Chasing the heaviest black holes of jetted Active Galactic Nuclei

We investigate the physical properties of the 10 blazars at redshift greater than 2 detected in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. We find that the jets of these blazars are among the most powerful known. Furthermore, the mass of their central black hole, inferred from the optical-UV bump, exceeds a few billions of solar masses, with accretion luminosities being a large fraction of the Eddington one. We compare their properties with those of the brightest blazars of the 3-months survey performed by the Large Area Telescope (LAT) onboard the Fermi satellite. We find that the BAT blazars have more powerful jets, more luminous accretion disks and larger black hole masses than LAT blazars. These findings can be simply understood on the basis of the blazar sequence, that suggests that the most powerful blazars have a spectral energy distribution with a high energy peak at MeV (or even sub-MeV) energies. This implies that the most extreme blazars can be found more efficiently in hard X-rays, rather than in the high energy gamma-ray band. We then discuss the implications of our findings for future missions, such as the New Hard X-ray Mission (NHXM) and especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which, during its planned 2 years all sky survey, is expected to detect thousands of blazars, with a few of them at z greater than 6.Comment: Accepted for publication in MNRAS. Absorption due to Lyman-alpha clouds calculated, and optical-UV data de-absorbed. 16 figures, 15 page

Tensor Regression with Applications in Neuroimaging Data Analysis

Classical regression methods treat covariates as a vector and estimate a corresponding vector of regression coefficients. Modern applications in medical imaging generate covariates of more complex form such as multidimensional arrays (tensors). Traditional statistical and computational methods are proving insufficient for analysis of these high-throughput data due to their ultrahigh dimensionality as well as complex structure. In this article, we propose a new family of tensor regression models that efficiently exploit the special structure of tensor covariates. Under this framework, ultrahigh dimensionality is reduced to a manageable level, resulting in efficient estimation and prediction. A fast and highly scalable estimation algorithm is proposed for maximum likelihood estimation and its associated asymptotic properties are studied. Effectiveness of the new methods is demonstrated on both synthetic and real MRI imaging data.Comment: 27 pages, 4 figure

Cerebral activations related to ballistic, stepwise interrupted and gradually modulated movements in parkinson patients

Patients with Parkinson's disease (PD) experience impaired initiation and inhibition of movements such as difficulty to start/stop walking. At single-joint level this is accompanied by reduced inhibition of antagonist muscle activity. While normal basal ganglia (BG) contributions to motor control include selecting appropriate muscles by inhibiting others, it is unclear how PD-related changes in BG function cause impaired movement initiation and inhibition at single-joint level. To further elucidate these changes we studied 4 right-hand movement tasks with fMRI, by dissociating activations related to abrupt movement initiation, inhibition and gradual movement modulation. Initiation and inhibition were inferred from ballistic and stepwise interrupted movement, respectively, while smooth wrist circumduction enabled the assessment of gradually modulated movement. Task-related activations were compared between PD patients (N = 12) and healthy subjects (N = 18). In healthy subjects, movement initiation was characterized by antero-ventral striatum, substantia nigra (SN) and premotor activations while inhibition was dominated by subthalamic nucleus (STN) and pallidal activations, in line with the known role of these areas in simple movement. Gradual movement mainly involved antero-dorsal putamen and pallidum. Compared to healthy subjects, patients showed reduced striatal/SN and increased pallidal activation for initiation, whereas for inhibition STN activation was reduced and striatal-thalamo-cortical activation increased. For gradual movement patients showed reduced pallidal and increased thalamo-cortical activation. We conclude that PD-related changes during movement initiation fit the (rather static) model of alterations in direct and indirect BG pathways. Reduced STN activation and regional cortical increased activation in PD during inhibition and gradual movement modulation are better explained by a dynamic model that also takes into account enhanced responsiveness to external stimuli in this disease and the effects of hyper-fluctuating cortical inputs to the striatum and STN in particular

Formation and Evolution of Supermassive Black Holes

The correlation between the mass of supermassive black holes in galaxy nuclei and the mass of the galaxy spheroids or bulges (or more precisely their central velocity dispersion), suggests a common formation scenario for galaxies and their central black holes. The growth of bulges and black holes can commonly proceed through external gas accretion or hierarchical mergers, and are both related to starbursts. Internal dynamical processes control and regulate the rate of mass accretion. Self-regulation and feedback are the key of the correlation. It is possible that the growth of one component, either BH or bulge, takes over, breaking the correlation, as in Narrow Line Seyfert 1 objects. The formation of supermassive black holes can begin early in the universe, from the collapse of Population III, and then through gas accretion. The active black holes can then play a significant role in the re-ionization of the universe. The nuclear activity is now frequently invoked as a feedback to star formation in galaxies, and even more spectacularly in cooling flows. The growth of SMBH is certainly there self-regulated. SMBHs perturb their local environment, and the mergers of binary SMBHs help to heat and destroy central stellar cusps. The interpretation of the X-ray background yields important constraints on the history of AGN activity and obscuration, and the census of AGN at low and at high redshifts reveals the downsizing effect, already observed for star formation. History appears quite different for bright QSO and low-luminosity AGN: the first grow rapidly at high z, and their number density decreases then sharply, while the density of low-luminosity objects peaks more recently, and then decreases smoothly.Comment: 31 pages, 13 figures, review paper for Astrophysics Update

