| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 2. |
- Feigin, Valery L., et al.
(författare)
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Global, regional, and national burden of stroke and its risk factors, 1990-2019 : a systematic analysis for the Global Burden of Disease Study 2019
- 2021
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Ingår i: Lancet Neurology. - : Elsevier. - 1474-4422 .- 1474-4465. ; 20:10, s. 795-820
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Tidskriftsartikel (refereegranskat)abstract
- Background Regularly updated data on stroke and its pathological types, including data on their incidence, prevalence, mortality, disability, risk factors, and epidemiological trends, are important for evidence-based stroke care planning and resource allocation. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) aims to provide a standardised and comprehensive measurement of these metrics at global, regional, and national levels. Methods We applied GBD 2019 analytical tools to calculate stroke incidence, prevalence, mortality, disability-adjusted life-years (DALYs), and the population attributable fraction (PAF) of DALYs (with corresponding 95% uncertainty intervals [UIs]) associated with 19 risk factors, for 204 countries and territories from 1990 to 2019. These estimates were provided for ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, and all strokes combined, and stratified by sex, age group, and World Bank country income level. Findings In 2019, there were 12.2 million (95% UI 11.0-13.6) incident cases of stroke, 101 million (93.2-111) prevalent cases of stroke, 143 million (133-153) DALYs due to stroke, and 6.55 million (6.00-7.02) deaths from stroke. Globally, stroke remained the second-leading cause of death (11.6% [10.8-12.2] of total deaths) and the third-leading cause of death and disability combined (5.7% [5.1-6.2] of total DALYs) in 2019. From 1990 to 2019, the absolute number of incident strokes increased by 70.0% (67.0-73.0), prevalent strokes increased by 85.0% (83.0-88.0), deaths from stroke increased by 43.0% (31.0-55.0), and DALYs due to stroke increased by 32.0% (22.0-42.0). During the same period, age-standardised rates of stroke incidence decreased by 17.0% (15.0-18.0), mortality decreased by 36.0% (31.0-42.0), prevalence decreased by 6.0% (5.0-7.0), and DALYs decreased by 36.0% (31.0-42.0). However, among people younger than 70 years, prevalence rates increased by 22.0% (21.0-24.0) and incidence rates increased by 15.0% (12.0-18.0). In 2019, the age-standardised stroke-related mortality rate was 3.6 (3.5-3.8) times higher in the World Bank low-income group than in the World Bank high-income group, and the age-standardised stroke-related DALY rate was 3.7 (3.5-3.9) times higher in the low-income group than the high-income group. Ischaemic stroke constituted 62.4% of all incident strokes in 2019 (7.63 million [6.57-8.96]), while intracerebral haemorrhage constituted 27.9% (3.41 million [2.97-3.91]) and subarachnoid haemorrhage constituted 9.7% (1.18 million [1.01-1.39]). In 2019, the five leading risk factors for stroke were high systolic blood pressure (contributing to 79.6 million [67.7-90.8] DALYs or 55.5% [48.2-62.0] of total stroke DALYs), high body-mass index (34.9 million [22.3-48.6] DALYs or 24.3% [15.7-33.2]), high fasting plasma glucose (28.9 million [19.8-41.5] DALYs or 20.2% [13.8-29.1]), ambient particulate matter pollution (28.7 million [23.4-33.4] DALYs or 20.1% [16.6-23.0]), and smoking (25.3 million [22.6-28.2] DALYs or 17.6% [16.4-19.0]). Interpretation The annual number of strokes and deaths due to stroke increased substantially from 1990 to 2019, despite substantial reductions in age-standardised rates, particularly among people older than 70 years. The highest age-standardised stroke-related mortality and DALY rates were in the World Bank low-income group. The fastest-growing risk factor for stroke between 1990 and 2019 was high body-mass index. Without urgent implementation of effective primary prevention strategies, the stroke burden will probably continue to grow across the world, particularly in low-income countries.
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| 3. |
- Hatem Mohammed, Mohammed, et al.
