Lasers incorporating two-dimensional photonic crystal mirrors

Photonic bandgap crystals are expected to be of use in defining microcavities for modifying spontaneous emission and as highly reflective mirrors. There are several reports of microfabricating one-dimensional structure. Here, we describe the incorporation of a microfabricated two-dimensional photonic lattice in an edge-emitting semiconductor laser structure. We demonstrate laser operation in a cavity formed between a cleaved facet and a microfabricated periodic lattice

Modal reflectivity in finite-depth two-dimensional photonic-crystal microcavities

We present finite-difference time-domain calculations of the Q factor for an optical microcavity defined by a slab waveguide and two-dimensional photonic-crystal end mirrors. The effect of the finite depth of the photonic crystal on the cavity s optical modes is examined. From these calculations, we can optimize the performance of the photonic-crystal mirrors and determine the loss mechanisms within optical cavities defined by these structures. The Q of the cavity modes is shown to be strongly dependent on the depth of the holes defining the photonic crystal, as well as the refractive index of the material surrounding the waveguide core

Alternative gravity rotation curves for the Little Things Survey

Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. These galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, the THINGS (The HI Nearby Galactic Survey) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we present a thorough application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity and Modified Newtonian Dynamics. An analysis and discussion of the results of the fitting procedure of the two alternative gravitational models are explored, as well as the resulting rotation curve predictions of each. Further, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. We posit here that both conformal gravity and MOND can provide an accurate description of the galactic dynamics without the need for dark matter.Comment: 13 Pages, 7 Figures, Accepted in Astrophysical Journa

Optical Synthesis of Terahertz and Millimeter-Wave Frequencies with Discrete Mode Diode Lasers

It is shown that optical synthesis of terahertz and millimeter-wave frequencies can be achieved using two-mode and mode-locked discrete mode diode lasers. These edge-emitting devices incorporate a spatially varying refractive index profile which is designed according to the spectral output desired of the laser. We first demonstrate a device which supports two primary modes simultaneously with high spectral purity. In this case sinusoidal modulation of the optical intensity at terahertz frequencies can be obtained. Cross saturation of the material gain in quantum well lasers prevents simultaneous lasing of two modes with spacings in the millimeter-wave region. We show finally that by mode-locking of devices that are designed to support a minimal set of four primary modes, we obtain a sinusoidal modulation of the optical intensity in this frequency region.Comment: 6 page

The international humanitarian sector and language translation in crisis situations: assessment of current practices and future needs

Assessment Focus During major social disruptions, such as civil conflicts, natural disasters, or other crises, access to information is of fundamental importance to response and recovery operations. Ability to understand the language in which information is disseminated is a key marker of social vulnerability to disasters or crises. Assessing the degree to which the service efforts of organizations involved in the humanitarian sector are informed by commitment to multilingual communication and language translation is important to understanding how these organizations contribute to risk reduction and improved community resilience. This short report provides an assessment of the current state of practice and key language access issues in the humanitarian sector. Guiding Questions Assessment of the efforts in the humanitarian sector in crisis relief and recovery work can be understood in the context of the 2016 World Humanitarian Summit’s Grand Bargain commitments to reform aspects of humanitarian organizations’ relief work. Among those goals are key pronouncements on accountability, localization, and participation; language is integral to each. Because of the importance of language access to risk reduction and resilience in crisis situations, the assessment here attempts to address three questions: (1) what is the significance of language access to international humanitarian assistance efforts?; (2) what constitutes effective practices or key challenges at present?; and (3) what is the prospect for humanitarian organizations’ managing language access needs in the future? Key Findings Study subjects voiced near unanimity that providing language access is fundamentally important to humanitarian operations, but, at present, the capacity to formalize or routinize such efforts is limited; There was wide-spread consensus that accommodating language needs is necessary for achieving the Grand Bargain’s aim of two-way communication for greater accountability of operational humanitarian organizations towards affected communities; Accommodating language needs is consistently seen as a complex task; currently, even when there is capacity to address the issue, there is no agreement on how language needs should be accommodated; Language access capabilities may go beyond budget or staff resources and include issues of modality, culture, politics, ownership within the organizations, etc.; Key gaps in practice render service delivery less effective. Implications & Recommendations Findings suggest defined “ownership” of language translation within an organization is key to effective practice; Incorporating more systematic efforts on language translation in humanitarian operations is directly relevant to the Grand Bargain goals of accountability, localization, and participation in serving affected communities; Establishing systematic provision for communication in local languages in humanitarian response plans is crucial as the world is facing increasing hazard vulnerability; Improving humanitarian assistance requires management solutions such as better integration of language access provision with the cluster system

