654 research outputs found
Data Assimilation by Stochastic Ensemble Kalman Filtering to Enhance Turbulent Cardiovascular Flow Data From Under-Resolved Observations
No full textWe propose a data assimilation methodology that can be used to enhance the spatial and temporal resolution of voxel-based data as it may be obtained from biomedical imaging modalities. It can be used to improve the assessment of turbulent blood flow in large vessels by combining observed data with a computational fluid dynamics solver. The methodology is based on a Stochastic Ensemble Kalman Filter (SEnKF) approach and geared toward pulsatile and turbulent flow configurations. We describe the observed flow fields by a mean value and its covariance. These flow fields are combined with forecasts obtained from a direct numerical simulation of the flow field. The method is validated against canonical pulsatile and turbulent flows. Finally, it is applied to a clinically relevant configuration, namely the flow downstream of a bioprosthetic valve in an aorta phantom. It is demonstrated how the 4D flow field obtained from experimental observations can be enhanced by the data assimilation algorithm. Results show that the presented method is promising for future use with in vivo data from 4D Flow Magnetic Resonance Imaging (4D Flow MRI). 4D Flow MRI returns spatially and temporally averaged flow fields that are limited by the spatial and the temporal resolution of the tool. These averaged flow fields and the associated uncertainty might be used as observation data in the context of the proposed methodology
Publication: 'Point d' Ironie issue number 16', published by Agnes B and Hans Ulrich Obrist, Paris, (2000)
No full textGiven out to the public, free of charge, 'Point d’Ironie' is an atypical periodical, distributed in a scattered way – 100,000 copies are spread around the world, available in museums, galleries, book shops, schools, cinemas, and at agnès b. stores worldwide.
It is published by Agnes B and Hans - Ulrich Obrist.
Created by French poet Alcanter de Brahm at the end of the 19th century, the Point d’Ironie is a punctuation mark used at the end of sentences to point an ironic passage within a text.
The Point d’Ironie originated following a discussion between agnès b., Christian Boltanski and Hans Ulrich Obrist in 1997. Six to eight issues are published every year, each one designed by an artist who makes it his own.
Since 1997, many international artists have taken part in the publications including Matthew Barney, Christian Boltanski, Louise Bourgeois, Frédéric Bruly Bouabré, Tobias Buche, Robert Crumb, Tacita Dean, Hans-Peter Feldmann, Michel Foucault, Yona Friedman, Gilbert & George, Douglas Gordon, Dan Graham, Damien Hirst, David Hockney, Roni Horn, Ryan McGinley, Jonas Mekas, Annette Messager, Yoko Ono, Gabriel Orozco, Raymond Pettibon, Richard Prince, Walid Raad, Raqs Media, Navin, Ed Ruscha, Nancy Spero, Dayanita Singh, Rosemarie Trockel
Rirkrit Tiravanija, Agnès Varda and Lawrence Weiner
Relation between hematocrit partitioning and red blood cell lingering in a microfluidic network.
No full textDespite increased interest in the effect of lingering red blood cells (LRBCs) on the heterogeneous hematocrit distribution in the microcirculation, quantitative data on LRBCs before and after the lingering event is still limited. The aim of the study was to investigate the relation between RBC lingering and hematocrit partitioning in a microfluidic model of a microvascular bifurcation in the limit of low hematocrit conditions (tube hematocrit < 10%). To this end, the classification of lingering RBCs was performed based on timing, position, and velocity of the RBCs. The investigation provided statistical information on the velocity, shape, and orientation of lingering RBCs as well as on their lateral distribution in the parent and daughter vessels. LRBCs traveled predominantly close to the centerline of the parent vessel, but they marginated close to the distal wall in the daughter vessels. Differently than the RBC flow observed in the smallest vessels, no influence of lingering events on the local hematocrit partitioning was observed in our experiments. However, we importantly found that lingering RBCs flowing in the daughter vessel after lingering may be connected to reverse hematocrit partitioning in downstream bifurcations by influencing the skewness of the hematocrit distribution in the daughter vessel which relates to the so-called network history effect
Obrist, H. U., Ai Weiwei Conversaciones [Reseña]
No full textReseña de la obra de Obrist, Hans Ulrich, Ai Weiwei Conversaciones, Gustavo Gili, Barcelona, 2014. Trad. Carles Muro. 120 pp
Microfluidic investigation of red blood cell phase separation in complex microchannel networks
No full textIn this study we provided quantitative data on the RBC distribution and partitioning in 21 divergent bifurcations embedded in a complex in vitro network mimicking the human microvasculature in terms of topology and characteristic geometrical scales. We found that in the majority of the bifurcations the RBC partitioning is heterogeneous and the branch receiving a higher blood fraction receives an even higher RBC fraction. However, we also found that some bifurcations presented an inverse partitioning with the low-flow branch receiving a higher RBC flow fraction
Sedimentary architecture, structural setting, and Late Cenozoic depocentre migration of an asymmetric transtensional basin: Lake Izabal, eastern Guatemala
