Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud [2] A. Giesen, H. Hügel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud [3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 74, 185 (2002).\ud [4] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud [5] M.C. Pujol, X. Mateos, R. Solé, J. Massons, J. Gavaldà, F. Díaz, M. Aguiló, Mater. Sci. Forum 378-381, 710 (2001).\ud [6] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75, 59 (2002)

Liquid phase epitaxy and spectroscopic investigation of optically active KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm, which provides high efficiency and reduced heat generation. A promising material for Yb3+ lasers is KYb(WO4)2 (KYbW) [1]. It can be grown from high-temperature solutions [2]. A suitable substrate material for the growth of single-crystalline layers with thicknesses in the range of the absorption length of ~13 µm at 981 nm is KY(WO4)2 (KYW).\ud We demonstrate the liquid phase epitaxy (LPE) of KYbW layers at start temperatures as low as 520°C from the chloride solvent KCl-NaCl-CsCl. This temperature is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented KYW substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. Our spectroscopic investigations show that the fluorescence lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [2]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 2002, 74, 185\ud [2] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 2002, 65, 16512

European macroeconomic imbalances at a sectorial level: Evidence from German and Spanish food industry

P u r p o s e: This research has analyzed the structural differences observed comparing medium size Spanish and German firms in the food industry, specifically biscuit production. A second objective has been to analyze if the different macroeconomic conditions in Spain and Germany have affected the performance of firms. Design/methodology: Using financial information from AMADEUS data base, a sample of firms (135 observations) in the food industry from Spain and Germany have been analyzed, considering the changes observed in the periods 2007-2009, 2010-2012 and 2013-2015. Productivity, real investment, cost per employee, profitability and interests paid by the firms are among the variables considered. The different hypotheses proposed have been tested using non-parametric test, mainly, Mann-Whitney test and Rho Spearman coefficient. Findings: Medium size German firms are bigger, using number of employees, than Spanish firms and show a higher profitability (using ROE) whatever the period consider. The evidence suggests that after a certain threshold size the correlation between size and productivity is negative. An interesting result is the negative correlation between interest rate and labour productivity; financial conditions can have a clear effect on firm’s performance. At this sector level there is no evidence of the process of internal devaluation, probably because the growth observed either by increase in real investment or sales have been accompanied by the need to hire skilled labour. Research limitations/implications: The main limitation is that this research has only focused on particular economic activity, biscuit producers, to include others firms in the food industry must be considered in future research. Practical implications: Size is a strategic decision that managers must face, to understand how labour productivity and financial performance is affected by size will help to take the optimum decision. The performance of the firm is also partially affected by the interest rate that the firm faces, the negative correlation found between interest rate and labour productivity is important in informing right decisions about increasing firm’s debt level. Social implications: Europe is rethinking industrial policy in the aftermath of the financial crisis (20082009) and in a global context with an increasing number of industrial activities locating in low labour costs destinations. Understanding the structural differences that industries across the European countries show is a key factor in deciding an efficient industrial policy. Originality/value: The last decade has accentuated the macroeconomic differences, in terms of long term interest rates or levels of unemployment between the core of Europe, Germany, and the periphery, including countries like Spain. This research is one the first ones in analyzing how these differences are affecting financial performance and structural differences in a particular industry, that is one of the most important exporters of the European Union.Peer Reviewe

Una estrategia de cambio conceptual en la enseñanza de la física : la resolución de problemas como actividad de investigación

We present in this paper the main results of a research aimed at the study of a learninglteaching process directed to familiarise the students with a researching methodology of open problem solving centered in the Physics field. We have studied how this process favours in the students a conceptual change, incardinated in the learning constructivist theory and whether this change lasts with time and is joined by a positive attitude towards the scientific learning

Resolver situaciones problemáticas en genética para modificar las actitudes relacionadas con la ciencia

Las actitudes como contenido escolar son difíciles a la hora de enseñar y de valorar su nivel de adquisición. En este estudio nos centramos en las actitudes sobre la ciencia como conocimiento y hacia la ciencia como asignatura académica. Presentamos los resultados de una investigación comparativa realizada con alumnos de 4º de educación secundaria obligatoria (15-16 años) que se acercaron a la genética desde dos perspectivas distintas, una metodología tradicional para el grupo control y una unidad didáctica basada en la resolución de situaciones problemáticas, «¿Soy así por puro azar?», para el experimental. Al fi nalizar el proceso de enseñanza-aprendizaje, el grupo control mantuvo sus actitudes iniciales mientras que el experimental manifestó actitudes más favorables y realistas sobre y hacia la ciencia.Attitudes as scholar content are diffi cult to teach and their level of acquisition is diffi cult to assess. In this study we focus on attitudes about Science as knowledge and towards Science as academic subject. We present the results of a comparative investigation carried out with students of fourth level of Obligatory Secondary Education (15-16 years) who approached Genetics from two different perspectives, a traditional methodology for the control group and a didactic unit based on the resolution of problematic situations, «Am I like this by pure chance?», for the experimental one. At the end of the teaching-learning process the control group maintained its initial attitudes while the experimental one showed realistic and more favourable attitudes about and toward Science

