The idea that systematic Faraday Rotation gradients across the parsec-scale jets of Active Galactic Nuclei (AGNs) can reveal the presence of helical magnetic (B) fields has been around since the early 1990s, although the first observation of this phenomenon was about ten years later. These gradients are taken to be due to the systematic variation of the line-of-sight B field across the jet. We present here the parsec-scale Faraday Rotation distributions for the BL Lac objects 0716+714 and 1749+701, based on polarization data obtained with the Very Long Baseline Array (VLBA) at two wavelengths near each of the 2cm, 4cm and 6cm bands (0716+714) and at four wavelengths in the range 18-22 cm (1749+701). The Rotation Measure (RM) maps for both these sources indicate systematic gradients across their jets, as expected if these jets have helical B fields. The significance of these transverse RM gradients is > 3σ in all cases. We present the results of Monte Carlo simulations directly demonstrating the possibility of observing such transverse RM gradients even if the intrinsic jet structure is much narrower than the observing beam. We observe an intriguing new feature in these sources, a reversal in the direction of the gradient in the jet as compared to the gradient in the core region. This provides new evidence to support models in which field lines emerging from the central region of the accretion disk and closing in the outer region of the accretion disk are both "wound up" by the differential rotation of the disk. The net observed RM gradient will essentially be the sum effect of two regions of helical field, one nested inside the other. The direction of the net RM gradient will be determined by whether the inner or outer helix dominates the RM integrated through the jet, and RM gradient reversals will be observed if the inner and outer helical fields dominate in different regions of the jet. This potentially provides new insights about the overall configuration of the jet B fields.

This paper describes a method of fitting total intensity and polarization profiles in VLBI images of astrophysical jets to profiles predicted by a theoretical model. As an example, the method is used to fit profiles of the jet in the Active Galactic Nucleus Mrk 501 with profiles predicted by a model in which a cylindrical jet of synchrotron plasma is threaded by a magnetic field with helical and disordered components. This fitting yields model Stokes Q profiles that agree with the observed profiles to within the 1 − 2σ uncertainties; the I model and observed profiles are overall not in such good agreement, with the model I profiles being generally more symmetrical than the observed profiles. Consistent fitting results are obtained for profiles derived from 6 cm VLBI images at two distances from the core, and also for profiles obtained for different wavelengths at a single location in the VLBI jet. The most striking success of the model is its ability to reproduce the spine-sheath polarization structure observed across the jet. Using the derived viewing angle in the jet rest frame, δ 83 • , together with a superluminal speed reported in the literature, β app = 3.3, yields a solution for the viewing angle and velocity of the jet in the observer's frame δ 15 • and β 0.96. Although these results for Mrk501 must be considered tentative, the combined analysis of polarization profiles and apparent component speeds holds promise as a means of further elucidating the magnetic field structures and other parameters of parsec-scale AGN jets.

Acute myeloid leukemia (AML) is an aggressive stem cell malignancy that is difficult to treat. There are limitations to the current treatment regimes especially after disease relapse, and therefore new therapeutic agents are urgently required which can overcome drug resistance whilst avoiding unnecessary toxicity. Among newer targeted agents, both tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and proteasome inhibitors show particular promise. In this report we show that a combination of the proteasome inhibitor bortezomib and TRAIL is effective against AML cell lines, in particular, AML cell lines displaying myelomonocytic/monocytic phenotype (M4/M5 AML based on FAB classification), which account for 20-30% of AML cases. We show that the underlying mechanism of sensitization is at least in part due to bortezomib mediated downregulation of c-FLIP and XIAP, which is likely to be regulated by NF-κB. Blockage of NF-κB activation with BMS-345541 equally sensitized myelomonocytic AML cell lines and primary AML blasts to TRAIL.

The second method of Liapunov is applied to a distributed parameter reaction system. A Liapunov functional is assumed and theorems are developed which yield sufficient conditions for analyzing the stability of a steady state. The method is applied to the problem of the catalyst particle treated as a slab. The conditions obtained are valid for general perturbations and general system parameters.

Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic fields that thread them. Faraday Rotation gradients are a very important way of investigating these magnetic fields, and can provide information on the orientation and structure of the magnetic field in the immediate vicinity of the jet; for example, a toroidal or helical field component should give rise to a systematic gradient in the observed Faraday rotation across the jet, as well as characteristic intensity and polarization profiles. However, real observed radio images have finite resolution, usually expressed via convolution with a Gaussian beam whose size corresponds to the central lobe of the point source response function. This will tend to blur transverse structure in the jet profile, raising the question of how well resolved a jet must be in the transverse direction in order to reliably detect transverse structure associated with a helical jet magnetic field. We present results of simulated intensity, polarization and Faraday rotation images designed to directly and empirically investigate the effect of finite resolution on observed transverse jet structures. arXiv:1109.4778v1 [astro-ph.HE]

Abstract. Faraday Rotation measurements are a very important tool for investigating the magnetic (B) fields associated with the relativistic jets of Active Galactic Nuclei (AGN); for example, a toroidal or helical B field component should give rise to a systematic gradient in the observed Faraday rotation across the jet. However, real observed radio images have finite resolution. Typical beam sizes for cm-wavelength Very Long Baseline Interferometry (VLBI) observations are often comparable to or larger than the observed jet widths, raising questions about how well resolved a jet must be in the transverse direction in order to reliably detect transverse Faraday-rotation structure. The results of new simulations of Faraday rotation images designed to directly investigate this question are presented, together with studies of the probabilities of observing spurious Faraday Rotation gradients as a result of random noise and finite resolution. These simulations clearly demonstrate the possibility of detecting transverse Faraday-rotation structures even when the observed intrinsic jet widths are considerably smaller than the beam width.

Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic (B) fields that thread them. Faraday Rotation measurements are a very important way of investigating these B fields, and can provide information on the orientation and structure of the B field in the immediate vicinity of the jet; for example, a toroidal or helical B field component should give rise to a systematic gradient in the observed Faraday rotation across the jet, as well as characteristic intensity and polarization profiles. However, real observed radio images have finite resolution, usually expressed via convolution with a Gaussian beam whose size corresponds to the central lobe of the point source response function. This will tend to blur the transverse structure of the jet, raising the question of how well resolved a jet must be in the transverse direction in order to reliably detect transverse structure. We present the results of simulated Faraday rotation images designed to directly investigate the effect of finite resolution on observed transverse Faraday rotation measure structures.

No abstract