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PubMed2005

[Improvement of the first cerebral stereotactic radiosurgery system of Hungary].

OBJECTIVE: The first cerebral stereotactic radiosurgery system in Hungary was built in 1991. This system was based on a Leksell stereotactic head frame and a Neptun 10p linear accelerator. We performed 624 radiosurgery treatments with this system between 1991 and 2000. Our objective was to increase the reliability of operation and to extend the applicability of our radiosurgery system. METHODS AND MATERIALS: We modified our stereotactic floor stand with specially designed adapter plates to make it compatible with the Mevatron KD and Neptun 10p linear accelerators and other stereotactic head frames (Riechert-Mundiger, CRW and BrainLab). We made a new tertiary collimator holder attachable to the Mevatron KD linac. The range of treatable cerebral lesion was increased from 10-30 mm to 5-42.5 mm with additional collimator inserts. With the above modifications our radiosurgery system is compatible simultaneously with the Neptun 10p and the Mevatron KD linear accelerators. This way we were able to increase the reliability of operation of the system, as the treatment can be performed with the Neptun 10p linac in case of breakdown of the Mevatron KD linac after fixation of the head frame to a patient's skull. RESULTS: The measured diameter of the radiation isocenter defined by the new radiosurgery collimator was less than 1 mm with the Mevatron KD linac. According to the Lutz-test the distance between the radiosurgery isocenter and the rotation axis of ZIV treatment table was less than 0.5 mm. Results of phantom test showed that the overall spatial precision of our modified radiosurgery system was better than 1.3 mm with Leksell head frame. CONCLUSIONS: On the basis of experiences with 662 patients' radiosurgery treatments, the extension of our first cerebral radiosurgery system to Mevatron KD linear accelerator resulted in a more reliable operation. In accordance with our phantom tests the extension of the original system did not worsen its overall spatial precision.

Brain Neoplasms↗

PubMed1997

A disk of scattered icy objects and the origin of Jupiter-family comets.

Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as approximately 6 x 10(8) objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ20 and 1996 TL66, have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified.

Evolution, Planetary↗

PubMedDate not supplied

The Voyager Interstellar Mission.

The Voyager Interstellar Mission began on January 1, 1990, with the primary objective being to characterize the interplanetary medium beyond Neptune and to search for the transition region between the interplanetary medium and the interstellar medium. At the start of this mission, the two Voyager spacecraft had already been in flight for over twelve years, having successfully returned a wealth of scientific information about the planetary systems of Jupiter, Saturn, Uranus, and Neptune, and the interplanetary medium between Earth and Neptune. The two spacecraft have the potential to continue returning science data until around the year 2020. With this extended operating lifetime, there is a high likelihood of one of the two spacecraft penetrating the termination shock and possibly the heliopause boundary, and entering interstellar space before that time. This paper describes the Voyager Interstellar Mission--the mission objectives, the spacecraft and science payload, the mission operations system used to support operations, and the mission operations strategy being used to maximize science data return even in the event of certain potential spacecraft subsystem failures. The implementation of automated analysis tools to offset and enable reduced flight team staffing levels is also discussed.

Astronomy↗

PubMed2004

Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits.

The Kuiper belt extends from the orbit of Neptune at 30 au to an abrupt outer edge about 50 au from the Sun. Beyond the edge is a sparse population of objects with large orbital eccentricities. Neptune shapes the dynamics of most Kuiper belt objects, but the recently discovered planet 2003 VB12 (Sedna) has an eccentric orbit with a perihelion distance of 70 au, far beyond Neptune's gravitational influence. Although influences from passing stars could have created the Kuiper belt's outer edge and could have scattered objects into large, eccentric orbits, no model currently explains the properties of Sedna. Here we show that a passing star probably scattered Sedna from the Kuiper belt into its observed orbit. The likelihood that a planet at 60-80 au can be scattered into Sedna's orbit is about 50 per cent; this estimate depends critically on the geometry of the fly-by. Even more interesting is the approximately 10 per cent chance that Sedna was captured from the outer disk of the passing star. Most captures have very high inclination orbits; detection of such objects would confirm the presence of extrasolar planets in our own Solar System.

Journal Article↗

PubMed2006

Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing.

In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M(o)) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (au), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 au from normal stars. Here we report the discovery of a 5.5(+5.5)(-2.7) M(o) planetary companion at a separation of 2.6+1.5-0.6 au from a 0.22+0.21-0.11 M(o) M-dwarf star, where M(o) refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.

Journal Article↗

PubMed2006

Reduced treatment success in lipid management among women with coronary heart disease or risk equivalents: results of a national survey.

