CCD photometry of distant comets. III - Ensemble properties of Jupiter-family comets

We describe the results of a ground-based observational "snapshot" study of Jupiter-family comets in the heliocentric range 2.29 AU less than or equal to R-h less than or equal to 5.72 AU. Results are presented based on observations from the 1m JKT on the island of La Palma. A total of 25 comets were targeted with 15 being positively detected. Broad-band VRI photometry was performed to determine dimensions, colour indices, and dust production rates in terms of the "A frho" formalism. The results for selected comets are compared with previous investigations. Ensemble properties of the Jupiter- family population have been investigated by combining the results presented here with those of Lowry et al. (1999), and Lowry & Fitzsimmons (2001). We find that the cumulative size distribution of the Jupiter-family comets can be described by a power law of the form; Sigma(> r) proportional to r(-1.6+/- 0.1). This size distribution is considerably shallower than that found for the observed Edgeworth-Kuiper belt objects, which may reflect either an intrinsic difference at small km- sizes in the belt, or the various processes affecting the nuclei of comets as their orbits evolve from the Edgeworth- Kuiper belt to the inner Solar system. Also, there would appear to be no correlation between nuclear absolute magnitude and perihelion distance. Finally, for the sample of active comets, there is a distinct correlation between absolute R band magnitude and perihelion distance, which can be explained by either a discovery bias towards brighter comets or in terms of "rubble" mantle formation.

‘Doing it with men’: feminist research practice and patriarchal inheritance practices in Welsh family farming

Internationally, the gender relations of the family farming ‘way of life’ have beenshown to be stubbornly persistent in their adherence to patriarchal inheritancepractices. This article demonstrates how such ‘agri-cultural’ practices are situated bothwithin the subjective sphere of farming individuals’ and within global agri-economics,bringing new challenges to patrilineal farm survival. It is suggested here that the recenttendency for post-structuralist theorisation in rural studies has underestimated theexistence and impact of patrilineal patterns in family farming. Such patterns mean thatwomen are shown to largely occupy relational gender identities as the ‘helper’, whilstmen are strongly identified as the ‘farmer’. Drawing on repeated life-history interviewsconducted with farming men and women from Powys, Mid Wales, the aim of thisarticle is to generate debate as to the extent to which men can be brought into feministresearch practice in order to reveal patriarchy to a greater degree. The article begins bysituating the near-exclusion of men from feminist research practice within theoreticaldevelopments in feminist geography. This discussion also assists in deriving issues ofresearch methods, positionality and interpretive power which focus the integration ofempirical material in the methodological reflections provided in section three. In sectiontwo, the rationale for the epistemological stance taken in the research is provided. Thearticle provides an example of the successful integration of men into a feminist researchframe, suggests avenues for theoretical development and identifies future researchdirections which can be informed by ‘doing it with men’.

Keywords: epistemology; family farming; feminist res

Further reflections on Habermas's contribution to discourse in child protection: An examination of power in social life

Hayes and Houston's positive review of Habermas's contribution to discourse in family group conferences (in this journal) has been challenged by Garrett. In this paper, one of the authors replies to Garrett but extends the analysis through a more considered, developed and detailed examination of Habermas's thoughts on power in social life. This leads to a conceptual framework that enables the participants in the conference to exercise power in a positive manner. In developing this earlier analysis, the paper also acknowledges Garrett's argument that Bourdieu helps us to understand the nature of constraining social structures in child protection. However, Bourdieu's ideas are subsequently challenged on the grounds that they lack a competent formulation on human agency - a faculty that Habermas cogently elucidates. This enlarged understanding of agency, it is argued, offers a theoretical resource that fits better with the ethos of emancipatory social work.

Home curation versus teenage photography: Photo displays in the family home

In this paper we report an empirical study of the photographic portrayal of family members at home. Adopting a social psychological approach and focusing oil intergenerational power dynamics, our research explores the use of domestic photo displays in family representation. Parents and their teenagers from eight families in the south of England were interviewed at home about their interpretations of both stored and displayed photos within the home. Discussions centred on particular photographs found by the participants to portray self and family in different ways. The findings show that public displays of digital photos are still curated by mothers of the households, but with more difficulty and less control all with analogue photos. In addition, teenagers both contribute and comply with this curation within the home, whilst at the same time developing additional ways of presenting their families and themselves online that are 'unsupervised' by the curator. We highlight the conflict of interest that is at play within teen and parent practices and consider the challenges that this presents for supporting the representation of family through the design of photo display technology. (C) 2009 Elsevier Ltd. All rights reserved.