The expanding bipolar shell of the helium nova V445 Puppis

From multi-epoch adaptive optics imaging and integral field unit spectroscopy, we report the discovery of an expanding and narrowly confined bipolar shell surrounding the helium nova V445 Puppis (Nova Puppis 2000). An equatorial dust disc obscures the nova remnant, and the outflow is characterized by a large polar outflow velocity of 6720 +/- 650 km s(-1) and knots moving at even larger velocities of 8450 +/- 570 km s(-1). We derive an expansion parallax distance of 8.2 +/- 0.5 kpc and deduce a pre-outburst luminosity of the underlying binary of log L/L-circle dot = 4.34 +/- 0.36. The derived luminosity suggests that V445 Puppis probably contains a massive white dwarf accreting at high rate from a helium star companion making it part of a population of binary stars that potentially lead to supernova Ia explosions due to accumulation of helium-rich material on the surface of a massive white dwarf

Learning to teach (LETS): developing curricular and cross curricular competences in becoming a 'good' secondary teacher: executive summary

The aim of this research, the Learning to Teach Study (LETS), the first of its kind on the Postgraduate Diploma in Education (PGDE) in Ireland, funded by the Department of Education and Skills (DES), was to develop and implement a study of initial teacher education in the PGDE in post-primary education, in the School of Education, University College Cork. Its aim was to identify the individual and contextual dynamics of how student teachers develop curricular and cross-curricular competences during initial teacher education (ITE). Within an overall framework that explores how student teachers develop their skills, competences and identity as teachers, it focuses on curricular competences in mathematics, science and language teaching, and on the cross-curricular competences of reading and digital literacy and the development of inclusive teaching practices. LETS is the first programme level research on the PGDE, familiarly known to generations of student teachers and teachers as ‘the Dip’ or ‘the HDip’. Drawing on research on teacher education both in Ireland and internationally, the LETS report is divided into six sections encompassing thirteen chapters. Section 1 includes the review of literature and study aims in Chapter 1 and the research methodology in Chapter 2. Adopting an interpretive approach, LETS involved the collaborative development of three interviews protocols and a survey by the research team. Seventeen (n=17) students were interviewed three times over the course of PGDE programme, and one hundred and thirty three students completed a detailed survey on their learning to teach experience (n=133, i.e. response rate of 62.7% of the 212 students in the PGDE 2008/09 cohort). The four chapters in Section 2 focus on professional identity as a central dimension of learning to teach. Among the dimensions of learning to teach addressed in this section are the role of observation and cultural scripts in becoming a teacher, the visibility/invisibility of PGDE students as learners and the relationships between emotions, resilience and commitment to teaching. The three chapters in Section 3 focus on mathematics, modern languages and science respectively in the context of conventional and reform-oriented visions of good teaching. A number of common as well as subject-specific themes emerged in this section in relation to subject matter teaching. Section 4 focuses on PGDE students’ experience of inclusion (chapter 10) and reading literacy (chapter 11) while learning to teach. Section 5 focuses on a key aspect of initial teacher education, namely, the school-university partnership. The final section provides a summary of the findings, identifies seven key issues emerging from these findings, makes Learning to Teach Study (LETS) recommendations under four headings (system, teacher education institutions, partnerships in ITE and further research) and discusses some implications for research, policy and practice in initial teacher education. Among the main findings emerging from the study are: (i) schools provide valuable support for PGDE students but this typically does not focus on classroom pedagogy, (ii) PGDE students typically felt that they had to be ‘invisible’ as learners in schools to gain and maintain authority and status, (iii) inherited cultural scripts about what it means to be a ‘good’ subject teacher shaped teacher identity and classroom practice, and (iv) as PGDE students begin to feel competent as teachers of maths, modern languages and science, this feeling of competence typically does not include their capacity to teach for inclusion and reading literacy within their subject teaching. In the context of research on teacher education, many of the findings are not unique to the PGDE or to UCC but reflect perennial dilemmas and emerging challenges in initial teacher education. This fact is important in setting a context for the wider dissemination2 of the Learning to Teach Study