BACKGROUND: This survey assessed and compared National Cholesterol Education Program (NCEP) Third Adult Treatment Panel lipid treatment goal achievement for men versus women undergoing treatment of dyslipidemia. METHODS: Patients receiving treatment for dyslipidemia from physicians (N = 376) in the United States who were high prescribers of lipid medications were enrolled in the NCEP Evaluation Project Utilizing Novel E-Technology (NEPTUNE) II. Data from a single office visit were collected and entered into the NEPTUNE software on a personal digital assistant and uploaded to a central database via the Internet. RESULTS: Of the 4885 patients evaluated, 2103 (43%) were women. NCEP Third Adult Treatment Panel low-density lipoprotein cholesterol (LDL-C) goal achievement was similar between women and men with 0 or 1 risk factor (89% and 88%, respectively) and 2 or more risk factors (75% and 76%, respectively). However, fewer women than men achieved goal in the coronary heart disease and risk equivalents (CHD + CHD RE) category (50% vs 60%, respectively; P < .001). Logistic regression analyses examining the association between sex and LDL-C treatment goal achievement, and evaluating potential confounding by other predictors of treatment success, indicated an age-adjusted odds ratio of 0.66 (95% confidence interval, 0.56-0.77; P < .001) and a multivariate odds ratio of 0.76 (95% confidence interval, 0.62-0.93; P = .009) for women compared with men in the CHD + CHD RE category. CONCLUSIONS: Female sex was associated with lower likelihood of LDL-C goal achievement among patients with CHD + CHD RE. This relationship remained significant after adjustment for other significant predictors of treatment success.

Anticholesteremic Agents↗

PubMed1997

External supply of oxygen to the atmospheres of the giant planets.

The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust. Here we report the detection, by infrared spectroscopy, of gaseous H2O in the upper atmospheres of Saturn, Uranus and Neptune. The implied H2O column densities are 1.5 x 10(15), 9 x 10(13) and 3 x 10(14) molecules cm(-2) respectively. CO2 in comparable amounts was also detected in the atmospheres of Saturn and Neptune. These observations can be accounted for by external fluxes of 10(5)-10(7) H2O molecules cm(-2) s(-1) and subsequent chemical processing in the atmospheres. The presence of gaseous water and infalling dust will affect the photochemistry, energy budget and ionospheric properties of these atmospheres. Moreover, our findings may help to constrain the injection rate and possible activity of distant icy objects in the Solar System.

Carbon Dioxide↗

PubMed1999

Superionic and metallic states of water and ammonia at giant planet conditions.

The phase diagrams of water and ammonia were determined by constant pressure ab initio molecular dynamic simulations at pressures (30 to 300 gigapascal) and temperatures (300 to 7000 kelvin) of relevance for the middle ice layers of the giant planets Neptune and Uranus. Along the planetary isentrope water and ammonia behave as fully dissociated ionic, electronically insulating fluid phases, which turn metallic at temperatures exceeding 7000 kelvin for water and 5500 kelvin for ammonia. At lower temperatures, the phase diagrams of water and ammonia exhibit a superionic solid phase between the solid and the ionic liquid. These simulations improve our understanding of the properties of the middle ice layers of Neptune and Uranus.

Ammonia↗

PubMed2005

Non-high-density lipoprotein cholesterol: the forgotten therapeutic target.

The National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATP III) has acknowledged mounting evidence of an independent association between hypertriglyceridemia and coronary artery disease risk by issuing guidelines that identify non-high-density lipoprotein (HDL) cholesterol as a secondary target for therapy in patients with elevated triglyceride levels. In 2003, a national survey of outpatient lipid management was conducted for patients undergoing treatment by physicians who were high prescribers of lipid-altering drugs. Results of the NCEP Evaluation Project Utilizing Novel E-Technology II (NEPTUNE II) survey indicated much higher frequencies of low-density lipoprotein (LDL) cholesterol goal achievement compared with frequencies observed in a similarly designed survey in 1997. However, non-HDL cholesterol treatment success in the NEPTUNE II survey was markedly lower than that for LDL cholesterol overall and across risk categories. More aggressive therapy is therefore needed to achieve non-HDL cholesterol goals than LDL cholesterol goals. After achievement of LDL cholesterol goals, non-HDL cholesterol can be managed more aggressively by lowering LDL cholesterol or by using strategies that target a reduction in very-low-density lipoprotein cholesterol. Because the prevalence of hypertriglyceridemia in the United States is high and increasing, enhanced efforts to improve non-HDL cholesterol goal achievement have the potential to produce a substantial effect on public health.

Cholesterol, HDL↗

PubMed2006

Ethnic differences in achievement of cholesterol treatment goals. Results from the National Cholesterol Education Program Evaluation Project Utilizing Novel E-Technology II.

