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  • 1.
    Barzegar, Hamid Reza
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Physics, University of California, Berkeley, CA 94720, USA; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
    Yan, Aiming
    Coh, Sinisa
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ojeda-Aristizabal, Claudia
    Dunn, Gabriel
    Cohen, Marvin L.
    Louie, Steven G.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Zettl, Alex
    Spontaneous twisting of a collapsed carbon nanotube2017Ingår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 10, nr 6, s. 1942-1949Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the collapsing and subsequent spontaneous twisting of a carbon nanotube by in situ transmission electron microscopy (TEM). A custom-sized nanotube is first created in the microscope by selectively extracting shells from a parent multi-walled tube. The few-walled, large-diameter daughter nanotube is driven to collapse via mechanical stimulation, after which the ribbon-like collapsed tube spontaneously twists along its long axis. In situ diffraction experiments fully characterize the uncollapsed and collapsed tubes. The experimental observations and associated theoretical analysis indicate that the origin of the twisting is compressive strain.

  • 2.
    Ingemarson, Rolf
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Herpes simplex ribonucleotide reductase1989Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In all bacterial, plant and animal cells, as well as in many viruses, genetic information resides in DNA (deoxyribonucleic acid). Replication of DNA is essential for proliferation, and DNA-containing viruses (such as herpesviruses) must carry out this process within the mammalian cells they infect. The enzyme ribonucleotide reductase catalyzes the first unique step leading to the production of the four deoxy-ribonucleotides used to make DNA. Each deoxyribonucleotide is produced by reduction of the corresponding ribonucleotide. After infection of a mammalian cell with herpes simplex virus (HSV) a new ribonucleotide reductase activity appears, which is distinct from the mammalian enzyme activity. This is due to induction of a separate, virally-encoded ribonucleotide reductase. Two monoclonal antibodies were raised against HSV (type 1) ribonucleotide reductase, and were found to bind but not neutralize its enzyme activity. One antibody recognized a larger (140 kD) protein and the other a smaller (40 kD) protein, suggesting the HSV 1 ribonucleotide reductase had a heterodimeric composition similar to that found in many other organisms. The 140 kD protein was sequentially degraded to 110 kD, 93 kD and 81 kD proteins by a host (Vero) cell-specific serine protease. Of these different proteolytic products, at least the 93 kD residue was enzymatically active, suggesting that part of the 140 kD protein may have functions unrelated to ribonucleotide reduction. The 140 and 40 kD proteins bound tightly to each other in a complex of the a2ß2 type, as shown by analytical glycerol gradient centrifugation. An assay system for functional small and large subunits of HSV 1 ribonucleotide reductase was developed, using two temperaturesensitive mutant viruses, defective in either the large (tsl207) or small (tsl222) subunits. Active holoenzyme was reconstituted both in vitro, by mixing extracts from cells infected with either mutant, and in vivo by coinfection of cells with both mutants. The gene encoding the small subunit of HSV 1 ribonucleotide reductase was cloned into an expression plasmid under control of a tac promoter. The recombinant protein was purified to homogeneity from extracts of transfected E. coli, and was active when combined with large subunit, as provided by extracts of tsl222- infected hamster (BHK) cells. The protein contained a novel tyrosyl free radical that spectroscopically resembled, but was distinguishable from, the active-site free radical found in either the E. coli or mammalian small subunits of ribonucleotide reductase. The gene encoding the large subunit of HSV 1 ribonucleotide reductase was also expressed in E. coli, using similar techniques. The recombinant large subunit was immunoprecipitated from extracts of transfected bacteria, and showed weak activity when combined with small subunit, provided by extracts of tsl20-infected hamster (BHK) cells.

  • 3. Mohl, Melinda
    et al.
    Dobo, Dorina
    Kukovecz, Akos
    Konya, Zoltan
    Kordas, Krisztian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wei, Jinquan
    Vajtai, Robert
    Ajayan, Pulickel M.
    Formation of CuPd and CuPt Bimetallic Nanotubes by Galvanic Replacement Reaction2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 19, s. 9403-9409Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A galvanic replacement reaction has been successfully applied to prepare CuPd and CuPt bimetallic nanotubes. The nanotubes were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Ultralong, single crystalline copper nanowires (NWs) with a diameter of similar to 64 nm and a length of several micrometers were used as template material. By controlling the amount of noble metal salt added, nanotubes with different compositions were obtained. After the replacement of Cu with Pt, nanotubes composed of a PtCu alloy were formed. EDS analysis revealed that the Pt content increased until about 66%. No further increase in the molar ratio resulted in any additional Pt incorporation into the alloy. As for the replacement of Cu with Pd, the thickening of the nanotubes was observed indicating that nanotubes composed of Pd nanoparticles were formed. Bacicscattered electron imaging and SEM-EDS revealed CuPd nanotubes with approximately 2.3% Cu content. These remarks indicate different evolution mechanism for the nanotubes in the two systems.

