Towards Noncommutative Linking Numbers Via the Seiberg-Witten Map

In the present work some geometric and topological implications of noncommutative Wilson loops are explored via the Seiberg-Witten map. In the abelian Chern-Simons theory on a three dimensional manifold, it is shown that the effect of noncommutativity is the appearance of $6^n$ new knots at the $n$-th order of the Seiberg-Witten expansion. These knots are trivial homology cycles which are Poincar\'e dual to the high-order Seiberg-Witten potentials. Moreover the linking number of a standard 1-cycle with the Poincar\'e dual of the gauge field is shown to be written as an expansion of the linking number of this 1-cycle with the Poincar\'e dual of the Seiberg-Witten gauge fields. In the process we explicitly compute the noncommutative 'Jones-Witten' invariants up to first order in the noncommutative parameter. Finally in order to exhibit a physical example, we apply these ideas explicitly to the Aharonov-Bohm effect. It is explicitly displayed at first order in the noncommutative parameter, we also show the relation to the noncommutative Landau levels.Comment: 19 pages, 1 figur

Towards concept identification using a knowledge-intensive approach

This paper presents a method for identifying concepts in microposts and classifying them into a predefined set of categories. The method relies on the DBpedia knowledge base to identify the types of the concepts detected in the messages. For those concepts that are not classified in the ontology we infer their types via the ontology properties which characterise the type

Identifying Topics in Social Media Posts using DBpedia

This paper describes a method for identifying topics in text published in social media, by applying topic recognition techniques that exploit DBpedia. We evaluate such method for social media in Spanish and we provide the results of the evaluation performed

A spectroscopic atlas of post-AGB stars and planetary nebulae selected from the IRAS Point Source Catalogue

Aims: We study the optical spectral properties of a sample of stars showing far infrared colours similar to those of well-known planetary nebulae. The large majority of them were unidentified sources or poorly known in the literature at the time when this spectroscopic survey started, some 15 years ago. Methods: We present low-resolution optical spectroscopy, finding charts and improved astrometric coordinates of a sample of 253 IRAS sources. Results: We have identified 103 sources as post-AGB stars, 21 as ``transition sources'', and 36 as planetary nebulae, some of them strongly reddened. Among the rest of sources in the sample, we were also able to identify 38 young stellar objects, 5 peculiar stars, and 2 Seyfert galaxies. Up to 49 sources in our spectroscopic sample do not show any optical counterpart, and most of them are suggested to be heavily obscured post-AGB stars, rapidly evolving on their way to becoming planetary nebulae. Conclusions: An analysis of the galactic distribution of the sources identified as evolved stars in the sample is presented together with a study of the distribution of these stars in the IRAS two-colour diagram. Finally, the spectral type distribution and other properties of the sources identified as post-AGB in this spectroscopic survey are discussed in the framework of stellar evolution.Comment: 69 pages, 413 figures. Accepted by Astronomy and Astrophysic

Power distribution in a 13 kW three-phase rectifier system: impact on weight, volume and efficiency

This paper addresses the power delivery strategy on an aircraft application consisting on seven isolated DC loads to be supplied from the AC grid. Distributed or centralized power processing is evaluated taking into account weight and efficiency. Additionally, the rectifier switching frequency has to be synchronized with an external frequency clock to minimize the interference of the converter harmonics with the loads

Nitric oxide-inhibited chloride transport in cortical thick ascending limbs is reversed by 8-iso-prostaglandin-F2α

Background: Salt reabsorption in the cortical thick ascending limb (cTAL) is regulated by opposing effects. Thus, while nitric oxide (NO) inhibits sodium chloride (NaCl) reabsorption, 8-iso-prostaglandin-F2α (8-iso-PGF2α) stimulates it. Their interaction, however, has not been evaluated in the cTAL. Because 8-iso-PGF2α has considerable stability while NO is a free radical with a short half-life, we hypothesized that, in the cTAL, the inhibition of NaCl absorption will be reversed by 8-iso-PGF2α. Methods: Chloride absorption (JCl) was measured in isolated perfused cTALs. We also evaluated whether activation of protein kinase A (PKA) is required for this interaction. Since cyclic adenosine monophosphate (cAMP) is a major messenger for the 8-iso-PGF2α signaling cascade, and NO inhibits JCl by decreasing cAMP bioavailability, we measured 8-iso-PGF2α-stimulated cAMP in the presence of sodium nitroprusside (SNP). Results: Basal JCl was 274 ± 85 pmol/min/mm. The NO donor, SNP (10-6 M), decreased JCl by 41% (333.5 ± 35.2 pmol/min/mm vs. 195.9 ± 26.1 pmol/min/mm), while 8-iso-PGF2α (100 μM) increased JCl to 315 ± 46 pmol/min/mm (p \u3c 0.01), reversing the effects of the NO donor. While SNP inhibited JCl, 8-iso-PGF2α failed to increase JCl in the presence of H89. Basal cAMP was 56.3 ± 13.1 fmol/min/mm, that in the presence of the NO donor was 57.8 ± 6.1 fmol/min/mm, and that with 8-iso-PGF2α increased it to 92.1 ± 2.9 fmol/min/mm (n = 10, p \u3c 0.04). Conclusion: We concluded that 1) NO-induced inhibition of JCl in the cTAL can be reversed by 8-iso-PGF2α, 2) 8-iso-PGF2α and NO interaction requires PKA to control JCl in this nephron segment, and 3) in the presence of NO, 8-iso-PGF2α continues to stimulate JCl because NO cannot reverse 8-iso-PGF2α-stimulated cAMP level

Weakened magnetic braking as the origin of anomalously rapid rotation in old field stars

