Hydrogen vs. Battery in the long-term operation. A comparative between energy management strategies for hybrid renewable microgrids

The growth of the world’s energy demand over recent decades in relation to energy intensity and demography is clear. At the same time, the use of renewable energy sources is pursued to address decarbonization targets, but the stochasticity of renewable energy systems produces an increasing need for management systems to supply such energy volume while guaranteeing, at the same time, the security and reliability of the microgrids. Locally distributed energy storage systems (ESS) may provide the capacity to temporarily decouple production and demand. In this sense, the most implemented ESS in local energy districts are small–medium-scale electrochemical batteries. However, hydrogen systems are viable for storing larger energy quantities thanks to its intrinsic high mass-energy density. To match generation, demand and storage, energy management systems (EMSs) become crucial. This paper compares two strategies for an energy management system based on hydrogen-priority vs. battery-priority for the operation of a hybrid renewable microgrid. The overall performance of the two mentioned strategies is compared in the long-term operation via a set of evaluation parameters defined by the unmet load, storage efficiency, operating hours and cumulative energy. The results show that the hydrogen-priority strategy allows the microgrid to be led towards island operation because it saves a higher amount of energy, while the battery-priority strategy reduces the energy efficiency in the storage round trip. The main contribution of this work lies in the demonstration that conventional EMS for microgrids’ operation based on battery-priority strategy should turn into hydrogen-priority to keep the reliability and independence of the microgrid in the long-term operation

Carbon Stars and other Luminous Stellar Populations in M33

The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its proximity and almost face-on inclination means that it projects over a large area on the sky, making it an ideal candidate for wide-field CCD mosaic imaging. Photometry was obtained for more than 10^6 stars covering a 74' x 56' field centered on M33. Main sequence (MS), supergiant branch (SGB), red giant branch (RGB) and asymptotic giant branch (AGB) populations are identified and classified based on broad-band V and I photometry. Narrow-band filters are used to measure spectral features allowing the AGB population to be further divided into C and M-star types. The galactic structure of M33 is examined using star counts, colour-colour and colour-magnitude selected stellar populations. We use the C to M-star ratio to investigate the metallicity gradient in the disk of M33. The C/M-star ratio is found to increase and then flatten with increasing galactocentric radius in agreement with viscous disk formation models. The C-star luminosity function is found to be similar to M31 and the SMC, suggesting that C-stars should be useful distance indicators. The ``spectacular arcs of carbon stars'' in M33 postulated recently by Block et al. (2004) are found in our work to be simply an extension of M33's disk.Comment: 20 pages, 20 figures. Accepted for publication in The Astronomical Journa

THE HIGH CADENCE TRANSIENT SURVEY (HITS). I. SURVEY DESIGN AND SUPERNOVA SHOCK BREAKOUT CONSTRAINTS

Indexación: Web of Science; Scopus.We present the first results of the High Cadence Transient Survey (HiTS), a survey for which the objective is to detect and follow-up optical transients with characteristic timescales from hours to days, especially the earliest hours of supernova (SN) explosions. HiTS uses the Dark Energy Camera and a custom pipeline for image subtraction, candidate filtering and candidate visualization, which runs in real-time to be able to react rapidly to the new transients. We discuss the survey design, the technical challenges associated with the real-time analysis of these large volumes of data and our first results. In our 2013, 2014, and 2015 campaigns, we detected more than 120 young SN candidates, but we did not find a clear signature from the short-lived SN shock breakouts (SBOs) originating after the core collapse of red supergiant stars, which was the initial science aim of this survey. Using the empirical distribution of limiting magnitudes from our observational campaigns, we measured the expected recovery fraction of randomly injected SN light curves, which included SBO optical peaks produced with models from Tominaga et al. (2011) and Nakar & Sari (2010). From this analysis, we cannot rule out the models from Tominaga et al. (2011) under any reasonable distributions of progenitor masses, but we can marginally rule out the brighter and longer-lived SBO models from Nakar & Sari (2010) under our best-guess distribution of progenitor masses. Finally, we highlight the implications of this work for future massive data sets produced by astronomical observatories, such as LSST.http://iopscience.iop.org/article/10.3847/0004-637X/832/2/155/meta;jsessionid=76BDFFFE378003616F6DBA56A9225673.c4.iopscience.cld.iop.or

