3,087 research outputs found
An Anomalous UV Extension in NGC6251
Deep U-band FOC images of the nuclear region of NGC6251 have revealed a
region of extended emission which is most probably radiation scattered from a
continuum source in the nucleus. This radiation lies interior to a dust ring,
is nearly perpendicular to the radio jet axis, and is seen primarily in the FOC
U and b filters. The extension has a low observed polarization(), and
is unlikely to arise from line emission. We know of no other examples similar
to what we have found in NGC 6251, and we offer some tentative explanations.
The nuclear morphology shows clear similarities to that seen in the nucleus of
NGC 4261 except for the extended U-band radiation.Comment: 14 pages AAStex format + 4 figures; accepted for publication in ApJ
Letter
Measurement of macroscopic plasma parameters with a radio experiment: Interpretation of the quasi-thermal noise spectrum observed in the solar wind
The ISEE-3 SBH radio receiver has provided the first systematic observations of the quasi-thermal (plasma waves) noise in the solar wind plasma. The theoretical interpretation of that noise involves the particle distribution function so that electric noise measurements with long antennas provide a fast and independent method of measuring plasma parameters: densities and temperatures of a two component (core and halo) electron distribution function have been obtained in that way. The polarization of that noise is frequency dependent and sensitive to the drift velocity of the electron population. Below the plasma frequency, there is evidence of a weak noise spectrum with spectral index -1 which is not yet accounted for by the theory. The theoretical treatment of the noise associated with the low energy (thermal) proton population shows that the moving electrical antenna radiates in the surrounding plasma by Carenkov emission which becomes predominant at the low frequencies, below about 0.1 F sub P
Estimation des formes du phosphore dans la rivière Venoge en crue
Des échantillons d'eau de rivière ont été prélevés près de l'embouchure de la Venoge, affluent du Léman, au cours de cinq crues survenues entre octobre 1986 et novembre 1987. Les échantillons ont été extraits de grands volumes d'eau à l'aide d'une centrifugeuse à débit continu. La concentration de matières en suspension, et les formes du phosphore de ces échantillons ont été dosés. L'interprétation de ces données, basée sur une méthode de régression progressive, montre que la concentration en phosphore particulaire total peut être estimée par deux paramètres, la fraction de suspensions supérieure à 63 µm et la concentration en phosphore réactif dissous. Par ailleurs, puisqu'il existe des relations statistiques entre le phosphore particulaire total et les autres formes du phosphore particulaire, il est possible d'évaluer la concentration de ces dernières (formes de phosphore apatitique, non apatitique, organique et inorganique). Le phosphore total dissous peut être pareillement estimé en fonction du phosphore réactif dissous. L'estimation des formes du phosphore et ainsi que celle de leur charge en crue peut donc se faire même lorsque le volume des échantillons est limité, c'est-à-dire, lorsque la quantité de matières en suspension n'est pas suffisante pour l'analyse de toutes les formes du phosphore particutaire.In order to gain a better understanding of phosphorus transport in a storm-dependent river system, water samples were collected near the mouth of the River Venoge, Switzerlang, during five storm events between october 1986 and november 1987. Suspended sediment (SS) was extracted from large-volume water samples by continuous flow centrifugation. Soluble and particulate forms of phosphorus were subsequently analysed with the centrifuged and filtered (0.45 µm) waters, and freeze-dried SS in a < 63 µm fraction.However, the sampling usually performed at more than 4-hour intervals could not guarantee that no information had been missed, for example, the instantaneous fluctuation of soluble reactive phosphorus (SRP) during the events. Although more frequent sampling using an auto-sampler is feasible, the small volume of raw water cannot provide sufficient sediment for all the analyses of phosphorus forms. Thus, it would be useful to find a model capable of estimating phosphorus concentration in different forms, whenever the present measurements are not possible.A multivariate progressive analysis of the measured phosphorus data set shows that total particulate phosphorus (TPP) concentration can be estimated as a function of two parameters, the percentage of a SS fraction coarser than 63 µm and the SRP concentration measured in filtered water. On the other hand, general statistical relationships exist between the various forms of phosphorus. Total soluble phosphorus (TSP) is dependent upon SRP. Organic phosphorus (OP) and non-apatite inorganic phosphorus (NAIP) can be approximately assessed from TPP, measured or calculated. Then, apatite phosphorus (AP), inorganic phosphorus (IP) and total phosphorus in raw water can be calculated by means of summation/substraction operations.Modelling is apparently suitable to the storm events during which only a limited volume of water samples could be collected. It also provides a rapid way to estimate the partitioning of phosphorus loads in high flow periods of the river system, thereby reducing the field and laboratory work required
Dust detection by the wave instrument on STEREO: nanoparticles picked up by the solar wind?
The STEREO/WAVES instrument has detected a very large number of intense
voltage pulses. We suggest that these events are produced by impact ionisation
of nanoparticles striking the spacecraft at a velocity of the order of
magnitude of the solar wind speed. Nanoparticles, which are half-way between
micron-sized dust and atomic ions, have such a large charge-to-mass ratio that
the electric field induced by the solar wind magnetic field accelerates them
very efficiently. Since the voltage produced by dust impacts increases very
fast with speed, such nanoparticles produce signals as high as do much larger
grains of smaller speeds. The flux of 10-nm radius grains inferred in this way
is compatible with the interplanetary dust flux model. The present results may
represent the first detection of fast nanoparticles in interplanetary space
near Earth orbit.Comment: In press in Solar Physics, 13 pages, 5 figure
Deep spectroscopy of the FUV-optical emission lines from a sample of radio galaxies at z~2.5: metallicity and ionization
We present long-slit NIR spectra, obtained using the ISAAC instrument at the
Very Large Telescope, for nine radio galaxies at z~2.5. One-dimensional spectra
have been extracted and cross calibrated with optical spectra from the
literature to produce line spectra spanning a rest wavelength of ~1200-7000 A.