No full textLake Izabal, located in eastern Guatemala, lies in an EW-trending basin located along the transform margin between the North American and Caribbean plates. This plate boundary consists of two main left-lateral, strike-slip faults known as the Polochic and Motagua Fault System (PMFS). The basin is a 100 × 20 km lens-shaped depression in which the lake occupies its eastern half. To the north, the basin is confined by a Principal Deformation Zone (PDZ) which is recognized in this area as the most important upper-crustal branch of the Polochic Fault. The eastern part of the basin has been uplifted and dissected, exposing the basin infill along the slopes of the Montaña del Mico. Analysis of a set of multichannel seismic reflection profiles, most of them acquired within the lake, combined with well and outcrop information, allowed to outline the structure and evolution of the basin and its stratigraphic architecture. The basin is strongly asymmetrical, both in cross and along-strike directions, and is filled up by Neogene to Quaternary sediments, with the deepest side of the basin being to the north, close and parallel to the PDZ. The base of the infill is a mid-Tertiary unconformity whose differential subsidence through time brought the basin to its present structural setting. Five main evolutionary stages are recognized based on seismo-stratigraphic and structural features, which are related to the development and activity of the bordering faults. Development of the basin began in its easternmost sector. A small half graben, tilted to the south, developed in response to the activity of an Oligocene (?) or Early-Middle Miocene growth fault. In the second stage (Late Miocene), the basin tilts to the north, causing the sedimentary sequences to thicken towards the northern PDZ. This stage is dominated by oblique extension, and by progressive migration of the basin depocenter towards the west. The third stage (Early Pliocene) records a strong acceleration of the strike-slip activity which causes a rapid westward migration of the depocenter. The fourth stage (Late Pliocene), although still dominated by regional transtension, is related to the development of a transpressional event along the eastern side of the basin, as evidenced by the occurrence of folds and reverse faults parallel to the northern bend of the Polochic Fault. During the fifth stage (Quaternary), the eastern part of the basin remains relatively quiescent while the western part undergoes subsidence with localized transtension, still related to the activity in this sector of the Polochic Fault. Left-lateral movement along the Polochic Fault caused the depocenter to migrate 75–80 km at different velocities, with slip rates ranging between 2.1 and 16.3 mm/yr. This study suggests that the Polochic Fault developed in the Early-Middle Miocene in connection to the deposition of the early sediments of the Izabal Basin, even though an older age (Oligocene?) could also be possible. To our knowledge, this is one of the best examples of sedimentary architecture documenting depocentre migration due to fault movement along a transform system
An immersed boundary method for fluid-structure interaction based on variational transfer
No full textWe present a novel framework inspired by the Immersed Boundary Method for predicting the fluid-structure interaction of complex structures immersed in laminar, transitional and turbulent flows.
The key elements of the proposed fluid-structure interaction framework are 1) the solution of elastodynamics equations for the structure, 2) the use of a high-order Navier–Stokes solver for the flow, and 3) the variational transfer (L 2 -projection) for coupling the solid and fluid subproblems.
The dynamic behavior of a deformable structure is simulated in a finite element framework by adopting a fully implicit scheme for its temporal integration. It allows for mechanical constitutive laws including inhomogeneous and fiber-reinforced materials. The Navier–Stokes equations for the incompressible flow are discretized with high-order finite differences which allow for the direct numerical simulation of laminar, transitional and turbulent flows.
The structure and the flow solvers are coupled by using an L 2 -projection method for the transfer of velocities and forces between the fluid grid and the solid mesh. This strategy allows for the numerical solution of coupled large scale problems based on nonconforming structured and unstructured grids. The transfer between fluid and solid limits the convergence order of the flow solver close to the fluid-solid interface.
The framework is validated with the Turek–Hron benchmark and a newly proposed benchmark modeling the flow-induced oscillation of an inert plate. A three-dimensional simulation of an elastic beam in transitional flow is provided to show the solver’s capability of coping with anisotropic elastic structures immersed in complex fluid flow
Intermittent preventive treatment during pregnancy and antenatal care in practice : a study from the Kilombero valley, Tanzania
No full textEach year an estimated 125 million pregnant women are at risk of getting infected with malaria in areas with P. falciparum and P. vivax transmission. In Tanzania, approximately 1.7 million pregnant women contract malaria each year leading to a high prevalence of maternal morbidity, maternal mortality and adverse birth outcomes.
