| 18171. |
- Zakaria, Mohamad, et al.
(author)
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The 2002/2003 radionuclide concentration in the marine environment at various distances from the Barseback nuclear power plant
- 2008
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In: Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 43:3, s. 429-438
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Journal article (peer-reviewed)abstract
- The activity concentration of (CS)-C-137, I-131, Zn-65, Co-60, Co-58, Mn-54, and K-40 were determined in samples of brown seaweed (Fucus) and some other marine plants using low background high-resolution gamma-spectrometry. The algae were mainly sampled in the bay just north of the Barseback NPP (55.4 N, 12.6 E) in the south of Sweden to study the contamination levels in the nearest shallow waters. One aim of the study was to investigate whether the levels were high enough to expect environmental effects. Some samples were also taken at longer distances up to 130 kin from the Barseback NPP. Measurable levels of the neutron activation products Zn-65 (up to 17 Bq/kg dw), Co-60 (100-600 Bq/kg dw), Co-58 (1-160 Bq/kg dw) and Mn-54 (12-90 Bq/kg dw) were found in the algae samples within a distance of 5 kin from the plant. The decrease in activity concentration with distance from the plant could he described by a power function with an exponent ranging from 1.4 to 2.4. This was in fair agreement with the value for a true two-dimensional dispersion model. The present-day concentrations were found to be considerably lower than in earlier studies made in the late 1970s, especially for Zn-65 and Co-58. The activity concentration of gamma emitting radionuclides in Fucus vesiculosus from the bay just north of Barseback in the period 2002-2003 was dominated by (in order of decreasing concentration): natural K-40, Co-60 from the plant, Cs-137 mainly from the Chernobyl debris, Mn-54 and Co-58 from the plant. It is not likely that any effects from the very marginal absorbed dose contribution from the Barseback NPP releases can he found even in the nearest environment. The study has also shown that the eelgrass Zostera marina may be a bioindicator to use in further studies of the radiation environment in shallow water, especially for Co-60 and Mn-54.
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| 18172. |
- Zakharova, A, et al.
(author)
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Effects of lattice mismatch and bulk anisotropy on interband tunneling in broken-gap heterostructures
- 2005
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In: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 97:6
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Journal article (peer-reviewed)abstract
- We have studied the effects of bulk anisotropy and the strain induced by lattice mismatch on the interband tunneling in broken-gap single-barrier InAs/AlSb/GaSb heterostructures and double-barrier InAs/AlSb/GaSb/InAs/AlSb/GaSb heterostructures. We have used the eight-band k.p model and the scattering matrix method, combined with the Burt envelope function theory, to calculate the interband transmission coefficients through the broken-gap heterostructures. We have found a noticeable anisotropy of the transmission coefficients when the magnitude of the in-plane wave vector increases to around 0.25 nm(-1). We have also found that the strain and the bulk anisotropy of quasiparticle dispersion produce additional peaks in the tunneling probability. For the double-barrier resonant-tunneling structures we discover a large spin splitting of the resonant-tunneling peaks caused by the lack of inversion symmetry. A strong influence of the strain induced by lattice mismatch appears in the current-voltage characteristics of the studied broken-gap heterostructures. In InAs/AlSb/GaSb structures the interband tunneling processes into the heavy-hole states contribute mainly to the peak current density if the sample is grown on InAs, but if the sample is grown on GaSb the interband tunneling processes into the light-hole states become the main contribution to the peak current density. As a result, the structure grown on GaSb has a much larger peak current density. This phenomenon was observed experimentally.
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| 18173. |
- Zakharova, A., et al.
(author)
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Optical absorption of polarized light in InAs/GaSb quantum wells
- 2008
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In: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 23:12
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Journal article (peer-reviewed)abstract
- Using an eight-band k p model Hamiltonian with the Burt-Foreman envelope function theory, we have investigated the optical absorption of both linearly and circularly polarized light, as well as related phenomena in InAs/GaSb broken-gap quantum wells grown along the [0 0 1] direction, with emphasis on the effects of electron-hole hybridization and the various symmetry-breaking mechanisms such as structural inversion asymmetry, bulk inversion asymmetry and interface Hamiltonian. The optical matrix elements exhibit unusual angular dependence in close connection with the spin-flip transitions which are originally forbidden. The spin split of the 2e subband results in two profound absorption peaks for the 1hh-2e transition for both linearly polarized and circularly polarized light. A large lateral optical anisotropy appears in the absorption coefficient of linearly polarized light, which can reach almost 100% with a reducing thickness of the quantum well. For the absorption of circularly polarized light, we found a large enhancement of electron spin polarization in the upper 2e subband, which was generally considered as forbidden if the polarization is along the direction perpendicular to the plane-of-light incidence. © 2008 IOP Publishing Ltd.
