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We discuss four different tests of the bow-shock theory of Herbig-Haro objects, emphasizing especially tests based on position-velocity diagrams and on the appearance of “double layer” structures in the spatial maxima of the high- and low-velocity components of the emission lines. Though this latter effect is surprising, it is a fundamental consequence of the bow shock theory.
It has recently been found that models of a radiating bow shock can explain qualitatively the strange emission line profiles observed in some Herbig-Haro (H-H) objects. It is also possible to compare directly the emission line intensity maps predicted from these models with CCD images of H-H objects. Such a comparison between our models and observations of HH 46/47 is presented, showing that the condensation HH 47A may tentatively be identified with a bow shock formed at the “head” of a jet.
An extremely weak circularly-polarized signature was recently detected in the spectral lines of the Am star Sirius A. With a prominent positive lobe, the shape of the phase-averaged Stokes V line profile is atypical of stellar Zeeman signatures, casting doubts on its magnetic origin. We report here on ultra-deep spectropolarimetric observations of two more bright Am stars: β Uma and θ Leo. Stokes V line signatures are detected in both objects, with a shape and amplitude similar to the one observed on Sirius A. We demonstrate that the amplitude of the Stokes V line profiles depend on various line parameters (Landé factor, wavelength, depth) as expected from a Zeeman signature, confirming that extremely weak magnetic fields are likely present in a large fraction of Am stars. We suggest that the strong asymmetry of the polarized signatures, systematically observed so far in Am stars and never reported in strongly magnetic Ap stars, bears unique information about the structure and dynamics of the thin surface convective shell of Am stars.
Until recently, the detection of magnetic fields at the surface of intermediate-mass main-sequence stars has been limited to Ap/Bp stars, a class of chemically peculiar stars. This class represents no more than 5-10% of the stars in this mass range. This small fraction is not explained by the fossil field paradigm that describes the Ap/Bp type magnetism as a remnant of an early phase of the star-life. Also, the limitation of the field measurements to a small and special group of stars is obviously a problem to study the effect of the magnetic fields on the stellar evolution of a typical intermediate-mass star.
Thanks to the improved sensitivity of a new generation of spectropolarimeters, a lower bound to the magnetic fields of Ap/Bp stars, a two orders of magnitude desert in the longitudinal magnetic field and a new type of sub-gauss magnetism first discovered on Vega have been identified. These advances provide new clues to understand the origin of intermediate-mass magnetism as well as its influence on stellar evolution. In particular, a scenario has been proposed whereby the magnetic dichotomy between Ap/Bp and Vega-like magnetism originate from the bifurcation between stable and unstable large scale magnetic configurations in differentially rotating stars. In this paper, we review these recent observational findings and discuss this scenario.
This work presents essential differences in the fill factors (FF) of pin and nip solar cell structures based on hydrogenated amorphous silicon (a-Si:H). The nomenclature “pin’ (‘nip’ respectively) determines the deposition sequence of the single layers. Fill factor measurements are carried out with illumination through p- and n-layers at different wavelengths. The use of laser light provides a wide range of illumination levels and photo current densities of up to 14mA/cm2. The spectrally resolved FF measurements indicate an incorporation of dopants in the i-layer depending on the layer deposited first. Nip and pin structures generally show opposite FF dispersion when illuminated through the same layer. However, due to the slight n-conductivity of intrinsic a-Si:H material, a weak boron incorporation leads to a net charge compensation in the ilayer. In contrast to other investigations we do not find a significant deviation in the open circuit voltages of the pin and nip devices as long as the deposition parameters of the single layers are identical.
Image sensors in TFA (Thin Film on ASIC) technology have been successfully fabricated and tested. This paper provides a survey of TFA research results so far and outlines future perspectives. The properties of different a-Si:H b/w and color thin film detectors are evaluated, including spectral sensitivity, dark current, temperature influence and transient behavior. Furthermore several TFA prototypes and emerging concepts are presented, ranging from a simple one-transistor cell design to a locally autoadaptive sensor.
