Saturn's Auroras and Polar Atmosphere from Cassini UVIS

Conference (2006, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn, with sufficient spatial resolution to image Saturn's auroral oval when Cassini leaves Saturn's equatorial plane. We will present new images and time-series data from summer 2006. Detailed spectral models of molecular hydrogen auroral emissions that include hydrocarbon absorption and hydrogen self- absorption have now been compared to UVIS data. We are analyzing a UV spectral feature detected in an auroral oval image from 2005. The feature is an absorption feature concentrated inside the oval, at wavelengths dominated by reflected sunlight and acetylene absorption. The absorption feature appears as a broad absorption "scoop". One plausible molecule that has a similar absorption feature is benzene, which has a cross-section some 500 times larger than acetylene in this spectral region. Thus UVIS is sensitive to small quantities of benzene. Enhanced polar benzene has been previously observed at Jupiter and can be generated in coupled photochemical/auroral models. We will explore the uniqueness of this interpretation, and compare the inferred benzene abundances to results from complementary Cassini CIRS infrared observations. Additional out of the equatorial plane UVIS Saturn data planned for the coming months will improve the signal- to-noise ratio and spatial resolution on the auroral ovals and their interior. Coordinated observations with Cassini VIMS and Hubble Space Telescope are being scheduled for 2007. [less ▲]

Saturn's auroral morphology and activity during quiet magnetospheric conditions

in Journal of Geophysical Research. Space Physics (2006), 111

We report the results of a coordinated Hubble Space Telescope-Cassini campaign that took place between 26 October and 2 November 2005. During this period, Saturn's magnetosphere was in an expanded state ... [more ▼]

We report the results of a coordinated Hubble Space Telescope-Cassini campaign that took place between 26 October and 2 November 2005. During this period, Saturn's magnetosphere was in an expanded state and the solar wind was quiet, as indicated by the location of the magnetopause, in situ particle measurements, weak auroral SKR emission, and the generally low brightness of the aurora. We describe the morphology and dynamics of the aurora during this period in parallel with concurrent Cassini measurements. We show that the aurora exhibits considerable longitudinal structure and time variations over intervals of a few hours, in spite of the absence of observable external triggers and generally low intensity. In particular, enhancements of the dawn-morning oval are seen while no apparent indication of solar wind activity is observed. These features rotate at a speed corresponding to about 65% of the planet's angular velocity. We also describe energetic neutral atom measurements indicating that an ENA acceleration event occurred in the magnetotail on 26 October without any measured signature of solar wind activation. These observations suggest an intrinsically dynamical magnetosphere where injection of hot plasma occasionally takes place in the night or dawn sector during quiet magnetospheric conditions, possibly connected with either the Dungey or the Vasyliunas convection cycle. [less ▲]

Magnetotail topology around substorm onset time

Conference (2006, December 01)

The time evolution of the magnetotail topology during minutes preceding and following substorm onset is an important question of the magnetospheric dynamic. The substorm onset is a local and explosive ... [more ▼]

The time evolution of the magnetotail topology during minutes preceding and following substorm onset is an important question of the magnetospheric dynamic. The substorm onset is a local and explosive phenomenon, which makes it difficult to describe with in situ data. In this study, we investigate this problem thanks the remote sensing data provided by the FUV camera onboard the IMAGE spacecraft. In the first part of this study, we use a set of IMAGE-FUV and GOES-8 simultaneous observations obtained during substorms periods to develop a model of the magnetic field elevation angle at geosynchronous orbit. In the second part, we use a set of 259 substorms observed by the IMAGE spacecraft between 2000 and 2002. Taking advantage of the global scale of the observations provided by IMAGE-FUV, we describe the time evolution of the magnetotail topology provided by the model. An interesting result shows that the field is symmetrically stretched around the onset position before the onset time and this symmetry is broken after onset, with a more important stretching duskward to the onset. [less ▲]

Part 13: Synthesis and biological evaluation of piperazine derivatives with dual anti-PAF and anti-HIV-1 or pure antiretroviral activity

in Bioorganic & Medicinal Chemistry (2006), 14(23), 8109-8125

HIV-1 infection of the brain and PAF neurotoxicity are implicated in AIDS dementia complex. We previously reported that a trisubstituted piperazine derivative is able to diminish both HIV-1 replication in ... [more ▼]

HIV-1 infection of the brain and PAF neurotoxicity are implicated in AIDS dementia complex. We previously reported that a trisubstituted piperazine derivative is able to diminish both HIV-1 replication in monocyte-derived macrophages and PAF-induced platelet aggregation. We report in this work new compounds obtained by modifying its piperazine substituents. The structure-activity relationship study shows that a better dual activity or even pure antiretroviral compounds can be obtained in this series. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

Structure-activity relationships in platelet-activating factor. Part 14: Synthesis and biological evaluation of piperazine derivatives with dual anti-PAF and anti-HIV-1 activity

in Bioorganic & Medicinal Chemistry (2006), 14(23), 7999-8013

As HIV-associated dementia prevalence has risen with the lifespan of HIV-infected individuals, there is an important need for antiretroviral and anti-inflammatory drugs targeting the central nervous ... [more ▼]

