On the orientation and magnitude of the black hole spin in galactic nuclei

Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.Comment: 14 pages, 7 figures, accepted for publication in Ap

Search for Dark Matter direct production in the monophoton plus missing transverse momentum final state in pp collisions at √s = 8TeV with the ATLAS detector

This paper presents a search for dark matter pair production in association with an energetic photon in 20.3 fb−1 of pp collisions collected at √s = 8TeV by the ATLAS detector at the LHC. The final state investigated in this analysis is defined by large missing transverse momentum (EmissT > 150GeV) and by the presence of an energetic photon (pT > 125 GeV). Observations in data are compared to the Standard Model expectations and no significant excess is found. A modelindependent limit is set on the presence of new physics in data. Data are also interpreted in the framework of effective field theories which describe the interaction between dark matter and incoming partons as a contact interaction parameterized by a set of dimensional operators

Optical Darboux Transformer

The Optical Darboux Transformer is introduced as a photonic device which performs the Darboux transformation directly in the optical domain. This enables two major advances for signal processing based on the nonlinear Fourier transform: (i) the multiplexing of different solitonic waveforms corresponding to arbitrary number of discrete eigenvalues of the Zakharov-Shabat system in the optical domain, and (ii) the selective filtering of an arbitrary number of individual solitons too. The Optical Darboux Transformer can be built using existing commercially available photonic technology components and constitutes a universal tool for signal processing, optical communications, optical rogue waves generation, and waveform shaping and control in the nonlinear Fourier domain

Developmental Effects of Chronic Low-Level Arsenic Exposure in Mouse Embryonic Stem Cells and in Human Induced Pluripotent Stem Cells

Arsenic is an environmental contaminant commonly found in food and drinking water. Exposure to arsenic during embryonic development has been linked to reduced muscle growth, disrupted muscle development and locomotor activity, impaired neurodevelopment, reduced IQ, impaired memory and learning deficits. While the mechanisms responsible for developmental changes following in utero exposure to arsenic are not well known, one possibility is that arsenic might disrupt proper cellular differentiation. Therefore, we aimed to investigate the mechanisms by which arsenic exposure could alter stem cell differentiation into neurons. First, we continuously exposed P19 mouse embryonic stem (ES) cells to 0.1 μM (7.5 ppb) arsenic for 28 weeks to assess if chronic, low level arsenic exposure would delay cellular differentiation into neuronal cells. Importantly, this concentration is below the current drinking water standard of 10 ppb. The results show temporal changes of genes associated with pluripotency and cellular differentiation. Specifically, starting at week 12, transcript levels of the pluripotency markers Sox2 and Oct4 were increased by 1.9- to 2.5- fold in arsenic-exposed cells. By week 16, SOX2 protein expression was increased, and starting at week 20, the expression of a SOX2 target protein, N-cadherin, was also increased. Concurrently, by week 16, levels of the differentiation marker Gdf3 were decreased by 3.4- fold, along with the reduced phosphorylation of the GDF3 target protein SMAD2/3. To investigate the mechanisms responsible for maintaining pluripotency and hindering cellular differentiation into neurons, RNA sequencing was performed in control and arsenic-exposed cells at week 8, 16 and 24. This analysis revealed significant exposure-dependent changes in gene expression starting at week 16. Pathway analysis showed that arsenic exposure disrupts the Hippo signaling pathway, which is involved in pluripotency maintenance and embryonic development. Immunohistochemistry revealed that the ratios between nuclear (active) and cytoplasmic (inactive) expression of the main effector YAP and the main transcription factor TEAD were significantly increased in arsenic-exposed cells at week 16 and 28. Consistently, expression of the Hippo pathway target genes Ctgf and c-Myc were also significantly upregulated following arsenic exposure. These results indicate that chronic arsenic exposure impairs the Hippo signaling pathway resulting in increased YAP activation, thereby reducing neuronal differentiation. Previous studies have shown that P19 cells differentiate into sensory neurons, so we also wanted to investigate whether arsenic impaired differentiation into motor neurons. Thus, we switched to using human induced pluripotent stem (iPS) cells, which can differentiate into day 6 neuroepithelial progenitors (NEPs), day 12 motor neuron progenitors (MNPs), day 18 early motor neurons (MNs) and day 28 mature MNs. During this process, cells were exposed to arsenic concentrations up to 0.75 μM (56.25 ppb), and morphological alterations along with pluripotency and stage-specific neuronal markers were assessed. Day 6 NEPs exposed to arsenic had reduced levels of the neural progenitor/stem cell marker NES and neuroepithelial progenitor marker SOX1, while levels of these transcripts were increased in MNPs at day 12. Additionally, levels of the motor neuron progenitor marker OLIG2 were increased in day 12 MNPs while levels of the cholinergic neuron marker CHAT were reduced by 2.5- fold in MNPs exposed arsenic. RNA sequencing and pathway analysis showed that the cholinergic synapse pathway was impaired following exposure to 0.5 μM arsenic, and that transcript levels of genes involved in acetylcholine synthesis (CHAT), transport (SLC18A3 and SLC5A7) and degradation (ACHE) were all downregulated in early motor neurons at day 18. In mature motor neurons at day 28, expression of MAP2 and ChAT protein was significantly downregulated by 2.8- and 2.1- fold, respectively, concomitantly with a reduction in neurite length by 1.8- fold following exposure to 0.5 μM arsenic. Similarly, adult mice exposed to 100 ppb arsenic for five weeks had significantly reduced hippocampal ChAT levels. Taken all together, the results of the dissertation show that environmentally relevant levels of arsenic have detrimental effects on neuronal differentiation

