Cyclotron Maser Emission from Blazar Jets?

We consider the production of electron cyclotron maser emission by low-density, highly magnetized plasmas in relativistic jets. The population inversion required to drive cyclotron maser instability could occur in localized, transient sites where hydromagnetic instabilities, shocks, and/or turbulence lead to magnetic mirroring along current-carrying flux tubes. The maser is pumped as electrons are accelerated by the parallel electric field that develops as a result of the mirror. We estimate the maximum brightness temperatures that can be obtained in a single maser site and in an array of many masers operating simultaneously, under conditions likely to apply in blazar jets. Synchrotron absorption, by relativistic electrons within the jet, presents the largest obstacle to the escape of the maser radiation, and may render most of it invisible. However, we argue that a high brightness temperature could be produced in a thin boundary layer outside the synchrotron photosphere, perhaps in the shear layer along the wall of the jet. Induced Compton scattering provides additional constraints on the maximum brightness temperature of a masing jet. We suggest that recent observations of diffractive scintillation in the blazar J1819+3845, indicating intrinsic brightness temperatures greater than 10^{14} K at 5 GHz, may be explained in terms of cyclotron maser emission. High brightness temperature maser emission from blazar jets may extend to frequencies as high as ~100 GHz, with the maximum possible T_B scaling roughly as 1/frequency. Less massive relativistic jet sources, such as microquasars, are even better candidates for producing cyclotron maser emission, primarily in the infrared and optical bands.Comment: 22 pages, 1 figure, accepted for publication in The Astrophysical Journa

Schizophrenia-risk variant rs6994992 in the neuregulin-1 gene on brain developmental trajectories in typically developing children

The neuregulin-1 (NRG1) gene is one of the best-validated risk genes for schizophrenia, and psychotic and bipolar disorders. The rs6994992 variant in the NRG1 promoter (SNP8NRG243177) is associated with altered frontal and temporal brain macrostructures and/or altered white matter density and integrity in schizophrenic adults, as well as healthy adults and neonates. However, the ages when these changes begin and whether neuroimaging phenotypes are associated with cognitive performance are not fully understood. Therefore, we investigated the association of the rs6994992 variant on developmental trajectories of brain macro- and microstructures, and their relationship with cognitive performance. A total of 972 healthy children aged 3–20 years had the genotype available for the NRG1-rs6994992 variant, and were evaluated with magnetic resonance imaging (MRI) and neuropsychological tests. Age-by-NRG1-rs6994992 interactions and genotype effects were assessed using a general additive model regression methodology, covaried for scanner type, socioeconomic status, sex and genetic ancestry factors. Compared with the C-carriers, children with the TT-risk-alleles had subtle microscopic and macroscopic changes in brain development that emerge or reverse during adolescence, a period when many psychiatric disorders are manifested. TT-children at late adolescence showed a lower age-dependent forniceal volume and lower fractional anisotropy; however, both measures were associated with better episodic memory performance. To our knowledge, we provide the first multimodal imaging evidence that genetic variation in NRG1 is associated with age-related changes on brain development during typical childhood and adolescence, and delineated the altered patterns of development in multiple brain regions in children with the T-risk allele(s)

Transition from ion-coupled to electron-only reconnection: Basic physics and implications for plasma turbulence

Using kinetic particle-in-cell (PIC) simulations, we simulate reconnection conditions appropriate for the magnetosheath and solar wind, i.e., plasma beta (ratio of gas pressure to magnetic pressure) greater than 1 and low magnetic shear (strong guide field). Changing the simulation domain size, we find that the ion response varies greatly. For reconnecting regions with scales comparable to the ion Larmor radius, the ions do not respond to the reconnection dynamics leading to ''electron-only'' reconnection with very large quasi-steady reconnection rates. The transition to more traditional ''ion-coupled'' reconnection is gradual as the reconnection domain size increases, with the ions becoming frozen-in in the exhaust when the magnetic island width in the normal direction reaches many ion inertial lengths. During this transition, the quasi-steady reconnection rate decreases until the ions are fully coupled, ultimately reaching an asymptotic value. The scaling of the ion outflow velocity with exhaust width during this electron-only to ion-coupled transition is found to be consistent with a theoretical model of a newly reconnected field line. In order to have a fully frozen-in ion exhaust with ion flows comparable to the reconnection Alfv\'en speed, an exhaust width of at least several ion inertial lengths is needed. In turbulent systems with reconnection occurring between magnetic bubbles associated with fluctuations, using geometric arguments we estimate that fully ion-coupled reconnection requires magnetic bubble length scales of at least several tens of ion inertial lengths