The current-voltage (I-V) characteristics of the interfaces between boron-doped hydrogenated amorphous silicon (p-a-Si:H) and transparent conductive oxides (TCOs) such as tin oxide (SnO2) and indium tin oxide (ITO) are experimentally determined. The measurements are performed on especially developed Kelvin cross bridge structures which allow the direct sensing of the contact region. All contacts exhibit for high dopant concentrations an almost linear I-V characteristic. The values of the contact resistance depend on the TCO type and range between 0.5 and 4 Ω· cm2 at 25°C. Gradual reduction of the boron doping level leads to a remarkable increase of the contact resistance and finally to a rectifying behavior. The results indicate that tunnelling across the interface contributes significantly to the current transport. This conclusion is also supported by the behavior of the I-V characteristics at low temperatures. Regarding degradation of the contacts a systematic reduction of the contact resistance is observed after ageing them for 1000 hours at 80°C.
Acute parvovirus B19 infection is a risk for pregnant women. After vertical transmission the infected fetus may develop hydrops fetalis. Since B19 infection occurs mainly during childhood, children represent a main source for virus transmission. In order to determine whether certain groups in the German population show increased risks for B19 infection we analysed the seroprevalence using 6583 sera collected from adults in former Eastern and Western Germany during the German National Health Survey and 649 sera from healthy Thuringian children and adolescents. In adults the overall seroprevalence was 72·1%, rising from 20·4% in children (1–3 years) and 66·9% in adolescents (18–19 years) to 79·1% in the elderly (65–69 years). Significant differences were observed between females (73·3%) and males (70·9%) and between inhabitants of small (74·8%) and big cities (69·0%) but not between people of the former Eastern (72·8%) and Western states (72·0%) of Germany. For women during childbearing age (18–49 years) highest values were observed in those living together with two or more children (81·6%) and in women with occupational contact with children aged <6 years (88·9%). In contrast seroprevalence was significantly lower in age-matched female singles (64·8%) and in women with occupational contact with children aged >6 years and adolescents (63·8%).
We investigate the entrainment, deposition and motion of coarse spherical particles within a turbulent shallow water stream down a steep slope. This is an idealization of bed-load transport in mountain streams. Earlier investigations have described this kind of sediment transport using empirical correlations or concepts borrowed from continuum mechanics. The intermittent character of particle transport at low-water discharges led us to consider it as a random process. Sediment transport in this regime results from the imbalance between entrainment and deposition of particles rather than from momentum balance between water and particles. We develop a birth–death immigration–emigration Markov process to describe the particle exchanges between the bed and the water stream. A key feature of the model is its long autocorrelation times and wide, frequent fluctuations in the solid discharge, a phenomenon never previously explained despite its ubiquity in both nature and laboratory experiments. We present experimental data obtained using a nearly two-dimensional channel and glass beads as a substitute for sediment. Entrainment, trajectories, and deposition were monitored using a high-speed digital camera. The empirical probability distributions of the solid discharge and deposition frequency were properly described by the theoretical model. Experiments confirmed the existence of wide and frequent fluctuations of the solid discharge, and revealed the existence of long autocorrelation time, but theory overestimates the autocorrelation times by a factor of around three. Particle velocity was weakly dependent on the fluid velocity contrary to the predictions of the theoretical model, which performs well when a single particle is moving. For our experiments, the dependence of the solid discharge on the fluid velocity is entirely controlled by the number of moving particles rather than by their velocity. We also noted significant changes in the behaviour of particle transport when the bed slope or the water discharge was increased. The more vigorous the stream was, the more continuous the solid discharge became. Moreover, although 90% of the energy supplied by gravity to the stream is dissipated by turbulence for slopes lower than 10%, particles dissipate more and more energy when the bed slope is increased, but surprisingly, the dissipation rate is nearly independent of fluid velocity. A movie is available with the online version of the paper.
Faber–Jackson and Tully–Fisher scaling relations for
elliptical and spiral galaxy samples up to z = 1
provide evidence for a differential behaviour of galaxy evolution with mass.
In compliance with the downsizing scenario, the stellar populations of less
massive galaxies display a stronger evolution than the more massive ones.
For spirals, this may be attributed to a suppressed star formation efficiency
in small dark matter halos.
For ellipticals, star formation must have been negligible at least
during the past ~4 Gyr in all environments.
