| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Graiver, D., et al.
(författare)
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Steel-corrosion inhibitors derived from soybean oil
- 2012
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Ingår i: Journal of the American Oil Chemists Society. - : Wiley. - 0003-021X .- 1558-9331. ; 89:10, s. 1895-1903
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Tidskriftsartikel (refereegranskat)abstract
- Soybean oil derivatives containing a Schiff-base (SOS-B) were prepared and evaluated as microbial corrosion inhibitors against sulfate-reducing bacteria using the gram-positive Desulfosporosinus orientis bacteria as a representative bacterium. These SOS-B compounds were also found to be excellent inhibitors against acidic corrosion of carbon steel. These soybean oil derivatives were prepared by ozonation of soybean oil to yield aldehyde functional intermediates which were then reacted with benzylamine to produce a mixture of imine functional triglycerides and linear compounds. The structure of these soy-based derivatives was confirmed by FTIR and NMR. It was found that the addition of these SOS-B compounds to D. orientis culture provided a complete inhibition of this bacterium. Furthermore, almost no corrosion of carbon steel panels was observed when the panels were aged in 2N HCl solution containing 10 ppm of these SOS-B compounds
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| 3. |
- Jaros, Adam, et al.
(författare)
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Effect of acetate on fermentation production of butyrate
- 2012
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 46:5-6, s. 341-347
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Tidskriftsartikel (refereegranskat)abstract
- A carbon source for the fermentation production of butyrate is xylose extracted from ligno-cellulosic material by hot water extraction. Although this auto-hydrolysis of hemicellulose can provide a low-cost source of xylose, the process generates a high level of acetic acid that might inhibit subsequent fermentations. This study focuses on the effects of acetate on the production of butyrate from xylose by batch fermentations with a selected strain Clostridium tyrobutyricum.At initial acetate concentrations of 17.6 g L-1 and 26.3 g L-1 in the media, C. tyrobutyricum cultures exhibited a lag phase (45 and 118 hours, respectively) in terms of sugar consumption, butyrate production and cell biomass growth, lowering the overall production rate. Butyrate fermentations performed with high concentrations of acetate in the media demonstrated a re-uptake of acetate into the butyrate production pathway and after the lag phase, all cultures adapted to the inhibitory acetate, which increased the final butyrate yields by 12.6% (32.6 g L-1 compared to 28.5 g L-1).
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| 4. |
- Jaros, Adam Marschall, et al.
(författare)
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Acetate adaptation of clostridia tyrobutyricum for improved fermentation production of butyrate
- 2013
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Ingår i: SpringerPlus. - : Springer Science and Business Media LLC. - 2193-1801. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Clostridium tyrobutyricum ATCC 25755 is an acidogenic bacterium capable of utilizing xylose for the fermentation production of butyrate. Hot water extraction of hardwood lingocellulose is an efficient method of producing xylose where autohydrolysis of xylan is catalysed by acetate originating from acetyl groups present in hemicellulose. The presence of acetic acid in the hydrolysate might have a severe impact on the subsequent fermentations. In this study the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 26.3 g/L acetate equivalents were studied. Analysis of xylose batch fermentations found that even in the presence of high levels of acetate, acetate adapted strains had similar fermentation kinetics as the parental strain cultivated without acetate. The parental strain exposed to acetate at inhibitory conditions demonstrated a pronounced lag phase (over 100 hours) in growth and butyrate production as compared to the adapted strain (25 hour lag) or non-inhibited controls (0 lag). Additional insight into the metabolic pathway of xylose consumption was gained by determining the specific activity of the acetate kinase (AK) enzyme in adapted versus control batches. AK activity was reduced by 63% in the presence of inhibitory levels of acetate, whether or not the culture had been adapted.
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| 5. |
- Jaros, Adam Marschall
(författare)
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Four carbon oxychemicals from renewable resources
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Butanol, butyric acid and butyraldehyde are important 4-carbon oxychemicals typically generated from petro-chemical sources. All have significant markets in the food industry either for direct use as flavorings or as chemical feedstocks for generating butyric acid and butyraldehyde derived flavour compounds. Strong consumer sentiment against the consumption of petro-chemical derived products yields a demand for butyrate and butyraldehyde generated through all-natural methods. The bacterial fermentation production of butyric acid as well as bioconversion of butanol to butyraldehyde by yeast is presented in this work as a means of producing these products naturally. This thesis demonstrates the fermentation production of butyric acid with the Gram-positive anaerobic bacteria Clostridia tyrobutyricum. The organism consumes monomeric hexoses and pentoses to generate the carboxylic acids lactate, acetate and butyrate. The fermentations undertaken in this thesis were performed with either glucose or xylose as the primary carbon source in minimal media. Butyric acid studies were performed under anaerobic conditions as batch fermentations with lag, log and stationary phase growth being monitored by the optical density of the fermentation broth. Samples were drawn throughout the fermentations and HPLC analysis was performed to determine sugar consumption and butyric acid production over time. Another element expounded in this thesis is the potential use of the economical and renewable resource hot water extracted (HWE) hemicellose as a substrate for Clostridial fermentation. HWE hemicellose is produced as a waste stream from the pulp and paper industry and is converted to fermentable xylose with the concomitant release of acetic acid from the acetyl groups on the xylan backbone. With the presence of such a high concentration of acetic acid, microbial inhibition occurs and the productivity of xylose fermentation to butyric acid is diminished with the increased lag phase. C. tyrobutyricum xylose fermentation studies were performed with synthetic media challenging the fermentation with up to 26.3 g/L acetic acid to gain an understanding of the effects of acetic acid inhibition. Once the acetic acid induced lag phase growth was characterized this work was furthered by adapting a strain of C. tyrobutyricum to 26.3 g/L acetic acid conditions and demonstrating that this pre-adaptation could drastically reduce the acetic acid induced lag phase of a batch fermentation. From this set of studies, it is noted that the presence of acetic acid in the media increases carbon efficiency of the fermentation as during stationary growth C. tyrobutyricum re-uptakes free acetic acid from the environment and converts it into butyric acid. This thesis also demonstrates the bioconversion of butanol to butyraldehyde by the methylotrophic yeast Pichia pastoris. P. pastoris were grown to high cell densities under glycerol feed and then induced to produce the endogenous alcohol oxidase (AOX) enzyme by beginning the culture on methanol consumption after a short starvation period. AOX converts short chain aliphatic alcohols to the corresponding aldehyde with the utilization of oxygen. The AOX enzyme is inhibited by the final product butyraldehyde so studies were performed utilizing alternative amine based pH buffering systems which also aid the bioconversion by binding free butyraldehyde as a Schiff-base. By binding the butyraldehyde longer bioconversions were observed. For these conversions, AOX activity was monitored with an absorbance based enzyme assay and the butanol substrate and butyraldehyde product were determined by gas chromatography.
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