| 1. |
- Al-Gburi, Majid
(författare)
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Restraint in structures with young concrete : Tools and estimations for practical use
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks. Restraint represents one of the main sources of thermal and shrinkage stresses at early age concrete. Paper I, deals with both the compensation plane method, CPM, and local restraint method, LRM, as alternative methods studying crack risks for early age concrete. It is shown that CPM can be used both for cooling and heating, but basic LRM cannot be applied to heating. This paper presents an improved equivalent restraint method, ERM, which easily can be applied both for usage of heating and cooling for general structures. Restraint curves are given for two different infrastructures, one founded on frictional materials and another on rock. Such curves might be directly applied in design using LRM and ERM.In Paper II, existing restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the wall for the typical structure wall-on-slab. It has been proven that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, it is shown that the results from the neural network can be represented by a series of basic weight and response functions. Thus, the results can easily be made available to any engineer without use of complicated software.Paper III, discusses the influence of five casting sequences for the typical structure slab-on-ground. The aim is to map restraints from adjacent structures for a number of possible casting sequences, and to identify the sequence with the lowest restraint. The paper covers both continuous and jumped casting sequences, which include one, two and three contact edges. The result shows that the best casting sequence is the continuous technique with one contact edge.
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| 2. |
- Badea, Silviu‐Laurentiu, et al.
(författare)
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Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of α‐hexachlorocyclohexane in the environment
- 2011
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Ingår i: Rapid Communications in Mass Spectrometry. - : John Wiley & Sons, Ltd. - 0951-4198 .- 1097-0231. ; 25:10, s. 1363-1372
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Tidskriftsartikel (refereegranskat)abstract
- α‐Hexachlorocyclohexane (α‐HCH) is the only chiral isomer of the eight 1,2,3,4,5,6‐HCHs and we have developed an enantiomer‐specific stable carbon isotope analysis (ESIA) method for the evaluation of its fate in the environment.The carbon isotope ratios of the α‐HCH enantiomers were determined for a commercially available α‐HCH sample using a gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS) system equipped with a chiral column. The GC‐C‐IRMS measurements revealed δ‐values of −32.5 ± 0.8‰ and −32.3 ± 0.5‰ for (−) α‐HCH and (+) α‐HCH, respectively. The isotope ratio of bulk α‐HCH was estimated to be −32.4 ± 0.6‰ which was in accordance with the δ‐values obtained by GC‐C‐IRMS (−32.7 ± 0.2‰) and elemental analyzer‐isotope ratio mass spectrometry (EA‐IRMS) of the bulk α‐HCH (−32.1 ± 0.1‰). The similarity of the isotope ratio measurements of bulk α‐HCH by EA‐IRMS and GC‐C‐IRMS indicates the accuracy of the chiral GC‐C‐IRMS method. The linearity of theα‐HCH ESIA method shows that carbon isotope ratios can be obtained for a signal size above 100mV. The ESIA measurements exhibited standard deviations (2σ) that were mostly < ± 0.5‰. In order to test the chiral GC‐C‐IRMS method, the isotope compositions of individual enantiomers in biodegradation experiments of α‐HCH withClostridium pasteurianum and samples from a contaminated field site were determined. The isotopic compositions of theα‐HCHenantiomers show a range of enantiomeric and isotope patterns, suggesting that enantiomeric and isotopefractionation can serve as an indicator for biodegradation and source characterization of α‐HCH in the environment.
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| 3. |
- Badea, Silviu-Laurentiu, et al.
(författare)
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Stable isotope fractionation of γ-Hexachlorocyclohexane (Lindane) during reductive dechlorination by two strains of sulfate-reducing bacteria
- 2009
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:9, s. 3155-3161
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Tidskriftsartikel (refereegranskat)abstract
- Carbon isotope fractionation factors were determined with the dichloro elimination of γ-hexachlorocyclohexane (γ-HCH) by the sulfate-reducing bacteria Desulfococcus multivorans DSM 2059 and Desulfovibrio gigas DSM 1382. Both strains are known for cometabolic HCH dechlorination. Degradation experiments with γ-HCH in concentrations of 22−25 μM were carried out using benzoate (for D. multivorans) and lactate (for D. gigas) as electron donors, respectively. γ-HCH was dechlorinated by both bacterial strains within four weeks, and the metabolites γ-3,4,5,6-tetrachlorocyclohexene (γ-TCCH), chlorobenzene (CB), and benzene were formed. The carbon isotope fractionation of γ-HCH dechlorination was quantified by the Rayleigh model, using a bulk enrichment factor (εC) of −3.9 ± 0.6 for D. gigas and −3.4 ± 0.5 for D. multivorans, which correspond to apparent kinetic isotope effect (AKIEC) values of 1.023 ± 0.004 or 1.02 ± 0.003 for stepwise Cl−C bond cleavage. The extent and range of isotope fractionation suggest that γ-HCH dechlorination can be monitored in anoxic environments by compound-specific isotope analysis (CSIA).