As HIV-associated dementia prevalence has risen with the lifespan of HIV-infected individuals, there is an important need for antiretroviral and anti-inflammatory drugs targeting the central nervous system. Platelet-activating factor, a mediator of inflammation, is an HIV-induced neurotoxin secreted in the infected brain. In this work, we developed piperazine derivatives bearing a heterocyclic moiety as PAF-antagonists and HIV-1 replication inhibitors with micromolar potency. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

High prevalence of pituitary adenomas: A cross-sectional study in the province of Liege, Belgium

in Journal of Clinical Endocrinology and Metabolism (2006), 91(12), 4769-4775

Context: Prevalence data are important for assessing the burden of disease on the health care system; data on pituitary adenoma prevalence are very scarce. Objective: The objective of the study was to ... [more ▼]

Context: Prevalence data are important for assessing the burden of disease on the health care system; data on pituitary adenoma prevalence are very scarce. Objective: The objective of the study was to measure the prevalence of clinically relevant pituitary adenomas in a well-defined population. Design: This was a cross-sectional, intensive, case-finding study performed in three regions of the province of Liège, Belgium, to measure pituitary adenoma prevalence as of September 30, 2005. Setting: The study was conducted in specialist and general medical practitioner patient populations, referral hospitals, and investigational centers. Methods: Three demographically and geographically distinct districts of the province of Liège were delineated precisely using postal codes. Medical practitioners in these districts were recruited, and patients with pituitary adenomas under their care were identified. Diagnoses were confirmed after retrieval of clinical, hormonal, radiological, and pathological data; full demographic and therapeutic follow-up data were collected in all cases. Results: Sixty-eight patients with clinically relevant pituitary adenomas were identified in a population of 71,972 individuals; the mean (± SD) prevalence was 94 ± 19.3 cases per 100,000 population (95% confidence interval, 72.2 to 115.8). The group was 67.6% female and had a mean age at diagnosis of 40.3 yr; 42.6% had macroadenomas and 55.9% underwent surgery. Prolactinomas comprised 66% of the group, with the rest having nonsecreting tumors (14.7%), somatotropinomas (13.2%), or Cushing’s disease (5.9%); 20.6% had hypopituitarism. Conclusion: The prevalence of pituitary adenomas in the study population (one case in 1064 individuals) was more than 3.5–5 times that previously reported. This increased prevalence may have important implications when prioritizing funding for research and treatment of pituitary adenomas. [less ▲]

Niets doet zo goed als slechte tijden

Article for general public (2006)

L'image du mois. Oesophagite infectieuse majeure mise en evidence par tomodensitometrie thoracique

in Revue Médicale de Liège (2006), 61(12), 793-4

Inferring Groups of Correlated Failures

Poster (2006, December)

We compare and evaluate different methods to infer groups of correlated failures. These methods try to group failure events occurring nearly simultaneously in clusters. Indeed if several failures occur ... [more ▼]

We compare and evaluate different methods to infer groups of correlated failures. These methods try to group failure events occurring nearly simultaneously in clusters. Indeed if several failures occur nearly at the same moment in a network, it is possible that these failures have the same root cause. The input data of our algorithms are IP failure notifications that can be provided by several sources. We consider two sources: IS-IS Link State Packets (LSPs) and Syslog messages. Our first results on the Abilene and GÉANT networks show that the inference methods behave differently and that using IS-IS LSPs provides more accurate results than using Syslog messages. [less ▲]

Mapping uncertainty and phylogenetic uncertainty in ancestral character state reconstruction: An example in the moss genus Brachytheciastrum

in Systematic Biology (2006), 55(6), 957-971

The evolution of species traits along a phylogeny can be examined through an increasing number of possible, but not necessarily complementary, approaches. In this paper, we assess whether deriving ... [more ▼]

The evolution of species traits along a phylogeny can be examined through an increasing number of possible, but not necessarily complementary, approaches. In this paper, we assess whether deriving ancestral states of discrete morphological characters from a model whose parameters are (i) optimized by ML on a most likely tree; (ii) optimized by ML onto each of a Bayesian sample of trees; and (iii) sampled by a MCMC visiting the space of a Bayesian sample of trees affects the reconstruction of ancestral states in the moss genus Brachytheciastrum. In the first two methods, the choice of a single- or two-rate model and of a genetic distance (wherein branch lengths are used to determine the probabilities of change) or speciational (wherein changes are only driven by speciation events) model based upon a likelihood-ratio test strongly depended on the sampled trees. Despite these differences in model selection, reconstructions of ancestral character states were strongly correlated to each others across nodes, often at r > 0.9, for all the characters. The Bayesian approach of ancestral character state reconstruction offers, however, a series of advantages over the single-tree approach or the ML model optimization on a Bayesian sample of trees because it does not involve restricting model parameters prior to reconstructing ancestral states, but rather allows a range of model parameters and ancestral character states to be sampled according to their posterior probabilities. From the distribution of the latter, conclusions on trait evolution can be made in a more satisfactorily way than when a substantial part of the uncertainty of the results is obscured by the focus on a single set of model parameters and associated ancestral states. The reconstructions of ancestral character states in Brachytheciastrum reveal rampant parallel morphological evolution. Most species previously described based on phenetic grounds are thus resolved of polyphyletic origin. Species polyphylly has been increasingly reported among mosses, raising severe reservations regarding current species definition. [less ▲]