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PubMedDate not supplied

A study of chemical systems using signal flow graph theory: application to Neptune.

Photochemistry of giant planets and their satellites is characterized by numerous reactions involving many chemical species. In the present paper, chemical systems are modeled by signal flow graphs. Such a technique evaluates the transmission of any input into the system (solar flux, electrons...) and gives access to the identification of the most important mechanisms in the chemical system. For a given chemical system, we first evaluate rate coefficients. Then, in order to obtain concentrations of each compound, we integrate the set of continuity equations by Gear's method. Gear's method is chosen rather than another classical method because it is recommended for a system of stiff equations due to the existence of greatly differing time constants. Finally, the technique of signal flow graphs is used. This method is applied to the production of hydrocarbons in the atmospheres of giant planets. In particular, the production of C2H6 in the atmosphere of Neptune from the photodissociation of CH4 is investigated. Different paths of dissociation of CH4 are possible from L alpha radiations. A chemical system containing 14 species and 30 reactions including these different paths of dissociation is integrated. The main mechanism of production of C2H6 is identified and evaluated for each model of dissociation. The importance of various reaction paths as a function of time is discussed.

Atmosphere↗

PubMed2006

A comparison of Canadian and American guidelines for lipid management using data from the National Cholesterol Education Program Evaluation ProjecT Utilizing Novel E-technology (NEPTUNE) II survey.

BACKGROUND: The United States' National Cholesterol Education Program (NCEP) Adult Treatment Panel III and the Canadian Working Group on Hypercholesterolemia and Other Dyslipidemias (CWG) have each issued guidelines for the treatment of dyslipidemia. OBJECTIVE: The present analysis compared the percentage of patients reaching target lipid levels according to NCEP and CWG guidelines among participants of the NCEP Evaluation ProjecT Utilizing Novel E-technology (NEPTUNE) II, a survey performed in the United States. METHODS: American physicians who were high prescribers of lipid-modifying medications (n=376) each enrolled 10 to 20 consecutive patients from February to September 2003. Medical information, laboratory measurements and treatment plans associated with a single office visit were entered into a personal digital assistant and uploaded to a central database via the Internet. RESULTS: Under both sets of guidelines, treatment success was strongly related to risk category (P<0.001). Treatment goal achievement in the low-risk (zero or one risk factor) and moderate-risk (two or more risk factors) categories was not substantially different between NCEP and CWG guidelines; however, in the high-risk category (coronary artery disease [CAD] and risk equivalents [RE]), CWG treatment goals were met less frequently than NCEP goals. NCEP combined low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol treatment goals were met by 39% of hypertriglyceridemic patients (27% in the CAD + CAD RE category). CWG combined low-density lipoprotein cholesterol and total cholesterol/high-density lipoprotein cholesterol ratio treatment goals were met by 38% of hypertriglyceridemic patients (19% in the CAD + CAD RE category). CONCLUSIONS: These data indicate substantial underachievement of treatment goals by patients at high risk under both the CWG and NCEP guidelines. The lower frequency of treatment success in high-risk patients according to the CWG definition indicates that more aggressive treatment is needed to reach CWG goals.

Anticholesteremic Agents↗

PubMed2002

The confinement of Neptune's ring arcs by the moon Galatea.

Neptune has five narrow ring arcs, spanning about 40 degrees in longitude, which are apparently confined against the rapid azimuthal and radial spreading that normally results from inter-particle collisions. A gravitational resonance based on the vertical motion of the nearby neptunian moon Galatea was proposed to explain the trapping of the ring particles into a sequence of arcs. But recent observations have indicated that the arcs are away from the resonance, leaving their stability again unexplained. Here we report that a resonance based on Galatea's eccentricity is responsible for the angular confinement of the arcs. The mass of the arcs affects the precession of Galatea's eccentric orbit, which will enable a mass estimate from future observations of Galatea's eccentricity.

Journal Article↗

PubMed2003

The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration.

The 'dynamically cold Kuiper belt' consists of objects on low-inclination orbits between approximately 40 and approximately 50 au from the Sun. It currently contains material totalling less than a tenth the mass of the Earth, which is surprisingly low because, according to accretion models, the objects would not have grown to their present size unless the cold Kuiper belt originally contained tens of Earth masses of solids. Although several mechanisms have been proposed to produce the observed mass depletion, they all have significant limitations. Here we show that the objects currently observed in the dynamically cold Kuiper belt were most probably formed within approximately 35 au and were subsequently pushed outward by Neptune's 1:2 mean motion resonance during its final phase of migration. Combining our mechanism with previous work, we conclude that the entire Kuiper belt formed closer to the Sun and was transported outward during the final stages of planet formation.

Journal Article↗

PubMed1989

[Radiation pneumonitis in the x-ray picture following megavoltage irradiation using the Neptune 10 p. linear accelerator].

For 105 patients with healthy lungs (76 breast carcinomas, 29 testicular tumors) irradiated from 1981 to 1983 with the linear accelerator Neptune 10p. the pulmonary effects of irradiation were monitored over several years. The true dose applied for breast carcinomas was 46 Gy (2 Gy per fraction), for testicular tumors 40 Gy were applied in the mediastinal field. 9% of the patients showed excessive infiltrations, 18% radiation pneumonitis of medium degree. In 35% of the patients slight infiltrations were found. The course of the pneumonitis was, according to its stage, regular. After a latency period 30 days post irradiation the early stadium occurs. Florid pneumonitis develops between the 45th and 90th day after irradiation. Extended radiographic effects occur up to 10 days earlier. Through a period of pneumonitis with pronounced shrinkage fibrosis develops. By CT-based individual radiation planning the pulmonary radiation reaction can be significantly reduced. The differential diagnostics of radiation effects and metastases is discussed.

Aged↗

PubMed1984

Dose-rate distribution in wedged beams of 9 MV X-rays from Linac Neptune 10p and of gamma-ray beams from Gammatron 80S.

The method of calculation of the two- and three-dimensional dose-rate distribution for wedged beams of 9 MV X-rays and Co-60 gamma-rays is presented. The method was examined for Linac Neptune 10p and Gammatron 80S. The experimental results show that for computing the dose-rate distribution of a wedged beam it is sufficient to know: 1. the profile function for open fields defined as the relative dose-rate distribution across the radiation beam and 2. the parameters of the wedge filter. The computed and measured results are presented in tables and on graphs.

Cobalt Radioisotopes↗

PubMed1981

Three-dimensional dose-rate distribution of X-ray beams of linac neptun 10p and gamma-rays from Co-60 gammatron 80S for rectangular fields.

A method of calculation of the three-dimensional dose-rate distribution for X-rays of Linac Neptun 10p and gamma-rays of Gamma-tron 80S is presented. The experimental results show that the profiles function defined as the relative dose-rate across the radiation beam is useful for this purpose, and it is sufficient to determine the profile function only at one depth and for one field size. The results of measurements are presented on the graphs.

Cobalt Radioisotopes↗

PubMed1980

Absorbed dose distribution for X-ray beams and beams of electrons from the Therac 10 Neptune linear accelerator.

After a brief presentation of the Therac 10 Neptune linear accelerator a complete set of dose distribution numerical values is given. These values define the depths on the axis as a function of the depth dose and define the penumbra (as characterized by the positions of the isodose curve intersections with parallel planes to the phantom surface) for beams of X-rays and for beams of electrons. Measurements of residual X-rays are given for a 10 MeV beam of electrons.

Electrons↗

PubMed2006