2,950 research outputs found
The Gaia-ASAS-SN classical cepheid sample. I. Sample selection
No full textWe present a well-defined and characterized all-sky sample of classical Cepheids in the Milky Way, obtained by combining two time-domain all-sky surveys: Gaia DR2 (Gaia Collaboration et al. 2018) and All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014). We first use parallax and variability information from Gaia to select ∼30,000 bright (G < 17) Cepheid candidates with MK < - 1. We then analyze their ASAS-SN V-band light curves, determining periods and classifying the light curves using their Fourier parameters. This results in ∼1900 likely Galactic Cepheids, which we estimate to be ≳90% complete and pure within our adopted selection criteria. This is the largest all-sky sample of Milky Way Cepheids that has such a well-characterized selection function, needed for population modeling and for systematic spectroscopic follow-up foreseen with Sloan Digital Sky Survey-V. About 130 of these potential Cepheids have not been documented in the literature even as possible candidates
Flow behaviour of dielectric liquids in an electric field
No full textA family of 10 silicone oils with electrical conductivity similar to 10(-13) S m(-1) (a regime hitherto systematically unexplored) and viscosities ranging from 1 to 2000mPas have been Subjected to an electrical field of up to 1.5kV mm(-1) during flow from a needle. The flow behaviour of these liquids is investigated experimentally in the flow rate regime 10(-8)-10(-12) m(3) s(-1) and we analyse the results using the Ohnesorge number. Due to the low electrical conductivity and high electrical relaxation time of the silicone oils, only unsteady transient jets were found. The onset of this type of jetting has been defined using current measurements and, in contrast to conducting liquids, the non-dimensional jet diameter increases with increase in Ohnesorge number. The time elapsed between the start and finish of jetting increases with increasing Ohnesorge number
Electrospray printing: Unravelling the history of a support free three-dimensional additive manufacturing technology
No full textIn this perspective article the author highlights a revolutionary technology, which makes reality, the ability to print true three-dimensional architectures, containing self-standing and self-supporting overhangs in the nano and micrometer scale, without the need for supports of any kind. There have been many attempts to achieve this feature in the rapid prototyping/additive manufacturing fields but has been met with little or no success. Current approaches to three-dimensional printing of self-standing and overhanging architectures have been achieved with the use of some form of supporting mould, secondary process or structure which could be either in the form of a viscous liquid or a solid structure to the coupling of lasers, temperature etc. Unfortunately, the use of such methodologies brings with them many issues and limitations, while destroying the concept of additive manufacturing. Note the author here defines additive manufacturing as a technology able to add materials when required during the fabrication of a 3D architecture without the need for external assistance or supports. These limitations in classical fabrication processes, restricts the use of advanced materials such as living biological cells to sensitive biomolecules to many others, for the forming of three-dimensional biological and non-biological architectures, whilst also increasing the costs and materials waste, which are required for acting as moulds, supports etc
Ordering of organic molecules on templated surfaces
No full textThis thesis describes the controlled growth of molecular nanostructures using modified metallic and semiconductor surfaces. The Ag/Si(lll)-(root3 x root3),the Sn/Cu(100) surface alloy system and the Bi/Si(100) nanolines and (2xn) surfaces were all investigated as suitable substrates for the controlled growth of pentacene, (C22H14) or trimesic acid, (C6H3(COOH)3) organic molecules. The following techniques were used in this study; Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED), Normal Incident X-Ray Standing Waves (NIXSW) and Temperature Programmed Desorption (TPD).
The room temperature growth and ordering of trimesic acid on the AgfSi(ll1)-(root3 x root3) surface was investigated. An oblique unit cell was determined and a model proposed for the highly ordered close-packed domains.
The discovery of a new submonolayer phase on Sn/Cu(100) and the re-examined known phase are discussed. New models for these reconstructions are proposed. Adsorption of trimesic acid at room temperature on the clean substrate the lowest Sn coverage phase were studied. Two new Sn coverage dependent structures were discovered and bonding schemes in upright and flat orientations are discussed.