Pushing 1D CCSNe to explosions: model and SN 1987A

We report on a method, PUSH, for triggering core-collapse supernova explosions of massive stars in spherical symmetry. We explore basic explosion properties and calibrate PUSH such that the observables of SN1987A are reproduced. Our simulations are based on the general relativistic hydrodynamics code AGILE combined with the detailed neutrino transport scheme IDSA for electron neutrinos and ALS for the muon and tau neutrinos. To trigger explosions in the otherwise non-exploding simulations, we rely on the neutrino-driven mechanism. The PUSH method locally increases the energy deposition in the gain region through energy deposition by the heavy neutrino flavors. Our setup allows us to model the explosion for several seconds after core bounce. We explore the progenitor range 18-21M$_{\odot}$. Our studies reveal a distinction between high compactness (HC) and low compactness (LC) progenitor models, where LC models tend to explore earlier, with a lower explosion energy, and with a lower remnant mass. HC models are needed to obtain explosion energies around 1 Bethe, as observed for SN1987A. However, all the models with sufficiently high explosion energy overproduce $^{56}$Ni. We conclude that fallback is needed to reproduce the observed nucleosynthesis yields. The nucleosynthesis yields of $^{57-58}$Ni depend sensitively on the electron fraction and on the location of the mass cut with respect to the initial shell structure of the progenitor star. We identify a progenitor and a suitable set of PUSH parameters that fit the explosion properties of SN1987A when assuming 0.1M$_{\odot}$ of fallback. We predict a neutron star with a gravitational mass of 1.50M$_{\odot}$. We find correlations between explosion properties and the compactness of the progenitor model in the explored progenitors. However, a more complete analysis will require the exploration of a larger set of progenitors with PUSH.Comment: revised version as accepted by ApJ (results unchanged, text modified for clarification, a few references added); 26 pages, 20 figure

Neutrino processes in partially degenerate neutron matter

We investigate neutrino processes for conditions reached in simulations of core-collapse supernovae. Where neutrino-matter interactions play an important role, matter is partially degenerate, and we extend earlier work that addressed the degenerate regime. We derive expressions for the spin structure factor in neutron matter, which is a key quantity required for evaluating rates of neutrino processes. We show that, for essentially all conditions encountered in the post-bounce phase of core-collapse supernovae, it is a very good approximation to calculate the spin relaxation rates in the nondegenerate limit. We calculate spin relaxation rates based on chiral effective field theory interactions and find that they are typically a factor of two smaller than those obtained using the standard one-pion-exchange interaction alone.Comment: 41 pages, 9 figures, NORDITA-2011-116; added comparison figures and fit function for use in simulations, to appear in Astrophys.

A linear optical coupler for cryogenic detectors

Abstract We present an improved version of a linear low-noise optical coupler having differential input and capable of driving a twisted cable to long distances, avoiding ground loops and electromagnetic interference. Owing to device optimization, this circuit version is able to be fast. Its frequency bandwidth is about 900 kHz, more than ten times larger than our previous implementation. The optical coupler presented is therefore suitable to be used with most of the applications with cryogenic detectors

Optimized schwarz methods for the bidomain system in electrocardiology

The propagation of the action potential in the heart chambers is accurately described by the Bidomain model, which is commonly accepted and used in the specialistic literature. However, its mathematical structure of a degenerate parabolic system entails high computational costs in the numerical solution of the associated linear system. Domain decomposition methods are a natural way to reduce computational costs, and Optimized Schwarz Methods have proven in the recent years their effectiveness in accelerating the convergence of such algorithms. The latter are based on interface matching conditions more efficient than the classical Dirichlet or Neumann ones. In this paper we analyze an Optimized Schwarz approach for the numerical solution of the Bidomain problem. We assess the convergence of the iterative method by means of Fourier analysis, and we investigate the parameter optimization in the interface conditions. Numerical results in 2D and 3D are given to show the effectiveness of the method