Collective resonances in plasmonic crystals: Size matters

Periodic arrays of metallic nanoparticles may sustain Surface Lattice Resonances (SLRs), which are collective resonances associated with the diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By investigating a series of arrays with varying number of particles, we traced the evolution of SLRs to its origins. Polarization resolved extinction spectra of arrays formed by a few nanoparticles were measured, and found to be in very good agreement with calculations based on a coupled dipole model. Finite size effects on the optical properties of the arrays are observed, and our results provide insight into the characteristic length scales for collective plasmonic effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than 20 x 20 particles, the Q-factors of SLRs saturate at a much larger value than those of LSPRs; in between, the Q-factors of SLRs are an increasing function of the number of particles in the array.Comment: 4 figure

Nekrasov-Shatashvili limit of the 5D superconformal index

C. P. is supported by the Royal Society through a University Research Fellowship. A. P. and D. R. G. are partly supported by the Spanish Government Grant No. MINECO-13-FPA2012-35043-C02-02. In addition, they acknowledge financial support from the Ramon y Cajal Grant No. RYC-2011-07593 as well as the EU CIG Grant No. UE-14-GT5LD2013-618459. The work of A. P. is funded by the Asturian Government SEVERO OCHOA Grant No. BP14-003

Modeling the Dynamics of Online Learning Activity

People are increasingly relying on the Web and social media to find solutions to their problems in a wide range of domains. In this online setting, closely related problems often lead to the same characteristic learning pattern, in which people sharing these problems visit related pieces of information, perform almost identical queries or, more generally, take a series of similar actions. In this paper, we introduce a novel modeling framework for clustering continuous-time grouped streaming data, the hierarchical Dirichlet Hawkes process (HDHP), which allows us to automatically uncover a wide variety of learning patterns from detailed traces of learning activity. Our model allows for efficient inference, scaling to millions of actions taken by thousands of users. Experiments on real data gathered from Stack Overflow reveal that our framework can recover meaningful learning patterns in terms of both content and temporal dynamics, as well as accurately track users' interests and goals over time

Modeling the Dynamics of Online Learning Activity

People are increasingly relying on the Web and social media to find solutions to their problems in a wide range of domains. In this online setting, closely related problems often lead to the same characteristic learning pattern, in which people sharing these problems visit related pieces of information, perform almost identical queries or, more generally, take a series of similar actions. In this paper, we introduce a novel modeling framework for clustering continuous-time grouped streaming data, the hierarchical Dirichlet Hawkes process (HDHP), which allows us to automatically uncover a wide variety of learning patterns from detailed traces of learning activity. Our model allows for efficient inference, scaling to millions of actions taken by thousands of users. Experiments on real data gathered from Stack Overflow reveal that our framework can recover meaningful learning patterns in terms of both content and temporal dynamics, as well as accurately track users' interests and goals over time

Dielectric branes in non-trivial backgrounds

We present a procedure to evaluate the action for dielectric branes in non-trivial backgrounds. These backgrounds must be capable to be taken into a Kaluza-Klein form, with some non-zero wrapping factor. We derive the way this wrapping factor is gauged away. Examples of this are AdS_5xS^5 and AdS_3xS^3xT^4, where we perform the construction of different stable systems, which stability relies in its dielectric character.Comment: 14 pages, published versio

Parental Involvement between Two Different Urban Communities

Parent involvement is an integral part of a child’s educational progress. In some cases, students’ academic achievement can be directly related to the level of parental involvement exhibited in schools. Families’ perception of roles toward parental involvement in schools may vary among groups from diverse cultures. In today’s urban schools, the increasing diversity of cultures may contribute to differences in levels of parental involvement. The purpose of this research is to address the need to promote parental participation in the educational process of their children. This study will focus on three research questions: Are there differences in levels of parental involvement after participating in a program designed to assist them with their children’s reading skills? Are there changes in the attitudes of families towards parental involvement after participating in the instructional cycle? Is there a relationship between the level of parental involvement and student academic achievement

Preliminary optical design of PANIC, a wide-field infrared camera for CAHA

In this paper, we present the preliminary optical design of PANIC (PAnoramic Near Infrared camera for Calar Alto), a wide-field infrared imager for the Calar Alto 2.2 m telescope. The camera optical design is a folded single optical train that images the sky onto the focal plane with a plate scale of 0.45 arcsec per 18 micron pixel. A mosaic of four Hawaii 2RG of 2k x 2k made by Teledyne is used as detector and will give a field of view of 31.9 arcmin x 31.9 arcmin. This cryogenic instrument has been optimized for the Y, J, H and K bands. Special care has been taken in the selection of the standard IR materials used for the optics in order to maximize the instrument throughput and to include the z band. The main challenges of this design are: to produce a well defined internal pupil which allows reducing the thermal background by a cryogenic pupil stop; the correction of off-axis aberrations due to the large field available; the correction of chromatic aberration because of the wide spectral coverage; and the capability of introduction of narrow band filters (~1%) in the system minimizing the degradation in the filter passband without a collimated stage in the camera. We show the optomechanical error budget and compensation strategy that allows our as built design to met the performances from an optical point of view. Finally, we demonstrate the flexibility of the design showing the performances of PANIC at the CAHA 3.5m telescope.Comment: This paper has been presented in the SPIE of Astronomical Telescopes and Instrumentation 2008 in Marseille (France