BifSi(100)-(2xn) surface was exploited as a template for the ordered growth of pentacene, which exhibited orientation specific adsorption. The Bi/Si(100)-(2xn) single domain surface created on vicinal silicon was used to test the suitable of Daresbury 4.2 beamline for NIXSW Imaging experiments and the quality of the results are discussed
A trio of gamma-ray burst supernovae : GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu
No full textWe present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical spectroscopy at t − t0 = 16.1 d, which covers rest-frame 3000–6250 Å. Based on Fe ii λ5169 and Si ii λ6355, our spectrum indicates an unusually low expansion velocity of ~4000–6350 km s-1, the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A/SN 2013fu, we used our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we took advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Mészáros (2001, ApJ, 552, L35), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P = 12 ms and a magnetic field of B = 1.1 × 1015 G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs
Silica supported Sn catalysts with tetrahedral Sn sites for selective isomerization of glucose to fructose
No full textLewis acid catalyzed isomerization of glucose to fructose is an important reaction for production of renewable chemicals. Here, we show the synthesis of an active and selective Lewis acid catalyst for this reaction by controlling Sn dispersion on SBA15. Sn loading of 1 wt. % over SBA15 (Sn/SBA15) maximized the formation of tetrahedral Sn species on the catalyst surface. Increasing the loading or changing support caused formation of SnO2 clusters which reduced fructose selectivity. A mechanism based on condensation of Sn with silanol group of SBA15 is proposed. The catalyst showed high selectivity of 93 % after 2 h with 57 % fructose yield. The Lewis acid catalyzed isomerization of glucose was proven by isotopic tracer study using D-glucose-2-d. The catalyst deactivated in the third cycle owing to byproduct deposition, but the activity was restored by recalcining the catalyst
Sn-Based Electrocatalyst Stability: A Crucial Piece to the Puzzle for the Electrochemical CO<sub>2</sub>Reduction toward Formic Acid
No full textNowadays, Sn-based electrocatalysts for the electrochemical CO2 reduction reaction (eCO2RR) toward formic acid have been reported to reach industrially relevant current densities and Faradaic efficiencies approaching 100%. However, electrocatalyst stability remains inadequate and appears to be a crucial piece to the puzzle, as lifetimes in the range of several thousands of hours should be reached for practical application and economic viability. Here, we provide insights into stability issues related to Sn-based electrocatalysts and electrolyzers for formic acid production. By determining the chemical and physical phenomena that occur during the electrochemical reduction reaction on the surface and bulk of Sn-based catalysts, we intend to elucidate the most common degradation mechanisms that impair long-term electrocatalytic activity of these catalysts. Moreover, highlighting the importance of correctly selected process conditions and an optimized reactor design allows us to unveil all necessary aspects for a stable Sn-based eCO2RR toward formic acid.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Large Scale Energy Storag
Influences of Nanostructures of Sn and Ir for the Oxygen Evolution Reaction in Polymer Electrolyte Membrane Water Electrolysis
No full textThe influence of nanostructures and interaction of Sn and Ir in oxygen evolution catalysts in a polymer electrolyte membrane electrolyzer were investigated. For this aim, two synthesis methods, namely, the one-step solution combustion method and the precipitation-deposition method with sodium borohydride reduction, were evaluated to prepare distinct nanostructures. Sn addition to Ir-based oxygen evolution reaction catalysts has been reported to yield materials with higher activity; however, in our case, this was observed only for Sn/Ir catalysts prepared by the precipitation-deposition method. The nanolayer of Sn/SnO2 deposited over metallic Ir particles was identified to enhance the interfacial contacts, resulting in synergistic interactions. By deconvolution of the polarization curves into constituting contributions, the performance improvement was attributed to the higher exchange current density of the Sn/Ir powder as a consequence of a higher number of surface reaction sites created by the Sn-Ir interactions.ChemE/Catalysis Engineerin
Study on locations for future coal-fired power plants
No full textEvaluation of suitable sites for coal-fired thermal power plants is very important as there are several such plants to come up in the future. All generating plants except Upper Kotmale Hydro Power plant in "Long Term Generation Expansion Plan 2009-2022" published by the
CEB are coal power plants.
Two locations already have been identified for coal power plants at Norochcholei and Sampur for 900MW and 1000MW respectively. The study reveals that there is no provision to expand beyond the designed capacity at Norochcholei plant. There is no technical limitation to expand the designed capacity at Sampur plant.
