The Effect of Expansion on Mass Entrainment and Stability of Super-Alfv\'enic Jets

We extend investigations of mass entrainment by jets, which previously have focused on cylindrical supermagnetosonic jets and expanding trans-Alfv\'enic jets, to a set of expanding supermagnetosonic jets. We precess these jets at the origin to excite the helical mode of the Kelvin-Helmholtz (or KH) instability, in order to compare the results with predictions from linear stability analysis. We analyze this simulation set for the spatial development of magnetized mass, which we interpret as jet plus entrained, initially unmagnetized external mass. As with the previous simulation sets, we find that the growth of magnetized mass is associated with the growth of the KH instability through linear, nonlinear, and saturated stages and with the expansion of magnetized material in simulated observations of the jet. From comparison of measured wavelengths and wave speeds with the predictions from linear stability analysis, we see evidence that the KH instability is the primary cause for mass entrainment in these simulations, and that the expansion reduces the rate of mass entrainment. This reduced rate can be observed as a somewhat greater distance between the two transition points separating the three stages of expansion.Comment: 18 pages, 6 figures, AASTeX, to appear in Nov 1 issue of ApJ (vol 543), postscript versions of Figures 3 and 5 are available at http://crux.astr.ua.edu/~rosen/supcon/rh.htm

Modeling Helical Structures in Relativistic Jets

Many jets exhibit twisted helical structures. Where superluminal motions are detected, jet orientation and pattern/flow speed are considerably constrained. In this case modeling efforts can place strong limits on conditions in the jet and in the external environment. This can be done by modeling the spatial development of helical structures which are sensitively dependent on these conditions. Along an expanding jet this sensitivity manifests itself in predictable changes in pattern speed and observed wavelength. In general, twists of low frequency relative to the local resonant frequency are advected along the expanding jet into a region in which the twist frequency is high relative to the local resonant frequency. The wave speed can be very different in these two frequency regimes. Potential effects include helical twists with a nearly constant apparent wavelength, an apparent wavelength scaling approximately with the jet radius for up to two orders of magnitude of jet expansion, or multiple twist wavelengths with vastly different intrinsic scale and vastly different wave speeds that give rise to similar observed twist wavelengths but with very different observed motion. In this paper I illustrate the basic intrinsic and observed behavior of these structures and show how to place constraints on jet conditions in superluminal jets using the apparent structures and motions in the inner 3C 120 jet.Comment: 18 pages, 7 figure

3-D GRMHD and GRPIC Simulations of Disk-Jet Coupling and Emission

We investigate jet formation in black-hole systems using 3-D General Relativistic Particle-In-Cell (GRPIC) and 3-D GRMHD simulations. GRPIC simulations, which allow charge separations in a collisionless plasma, do not need to invoke the frozen condition as in GRMHD simulations. 3-D GRPIC simulations show that jets are launched from Kerr black holes as in 3-D GRMHD simulations, but jet formation in the two cases may not be identical. Comparative study of black hole systems with GRPIC and GRMHD simulations with the inclusion of radiate transfer will further clarify the mechanisms that drive the evolution of disk-jet systems.Comment: 3 pages, 1 figure, Proceedings of the Eleventh Marcel Grossmann Meeting on General Relativity, edited by H. Kleinert, R.T. Jantzen and R. Ruffini, World Scientific, Singapore, 200

Lentiviral vectors with amplified beta cell-specific gene expression.

An important goal of gene therapy is to be able to deliver genes, so that they express in a pattern that recapitulates the expression of an endogenous cellular gene. Although tissue-specific promoters confer selectivity, in a vector-based system, their activity may be too weak to mediate detectable levels in gene-expression studies. We have used a two-step transcriptional amplification system to amplify gene expression from lentiviral vectors using the human insulin promoter. In this system, the human insulin promoter drives expression of a potent synthetic transcription activator (the yeast GAL4 DNA-binding domain fused to the activation domain of the Herpes simplex virus-1 VP16 activator), which in turn activates a GAL4-responsive promoter, driving the enhanced green fluorescent protein reporter gene. Vectors carrying the human insulin promoter did not express in non-beta-cell lines, but expressed in murine insulinoma cell lines, indicating that the human insulin promoter was capable of conferring cell specificity of expression. The insulin-amplifiable vector was able to amplify gene expression five to nine times over a standard insulin-promoter vector. In primary human islets, gene expression from the insulin-promoted vectors was coincident with insulin staining. These vectors will be useful in gene-expression studies that require a detectable signal and tissue specificity

On the Dynamics and Structure of Three-Dimensional Trans-Alfvenic Jets

Three-dimensional magnetohydrodynamical simulations of strongly magnetized ``light'' conical jets have been performed. An investigation of the transition from sub-Alfv\'enic to super-Alfv\'enic flow has been made for nearly poloidal and for helical magnetic fields. The jets are stable to asymmetric modes of jet distortion provided they are sub-Alfv\'enic over most of their interior but destabilize rapidly when they become on average super-Alfv\'enic. The jets are precessed at the origin and the resulting small amplitude azimuthal motion is communicated down the jet to the Alfv\'en point where it couples to a slowly moving and rapidly growing helical twist. Significant jet rotation can contribute to destabilization via increase in the velocity shear between the jet and the external medium. Destabilization is accompanied by significant mass entrainment and the jets slow down significantly as denser external material is entrained. Synchrotron intensity images satisfactorily reveal large scale helical structures but have trouble distinguishing a large amplitude elliptical jet distortion that appears as an apparent pinching in an intensity image. Smaller scale jet distortions are not clearly revealed in intensity images, largely as a result of the relatively small total pressure variations that accompany destabilization and growing distortions. Fractional polarization is high as a result of the strong ordered magnetic fields except where the intensity image suggests cancellation of polarization vectors by integration through twisted structures.Comment: 27 pages, 11 figures, AASTeX, to appear in Oct 20 issue of ApJ, postscript versions of Figures 5 and 6 are available at this URL http://crux.astr.ua.edu/~rosen/tralf/hr.htm

