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Sökning: WFRF:(Kumar A) > Högskolan i Halmstad

  • Resultat 1-4 av 4
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1.
  • Johannes, A., et al. (författare)
  • Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires
  • 2014
  • Ingår i: Journal of Physics D: Applied Physics. - Bristol : IOP Publishing. - 1361-6463 .- 0022-3727. ; 47:39
  • Tidskriftsartikel (refereegranskat)abstract
    • We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-x-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clearly enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency.
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2.
  • Kumar, Ashok, et al. (författare)
  • Affinity binding of cells to cryogel adsorbents with immobilized specific ligands : effect of ligand coupling and matrix architecture
  • 2005
  • Ingår i: Journal of Molecular Recognition. - : Wiley. - 0952-3499 .- 1099-1352. ; 18:1, s. 84-93
  • Tidskriftsartikel (refereegranskat)abstract
    • The capture of human acute myeloid leukemia KG-1 cells expressing the CD34 surface antigen and the fractionation of human blood lymphocytes were evaluated on polyvinyl alcohol (PVA)-cryogel beads and dimethyl acrylamide (DMAAm) monolithic cryogel with immobilized protein A. The affinity ligand (protein A) was chemically coupled to the reactive PVA-cryogel beads and epoxy-derivatized monolithic cryogels through different immobilization techniques and the binding efficiency of the cell surface receptors specific antibody-labeled cells to the gels/beads was determined. The binding of cells to monolithic cryogel was higher (90-95%) compared with cryogel beads (76%). B-lymphocytes, which bound to the protein A-cryogel beads, were separated from T-lymphocytes with yields for the two cell types 74 and 85%, respectively. About 91% of the bound B-cells could be recovered without significantly impairing their viability. Our results show differences in the percentage of cell-binding to the immunosorbents caused by ligand density, flow shear forces and bond strength between the cells and the affinity surface once distinct chemical coupling of protein A, size of beads, sequence of antibody binding to protein A adsorbents, morphology and geometry of surface matrices were compared.
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3.
  • Paschoal Jr., Waldomiro, 1977-, et al. (författare)
  • Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires
  • 2014
  • Ingår i: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:15
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the magnetoresistance (MR) in a series of Zn doped (p-type) GaAs nanowires implanted with different Mn concentrations. The nanowires with the lowest Mn concentration (~0.0001%) exhibit a low resistance of a few kΩ at 300K and a 4% positive MR at 1.6K, which can be well described by invoking a spin-split subband model. In contrast, nanowires with the highest Mn concentration (4%) display a large resistance of several MΩ at 300K and a large negative MR of 85% at 1.6K. The large negative MR is interpreted in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins. Sweeping the magnetic field back and forth for the 4% sample reveals a hysteresis that indicates the presence of a weak ferromagnetic phase. We propose co-doping with Zn to be a promising way to reach the goal of realizing ferromagnetic Ga1-xMnxAs nanowires for future nanospintronics. © 2014 AIP Publishing LLC.
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4.
  • Shakya, A. K., et al. (författare)
  • Characterization of chemically defined poly-N-isopropylacrylamide based copolymeric adjuvants
  • 2013
  • Ingår i: Vaccine. - : Elsevier BV. - 0264-410X .- 1873-2518. ; 31:35, s. 3519-3527
  • Tidskriftsartikel (refereegranskat)abstract
    • PNiPAAm is a thermo-responsive polymer with an adjuvant activity. To identify the minimal chemical structure present within PNiPAAm responsible for its adjuvant property, three different constituent polymers with specific functional groups were synthesized through free radical reaction and tested their adjuvant potential along with PNiPAAm. Among them, polymer with isopropyl attached to an amide showed maximal adjuvant activity in rodents followed by polymer with amide or ketone functional groups. However, secondary amine containing polymer did not show any adjuvant activity. In addition, to improve the adjuvant properties of PNiPAAm, we incorporated an affinity ligand, boronate. At first, we synthesized and characterized the dual responsive copolymers PNiPAAm-co-VPBA and PNiPAAm-co-VPBA-co-DMAEMA. Biocompatibility of these copolymers was confirmed both in vitro and in vivo. Mice injected with these copolymers mixed with collagen (CII) developed significant levels of anti-CII antibodies comprising of all the major IgG subclasses and an increased T cell activation. At the injection site, massive infiltration of immune cells was observed. However, only PNiPAAm-co-VPBA-co-DMAEMA-CII induced arthritis in mice after injection of 0.5M fructose confirming the importance of effective release of CII from the polymer for its adjuvant activity. Thus, a fine balance of hydrophobicity and hydrophilicity promotes adjuvant properties and continuous release of antigen, in this case CII, from polymer is essential for its adjuvant activity.
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