Expansion in perfect groups

Let Ga be a subgroup of GL_d(Q) generated by a finite symmetric set S. For an integer q, denote by Ga_q the subgroup of Ga consisting of the elements that project to the unit element mod q. We prove that the Cayley graphs of Ga/Ga_q with respect to the generating set S form a family of expanders when q ranges over square-free integers with large prime divisors if and only if the connected component of the Zariski-closure of Ga is perfect.Comment: 62 pages, no figures, revision based on referee's comments: new ideas are explained in more details in the introduction, typos corrected, results and proofs unchange

Roadwork:Expertise at work building roads in the Maldives

This article engages critically with concepts of ‘skill’, ‘expertise’, and ‘capacity’ as they operate as markers of distinction and domination and shape migratory labour relations among road construction workers from across South Asia in the Maldives archipelago. The article examines roadwork at three levels: the professional biographies leading to ‘flexible specialization’ rather than technical expertise amongst Maldivian managers; the technical expertise and social incorporation of ‘skilled’ Sri Lankan supervisors; and the key material expertise of ‘non-skilled’ Bangladeshi labourers in precarious employment. Whilst discussions of South Asian labour migration have been dominated by caste and class, this article argues that it is important to consider how the cultural production and understanding of concepts such as ‘expertise’, ‘capacity’, and ‘exposure’ at worksites can (also) become distinguishing factors in (hierarchical) migratory labour relations

Expansion in SL_d(Z/qZ), q arbitrary

Let S be a fixed finite symmetric subset of SL_d(Z), and assume that it generates a Zariski-dense subgroup G. We show that the Cayley graphs of pi_q(G) with respect to the generating set pi_q(S) form a family of expanders, where pi_q is the projection map Z->Z/qZ

Regular graphs of large girth and arbitrary degree

For every integer d > 9, we construct infinite families {G_n}_n of d+1-regular graphs which have a large girth > log_d |G_n|, and for d large enough > 1,33 log_d |G_n|. These are Cayley graphs on PGL_2(q) for a special set of d+1 generators whose choice is related to the arithmetic of integral quaternions. These graphs are inspired by the Ramanujan graphs of Lubotzky-Philips-Sarnak and Margulis, with which they coincide when d is prime. When d is not equal to the power of an odd prime, this improves the previous construction of Imrich in 1984 where he obtained infinite families {I_n}_n of d+1-regular graphs, realized as Cayley graphs on SL_2(q), and which are displaying a girth > 0,48 log_d |I_n|. And when d is equal to a power of 2, this improves a construction by Morgenstern in 1994 where certain families {M_n}_n of 2^k+1-regular graphs were shown to have a girth > 2/3 log_d |M_n|.Comment: (15 pages) Accepted at Combinatorica. Title changed following referee's suggestion. Revised version after reviewing proces

Quantum cat maps with spin 1/2

We derive a semiclassical trace formula for quantized chaotic transformations of the torus coupled to a two-spinor precessing in a magnetic field. The trace formula is applied to semiclassical correlation densities of the quantum map, which, according to the conjecture of Bohigas, Giannoni and Schmit, are expected to converge to those of the circular symplectic ensemble (CSE) of random matrices. In particular, we show that the diagonal approximation of the spectral form factor for small arguments agrees with the CSE prediction. The results are confirmed by numerical investigations.Comment: 26 pages, 3 figure

From Victims of Trafficking to Freedom Fighters: Rethinking Migrant Domestic Workers in the Middle East

Throughout the Middle East migrant women are employed to work in people’s homes. While some experience good working relations with employers, others experience forms of abuse and labour coercion. This chapter evaluates critically different ways that system of unfree labour has been variously described and analysed as a form of ‘contract slavery’, ‘debt bondage’ and ‘trafficking’. It also shows how migrant women who describe themselves as ‘freelancers’ exit their original employer’s home both to escape that relation and in hopes of securing a better situation outside of the regular system of employment. Freelancing is more than simply a form of resistance. Rather, women who work as freelance migrant domestic workers challenge directly that state enforced control over their mobility and are on the vanguard of those migrants who are seeking through their own actions to effect social change

Democracy, development and the executive presidency in Sri Lanka

This paper examines the developmental causes and consequences of the shift from a parliamentary to a semi-presidential system in Sri Lanka in 1978, examining its provenance, rationale, and its unfolding trajectory. drawing on a wide range of sources, it set out an argument that the executive presidency was born out of an elite impulse to create a more stable, centralised political structure to resist the welfarist electoral pressures that had taken hold in the post-independence period, and to pursue a market-driven model of economic growth. This strategy succeeded in its early years 197801993, when presidents retained legislative control, maintained a strong personal commitment to market reforms, and cultivated alternative sources of legitimacy. In the absence of these factors, the presidency slipped into crisis over 1994-2004 as resistance to elite-led projects of state reform mounted and as the president lost control of the legislature. Since 2005 the presidency has regained its power, but at the cost of abandoning its original rationale and function as a means to recalibrate the elite/mass power relations to facilitate elite-led reform agendas

Diasporic Encounters, Sacred Journeys: Ritual, Normativity and the Religious Imagination Among International Asian Migrant Women

This issue highlights recent ethnographic work that discloses migrant women’s creative engagements with the people and landscapes in the places they migrate to. We challenge a dominant view that construes women international migrants from Asia as docile bodies shaped and constrained by their transnational (re)productive labours. And we reject simplistic contemporary formulations of transnational migration that posit a singular, homogeneous ‘transnational social field’. Three key processes, relatively ignored and under theorised are interrogated: diaspora formation, ritual performance and changing normativities. A focus on diaspora encourages us to move beyond a political and economic analysis to consider cultural practices, continuities and discontinuities in migrants’ relationships with the people and places they travel to, as well as those left behind. A focus on ritual emphasises the significance of religious performance in the making of place and convivial sociality. A focus on normativity foregrounds the ways that people’s affective relationships are performatively reworked and transgressed within and across discrepant diasporic spaces

Transnational migration, changing care arrangements and left-behind children's responses in South-east Asia

The authors are grateful to the Wellcome Trust, UK, for funding the CHAMPSEA project [GR079946/B/06/Z and GR079946/Z/06/Z], Asia Research Institute for funding the conference ‘Inter-Asia Roundtable 2010 – Transnational Migration and Children in Asian Contexts' where this paper was first presented and Singapore Ministry of Education Academic Research Fund Tier 1 (R-109-000-156-112) for supporting the work behind the publication of this paper.Recent increases in the volume of labour migration from South-east Asia – and in particular the feminisation of these movements – suggest that millions of children are growing up in transnational families, separated from their migrant parents. Drawing on both quantitative and qualitative data collected in Indonesia, the Philippines, Thailand and Vietnam, the study seeks to elucidate care arrangements for left-behind children and to understand the ways in which children respond to shifts in intimate family relations brought about by (re)configurations of their care. Our findings emphasise that children, through strategies of resistance, resilience and reworking, are conscious social actors and agents of their own development, albeit within constrained situations resulting from their parents’ migration.Publisher PDFPeer reviewe