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| 4. |
- Hambäck, Peter, et al.
(författare)
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Top-down and bottom-up effects on the spatiotemporal dynamics of cereal aphids: testing scaling theory for local density
- 2007
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Ingår i: Oikos. - : Wiley. - 0030-1299. ; 116:12, s. 1995-2006
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the densityarearelationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics ofdensity-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids’ dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity.
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| 5. |
- Justice, Anne E., et al.
(författare)
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Protein-coding variants implicate novel genes related to lipid homeostasis contributing to body-fat distribution
- 2019
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 51:3, s. 452-469
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Tidskriftsartikel (refereegranskat)abstract
- Body-fat distribution is a risk factor for adverse cardiovascular health consequences. We analyzed the association of body-fat distribution, assessed by waist-to-hip ratio adjusted for body mass index, with 228,985 predicted coding and splice site variants available on exome arrays in up to 344,369 individuals from five major ancestries (discovery) and 132,177 European-ancestry individuals (validation). We identified 15 common (minor allele frequency, MAF >= 5%) and nine low-frequency or rare (MAF < 5%) coding novel variants. Pathway/gene set enrichment analyses identified lipid particle, adiponectin, abnormal white adipose tissue physiology and bone development and morphology as important contributors to fat distribution, while cross-trait associations highlight cardiometabolic traits. In functional follow-up analyses, specifically in Drosophila RNAi-knockdowns, we observed a significant increase in the total body triglyceride levels for two genes (DNAH10 and PLXND1). We implicate novel genes in fat distribution, stressing the importance of interrogating low-frequency and protein-coding variants.
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| 6. |
- Keller, Andreas Hardy, et al.
(författare)
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Metagenome-based metabolic reconstruction reveals the ecophysiological function of Epsilonproteobacteria in a hydrocarbon-contaminated sulfidic aquifer
- 2015
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The population genome of an uncultured bacterium assigned to the Campylobacterales (Epsilonproteobacteria) was reconstructed from a metagenome dataset obtained by whole-genome shotgun pyrosequencing. Genomic DNA was extracted from a sulfate-reducing, m-xylene-mineralizing enrichment culture isolated from groundwater of a benzene-contaminated sulfidic aquifer. The identical epsilonproteobacterial phylotype has previously been detected in toluene- or benzene-mineralizing, sulfate-reducing consortia enriched from the same site. Previous stable isotope probing (SIP) experiments with 13C6-labeled benzene suggested that this phylotype assimilates benzene-derived carbon in a syntrophic benzene-mineralizing consortium that uses sulfate as terminal electron acceptor. However, the type of energy metabolism and the ecophysiological function of this epsilonproteobacterium within aromatic hydrocarbon-degrading consortia and in the sulfidic aquifer are poorly understood. Annotation of the epsilonproteobacterial population genome suggests that the bacterium plays a key role in sulfur cycling as indicated by the presence of an sqr gene encoding a sulfide quinone oxidoreductase and psr genes encoding a polysulfide reductase. It may gain energy by using sulfide or hydrogen/formate as electron donors. Polysulfide, fumarate, as well as oxygen are potential electron acceptors. Auto- or mixotrophic carbon metabolism seems plausible since a complete reductive citric acid cycle was detected. Thus the bacterium can thrive in pristine groundwater as well as in hydrocarbon-contaminated aquifers. In hydrocarbon-contaminated sulfidic habitats, the epsilonproteobacterium may generate energy by coupling the oxidation of hydrogen or formate and highly abundant sulfide with the reduction of fumarate and/or polysulfide, accompanied by efficient assimilation of acetate produced during fermentation or incomplete oxidation of hydrocarbons. The highly efficient assimilation of acetate was recently demonstrated by a pulsed 13C2-acetate protein SIP experiment. The capability of nitrogen fixation as indicated by the presence of nif genes may provide a selective advantage in nitrogen-depleted habitats. Based on this metabolic reconstruction, we propose acetate capture and sulfur cycling as key functions of Epsilonproteobacteria within the intermediary ecosystem metabolism of hydrocarbon-rich sulfidic sediments.
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| 9. |
- Lagerblad, Björn, et al.