Detection of a population gradient in the Sagittarius Stream

We present a quantitative comparison between the Horizontal Branch morphology in the core of the Sagittarius dwarf spheroidal galaxy (Sgr) and in a wide field sampling a portion of its tidal stream (Sgr Stream), located tens of kpc away from the center of the parent galaxy. We find that the Blue Horizontal Branch (BHB) stars in that part of the Stream are five times more abundant than in the Sgr core, relative to Red Clump stars. The difference in the ratio of BHB to RC stars between the two fields is significant at the 4.8 sigma level. This indicates that the old and metal-poor population of Sgr was preferentially stripped from the galaxy in past peri-Galactic passages with respect to the intermediate-age metal rich population that presently dominates the bound core of Sgr, probably due to a strong radial gradient that was settled within the galaxy before its disruption. The technique adopted in the present study allows to trace population gradients along the whole extension of the Stream.Comment: 4 pages, 3 .ps figures (fig. 1 at low resolution); Accepted for publication by A&A Letter

Substructure revealed by RR Lyraes in SDSS Stripe 82

We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high accuracy using a string-length method. A subset of 178 RR Lyraes with spectrally derived metallicities are employed to derive metallicity-period-amplitude relations, which are then used to find metallicities and distances for the entire sample. The RR Lyraes lie between 5 and 115 kpc from the Galactic center. They are divided into subsets of 316 RRab types and 91 RRc types based on their period, colour and metallicity. The density distribution is not smooth, but dominated by clumps and substructure. Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the Hercules-Aquila Cloud respectively are identified. Hence, ~ 70 % of the RR Lyraes in Stripe 82 belong to known substructure. There is a sharp break in the density distribution at Galactocentric radii of 40 kpc, reflecting the fact that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the Sagittarius Stream - lies within 40 kpc. In fact, almost 60 % of all the RR Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which emphasises its pre-eminence. Additionally, evidence of a new and distant substructure - the Pisces Overdensity - is found, consisting of 28 faint RR Lyraes centered on Galactic coordinates (80 deg, -55 deg) and with distances of ~ 80 kpc. The total stellar mass in the Pisces Overdensity is ~10000 solar masses and its metallicity is [Fe/H] ~ -1.5.Comment: 15 pages, submitted to MNRA

Evidence of suppression of onchocerciasis transmission in the Venezuelan Amazonian focus.

BACKGROUND: The World Health Organization (WHO) has set goals for onchocerciasis elimination in Latin America by 2015. Most of the six previously endemic countries are attaining this goal by implementing twice a year (and in some foci, quarterly) mass ivermectin (Mectizan®) distribution. Elimination of transmission has been verified in Colombia, Ecuador and Mexico. Challenges remain in the Amazonian focus straddling Venezuela and Brazil, where the disease affects the hard-to-reach Yanomami indigenous population. We provide evidence of suppression of Onchocerca volvulus transmission by Simulium guianense s.l. in 16 previously hyperendemic Yanomami communities in southern Venezuela after 15 years of 6-monthly and 5 years of 3-monthly mass ivermectin treatment. METHODS: Baseline and monitoring and evaluation parasitological, ophthalmological, entomological and serological surveys were conducted in selected sentinel and extra-sentinel communities of the focus throughout the implementation of the programme. RESULTS: From 2010 to 2012–2015, clinico-parasitological surveys indicate a substantial decrease in skin microfilarial prevalence and intensity of infection; accompanied by no evidence (or very low prevalence and intensity) of ocular microfilariae in the examined population. Of a total of 51,341 S. guianense flies tested by PCR none had L3 infection (heads only). Prevalence of infective flies and seasonal transmission potentials in 2012–2013 were, respectively, under 1 % and 20 L3/person/transmission season. Serology in children aged 1–10 years demonstrated that although 26 out of 396 (7 %) individuals still had Ov-16 antibodies, only 4/218 (2 %) seropositives were aged 1–5 years. CONCLUSIONS: We report evidence of recent transmission and morbidity suppression in some communities of the focus representing 75 % of the Yanomami population and 70 % of all known communities. We conclude that onchocerciasis transmission could be feasibly interrupted in the Venezuelan Amazonian focus. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13071-016-1313-z) contains supplementary material, which is available to authorized users

