Spatially resolved physical and chemical properties of the planetary nebula NGC 3242

Optical integral-field spectroscopy was used to investigate the planetary nebula NGC 3242. We analysed the main morphological components of this source, including its knots, but not the halo. In addition to revealing the properties ofthe physical and chemical nature of this nebula, we also provided reliable spatially resolved constraints that can be used for future photoionisation modelling of the nebula. The latter is ultimately necessary to obtain a fully self-consistent 3D picture of the physical and chemical properties of the object. The observations were obtained with the VIMOS instrument attached to VLT-UT3. Maps and values for specific morphological zones for the detected emission-lines were obtained and analysed with routines developed by the authors to derive physical and chemical conditions of the ionised gas in a 2D fashion. We obtained spatially resolved maps and mean values of the electron densities, temperatures, and chemical abundances, for specific morphological structures in NGC 3242. These results show the pixel-to-pixel variations of the the small- and large-scale structures of the source. These diagnostic maps provide information free from the biases introduced by traditional single long-slit observations. In general, our results are consistent with a uniform abundance distribution for the object, whether we look at abundance maps or integrated fluxes from specified morphological structures. The results indicate that special care should be taken with the calibration of the data and that only data with extremely good signal-to-noise ratio and spectral coverage should be used to ensure the detection of possible spatial variations.Comment: 11 pages, 8 figures accepted for publication in Astronomy & Astrophysic

Integrability of the Minimal Strain Equations for the Lapse and Shift in 3+1 Numerical Relativity

Brady, Creighton and Thorne have argued that, in numerical relativity simulations of the inspiral of binary black holes, if one uses lapse and shift functions satisfying the ``minimal strain equations'' (MSE), then the coordinates might be kept co-rotating, the metric components would then evolve on the very slow inspiral timescale, and the computational demands would thus be far smaller than for more conventional slicing choices. In this paper, we derive simple, testable criteria for the MSE to be strongly elliptic, thereby guaranteeing the existence and uniqueness of the solution to the Dirichlet boundary value problem. We show that these criteria are satisfied in a test-bed metric for inspiraling binaries, and we argue that they should be satisfied quite generally for inspiraling binaries. If the local existence and uniqueness that we have proved holds globally, then, for appropriate boundary values, the solution of the MSE exhibited by Brady et. al. (which tracks the inspiral and keeps the metric evolving slowly) will be the unique solution and thus should be reproduced by (sufficiently accurate and stable) numerical integrations.Comment: 6 pages; RevTeX; submitted to Phys. Rev. D15. Technical issue of the uniqueness of the solution to the Dirichlet problem clarified. New subsection on the nature of the boundary dat

The deposition of Bi2Te3 and Sb2Te3 thermoelectric thin-films by thermal co-evaporation and applications in energy harvesting

First Published 2012Bismuth, antimony and tellurium compounds (Bi/Sb/Te) are known as the best thermoelectric materials for room temperature operation. Despite thermoelectric devices with these materials being used for many years in macro-scale dimensions (millimetres sized devices), only few attempts were done to reduce these devices to the micro-scale (micrometers sized devices). The deposition of thermoelectric films was reported before using techniques like electrochemical deposition (ECD), metal-organic chemical vapour deposition (MOCVD), pulsed laser deposition (PLD), sputtering and thermal evaporation [1-8]. Each technique has its vantages and disadvantages, and a summary can be found in the table 5.1. In this table, CVD and ECD present opposite characteristics: While CVD films present high figure of merit (ZT), but a low deposition rate and expensive and complicated equipment is required (specific gases are needed for the deposition), ECD is a simple process, allowing high deposition rates (tens of μm can be achieved) but resultant films present low ZT. However, ECD allows the creation of structures during the deposition process, using the LIGA process (from German “Lithographie, Galvanoformung, Abformung”, meaning Lithography, Electroplating and Molding). In this chapter, the deposition of Bi2Te3 and Sb2Te3 thin films by thermal co-evaporation is described.FCT/PTDC/EEA-ENE/66855/200

