Supertubes and special holonomy

We obtain a $\frac 14$-supersymmetric 6-brane solution of IIA Supergravity by T-dualizing the supertube recently found. The resulting $C_{\it 1}$ electric charge is related to the original $D0$-brane charge. The uplifted solution to eleven dimensions results to be a purely geometrical configuration, which can be interpreted as a bound state of a Taub-NUT space and a pp-wave. Being the non trivial part of the metric pseudo-Riemannian, the resulting reduced holonomy group is non-compact and locally isomorphic to a semidirect product of an Abelian four dimensional group and SU(2).Comment: 11 pages, latex, no figure

Prediction of a Photon Peak in Heavy Ion Collisions

We show that if a flavour-less vector meson remains bound after deconfinement, and if its limiting velocity in the quark-gluon plasma is subluminal, then this meson produces a distinct peak in the spectrum of thermal photons emitted by the plasma. We also demonstrate that this effect is a universal property of all strongly coupled, large-Nc plasmas with a gravity dual. For the J/psi the corresponding peak lies between 3 and 5 GeV and could be observed at LHC.Comment: 4 pages, 5 figures. Minor corrections; references adde

A New Mechanism of Quark Energy Loss

We show that a heavy quark moving sufficiently fast through a quark-gluon plasma may lose energy by Cherenkov-radiating mesons. We demonstrate that this takes place in all strongly coupled, large-Nc plasmas with a gravity dual. The energy loss is exactly calculable in these models despite being an O(1/Nc)-effect. We discuss phenomenological implications for heavy-ion collision experiments.Comment: 4 pages, 4 figures; v2: plot modified, conclusions unchange

Noise characterization of an atomic magnetometer at sub-millihertz frequencies

Noise measurements have been carried out in the LISA bandwidth (0.1 mHz to 100 mHz) to characterize an all-optical atomic magnetometer based on nonlinear magneto-optical rotation. This was done in order to assess if the technology can be used for space missions with demanding low-frequency requirements like the LISA concept. Magnetometry for low-frequency applications is usually limited by $1/f$ noise and thermal drifts, which become the dominant contributions at sub-millihertz frequencies. Magnetic field measurements with atomic magnetometers are not immune to low-frequency fluctuations and significant excess noise may arise due to external elements, such as temperature fluctuations or intrinsic noise in the electronics. In addition, low-frequency drifts in the applied magnetic field have been identified in order to distinguish their noise contribution from that of the sensor. We have found the technology suitable for LISA in terms of sensitivity, although further work must be done to characterize the low-frequency noise in a miniaturized setup suitable for space missions.Comment: 11 pages, 12 figure

Black-hole masses of type 1 AGN in the XMM-Newton bright serendipitous survey

We derive masses of the central super-massive black hole (SMBH) and accretion rates for 154 type1 AGN belonging to a well-defined X-ray-selected sample, the XMM-Newton Serendipitous Sample (XBS). To this end, we use the most recent "single-epoch" relations, based on Hbeta and MgII2798A emission lines, to derive the SMBH masses. We then use the bolometric luminosities, computed on the basis of an SED-fitting procedure, to calculate the accretion rates, both absolute and normalized to the Eddington luminosity (Eddington ratio). The selected AGNs cover a range of masses from 10^7 to 10^10 Msun with a peak around 8x10^8 Msun and a range of accretion rates from 0.01 to ~50 Msun/year (assuming an efficiency of 0.1), with a peak at ~1 Msun/year. The values of Eddington ratio range from 0.001 to ~0.5 and peak at 0.1.Comment: 14 pages, 11 figures. Accepted for publication in Astronomy & Astrophysic

Bifurcation and Chaos in Coupled Ratchets exhibiting Synchronized Dynamics

The bifurcation and chaotic behaviour of unidirectionally coupled deterministic ratchets is studied as a function of the driving force amplitude ($a$) and frequency ($\omega$). A classification of the various types of bifurcations likely to be encountered in this system was done by examining the stability of the steady state in linear response as well as constructing a two-parameter phase diagram in the ($a -\omega$) plane. Numerical explorations revealed varieties of bifurcation sequences including quasiperiodic route to chaos. Besides, the familiar period-doubling and crises route to chaos exhibited by the one-dimensional ratchet were also found. In addition, the coupled ratchets display symmetry-breaking, saddle-nodes and bubbles of bifurcations. Chaotic behaviour is characterized by using the sensitivity to initial condition as well as the Lyapunov exponent spectrum; while a perusal of the phase space projected in the Poincar$\acute{e}$ cross-section confirms some of the striking features.Comment: 7 pages; 8 figure

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

Modeling runoff with AnnAGNPS model in a small agricultural catchment, in Mediterranean environment

Agricultural activities, as part of the natural resource management practice, impact soil and water quality at the watershed or catchment level. Field monitoring is often used to evaluate and acquire knowledge of the impacts of management practices on productivity and environment. Computer simulation models, after calibrated and validated, provide an efficient and effective alternative for evaluating the effects of agricultural practices on soil and water quality at the watershed level. The main objective is calibrate and validate the AnnAGNPS model relatively to runoff and peak flow using five hydrologic years data, for the rain and irrigation season. The study watershed is located in Portugal, and covers an area of 189 ha, divided into 18 fields belonging to four farmers. The climate is typically Mediterranean with continental influence, and the main crops are oat, tobacco, sorghum and maize. The calibration was done manually, but in a systematic away, in order to select values for the statistical parameters so that the model closely simulates runoff and peak flow. The results obtained in calibration and validation of the AnnAGNPS model, confirm a good or very good performance to simulate the peak flow and runoff volume at daily or event scale, in rainfall season. Also, the obtained results are a good indication of the validity of AnnAGNPS model to simulate runoff in irrigation to larger periods of time, for example irrigation season