Simulating open quantum systems: from many-body interactions to stabilizer pumping

In a recent experiment, Barreiro et al. demonstrated the fundamental building blocks of an open-system quantum simulator with trapped ions [Nature 470, 486 (2011)]. Using up to five ions, single- and multi-qubit entangling gate operations were combined with optical pumping in stroboscopic sequences. This enabled the implementation of both coherent many-body dynamics as well as dissipative processes by controlling the coupling of the system to an artificial, suitably tailored environment. This engineering was illustrated by the dissipative preparation of entangled two- and four-qubit states, the simulation of coherent four-body spin interactions and the quantum non-demolition measurement of a multi-qubit stabilizer operator. In the present paper, we present the theoretical framework of this gate-based ("digital") simulation approach for open-system dynamics with trapped ions. In addition, we discuss how within this simulation approach minimal instances of spin models of interest in the context of topological quantum computing and condensed matter physics can be realized in state-of-the-art linear ion-trap quantum computing architectures. We outline concrete simulation schemes for Kitaev's toric code Hamiltonian and a recently suggested color code model. The presented simulation protocols can be adapted to scalable and two-dimensional ion-trap architectures, which are currently under development.Comment: 27 pages, 9 figures, submitted to NJP Focus on Topological Quantum Computatio

Population policies and education: exploring the contradictions of neo-liberal globalisation

The world is increasingly characterised by profound income, health and social inequalities (Appadurai, 2000). In recent decades development initiatives aimed at reducing these inequalities have been situated in a context of increasing globalisation with a dominant neo-liberal economic orthodoxy. This paper argues that neo-liberal globalisation contains inherent contradictions regarding choice and uniformity. This is illustrated in this paper through an exploration of the impact of neo-liberal globalisation on population policies and programmes. The dominant neo-liberal economic ideology that has influenced development over the last few decades has often led to alternative global visions being overlooked. Many current population and development debates are characterised by polarised arguments with strongly opposing aims and views. This raises the challenge of finding alternatives situated in more middle ground that both identify and promote the socially positive elements of neo-liberalism and state intervention, but also to limit their worst excesses within the population field and more broadly. This paper concludes with a discussion outling the positive nature of middle ground and other possible alternatives

3D Magnetic Reconnection with a spatially confined X-line extent -- Implications for Dipolarizing Flux Bundles and the Dawn-Dusk Asymmetry

Using 3D particle-in-cell (PIC) simulations, we study magnetic reconnection with the x-line being spatially confined in the current direction. We include thick current layers to prevent reconnection at two ends of a thin current sheet that has a thickness on an ion inertial (di) scale. The reconnection rate and outflow speed drop significantly when the extent of the thin current sheet in the current direction is < O(10 di). When the thin current sheet extent is long enough, we find it consists of two distinct regions; an inactive region (on the ion-drifting side) exists adjacent to the active region where reconnection proceeds normally as in a 2D case. The extent of this inactive region is ~ O(10 di), and it suppresses reconnection when the thin current sheet extent is comparable or shorter. The time-scale of current sheet thinning toward fast reconnection can be translated into the spatial-scale of this inactive region; because electron drifts inside the ion diffusion region transport the reconnected magnetic flux, that drives outflows and furthers the current sheet thinning, away from this region. This is a consequence of the Hall effect in 3D. While this inactive region may explain the shortest possible azimuthal extent of dipolarizing flux bundles at Earth, it may also explain the dawn-dusk asymmetry observed at the magnetotail of Mercury, that has a global dawn-dusk extent much shorter than that of Earth.Comment: 9 pages, 9 figures, submitted to JGR on 01/23/201

