| 1. |
- Buder, Sven, et al.
(författare)
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The GALAH Survey : second data release
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 478:4, s. 4513-4552
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Tidskriftsartikel (refereegranskat)abstract
- The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way, designed to deliver complementary chemical information to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342 682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction, and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multistep approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T-eff, log g, [Fe/H], [X/Fe], v(mic), vsin i, AKS) for a representative training set of stars. This information is then propagated to the whole sample with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D MARCS stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.
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| 2. |
- Gao, Xudong, et al.
(författare)
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The GALAH survey : verifying abundance trends in the open cluster M67 using non-LTE modelling
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 481:2, s. 2666-2684
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Tidskriftsartikel (refereegranskat)abstract
- Open cluster members are coeval and share the same initial bulk chemical composition. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, and Fe) in 66 stars belonging to the open cluster m67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and non-local thermodynamic equilibrium (non-LTE) radiative transfer. From the non-LTE analysis, we find a typical star-to-star scatter in the abundance ratios of around O.05 dex. We find trends in the abundance ratios with effective temperature, indicating systematic differences in the surface abundances between turn-off and giant stars; these trends are more pronounced when LTE is assumed. However, trends with effective temperature remain significant for Al and Si also in non-LTE. Finally, we compare the derived abundances with prediction from stellar evolution models including effects of atomic diffusion. We find overall good agreement for the abundance patterns of dwarfs and sub-giant stars, but the abundances of cool giants are lower relative to less evolved stars than predicted by the diffusion models, in particular for Mg.
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| 3. |
- Gao, Xudong, et al.
(författare)
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The GALAH survey : a new constraint on cosmological lithium and Galactic lithium evolution from warm dwarf stars
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 497:1, s. L30-L34
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Tidskriftsartikel (refereegranskat)abstract
- Lithium depletion and enrichment in the cosmos is not yet well understood. To help tighten constraints on stellar and Galactic evolution models, we present the largest high-resolution analysis of Li abundances A(Li) to date, with results for over 100000 GALAH (Galactic Archeology with HERMES) field stars spanning effective temperatures 5900K≲Teff≲7000K and metallicities −3 ≲ [Fe/H] ≲ +0.5. We separated these stars into two groups, on the warm and cool sides of the so-called Li dip, a localized region of the Kiel diagram wherein lithium is severely depleted. We discovered that stars in these two groups show similar trends in the A(Li)–[Fe/H] plane, but with a roughly constant offset in A(Li) of 0.4dex, the warm group having higher Li abundances. At [Fe/H]≳−0.5, a significant increase in Li abundance with increasing metallicity is evident in both groups, signalling the onset of significant Galactic production. At lower metallicity, stars in the cool group sit on the Spite plateau, showing a reduced lithium of around 0.4dex relative to the primordial value predicted from big bang nucleosynthesis (BBN). However, stars in the warm group between [Fe/H] = −1.0 and −0.5 form an elevated plateau that is largely consistent with the BBN prediction. This may indicate that these stars in fact preserve the primordial Li produced in the early Universe.
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| 4. |
- Vaidya, Kirit, et al.
(författare)
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Capabilities and Competitiveness of Chinese State Owned Manufacturing Enterprises: What Has Been Learned Over 20 years and What Remains to be Learned
- 2012
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Ingår i: Singh J, Harrington T, Kumar M and Shi Y (Eds) “Capturing Value in International Manufacturing and Supply Networks: New Models for a Changing World”, Proceedings of 16th Cambridge International Manufacturing Symposium, IfM, Cambridge, UK.. - 9781902546308 ; , s. CIM2012_23-
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Konferensbidrag (refereegranskat)abstract
- Technological capabilities in Chinese manufacturing have been transformed in the last three decades. However, the extent to which and how domestic market oriented state owned enterprises (SOEs) have developed their capabilities remain important questions. The East Asian latecomermodel has been adapted to study six Chinese SOEs in the automotive, steel and machine tools sectors to assess capability levels attained and the role of external sources and internal efforts in developing them. All six enterprises demonstrate high competence in operating established technology, managing investment and making product and process improvements but differ in innovative capability. While the East Asian latecomer model in which linking, leveraging and learning explain technological capability development is relevant for the companies studied, it needs to be adapted for Chinese SOEs to take account of types of external links and leverage ofenterprises, the role of government, enterprise level management motives and means of financing development
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| 5. |
- Vaidya, Kirit, et al.
(författare)
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International Technology Transfer and Development of Capabilities in Chinese State-Owned Manufacturing Enterprises: Lessons from 20 Years of Case Research
- 2012
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Ingår i: Baines T S, Clegg B T and Harrison D K (Eds) “Advances in Manufacturing Technology”, Proceedings of the Tenth International Conference on Manufacturing Research), Aston Business School / COMEH, Birmingham, UK. - 9781905866601 ; , s. 656-661
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Konferensbidrag (refereegranskat)abstract
- Technological capabilities in Chinese manufacturing have been transformed in the last three decades.However, the extent to which domestic market oriented state owned enterprises (SOEs) have developedtheir capabilities is not clear. Six SOEs in the automotive, steel and machine tools sectors in Beijing andTianjin have been studied since the mid-1990s to assess the capability levels attained and the role ofexternal sources and internal efforts in developing them. Aided by government policies, acquisition oftechnology and their own efforts, the case study companies appear to be broadly following the East Asianlate industrialisation model. All six enterprises demonstrate competences in operating establishedtechnology, managing investment and making product and process improvements. The evidence suggeststhat companies without foreign joint venture (JV) collaborations have made more progress in this respect
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| 6. |
- Wang, Jianpu, et al.
(författare)
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Entirely solution-processed write-once-read-many-times memory devices and their operation mechanism
- 2011
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 12:7, s. 1271-1274
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mechanism of operation of low-power write-once-read-many-times (WORM) memory devices based on injection of electrons from ZnO into PEDOT:PSS (polydioxythiophene doped with polystyrenesulfonic acid). Using Raman spectroscopy and in situ absorbance measurements, we directly observe the change of doping level of PEDOT during the device switching. Our results clearly show that the change of device conductance is due to the dedoping of p-doped PEDOT by injected electrons. Based on this understanding, we further demonstrate an entirely solution-processed low-power WORM device by inkjet printing metal electrodes onto arbitrary substrates. (C) 2011 Elsevier B.V. All rights reserved.
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| 7. |
- Zhu, Xudong, et al.
(författare)
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A distributed approximation for multi-hop clustering problem in wireless sensor networks
- 2016
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Ingår i: 2015 IEEE Global Communications Conference (GLOBECOM). - Piscataway, NJ : IEEE Communications Society. - 9781479959525
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Konferensbidrag (refereegranskat)abstract
- In wireless sensor networks (WSNs), there is no predefined infrastructure. Nodes need to frequently flood messages to discover routes, which badly decreases the network performance. To overcome such drawbacks, WSNs are often grouped into several disjointed clusters, each with a representative cluster head (CH) in charge of the routing process. In order to further improve the efficiency of WSNs, it is crucial to find a cluster partition with minimum number of clusters and the distance between each node to its corresponding CH can be bounded by a constant number of hops. Finding such a partition is defined as minimum d-hop cluster head set (d-MCHS) problem, which is proved to be NP-hard. In this paper, we propose a distributed approximation algorithm, named d^2-Cluster, to address d-MCHS problem and prove that the approximation ratio of d^2-Cluster under unit disk graph (UDG) is a constant factor \lambda which is related to d. To the best of our knowledge, it is the first constant approximation ratio for d-MDS problem in UDG
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