Microssistema termoeléctrico baseado em teluretos de bismuto e antimónio

Tese de Doutoramento em Electrónica Industrial - Área de Conhecimento de Electrónica e InstrumentaçãoEste trabalho apresenta o fabrico e caracterização do primeiro microdispositivo planar para arrefecimento por efeito Peltier, em substrato flexível. O dispositivo foi fabricado em poliimida Kapton, com 25 µm de espessura, utilizando filmes termoeléctricos de Bi2Te3 e Sb2Te3, depositados por co-evaporação térmica de bismuto e telúrio ou antimónio e telúrio, respectivamente. A área fria do dispositivo (4 mm2) é arrefecida com quatro pares de junções termoeléctricas, ligadas em série através de contactos de alumínio/níquel. O Kapton foi seleccionado para o substrato, pela sua baixa condutividade térmica (0.15 Wm−1K−1), permitindo maior desempenho do dispositivo. Este substrato proporciona também propriedades mecânicas inovadoras e permite a integração com vários tipos de dispositivos electrónicos. As técnicas de análise EDX, XRD e FTIR confirmam a formação de filmes finos de Bi2Te3 e Sb2Te3. Foram obtidos valores absolutos do coeficiente de Seebeck entre 150 e 250 µVK־1 e resistividade entre 7 e 15 µΩm. Mais de 100 filmes foram fabricados, de forma a correlacionar os parâmetros de deposição e as propriedades electrónicas. Os parâmetros óptimos de fabrico permitiram obter a figura de mérito ZT = 0.85 e ZT = 0.3 em filmes de Bi2Te3 e Sb2Te3, respectivamente. Estes valores são melhores que os obtidos na literatura, para os mesmos materiais, depositados por co-evaporação térmica, sputtering, evaporação flash ou electrodeposição e equivalentes aos obtidos por MOCVD. Os filmes termoeléctricos foram gravados por fotolitografia e corrosão química em solução aquosa de HNO3/HCl e por máscara de sombra. A influência da composição e concentração da solução na gravação é apresentada, e optimizada para obter elevadas taxas de gravação, sem danificar os filmes. Com estas técnicas foram fabricados e caracterizados dispositivos de arrefecimento por efeito Peltier e termopilhas sensores de radiação IV. O dispositivo de arrefecimento Peltier foi analisado por microscopia de infravermelhos, ao ar e em vácuo, e uma diferença de temperatura de 5 ºC foi obtida entre a região fria e a região quente do dispositivo. A sensibilidade de 6.5×10-14 VK-4 foi obtida na termopilha do sensor de radiação IV.The present work reports on the fabrication and characterization of the first planar Peltier microcooler on a flexible substrate. The microcooler was fabricated on flexible Kapton polyimide substrate, 25 µm in thickness, using Bi2Te3 and Sb2Te3 thermoelectric films deposited by thermal co-evaporation of bismuth and tellurium or antimony and tellurium, respectively. The cold area of the device (4 mm2) is cooled using four pairs of thermoelectric junctions, connected in series with aluminum/nickel contacts. Kapton was chosen as substrate because of its low thermal conductivity (0.15 Wm−1K−1), thus allowing for higher performance of cooler devices. Flexible substrate adds uncommon mechanical properties to the composite film-substrate and enables their integration with many novel types of electronic devices. Energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the formation of Bi2Te3 and Sb2Te3 thin-films. Absolute value of Seebeck coefficient in the range 150-250 µVK-1 and in-plane electrical resistivity of 7- 15 µΩm were measured. More than 100 films were deposited to correlate growing deposition parameters and film electronic properties. Optimal parameters allowed the fabrication of films with figure of merit ZT = 0.85 and ZT = 0.3 for Bi2Te3 and Sb2Te3, respectively. These values are better then the best published results for the same material, under various fabrication methods (thermal co-evaporation, sputtering, flash-evaporation, or electrodeposition) and as good as values of films deposited by MOCVD. The thermoelectric films were patterned by photolithography and wet-etching techniques, using HNO3/HCl-based etchants and by shadow mask technique. Influence of composition and concentration of etchants in the process was optimized to achieve high deposition rates without damage the thin-films. Microcoolers and thermopile infrared sensors were fabricated and tested using these techniques. The performance of Peltier microcooler was analyzed by infrared image microscopy, on still-air and under vacuum conditions, and the 5 ºC temperature difference was obtained between the cold side and the hot side of the device. The IR thermopile sensor was tested in pirometry applications and a sensibility of 6.5×10-14 VK-4 was measured

No-horizon theorem for spacetimes with spacelike G1 isometry groups

We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike $G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on ${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent horizons. Given any (3+1) spacetime with spacelike translational isometry, the no-horizon condition can be readily tested without the need for dimensional reduction. This provides thus a useful and encompassing apparent horizon test for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence towards the validity of the hoop conjecture, and signals possible violations of strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra

Erratum: Martins, M.S., et al. Wideband and wIde beam polyvinylidene difluoride (PVDF) acoustic transducer for broadband underwater. Sensors 2019, 19, 3991

The authors wish to make the following erratum to this paper [...].info:eu-repo/semantics/publishedVersio