(författare)
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Hydrothermal alteration of clay and low pH concrete applicable to deep borehole disposal of high-level radioactive waste : A pilot study
- 2016
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 104, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- In the very deep borehole (VDH) concept for high level radioactive waste disposal, the combined usage of clay and concrete provides an attractive way of achieving both high strength and low permeability required for sealing the various sections of the hole. The concrete is required for mechanical stability where water-bearing fracture zones are intersected, whereas the clay effectively seals sections in stable rock masses. As both the clay and concrete may be exposed to temperatures in the range of 60–150 °C in various parts of the hole, there is a need to address the stability of these materials under thermally enhanced aqueous conditions. In this pilot study, a new type of organic-free, low pH concrete based on granulated blast furnace slag is tested, which is hardened and altered under hydrothermal conditions in the laboratory. The results presented show that both adequate compressive strength (up to ∼9 MPa) and low hydraulic conductivity (down to ∼5.6 × 10−10) is attained at elevated temperatures ranging up to 150 °C, indicating that clay-concrete sealing can be a successful method used to prevent radionuclides from migrating vertically up through the borehole repository.
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| 4. |
- Pusch, Roland, et al.
(författare)
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A talc-based cement-poor concrete for sealing boreholes in rock
- 2013
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 5:3, s. 251-267
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Tidskriftsartikel (refereegranskat)abstract
- Deep investigation boreholes in crystalline rock for site selection of repositories for high-level radioactive waste are proposed to be sealed by installing a series of dense concrete and clay plugs. These should prevent radionuclides from leaking canisters at depth to migrate to the biosphere through the holes. The concrete seals will be installed where the holes intersect water-bearing fracture zones to serve as stable and low-permeable supports for adjacent clay plugs. Low porosity and microstructural stability must be guaranteed for many thousands of years and ordinary Portland cement with organic superplastizer will not fulfil the requirements since the high pH will cause degradation of contacting clay and the organic additive can produce colloids with a capacity to carry radionuclides up to the biosphere. Very cement-poor concrete (<8 %) based on low-pH cement and with talc as plasticizer is an option but it matures more slowly, which requires that the construction of seals is made so that sufficient bearing capacity for carrying overlying clay seals is reached.
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| 5. |
- Pusch, Roland, et al.
(författare)
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Can sealing of rock hosting a repository for highly radioactive waste be relied on?
- 2012
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Ingår i: Natural Science. - : Scientific Research Publishing, Inc.. - 2150-4091 .- 2150-4105. ; 4:11A, s. 895-905
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Tidskriftsartikel (refereegranskat)abstract
- Multibarrier systems are commonly proposed for effective isolation of highly radioactive waste (HLW). Presently considered concepts take the host rock as a barrier claiming it to retard migration of possibly released radionuclides from HLW containers to the biosphere. This capacity is small unless water-bearing fracture zones intersecting the blasted waste-containing tunnels and excavation-disturbance zones around them can be sealed by grouting and construction of bulkheads, but this is effective only for a very limited period of time as explained in the paper. The disturbed zones thence make the entire repository serve as a continuous hydraulic conductor causing quick transport of released radionuclides up to the biosphere. The dilemma can be solved by accepting the short-circuiting function of the disturbed zones along the tunnels on the condition that totally tight waste containers be used. Deep holes bored in the site selection phase through the forthcoming repository can be effective pathways for radionuclides unless they are properly sealed. They are small-scale equivalents of tunnels but do not have any ex-cavation damage and can be effectively sealed by using clay and concrete of new types. Applying this principle to very deep boreholes with a diameter of a few decimeters would make it possible to safely store slim, tight HLW canisters for any period of time.