Spitzer Space Telescope study of disks in the young σ\sigma Orionis cluster

We report new Spitzer Space Telescope observations from the IRAC and MIPS instruments of the young (~ 3 Myr) sigma Orionis cluster. We identify 336 stars as members of the cluster using optical and near-infrared color magnitude diagrams. Using the spectral energy distribution (SED) slopes in the IRAC spectral range, we place objects in several classes: non-excess stars, stars with optically thick disks(like classical T Tauri stars), class I (protostellar) candidates, and stars with ``evolved disks''; the last exhibit smaller IRAC excesses than optically thick disk systems. In general, this classification agrees with the location expected in IRAC-MIPS color-color diagrams for these objects. We find that the evolved disk systems are mostly a combination of objects with optically thick but non-flared disks, suggesting grain growth and/or settling, and transition disks, systems in which the inner disk is partially or fully cleared of small dust. In all, we identify 7 transition disk candidates and 3 possible debris disk systems. As in other young stellar populations, the fraction of disks depends on the stellar mass, ranging from ~10% for stars in the Herbig Ae/Be mass range (>2 msun) to ~35% in the T Tauri mass range (1-0.1 msun). We find that the disk fraction does not decrease significantly toward the brown dwarf candidates (<0.1 msun). The IRAC infrared excesses found in stellar clusters and associations with and without central high mass stars are similar, suggesting that external photoevaporation is not very important in many clusters. Finally, we find no correlation between the X-ray luminosity and the disk infrared excess, suggesting that the X-rays are not strongly affected by disk accretion.Comment: 44pages, 17 figures. Sent to Ap

Perpendicular magnetic anisotropy in granular multilayers of COPD alloyed nanoparticles

Co-Pd multilayers obtained by Pd capping of pre-deposited Co nanoparticles on amorphous alumina are systematically studied by means of high-resolution transmission electron microscopy, x-ray diffraction, extended x-ray absorption fine structure, SQUID-based magnetometry, and x-ray magnetic circular dichroism. The films are formed by COPD alloyed nanoparticles self-organized across the layers, with the interspace between the nanoparticles filled by the non-alloyed Pd metal. The nanoparticles show atomic arrangements compatible with short-range chemical order of L10 strucure type. The collective magnetic behavior is that of ferromagnetically coupled particles with perpendicular magnetic anisotropy, irrespective of the amount of deposited Pd. For increasing temperature three magnetic phases are identified: hard ferromagnetic with strong coercive field, soft-ferromagnetic as in an amorphous asperomagnet, and superparamagnetic. Increasing the amount of Pd in the system leads to both magnetic hardness increment and higher transition temperatures. Magnetic total moments of 1.77(4) µB and 0.45(4) µB are found at Co and Pd sites, respectively, where the orbital moment of Co, 0.40(2) µB, is high, while that of Pd is negligible. The effective magnetic anisotropy is the largest in the capping metal series (Pd, Pt, W, Cu, Ag, Au), which is attributed to the interparticle interaction between de nanoparticles, in addition to the intraparticle anisotropy arising from hybridization between the 3d-4d bands associated to the Co and Pd chemical arrangement in a L10 structure type

The celiac axis compression syndrome (CACS): critical review in the laparoscopic era

The celiac axis compression syndrome (CACS) due to median arcuate ligament (MAL) was first described by Harjola in 1963; originating postpandrial abdominal pain, weight loss, epigastric bruit and celiac axis stenosis > 75% in angiographic studies. This clinical condition has been the origin of controversies about its pathogenesis, diagnosis and its long term clinical results. Advances in diagnostic imaging as 64 multidetector–row CT (MDCT), 3-D reconstruction, magnetic resonance (MR) and color duplex ultrasonography, provide better understanding of the syndrome and allow to identify the best candidates for surgical division of MAL fibers. Since the introduction of laparoscopic approach, and also endovascular procedures, in 2000, a new perspective has established in this challenging syndrome. With the occasion of our own experience, a critical review of the syndrome is presented