| 1. |
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| 2. |
- Ardö, Jonas, et al.
(författare)
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Critical levels of SO2 - uncertainty and relationships to Regional Forest Decline
- 2000
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Ingår i: Geographical & Environmental Modelling. - 1469-8323. ; 4:2, s. 131-161
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Tidskriftsartikel (refereegranskat)abstract
- Three methods estimating adverse effects of SO2 on Norway spruce forests were applied and evaluated on a regional level in northern Czech Republic. The methods, assuming adverse effects to occur when predetermined thresholds are exceeded, include the critical level of SO2 concentration (1), the ratio of the SO2 concentration to the vegetation period (SO2/VP) (2) and a model predicting needle loss from environmental data and SO2 (3). Comparing the estimated impact with observed regional forest decline reveals significant relationships for all methods. The influence of data uncertainty, quantified using Monte Carlo simulation, was used to map areas significantly over or below the critical thresholds. The main results show: (1) that there are strong linear relationships between accumulated salvage fellings and the SO2 concentrations, the SO2/VP ratio and a model predicting needle loss in response to elevated SO2 concentrations, (2) there is a clear relationship between damage classes based on defoliation and SO2 concentration. A critical value of 20 [mug m - 3 yr - 1] (mean annual concentration) seems a reasonable choice to distinguish between no effects below this level and possible effects above this level. The same is true for the SO2/VP ratio of 0.07 [nPa Pa - 1 day - 1]. The results indicate no substantial contribution from the increased structural complexity and data demand for methods 2 and 3. High quality SO2 data with known uncertainty and integration with high - resolution land cover data are the main requirements for improved mapping and identification of various receptors at risk.
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| 3. |
- Arvidsson, Pär, et al.
(författare)
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Chromatography of microbial cells using continuous supermacroporous affinity and ion-exchange columns
- 2002
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Ingår i: Journal of Chromatography A. - 0021-9673. ; 977:1, s. 27-38
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Tidskriftsartikel (refereegranskat)abstract
- Continuous supermacroporous chromatographic columns with anion-exchange ligands [2-(dimethylanlino)ethyl group] and immobilized metal affinity (IMA) ligands (Cu2+-loaded iminodiacetic acid) have been developed allowing binding of Escherichia coli cells and the elution of bound cells with high recoveries. These poly(acrylamide)-based continuous supermacroporous columns have been produced by radical co-polymerization of monomers in aqueous solution frozen inside a column (cryo-polymerization). After thawing, the column contains a continuous matrix (so-called cryogel) with interconnected pores of 10-100 mum in size. The large pore size of the matrix makes it possible for E. coli cells to pass unhindered through a plain column containing no ligands. E. coli cells bound to an ion-exchange column at low ionic strength were eluted with 70-80% recovery at NaCl concentrations of 0.35-0.40 M, while cells bound to an IMA-column were eluted with around 80% recovery using either 10 mM imidazole or 20 mM EDTA solutions, respectively. The cells maintain their viability after the binding/elution procedure. These preliminary results indicate that microbial cells can be handled in a chromatographic mode using supermacroporous continuous columns. These columns are easy to manufacture from cheap and readily available starting materials, which make the columns suitable for single-time use. (C) 2002 Published by Elsevier Science B.V.
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| 4. |
- Arvidsson, Pär, et al.
(författare)
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Direct chromatographic capture of enzyme from crude homogenate using immobilized metal affinity chromatography on a continuous supermacroporous adsorbent
- 2003
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Ingår i: Journal of Chromatography A. - 0021-9673. ; 986:2, s. 275-290
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Tidskriftsartikel (refereegranskat)abstract
- A continuous supermacroporous matrix has been developed allowing direct capture of enzyme from non-clarified crude cell homogenate at high flow-rates. The continuous supermacroporous matrix has been produced by radical co-polymerization of acrylamide, allyl glycidyl ether and N,N′-methylene-bis(acrylamide) which proceeds in aqueous solution of monomers frozen inside a column (cryo-polymerization). After thawing, the column contains a continuous matrix having interconnected pores of 10–100 m size. Iminodiacetic acid covalently coupled to the cryogel is a rendering possibility for immobilized metal affinity chromatographic purification of recombinant His-tagged lactate dehydrogenase, (His)6-LDH, originating from thermophilic bacterium Bacillus stearothermophilus, but expressed in Escherichia coli. The large pore size of the adsorbent makes it possible to process particulate-containing material without blocking the column. No preliminary filtration or centrifugation is needed before application of crude extract on the supermacroporous column. A total of 210 ml crude homogenate, 75 ml of it non-clarified, was processed on a single 5.0 ml supermacroporous column at flow speeds up to 12.5 ml/min without noticeable impairment of the column properties. Mechanically the cryogel adsorbent is very stable. The continuous matrix could easily be removed from the column, dried at 70 °C and kept in a dry state. After rehydration and reinsertion of the matrix into an empty column, (His)6-LDH was purified as efficiently as on the newly prepared column. The procedure of manufacturing the supermacroporous continuous cryogel is technically simple. Starting materials and initiators are cheap and available and are simply mixed and frozen under specified conditions. Altogether these qualities reveal that the supermacroporous continuous cryogels is a very interesting alternative to existing methods of protein purification from particulate-containing crude extracts
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| 5. |
- Arvidsson, Pär, 1977, et al.