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| 18174. |
- Zakharova, A, et al.
(author)
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Six-band k center dot p calculation of spin-dependent interband tunneling in strained broken-gap heterostructures under a quantizing magnetic field
- 2005
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:11
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Journal article (peer-reviewed)abstract
- We investigate spin-dependent interband magnetotunneling processes in strained broken-gap resonant tunneling structures made from InAs, AlSb, and GaSb, which are promising materials for quantum devices. InAs/AlSb/GaSb/InAs/AlSb/GaSb double-barrier structures grown on both InAs and GaSb are considered. Transmission coefficients for interband tunneling processes from individual eigenstates in the InAs emitter as well as current-voltage characteristics were calculated using a six-band k center dot p model and the scattering matrix method. We predict that due to lattice-mismatch induced strain, the interband tunneling current density for the structure grown on InAs can be one or two orders of magnitude less than that for the structure grown on GaSb. Furthermore, as a consequence of interband magnetotunneling, structures grown on different substrates yield different spin polarization of the tunneling current. It is obtained that the current spin polarization can be greater than 90%. These resonant tunneling structures can be used as spin filters in the rapidly growing field of spintronics.
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| 18175. |
- Zakharova, A, et al.
(author)
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Spin polarization of an electron-hole gas in InAs/GaSb quantum wells under a dc current
- 2006
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 73:12
-
Journal article (peer-reviewed)abstract
- We have investigated the spin polarization of electrons and holes in InAs/GaSb broken-gap quantum wells under nonequilibrium conditions when a dc electric field is applied parallel to interfaces. The existence of a nonzero asymmetric part of the quasiparticle distribution function caused by the dc current and the spin-split of the electron-hole hybridized states generates a finite spin polarization in both the InAs layer and the GaSb layer. With a very weak asymmetry of the distribution function, our self-consistent calculation yields about 1% spin polarization for electrons in the InAs layer and holes in the GaSb layer. The signs of these spin polarizations depend on the widths of the layers, changing the widths drives a phase transition in the electron-hole gas between the hybridized semiconducting phase and the normal semiconducting phase. In the hybridized semiconducting phase, the spin polarizations in both the InAs layer and the GaSb layer have the same sign. Crossing the phase boundary, the electron spin polarization and the total spin polarization in the InAs/GaSb quantum well can change their signs.
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| 18176. |
- Zakhary, Mina M., et al.
(author)
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Prevalence and Etiology of Intracranial Hemorrhage in Term Children Under the Age of Two Years: A Retrospective Study of Computerized Tomographic Imaging and Clinical Outcome in 798 Children
- 2009
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In: Academic Radiology. - : Elsevier BV. - 1878-4046 .- 1076-6332. ; 16:5, s. 572-577
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Journal article (peer-reviewed)abstract
- Rationale and Objectives. The purposes of this study were to retrospectively identify various etiologies underlying intracranial hemorrhages (ICHs) in term infants aged <2 years and their respective prevalence in this population and to describe the long-term clinical outcomes in these patients. Materials and Methods. A retrospective review of the medical records and computed tomographic studies of the head in 798 term infants aged 0 to 24 months with suspected or known ICHs was conducted. Results. ICHs were present in 195 of the 798 infants (24%). More than one type of ICH was present in 32%. Subdural hemorrhage was the most frequent type of ICH, occurring in 63% of the infants. Good clinical outcomes were present in 49% of the infants but varied depending on the location, etiology, and timing of the ICH. Conclusion. The incidence of various etiologies of ICH depended on the ages of the infants. The overall clinical outcomes were good, with no long-term sequelae in half of the infants presenting with ICHs. In infants aged >4 weeks presenting with ICHs, special attention should be given to the possibility of nonaccidental trauma etiology, because this is common and has worse long-term outcomes.
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| 18177. |
- Zakhrabekova, Shakhira, et al.
(author)
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Comparing two microarray platforms for identifying mutated genes in barley (Hordeum vulgare L.)
