8,318 research outputs found
5 year Global 3-mm VLBI survey of Gamma-ray active blazars
The Global mm-VLBI Array (GMVA) is a network of 14 3\,mm and 7\,mm capable
telescopes spanning Europe and the United States, with planned extensions to
Asia. The array is capable of sensitive maps with angular resolution often
exceeding 50\,as. Using the GMVA, a large sample of prominent -ray
blazars have been observed approximately 6 monthly from later 2008 until now.
Combining 3\,mm maps from the GMVA with near-in-time 7\,mm maps from the
VLBA-BU-BLAZAR program and 2\,cm maps from the MOJAVE program, we determine the
sub-pc morphology and high frequency spectral structure of -ray
blazars. The magnetic field strength can be estimated at different locations
along the jet under the assumption of equipartition between magnetic field and
relativistic particle energies. Making assumptions on the jet magnetic field
configuration (e.g. poloidal or toroidal), we can estimate the separation of
the mm-wave "core" and the jet base, and estimate the strength of the magnetic
field there. The results of this analysis show that on average, the magnetic
field strength decreases with a power-law , .
This suggests that on average, the mm-wave "core" is \,pc downstream
of the de-projected jet apex and that the magnetic field strength is of the
order \,kG, broadly consistent with the predictions of
magnetic jet launching (e.g. via magnetically arrested disks (MAD)).Comment: 6 pages, 1 figur
On the Calibration of Full-polarization 86GHz Global VLBI Observations
We report the development of a semi-automatic pipeline for the calibration of
86 GHz full-polarization observations performed with the Global Millimeter-VLBI
array (GMVA) and describe the calibration strategy followed in the data
reduction. Our calibration pipeline involves non-standard procedures, since
VLBI polarimetry at frequencies above 43 GHz is not yet well established. We
also present, for the first time, a full-polarization global-VLBI image at 86
GHz (source 3C 345), as an example of the final product of our calibration
pipeline, and discuss the effect of instrumental limitations on the fidelity of
the polarization images. Our calibration strategy is not exclusive for the
GMVA, and could be applied on other VLBI arrays at millimeter wavelengths. The
use of this pipeline will allow GMVA observers to get fully-calibrated datasets
shortly after the data correlation.Comment: 10 pages, 10 figures. Accepted for publication in A&
Particle fluxes and their drivers in the Avilés submarine canyon and adjacent slope, central Cantabrian margin, Bay of Biscay
Versión del edito
Strong coupling between weakly guided semiconductor nanowire modes and an organic dye
The light-matter coupling between electromagnetic modes guided by a semiconductor nanowire and excitonic states of molecules localized in its surrounding media is studied from both classical and quantum perspectives, with the aim of describing the strong-coupling regime. Weakly guided modes (bare photonic modes) are found through a classical analysis, identifying those lowest-order modes presenting large electromagnetic fields spreading outside the nanowire while preserving their robust guided behavior. Experimental fits of the dielectric permittivity of an organic dye that exhibits excitonic states are used for realistic scenarios. A quantum model properly confirms through an avoided mode crossing that the strong-coupling regime can be achieved for this configuration, leading to Rabi splitting values above 100 meV. In addition, it is shown that the coupling strength depends on the fraction of energy spread outside the nanowire, rather than on the mode field localization. These results open up a new avenue towards strong-coupling phenomenology involving propagating modes in nonabsorbing media
Estudio de la vulnerabilidad sísmica del centro histórico de Tapachula, Chiapas, con el método del índice de vulnerabilidad
Los sismos destructores históricos y recientes han mostrado que el colapso de las edificaciones es el factor que más contribuye a la pérdida de vidas humanas. Un estudio de vulnerabilidad sísmica determina el nivel de seguridad de una zona urbana o de una serie de edificaciones ante los movimientos sísmicos que pueden ocurrir en dicho sitio. Mediante este tipo de estudio se hace un diagnóstico de niveles de desempeño de cada edificación y se evalúa su posible comportamiento y susceptibilidad al daño sísmico. En este trabajo se ha estimado lavulnerabilidad sísmica de 399 edificaciones de 22 manzanas del Centro Histórico de Tapachula, Chiapas, con dos métodos: primero el de clasificación tipológica según la Escala Macrosísmica Europea (EMS-98) y posteriormente mediante el método del índice de vulnerabilidad sísmica(MIV) de RISK-UE. Este método es un refinamiento del primero que cuantifica mejor los factores de construcción y comportamiento de cada edificio que modifican su vulnerabilidad. Los resultados obtenidos se presentan en tablas y mapas de lnerabilidad sísmica y muestran que en la zona estudiada predominan las edificaciones con clases de vulnerabilidad alta (B) y muy alta (A) y que la estimación de la vulnerabilidad aplicando los criterios de la Escala EMS mejoran significativamente al aplicar MIV, que detecta un incremento de construcciones de clase A (de 36 a 44) y una disminución de las de clase E (de 13 a 5) respecto a la evaluación con EMS
Multi-year particle fluxes in Kongsfjorden, Svalbard
Abstract. High-latitude regions are
warming faster than other areas due to reduction of snow cover and sea ice
loss and changes in atmospheric and ocean circulation. The combination of
these processes, collectively known as polar amplification, provides an
extraordinary opportunity to document the ongoing thermal destabilisation of
the terrestrial cryosphere and the release of land-derived material into the
aquatic environment. This study presents a 6-year time series (2010–2016) of
physical parameters and particle fluxes collected by an oceanographic mooring
in Kongsfjorden (Spitsbergen, Svalbard). In recent decades, Kongsfjorden has
been experiencing rapid loss of sea ice coverage and retreat of local
glaciers as a result of the progressive increase in ocean and air
