83 research outputs found
Bayesian analysis of ages, masses, and distances to cool stars with non-LTE spectroscopic parameters
For studies of Galactic evolution, the accurate characterization of stars in
terms of their evolutionary stage and population membership is of fundamental
importance. A standard approach relies on extracting this information from
stellar evolution models but requires the effective temperature, surface
gravity, and metallicity of a star obtained by independent means. In previous
work, we determined accurate effective temperatures and non-LTE logg and [Fe/H]
(NLTE-Opt) for a large sample of metal-poor stars, -3<[Fe/H]<-0.5, selected
from the RAVE survey. As a continuation of that work, we derive here their
masses, ages, and distances using a Bayesian scheme and GARSTEC stellar tracks.
For comparison, we also use stellar parameters determined from the widely-used
1D LTE excitation-ionization balance of Fe (LTE-Fe). We find that the latter
leads to systematically underestimated stellar ages, by 10-30%, but
overestimated masses and distances. Metal-poor giants suffer from the largest
fractional distance biases of 70%. Furthermore, we compare our results with
those released by the RAVE collaboration for the stars in common (DR3, Zwitter
et al. 2010, Seibert et al. 2011). This reveals -400 to +400 K offsets in
effective temperature, -0.5 to 1.0 dex offsets in surface gravity, and 10 to
70% in distances. The systematic trends strongly resemble the correlation we
find between the NLTE-Opt and LTE-Fe parameters, indicating that the RAVE DR3
data may be affected by the physical limitations of the 1D LTE synthetic
spectra. Our results bear on any study, where spectrophotometric distances
underlie stellar kinematics. In particular, they shed new light on the debated
controversy about the Galactic halo origin raised by the SDSS/SEGUE
observations.Comment: 13 pages and 15 figures. Accepted for publication in MNRA
First evidence of multiple populations along the AGB from Str\"omgren photometry
Spectroscopic studies have demonstrated that nearly all Galactic globular
clusters (GCs) harbour multiple stellar populations with different chemical
compositions. Moreover, colour-magnitude diagrams based exclusively on
Str\"omgrem photometry have allowed us to identify and characterise multiple
populations along the RGB of a large number of clusters. In this paper we show
for the first time that Str\"omgren photometry is also very effcient at
identifying multiple populations along the AGB, and demonstrate that the AGB of
M3, M92, NGC362, NGC1851, and NGC6752 are not consistent with a single stellar
population. We also provide a catalogue of RGB and AGB stars photometrically
identified in these clusters for further spectroscopic follow-up studies.We
combined photometry and elemental abundances from the literature for RGB and
AGB stars in NGC6752 where the presence of multiple populations along the AGB
has been widely debated. We find that, while the MS, SGB, and RGB host three
stellar populations with different helium and light element abundances, only
two populations of AGB stars are present in the cluster. These results are
consistent with standard evolutionary theory.Comment: 9 pages, 3 figures, 1 table in the main article, 3 tables in the
appendix of which 2 tables containing coordinates and photometry of
photometrically identified RGB and AGB star
Porous silicon solar cells
We developed a new process for the fabrication of crystalline solar cell, based on an ultrathin silicon membrane, taking advantage of porous silicon technology. The suggested architecture allows the costs reduction of silicon based solar cell reusing the same wafer to produce a great number of membranes. The architectures combines the efficiency of crystalline silicon solar cell, with the great absorption of porous silicon, and with a more efficient way to use the material. The new process faces the main challenge to achieve an effective and not expensive passivation of the porous silicon surface, in order to achieve an efficient photovoltaic device. At the same time the process suggests a smart way to selective doping of the macroporous silicon layers despite the through-going pores. © 2015 IEEE.