BACKGROUND: African Americans (AA) have the highest coronary heart disease mortality rate of any ethnic group in the United States. Data from the National Cholesterol Education Program Evaluation ProjecT Utilizing Novel E-Technology (NEPTUNE) II survey were used to assess ethnic differences in low-density lipoprotein cholesterol (LDL-C) goal achievement. METHODS: NEPTUNE II surveyed patients with treated dyslipidemia to assess achievement of treatment goals established by the Adult Treatment Panel III of the National Cholesterol Education Program. United States physicians working in primary care or relevant subspecialties enrolled 10 to 20 consecutive patients (May to September 2003), and patient data were recorded in Personal Digital Assistants and uploaded to a central database via the internet. RESULTS: Among 4,885 patients receiving treatment for dyslipidemia, 79.7% were non-Hispanic white (NHW) and 8.4% were AA. Non-Hispanic white and AA patients had significantly different frequencies of treatment success, with 69.0% and 53.7%, respectively, having achieved their LDL-C goal (P<.001). African-American patients were more likely to be in the highest risk category, and less likely to be using lipid drug therapy, taking high-efficacy statins, and receiving care from a subspecialist, but the difference in goal achievement remained significant (P<.001) after adjustment for these and other predictors of treatment success. CONCLUSIONS: The frequency of treatment success in dyslipidemia management was significantly lower in AA than NHW patients. Additional research is needed to elucidate reasons for this disparity and to evaluate strategies for improving goal achievement among AA patients receiving therapy for dyslipidemia.

Black or African American↗

PubMed1993

Hydrothermal processing of cometary volatiles--applications to Triton.

Subsequent to its capture by Neptune, Triton could have experienced an episode of tidal heating sufficient to melt its icy mantle and possibly its rocky core as well. This heating would have driven hydrothermal circulation at the core-rock/mantle-ocean boundary. We consider the chemical consequences of this hydrothermal reprocessing on Triton's volatile budget by assuming an initial cometary composition for the icy mantle and evaluating the effects of changes in temperature and oxidation state. We assume that the latter would have been controlled by mineral assemblages in the rock. Such reprocessing could explain the lack of carbon monoxide in the atmosphere of Triton and its depletion relative to N2 and (apparently) CO2 in the satellite's surface ices. Our calculations also show that whatever the original source of nitrogen in Triton, N2 and/or NH3 are likely abundant products of hydrothermal reprocessing. Depending on the temperature and prevailing oxidation state, acetic acid, ethanol, urea, methanol, and ethanamine are possible important components, in addition to ammonia, of the resulting mantle material. Triton may thus preserve the organic chemistry that might have led to the origin of life in early terrestrial hydrothermal systems.

Ammonia↗

PubMed1995

A study of chemical systems using signal flow graph theory.

Photochemistry of giant planets and their satellites is characterized by numerous reactions involving a lot of 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. 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 pathways of dissociation of CH4 are possible from L alpha radiation. A chemical system containing 14 species and 30 reactions including these different pathways 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 pathways as a function of time is presented.

Ethane↗

PubMed1995

Infrared spectroscopy of organics of planetological interest at low temperatures.

In the context of prebiotic chemistry in space, some of the outer planetary objects display H, C, N and O rich chemistry similar to the one in the biosphere of Earth. Of particular interest are Saturn's moon, Titan; Neptune's moon, Triton; and Pluto where extreme cold conditions prevail. Identifications of chemical species on these objects (surfaces and atmospheres) is essential to a better understanding of the radiation induced chemical reactions occurring thereon. There have been several ground based observations of these planetary objects in the infrared windows from 1 to 2.5 micrometers. Voyager also provided spectra in the thermal infrared (6 to 50 micrometers) region. Interpretation of these data require laboratory infrared spectra of relevant species under the temperature conditions appropriate to these objects. The results of some of these studies carried out in our laboratory and elsewhere and their impact on the analyses of the observed data will be summarized.

Cold Temperature↗

PubMed1989

Triton: stratospheric molecules and organic sediments.

Hydrocarbons and nitriles are produced in Triton's stratosphere by energetic electrons from Neptune's magnetosphere and other charged particle sources. Laboratory plasma experiments reported here show a substantial yield of molecules from low pressure flows of 10(-3) CH4 in N2 appropriate to Triton if both CH4 and N2 are saturated at the surface. An active magnetosphere similar to that of Uranus would result in a flux approximately 0.3 erg cm-2 s-1 of 0.1-1 MeV electrons in Triton's stratosphere; molecular production rates are then 10(6)-10(8) cm-2 s-1 for NH3, C2H2, HCN, and NCCN; tens of hundreds of gm cm-2 of these compounds per 10(9) yr (and lesser quantities of at least eight other molecules experimentally detected) would freeze to fine-grained white condensates in the lower stratosphere and sediment to the surface. Along with dark/colored organic haze produced in the stratosphere and other heteropolymers produced at the surface, these condensates are subjects to redistribution by aeolian processes and may appear as lag deposits and/or sediment layers. A simple eddy diffusion model indicates abundances approximately 10(19) molec cm-2 for HCN and C2H2, and > 10(17) molec cm-2 for NCCN, CH3CCH, CH2CCH2, and CH3CN in the stratosphere; these and other organic molecules will be detectable by IRIS if the stratosphere is (as expected) heated through ultraviolet and visible light absorption by the haze.