We have also produced a composite of the rest-frame UV-optical line fluxes of
powerful, z~2.5 radio galaxies. We have investigated the relative strengths of
Ly-alpha, H-beta, H-alpha, HeII 1640 and HeII 4687, and we find that Av can
vary significantly from object to object. In addition, we identify new line
ratios to calculate electron temperature: [NeV] 1575/[NeV] 3426, [NeIV]
1602/[NeIV] 2423, OIII] 1663/[OIII] 5008 and [OII] 2471/[OII]3728. We model the
emission line spectra and conclude they are best explained by
AGN-photoionization with the ionization parameter U varying between objects.
Single slab photoionization models are unable to reproduce the high- and the
low-ionization lines simultaneously: this may be alleviated either by combining
two or more single slab photoionization models with different U, or by using
mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann (1996).
On the basis of NV/NIV] and NIV]/CIV we argue that shocks make a fractional
contribution to the ionization of the EELR. We find that in the EELR of z~2
radio galaxies the N/H abundance ratio is close to its solar value. We conclude
that N/H and metallicity do not vary by more than a factor of two in our
sample. This is consistent with the idea that massive ellipticals are assembled
very early in the history of the universe, and then evolve relatively passively
up to the present day.Comment: Accepted for publication by MNRA
Polarization and kinematics in Cygnus A
From optical spectropolarimetry of Cygnus A we conclude that the scattering
medium in the ionization cones in Cygnus A is moving outward at a speed of
170+-34 km/s, and that the required momentum can be supplied by the radiation
pressure of an average quasar. Such a process could produce a structure
resembling the observed ionization cones, which are thought to result from
shadowing by a circumnuclear dust torus. We detect a polarized red wing in the
[O III] emission lines arising from the central kiloparsec of Cygnus A. This
wing is consistent with line emission created close to the boundary of the
broad-line region.Comment: 5 pages, accepted for publication in MNRAS letter
Third ventriculostomy vs ventriculoperitoneal shunt in pediatric obstructive hydrocephalus: results from a Swiss series and literature review
Introduction: Few series compare endoscopic third ventriculostomies (ETV) and ventriculoperitoneal shunts (VPS). To avoid the complications after a shunt insertion, there is an increased tendency to perform a third ventriculostomy. We reviewed all pediatric patients operated in the French-speaking part of Switzerland for a newly diagnosed obstructive hydrocephalus since 1992 and compared the outcome of patients who benefited from ETV to the outcome of patients who benefited from VPS. There were 24 ETV and 31 VPS. Discussion: At 5years of follow-up, the failure rate of ETV was 26%, as compared to 42% for the VPS group. This trend is also found in the pediatric series published since 1990 (27 peer-reviewed articles analyzed). Conclusion: In accordance to this trend, although a statistical difference cannot be assessed, we believe that ETV should be the procedure of choice in pediatric obstructive hydrocephalu
The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9
We present a detailed study of the kinematic, chemical and excitation
properties of the giant Ly emitting nebula and the giant \ion{H}{I}
absorber associated with the radio galaxy MRC 0943--242, using
spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments.
Together, these data provide a wide range of rest-frame wavelength (765 \AA
-- 6378 \AA at ) and 2D spatial information. We find clear
evidence for jet gas interactions affecting the kinematic properties of the
nebula, with evidence for both outflows and inflows being induced by radio-mode
feedback. We suggest that the regions of relatively lower ionization level,
spatially correlated with the radio hotspots, may be due to localised
compression of photoionized gas by the expanding radio source, thereby lowering
the ionization parameter, or due to a contribution from shock-heating. We find
that photoionization of super-solar metallicity gas ( = 2.1) by an
AGN-like continuum (=--1.0) at a moderate ionization parameter ( =
0.018) gives the best overall fit to the complete X-SHOOTER emission line
spectrum. We identify a strong degeneracy between column density and Doppler
parameter such that it is possible to obtain a reasonable fit to the \ion{H}{I}
absorption feature across the range log N(\ion{H}{I}/cm) = 15.20 and
19.63, with the two best-fitting occurring near the extreme ends of this range.
The extended \ion{H}{I} absorber is blueshifted relative to the emission line
gas, but shows a systematic decrease in blueshift towards larger radii,
consistent with a large scale expanding shell.Comment: 25 pages, 18 figures, 10 tables. Accepted for publication in MNRAS.
Published: 23 November 201
Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles
In view of potential applications of magnetic particles in biomedicine and
electromagnetic devices, we made use of the classical Stober method
base-catalysed hydrolysis and condensation of tetraethoxysilane (TEOS) to
encapsulate FeNi nanoparticles within a silica shell. An original stirring
system under high power ultrasounds made possible to disperse the otherwise
agglomerated particles. Sonication guaranteed particles to remain dispersed
during the Stober synthesis and also improved the efficiency of the method. The
coated particles are characterized by electron microscopy (TEM) and
spectroscopy (EDX) showing a core-shell structure with a uniform layer of
silica. Silica-coating does not affect the core magnetic properties. Indeed,
all samples are ferromagnetic at 77 K and room temperature and the Curie point
remains unchanged. Only the coercive force shows an unexpected non-monotonous
dependence on silica layer thickness.Comment: Regular paper submited to international peer-reveiwed journa
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