A Look at What Is (and Isn't) Known About Quasar Broad Line Regions and How Narrow-Line Seyfert 1 Galaxies Fit In

The evidence is reviewed that the Broad Line Region (BLR) probably has two distinct components located at about the same distance from the central black hole. One component, BLR II, is optically-thick, low-ionization emission at least some of which arises from a disc and the other, BLR I, is probably optically-thin emission from a more spherically symmetric halo or atmosphere. The high Fe II/H-beta ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are not due to strong Fe II emission, as is commonly thought, but to unusually weak Balmer emission, probably caused by higher densities. NLS1s probably differ from non-NLS1s because of the higher density of gas near the black hole. This produces a higher accretion rate, a denser BLR, and a view of the central regions that is more face-on.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

Agile Software Development

In this article, we contrast the results of a series of interviews with agile software development organizations with a case study of a distributed agile development effort, focusing on how information security is taken care of in an agile context. The interviews indicate that small and medium-sized agile software development organizations do not use any particular methodology to achieve security goals, even when their software is web-facing and potential targets of attack, and our case study confirms that even in cases where security is an articulated requirement, and where security design is fed as input to the implementation team, there is no guarantee that the end result meets the security objectives. We contend that security must be built as an intrinsic software property and emphasize the need for security awareness throughout the whole software development lifecycle. We suggest two extensions to agile methodologies that may contribute to ensuring focus on security during the complete lifecycleacceptedVersionpublishedVersio

REPLICA ORNSTEIN-ZERNIKE EQUATIONS FOR POSITIONALLY FROZEN HEISENBERG SYSTEMS

We present the formulation of the Replica Ornstein-Zernike equations for a model of positionally frozen disordered Heisenberg spin system. The results are obtained for various models, one in which the particle positions correspond to a frozen hard sphere fluid, another system in which the configurations are generated by a random insertion of hard spheres, a system of randomly distributed spins, and finally a system corresponding to a soft sphere fluid quenched at high and low temperatures. We will see that the orientational structure of the spin system is fairly well reproduced by the integral equation which, however, does not correctly account for the critical behaviour

A Suboptimal src 3′ Splice Site Is Necessary for Efficient Replication of Rous Sarcoma Virus

AbstractRegulation of splicing of Rous sarcoma virus (RSV) RNA primary transcripts is necessary, as with other retroviruses, to allow for the accumulation of unspliced RNA and approximately equivalent amounts of spliced env and src mRNAs. Previous studies have indicated that the env 3′ splice site is suboptimal because it has a nonconsensus branchpoint sequence and that this suboptimal splice site is required for virus replication (R. A. Katz and A.M. Skalka, 1990, Mol. Cell Biol. 10:696-704). We show in this report that the RSV src 3′ splice site is also suboptimal. Mutagenesis of the src polypyrimidine-rich tract, which is interspersed with purines, to an uninterrupted 14-nt pyrimidine tract resulted in a three- to fourfold increase in the level of src splicing. Concomitant with this increase in src splicing, a cryptic 5′ splice site within the env gene was activated. Splicing at this splice site is normally detected in nonpermissive mammalian cells where src splicing is elevated but occurs at low levels in permissive chicken embryo fibroblasts (CEF). In CEF, mutant viruses with the improved src 3′ splice site replicated significantly slower than the wild-type virus. Transformation-defective revertants lacking the src 3′ splice site were rapidly selected after passage of the chicken cells infected with the mutant virus. Thus, an inefficient src 3′ splice site appears to be necessary for the efficient replication of RSV

Measures on the Lattice of Closed Inner Ideals in a Spin Triple

AbstractTwo elements J and K of the complete lattice I(A) of weak*-closed inner ideals in a JBW*-triple A are said to be centrally orthogonal if there exists a weak*-closed ideal I in A such that A2(J)⊆A2(I) and A2(K)⊆A0(I), and are said to be rigidly collinear when A2(J)⊆A1(K) and A2(K)⊆A1(J), where, for j equal to 0, 1, or 2, Aj(I), Aj(J), and Aj(K), are the components in the generalized Peirce decomposition of A relative to the weak*-closed inner ideals I, J, and K, respectively. A measure m on I(A) is a mapping from I(A) to C such that, if J and K are either centrally orthogonal or rigidly collinear, thenmJ∨K=mJ+mK.A complex Hilbert space A endowed with a conjugation possesses a triple product and norm with respect to which it forms a JBW*-triple, known as a spin triple. In this paper the structure of the complete lattice I(A) of closed inner ideals in a spin triple A and the measures on it are investigated. It is shown that, if the dimension of A is greater than 5, then there are no non-zero measures on I(A). When the dimension of A is 5, non-zero measures exist and, up to multiplication by a constant, a unique measure exists that is invariant under automorphisms of A. When the dimension of A is 4, then A is triple isomorphic to the W*-algebra of 2×2 complex matrices. In this case results of Bunce and Wright are used to show that there is an uncountable number of measures on I(A). The situation when the dimension of A is less than 4 is also described