Radius of a Photon Beam with Orbital Angular Momentum

We analyze the transverse structure of the Gouy phase shift in light beams carrying orbital angular momentum and show that the Gouy radius $r_G$ characterizing the transverse structure grows as $\sqrt{2p+|\ell|+1}$ with the nodal number $p$ and photon angular momentum number $\ell$. The Gouy radius is shown to be closely related to the root-mean-square radius of the beam, and the divergence of the radius away from the focal plane is determined. Finally, we analyze the rotation of the Poynting vector in the context of the Gouy radius.Comment: 11 page

Are British Muslims alienated from mainstream politics by Islamophobia and British foreign policy?

This paper uses the 2010 Ethnic Minority British Election Study to look at the political attitudes of Muslims in Britain. It tests the relationship between political alienation and political participation on the one hand, and Islamophobia and disapproval of British military involvement in Afghanistan on the other. The principal findings are that perceptions of Islamophobia are linked to greater political alienation, to a greater likelihood of non-electoral participation and to a lower likelihood of voting among Muslims. Likewise, disapproval of the war in Afghanistan is associated with greater political alienation and a greater likelihood of some types of non-electoral participation. There is strong evidence that British Muslims are more likely to interpret discrimination they experience as motivated by their religion and that they perceive more prejudice at the group level. These findings have two theoretical implications. First, they support the theory that non-electoral participation is motivated by dissatisfaction with the party political system. Second, they suggest that perceptions of sociotropic discrimination (for minorities) and a rare salient political issue in which all parties are in opposition to most voters can lead to negative affect towards the political system and stimulate non-electoral participation at the expense of voting. </jats:p

The general relativistic Poynting-Robertson effect

The general relativistic version is developed for Robertson's discussion of the Poynting-Robertson effect that he based on special relativity and Newtonian gravity for point radiation sources like stars. The general relativistic model uses a test radiation field of photons in outward radial motion with zero angular momentum in the equatorial plane of the exterior Schwarzschild or Kerr spacetime.Comment: 19 pages iop style, 8 eps figure files for 5 figure

The song of the dunes as a self-synchronized instrument

Since Marco Polo (1) it has been known that some sand dunes have the peculiar ability of emitting a loud sound with a well defined frequency, sometimes for several minutes. The origin of this sustained sound has remained mysterious, partly because of its rarity in nature (2). It has been recognized that the sound is not due to the air flow around the dunes but to the motion of an avalanche (3), and not to an acoustic excitation of the grains but to their relative motion (4-7). By comparing several singing dunes and two controlled experiments, one in the laboratory and one in the field, we here demonstrate that the frequency of the sound is the frequency of the relative motion of the sand grains. The sound is produced because some moving grains synchronize their motions. The existence of a velocity threshold in both experiments further shows that this synchronization comes from an acoustic resonance within the flowing layer: if the layer is large enough it creates a resonance cavity in which grains self-synchronize.Comment: minor changes, essentially more references

Nonlinear Stability in the Generalised Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag

The Nonlinear stability of triangular equilibrium points has been discussed in the generalised photogravitational restricted three body problem with Poynting-Robertson drag. The problem is generalised in the sense that smaller primary is supposed to be an oblate spheroid. The bigger primary is considered as radiating. We have performed first and second order normalization of the Hamiltonian of the problem. We have applied KAM theorem to examine the condition of non-linear stability. We have found three critical mass ratios. Finally we conclude that triangular points are stable in the nonlinear sense except three critical mass ratios at which KAM theorem fails.Comment: Including Poynting-Robertson Drag the triangular equilibrium points are stable in the nonlinear sense except three critical mass ratios at which KAM theorem fail

Minority youth, crime, conflict, and belonging in Australia

In recent decades, the size and diversity of the minority population of contemporary western societies has increased significantly. To the critics of immigration, minority youth have been increasingly linked to crime, criminal gangs, anti-social behaviour, and riots. In this article, we draw on fieldwork conducted in Sydney, Australia's largest and most ethnically diverse city, to probe aspects of the criminality, anti-social behaviour, national identity, and belonging of ethnic minority youth in Australia. We conclude that the evidence on minority youth criminality is weak and that the panic about immigrant youth crime and immigrant youth gangs is disproportionate to the reality, drawing on and in turn creating racist stereotypes, particularly with youth of 'Middle Eastern appearance'. A review of the events leading up to the Sydney Cronulla Beach riots of December 2005 suggests that the underlying cause of the riots were many years of international, national, and local anti-Arab, anti-Muslim media discourse, and political opportunism, embedded in changing but persistent racist attitudes and practises. Our argument is that such inter-ethnic conflict between minority and majority youth in Sydney is the exception, not the rule. Finally, we draw on a hitherto unpublished survey of youth in Sydney to explore issues of national identity and belonging among young people of diverse ethnic and religious background. We conclude that minority youth in Sydney do not live 'parallel lives' but contradictory, inter-connected cosmopolitan lives. They are connected to family and local place, have inter-ethnic friendships but are often disconnected to the nation and the flag. © 2009 Springer Science+Business Media B.V

Tidal Heating Models for the Radii of the Inflated Transiting Giant Planets WASP-4b, WASP-6b, WASP-12b, and TrES-4