Income and Health in Cities: the Messages from Stylized Facts

The benefits of good health to individuals and to society are strongly positive, and improving the health of the poor is a key millennium development goal (MDG). A typical health strategy advocated by some calls for increased public spending on health targeted to favor the poor backed by foreign assistance, combined with an international effort to perfect drugs and vaccines to ameliorate the major infectious diseases prevalent in developing nations. However, if the objective is better health outcomes at the least cost and a reduction in urban health inequity, our research suggests that the four most potent policy interventions are: improving access to clean water and sanitation; widely available primary care and health programs aimed at influencing diets and lifestyles; raising the level of education; and better urban land use and transport planning which contains urban sprawl and minimizes the trend towards sedentary living habits. The payoff from these four, in terms of health outcomes especially for those in low-income categories, dwarfs the returns from new drugs and curative hospital-based medicine, although these certainly have their place in a modern urban health system. We find, moreover, that the resource requirements for successful health care policies are likely to depend on an acceleration of economic growth rates, which increase household purchasing power and enlarge the pool of resources available to national and subnational governments to invest in and maintain health-related infrastructure and services. Thus, an acceleration of growth rates may be necessary to sustain a viable urban health strategy, which is equitable, and to ensure steady gains in health outcomes

South Sudan's Capability Trap: Building a State with Disruptive Innovation

The prevailing aid orthodoxy works well enough in stable environments, but is ill-equipped to navigate contexts of volatility and fragility. The orthodox approach is adept at solving straightforward technical or logistical problems (paving roads, building schools, immunizing children), but often struggles or outright fails when faced with complex, adaptive challenges (fighting corruption, upholding the rule of law, establishing democratic institutions). South Sudan, the world's newest country, presents a post-conflict environment full of complex, adaptive challenges. Prior to the signing of the Comprehensive Peace Agreement in 2005 South Sudan had no formal institutions of self-governance. During the Comprehensive Peace Agreement period and after independence in 2011, foreign development agencies have contributed billions of dollars of aid and technical assistance to 'build capacity' in the nascent Government of South Sudan. The donors utilized approaches and mechanisms of support that at least nominally reflect the prevailing aid orthodoxy. We argue that orthodox state-building and capacity building more or less failed in South Sudan, leaving the world's newest country mired in a 'capability trap' (Andrews et al. 2012). Despite countless trainings, workshops, reforms, and a large corps of foreign technical assistants embedded within state ministries, there is an absence of real change, and the Government of South Sudan now 'looks like a state' but performs as anything but. The challenges presented by this new, complicated, post-conflict country demand innovative approaches to building state capability which go beyond importing 'best practice' solutions while feigning 'client ownership'. We explore one such approach to disruptive innovation that has emerged: Problem Driven Iterative Adaptation. To escape from the world's newest capability trap, South Sudan's government and its international donors must challenge themselves to imagine innovative paths to state-building, which diverge from 'business as usual' and attempt to create something that lasts

Identifying National Level Education Reforms in Developing Settings: An Application to Ethiopia

Increasing enrollment in primary education has been at the center of international education policy for well over a decade. In developing parts of the world, significant increases in primary enrollment are often generated by large national level programs, which can simultaneously promote overcrowding and reductions in education quality. However, to analyze the trade-off between increased enrollment and potential reductions in quality one must first identify and evaluate the impact of the national reform on schooling. This paper provides a method with which these types of reforms can be identified in developing settings using both temporal and geographic variation, and readily available data. The method is applied to an early 1990s reform in Ethiopia based around the release of the Education and Training Policy, which removed schooling fees from grades one to ten. The model estimates that the reform led to an increase in schooling of at least 1.2 years, and provides initial evidence that the increased enrollment in Ethiopia outweighed any cost due to reductions in quality