On the arcmin structure of the X-ray Universe

We present the angular correlation function of the X-ray population of 1063 XMM-Newton observations at high Galactic latitudes, comprising up to ~30000 sources over a sky area of ~125 sq. degrees in the energy bands: soft (0.5-2 keV) and hard (2-10 keV). This is the largest sample of serendipitous X-ray sources ever used for clustering analysis purposes to date and the results have been determined with unprecedented accuracy. We detect significant clustering signals in the soft and hard bands (~10 sigma and ~5 sigma, respectively). We deproject the angular correlation function via Limber's equation and calculate the typical spatial lengths. We infer that AGN at redshifts ~1 are embedded in dark matter halos with typical masses of log M ~ 12.6/h Msol and lifetimes in the range ~3-5 x 10^8 years, which indicates that AGN activity is a transient phase in the life of galaxies.Comment: 4 pages, 1 figure. Proc. of the conference "X-ray Astronomy 2009: Present status, multiwavelength approach and future perspectives", September 2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi, L. Angelini)

The Holographic Life of the eta'

In the string holographic dual of large-N_c QCD with N_f flavours of Kruczenski et al, the eta' meson is massless at infinite N_c and dual to a collective fluctuation of N_f D6-brane probes in a supergravity background. Here we identify the string diagrams responsible for the generation of a mass of order N_f/N_c, consistent with the Witten-Veneziano formula, and show that the supregravity limit of these diagrams corresponds to mixings with pseudoscalar glueballs. We argue that the dependence on the theta-angle in the supergravity description occurs only through the combination theta + 2 \sqrt{N_f} eta' / f_pi, as dictated by the U(1) anomaly. We provide a quantitative test by computing the linear term in the eta' potential in two independent ways, with perfect agreement.Comment: 1+26 pages, 8 figures; V4: Appendix added, version published in JHE

Bubbling solutions, entropy enhancement and the fuzzball proposal

In this short note we explain the main idea of the work done in arXiv:0804.4487[hep-th] and arXiv:0812.2942[hep-th]. We present a family of black hole microstates, the bubbling solutions. We then explain how supertubes placed in such backgrounds have their entropy enhanced by the presence of the background dipole charges. This indicates this could account for a large amount in the entropy of the three charge black hole.Comment: 2 pages, contribution to the Cargese 2008 proceedings: Theory and Particle Physics: the LHC perspective and beyon

Detectability of low energy X-ray spectral components in type 1 AGN

In this paper we examine the percentage of type 1 AGN which require the inclusion of a soft excess component and/or significant cold absorption in the modelling of their X-ray spectra obtained by XMM-Newton. We do this by simulating spectra which mimic typical spectral shapes in order to find the maximum detectability expected at different count levels. We then apply a correction to the observed percentages found for the Scott et al. (2011) sample of 761 sources. We estimate the true percentage of AGN with a soft excess component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count spectra in narrow z bins in which additional spectral components were not originally detected, we show that the soft excess feature is recovered with a mean temperature kT and blackbody to power-law normalisation ratio consistent with those of components detected in individual high count spectra. Cold absorption with nH values broadly consistent with those reported in individual spectra are also recovered. We suggest such intrinsic cold absorption is found in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in MNRA

Poly(amido amine)s as Gene Delivery Vectors: Effects of Quaternary Nicotinamide Moieties in the Side Chains