On the possible observational signatures of white dwarf dynamical interactions

We compute the possible observational signatures of white dwarf dynamical interactions in dense stellar environments. Specifically, we compute the emission of gravitational waves, and we compare it with the sensitivity curves of planned space-borne gravitational wave detectors. We also compute the light curves for those interactions in which a detonation occurs, and one of the stars is destroyed, as well as the corresponding neutrino luminosities. We find that for the three possible outcomes of these interactions - which are the formation of an eccentric binary system, a lateral collision in which several mass transfer episodes occur, and a direct one in which just a single mass transfer episode takes place - only those in which an eccentric binary are formed are likely to be detected by the planned gravitational wave mission eLISA, while more sensitive detectors would be able to detect the signals emitted in lateral collisions. On the other hand, the light curves (and the thermal neutrino emission) of these interactions are considerably different, producing both very powerful outbursts and low luminosity events. Finally, we also calculate the X-ray signature produced in the aftermath of those interactions for which a merger occurs. We find that the temporal evolution follows a power law with the same exponent found in the case of the mergers of two neutron stars, although the total energy released is smaller.Comment: 14 pages, 11 figures. Accepted for publication in MNRA

Creative economy employment in the EU and the UK: a comparative analysis

Analysts and policymakers have long complained of the dearth of internationally comparable statistics on the creative industries because it has made it impossible to benchmark the performance of different countries. In January 2014, the Department for Culture, Media and Sport (DCMS) adopted the Dynamic Mapping methodology for classifying some industries as ‘creative’ and others not, for the purposes of producing the UK’s Creative Industries Economic Estimates (DCMS, 2014). This methodology is based on the theoretical and empirical argument that the creative industries are “those industries that specialise in the employment of creative talent for commercial purposes” (Bakhshi, Hargreaves and Mateos–Garcia, 2013) – that is, have unusually high proportions of their workforce employed in creative occupations (‘creative intensity’). Through its use of Standard Industrial Classification (SIC) codes and labour force survey data, the Dynamic Mapping methodology was designed to enable the production of internationally comparable statistics (Bakhshi, Freeman and Higgs 2013)

Reproductive inequalities in the acanthocephalan Corynosoma cetaceum: looking beyond "crowding" effects

Background: At present, much research effort has been devoted to investigate overall (average) responses of parasite populations to specific factors, e.g., density-dependence in fecundity or mortality. However, studies on parasite populations usually pay little attention to individual variation (inequality) in reproductive success. A previous study on the acanthocephalan Corynosoma cetaceum in franciscana dolphins, Pontoporia blainvillei, revealed no overall intensity-dependent, or microhabitat effects, on mass and fecundity of worms. In this study, we investigated whether the same factors could influence mass inequalities for this species of acanthocephalan.Methods: A total of 10,138 specimens of C. cetaceum were collected from 10 franciscana dolphins accidentally caught in Buenos Aires Province between 1988-1990. To investigate mass inequalities, all the specimens were sexed, and females were classified according to their developmental stage and weighted. Additionally, the relationship between biomass and fecundity (estimated as the number of acanthors) was investigated for some females. Inequalities in fecundity and biomass were assessed using standard methods, i.e. the Lorenz curve and the Gini coefficient (G).Results: We found a modest, but highly significant linear relationship between mass and fecundity. The G was very low (0.314) compared with that from other helminth species. G values were significantly lower in gravid females, which presumably exhibit a slow rate of growth. Also, G values significantly increased with total intensity, but only for gravid females, and the effect was more predictable considering only the number of gravid females.Conclusions: Apparently, competition between reproducing females increases inequality without producing crowding effects. Although the mechanism whereby this occurs is unclear, gravid females, at higher intensities, expanded their distribution and occupied gut chambers with contrasting environmental conditions, which might result in greater variability in body size. The observed inequalities are not expected to strongly influence the population genetics of C. cetaceum, but they reveal subtle individual effects beyond an overall population impact.Fil: Aznar Avendaño, Francisco Javier. Universidad de Valencia; EspañaFil: Hernández Orts, Jesús Servando. Universidad Nacional del Comahue. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni". - Provincia de Río Negro. Ministerio de Agricultura, Ganadería y Pesca. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni". Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Centro Nacional Patagónico. Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos "Almirante Storni"; ArgentinaFil: Vélez Rubio, Gabriela Manuela. Universidad de Valencia; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de la República; UruguayFil: Fernández, Luis M.. Ceiba Foundation for Tropical Conservation; Estados UnidosFil: Muriel, Nadia T.. No especifíca;Fil: Raga, Juan Antonio. Universidad de Valencia; Españ

Discovery of kilogauss magnetic fields in three DA white dwarfs

We have detected longitudinal magnetic fields between 2 and 4 kG in three (WD 0446$-$790, WD 1105$-$048, WD 2359$-$434) out of a sample of 12 normal DA white dwarfs by using optical spectropolarimetry done with the VLT Antu 8 m telescope equipped with FORS1. With the exception of 40 Eri B (4 kG) these are the first positive detections of magnetic fields in white dwarfs below 30 kG. Although suspected, it was not clear whether a significant fraction of white dwarfs contain magnetic fields at this level. These fields may be explained as fossil relics from magnetic fields in the main-sequence progenitors considerably enhanced by magnetic flux conservation during the shrinkage of the core. A detection rate of 25 % (3/12) may indicate now for the first time that a substantial fraction of white dwarfs have a weak magnetic field. This result, if confirmed by future observations, would form a cornerstone for our understanding on the evolution of stellar magnetic fields. Keywords: stars: white dwarfs - stars: magnetic fields - stars: individual: WD0446-790, WD1105-048, WD2359-434Comment: 15 pages, 7 figures, Astronomy and Astrophysics, in pres