(författare)
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Free tensor multiplets and strings in spontaneously broken six-dimensional (2,0) theory
- 2003
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Ingår i: Journal of High Energy Physics (JHEP). ; 06, s. 039-
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Tidskriftsartikel (refereegranskat)abstract
- We first review the representations of the six-dimensional (2,0) superalgebra on a free tensor multiplet and on a free string. We then construct a supersymmetric lagrangian describing a free tensor multiplet. (It also includes a decoupled anti self-dual part of the three-form field strength.) This field theory is then rewritten in variables appropriate for analyzing a situation where the R-symmetry is spontaneously broken by the vacuum expectation values of the scalar moduli fields. Finally, we construct a supersymmetric and κ-symmetric action for a free string.
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| 6. |
- Arvidsson, Pär, 1977
(författare)
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Manifest superconformal covariance in six-dimensional (2,0) theory
- 2006
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Ingår i: Journal of High Energy Physics. ; 03, s. 076-
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Tidskriftsartikel (refereegranskat)abstract
- A superconformal generalization of Dirac's formalism for manifest conformal covariance is presented and applied to the free (2,0) tensor multiplet field theory in six dimensions. A graded symmetric superfield, defined on a supercone in a higher-dimensional superspace is introduced. This superfield transforms linearly under the transformations of the supergroup OSp(8*|4), which is the superconformal group of the six-dimensional (2,0) theory. We find the relationship between the new superfield and the conventional (2,0) superfields in six dimensions and show that the implied superconformal transformation laws are correct. Finally, we present a manifestly conformally covariant constraint on the supercone, which reduces to the ordinary differential constraint for the superfields in the six-dimensional space-time.
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| 7. |
- Arvidsson, Pär
(författare)
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Polymer Displacement and Supermacroporous Cryogels - Two New Tools in Chromatographic Separation of Biomolecules and Bioparticles
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Production of protein is often accompanied with difficulties due to the large amounts of different biological material resulting from fermentation. This makes purification necessary and affinity chromatography is usually involved as being biospecific, although suffering from limitations as low recovery due to ineffective elution and inability to handle particulate materials. Displacement of lactate dehydrogenase (LDH) from dye-affinity matrices with poly(ethyleneimine) (PEI) resulted in better recoveries and sharper elution profiles than traditional non-specific elution but with unchanged purification factors. Hence, displacement with PEI is a promising strategy for eluting proteins with reported low recoveries in dye-affinity chromatography. Displacement of (His)6-LDH, a hexahistidine-tagged thermostable LDH originating from a thermophilic bacterium, was carried out using a synthetic copolymer of vinyl imidazole and vinyl caprolactam as displacer from an immobilized metal affinity chromatography (IMAC) column. Complete elution of bound (His)6-LDH from Cu2+-imminodiacetic acid Sepharose was achieved at a co-polymer concentration of 5 mg/ml, corresponding to 3.7 mM imidazole units, while 160 mM free imidazole was needed to obtain the same result. Thus, efficiency could be significantly improved by a polymeric displacer having interacting groups of the same chemical nature as the corresponding low-molecular mass displacer. Continuous supermacroporous chromatographic columns with anion exchange ligands (2-(dimethylamino)ethyl group) and IMAC ligands (Cu2+-loaded iminodiacetic acid) have been developed allowing binding of E. coli cells and elution of bound cells with high recoveries and retained viability as well as direct capture of enzyme from non-clarified crude cell homogenate at high flow rates without mechanical obstruction. These poly(acrylamide)-based matrices were produced by radical co-polymerization of monomers in aqueous solution frozen inside a column (cryogelation). After thawing, the column contains a continuous cryogel matrix with interconnected 10 - 100 mm pores. These large pores make processing of particulate-containing material without blocking possible. Purification of (His)6-LDH from non-clarified crude extract without preliminary filtration or centrifugation was possible on the IMAC cryogel column. Totally, 210 ml crude homogenate was processed on a single five ml supermacroporous column at flow speeds