Dynamics and Structure of Three-Dimensional Trans-Alfvenic Jets. II. The Effect of Density and Winds

Two three-dimensional magnetohydrodynamical simulations of strongly magnetized conical jets, one with a poloidal and one with a helical magnetic field, have been performed. In the poloidal simulation a significant sheath (wind) of magnetized moving material developed and partially stabilized the jet to helical twisting. The fundamental pinch mode was not similarly affected and emission knots developed in the poloidal simulation. Thus, astrophysical jets surrounded by outflowing winds could develop knotty structures along a straight jet triggered by pinching. Where helical twisting dominated the dynamics, magnetic field orientation along the line-of-sight could be organized by the toroidal flow field accompanying helical twisting. On astrophysical jets such structure could lead to a reversal of the direction of Faraday rotation in adjacent zones along a jet. Theoretical analysis showed that the different dynamical behavior of the two simulations could be entirely understood as a result of dependence on the velocity shear between jet and wind which must exceed a surface Alfven speed before the jet becomes unstable to helical and higher order modes of jet distortion.Comment: 25 pages, 15 figures, in press Astrophysical Journal (September

Ewing sarcoma in a child with neurofibromatosis type 1.

We report here on a case of Ewing sarcoma (ES) occurring in a child with neurofibromatosis type 1. The sarcoma had an EWSR1-ERG translocation as well as loss of the remaining wild-type allele of NF1. Loss of the NF1 wild-type allele in the tumor suggests that activation of the Ras pathway contributed to its evolution. Review of available public data suggests that secondary mutations in the Ras pathway are found in ∼3% of ESs. This case suggests that Ras pathway activation may play a role in tumor progression in a subset of ESs

A Comparison of the Morphology and Stability of Relativistic and Nonrelativistic Jets

We compare results from a relativistic and a nonrelativistic set of 2D axisymmetric jet simulations. For a set of five relativistic simulations that either increase the Lorentz factor or decrease the adiabatic index we compute nonrelativistic simulations with equal useful power or thrust. We examine these simulations for morphological and dynamical differences, focusing on the velocity field, the width of the cocoon, the age of the jets, and the internal structure of the jet itself. The primary result of these comparisons is that the velocity field of nonrelativistic jet simulations cannot be scaled up to give the spatial distribution of Lorentz factors seen in relativistic simulations. Since the local Lorentz factor plays a major role in determining the total intensity for parsec scale extragalactic jets, this suggests that a nonrelativistic simulation cannot yield the proper intensity distribution for a relativistic jet. Another general result is that each relativistic jet and its nonrelativistic equivalents have similar ages (in dynamical time units, = R/a_a, where R is the initial radius of a cylindrical jet and a_a is the sound speed in the ambient medium). In addition to these comparisons, we have completed four new relativistic simulations to investigate the effect of varying thermal pressure on relativistic jets. The simulations generally confirm that faster (larger Lorentz factor) and colder jets are more stable, with smaller amplitude and longer wavelength internal variations. The apparent stability of these jets does not follow from linear normal mode analysis, which suggests that there are available growing Kelvin-Helmholtz modes. (Abridged.)Comment: 32 pages, AASTEX, to appear in May 10, 1999 issue of ApJ, better versions of Figures 1 and 6 are available at http://crux.astr.ua.edu/~rosen/rel/rhdh.htm

The kinematics in the pc-scale jets of AGN The case of S5 1803+784

We present a kinematic analysis of jet component motion in the VLBI jet of the BL Lac object S5 1803+784, which does not reveal long-term outward motion for most of the components. Understanding the complex kinematic phenomena can possibly provide insights into the differences between quasars and BL Lac objects. The blazar S5 1803+784 has been studied with VLBI at $\nu$ =1.6, 2.3, 5, 8.4, and 15 GHz between 1993.88 and 2005.68 in 26 observing runs. We (re)analyzed the data and present Gaussian model-fits. We collected the already published kinematic information for this source from the literature and re-identified the components according to the new scenario presented in this paper. Altogether, 94 epochs of observations have been investigated. A careful study of the long-term kinematics reveals a new picture for component motion in S5 1803+784. In contrast to previously discussed motion scenarios, we find that the jet structure within 12 mas of the core can most easily be described by the coexistence of several bright jet features that remain on the long-term at roughly constant core separations (in addition to the already known {\it stationary} jet component $\sim$ 1.4 mas) and one faint component moving with an apparent superluminal speed ($\sim$ 19c, based on 3 epochs). While most of the components maintain long-term roughly constant distances from the core, we observe significant, smooth changes in their position angles. We report on an evolution of the whole jet ridge line with time over the almost 12 years of observations. The width of the jet changes periodically with a period of $\sim$ 8 to 9 years. We find a correlation between changes in the position angle and maxima in the total flux-density. We present evidence for a geometric origin of the phenomena and discuss possible models.Comment: The manuscript will be published by A&