Analysis and Design of Class-E3F and Transmission-Line Class-E3F2 Power Amplifiers

In this paper, analysis and synthesis approach for two new variants within the Class-EF power amplifier (PA) family is elaborated. These amplifiers are classified here as Class-E3 F2 and transmission-line (TL) Class-E3 F 2. The proposed circuits offer means to alleviate some of the major issues faced by existing topologies such as substantial power losses due to the parasitic resistance of the large inductor in the Class-EF load network and deviation from ideal Class-EF operation due to the effect of device output inductance at high frequencies. Both lumped-element and transmission-line load networks for the Class-E 3 F PA are described. The load networks of the Class-E3 F and TL Class-E 3 F2amplifier topologies developed in this paper simultaneously satisfy the Class-EF optimum impedance requirements at fundamental frequency, second, and third harmonics as well as simultaneously providing matching to the circuit optimum load resistance for any prescribed system load resistance. Optimum circuit component values are analytically derived and validated by harmonic balance simulations. Trade-offs between circuit figures of merit and component values with some practical limitations being considered are discussed. © 2010 IEEE.

The size distribution of Jupiter Family comet nuclei

We present an updated cumulative size distribution (CSD) for Jupiter Family comet (JFC) nuclei, including a rigorous assessment of the uncertainty on the slope of the CSD. The CSD is expressed as a power law, N(>rN) ?r-qN, where rN is the radius of the nuclei and q is the slope. We include a large number of optical observations published by us and others since the comprehensive review in the Comets II book, and make use of an improved fitting method. We assess the uncertainty on the CSD due to all of the unknowns and uncertainties involved (photometric uncertainty, assumed phase function, albedo and shape of the nucleus) by means of Monte Carlo simulations. In order to do this we also briefly review the current measurements of these parameters for JFCs. Our final CSD has a slope q= 1.92 ± 0.20 for nuclei with radius rN= 1.25 km.

The legacy of Hillsborough:Liberating truth, challenging power

In April 1989, ninety-six men, women and children, supporters of Liverpool Football Club, died in a severe crush at an FA Cup semi-final at Hillsborough Stadium, Sheffield. Hundreds were injured and thousands traumatised. Within hours, the causes and circumstances of the disaster were contested. While a judicial inquiry found serious institutional failures in the policing and management of the capacity crowd, no criminal prosecutions resulted, and the inquests returned ‘accidental death’ verdicts. Immediately, the authorities claimed that drunken, violent fans had caused the fatal crush. Denied legitimacy, survivors’ accounts revealed a different story criticising the parlous state of the stadium, inadequate stewarding, negligent policing, failures in the emergency response and flawed processes of inquiry and investigation. Reflecting on two decades of research and contemporaneous interviews with bereaved families and survivors, this article contrasts the official discourse with those alternative accounts – the ‘view from below’. It demonstrates the influence of powerful institutional interests on the inquiries and investigations. It maps the breakthrough to full documentary disclosure following the appointment of the Hillsborough Independent Panel, its research and key findings published in September 2012. The campaigns by families and survivors were vindicated and the fans, including those who died, were exonerated. The process is discussed as an alternative method for liberating truth, securing acknowledgement and pursuing justice.

Thermal properties, sizes, and size distribution of Jupiter-family cometary nuclei

We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 using imaging capabilities of the Spitzer Space Telescope. The comets were typically 4-5 AU from the Sun when observed and most showed only a point-source with little or no extended emission from dust. For those comets showing dust, we used image processing to photometrically extract the nuclei. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We have six main conclusions: (a) The average beaming parameter of the JFC population is 1.03 ± 0.11, consistent with unity; coupled with the large distance of the nuclei from the Sun, this indicates that most nuclei have Tempel 1-like thermal inertia. Only two of the 57 nuclei had outlying values (in a statistical sense) of infrared beaming. (b) The known JFC population is not complete even at 3 km radius, and even for comets that approach to ˜2 AU from the Sun and so ought to be more discoverable. Several recently-discovered comets in our survey have small perihelia and large (above ˜2 km) radii. (c) With our radii, we derive an independent estimate of the JFC nuclear cumulative size distribution (CSD), and we find that it has a power-law slope of around -1.9, with the exact value depending on the bounds in radius. (d) This power-law is close to that derived by others from visible-wavelength observations that assume a fixed geometric albedo, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3-6 km. (f) Our CSD is consistent with the idea that the intrinsic size distribution of the JFC population is not a simple power-law and lacks many sub-kilometer objects.

Time-dependent Suppression of Oscillatory Power in Evolving Solar Magnetic Fields

Oscillation amplitudes are generally smaller within magnetically active regions like sunspots and plage when compared to their surroundings. Such magnetic features, when viewed in spatially resolved power maps, appear as regions of suppressed power due to reductions in the oscillation amplitudes. Employing high spatial- and temporal-resolution observations from the Dunn Solar Telescope (DST) in New Mexico, we study the power suppression in a region of evolving magnetic fields adjacent to a pore. By utilizing wavelet analysis, we study for the first time how the oscillatory properties in this region change as the magnetic field evolves with time. Image sequences taken in the blue continuum, G-band, Ca ii K, and Hα filters were used in this study. It is observed that the suppression found in the chromosphere occupies a relatively larger area, confirming previous findings. Also, the suppression is extended to structures directly connected to the magnetic region, and is found to get enhanced as the magnetic field strength increased with time. The dependence of the suppression on the magnetic field strength is greater at longer periods and higher formation heights. Furthermore, the dominant periodicity in the chromosphere was found to be anti-correlated with increases in the magnetic field strength.