SciVal Topic Prominence
Topic: Porous silicon | Silicon | macroporous silicon
Prominence percentile: 66.984
Author keywords
nanofabricationporous siliconsilicon nanoelectronicssolar cells
Indexed keywords
Engineering controlled terms:
Crystalline materialsNanoelectronicsNanostructured materialsNanotechnologyPorous siliconSiliconSilicon wafersSolar cells
Engineering uncontrolled terms
Crystalline silicon solar cellsCrystalline solar cellsMacro porous siliconPhotovoltaic devicesPorous silicon surfacesPorous silicon technologySilicon nanoelectronicsUltrathin silicon membrane
Engineering main heading:
Silicon solar cells
ISBN: 978-146738155-0
Source Type: Conference Proceeding
Original language: English
DOI: 10.1109/NANO.2015.7388710
Document Type: Conference Paper
Sponsors: Nanotechnology Council
Publisher: Institute of Electrical and Electronics Engineers Inc.
References (9)
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(2012) International Technology Roadmap for Photovoltaics Results 2012. Cited 24 times.
ITRPV, Third Edition, Berlin 2012
www.ITRPV.net
2
Lehmann, V., Honlein, W., Stengl, R., Willer, J., Wendt, H.
(1992) Verfahren Zur Herstellung Einer Solarzelle Aus Einer Substratscheibe. Cited 6 times.
German patent DE4204455C1; Filing date: 29. 01.
3
Brendel, R., Ernst, M.
Macroporous Si as an absorber for thin-film solar cells
(2010) Physica Status Solidi - Rapid Research Letters, 4 (1-2), pp. 40-42. Cited 22 times.
http://www3.interscience.wiley.com/cgi-bin/fulltext/123215552/PDFSTART
doi: 10.1002/pssr.200903372
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4
Ernst, M., Brendel, R., Ferré, R., Harder, N.-P.
Thin macroporous silicon heterojunction solar cells
(2012) Physica Status Solidi - Rapid Research Letters, 6 (5), pp. 187-189. Cited 16 times.
doi: 10.1002/pssr.201206113
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5
Ernst, M., Brendel, R.
Macroporous silicon solar cells with an epitaxial emitter
(2013) IEEE Journal of Photovoltaics, 3 (2), art. no. 6472253, pp. 723-729. Cited 7 times.
doi: 10.1109/JPHOTOV.2013.2247094
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6
Ernst, M., Schulte-Huxel, H., Niepelt, R., Kajari-Schröder, S., Brendel, R.
Thin crystalline macroporous silicon solar cells with ion implanted emitter (Open Access)
(2013) Energy Procedia, 38, pp. 910-918. Cited 2 times.
http://www.sciencedirect.com/science/journal/18766102
doi: 10.1016/j.egypro.2013.07.364
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7
Nenzi, P., Kholostov, K., Crescenzi, R., Bondarenka, H., Bondarenko, V., Balucani, M.
Electrochemically etched TSV for porous silicon interposer technologies
(2013) Proceedings - Electronic Components and Technology Conference, art. no. 6575887, pp. 2201-2207. Cited 2 times.
ISBN: 978-147990233-0
doi: 10.1109/ECTC.2013.6575887
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8
Perticaroli, S., Varlamava, V., Palma, F.
Microwave sensing of nanostructured semiconductor surfaces
(2014) Applied Physics Letters, 104 (1), art. no. 013110. Cited 3 times.
doi: 10.1063/1.4861424
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9
De Cesare, G., Caputo, D., Tucci, M.
Electrical properties of ITO/crystalline-silicon contact at different deposition temperatures
(2012) IEEE Electron Device Letters, 33 (3), art. no. 6142006, pp. 327-329. Cited 28 times.
doi: 10.1109/LED.2011.2180356
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Thin crystalline macroporous silicon solar cells with ion implanted emitter
Ernst, M. , Schulte-Huxel, H. , Niepelt, R.
(2013) Energy Procedia
Multilayer etching for kerf-free solar cells from macroporous silicon
Schäfer, S. , Ernst, M. , Kajari-Schröder, S.
