| 1. |
- Wynberg, Elke, et al.
(författare)
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Variability in white blood cell count during uncomplicated malaria and implications for parasite density estimation : a WorldWide Antimalarial Resistance Network individual patient data meta-analysis
- 2023
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Ingår i: Malaria Journal. - : Springer Nature. - 1475-2875. ; 22
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Tidskriftsartikel (refereegranskat)abstract
- Background: The World Health Organization (WHO) recommends that when peripheral malarial parasitaemia is quantified by thick film microscopy, an actual white blood cell (WBC) count from a concurrently collected blood sample is used in calculations. However, in resource-limited settings an assumed WBC count is often used instead. The aim of this study was to describe the variability in WBC count during acute uncomplicated malaria, and estimate the impact of using an assumed value of WBC on estimates of parasite density and clearance.Methods: Uncomplicated malaria drug efficacy studies that measured WBC count were selected from the WorldWide Antimalarial Resistance Network data repository for an individual patient data meta-analysis of WBC counts. Regression models with random intercepts for study-site were used to assess WBC count variability at presentation and during follow-up. Inflation factors for parasitaemia density, and clearance estimates were calculated for methods using assumed WBC counts (8000 cells/mu L and age-stratified values) using estimates derived from the measured WBC value as reference.Results: Eighty-four studies enrolling 27,656 patients with clinically uncomplicated malaria were included. Geometric mean WBC counts (x 1000 cells/mu L) in age groups < 1, 1-4, 5-14 and >= 15 years were 10.5, 8.3, 7.1, 5.7 and 7.5, 7.0, 6.5, 6.0 for individuals with falciparum (n = 24,978) and vivax (n = 2678) malaria, respectively. At presentation, higher WBC counts were seen among patients with higher parasitaemia, severe anaemia and, for individuals with vivax malaria, in regions with shorter regional relapse periodicity. Among falciparum malaria patients, using an assumed WBC count of 8000 cells/mu L resulted in parasite density underestimation by a median (IQR) of 26% (4-41%) in infants < 1 year old but an overestimation by 50% (16-91%) in adults aged = 15 years. Use of age-stratified assumed WBC values removed systematic bias but did not improve precision of parasitaemia estimation. Imprecision of parasite clearance estimates was only affected by the within-patient WBC variability over time, and remained < 10% for 79% of patients.Conclusions: Using an assumed WBC value for parasite density estimation from a thick smear may lead to underdiagnosis of hyperparasitaemia and could adversely affect clinical management; but does not result in clinically consequential inaccuracies in the estimation of the prevalence of prolonged parasite clearance and artemisinin resistance.
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| 2. |
- Menzel, Andreas, et al.
(författare)
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Nonlinear piezoelectric effects - towards physics-based computational modelling of micro-cracking, fatigue, and switching
- 2008
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. - 9780735405530 ; 1029:1, s. 209-220
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Konferensbidrag (refereegranskat)abstract
- Piezoelectric ceramics -- as one widely commercialised group of smart materials -- exhibit a great potential for various engineering applications. Their high-frequency capabilities are in particular attractive for actuator and sensor devices, which nowadays are present in daily-life-technologies such as cellular phones, fuel injection systems, and so forth. At high loading levels however, severely nonlinear behaviour of these materials is observed which, from the control point of view, must be further investigated in order to be able to precisely account for such effects within the design of intelligent systems. The reasons for these nonlinearities are manifold and, even investigated within the last decades, not fully understood. Nevertheless, two important sources for these observations are so-called micro-cracking, together with fatigue phenomena, as well as switching or rather phase transformations. Accordingly, the main goal of this contribution is to study these effects by means of developing related constitutive models that can be embedded into iterative algorithmic schemes such as the finite element method. One the one hand, the grain-structure of a piezoceramic specimen will be modelled via the direct incorporation of the grain-boundaries as so-called interface elements. The underlying cohesive-like constitutive law of this layer includes both degrees of freedom of the surrounding bulk material -- or rather the jumps in these fields -- namely displacements and the electric potential. Based on the resulting traction-separation-type relations, micro-cracking is directly accounted for on this micro-level. Moreover, the constitutive law of the interfacial layer is supplemented by additional variables that enable the formulation of fatigue under cyclic loading conditions. On the other hand, phase transformations -- modelled in terms of an energy-based switching criterion -- are discussed and embedded into an iterative finite element context. Symmetry relations of the underlying unit cells are directly included so that the switching model accounts for the micro-mechanical properties of the piezoelectric materials of interest. At this stage, representative numerical simulations of polycrystalline specimens are based on straightforward averaging-techniques, while the combination of the developed micro-cracking model (grain boundaries) with the proposed switching model (bulk) constitutes future research.