In order to explain the inflated radii of some transiting extrasolar giant planets, we investigate a tidal heating scenario for the inflated planets WASP-4b, WASP-6b, WASP-12b, WASP-15b, and TrES-4. To do so, we assume that they retain a nonzero eccentricity, possibly by dint of continuing interaction with a third body. We calculate the amount of extra heating in the envelope that is then required to fit the radius of each planet, and we explore how this additional power depends on the planetary atmospheric opacity and on the mass of a heavy-element central core. There is a degeneracy between the core mass $M_{\rm core}$ and the heating $\dot{E}_{\rm heating}$. Therefore, in the case of tidal heating, there is for each planet a range of the couple $\{M_{\rm core},e^2/Q'_p\}$ that can lead to the same radius, where $Q'_p$ is the tidal dissipation factor and $e$ is the eccentricity. With this in mind, we also investigate the case of the non-inflated planet HAT-P-12b, which can admit solutions combining a heavy-element core and tidal heating. A substantial improvement of the measured eccentricities of such planetary systems could simplify this degeneracy by linking the two unknown parameters $\{M_{\rm core},Q'_p\}$. Further independent constraints on either of these parameters would, through our calculations, constrain the other.Comment: Accepted in ApJ; 17 pages, 3 figures, 6 tables (emulateapj format); expanded explanatory tex

Does the Radiative Avalanche Fueling Work in Any Active Galactic Nuclei ?

Recently Umemura, Fukue, & Mineshige (1997) proposed the radiative avalanche fueling to active galactic nuclei; gas accretion is driven by radiation drag exerted by stellar radiation from circumnuclear starburst regions. This mechanism is also interesting in terms of starburst-AGN connections. We therefore present observational tests for the radiative avalanche fueling. Our tests, however, show that gas accretion rates driven by the radiative avalanche are significantly lower than those expected from the standard accretion theory applied for typical active galactic nuclei with the circumnuclear starburst regions. Instead we propose an alternative, possible starburst-AGN connection; a minor merger with a nucleated satellite drives circumnuclear starbursts and then leads to gas fueling onto the central engine as the merger proceeds.Comment: 12 page

Bring a plate: facilitating experimentation in the Welcome Dinner Project

Drawing on in-depth empirical research, we explore a project called The Welcome Dinner (WDP). The WDP aims to bring together ‘newly arrived’ people and ‘established Australians’ to meet and ‘share stories’ over a potluck meal in ‘the comfort of their own home’. The purpose is to create meaningful connections, new friendships and social solidarities. In this paper, we focus on the micro-contexts of the dinners and the minute activities and techniques that facilitators use in hosting. Our aim is not to analyse the effects of the project but rather the design and meaning of the activities. As a form of ‘designed everyday multiculturalism’, focused on welcoming new arrivals to Australia, it takes effort, skill and labour to manage the contact between different cultural groups over organised meals. Thus, facilitators take over the hosting of the lunches and dinners to run activities, which are imagined to lubricate social dynamics and relations, and produce convivial commensal affects and behaviours. Drawing on theories of training activities as embodied and cognitive experimentations, which enable new knowledge practices and social relations, we analyse field notes and interviews about the facilitation, structure and activities at the WDP home dinners

Alert but less alarmed: a pooled analysis of terrorism threat perception in Australia

<p>Abstract</p> <p>Background</p> <p>Previous Australian research has highlighted disparities in community perceptions of the threat posed by terrorism. A study with a large sample size is needed to examine reported concerns and anticipated responses of community sub-groups and to determine their consistency with existing Australian and international findings.</p> <p>Methods</p> <p>Representative samples of New South Wales (NSW) adults completed terrorism perception questions as part of computer assisted telephone interviews (CATI) in 2007 (N = 2081) and 2010 (N = 2038). Responses were weighted against the NSW population. Data sets from the two surveys were pooled and multivariate multilevel analyses conducted to identify health and socio-demographic factors associated with higher perceived risk of terrorism and evacuation response intentions, and to examine changes over time.</p> <p>Results</p> <p>In comparison with 2007, Australians in 2010 were significantly more likely to believe that a terrorist attack would occur in Australia (Adjusted Odd Ratios (AOR) = 1.24, 95%CI:1.06-1.45) but felt less concerned that they would be directly affected by such an incident (AOR = 0.65, 95%CI:0.55-0.75). Higher perceived risk of terrorism and related changes in living were associated with middle age, female gender, lower education and higher reported psychological distress. Australians of migrant background reported significantly lower likelihood of terrorism (AOR = 0.52, 95%CI:0.39-0.70) but significantly higher concern that they would be personally affected by such an incident (AOR = 1.57, 95%CI:1.21-2.04) and having made changes in the way they live due to this threat (AOR = 2.47, 95%CI:1.88-3.25). Willingness to evacuate homes and public places in response to potential incidents increased significantly between 2007 and 2010 (AOR = 1.53, 95%CI:1.33-1.76).</p> <p>Conclusion</p> <p>While an increased proportion of Australians believe that the national threat of terrorism remains high, concern about being personally affected has moderated and may reflect habituation to this threat. Key sub-groups remain disproportionately concerned, notably those with lower education and migrant groups. The dissonance observed in findings relating to Australians of migrant background appears to reflect wider socio-cultural concerns associated with this issue. Disparities in community concerns regarding terrorism-related threat require active policy consideration and specific initiatives to reduce the vulnerabilities of known risk groups, particularly in the aftermath of future incidents.</p