  • 4.
    Olofsson, Martin
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Lamela, Teresa
    Necton SA, Olhao, Portugal.
    Nilsson, Emmelie
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Bergé, Jean-Pascal
    IFREMER, Nantes, France.
    del Pino, Victória
    Necton SA, Olhao, Portugal.
    Uronen, Pauliina
    Neste Oil, Ctr Technol, Porvoo, Finland.
    Legrand, Catherine
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Combined Effects of Nitrogen Concentration and Seasonal Changes on the Production of Lipids in Nannochloropsis oculata 2014Ingår i: Marine Drugs, ISSN 1660-3397, E-ISSN 1660-3397, Vol. 12, nr 4, s. 1891-1910Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Instead of sole nutrient starvation to boost algal lipid production, we addressed nutrient limitation at two different seasons (autumn and spring) during outdoor cultivation in flat panel photobioreactors. Lipid accumulation, biomass and lipid productivity and changes in fatty acid composition of Nannochloropsis oculata were investigated under nitrogen (N) limitation (nitrate:phosphate N:P 5, N:P 2.5 molar ratio). N. oculata was able to maintain a high biomass productivity under N-limitation compared to N-sufficiency (N:P 20) at both seasons, which in spring resulted in nearly double lipid productivity under N-limited conditions (0.21 g L−1 day−1) compared to N-sufficiency (0.11 g L−1 day−1). Saturated and monounsaturated fatty acids increased from 76% to nearly 90% of total fatty acids in N-limited cultures. Higher biomass and lipid productivity in spring could, partly, be explained by higher irradiance, partly by greater harvesting rate (~30%). Our results indicate the potential for the production of algal high value products (i.e., polyunsaturated fatty acids) during both N-sufficiency and N-limitation. To meet the sustainability challenges of algal biomass production, we propose a dual-system process: Closed photobioreactors producing biomass for high value products and inoculum for larger raceway ponds recycling waste/exhaust streams to produce bulk chemicals for fuel, feed and industrial material.

  • 5.
    Wang, Zhao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Lignocellulose is an inexpensive and abundant renewable resource that can be used to produce advanced biofuels, green chemicals, and other bio-based products. Pretreatment and efficient enzymatic saccharification are essential features of bioconversion of lignocellulosic biomass. The aims of the research were to achieve a better understanding of the recalcitrance of woody biomass to bioconversion, to explore different pretreatment techniques that can be used to decrease the recalcitrance of the biomass and improve the digestibility of the cellulose, and to investigate by-products of acid pretreatment that cause enzymes and microorganisms to work less efficiently.

    The recalcitrance of wood from aspen, birch, and spruce was investigated before and after acid pretreatment. Before pretreatment, birch exhibited the highest recalcitrance, which was attributed to structural factors. After pretreatment, spruce showed the highest recalcitrance, which was attributed to chemical factors, such as high lignin content. Deacetylation of hybrid aspen in planta by a CE5 acetyl xylan esterase decreased the recalcitrance, and the glucose yield of enzymatic saccharification of non-pretreated wood increased with 27%.

    Pretreatment options based on ionic liquids and steam explosion were further explored. The effects of the anionic constituents of a series of imidazolium-based ionic liquids on pretreatment of aspen and spruce were investigated. [HSO4]− was efficient only for aspen, which was attributed to acid degradation of xylan. [MeCO2]− was efficient for both aspen and spruce, which was attributed to its capability to create a disordered cell wall structure rather than to removal of lignin and hemicellulose. A comparison was made between using sulfuric acid and sulfur dioxide for pretreatment of spruce. Although sulfur dioxide resulted in a pretreatment liquid that was more inhibitory to both enzymes and yeast, it was still superior to pretreatment with sulfuric acid, a phenomenon that was attributed to the particle size of the pretreated material.

    In a comparison of microbial inhibitors in pretreatment liquids from steam explosion of spruce, formaldehyde was found to be the most important inhibitor of yeast. Enzyme inhibition by catalytically non-productive adsorption to lignins and pseudo-lignin was investigated using quantitative proteomics. The results indicate that protein adsorption to pseudo-lignin can be as extensive as adsorption to real lignin. 

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