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| 3. |
- Streatfield, P. Kim, et al.
(författare)
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Cause-specific childhood mortality in Africa and Asia : evidence from INDEPTH health and demographic surveillance system sites
- 2014
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Ingår i: Global Health Action. - : Informa UK Limited. - 1654-9716 .- 1654-9880. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Childhood mortality, particularly in the first 5 years of life, is a major global concern and the target of Millennium Development Goal 4. Although the majority of childhood deaths occur in Africa and Asia, these are also the regions where such deaths are least likely to be registered. The INDEPTH Network works to alleviate this problem by collating detailed individual data from defined Health and Demographic Surveillance sites. By registering deaths and carrying out verbal autopsies to determine cause of death across many such sites, using standardised methods, the Network seeks to generate population-based mortality statistics that are not otherwise available.OBJECTIVE: To present a description of cause-specific mortality rates and fractions over the first 15 years of life as documented by INDEPTH Network sites in sub-Saharan Africa and south-east Asia.DESIGN: All childhood deaths at INDEPTH sites are routinely registered and followed up with verbal autopsy (VA) interviews. For this study, VA archives were transformed into the WHO 2012 VA standard format and processed using the InterVA-4 model to assign cause of death. Routine surveillance data also provided person-time denominators for mortality rates. Cause-specific mortality rates and cause-specific mortality fractions are presented according to WHO 2012 VA cause groups for neonatal, infant, 1-4 year and 5-14 year age groups.RESULTS: A total of 28,751 childhood deaths were documented during 4,387,824 person-years over 18 sites. Infant mortality ranged from 11 to 78 per 1,000 live births, with under-5 mortality from 15 to 152 per 1,000 live births. Sites in Vietnam and Kenya accounted for the lowest and highest mortality rates reported.CONCLUSIONS: Many children continue to die from relatively preventable causes, particularly in areas with high rates of malaria and HIV/AIDS. Neonatal mortality persists at relatively high, and perhaps sometimes under-documented, rates. External causes of death are a significant childhood problem in some settings.
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| 4. |
- Streatfield, P. Kim, et al.
(författare)
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Malaria mortality in Africa and Asia : evidence from INDEPTH health and demographic surveillance system sites
- 2014
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Ingår i: Global Health Action. - : Informa UK Limited. - 1654-9716 .- 1654-9880. ; 7, s. 25369-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Malaria continues to be a major cause of infectious disease mortality in tropical regions. However, deaths from malaria are most often not individually documented, and as a result overall understanding of malaria epidemiology is inadequate. INDEPTH Network members maintain population surveillance in Health and Demographic Surveillance System sites across Africa and Asia, in which individual deaths are followed up with verbal autopsies.OBJECTIVE: To present patterns of malaria mortality determined by verbal autopsy from INDEPTH sites across Africa and Asia, comparing these findings with other relevant information on malaria in the same regions.DESIGN: From a database covering 111,910 deaths over 12,204,043 person-years in 22 sites, in which verbal autopsy data were handled according to the WHO 2012 standard and processed using the InterVA-4 model, over 6,000 deaths were attributed to malaria. The overall period covered was 1992-2012, but two-thirds of the observations related to 2006-2012. These deaths were analysed by site, time period, age group and sex to investigate epidemiological differences in malaria mortality.RESULTS: Rates of malaria mortality varied by 1:10,000 across the sites, with generally low rates in Asia (one site recording no malaria deaths over 0.5 million person-years) and some of the highest rates in West Africa (Nouna, Burkina Faso: 2.47 per 1,000 person-years). Childhood malaria mortality rates were strongly correlated with Malaria Atlas Project estimates of Plasmodium falciparum parasite rates for the same locations. Adult malaria mortality rates, while lower than corresponding childhood rates, were strongly correlated with childhood rates at the site level.CONCLUSIONS: The wide variations observed in malaria mortality, which were nevertheless consistent with various other estimates, suggest that population-based registration of deaths using verbal autopsy is a useful approach to understanding the details of malaria epidemiology.