We report on our studies of the physical structure of the planetary nebula (PN) NGC 7662. Using (3D) Integral Field Spectroscopy we have been able to measure the electron temperature more accurately and at a larger number of radial locations than before. Here we briefly present our method by which we find a strong positive temperature gradient with increasing radius. According to hydrodynamic models a hot halo, when compared to the central star, can be the product of the passage of an ionization front (e.g. Marten 1993). Such a gradient is not found in equilibrium models, and this finding – when confirmed for other objects – strongly advocates the use of hydrodynamic models when modeling PN halos.
Most steel grades undergo a ductility trough in the temperature
range 700 to 1100 °C that may bring about surface cracks in the CC
strands. Micro-mechanical modelling of the as solidified austenite-ferrite
microstructure, supported by experimental evaluations of the fracture
surfaces, affords a comprehensive description of the crack formation
mechanism. This opens the way for a quantitative evaluation
of the sensitivity of CC strands to transverse cracks.
We report the discovery, using FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, of magnetic fields and chemical peculiarities in the Herbig Ae/Be stars HD 72106 and HD 101412. These stars may well represent pre-main sequence progenitors of the magnetic Ap/Bp stars. At the same time, we fail to confirm claims by Hubrig et al. (2004) of the presence of magnetic fields in the Herbig Ae star HD 139614.
We present our project on galaxy evolution in the environment of distant rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of field galaxies. Spatially resolved MOS spectra were gained with VLT/FORS to analyze the internal kinematics of disk galaxies. First results are shown for the clusters MS 1008.1–1224 ($z=0.30$), Cl 0303+1706 ($z=0.42$), and Cl 0413–6559 ($z=0.51$). Out of 35 late-type cluster members, 13 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing over into a flat part. The other members have peculiar kinematics. The 13 cluster galaxies for which a maximum rotation velocity could be derived are distributed in the Tully-Fisher diagram very similarly to field galaxies from the FORS Deep Field with corresponding redshifts. The same is true for seven non-cluster galaxies observed in the cluster fields. The TF-cluster spirals do not show any significant luminosity evolution as might be expected from certain phenomena specific to clusters. Contrary to that, the disturbed kinematics of the non–TF cluster spirals indicate ongoing or recent interaction processes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
The results achieved with the COREX plants presently in operation show that this
technology is a true alternative to the conventional blast furnace. With the experience
gained from these plants, continuing developments have been made for the COREX process
itself (recycling of steel plant wastes and use of other raw materials), for the equipment
design and in the area of investment costs and profitability.
The development of Filaroides hirthi has been shown to proceed through all 5 stages in the lungs of experimental dogs and the attendant morphological changes are described and illustrated. These observations are interpreted as proof that the unhatched larva of F. hirthi is the 1st stage and that the 1st stage is infective. Moults occurred at approximately 1, 2, 6 and 9 days after infection in the lung tissue. Larvae also developed in vitro to the doubly ensheathed 3rd stage which is the stage achieved by heteroxenous metastrongyloids in their molluscan intermediate hosts. The arrival of 1st-stage larvae in the lungs as early as 6h after oral administration and the anatomical distribution of larvae during the first 24 h indicates that larvae are transported from the alimentary tract to the lungs by way of the hepatic portal circulation, the mesenteric lymphatic drainage, or both. First-stage larvae and eggs containing 1st-stage larvae, when injected into the jugular vein, developed into adult F. hirthi lung- worms in the usual 5 week pre-patent period. This was interpreted as demonstrating that the canine alimentary canal, although undoubtedly the normal portal of entry, is not a site of reactions indispensable to the activation or development of the larvae. Eggs containing 1st-stage larvae, when introduced by jugular and portal venous and mesenteric lymphatic routes, yielded equivalent numbers of adult lungworms indicating that neither the hepatic capillary bed nor the mesenteric lymph nodes presented quantitatively significant impediments to their passage. The question is raised whether the mesenteric lymphatics really are the exclusive migration pathways of certain other species of metastrongyloid larvae. The suggestion is made that conventional studies based on the anatomical/time distribution of larvae be supplemented by intravascular experiments like those described in this report, to provide an independent line of evidence.
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