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| 6. |
- Hatem, Mohammed
(författare)
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Cement-Poor Concrete and Grout for Use in Underground Constructions
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the composition and properties of cement-based materials, concrete and grout, for use as seals and for stabilizing fracture zones in underground facilities like mines and repositories for chemical and radioactive waste. It is of general character with respect to the composition and preparation of concretes and grouts but focuses on the sealing of boreholes for mineral prospection and site investigation for locating underground repositories of hazardous waste.The proposed principle of constructing concrete seals in very deep boreholes (VDH) where they are intersected by fracture zones is to cast the concrete on-site over placed clay seals to the upper end of the respective fracture zones where the next clay seal is installed. The chemical interaction between concrete and clay causes mutual degradation that must be taken into consideration. Ordinary concrete with Portland cement as binder is not suitable because of its poor chemical stability over long periods of time and because of its high pH, more than 12, which attacks contacting clay seals. Another drawback is that such concrete requires organic superplasticizers for achieving fluidity and they can give off organic colloids that can transport radionuclides. Inorganic fluidizers like talc and use of low-pH cement offer new possibilities to prepare suitable concretes and grouts. They are the focus of this present document.The criteria for the concrete seals are: sufficient fluidity and coherence at casting and sufficiently high bearing capacity and low compressibility for maintaining constant volume conditions under the load of the overlying series of clay and concrete. The hydraulic conductivity of the hardened concrete should be lower than that of the surrounding fracture zone.Since the concrete must perform acceptably for up to 100,000 years and the cement component will ultimately be dissolved and lost, the rest, i.e. the aggregate components, must still provide acceptable support for overlying clay and concrete seals in deep boreholes. The aggregate component must therefore be very densely packed and have a granular composition that resists erosion.The main objectives of this study are: 1) To investigate the performance of new types of cement-poor, organic-free concrete for long-term duty under normal and extreme hydrothermal conditions at varying temperatures. Properties of special importance are fluidity, mechanical strength, rate of strengthening, pH, and minimum impact on contacting seals of smectite-rich clay seals.2) To investigate the function of new cement-based grouts proposed for sealing finely fractured rock around boreholes, tunnels and shafts where concrete seals will be cast, especially with respect to fluidity, rheological behaviour, mechanical strength, rate of strengthening, and penetrability into fine fractures. The study comprised testing of low-pH cement concretes and grouts with talc and other silicate minerals added for achieving fluidity and high strength. They were composed according to modern packing theories for obtaining low porosity and a minimum amount of cement paste. The use of talc is firstly for decreasing the viscosity of the mixture at casting or injection and secondly for assuring that it can really contribute to the mechanical strength by chemical interaction with the cement component. The need for chemical integrity led to the choice of quartzite as main aggregate in the study. The low-pH cement used was Merit 5000 manufactured by SSAB Merox AB, Oxelösund.For one of the candidate grouts, Portland cement was used in order to get quick hardening, whilst the other contained low-pH cement for providing high strength in the course of time. The principle of composing the aggregate was to obtain a filtering function so that the risk of losing fines is minimized in the construction period when local hydraulic gradients may still be high.It was concluded from this study that theoretical modeling as well as experimental results confirm that concrete mixtures can get high packing degrees and bulk densities if the ballast gradation is suitable and that the role of the fine fraction is thereby very important. The achieved density of the concrete is believed to be sufficiently high in order to make the concrete perform acceptably for very long periods of time even after complete loss of the cement. It was documented that talc serves to reduce the viscosity and contribute to the strength. The relatively low pH of Merit concrete (≈10) in contact with clay indicates that chemically generated destruction of either of the materials will be low. Such concrete, containing properly composed quartz-rich aggregate, and with talc added, fulfills the criteria set for its performance under both normal and high temperature conditions. It was also concluded that grout fluidity is positively affected by the hydrophobic nature of talc and negatively by thixotropic action of other silicates and by early cement hydration. The experiments highlight the role of the rheological properties and the need for proper composition of the grouts. A general conclusion from the grout flow study was that effective injection of grouts into fractures narrower than 100 µm requires that the viscosity is as low as 0.05 Pas and that high injection pressures are used.
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| 7. |
- Hatem, Mohammed, et al.
(författare)
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Design of concrete mixes by systematic steps and ANN
- 2012
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Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 2:4, s. 232-251
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Tidskriftsartikel (refereegranskat)abstract
- The current research caters for the possibility of arriving at a system for designing concrete mixeseasily using available materials locally by specified wide ranges of pre-requisites of three mainprescribed properties to cover a good variety of practical mixes, which are water, water-cement ratioand total aggregate-cement ratio. Using these three properties, a tri-linear form was constructed bygraphical technique manner based on absolute volume approach. This approach defines as asummation of absolute volume for each of these three materials individually water, cement andaggregate should be equal to the absolute volume of whole concrete mixture based on thesealtogether. A quad-form area which includes a wide range of mixes can be formed from thisrepresentation. This area should achieve all the prescribed properties aforementioned. Artificial neuralnetwork concept used in this study also to build easily and quickly system which can be translatedinto Excel sheet. This system predict proportions of concrete mixture and the compressive strengthusing the results designed by the quad-form area method in addition to the data from literature around500 mixes based on local materials used in Iraq. Six input parameters (water to cement ratio, theslump, % of fine to total aggregate content, maximum aggregate size, fineness modulus of fineaggregate and the compressive strength) were used in this system to get the outputs. In addition, nineinput parameters ((water, cement, sand and gravel contents) and the properties of the mix (Finenessmodulus, W/C ratio, the slump, % of fine to total aggregate and the M.A.S)) were used as basis ofcompressive strength model. The algorithm of this system aimed to reduce the high number of trailmixes error as well as saving the labors, cost and time. Results indicated that the concrete mix designand the compressive strength model can be predicted accurately by using graphical perspective andthe ANN approach.