Atmosphere↗

PubMed1990

Triton: topside ionosphere and nitrogen escape.

The principal ion in the ionosphere of Triton is N+. Energetic electrons of magnetospheric origin are the primary source of ionization, with a smaller contribution due to photoionization. To explain the topside plasma scale height, we postulate that N+ ions escape from Triton. The loss rate is 3.4 x 10(7) cm-2 s-1 or 7.9 x 10(24) ions s-1. Dissociative recombination of N2+ produces neutral exothermic fragments that can escape from Triton. The rate is estimated to be 8.6 x 10(6) N cm-2 s-1 or 2.0 x 10(24) atoms s-1. Implications for the magnetosphere of Neptune and Triton's evolution are discussed.

Atmosphere↗

PubMed1987

Solid hydrocarbon aerosols produced in simulated Uranian and Neptunian stratospheres.

Optical constants n and k are measured for thin hydrocarbon films produced from charged particles (RF plasma) irradiation of (1) 100% CH4; (2) 7% CH4, 93% H2; (3) 0.5% CH4, 99.5% H2; (4) 0.0002% CH4, 99.3% H2 (with impurities); and (5) 3 to 25% CH4, 25% He, remainder H2--all at submillibar pressures. In all experiments, yellow to deep brown-red solid products are synthesized which are hypothesized to be, at least in part, the unidentified visible and near-UV chromophores in the stratospheres of Uranus and Neptune. Results for experiments 2, 3, and 4 are in good mutual accord, but are significantly different from experiments 1 and 5. He in the precursor gases affects the product composition. Typical solid products for experiments 5 show, at 0.55 micrometer wavelength, n = 1.60 +/- 0.05, 3 x 10(-2) > or = k > or = 3 x 10(-3), and [C/H] approximately equal to 0.7. These results are, for n and k respectively, consistent with and in excellent agreement with those derived from high phase angle Voyager 2 photometry of Uranus (Pollack et al., this issue). Aerosols produced directly from the atmosphere by precipitating magnetospheric charged particles may be competitive with those produced by UV and charged particle irradiation of simple hydrocarbon condensates. The optical and chemical properties of aerosols in the Uranian and Neptunian atmospheres may evolve toward higher values of n and k and higher carbon content as the particles sediment through changing radiation and thermal environments.

Aerosols↗

PubMed1998

Detection of water ice on Nereid.

We report the detection of the 1.5 and 2.0 micrometers absorption bands of water ice in the near-infrared reflection spectrum of Neptune's distant irregular satellite Nereid. The spectrum and albedo of Nereid appear intermediate between those of the Uranian satellites Umbriel and Oberon, suggesting a surface composed of a combination of water ice frost and a dark and spectrally neutral material. In contrast, the surface of Nereid appears dissimilar to those of the outer solar system minor planets Chiron, Pholus, and 1997 CU26. The spectrum thus provides support for the hypothesis that Nereid is a regular satellite formed in a circumplanetary environment rather than a captured object.

Astronomical Phenomena↗

PubMed1998

Evaluation of performance criteria for simulation of submaximal steady-state cycling using a forward dynamic model.

The objectives of this study were twofold. The first was to develop a forward dynamic model of cycling and an optimization framework to simulate pedaling during submaximal steady-state cycling conditions. The second was to use the model and framework to identify the kinetic, kinematic, and muscle timing quantities that should be included in a performance criterion to reproduce natural pedaling mechanics best during these pedaling conditions. To make this identification, kinetic and kinematic data were collected from 6 subjects who pedaled at 90 rpm and 225 W. Intersegmental joint moments were computed using an inverse dynamics technique and the muscle excitation onset and offset were taken from electromyographic (EMG) data collected previously (Neptune et al., 1997). Average cycles and their standard deviations for the various quantities were used to describe normal pedaling mechanics. The model of the bicycle-rider system was driven by 15 muscle actuators per leg. The optimization framework determined both the timing and magnitude of the muscle excitations to simulate pedaling at 90 rpm and 225 W. Using the model and optimization framework, seven performance criteria were evaluated. The criterion that included all of the kinematic and kinetic quantities combined with the EMG timing was the most successful in replicating the experimental data. The close agreement between the simulation results and the experimentally collected kinetic, kinematic, and EMG data gives confidence in the model to investigate individual muscle coordination during submaximal steady-state pedaling conditions from a theoretical perspective, which to date has only been performed experimentally.

Adult↗