The radial abundance gradient of oxygen towards the Galactic anticentre

We present deep optical spectroscopy of eight HII regions located in the anticentre of the Milky Way. The spectra were obtained at the 10.4m GTC and 8.2m VLT. We determined Te([NII]) for all objects and Te([OIII]) for six of them. We also included in our analysis an additional sample of 13 inner-disc Galactic Hii regions from the literature that have excellent T_e determinations. We adopted the same methodology and atomic dataset to determine the physical conditions and ionic abundances for both samples. We also detected the CII and OII optical recombination lines in Sh 2-100, which enables determination of the abundance discrepancy factor for this object. We found that the slopes of the radial oxygen gradients defined by the HII regions from R_25 (= 11.5 kpc) to 17 kpc and those within R_25 are similar within the uncertainties, indicating the absence of flattening in the radial oxygen gradient in the outer Milky Way. In general, we found that the scatter of the O/H ratios of Hii regions is not substantially larger than the observational uncertainties. The largest possible local inhomogeneities of the oxygen abundances are of the order of 0.1 dex. We also found positive radial gradients in Te([O III]) and Te([N II]) across the Galactic disc. The shapes of these temperature gradients are similar and also consistent with the absence of flattening of the metallicity distribution in the outer Galactic disc.Comment: 20 pages, 11 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Los políticos, la política y la hacienda : breve opúsculo

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

The effect of heat treatments on the constituent materials of a nuclear reactor pressure vessel in hydrogen environment

AbstractA nuclear reactor pressure vessel (NRPV) wall is formed by two layer of different materials: an inner layer of stainless steel (cladding material) and an outer layer of low carbon steel (base material) which is highly susceptible to corrosion related phenomena. A reduction of the mechanical properties of both materials forming the wall would appear due to the action of the harsh environment causing hydrogen embrittlement (HE) related phenomena. As a result of the manufacturing process, residual stresses and strains appear in the NRPV wall, thereby influencing the main stage in HE: hydrogen diffusion. A common engineering practice for reducing such states is to apply a tempering heat treatment. In this paper, a numerical analysis is carried out for revealing the influence of the heat treatment parameters (tempering temperature and tempering time) on the HE of a commonly used NRPV. To achieve this goal, a numerical model of hydrogen diffusion assisted by stress and strain was used considering diverse residual stress-strain states after tempering. This way, the obtained hydrogen accumulation during operation time of the NRPV provides insight into the better tempering conditions from the structural integrity point of view

Environmentally-assisted fatigue crack growth in prestressing steel wires

This paper presents the evolution of the surface crack front in prestressing reinforced concrete steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)₂+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan law, and using a threeparameter solution for stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth and by the variation of the maximum dimensionless SIF at the crack front.Описано еволюцію фронту поверхневої тріщини в сталевих дротах для переднапруженого стану залізобетону, підданих втомному навантаженню на повітрі і корозійній втомі в середовищі Ca(OH)₂ + NaCl. На основі дискретизації чисельно змодельовано фронт тріщини, який приймали еліптичним, і вважали, що тріщина в кожній точці просувається перпендикулярно до її фронту згідно з законом Періса–Ердогана. Використовували трипараметричний розв’язок для коефіцієнта інтенсивності напружень (КІН). Кожний з аналізованих випадків, якому відповідала певна початкова геометрія тріщини, характеризувався еволюцією форми напівеліптичної тріщини (відношення півосей еліпса) і відносної її глибини, а також варіацією значень максимального безрозмірного КІН вздовж фронту тріщини.Описана эволюция фронта поверхностной трещины в стальных проволоках для преднапряженного состояния железобетона, подвергаемых усталости на воздухе и коррозионной усталости в среде Ca(OH)₂+ NaCl. На основе дискретизации численно смоделирован фронт трещины, который принимали полуэллиптическим, и считали, что трещина в каждой точке движется перпендикулярно к ее фронту согласно закону Пэриса– Эрдогана. Использовали трехпараметрическое решение для коэффициента интенсивности напряжений (КИН). Каждый из анализированных случаев, которому соответствовала определенная начальная геометрия трещины, характеризовался эволюцией формы полуэллиптической трещины (отношение полуосей эллипса) и относительной ее глубины, а также изменением значений максимального безразмерного КИН вдоль фронта трещины