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- Herbschleb, C. T., et al.
(författare)
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The ReactorSTM : Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions
- 2014
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 85:8
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Tidskriftsartikel (refereegranskat)abstract
- To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.
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- Stoltz, D., et al.
(författare)
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Atomic origin of the scanning tunneling microscopy images of charge-density-waves on 1T-TaSe2
- 2008
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 403
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Tidskriftsartikel (refereegranskat)abstract
- We show atomically resolved scanning tunneling microscopy (STM) images of charge density waves (CDWs) at room temperature together with angle-resolved photoelectron band-mapping of 1T-TaSe2. By comparing the results of these two techniques, we demonstrate the atomic structure of the CDW-features observed by the STM and atomic origin of the reconstructed band-structure in this material.
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- Javed, M. Tariq, et al.
(författare)
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Cadmium spiked soil modulates root organic acids exudation and ionic contents of two differentially Cd tolerant maize (Zea mays L.) cultivars
- 2017
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Ingår i: Ecotoxicology and Environmental Safety. - : Elsevier BV. - 0147-6513 .- 1090-2414. ; 141, s. 216-225
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Tidskriftsartikel (refereegranskat)abstract
- Our earlier work described that the roots of two maize cultivars, grown hydroponically, differentially responded to cadmium (Cd) stress by initiating changes in medium pH depending on their Cd tolerance. The current study investigated the root exudation, elemental contents and antioxidant behavior of the same maize cultivars (cv. 3062 (Cd-tolerant) and cv. 31P41 (Cd-sensitive)] under Cd stress. Plants were maintained in a rhizobox-like system carrying soil spiked with Cd concentrations of 0, 10, 20, 30, 40 and 50 mu mol/kg soil. The root and shoot Cd contents increased, while Mg, Ca and Fe contents mainly decreased at higher Cd levels, and preferentially in the sensitive cultivar. Interestingly, the K contents increased in roots of cv. 3062 at low Cd treatments. The Cd stress caused acidosis of the maize root exudates predominantly in cv. 3062. The concentration of various organic acids was significantly increased in the root exudates of cv. 3062 with applied Cd levels. This effect was diminished in cv. 31P41 at higher Cd levels. Cd exposure increased the relative membrane permeability, anthocyanin (only in cv. 3062), proline contents and the activities of peroxidases (POD) and superoxide dismutase (SOD). The only exception was the catalase activity, which was diminished in both cultivars. Root Cd contents were positively correlated with the secretion of acetic acid, oxalic acid, glutamic acid, citric acid, and succinic acid. The antioxidants like POD and SOD exhibited a positive correlation with the organic acids under Cd stress. It is likly that a high exudation of dicarboxylic organic acids improves nutrient uptake and activities of antioxidants, which enables the tolerant cultivar to acclimatize in Cd polluted environment.
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- Stoltz, Dunja, et al.
(författare)
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Investigation of surface structure related features in the multiple-scattering simulations of photoelectron diffraction of 3C-SiC(001)-c(4 x 2)
- 2007
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 395:1-2, s. 130-137
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we have conducted a systematic study of the photoelectron diffraction (PED) effects from the 3C-SiC(0 0 1)-c(4 x 2) surface by means of multiple-scattering calculations. Two models have been proposed to describe this surface: alternately up and down dimers (AUDD) [P. Soukiassian, F. Semond, L. Douillard, A. Mayne, G. Djuradin, L. Pizzagalli, C. Joachim, Phys. Rev. Lett. 78 (1997) 9071, based on the scanning tunneling microscopy data, and missing-row asymmetric-dimer (MRAD) [W. Lit, P. Kruger, J. Pollmann, Phys. Rev. Lett. 81 (1998) 2292], based on the total energy pseudopotential calculations. By calculating PED patterns from different emitters in these two models, we show that the surface structure induced features are visible even in total emission diffraction patterns. For the overall diffractogram a scatterer properties of the first layer under the surface become crucial due to the backscattering at low kinetic energies. This layer is Si-layer in the MRAD model, but C-layer in the AUDD model. While this causes clear differences between the diffraction patterns of the AUDD and the MRAD models, it is shown to diminish the differences between the PED patterns of the AUDD and the other models which consist of only one monolayer of Si on top.
