Probing the parton densities of polarized photons at a linear e^+e^- collider

The present theoretical status of spin-dependent parton densities Delta f^{\gamma}(x,Q^2) of circularly polarized photons is briefly reviewed. It is then demonstrated that measurements of the deep-inelastic spin asymmetry A_1^{\gamma}\simeq g_1^{\gamma}/F_1^{\gamma} and of di-jet rapidity distributions at a future linear e^+e^- collider appear to be particularly suited for a determination the spin-dependent photonic quark and gluon densities, respectively. Special emphasis is devoted to a comparison of the different sources of polarized photons at a linear collider: the equivalent photon approximation and backscattered laser (Compton) photons. It is shown that backscattered laser photons are highly favorable, even indispensable, for decent measurements of the Delta f^{\gamma}(x,Q^2).Comment: 7 pages, LaTeX, 4 eps figures, uses amssymb, espcrc2 (included), and epsfig styles; Contribution to the Proceedings of the `International Conference on the Structure and Interactions of the Photon (Photon99)' [Nucl. Phys. B (Proc. Suppl.)], Freiburg, Germany, May 199

Transcriptional control of the H-NS antagonists LeuO and RcsB-BglJ in Escherichia coli

The bacterial nucleoid-associated protein (NAP) H-NS is involved in the organization and compaction of the bacterial chromatin and acts as a global respressor, mainly of genes that have been acquired by horizontal gene transfer and that are related to stress responses and pathogenicity. Binding of H-NS to the DNA and formation of a nucleoprotein complex at promoter regions leads to repression. This repressor effect of H-NS can be antagonized by gene-specific transcription factors (H-NS antagonists) that activate transcription of H NS-repressed genes by competing with H-NS for binding or by disturbing formation of the nucleoprotein complex. Two examples of such H NS antagonists are the LysR-type transcription factor LeuO and the FixJ/NarL-type transcription factor heterodimer RcsB-BglJ. LeuO is a pleiotropic regulator of stress responses and virulence determinants. RcsB-BglJ activates transcription of the H NS-repressed bgl (aryl-β,D-glucoside) operon. In this work, novel targets of RcsB-BglJ were identified in Escherichia coli by microarray analyses. The results suggest that heterodimerization of RcsB and BglJ is essential for regulation. Further, in addition to genes related to unknown or predicted function in the membrane the leuO gene was identified as a target gene. Detailed analysis of transcriptional regulation of leuO demonstrated that RcsB-BglJ strongly activates transcription of leuO by binding proximal to a newly mapped leuO promoter. Thus RcsB-BglJ antagonizes repression of leuO by H-NS and the H-NS-like protein StpA. Additional data presented here show that LeuO negatively autoregulates its own expression and inhibits activation of leuO by RcsB-BglJ. Regulation of leuO by RcsB-BglJ and autoregulation by LeuO, as shown here, as well as activation of bglJ by LeuO, as published previously, indicates a feedback control mechanism of two global transcriptional regulators and H-NS antagonists.This feedback regulation may ensure turn on of their expression in response to specific environmental signals. Screens to search for novel regulators or upstream signals were performed by transposon mutagenesis and by using a genomic expression library. These screens indicate that additional factors may be involved in the regulation of this leuO-bglJ feedback loop

Exploring Nucleon Spin Structure in Longitudinally Polarized Collisions

We review how RHIC is expected to deepen our understanding of the spin structure of longitudinally polarized nucleons. After briefly outlining the current status of spin-dependent parton densities and pointing out open questions, we focus on theoretical calculations and predictions relevant for the RHIC spin program. Estimates of the expected statistical accuracy for such measurements are presented, taking into account the acceptance of the RHIC detectors.Comment: 10 pages, 7 figures, uses aipproc style, invited talk presented at the 15th International Spin Physics Symposium 'SPIN 2002', Sept. 9-14 2002, Brookhaven National Laboratory, Upton, N

Spin Physics at RHIC - a Theoretical Overview

We review how RHIC is expected to deepen our understanding of the spin structure of longitudinally and transversely polarized nucleons. After briefly outlining the current status of spin-dependent parton densities and pointing out open questions, we focus on theoretical calculations and predictions relevant for the RHIC spin program. Estimates of the expected statistical accuracy for such measurements are presented, taking into account the acceptance of the RHIC detectors.Comment: 13 pages, 8 figures, uses ws-procs9x6 style, invited talk presented at the workshop `Testing QCD through Spin Observables in Nuclear Targets', Charlottesville, VA, April 18-20, 200

Do Strict Electoral Campaign Finance Rules Limit Corruption?

Wahlkampffinanzierung, Parteienfinanzierung, Korruption, Österreich, Frankreich, Deutschland, Japan, , Vereinigte Staaten, Campaign finance, Party finance, Corruption, Austria, France, Germany, United States