The World Health Organization (WHO) recommends for sub-Saharan Africa a package of prompt and effective case-management combined with the delivery of insecticide-treated nets (ITN) and intermittent preventive treatment during pregnancy (IPTp) with sulphadoxine-pyrimethamine (SP) through the national antenatal care (ANC) programs. Implemented in Tanzania around 2001, uptake of IPTp has been poor up to date with less then 30% of pregnant women receiving a full course of two SP doses.
The aim of this thesis was to contribute to a better understanding of women’s access to and use of IPTp and other ANC services in the Kilombero Valley, Tanzania. In order to explain low IPTp coverage levels, factors influencing ANC utilization on the demand side and the quality of ANC on the supply side were investigated. Drawing on conceptualizations of scholars from the “New Institutionalism” this thesis sought to provide a more in-depth understanding of 1) how rules, regulations and guidelines at the health system level influence health providers’ implementation of health policies and guidelines concerning IPTp and ANC and 2) how old and new norms and values at the household level and beyond influence women’s access to and use of ANC and IPTp services.
The study was conducted in close collaboration with the ACCESS Programme and was carried out in the Demographic and Surveillance System (DSS) area of the Kilombero and Ulanga district in south-eastern Tanzania. Research was conducted in three phases between April 2007 and June 2009 and combined a set of qualitative and quantitative methods for data collection.
Our findings revealed a high coverage level of the first IPTp dose (79%) but confirmed a low uptake of the second one with only 27% of pregnant women having received two SP doses. Although 71% of all women started ANC after the four gestational months recommended by guidelines, their late attendance was not found to be the main constraint for IPTp delivery since 81% of the women had attended the ANC clinic at the time of the first IPTp delivery and 60% had attended both during the first and the second IPTp delivery period. The observation that among these women only 73% actually received one dose and only 29% received two doses of IPTp, pointed to the high number of missed opportunities. Low coverage levels for the second IPTp dose could be explained by health workers delivering IPTp to significantly less women during the second IPTp delivery period than the first one (55% vs. 73%) despite their high knowledge about the IPTp policy.
Apart from women’s late ANC initiation, it appeared that the majority of pregnant women respected the ANC schedule. However, it seemed that women’s attendance was rather based on norms than on their awareness of the benefits of ANC services for their own and their child’s health. Late ANC initiation was associated with belonging to the Sukuma ethnic group, multiparity, and late recognition of pregnancy. Early ANC attendance, on the other hand, was triggered by primiparity, experience of a previous reproductive loss and feeling supported by the partner or husband. Male’s support during pregnancy appeared to be facilitated and constrained by a broad range of institutions working along the lines of gender, family and kinship. On the other hand new norms and values imposed by the legal system or the ‘modern’ health system were identified as being influential on men’s support during the prenatal period.
Case studies in four health facilities revealed that the quality of ANC care was generally poor. Among a sample of 36 observed ANC consultations, 12 of the services recommended by the FANC guidelines were not given to any women, a further 18 services were given to 3%-58% and eight services were given to over 80% of women. Instead of FANC guidelines, health workers rather complied to ANC cards; analysis showed that health services for which information was required on the ANC card were delivered far better than services not listed on the ANC card but recommended by the FANC guidelines. Moreover, dichotomous IPTp schedules in the guidelines for ANC and malaria resulted in health workers’ continued delivery of IPTp according to restrictive IPTp schedules despite the existence of a more simplified IPTp schedule recommended by WHO. Calculations showed that the effective implementation of the latter guidelines could potentially increase IPTp coverage by up to 20 percentage points, which urgently calls for a revision of the national IPTp guidelines. Besides health policy factors, health care practices were found to be clearly shaped by health providers’ difficult working conditions. In order to cope with constraints caused by lack of trained staff, resource shortages and a high demand for their services, health workers appeared to adopt informal rules and routines such as attendance and diagnostics schedules and routines that allowed for mass treatment such as health education and counselling in groups.
In order to better understand how the availability of material and human resources and health workers’ access to them influence health service delivery and its quality, this thesis proposed and applied the concept of “workhood” as a new analytical device. By introducing an actors-perspective to the health system, the concept allowed light to be shed on the limitations and potentials of health workers’ capabilities
Dialogical Skirmishes
No full textTan was guest editor for 'And Now China?', a special print edition of the Ctrl+P journal, which critically responded to the celebratory rhetoric’s of ‘China Now’ and other celebratory markers of China's global ascent in 2008. As well as the introductory article 'Dialogical Skirmishes', Tan also interviewed Hans Ulrich Obrist
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