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- Stoltz, Dunja, et al.
(författare)
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Tunneling evidence for spatial location of the charge-density-wave induced band splitting in 1T-TaSe2
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:7, s. 073410-
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Tidskriftsartikel (refereegranskat)abstract
- We present the atomically resolved room temperature scanning-tunneling microscopy study of bias dependent images of charge density waves (CDWs) in 1T-TaSe2. With the help of angle-resolved photoemission of the CDW-split Ta d(z)(2) band in 1T-TaSe2, we determine the electronic location of Ta d(z)(2) subbands on inequivalent atoms of the reconstructed Ta plane. We thus demonstrate the atomic origin of the CDW-formation related effects observed in the band structure of this material.
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- Javed, M. Tariq, 1983-, et al.
(författare)
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Changes in pH and organic acids in mucilage of Eriophorum angustifolium roots after exposure to elevated concentrations of toxic elements
- 2012
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Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 20:3, s. 1876-1880
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Tidskriftsartikel (refereegranskat)abstract
- The presence of Eriophorum angustifolium in mine tailings of pyrite maintains a neutral pH, despite weathering, thus lowering the release of toxic elements into acid mine drainage water. We investigated if the presence of slightly elevated levels of free toxic elements triggers the plant rhizosphere to change the pH towards neutral by increasing organic acid content. Plants were treated with a combination of As, Pb, Cu, Cd and Zn at different concentrations in nutrient medium and in soil in a rhizobox-like system for 48-120 hrs. The pH and organic acids were detected in the mucilage dissolved from root surface, reflecting the rhizosphere solution. Also the pH of root-cell apoplasm was investigated. Both apoplasmic and mucilage pH increased and the concentrations of organic acids enhanced in the mucilage with slightly elevated levels of toxic elements. When organic acid concentration was high, also the pH was high. Thus, efflux of organic acids from the roots of E. angustifolium may induce rhizosphere basification.
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- Zamir, Itay, et al.
(författare)
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Postnatal nutritional intakes and hyperglycemia as determinants of blood pressure at 6.5 years of age in children born extremely preterm
- 2019
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Ingår i: Pediatric Research. - : Nature Publishing Group. - 0031-3998 .- 1530-0447. ; 86:1, s. 115-121
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Tidskriftsartikel (refereegranskat)abstract
- Background: Adverse developmental programming by early-life exposures might account for higher blood pressure (BP) in children born extremely preterm. We assessed associations between nutrition, growth and hyperglycemia early in infancy, and BP at 6.5 years of age in children born extremely preterm.Methods: Data regarding perinatal exposures including nutrition, growth and glycemia status were collected from the Extremely Preterm Infants in Sweden Study (EXPRESS), a population-based cohort including infants born <27 gestational weeks during 2004–2007. BP measurements were performed at 6.5 years of age in a sub-cohort of 171 children (35% of the surviving children).Results: Higher mean daily protein intake (+1 g/kg/day) during postnatal weeks 1–8 was associated with 0.40 (±0.18) SD higher diastolic BP. Higher mean daily carbohydrate intake (+1 g/kg/day) during the same period was associated with 0.18 (±0.05) and 0.14 (±0.04) SD higher systolic and diastolic BP, respectively. No associations were found between infant growth (weight, length) and later BP. Hyperglycemia and its duration during postnatal weeks 1–4 were associated primarily with higher diastolic BP z-scores.Conclusions: These findings emphasize the importance of modifiable early-life exposures, such as nutrition and hyperglycemia, in determining long-term outcomes in children born extremely preterm.
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