- 2007
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In: Plant Physiology and Biochemistry. - : Elsevier BV. - 1873-2690 .- 0981-9428. ; 45:8, s. 617-622
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Journal article (peer-reviewed)abstract
- We have previously described the evaluation of a cDNA microarray platform to identify and clone mutated barley (Hordeum vulgare L.) genes, using their transcriptionally defective mutant alleles (S. Zakhrabekova, C.G. Karmangara, D. von Wettstein, M. Hansson, A microarray approach for identification of mutated genes, Plant Physiol. Biochem. 40 (2002) 189-197). It was concluded that competitive hybridization between phenotypically similar mutants could specifically highlight an arrayed clone, corresponding to the mutated gene. In this study we evaluate whether the Affymetrix microarray platform can be used for the same purpose. The Affymetrix barley microarray contains a large number of clones (22,792 probe sets). In this and the previous study we used two barley mutant strains, xantha-h.57 and xantha-f.27, with known mutations in different subunit genes of the chlorophyll biosynthetic enzyme magnesium chelatase (EC 6.6. 1. 1). Mutant xantha-h.57 produces no Xantha-h mRNA whereas in xantha-f27 the nonsense mutation in the last exon of the gene, results in nonsense-mediated decay of Xantha-f mRNA. We conclude that the Affyinetrix platform meets our requirements and that our approach successfully highlighted the arrayed Xantha-h clone and that Xantha-f was among the top fourteen candidates.
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| 18178. |
- Zaldivar, J, et al.
(author)
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Ethanolic fermentation of acid pre-treated starch industry effluents by recombinant Saccharomyces cerevisiae strains
- 2005
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In: Bioresource Technology. - : Elsevier BV. - 1873-2976 .- 0960-8524. ; 96:15, s. 1670-1676
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Journal article (peer-reviewed)abstract
- Two industrial effluents, a pre-fermentation effluent and a post-fermentation effluent from a wheat starch production plant, were used as substrates for fuel ethanol production in anaerobic batch cultures using minimal nutritional amendment. The performances of three metabolically engineered xylose-utilizing Saccharomyces cerevisiae strains: TMB 3001 expressing XYL1, XYL2 and XKS1, redox metabolism modulated CPB.CR1 and glucose de-repressed CPB.CR2, as well as a reference strain CEN.PK 113-7D not fermenting xylose, were evaluated. For the recombinant strains a glucose consumption phase preceded the xylose consumption phase. In both effluents, biomass and ethanol production occurred predominantly during the glucose consumption phase, whereas xylitol and glycerol formation were predominant in the xylose consumption phase. Total specific ethanol productivities on glucose were 6-fold higher than on xylose in the pre-fermentation effluent and 15-fold higher than on xylose in the post-fermentation effluent. CPB.CR1 showed impaired growth compared to the two other xylose-utilizing strains, but displayed 18% increased ethanol yield in the post-fermentation effluent. (c) 2005 Elsevier Ltd. All rights reserved.
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| 18179. |
- Zameitat, Elke, et al.
(author)
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Biochemical characterization of recombinant dihydroorotate dehydrogenase from the opportunistic yeast Candida albicans
- 2006
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In: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 273:14, s. 3183-3191
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Journal article (peer-reviewed)abstract
- Candida albicans is the most prevalent yeast pathogen in humans, and recently it has become increasingly resistant to the current antifungal agents. In this study we investigated C. albicans dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11), which catalyzes the fourth step of de novo pyrimidine synthesis, as a new target for controlling infection. We propose that the enzyme is a member of the DHODH family 2, which comprises mitochondrially bound enzymes, with quinone as the direct electron acceptor and oxygen as the final electron acceptor. Full-length DHODH and N-terminally truncated DHODH, which lacks the targeting sequence and the transmembrane domain, were subcloned from C. albicans, recombinantly expressed in Escherichia coli, purified, and characterized for their kinetics and substrate specificity. An inhibitor screening with 28 selected compounds was performed. Only the dianisidine derivative, redoxal, and the biphenyl quinoline-carboxylic acid derivative, brequinar sodium, which are known to be potent inhibitors of mammalian DHODH, markedly reduced C. albicans DHODH activity. This study provides a background for the development of antipyrimidines with high efficacy for decreasing in situ pyrimidine nucleotide pools in C. albicans.
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| 18180. |
- Zander, Claes-Göran, et al.
(author)
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Investigation of the 'magnetic bands' in Pb-199
- 2006
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In: Physica Scripta. - 0031-8949. ; T125, s. 230-231
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Journal article (peer-reviewed)abstract
- The cranked Nilsson-Strutinsky formalism is developed to include the perpendicular spin component of specific orbitals. The formalism is applied to the 'magnetic bands' in Pb-199.
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