44 research outputs found
Transport and Localisation in the Presence of Strong Structural and Spin Disorder
We study a tight binding model including both on site disorder and coupling
of the electrons to randomly oriented magnetic moments. The transport
properties are calculated via the Kubo-Greenwood scheme, using the exact
eigenstates of the disordered system and large system size extrapolation of the
low frequency optical conductivity. We first benchmark our method in the model
with only structural disorder and then use it to map out the transport regimes
and metal- insulator transitions in problems involving (i) scattering from
random magnetic moments, and (ii) the combined effect of structural disorder
and magnetic scattering. We completely map out the dependence of the d.c
conductivity on electron density (n) the structural disorder (\Delta) and the
magnetic coupling (J'), and locate the insulator-metal phase boundary in the
space of n-\Delta-J'. These results serve as a reference for understanding
transport in systems ranging from magnetic semiconductors to double exchange
`colossal magnetoresistance' systems. A brief version of this study appears in
our earlier paper Europhys. Lett. vol 65, 75 (2004).Comment: 14 pages revtex. Final version, to appear in EPJ
Macroscopic Strings and "Quirks" at Colliders
We consider extensions of the standard model containing additional heavy
particles ("quirks") charged under a new unbroken non-abelian gauge group as
well as the standard model. We assume that the quirk mass m is in the
phenomenologically interesting range 100 GeV--TeV, and that the new gauge group
gets strong at a scale Lambda < m. In this case breaking of strings is
exponentially suppressed, and quirk production results in strings that are long
compared to 1/Lambda. The existence of these long stable strings leads to
highly exotic events at colliders. For 100 eV < Lambda < keV the strings are
macroscopic, giving rise to events with two separated quirk tracks with
measurable curvature toward each other due to the string interaction. For keV <
Lambda < MeV the typical strings are mesoscopic: too small to resolve in the
detector, but large compared to atomic scales. In this case, the bound state
appears as a single particle, but its mass is the invariant mass of a quirk
pair, which has an event-by-event distribution. For MeV < Lambda < m the
strings are microscopic, and the quirks annihilate promptly within the
detector. For colored quirks, this can lead to hadronic fireball events with
10^3 hadrons with energy of order GeV emitted in conjunction with hard decay
products from the final annihilation.Comment: Added discussion of photon-jet decay, fixed minor typo
Are Managers’ Perceptions of Constraints to Growth Reliable? Evidence from a Natural Experiment in South Africa
A systematic review of mental disorder, suicide, and deliberate self harm in lesbian, gay and bisexual people
Background: Lesbian, gay and bisexual (LGB) people may be at higher risk of mental disorders than heterosexual people.Method: We conducted a systematic review and meta-analysis of the prevalence of mental disorder, substance misuse, suicide, suicidal ideation and deliberate self harm in LGB people. We searched Medline, Embase, PsycInfo, Cinahl, the Cochrane Library Database, the Web of Knowledge, the Applied Social Sciences Index and Abstracts, the International Bibliography of the Social Sciences, Sociological Abstracts, the Campbell Collaboration and grey literature databases for articles published January 1966 to April 2005. We also used Google and Google Scholar and contacted authors where necessary. We searched all terms related to homosexual, lesbian and bisexual people and all terms related to mental disorders, suicide, and deliberate self harm. We included papers on population based studies which contained concurrent heterosexual comparison groups and valid definition of sexual orientation and mental health outcomes.Results: Of 13706 papers identified, 476 were initially selected and 28 (25 studies) met inclusion criteria. Only one study met all our four quality criteria and seven met three of these criteria. Data was extracted on 214,344 heterosexual and 11,971 non heterosexual people. Meta-analyses revealed a two fold excess in suicide attempts in lesbian, gay and bisexual people [ pooled risk ratio for lifetime risk 2.47 (CI 1.87, 3.28)]. The risk for depression and anxiety disorders (over a period of 12 months or a lifetime) on meta-analyses were at least 1.5 times higher in lesbian, gay and bisexual people (RR range 1.54-2.58) and alcohol and other substance dependence over 12 months was also 1.5 times higher (RR range 1.51-4.00). Results were similar in both sexes but meta analyses revealed that lesbian and bisexual women were particularly at risk of substance dependence (alcohol 12 months: RR 4.00, CI 2.85, 5.61; drug dependence: RR 3.50, CI 1.87, 6.53; any substance use disorder RR 3.42, CI 1.97-5.92), while lifetime prevalence of suicide attempt was especially high in gay and bisexual men (RR 4.28, CI 2.32, 7.88).Conclusion: LGB people are at higher risk of mental disorder, suicidal ideation, substance misuse, and deliberate self harm than heterosexual people