| 101871. |
- Seibert, Philipp, et al.
(författare)
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Runner cone separation in Kaplan turbines
- 2011
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Ingår i: 4-th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems. - Belgrade : IAHR. - 9788670837409 ; , s. 265-271
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Konferensbidrag (refereegranskat)abstract
- Low head machines of the Kaplan type are composed of several components to ensure high efficiency. Downstream the runner, a draft tube ensures pressure recovery of the flow leaving the runner. Modern draft tubes are mainly composed of a conical diffuser followed by an elbow and a straight diffuser. The runner cone, attached to the runner, is included in the conical diffuser and thus counter-acts the function of the draft tube since adding angular momentum to the fluid. Variation of the runner cone angular velocity may increase draft tube pressure recovery by delaying eventual separation. While previous research focused only on the draft tube flow, this work presents calculations including runner and draft tube in order to point out possible joint effects. The initial calculations with ω*=1 are validated by comparison of mean and angular resolved axial and tangential velocity with LDA measurements. Two runner cone angular velocities are simulated: ω*=-1 (counter-rotating) and ω*=0 (stationary). A significant efficiency increase is obtained for a stationary runner cone.
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| 101872. |
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| 101873. |
- Seidel, David, et al.
(författare)
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Measurement of stressful postures during daily activities : An observational study with older people
- 2011
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Ingår i: Gait & Posture. - : Elsevier. - 0966-6362 .- 1879-2219. ; 34:3, s. 397-401
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Tidskriftsartikel (refereegranskat)abstract
- This study measured the postures of older people during cooking and laundry. A sample of men and women aged 75+ years (n=27) was recruited and observed in a home-like environment. Postures were recorded with a measurement system in an objective and detailed manner. The participants were videotaped to be able to see where 'critical' postures occurred, as defined by a trunk inclination of ≥60°. Analysis of data was facilitated by specially developed software. Critical postures accounted for 3% of cooking and 10% of laundry, occurring primarily during retrieving from and putting in lower cabinets, the refrigerator, laundry basket or washing machine as well as disposing into the waste bin. These tasks involve a great variation in postural changes and pose a particular risk to older people. The results suggest that the use of stressful postures may decrease efficiency and increase fatigue, eventually leading to difficulties with daily activities. The specific tasks identified during which critical postures occurred should be targeted by designers in order to improve the activities. A few examples are given of how better design can reduce or eliminate some of the postural constraints.
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| 101874. |
- Seidel, Sascha, et al.
(författare)
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A hypoxic niche regulates glioblastoma stem cells through hypoxia inducible factor 2 alpha
- 2010
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Ingår i: Brain. - : Oxford University Press (OUP). - 0006-8950 .- 1460-2156. ; 133, s. 983-995
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Tidskriftsartikel (refereegranskat)abstract
- Glioma growth and progression depend on a specialized subpopulation of tumour cells, termed tumour stem cells. Thus, tumour stem cells represent a critical therapeutic target, but the molecular mechanisms that regulate them are poorly understood. Hypoxia plays a key role in tumour progression and in this study we provide evidence that the hypoxic tumour microenvironment also controls tumour stem cells. We define a detailed molecular signature of tumour stem cell genes, which are overexpressed by tumour cells in vascular and perinecrotic/hypoxic niches. Mechanistically, we show that hypoxia plays a key role in the regulation of the tumour stem cell phenotype through hypoxia-inducible factor 2 alpha and subsequent induction of specific tumour stem cell signature genes, including mastermind-like protein 3 (Notch pathway), nuclear factor of activated T cells 2 (calcineurin pathway) and aspartate beta-hydroxylase domain-containing protein 2. Notably, a number of these genes belong to pathways regulating the stem cell phenotype. Consistently, tumour stem cell signature genes are overexpressed in newly formed gliomas and are associated with worse clinical prognosis. We propose that tumour stem cells are maintained within a hypoxic niche, providing a functional link between the well-established role of hypoxia in stem cell and tumour biology. The identification of molecular regulators of tumour stem cells in the hypoxic niche points to specific signalling mechanisms that may be used to target the glioblastoma stem cell population.
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| 101875. |
- Seidel, Y.E., et al.
(författare)
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Oscillatory behaviour in Galvanostatic Formaldehyde Oxidation on Nanostructured Pt/Glassy Carbon Model Electrodes
- 2010
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 11:7, s. 1405-1415
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Tidskriftsartikel (refereegranskat)abstract
- The electrocatalytic oxidation of formaldehyde, which results in CO, and HCOOH formation, was investigated under galvanostatic conditions on nanostructured Pt/glassy carbon (GC) electrodes fabricated by employing colloidal lithography (CL). The measurements were performed on structurally well-defined model electrodes of different Pt surface coverages under different applied currents (current densities) and at constant electrolyte transport in a thin-layer flow cell connected to a differential electrochemical mass spectrometry (DEMS) setup to monitor the dynamic response of the reaction selectivity under these conditions. Periodic oscillations of the electrode potential and the CO, formation rate appear not only for a continuous Pt film, but also for the nanostructured Pt/GC electrodes when a critical current density is exceeded. The critical current density for achieving regular osillation patterns increased with decreasing Pt nanodisk density. Lower oscillation frequencies of the electrode potential and lower CO2 formation rate for nanostructured Pt/GC electrodes compared to continuous Pt film at similar applied current densities suggest that transport processes play an essential role. Moreover, from the simple periodic response of the nanostructured electrodes it follows that all individual Pt disks in the array oscillate in synchrony. This result is discussed in terms of the different modes of spatial coupling present in the system: global coupling, migration coupling and mass transport of the essential chemical species, and the coverage of corresponding adsorbates.
