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Non peer reviewe

Coexistence of Haldane gap excitations and long-range order in R_2BaNiO_5 (RR=rare earth)

$R_2BaNiO_5$ ($R=$ rare earth) quasi-1-D antiferromagnets are structurally equivalent to the well-studied 1-D S=1 Haldane-gap compound Y_2BaNiO_5. Unlike the Y-nickelate though, these materials undergo 3-D magnetic ordering at finite temperatures. Recent inelastic neutron scattering studies of Pr_2BaNiO_5 and (Nd_{x}Y_{1-x})_2BaNiO_5 revealed purely 1-dimensional gap excitations that propagate exclusively on the Ni-chains and are strikingly similar to Haldane gap modes in Y_2BaNiO_5. In the ordered phase these excitations survive and actually coexist with conventional spin waves. Below $T_{N}$ the gap energy increases and scales as the square of the ordered moment on the Ni sites. The results suggest that the Haldane singlet ground state of the Ni-chains is not fully destroyed by N\'{e}el ordering.Comment: Invited paper for the International Conference on Neutron Scattering, Toronto, Canada, August 17-21, 199

Neutron-diffraction study of field-induced transitions in the heavy-fermion compound Ce2RhIn8

We present neutron diffraction measurements in high magnetic fields (0 to 14.5 T) and at low temperatures (2.5, 2.3, 0.77 and 0.068 K) on single crystals of the tetragonal heavy fermion antiferromagnet Ce2RhIn8. For B//[110] the field dependence of selected magnetic and nuclear reflections reveals that the material undergoes several transitions, the temperature dependence of which suggests a complex B-T phase diagram. We present the detailed evolution of the integrated intensities of selected reflections and discuss the associated field-induced transitions.Comment: 12 pages, 3 figures Proceeding Euro-conference "Properties of Condensed Matter probed by x-ray and neutron scattering"; to appear in Physica

1001 Caras : aprender a través del arte en el aula de 3 años

Este artículo recoge la experiencia en un Centro Educativo de la Sierra de Madrid, llevada a cabo con un grupo de primero de Educación Infantil (3 años).\ud Se trata de un proyecto globalizado enmarcado dentro de una pedagogía\ud activa en el que todas las áreas se entremezclan: expresión oral, educación artística, conocimiento del medio¿\ud El punto de partida es un cuadro de la segunda mitad del siglo XVIII: «Retrato\ud femenino»atribuido a un seguidor de Antón Van Dyck.\ud El proyecto se estructura en tres momentos: antes, durante y después de la visita al Gabinete Artístico donde se encuentra el cuadro escogido.This article shows an experience developed in a school located in the Sierra de Madrid area with children aged three (1st grade Early Children Education). The experience is a global project framed within an active pedagogy, in which all areas are entwined: oral expression, arts education, environment knowledge,\ud etc. The main resource has been a painting from the 2nd half of the 18th century titled «Feminine Portrait», attributed to a follower of the Flemish painter Anton Van\ud Dyck. The project is divided into three stages: before, during, and after the visit to an\ud art gallery, named El Gabinete Artístico, where the chosen painting is shown

A microscopic model for a class of mixed-spin quantum antiferromagnets

We propose a microscopic model that describes the magnetic behavior of the mixed-spin quantum systems R$_2$BaNiO$_5$ (R= magnetic rare earth). An evaluation of the properties of this model by Quantum Monte Carlo simulations shows remarkable good agreement with the experimental data and provides new insight into the physics of mixed-spin quantum magnets.Comment: revised version to be published in Phys. Rev.

An experimental measurement of the staggered magnetization curve for a Haldane spin chain

Long-range magnetic ordering in R_2 Ba Ni O_5 (R=magnetic rare earth) quasi-1-dimensional mixed-spin antiferromagnets is described by a simple mean-field model that is based on the intrinsic staggered magnetization function of isolated Haldane spin chains for the Ni-subsystem, and single-ion magnetization functions for the rare earth ions. The model is applied to new experimental results obtained in powder diffraction experiments on Nd_2 Ba Ni O_5 and Nd Y Ba Ni O_5, and to previously published diffraction data for Er_2 Ba Ni O_5. From this analysis we extract the bare staggered magnetization curve for Haldane spin chains in these compounds.Comment: some revisions in text and figures 5 pages, 2 figures, PRL accepted for publicatio

Magnetic ordering, spin waves, and Haldane gap excitations in (Nd_x Y_{1-x})_2 Ba Ni O_5 linear-chain mixed-spin antiferromagnets

Linear-chain nickelates with the composition (Nd_x Y_{1-x})_2 Ba Ni O_5 (x=1, x=0.75, x=0.5, and x=0.25) are studied in a series of neutron scattering experiments. Powder diffraction is used to determine the temperature dependence of the magnetic structure in all four systems. Single-crystal inelastic neutron scattering is employed to investigate the temperature dependence of the Haldane-gap excitations and low-energy spin waves in the x=1 compound Nd_2 Ba Ni O_5. The results of these experiments are discussed in the context of the ``Haldane chain in a staggered field'' model for R_2 Ba Ni O_5 systems, and quantitative agreement with theory is obtained.Comment: Major rewriting and inclusion of new experimental data 30 pages, 14 figure

Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings

This paper was published in OPTICS LETTERS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.36.002104. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law[EN] Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment. © 2011 Optical Society of America.This work was financially supported by the European Commission under the FP7 EURO-FOS Network of Excellence (ICT-2007-2-224402), the Ministerio de Educación y Ciencia SINADEC project (TEC2008-06333), and the Natural Sciences and Engineering Research Council of Canada (NSERC). The work of G. E. Villanueva was supported by the Ministerio de Educación y Ciencia Formación de Profesorado Universitario programs. The work of P. Pérez-Millán was supported by the Juan de la Cierva program, JCI-2009-05805.Villanueva Ibáñez, GE.; Jakubinek, M.; Simard, B.; Oton Nieto, CJ.; Matres Abril, J.; Shao, L.; Pérez Millán, P.... (2011). Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings. Optics Letters. 36(11):2104-2106. https://doi.org/10.1364/OL.36.002104S210421063611Sakakibara, Y., Rozhin, A. G., Kataura, H., Achiba, Y., & Tokumoto, M. (2005). Carbon Nanotube-Poly(vinylalcohol) Nanocomposite Film Devices: Applications for Femtosecond Fiber Laser Mode Lockers and Optical Amplifier Noise Suppressors. Japanese Journal of Applied Physics, 44(4A), 1621-1625. doi:10.1143/jjap.44.1621Chow, K. K., Yamashita, S., & Song, Y. W. (2009). A widely tunable wavelength converter based on nonlinear polarization rotation in a carbon-nanotube-deposited D-shaped fiber. Optics Express, 17(9), 7664. doi:10.1364/oe.17.007664Set, S. Y., Yaguchi, H., Tanaka, Y., & Jablonski, M. (2004). Ultrafast Fiber Pulsed Lasers Incorporating Carbon Nanotubes. IEEE Journal of Selected Topics in Quantum Electronics, 10(1), 137-146. doi:10.1109/jstqe.2003.822912Chow, K. K., Tsuji, M., & Yamashita, S. (2010). Single-walled carbon-nanotube-deposited tapered fiber for four-wave mixing based wavelength conversion. Applied Physics Letters, 96(6), 061104. doi:10.1063/1.3304789Chow, K. K., & Yamashita, S. (2009). Four-wave mixing in a single-walled carbon-nanotube-deposited D-shaped fiber and its application in tunable wavelength conversion. Optics Express, 17(18), 15608. doi:10.1364/oe.17.015608Choi, S. Y., Rotermund, F., Jung, H., Oh, K., & Yeom, D.-I. (2009). Femtosecond mode-locked fiber laser employing a hollow optical fiber filled with carbon nanotube dispersion as saturable absorber. Optics Express, 17(24), 21788. doi:10.1364/oe.17.021788Chan, C.-F., Chen, C., Jafari, A., Laronche, A., Thomson, D. J., & Albert, J. (2007). Optical fiber refractometer using narrowband cladding-mode resonance shifts. Applied Optics, 46(7), 1142. doi:10.1364/ao.46.001142Kingston, C. T., Jakubek, Z. J., Dénommée, S., & Simard, B. (2004). Efficient laser synthesis of single-walled carbon nanotubes through laser heating of the condensing vaporization plume. Carbon, 42(8-9), 1657-1664. doi:10.1016/j.carbon.2004.02.020Jakubinek, M. B., Johnson, M. B., White, M. A., Guan, J., & Simard, B. (2010). Novel Method to Produce Single-Walled Carbon Nanotube Films and Their Thermal and Electrical Properties. Journal of Nanoscience and Nanotechnology, 10(12), 8151-8157. doi:10.1166/jnn.2010.3014Vallaitis, T., Koos, C., Bonk, R., Freude, W., Laemmlin, M., Meuer, C., … Leuthold, J. (2008). Slow and fast dynamics of gain and phase in a quantum dot semiconductor optical amplifier. Optics Express, 16(1), 170. doi:10.1364/oe.16.00017

“Ha! Suck on that Corona, I Found Something to Do” : Capturing Adolescent Experiences during Lockdown in Finland

Peer reviewe

From bits to templates: Uncovering digital interventions in everyday history assignments at secondary school

This article explores the way students construct historical narrations in the digital age. The study, which is based on participant observation in two secondary schools in Finland, aligns with previous ethnographic research on how digital media interrupts and integrates in the formation of everyday habits and routines. The focus of the analysis is on short oral presentations of historical phenomena given by students in front of the class. During these short assignments students engage more in digital practices than doing other activities. The findings show that the accumulation of these brief assignments allows students to develop “templates for history”, which I argue are elements from which they develop expectations of historical accounts for use in building their own stories. These templates include frequently consulted digital sources such as Wikipedia, and images that students find online that affect the perspective of their presentations. To these can be added other situated factors that derive from the course dynamics, such as the limited time allocated for assignments, teacher instruction in the form of inquiry or a presentation structure, and historical substance that is fragmented and arranged around single assignments. Thus far, studies on digital transformations in school history have focused on how the use of digitized primary sources can teach students to walk in the shoes of historians. The present study, in turn, concerns the ubiquitous digital culture and paraphernalia in schools. The aim is to offer teachers ways of connecting with familiar practices and to shed light on how these practices can support peer-learning, as well as to promote the idea of doing history as a collective and ever-revisiting task: all these are important objectives of school history.Peer reviewe