Low-ionization structures in planetary nebulae: confronting models with observations

Around 50 PNe are presently known to possess "small-scale" low-ionization structures (LISs). We consider here jets, jet-like, symmetrical and non-symmetrical LISs and present a detailed comparison of the existing model predictions with the observational morphological and kinematical properties. We find that nebulae with LISs appear indistinctly spread among all morphological classes of PNe, indicating that the processes leading to the formation of LISs are not necessarily related to those responsible for the asphericity of the large-scale morphological components of PNe. We show that both the observed velocities and locations of most non-symmetrical LISs can be reasonably well reproduced assuming either fossil condensations originated in the AGB wind or in-situ instabilities. The jet models proposed to date (HD and MHD interacting winds or accretion-disk collimated winds) appear unable to account simultaneously for the kinematical ages and the angle between the jet and the symmetry axes of the nebulae. The linear increase in velocity observed in several jets favors MHD confinement compared to pure HD interacting wind models. On the other hand, we find that the formation of jet-like systems characterized by relatively low expansion velocities cannot be explained by any of the existing models. Finally, the knots which appear in symmetrical and opposite pairs of low velocity could be understood as the survival of fossil (symmetrical) condensations formed during the AGB phase or as structures that have experienced substantial slowing down by the ambient medium.Comment: 21 pages including 5 tables. To appear in ApJ 547, Jan 2001. Also available at http://www.iac.es/publicaciones/preprints.htm

Baseline characteristics and prevalence of HPV 6, 11, 16, 18 in young German women participating in phase III clinical trials of a quadrivalent HPV (6/11/16/18) vaccine.

INTRODUCTION: As limited data among German women exist about HPV, Chlamydia trachomatis (CT) and Neisseria gonorrhoeae, we report the prevalence of these genital infections and general baseline demographics of the young German women enrolled in the phase III trials of the quadrivalent HPV vaccine. MATERIALS AND METHODS: German females (n = 437; 9-23 years) were recruited among 3 international phase 3 studies of an HPV-6/11/16/18 vaccine. We present baseline characteristics, prevalence of HPV-6/11/16/18 and, for women aged 16-23, abnormal cervical cytology and sexually transmitted diseases. RESULTS: Chlamydia trachomatis and Neisseria gonorrhoeae prevalence was 5 and 0.3%, respectively. Approximately 17% of participants had HPV-6, 11, 16, or 18 DNA or antibodies. All subjects <17 years were naïve to the four vaccine types. DISCUSSION: The results of the vaccine trials have demonstrated that it is worth administering prophylactic HPV vaccines before sexual debut; however, none of these sexually active German women were positive to all four types and most were positive to only one type. Thus, all women had the potential to benefit from vaccination with a quadrivalent HPV vaccine

Metrology for LNG custody transfer and transport fuel applications

Liquefied natural gas (LNG) is a strategic and, in case of long distances, more economical alternative for pipeline natural gas. LNG is seen as the only alternative for diesel fuel for heavy duty transport (trucks, ships), with a better CO2 footprint and less noise produced by the engine. To enable the large scale roll-out of LNG as a transport fuel, a well established metrological infrastructure for LNG has to be realized. Within the framework of the EMRP Joint research Project ENG60 “Metrology for LNG” (LNG II), a number of metrological challenges are faced. The goals are to provide traceable mass and volume flow calibrations up to 400m3 LNG/h, to improve and validate sampling techniques for composition measurements, to improve the measurement of the LNG density and to prepare and validate an algorithm for the determination of the methane number. This paper gives an overview of the objectives that have been achieved and it provides an outlook to future activities that will be performed within a.o. the EMPIR 16ENG09 LNG III project