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| 5. |
- Utzinger, J, et al.
(författare)
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Aspects of bifurcation in an isotropic elastic continuum with orthotropic inelastic interface
- 2008
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Ingår i: European Journal of Mechanics. A, Solids. - : Elsevier BV. - 1873-7285 .- 0997-7538. ; 27:4, s. 532-547
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Tidskriftsartikel (refereegranskat)abstract
- This manuscript investigates possible bifurcations into stationary wave-type solutions in situations where an isotropic elastic bulk is bonded by a non-coherent orthotropic interface to a rigid substrate. The interface is characterised by a tractionseparation-law capturing elastic and inelastic material behaviour. Based on an ansatz for stationary waves at the surface of the bulk being connected to the interface, a bifurcation condition is elaborated. Thereby, the orthotropy of the interface is taken into account by considering the fully three-dimensional elastic half space and allowing for arbitrary orientations of the stationary wave-type solutions with respect to the interface co-ordinate system. The bifurcation condition is studied under the assumption of prevailing ellipticity in the bulk for a number of different examples. The results are graphically explored.
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| 6. |
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| 7. |
- Utzinger, J, et al.
(författare)
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Investigation of microcracks in ferroelectric materials by application of a grain--boundary--motivated cohesive law
- 2008
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Ingår i: PAMM. - : Wiley. - 1617-7061. ; 7:1, s. 4070017-4070018
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Konferensbidrag (refereegranskat)abstract
- Ferroelectric materials exhibit a huge potential for engineering applications - ranging from electrical actuators (inverse piezoelectric effect) to sensor technology (direct piezoelectric effect). To give an example, lead zirconate titanate (PZT) is a typical perovskite ion crystal possessing ferroelectric properties. In this contribution, we are particularly interested in the modelling of microcracking effects in ferroelectric materials. In view of Finite-Element-based simulations, the geometry of a natural grain structure, as observed on the so-called micro-level, is represented by an appropriate mesh. While the response on the grains themselves is approximated by coupled continuum elements, grain boundaries are numerically incorporated via so-called cohesive-type elements. For the sake of simplicity, switching effects in the bulk material will be neglected. The behaviour of the grain boundaries is modelled by means of cohesive-type laws. Identifying grain boundaries as potential failure zones leading to microcracking, cohesive-type elements consequently offer a great potential for numerical simulations. As an advantage, in the case of failure they do not a priori result in ill-conditioned systems of equations as compared with the application of standard continuum elements to localised deformations. Finally, representative constitutive relations for both the bulk material and the grain boundaries, enable two-dimensional studies of low-cycle-fatigue motivated benchmark boundary value problems.
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| 8. |
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| 9. |
- Utzinger, J, et al.
(författare)
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On the simulation of cohesive fatigue effects in grain boundaries of a piezoelectric mesostructure
- 2008
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 45:17, s. 4687-4708
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric materials offer a variety of new applications in the field of smart structures and intelligent systems. Accordingly, the modelling of these materials constitutes an active field of research. A critical limitation of the performance of such materials is given when electrical, mechanical, or mixed loading fatigue occurs, combined with, for instance, microcracking phenomena. In this contribution, fatigue effects in ferroelectric materials are numerically investigated by utilisation of a cohesive-type approach. In view of finite element-based simulations, the geometry of a natural grain structure, as observed on the so-called meso-level, is represented by an appropriate mesh. While the response of the grains themselves is approximated by coupled continuum elements, grain boundaries are numerically incorporated via so-called cohesive-type or interface elements. These offer a great potential for numerical simulations: as an advantage, they do not result in bad-conditioned systems of equations as compared with the application of standard continuum elements inhering a very high ratio of length and height. The grain boundary behaviour is modelled by cohesive-type constitutive laws, designed to capture fatigue phenomena. Being a first attempt, switching effects are planned to be added to the grain model in the future. Two differently motivated fatigue evolution techniques are applied, the first being appropriate for low-cycle-fatigue, and a second one adequate to simulate high-cycle-fatigue. Subsequent to a demonstration of the theoretical and numerical framework, studies of benchmark boundary value problems with fatigue-motivated boundary conditions are presented.
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