On the occurrence of buoyancy-induced oscillatory growth instability in directional solidification of alloys

Recent solidification experiments identified an oscillatory growth instability during directional solidification of Ni-based superalloy CMSX4 under a given range of cooling rates. From a modeling perspective, the quantitative simulation of dendritic growth under convective conditions remains challenging, due to the multiple length scales involved. Using the dendritic needle network (DNN) model, coupled with an efficient Navier-Stokes solver, we reproduced the buoyancy-induced growth oscillations observed in CMSX4 directional solidification. These previous results have shown that, for a given alloy and temperature gradient, oscillations occur in a narrow range of cooling rates (or pulling velocity, $V_p$) and that the selected primary dendrite arm spacing ($\Lambda$) plays a crucial role in the activation of the flow leading to oscillations. Here, we show that the oscillatory behavior may be generalized to other binary alloys within an appropriate range of $(V_p,\Lambda)$ by reproducing it for an Al-4at.%Cu alloy. We perform a mapping of oscillatory states as a function of $V_p$ and $\Lambda$, and identify the regions of occurrence of different behaviors (e.g., sustained or damped oscillations) and their effect on the oscillation characteristics. Our results suggest a minimum of $V_p$ for the occurrence of oscillations and confirm the correlation between the oscillation type (namely: damped, sustained, or noisy) with the ratio of average fluid velocity $\overline V$ over $V_p$. We describe the different observed growth regimes and highlight similarities and contrasts with our previous results for a CMSX4 alloy

How urban green management is influencing passerine birds' nesting in the Mediterranean : a case study in a Catalan city

Unidad de excelencia María de Maeztu MdM-2015-0552The vegetation within the urban system provides sheltering and food provisions to birds, influencing their nesting options. This study analyses for the first time in the Mediterranean area how different socio-ecological factors related with public urban green management can influence the nesting of the passerine bird order. It uses a case study in the city of Valls (Catalonia, Spain). First, the public urban green was quantitatively and qualitatively characterised; then the nests from the passerine birds were collected and identified, and finally, potential associations between nests and urban green-related socio-ecological factors such as vegetation type (tree, shrub, herb, liana), plant species, neighbourhood type, pruning type, fruit and seed production, and presence of insect plague were analysed. A total of 300 nests were identified and belonged, mostly, to the family of Fringillidae and Sylviidae, all from Mediterranean agroforestry areas. Passerine birds show preference for the historic centre, being this area the one with highest biodiversity of vegetation in the city, in detriment of surrounding neighbourhoods, which in turn are less biodiverse. Passerine birds do not consider four tree species (Celtis australis, Laurus nobilis, Robinia pseudoacacia and Pinus pinea) suitable for nesting whereas showing preference for two tree species of medium height and size (Hibiscus syriacus and Melia azederach). Also, passerine birds seem to preferably nest in trees that have been pruned intensively. These results suggest that, to strengthen the passerine bird diversity in cities, urban green management should promote certain species of trees of medium size and intensive pruning while supporting the overall biodiversity of the urban green. All these results contribute to inform effective urban planning and management strategies for passerine birds conservation that aim to reconcile urban development and urban biodiversity protection

One-pot electrosynthesis of multi-layered magnetic metallopolymer nanocomposites

Researchers have been investigating various methodologies for fabricating well-defined, homogenous composites consisting of nanoparticles (NPs) dispersed in a matrix. The main challenges are to prevent particle agglomerations during fabrication and to obtain nanoparticles whose size distribution could be tuned on demand. One of the methods that can provide these features is electrodeposition. We report for the first time the fabrication of a thin magnetic multilayer nanocomposite film by electrodeposition from one bath containing both a monomer and metal salts. Cobalt and cobalt-nickel NPs were deposited on conductive polymer polypyrrole thin films using different electrodeposition potentials and times. Multilayer nanocomposite films were fabricated by subsequent electrodeposition of polymer and nanoparticle layers. Scanning electron microscopy analysis showed that a wide range of NPs (70-230 nm) could be synthesized by manipulating growth potentials and times. The cobalt-nickel NPs were found to contain hexagonal close-packed (hcp) and face-centered cubic (fcc) phases based on X-ray diffraction and selected area electron diffraction. Magnetic measurements proved that both the single and the multi-layered nanocomposites were magnetic at room temperature

One-pot electrosynthesis of multi-layered magnetic metallopolymer nanocomposites

Researchers have been investigating various methodologies for fabricating well-defined, homogenous composites consisting of nanoparticles (NPs) dispersed in a matrix. The main challenges are to prevent particle agglomerations during fabrication and to obtain nanoparticles whose size distribution could be tuned on demand. One of the methods that can provide these features is electrodeposition. We report for the first time the fabrication of a thin magnetic multilayer nanocomposite film by electrodeposition from one bath containing both a monomer and metal salts. Cobalt and cobalt-nickel NPs were deposited on conductive polymer polypyrrole thin films using different electrodeposition potentials and times. Multilayer nanocomposite films were fabricated by subsequent electrodeposition of polymer and nanoparticle layers. Scanning electron microscopy analysis showed that a wide range of NPs (70-230 nm) could be synthesized by manipulating growth potentials and times. The cobalt-nickel NPs were found to contain hexagonal close-packed (hcp) and face-centered cubic (fcc) phases based on X-ray diffraction and selected area electron diffraction. Magnetic measurements proved that both the single and the multi-layered nanocomposites were magnetic at room temperature

How urban green management is influencing passerine birds' nesting in the Mediterranean : a case study in a Catalan city