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RELX Group
We developed a new process for the fabrication of crystalline solar cell, based on an ultrathin silicon membrane, taking advantage of porous silicon technology. The suggested architecture allows the costs reduction of silicon based solar cell reusing the same wafer to produce a great number of membranes. The architectures combines the efficiency of crystalline silicon solar cell, with the great absorption of porous silicon, and with a more efficient way to use the material. The new process faces the main challenge to achieve an effective and not expensive passivation of the porous silicon surface, in order to achieve an efficient photovoltaic device. At the same time the process suggests a smart way to selective doping of the macroporous silicon layers despite the through-going pores
Laser Treatment to form An Effective Base Contact in a - Si:H/c-Si Heterojunction Solar Cells☆
Abstract In this paper we investigate the p-type a-Si:H/ia-Si:H/p-type c-Si structure, commonly used as base contact in amorphous/crystalline silicon heterojunction solar cell when fabricated on p-type c-Si wafer. Even though the most effective amorphous silicon/crystalline silicon heterostructure is based on n-type c-Si due to higher bulk lifetime, the p-type c-Si still remains the most common and cheaper substrate for silicon based solar cell. In particular we study the effect of localized 532 nm pulsed laser treatment at different laser conditions in order to reduce the cell series resistance due to the base contact. In this approach the p-type a-Si:H layer is used as a source of boron dopant. Depending on the thickness of the p-type a-Si:H film, when the laser beam is focused on p-type a-Si:H layer the boron can be transferred into the c-Si base to form an overdoped region and then an effective local Back Surface Field, able to enhance the hole collection at the metal of the base electrode in the p-type c-Si based heterojunction solar cell. The application of a thin Aluminum layer on top of the amorphous silicon to be treated by laser is also concerned. Series resistance of a transverse structure composed by the laser treated p-type a-Si:H/c-Si/opposite surface contacted by InGa is considered to optimize the laser procedure. Values as low as 0.5 Ωcm 2 are obtained when the aluminum layer is adopted
unveiling systematic biases in the 1d lte excitation-ionization balance of fe for fgk stars: A novel approach to determination of stellar parameters
We present a comprehensive analysis of different techniques available for the spectroscopic analysis of FGK stars and provide a recommended methodology which efficiently estimates accurate stellar atmospheric parameters for large samples of stars. Our analysis includes a simultaneous equivalent width analysis of Fe I and Fe II spectral lines, and for the first time, utilizes on-the-fly non-local thermodynamic equilibrium (NLTE) corrections of individual Fe I lines. We further investigate several temperature scales, finding that estimates from Balmer line measurements provide the most accurate effective temperatures at all metallicities. We apply our analysis to a large sample of both dwarf and giant stars selected from the Radial Velocity Experiment (RAVE) survey. We then show that the difference between parameters determined by our method and that by the standard 1D LTE excitation-ionization balance of Fe reveals substantial systematic biases: up to 400 K in effective temperature, 1.0 dex in surface gravity and 0.4 dex in metallicity for stars with [Fe/H] -2.5. This has large implications for the study of the stellar populations in the Milky Wa
Hydrogen Plasma and Thermal Annealing Treatments on a-Si:H Thin Film for c-Si Surface Passivation☆
Abstract High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high V oc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si-H 2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H 2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H + ions accumulated during the plasma exposure, leading to a more stable configuration
Hydrogen plasma and thermal annealing treatments on a-Si:H thin film for c-Si surface passivation
High efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high Voc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si-H2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H+ ions accumulated during the plasma exposure, leading to a more stable configuration
Discovery of Extended Main Sequence Turnoffs in Galactic Open Clusters
The color-magnitude diagrams (CMDs) of Galactic open clusters are widely considered to be the prototypes of single stellar populations. By using photometry in ultraviolet and optical bands we discovered that the nearby young cluster NGC 6705 (M11) exhibits an extended main-sequence turnoff (eMSTO) and a broadened main sequence (MS). This is the first evidence of multiple stellar populations in a Galactic open cluster. By using high-resolution Very Large Telescope (VLT) spectra we provide direct evidence that the multiple sequences along the CMD correspond to stellar populations with different rotation rates. Specifically, the blue MS (bMS) is formed of slow-rotating stars, while red-MS (rMS) stars are fast rotators. Moreover, we exploit photometry from Gaia data release 2 (DR2) to show that three Galactic open clusters, namely NGC 2099, NGC 2360, and NGC 2818, exhibit the eMSTO, thus suggesting that it is a common feature among these objects. Our previous work on the Large Magellanic Cloud star cluster NGC 1818 shows that slowly and rapidly rotating stars populate the bMS and rMS observed in its CMD. The similarities between M11 and the young clusters of the Magellanic Clouds (MCs) suggest that rotation is responsible for the appearance of multiple populations in the CMDs of both Milky Way open clusters and MCs young clusters.A.F.M.
and L.C. acknowledge support by the Australian Research
Council through Discovery Early Career Researcher Award
DE160100851 and the Future Fellowship FT160100402.