Disrupted Functional Connectivity with Dopaminergic Midbrain in Cocaine Abusers

Background: Chronic cocaine use is associated with disrupted dopaminergic neurotransmission but how this disruption affects overall brain function (other than reward/motivation) is yet to be fully investigated. Here we test the hypothesis that cocaine addicted subjects will have disrupted functional connectivity between the midbrain (where dopamine neurons are located) and cortical and subcortical brain regions during the performance of a sustained attention task. Methodology/Principal Findings: We measured brain activation and functional connectivity with fMRI in 20 cocaine abusers and 20 matched controls. When compared to controls, cocaine abusers had lower positive functional connectivity of midbrain with thalamus, cerebellum, and rostral cingulate, and this was associated with decreased activation in thalamus and cerebellum and enhanced deactivation in rostral cingulate. Conclusions/Significance: These findings suggest that decreased functional connectivity of the midbrain interferes with the activation and deactivation signals associated with sustained attention in cocaine addicts

Surprised at All the Entropy: Hippocampal, Caudate and Midbrain Contributions to Learning from Prediction Errors

Influential concepts in neuroscientific research cast the brain a predictive machine that revises its predictions when they are violated by sensory input. This relates to the predictive coding account of perception, but also to learning. Learning from prediction errors has been suggested for take place in the hippocampal memory system as well as in the basal ganglia. The present fMRI study used an action-observation paradigm to investigate the contributions of the hippocampus, caudate nucleus and midbrain dopaminergic system to different types of learning: learning in the absence of prediction errors, learning from prediction errors, and responding to the accumulation of prediction errors in unpredictable stimulus configurations. We conducted analyses of the regions of interests' BOLD response towards these different types of learning, implementing a bootstrapping procedure to correct for false positives. We found both, caudate nucleus and the hippocampus to be activated by perceptual prediction errors. The hippocampal responses seemed to relate to the associative mismatch between a stored representation and current sensory input. Moreover, its response was significantly influenced by the average information, or Shannon entropy of the stimulus material. In accordance with earlier results, the habenula was activated by perceptual prediction errors. Lastly, we found that the substantia nigra was activated by the novelty of sensory input. In sum, we established that the midbrain dopaminergic system, the hippocampus, and the caudate nucleus were to different degrees significantly involved in the three different types of learning: acquisition of new information, learning from prediction errors and responding to unpredictable stimulus developments. We relate learning from perceptual prediction errors to the concept of predictive coding and related information theoretic accounts

Globalization and the sociology of Immanuel Wallerstein: A critical appraisal

By the turn of the 21st century the concept of globalization had earned its place in the social sciences and debate turned more squarely to the theoretical significance of globalization. Yet not all scholars were happy with the notion of globalization. Some claim that is merely a new name for earlier theories and concepts. Among those who reject new paradigmatic thinking on the current age is Immanuel Wallerstein, the world-renowned sociologist and ‘father’ of the worldsystem paradigm. This article is intended as an appraisal of Wallerstein’s oeuvre in the context of the debate on global transformations in the late 20th and early 21st centuries and from the vantage point of the present author’s own critical globalization perspective. The first three parts summarize and assess Wallerstein’s theoretical system and his many contributions to macro, historical and comparative sociology, to development studies and international political economy. The fourth discusses Wallerstein’s assessment of the evolution of the world capitalist system in recent decades, including his views on the concept of globalization, and the fifth focuses on earlier and more recent critical appraisals of his work, including the present author’s own, in light of the recent transformations in world capitalism identified with globalization

Gothic Revival Architecture Before Horace Walpole's Strawberry Hill

The Gothic Revival is generally considered to have begun in eighteenth-century Britain with the construction of Horace Walpole’s villa, Strawberry Hill, Twickenham, in the late 1740s. As this chapter demonstrates, however, Strawberry Hill is in no way the first building, domestic or otherwise, to have recreated, even superficially, some aspect of the form and ornamental style of medieval architecture. Earlier architects who, albeit often combining it with Classicism, worked in the Gothic style include Sir Christopher Wren, Nicholas Hawksmoor, William Kent and Batty Langley, aspects of whose works are explored here. While not an exhaustive survey of pre-1750 Gothic Revival design, the examples considered in this chapter reveal how seventeenth- and eighteenth-century Gothic emerged and evolved over the course of different architects’ careers, and how, by the time that Walpole came to create his own Gothic ‘castle’, there was already in existence in Britain a sustained Gothic Revivalist tradition