Effective medium theories for irregular fluffy structures: aggregation of small particles

We study the extinction efficiencies as well as scattering properties of particles of different porosity. Calculations are performed for porous pseudospheres with small size (Rayleigh) inclusions using the discrete dipole approximation. Five refractive indices of materials covering the range from $1.20+0.00i$ to $1.75+0.58i$ were selected. They correspond to biological particles, dirty ice, silicate, amorphous carbon and soot in the visual part of spectrum. We attempt to describe the optical properties of such particles using Lorenz-Mie theory and a refractive index found from some effective medium theory (EMT) assuming the particle is homogeneous. We refer to this as the effective model. It is found that the deviations are minimal when utilizing the EMT based on the Bruggeman mixing rule. Usually the deviations in extinction factor do not exceed $\sim 5$ for particle porosity ${\cal P}=0 - 0.9$ and size parameters x_{\rm porous} = 2 \pi r_{\rm s, porous}/\lambda \la 25. The deviations are larger for scattering and absorption efficiencies and smaller for particle albedo and asymmetry parameter. Our calculations made for spheroids confirm these conclusions. Preliminary consideration shows that the effective model represents the intensity and polarization of radiation scattered by fluffy aggregates quite well. Thus, the effective models of spherical and non-spherical particles can be used to significantly simplify computations of the optical properties of aggregates containing only Rayleigh inclusions.Comment: 24 pages, 9 figures, accepted for publication in Applied Optic

University-affiliated schools as sites for research learning in pre-service teacher education

This article proposes that the ‘teaching/practice schools’ formally affiliated to initial teacher education programmes at universities, can be utilised more optimally as research sites by student teachers. The argument is put forward with reference to the role that such schools have played historically in teacher education in the United States (US), and more recently, in the successful Finnish teacher education system, in which research is highly valued as a requisite part of a teaching qualification. The authors propose that the single component of these schools, which has historically distinguished them from schools for work integrated learning (WIL), is that they are also research spaces and have retained some of the ‘lab’ character of earlier schools, such as the one established by John Dewey. In such schools, the authors argue, students learn to be reflective practitioners by positioning themselves as researchers, who reflect on practice in a research-rich environment. In a pilot study, the authors found that university and school personnel hold different views about research in the schools. The article recommends that careful consideration be given to the research function in these public schools as part of teacher training.Keywords: activity systems; Dewey; experimental schools; Finland; lab schools; practice schools; practitioner research;reflective practice; teacher education; teaching school

Refined physical properties and g',r',i',z',J,H,K transmission spectrum of WASP-23b from the ground

Multi-band observations of planetary transits using the telescope defocus technique may yield high-quality light curves suitable for refining the physical properties of exoplanets even with small or medium size telescopes. Such observations can be used to construct a broad-band transmission spectrum of transiting planets and search for the presence of strong absorbers. We have thoroughly characterised the orbital ephemeris and physical properties of the transiting planet and host star in the WASP-23b system, constructed a broad-band transmission spectrum of WASP-23b and performed a comparative analysis with theoretical models of hot Jupiters. We observed a complete transit of WASP-23b in seven bands simultaneously, using the GROND instrument on the MPG/ESO 2.2m telescope at La Silla Observatory and telescope defocussing. The optical data were taken in the Sloan g',r',i' and z' bands. The resulting light curves are of high quality, with a root-mean-square scatter of the residual as low as 330ppm in the z'-band, with a cadence of 90s. Near-infrared data were obtained in the JHK bands. We performed MCMC analysis of our photometry plus existing radial velocity data to refine measurements of the ephemeris and physical properties of the WASP-23. We constructed a broad-band transmission spectrum of WASP-23b and compared it with a theoretical transmission spectrum of a Hot Jupiter. We measured the central transit time with a precision about 8s. From this and earlier observations we obtain an orbital period of P=2.9444300+/-0.0000011d. Our analysis also yielded a larger radius and mass for the planet (Rp=1.067+0.045-0.038 RJup and, Mp=0.917+0.040-0.039MJup). The transmission spectrum is marginally flat, given the limited precision of the measurements for the planet radius and poor spectral resolution of the data.Comment: 8 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Leaving the nest: the rise of regional financial arrangements and the future of global governance