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| 101876. |
- Seidel, Y.E., et al.
(författare)
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Transport effects in the electrooxidation of methanol studied on nanostructured Pt/glassy carbon electrodes
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:5, s. 3569-3578
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Tidskriftsartikel (refereegranskat)abstract
- Transport effects in the methanol oxidation reaction (MOR) were investigated using nanostructured Pt/glassy carbon (GC) electrodes and, for comparison, a polycrystalline Pt electrode. The nanostructured Pt/GC electrodes, consisting of a regular array of catalytically active cylindrical Pt nanostructures with 55 +/- 10 nm in diameter and different densities supported on a planar GC substrate, were fabricated employing hole-mask colloidal lithography (HCL). The MOR measurements were performed under controlled transport conditions in a thin-layer flow cell interfaced to a differential electrochemical mass spectrometry (DEMS) setup. The measurements reveal a distinct variation in the MOR activity and selectivity (product distribution) with Pt nanostructure density and with electrolyte rate, showing an increasing overall activity, reflected by a higher Faradaic reaction current, as well as a pronounced increase of the turnover frequency for CO(2) formation and of the CO(2) current efficiency with decreasing flow rate and increasing Pt coverage. These findings are discussed in terms of the "desorption-readorption-reaction" model introduced recently (Seidel et al. Faraday Discuss 2008, 140, 67). Finally, consequences for applications in direct methanol fuel cells are outlined.
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| 101877. |
- Seidl, Rupert, et al.
(författare)
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Modelling natural disturbances in forest ecosystems: a review
- 2011
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800. ; 222:4, s. 903-924
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Forskningsöversikt (refereegranskat)abstract
- Natural disturbances play a key role in ecosystem dynamics and are important factors for sustainable forest ecosystem management. Quantitative models are frequently employed to tackle the complexities associated with disturbance processes. Here we review the wide variety of approaches to modelling natural disturbances in forest ecosystems, addressing the full spectrum of disturbance modelling from single events to integrated disturbance regimes. We applied a general, process-based framework founded in disturbance ecology to analyze modelling approaches for drought, wind, forest fires, insect pests and ungulate browsing. Modelling approaches were reviewed by disturbance agent and mechanism, and a set of general disturbance modelling concepts was deduced. We found that although the number of disturbance modelling approaches emerging over the last 15 years has increased strongly, statistical concepts for descriptive modelling are still largely prevalent over mechanistic concepts for explanatory and predictive applications. Yet, considering the increasing importance of disturbances for forest dynamics and ecosystem stewardship under anthropogenic climate change, the latter concepts are crucial tool for understanding and coping with change in forest ecosystems. Current challenges for disturbance modelling in forest ecosystems are thus (i) to overcome remaining limits in process understanding, (ii) to further a mechanistic foundation in disturbance modelling, (iii) to integrate multiple disturbance processes in dynamic ecosystem models for decision support in forest management, and (iv) to bring together scaling capabilities across several levels of organization with a representation of system complexity that captures the emergent behaviour of disturbance regimes. (C) 2010 Elsevier B.V. All rights reserved.
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| 101878. |
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| 101879. |
- Seidlitz, M., et al.
(författare)
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Coulomb excitation of Mg-31
- 2011
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 700:3-4, s. 181-186
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Tidskriftsartikel (refereegranskat)abstract
- The ground state properties of Mg-31 indicate a change of nuclear shape at N = 19 with a deformed J(pi) = 1/2(+) intruder state as a ground state, implying that Mg-31 is part of the "island of inversion". The collective properties of excited states were the subject of a Coulomb excitation experiment at REX-ISOLDE, CERN, employing a radioactive Mg-31 beam. De-excitation gamma-rays were detected by the MINIBALL gamma-spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of Mg-3I was extended. Spin and parity assignment of the 945 keV state yielded 5/2(+) and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of Mg-30,Mg-31,Mg-32 establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration. (C) 2011 Elsevier B.V. All rights reserved.
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| 101880. |
- Seifarth, O., et al.
(författare)
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Graphene directly grown on SiO2-based insulators
- 2011
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Ingår i: IEEE - Semicond. Conf. Dresden: Technol., Des., Packag., Simul. Test, SCD - Int. Conf., Workshop Table-Top Exhibit.. - 9781457704291
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Konferensbidrag (refereegranskat)abstract
- Strong effort is devoted to grow graphene directly on insulators to create a technological step towards cost effective mass production of high-frequency transistors on Si. We have shown recently, that direct graphene growth can be achieved on silicate substrates by solid carbon source deposition. Here, we present a study on the growth of graphene on insulator by means of Raman and photoelectron spectroscopy, corroborated by density functional theory calculations. We address temperature dependence and the correlation between graphene quality and the number of layers. We show that this approach may open a pathway to Si-compatible graphene growth for electronic applications.
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