(författare)
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Shrinkage and durability of shotcrete
- 2010
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Ingår i: Shotcrete. - London : Taylor & Francis Group. - 9780415475891 ; , s. 173-180
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Cracking of shotcrete in tunnels has in recent years become a problem in Sweden. Thusan investigation was initiated. The results show that shotcrete differs from of ordinary cast concrete inmany ways. Basically, wet shotcrete is ordinary concrete but is mixed with a set accelerator at the nozzleand as a result the major cement reactions will take place in a stiff (but not hardened) material. Cementhydration results in shrinkage that in ordinary concrete will be compensated for due to settlement, but inthe stiffened shotcrete it will change the properties of the concrete. It will give a different structure andmode of porosity, which in turn will increase shrinkage. Especially with an alkali free set accelerator theshotcrete develops a larger amount and coarser porosity, which in turn will generate significantly largerdrying shrinkage than in cast concrete. Moreover, the shotcrete is very sensitive to early shrinkage if notproperly water cured. Water must be added to compensate for the chemical shrinkage in the stiff but nothard structure of the young shotcrete.
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| 10. |
- Lagerblad, Björn, et al.
(författare)
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Ultrafine particles to save cement and improve concrete properties
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Fine particles play an important role in both fresh and hardened concrete and are often added as filler to give concrete specific properties. For example the development of more efficient superplasticizer allows increased amount of fillers to be used, which in turn has resulted in the development of self-compacting concrete (SCC). In SCC particles less than um are regarded as filler. Due to the new generations of very effective superplasticizers, it is today possible to include large amounts of even finer particles, particles much smaller (< 10 μm) than cement in size. These fillers here called ultrafillers. These ultrafillers will increase the strength of concrete and can thus act as a cement replacement. This is basically the effect behind CEM II/A-LL cement where the co-ground limestone due to the milling process will be an ultrafilier. In these cements the limestone filler has an efficiency factor of 1, i.e. the cement does not loose strength when substituted with UF. It is obvious that UF have other effects on concrete properties than ordinary fillers. It is also known from earlier work that different minerals have different influence on hydration properties. Thus several series of experiments with ultrafillers were conducted in order to obtain a better understanding of the reasons behind the effects and how they can be used in concrete production. The effect of different ultrafiller on hydration, paste structure, shrinkage and strength has been investigated. In the main experimental series quartz was chosen, as this mineral is easy to access and may act pozzolanic. Quartz in the size of cement, quartz finer than cement and ultrafine cristobalite quartz were tested. To compare it with other minerals, commercial ultrafine wollastonite and nepheline syenite (rock composed of nepheline and k-feldspar) were also tested. As quartz dust may result in silicosis, wet ground quartz was used in many of the experiments. All the ultrafine particles resulted in a pronounced increase in strength. It is possible to replace up to 40 % of the cement and still obtain similar strength. The best effect is achieved, when the cement is replaced but the water/cement is kept constant. The main effect on the hardened concrete seems to be due to the fact that the small mineral grains become an integrated part of the hydrated cement paste instead of discrete particles. Moreover, the ultrafine particles result in a more homogeneous interfacial zone. Mercury intrusion tests show that the ultrafiller gives a finer pore system. Basically the strength increase is due to the fineness, but increases in long-term strength also indicate that fine quartz also acts as slow pozzolana. With an optimised recipe and only 150-kg cement concrete with a compressive strength of 80 MPa can be produced. With a combination of ultrafiller, cement and silica fume concrete with more than 100 MPa in compressive strength can be produced with only 180 kg of binder. The incorporation of ultrafine particles accelerates the cement hydration. The effect increases with the fineness. Some minerals like wollastonite and calcite influence the onset of the acceleration period but the major influence is on the heat release during the acceleration period. Comparison between different minerals and production forms of the ultrafilier shows that the surface of the ultrafiller and aging is of major importance. The results show that ultrafine fillers can replace a substantial amount of cement, which will reduce the environmental impact by reducing energy consumption and CO2 release. Much of the potential is, however, already taken into account by the introduction of CEM II/A-LL cement that contains ultrafine limestone, but it is possible to reduce the amount of cement even further. In this case cement is replaced with ultrafiller while the water/cement is kept constant. This, however, demands superplasticizer and the result is that cement is replaced by a combination of ultrafine filler and superplasticizer. The concept with ultrafiller is currently probably not economical for the bulk production of concrete. This is due to the cost of grinding and handling of the fine materials in concrete production. By the use of wet ground material as slurry it is possible to avoid silicosis and other dust problems. If ultra fine particles are available as a by-product, however, it may be commercially interesting. The ultrafine particles are, however, interesting when one want to produce concretes for special applications or environments. Interesting areas are where one wants a lower energy release (heat development), dense concretes and special high performance concretes or other cementitious products where one wants to keep the amount of cement down. For example one can produce high strength concrete with relatively small amounts of cement to avoid thermal cracking and shrinkage. Ultrafine fillers were found to be an important ingredient in formulating ultra high performance concretes (reactive powder concrete).
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