A knowledge of stellar ages is crucial for our understanding of many astrophysical phenomena, and yet ages can be difficult to determine. As they become older, stars lose mass and angular momentum, resulting in an observed slowdown in surface rotation. The technique of 'gyrochronology' uses the rotation period of a star to calculate its age. However, stars of known age must be used for calibration, and, until recently, the approach was untested for old stars (older than 1 gigayear, Gyr). Rotation periods are now known for stars in an open cluster of intermediate age (NGC 6819; 2.5 Gyr old), and for old field stars whose ages have been determined with asteroseismology. The data for the cluster agree with previous period-age relations, but these relations fail to describe the asteroseismic sample. Here we report stellar evolutionary modelling, and confirm the presence of unexpectedly rapid rotation in stars that are more evolved than the Sun. We demonstrate that models that incorporate dramatically weakened magnetic braking for old stars can---unlike existing models---reproduce both the asteroseismic and the cluster data. Our findings might suggest a fundamental change in the nature of ageing stellar dynamos, with the Sun being close to the critical transition to much weaker magnetized winds. This weakened braking limits the diagnostic power of gyrochronology for those stars that are more than halfway through their main-sequence lifetimes.Comment: 25 pages, 3 figures in main paper, 6 extended data figures, 1 table. Published in Nature, January 2016. Please see https://youtu.be/O6HzYgP5uyc for a video description of the resul

Design of energy control method for three-phase buck-type rectifier with very demanding load steps

Conventional three-phase rectifiers are controlled to achieve good power factor and low THD in the input. In the case of pulsating power loads, the fast dynamic response implies that the load pulses are reflected in the generator. These pulsating loads affect the life time operation of the generator, especially when it is not oversized (that is the case in aircraft applications). In order to smooth the power demanded from the generator, it is preferable to reduce the bandwidth of the controller to the rectifier but it affects its stability due to the fact that the right half plane pole given by the negative impedance of a constant power load requires high bandwidth control loop to compensate it. In this paper, an energy control method is proposed to employ the energy stored in the output capacitor of the rectifier to control the amount of power demanded through the rectifier. In such a way the bandwidth restriction for stability is eliminated and the bandwidth of the loop can be set slow enough to ensure smooth power demanded from the generator

Turning Carbon Dioxide and Ethane into Ethanol by Solar-Driven Heterogeneous Photocatalysis over RuO2- and NiO-co-Doped SrTiO3

[EN] The current work focused on the sunlight-driven thermo-photocatalytic reduction of carbon dioxide (CO2), the primary greenhouse gas, by ethane (C2H6), the second most abundant element in shale gas, aiming at the generation of ethanol (EtOH), a renewable fuel. To promote this process, a hybrid catalyst was prepared and properly characterized, comprising of strontium titanate (SrTiO3) co-doped with ruthenium oxide (RuO2) and nickel oxide (NiO). The photocatalytic activity towards EtOH production was assessed in batch-mode and at gas-phase, under the influence of different conditions: (i) dopant loading; (ii) temperature; (iii) optical radiation wavelength; (vi) consecutive uses; and (v) electron scavenger addition. From the results here obtained, it was found that: (i) the functionalization of the SrTiO3 with RuO2 and NiO allows the visible light harvest and narrows the band gap energy (ca. 14-20%); (ii) the selectivity towards EtOH depends on the presence of Ni and irradiation; (iii) the catalyst photoresponse is mainly due to the visible photons; (iv) the photocatalyst loses > 50% efficiency right after the 2nd use; (v) the reaction mechanism is based on the photogenerated electron-hole pair charge separation; and (vi) a maximum yield of 64 mu mol EtOH g(cat)(-1) was obtained after 45-min (85 mu mol EtOH g(cat)(-1) h(-1)) of simulated solar irradiation (1000 W m(-2)) at 200 degrees C, using 0.4 g L-1 of SrTiO3:RuO2:NiO (0.8 wt.% Ru) with [CO2]:[C2H6] and [Ru]:[Ni] molar ratios of 1:3 and 1:1, respectively. Notwithstanding, despite its exploratory nature, this study offers an alternative route to solar fuels' synthesis from the underutilized C2H6 and CO2.This work was financially supported by the Base Funding-UIDB/50020/2020 of the Associate Laboratory LSRE-LCM-funded by national funds through FCT/MCTES (PIDDAC). Larissa O. Paulista also wants to acknowledge for her doctoral fellowship (reference SFRH/BD/137639/2018), supported by FCT. Tania F. C. V. Silva and Vitor J. P. Vilar acknowledge the FCT Individual Call to Scientific Employment Stimulus 2017 (CEECIND/01386/2017 and CEECIND/01317/2017, respectively). Josep Albero and Hermenegildo Garcia are also grateful to the Spanish Ministry of Science and Innovation (RTI2018-098237-CO2-R1 and Severo Ochoa), Generalitat Valencia (Prometeo 2017/083) and European Union's Horizon 2020 research and innovation programme under grant agreement No 862453, project FlowPhotochem, by financial contribution.Paulista, LO.; Albero-Sancho, J.; Martins, RJE.; Boaventura, RAR.; Vilar, VJP.; Silva, TFCV.; García Gómez, H. (2021). Turning Carbon Dioxide and Ethane into Ethanol by Solar-Driven Heterogeneous Photocatalysis over RuO2- and NiO-co-Doped SrTiO3. Catalysts. 11(4):1-18. https://doi.org/10.3390/catal1104046111811

Elastic differential cross sections for C4F6 isomers in the 1.5-200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering

11 págs.; 4 figs.; 4 tabs.© 2014 AIP Publishing LLC. We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases.F.B. and G.G. acknowledge the partial financial support from the Spanish Ministerio de Economia y Competitividad (Project No. FIS 2012-31230). This work forms part of the EU/ESF COST Action CM0805 programme “The Chemical Cosmos”.Peer Reviewe