up to 12.5 ml/min (625 cm/h) without impairment of column properties. E. coli cells bound to an IMAC-column were eluted with 80 % recovery using either 10 mM imidazole or 20 mM EDTA solutions and cells bound to an ion-exchange column at low ionic strength were eluted with 70 - 80% recovery at NaCl concentrations of 0.35 - 0.40 M, while it was possible for cells to pass unhindered through a column without ligands. Cells maintained viability after the chromatographic procedures. Mechanically the cryogel adsorbent is very stable. The matrix could easily be removed from the column, dried at 70 °C and kept in a dry state. After rehydration, (His)6-LDH was purified as efficiently as on a newly prepared column. Materials for manufacturing the cryogels are cheap, available and are simply mixed and frozen under specified conditions. Altogether, these qualities reveal that supermacroporous continuous cryogels is a very interesting alternative to existing methods of protein purification from particulate-containing crude extracts as well as an exciting new support for handling of microbial cells in a chromatographic mode.
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| 8. |
- Arvidsson, Pär, 1977
(författare)
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Six-dimensional theories with (2,0) supersymmetry
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the so called (2,0) theories in six dimensions are discussed. These theories are of special interest because they do not contain dynamical gravity despite their high dimensionality. The origin of (2,0) theory in terms of higher-dimensional theories (Type IIB string theory and M-theory) is treated, as well as compactifications of the six-dimensional theory to supersymmetric Yang-Mills theories in five and four dimen- sions. The representations of the (2,0) algebra on a free massless tensor multiplet and on a free tensile string are discussed and actions are derived describing the dynamics of these. Furthermore, the bosonic part of the string is coupled to the bosonic part of the tensor multiplet action; this is then used as a starting point for the supersymmetric coupling of a spinning string to a background consisting of tensor multiplet fields.
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| 9. |
- Arvidsson, Pär, 1977
(författare)
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Superconformal symmetry in the interacting theory of (2,0) tensor multiplets and self-dual strings
- 2006
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Ingår i: Journal of Mathematical Physics. ; 47, s. 042301-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the concept of superconformal symmetry in six dimensions, applied to the interacting theory of (2,0) tensor multiplets and self-dual strings. The action of a superconformal transformation on the superspace coordinates is found, both from a six-dimensional perspective and by using a superspace with eight bosonic and four fermionic dimensions. The transformation laws for all fields in the theory are derived, as well as general expressions for the transformation of on-shell superfields. Superconformal invariance is shown for the interaction of a self-dual string with a background consisting of on-shell tensor multiplet fields, and we also find an interesting relationship between the requirements of superconformal invariance and those of a local fermionic kappa-symmetry. Finally, we construct a superspace analogue of the Poincare dual to the string world-sheet and consider its properties under superconformal transformations.
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| 10. |
- Arvidsson, Pär, 1977
(författare)
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Superconformal Theories in Six Dimensions
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of an introductory text, which is divided into two parts, and six appended research papers.The first part contains a general discussion on conformal and superconformal symmetry in six dimensions, and treats how the corresponding transformations act on space-time and superspace fields. We specialize to the case with chiral (2,0) supersymmetry. A formalism is presented for incorporating these symmetries in a manifest way.The second part of the thesis concerns the so called (2,0) theory in six dimensions. The different origins of this theory in terms of higher-dimensional theories (Type IIB string theory and M-theory) are treated, as well as compactifications of the six-dimensional theory to supersymmetric Yang-Mills theories in five and four space-time dimensions. The free (2,0) tensor multiplet field theory is introduced and discussed, and we present a formalism in which its superconformal covariance is made manifest. We also introduce a tensile self-dual string and discuss how to couple this string to the tensor multiplet fields in a way that respects superconformal invariance.
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