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| 8. |
- Hatem, Mohammed, et al.
(författare)
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Enhancement of Workability of Cement-Poor Concrete by Optimizing Paste Content
- 2014
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 6:13, s. 869-876
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the performance of concrete in fresh state, intended for sealing deep boreholes in the host rock of radioactive repositories. Set of different paste volumes, combinations of water-to-powder ratios and fine aggregate contents have been performed within the frame of this study. The main objective was to search for tendencies, logical connections and phenomena that occur for different combination of materials regarding the fluidity and segregation and mainly the effect from the (paste) or fine aggregate content. It shall be pointed out that this investigation is a suggestion on how concrete can be optimized using two simple test methods based on changing the paste content. The results highlighted the importance of having sufficient amounts of filler and cement paste for separate and carry larger particles, which gives the concrete good workability and fluidity at casting. It was concluded that the slump behaviors can be optimized based on the adjustments of the superplastisizer dosage.
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| 9. |
- Hatem, Mohammed, et al.
(författare)
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Interaction of clay and concrete relevant to the deep disposal of high-level radioactive waste
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 118, s. 178-187
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Tidskriftsartikel (refereegranskat)abstract
- A concept for the disposal of highly radioactive waste at depth in the Earth’s crust using very deep bore-holes requires that the upper 2 km’s of the 800 mm diameter, steeply drilled holes, be effectively sealed. This can be achieved by using dense smectitic clay where the rock is weakly fractured and strengthening with concrete when fracture zones are encountered. Earlier investigations have shown that chemical reactions between the clay and concrete can be expected both in the upper part where the temperature is lower than 90oC and in the deeper section where the temperature reaches up to 150oC. To study further this interaction, hydrothermal experiments were conducted using mixed-layer (illite/smectite) Holmehus clay and a low pH slag-based concrete placed in contact under isothermal conditions at 21°C, 100oC and 150oC for a period of 8 weeks. The sample sets, which consisted of two clay discs separated by concrete cast on the lower clay disc, were extracted in undisturbed form and exposed to uniaxial pressure for measuring the compressive strength at successively increasing pressures. Compression tests underenhanced thermal conditions led to strengthening of both the clay and concrete. X-ray diffraction and electron microscopy analysis of the material revealed an increasing degree of cation exchange at higher temperatures with the cement, whereby Ca replaced Na in the interlayer sites of smectite layers. Dissolution of illite/smectite was also evident occurring at enhanced temperatures, with a decrease in K, Mg and Fe content with advanced alteration. The enhanced strength of clay can be partly attributed to the precipitation of cement phases from circulating fluids, including precipitation of gypsum.
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| 10. |
- Hatem, Mohammed, et al.
(författare)
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Optimization of concrete by minimizing void volume in aggregate mixture system
- 2012
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Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 2:3, s. 208-222
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of concrete is affected by the size, distribution of the voids, the porosity and of the granulometry of the aggregate mixture. As a consequence it necessary for engineers to consider in detail particle packing concepts and their influence on the physical performance of concrete. The present study included determination of the fineness modulus, cement paste volume based on slump test and the properties of fresh and hardened concrete. It also comprised a study of the applicability of two theoretical models Toufar’s and 4C-packing program for selecting suitable relative amounts of the concrete constituents, for obtaining a minimum void ratio. Comparison of the results was made from using these theoretical models literature-derived experimental data. The models gave similar results and suggest similar combinations of materials to give minimum void ratio. Optimization of the composition of the aggregate material in concrete is beneficial with respect to economy (low cement content), strength and durability. It was noted that minimizing the void ratio (V) tends to raise the stiffness and that the compressive strength (푓푐′) is closely related also to their molding (R) and fineness modules (FM). It was found that the compressive strength can be predicted by applying the formula;푓푐′=−2.1−63.8 푉+0.150 푅+10.4 퐹푀; R2=0.94, and two other relationships related to slump data and cement content.
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