Unidad de excelencia María de Maeztu MdM-2015-0552The vegetation within the urban system provides sheltering and food provisions to birds, influencing their nesting options. This study analyses for the first time in the Mediterranean area how different socio-ecological factors related with public urban green management can influence the nesting of the passerine bird order. It uses a case study in the city of Valls (Catalonia, Spain). First, the public urban green was quantitatively and qualitatively characterised; then the nests from the passerine birds were collected and identified, and finally, potential associations between nests and urban green-related socio-ecological factors such as vegetation type (tree, shrub, herb, liana), plant species, neighbourhood type, pruning type, fruit and seed production, and presence of insect plague were analysed. A total of 300 nests were identified and belonged, mostly, to the family of Fringillidae and Sylviidae, all from Mediterranean agroforestry areas. Passerine birds show preference for the historic centre, being this area the one with highest biodiversity of vegetation in the city, in detriment of surrounding neighbourhoods, which in turn are less biodiverse. Passerine birds do not consider four tree species (Celtis australis, Laurus nobilis, Robinia pseudoacacia and Pinus pinea) suitable for nesting whereas showing preference for two tree species of medium height and size (Hibiscus syriacus and Melia azederach). Also, passerine birds seem to preferably nest in trees that have been pruned intensively. These results suggest that, to strengthen the passerine bird diversity in cities, urban green management should promote certain species of trees of medium size and intensive pruning while supporting the overall biodiversity of the urban green. All these results contribute to inform effective urban planning and management strategies for passerine birds conservation that aim to reconcile urban development and urban biodiversity protection

Gonorrhoea diagnoses in a network of STI clinics in Spain during the period 2006-2010: differences by sex and transmission route

BACKGROUND: Gonorrhoea infection is one of the most common bacterial sexually transmitted infections and an important cause of morbidity and serious complications. The objectives of this paper are: a) to describe gonorrhoea cases diagnosed in a network of 15 (out of 16) STI clinics in Spain during 2006-2010; b) to analyse differences among men who have sex with men (MSM), men who have sex exclusively with women (MSW) and women; and c) to evaluate factors associated to with HIV co-infection. METHODS: All gonorrhoea cases diagnosed in the network were included (25.7% of total cases notified in Spain). Data were collected by clinical staff. Descriptive/bivariate analyses were carried out stratifying by sex and transmission category; association and trends were evaluated using the chi-square test. Factors associated with HIV co-infection were estimated using a logistic regression model. RESULTS: 2385 cases were included: 55.3% among MSM, 31.3% among MSW and 13.3% among females; cases among MSM increased from 55.8% in 2006 to 62.9% in 2010 while no trends were found among the other two groups.Most MSM cases were Spaniards (72%), aged 25-34 years (46%), 49% reported previous STI and 25% concurrent STI (excluding HIV); casual partners were the commonest source of infection, and 21% of cases had rectal gonorrhoea. MSW cases did not differ from MSM by age, origin or source of infection, but frequencies of prior or concurrent STI were lower. Female cases were younger than male, were mostly foreigners (58%), and 41% were sex workers; concurrent STI (other than HIV) were diagnosed in 30%; 20.4% had symptoms (72.5% and 89.2% in MSM and MSW), and pharyngeal location was present in 30%.HIV co-infection was highest in MSM (20.9%). Co-infection was associated with age > 35 years, low educational level, being Western European or Latin-American, being MSM, having previous or concurrent STI and reporting contact with an HIV-infected partner; it was inversely associated with female sex. CONCLUSION: Differences by sex, transmission route and origin should be considered when implementing care and preventive programmes for gonorrhoea, and MSM are a priority group for intervention, in particular HIV-infected MSM.This work was supported by the Foundation for Research and Prevention of AIDS in Spain (Fundación para la Investigación y la Prevención del SIDA en España–FIPSE) grant number 36646/07, by the Instituto de Salud Carlos III grant number EPY-1352/10 and CIBER de Epidemiología y Salud Pública (CIBERESP)S

Very high energy gamma-ray observation of the peculiar transient event Swift J1644+57 with the MAGIC telescopes and AGILE

Context. On March 28, 2011, the BAT instrument on board the Swift satellite detected a new transient event that in the very beginning was classified as a gamma ray burst (GRB). However, the unusual X-ray flaring activity observed from a few hours up to days after the onset of the event made a different nature seem to be more likely. The long-lasting activity in the X-ray band, followed by a delayed brightening of the source in infrared and radio activity, suggested that it is better interpreted as a tidal disruption event that triggered a dormant black hole in the nucleus of the host galaxy and generated an outflowing jet of relativistic matter. Aims. Detecting a very high energy emission component from such a peculiar object would be enable us to constrain the dynamic of the emission processes and the jet model by providing information on the Doppler factor of the relativistic ejecta. Methods. The MAGIC telescopes observed the peculiar source Swift J1644+57 during the flaring phase, searching for gamma-ray emission at very-high energy (VHE, E > 100 GeV), starting observations nearly 2.5 days after the trigger time. MAGIC collected a total of 28 h of data during 12 nights. The source was observed in wobble mode during dark time at a mean zenith angle of 35 degrees. Data were reduced using a new image-cleaning algorithm, the so-called sum-cleaning, which guarantees a better noise suppression and a lower energy threshold than the standard analysis procedure. Results. No clear evidence for emission above the energy threshold of 100 GeV was found. MAGIC observations permit one to constrain the emission from the source down to 100 GeV, which favors models that explain the observed lower energy variable emission. Data analysis of simultaneous observations from AGILE, Fermi and VERITAS also provide negative detection, which additionally constrain the self-Compton emission component

Chasing Gravitational Waves with the Chereknov Telescope Array

Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 2023 (arXiv:2309.08219)2310.07413International audienceThe detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA

Chasing Gravitational Waves with the Chereknov Telescope Array

Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 2023 (arXiv:2309.08219)2310.07413International audienceThe detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA