0006) and AgroBioSE (ANR-13-AGRO-0001).This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.tree.2015.12.00