To evaluate the effect of quaternary nicotinamide pendant groups on gene delivery properties, a series of poly(amido amine) (co)polymers were synthesized by Michael addition polymerization of N, N-cystaminebisacrylamide with variable ratios of 1-(4-aminobutyl)-3-carbamoylpyridinium (Nic-BuNH2), and tert-butyl-4-aminobutyl carbamate (BocNH-BuNH2), yielding poly(amido amine)s (NicX-NHBoc) with X=0, 10, 30, and 50 % of quaternary nicotinamide groups in the polymer side chains. Deprotection of the pendant Boc-NH groups afforded an analogous series of polymers (NicX-NH2) with higher charge density (due to the presence of protonated primary amino groups in the side chains) and subsequent acetylation yielded a series of polymers (NicX-NHAc) of lower hydrophobicity than the Boc-protected polymers. The polymers with the Boc-protected or the acetylated amino groups showed high buffer capacity in the range pH 5.1-7.4, which is a property that can contribute to endosomal escape of polyplexes. The presence of quaternary nicotinamide groups has distinct beneficial effects on the gene vector properties of these polymers. The polymers containing 30 % of quaternary nicotinamide groups in their side chains condense DNA into small, nanosized particles (200 nm) with positive surface charge (+15 mV). Fluorescence experiments using ethidium bromide as a competitor showed that the quaternary nicotinamide groups intercalate with DNA, contributing to a more intimate polymer-DNA binding and shielding. Polyplexes of nicotinamide-functionalized poly(amido amine)s NicX-NHBoc and NicX-NHAc, formed at 12/1 polymerDNA mass ratio, efficiently transfect COS-7 cells with efficacies up to four times higher than that of PEI (Exgen 500), and with essentially absence of cytotoxicity. NicX-NH2 polymers, possessing protonated primary amino groups in their side chains, have a higher cytotoxicity profile under these conditions, but at lower 3/1 polymer-DNA mass ratio also these polymers are capable of efficient transfection, while retaining full cell viability

Activated carbons as catalytic support for Cu nanoparticles

There are a wide range of catalytic applications for Cu-based nanoparticles materials, since Cu is an abundant and inexpensive metal and Cu nanoparticles possess unusual electrical, thermal and optical properties. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. A previous work have explored the possibilities of SBA-15 (1,2) as support for Cu nanoparticles. In the present contribution, those results will be compared with the use of a carbon material as support, since activated carbon present many advantages with respect SBA, as the high surface area.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Finite energy Dirac-Born-Infeld monopoles and string junctions

It is shown that the world volume field theory of a single D3-brane in a supergravity D3-brane background admits finite energy, and non-singular, Abelian monopoles and dyons preserving 1/2 or 1/4 of the N=4 supersymmetry and saturating a Bogomolnyi-type bound. The 1/4 supersymmetric solitons provide a world volume realization of string-junction dyons. We also discuss the dual M-theory realization of the 1/2 supersymmetric dyons as finite tension self-dual strings on the M5-brane, and of the 1/4 supersymmetric dyons as their intersections

Lagged and instantaneous dynamical influences related to brain structural connectivity

Contemporary neuroimaging methods can shed light on the basis of human neural and cognitive specializations, with important implications for neuroscience and medicine. Different MRI acquisitions provide different brain networks at the macroscale; whilst diffusion-weighted MRI (dMRI) provides a structural connectivity (SC) coincident with the bundles of parallel fibers between brain areas, functional MRI (fMRI) accounts for the variations in the blood-oxygenation-level-dependent T2* signal, providing functional connectivity (FC).Understanding the precise relation between FC and SC, that is, between brain dynamics and structure, is still a challenge for neuroscience. To investigate this problem, we acquired data at rest and built the corresponding SC (with matrix elements corresponding to the fiber number between brain areas) to be compared with FC connectivity matrices obtained by 3 different methods: directed dependencies by an exploratory version of structural equation modeling (eSEM), linear correlations (C) and partial correlations (PC). We also considered the possibility of using lagged correlations in time series; so, we compared a lagged version of eSEM and Granger causality (GC). Our results were two-fold: firstly, eSEM performance in correlating with SC was comparable to those obtained from C and PC, but eSEM (not C nor PC) provides information about directionality of the functional interactions. Second, interactions on a time scale much smaller than the sampling time, captured by instantaneous connectivity methods, are much more related to SC than slow directed influences captured by the lagged analysis. Indeed the performance in correlating with SC was much worse for GC and for the lagged version of eSEM. We expect these results to supply further insights to the interplay between SC and functional patterns, an important issue in the study of brain physiology and function.Comment: Accepted and published in Frontiers in Psychology in its current form. 27 pages, 1 table, 5 figures, 2 suppl. figure

String Theory and Quantum Chromodynamics

I review recent progress on the connection between string theory and quantum chromodynamics in the context of the gauge/gravity duality. Emphasis is placed on conciseness and conceptual aspects rather than on technical details. Topics covered include the large-Nc limit of gauge theories, the gravitational description of gauge theory thermodynamics and hydrodynamics, and confinement/deconfinement thermal phase transitions.Comment: 38 pages, 24 figures. Lectures given at the RTN Winter School on "Strings, Supergravity and Gauge Theories" at CERN on January 15-19, 200