The aim of this study is to evaluate a further eight proposed sites analyzing following important factors which influence site suitability. These factors are;
1 Supply of coal and transportation facilities on land and at sea
2 Availability of sufficient cooling water and feed water
3 Proximity to the load centers / access to the national grid
4 Distance from populated area (Environmental aspects including impact on the population)
5 Depth of the sea near the coast
6 Availability of sufficient area for power plant, coal storage and ash disposal
7 Other factors
7.1 Access to the land
7.2 Topography/ geology
7.3 Meteorology
7.4 Hydrogeology
7.5 Natural hazards
Of the eight sites to be evaluated the CEB has identified five tentative locations in its "Long Term Generation Expansion Plan 2009-2022" near Athuruwella, Mawella, Mirijjawela, Karagan Lewaya, and Mirissa along the southern coast. No detailed study has been done for these locations. Hence, initially, these five locations were taken into consideration for the study from among the eight proposed sites.
Three additional locations are proposed by the author for consideration along the eastern coast. They are near Panama, Sangamankanda Point and Vakarei. Although CEB proposed Karagan Lewaya to be considered as a site it had to be abandoned subsequently because the GOSL has used this site for the recently commissioned Hambantota harbor. As a result of that the study is carried out based on the other seven proposed sites for detailed evaluation.
Sri Lanka has no coal mines, thus coal needs to be imported to the sites from countries such as Indonesia, South Africa or Australia who have indigenous coal mines. Hence coal transporting has to be done by vessels to the site especially with Panamax size vessels and Cape size vessels to keep the cost at a minimum level. Another major factor is the supply sufficient water to the site in order to cool the process and process water. These two factors require that the site has to be close to the coast.
It can be seen that the four sites Athuruwella, Mawella, Mirissa and Mirijjawela on the southern coast are close to the populated areas and the lands in the vicinity are ideal for agriculture as well as tourism. Some major resettlement plans are required with a suitable compensation scheme when acquiring the lands for the sites at these four locations in the southern province. In contrast, however, the population density at Panama, Sangamankanda Point and Vakarei in the eastern province is comparatively low but the infrastructure needs to be developed.
The grid substations at Ambalangoda, Matara, Hambantota, Ampara and Valachchena are considered as gateways to the national grid from the proposed locations. These can access only the 132kV grid and needs to be augmented to handle 220kV at the substation andtransmission lines.
Other major factor to be considered is the depth of the sea near the proposed site as this determines how far the vessels can approach the coast and hence estimates the distance of the coal unloading conveyor and the size of the jetty in the sea. Mirijjawela has the advantage of having use of the newly commissioned Hambantota harbor for this purpose as it is about 1 km away from the site.
Acquiring of required land area for the proposed site needs to be carefully done. When it is needed to acquire the lands from the residents in the area a reasonable compensation scheme and resettlement plan has to be introduced. Therefore it is of great benefit and cost saving if government owned bare land is available in the proposed areas.
Although access to the lands, topography/ geology, meteorology, hydrogeology, natural hazards are minor factors for site selection of a coal power plant, these should also be taken into consideration because the damages can be very high when natural hazards occur like the Tsunami in 2004, although this occurs rarely.
The proposed locations should be selected away from any protected wildlife zones, sanctuaries and places with historical values in the country.
Then proposed locations are analyzed based on the above factors and for comparison a site validation matrix is prepared with introducing a suitable marking scheme in order to select the best location for the next coal power generation plant
Surfactant-assisted synthesis of Sn nanoparticles via solution plasma technique
No full textWe have adopted a solution plasma synthesis for preparing Sn nanoparticles (Sn-NPs) directly from metallic Sn electrode. The Sn-NPs were synthesized in the presence of the surfactant, cetyltrimethylammonium bromide (CTAB), and the effect of the concentration of CTAB on the Sn-NPs was investigated. Without CTAB addition, SnO plates were precipitated. Sn-NPs with less than 200 nm were synthesized at a high concentration of 200 x 10(-6) g ml(-1) of CTAB. Electrochemical properties of SnO plates and Sn-NPs were analyzed for use as an anode material in Li-ion batteries. A composite of Sn-NPs and graphite enhanced the cyclic stability owing to the buffer space provided by the graphite for volume expansion. In the case of the 30 wt% loaded Sn-NPs, the capacity was measured to be 414 mA h g(-1) after 20 cycles
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