This article examines the impact of regional financial arrangements (RFAs) on the global liquidity regime. It argues that the design of RFAs could potentially alter the global regime, whether by strengthening it and making it more coherent or by decentring the International Monetary Fund (IMF) and destabilizing it. To determine possible outcomes, this analysis deploys a ‘middle‐up’ approach that focuses on the institutional design of these RFAs. It first draws on the rational design of institutions framework to identify the internal characteristics of RFAs that are most relevant to their capabilities and capacities. It then applies these insights to the interactions of RFAs with the IMF, building on Aggarwal's (1998) concept of ‘nested’ versus ‘parallel’ institutions, to create an analytical lens through which to assess the nature and sustainability of nested linkages. Through an analysis of the Chiang Mai Initiative Multilateralization (CMIM) and the Latin American Reserve Fund (FLAR), the article demonstrates the usefulness of this lens. It concludes by considering three circumstances in which fault lines created by these RFAs’ institutional design could be activated, permitting an institution to ‘leave the nest’, including changing intentions of principals, creation of parallel capabilities and facilities, and failure of the global regime to address regional needs in a crisis.The authors would like to thank Veronica Artola, Masatsugu Asakawa, Ana Maria Carrasquilla, Junhong Chang, Paolo Hernando, Hoe Ee Khor, Kazunori Koike, Jae Young Lee, Ser-Jin Lee, Guillermo Perry, Yoichi Nemoto, Freddy Trujillo, Masaaki Watanabe, Yasuto Watanabe, Akihiko Yoshida, and others who wished to remain anonymous, for their generosity in providing in-person interviews. Further, the authors would like to thank various central bank and ministry of finance officials of both FLAR and CMIM member countries. We also thank Jose Antonio Ocampo, Diana Barrowclough, and participants in the 'Beyond Bretton Woods' Workshop at Boston University (where an earlier version of this article was presented in September 2017) for their feedback on our broader research projects on RFAs. Last but not least, the authors wish to thank the anonymous referees for their constructive comments. This work builds upon previous work funded by UNCTAD and the Global Economic Governance Initiative at the Global Development Policy Center at Boston University. (UNCTAD; Global Economic Governance Initiative at the Global Development Policy Center at Boston University)Accepted manuscrip

Accretion Disks Around Young Objects. III. Grain Growth

We present detailed models of irradiated T Tauri disks including dust grain growth with power-law size distributions. The models assume complete mixing between dust and gas and solve for the vertical disk structure self-consistentlyincluding the heating effects of stellar irradiation as well as local viscous heating. For a given total dust mass, grain growth is found to decrease the vertical height of the surface where the optical depth to the stellar radiation becomes unit and thus the local irradiation heating, while increasing the disk emission at mm and sub-mm wavelengths. The resulting disk models are less geometrically thick than our previous models assuming interstellar medium dust, and agree better with observed spectral energy distributions and images of edge-on disks, like HK Tau/c and HH 30. The implications of models with grain growth for determining disk masses from long-wavelength emission are considered.Comment: 29 pages, including 11 figures and 1 table, APJ accepte

Simultaneous follow-up of planetary transits: revised physical properties for the planetary systems HAT-P-16 and WASP-21

Context. By now more than 300 planets transiting their host star have been found, and much effort is being put into measuring the properties of each system. Light curves of planetary transits often contain deviations from a simple transit shape, and it is generally difficult to differentiate between anomalies of astrophysical nature (e.g. starspots) and correlated noise due to instrumental or atmospheric effects. Our solution is to observe transit events simultaneously with two telescopes located at different observatories. Aims. Using this observational strategy, we look for anomalies in the light curves of two transiting planetary systems and accurately estimate their physical parameters. Methods. We present the first photometric follow-up of the transiting planet HAT-P-16 b, and new photometric observations of WASP-21 b, obtained simultaneously with two medium-class telescopes located in different countries, using the telescope defocussing technique. We modeled these and other published data in order to estimate the physical parameters of the two planetary systems. Results. The simultaneous observations did not highlight particular features in the light curves, which is consistent with the low activity levels of the two stars. For HAT-P-16, we calculated a new ephemeris and found that the planet is 1.3 \sigma colder and smaller (Rb = 1.190 \pm 0.037 RJup) than the initial estimates, suggesting the presence of a massive core. Our physical parameters for this system point towards a younger age than previously thought. The results obtained for WASP-21 reveal lower values for the mass and the density of the planet (by 1.0 \sigma and 1.4 \sigma respectively) with respect to those found in the discovery paper, in agreement with a subsequent study. We found no evidence of any transit timing variations in either system.Comment: 8 pages, 6 figures, accepted for publication in A&

Physical properties of the WASP-44 planetary system from simultaneous multi-colour photometry

We present ground-based broad-band photometry of two transits in the WASP-44 planetary system obtained simultaneously through four optical (Sloan g', r', i', z') and three near-infrared (NIR; J, H, K) filters. We achieved low scatters of 1-2 mmag per observation in the optical bands with a cadence of 48 s, but the NIR-band light curves present much greater scatter. We also observed another transit of WASP-44 b by using a Gunn-r filter and telescope defocussing, with a scatter of 0.37 mmag per point and an observing cadence around 135 s. We used these data to improve measurements of the time of mid-transit and the physical properties of the system. In particular, we improved the radius measurements of the star and planet by factors of 3 and 4, respectively. We find that the radius of WASP-44 b is 1.002 R_Jup, which is slightly smaller than previously thought and differs from that expected for a core-free planet. In addition, with the help of a synthetic spectrum, we investigated the theoretically-predicted variation of the planetary radius as a function of wavelength, covering the range 370-2440 nm. We can rule out extreme variations at optical wavelengths, but unfortunately our data are not precise enough (especially in the NIR bands) to differentiate between the theoretical spectrum and a radius which does not change with wavelength.Comment: 13 pages, 6 figures, to appear in Monthly Notices of the Royal Astronomical Societ