A.P.M. has been supported by the European Research Council
through the Starting Grant “GALFOR” (716082) and the FAREMIUR project R164RM93XW “SEMPLICE”. A.S., L.B.N., and
F.V. are partially supported by the MINECO (Spanish Ministry of
Economy) through grants ESP2017-82674-R and ESP2016-
80079-C2-1-R (MINECO/FEDER, UE), SGR-1131 (Generalitat
Catalunya), and MDM-2014-0369 of ICCUB (Unidad de
Excelencia “María de Maeztu”)
The role of stress echocardiography in transcatheter aortic valve implantation and transcatheter edge-to-edge repair era: A systematic review
Objectives: In the last decade, percutaneous treatment of valve disease has changed the approach toward the treatment of aortic stenosis (AS) and mitral regurgitation (MR). The clinical usefulness of stress echocardiography (SE) in the candidates for transcatheter aortic valve implantation (TAVI) and transcatheter edge-to-edge repair (TEER) of MR remains to be established. Therefore, the key aim of this review is to assess the main applications of SE in patients undergoing TAVI or TEER. Methods: We searched for relevant studies to be included in the systematic review on PubMed (Medline), Cochrane library, Google Scholar, and Biomed Central databases. The literature search was conducted in February 2022. The inclusion criteria of the studies were: observational and clinical trials or meta-analysis involving patients with AS or MR evaluated with SE (excluding those in which SE was used only for screening of pseudo-severe stenosis) and treated with percutaneous procedures. Results: Thirteen studies published between 2013 and 2021 were included in the review: five regarding candidates for TEER and eight for TAVI. In TEER candidates, seeing an increase in MR grade, and stroke volume of > 40% during SE performed before treatment was, respectively, related to clinical benefits (p = 0.008) and an increased quality of life. Moreover, overall, 25% of patients with moderate secondary MR at rest before TEER had the worsening of MR during SE. At the same time, in SE performed after TEER, an increase in mean transvalvular diastolic gradient and in systolic pulmonary pressure is expected, but without sign and symptoms of heart failure. Regarding TAVI, several studies showed that contractile reserve (CR) is not predictive of post-TAVI ejection fraction recovery and mortality in low-flow low-gradient AS either at 30 days or at long-term. Conclusion: This systematic review shows in TEER candidates, SE has proved useful in the optimization of patient selection and treatment response, while its role in TAVI candidates is less defined. Therefore, larger trials are needed to test and confirm the utility of SE in candidates for percutaneous procedures of valve diseases
First evidence of multiple populations along the AGB from Strömgren photometry
Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams based exclusively on Strömgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Strömgren photometry is also very efficient at identifying multiple populations along the AGB, and demonstrate that the AGB of M 3, M 92, NGC 362, NGC 1851, and NGC 6752 are not consistent with a single stellar population. We also provide a catalogue of RGB and AGB stars photometrically identified in these clusters for further spectroscopic follow-up studies. We combined photometry and elemental abundances from the literature for RGB and AGB stars in NGC 6752 where the presence of multiple populations along the AGB has been widely debated. We find that, while the MS, SGB, and RGB host three stellar populations with different helium and light element abundances, only two populations of AGB stars are present in the cluster. These results are consistent with standard evolutionary theory.P.G. acknowledges support from grant No. 2011- 5042 from the Swedish Research Council. S.F acknowledge the grant The New Milky Way from the Knut and Alice Wallenberg Foundation. P.G. and S.F. acknowledges support from the Swedish National Space Board. AS acknowledges support from MINECO (ESP2015-66134-R) and Generalitat de Catalunya (SGR2014-1458). L.C gratefully acknowledge support from the Australian Research Council (grants DP150100250, FT160100402). A. P. M. acknowledges support by the Australian Research Council through Discovery Early Career Researcher Award DE150101816
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