temperatures. The overarching goal of this study was to continuously monitor
the inner fjord particle sinking and to understand to what extent the
temporal evolution of particulate fluxes was linked to the progressive
changes in both Atlantic and freshwater input. Our data show high peaks of
settling particles during warm seasons, in terms of both organic and
inorganic matter. The different sources of suspended particles were described
as a mixing of glacier carbonate, glacier siliciclastic and autochthonous marine input. The glacier releasing
sediments into the fjord was the predominant source, while the sediment input
by rivers was reduced at the mooring site. Our time series showed that the
seasonal sunlight exerted first-order control on the particulate fluxes in
the inner fjord. The marine fraction peaked when the solar radiation was at a
maximum in May–June while the land-derived fluxes exhibited a 1–2-month lag
consistent with the maximum air temperature and glacier melting. The
inter-annual time-weighted total mass fluxes varied by 2 orders of magnitude
over time, with relatively higher values in 2011, 2013, and 2015. Our results
suggest that the land-derived input will remarkably increase over time in a
warming scenario. Further studies are therefore needed to understand the
future response of the Kongsfjorden ecosystem alterations with respect to the
enhanced release of glacier-derived material
Sinking diatom assemblages as a key driver for deep carbon and silicon export in the Scotia Sea (Southern Ocean)
Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global ocean carbon sequestration, has been identified as a scientific priority. Here we use
novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental
conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.CTM2009-08287-E/ANT, CTM2011-14056E/ANT, SGR 315 2017info:eu-repo/semantics/publishedVersio
Retinal thickness study with optical coherence tomography in patients with diabetes
To quantitatively assess retinal thickness by optical coherence
tomography (OCT) in normal subjects and patients with diabetes. This study was
intended to determine which retinal thickness value measured with OCT best
discriminates between diabetic eyes, with and without macular edema. METHODS: OCT
retinal thickness was measured by a manual technique in a total of 26 healthy
volunteers (44 control eyes) and 85 patients with diabetes (148 eyes) with the
clinical diagnosis of no diabetic retinopathy (45 eyes), nonproliferative
diabetic retinopathy without clinically significant macular edema (CSME; 54
eyes), proliferative diabetic retinopathy without CSME (21 eyes), and 28 eyes
with diabetic retinopathy with CSME. Independent predictors of the presence of
CSME were quantified by using univariate and multivariate logistic regression
analyses. Receiver operating characteristic (ROC) curves were generated to
evaluate and compare the predictor variables. The correlation of retinal
thickness measurements and visual acuity was calculated. RESULTS: There were
statistically significant differences in foveal thickness between control eyes
and all the other eye groups (P = 0.001). Diabetic eyes with CSME had a
statistically significant greater thickness in each of the areas compared with
the other groups. In a multivariate logistic regression model, foveal thickness
was a strong and independent predictor of CSME (odds ratio [OR], 1.037; 95%
confidence interval [CI] 1.02-1.05). The area under the ROC curve of this
predictor variable was 0.94 (P = 0.001). For a cutoff point of 180 microm, the
sensitivity was 93%, and specificity was 75%. Foveal thickness correlated with
visual acuity in a log minimum angle of resolution (logMAR) scale (Spearman's rho
= 0.9, P = 0.001). CONCLUSIONS: These results suggest that foveal thickening over
180 microm measured by OCT may be useful for the early detection of macular
thickening and may be an indicator for a closer follow-up of the patient with
diabetes
Journals’ policies of storage and reuse of raw research data and their impact in five scientific areas
Analisys of journals' policies about storage and re-use of raw research data
Validity of a self-reported diagnosis of depression among participants in a cohort study using the Structured Clinical Interview for DSM-IV (SCID-I).
Abstract
Background: Depression assessment in population studies is usually based on depressive
symptoms scales. However, the use of scales could lead to the choice of an arbitrary cut-off
point depending on the sample characteristics and on the patient diagnosis. Thus, the use of a
medical diagnosis of depression could be a more appropriate approach.
Objective: To validate a self-reported physician diagnosis of depression using the Structured
Clinical Interview for DSM-IV (SCID-I) as Gold Standard and to assess the factors associated to
a valid self-reported diagnosis.
Methods: The SUN Project is a cohort study based on university graduates followed-up through
postal questionnaires. The response to the question included in the questionnaire: Have you
ever been diagnosed of depression by a physician? was compared to that obtained through the
SCID-I applied by a psychiatrist or a clinical psychologist. The percentages of confirmed
depression and non-depression were assessed for the overall sample and according to several
characteristics. Logistic regression models were fitted to ascertain the association between
different factors and a correct classification regarding depression status.
Results: The percentage of confirmed depression was 74.2%; 95% confidence interval (95%
CI) =63.3-85.1. Out of 42 participants who did not report a depression diagnosis in the
questionnaire, 34 were free of the disease (%confirmed non-depression=81.1%; 95% CI=69.1-
92.9). The probability of being a true positive was higher among ex- smokers and non-smokers
and among those overweight or obese but the differences were not statistically significant.
Conclusion: The validity of a self-reported diagnosis of depression in the SUN cohort is
adequate. Thus, this question about depression diagnosis could be used in further
investigations regarding this disease in this graduate cohort study
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