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We report on a study of 9 nearby primitive galaxies observed by Hubble's COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. By "primitive galaxies," we mean galaxies having a low stellar mass, and low gas metallicity, , whether they are local or at high redshift. We find that far-UV spectra of these galaxies show evidence of hard radiation, including X-rays. Following Thuan et al. (2004), we identify these galaxies as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of extremely strong X-radiation. Following Heger et al. (2003), we suggest that the accreting black hold is produced by direct collapse of stars having initial masses greater than 50. The X-radiation produced by black hole disk directly affects the surrounding interstellar medium, and many of these effects are observable in far-UV spectra. [ABSTRACT FROM AUTHOR]

We report on a study of 9 nearby primitive galaxies observed by Hubble's COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. By "primitive galaxies," we mean galaxies having a low stellar mass, and low gas metallicity, , whether they are local or at high redshift. We find that far-UV spectra of these galaxies show evidence of hard radiation, including X-rays. Following Thuan et al. (2004), we identify these galaxies as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of extremely strong X-radiation. Following Heger et al. (2003), we suggest that the accreting black hold is produced by direct collapse of stars having initial masses greater than 50. The X-radiation produced by black hole disk directly affects the surrounding interstellar medium, and many of these effects are observable in far-UV spectra. [ABSTRACT FROM AUTHOR]

Context. We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch (AGB) stars, and post-early AGB stars. There are indications that old stellar systems like globular clusters produce fewer post-(early) AGB stars than currently predicted by evolutionary models, but observations are still scarce. Aims. We wish to derive effective temperatures, surface gravities, and helium abundances of the luminous hot UV-bright stars in these clusters to determine their evolutionary status and compare the observed numbers to predictions from evolutionary theory. Methods. We obtained FORS2 spectroscopy of eleven of these UV-selected objects (covering a range of −2.3 <  [Fe/H] <  −1.0), which we (re-)analysed together with previously observed data. We used model atmospheres of different metallicities, including super-solar ones. Where possible, we verified our atmospheric parameters using UV spectrophotometry and searched for metal lines in the optical spectra. We calculated evolutionary sequences for four metallicity regimes and used them together with information about the HB morphology of the globular clusters to estimate the expected numbers of post-AGB stars. Results. We find that metal-rich model spectra are required to analyse stars hotter than 40 000 K. Seven of the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars, while two are evolving away from the HB, one is a foreground white dwarf, and another is a white dwarf merger. Taking into account published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low. Conclusions. Spectroscopy is clearly required to identify the evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model spectra are required to reproduce their optical and UV spectra, which may affect the flux contribution of hot post-AGB stars to the UV spectra of evolved populations. While the observed numbers of post-AGB and post-early AGB stars roughly agree with the predictions, our current comparison is affected by low number statistics. [ABSTRACT FROM AUTHOR]

Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk. Aims. Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4−15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk. Methods. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances. Results. Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800−31 300 K, and surface gravities between 3.23−4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of −0.07 dex kpc−1 and −0.09 dex kpc−1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc. Conclusions. The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane. [ABSTRACT FROM AUTHOR]

We present mid-infrared (mid-IR) observations for a sample of 16 O-type stars. The data were acquired with the NASA Spitzer Space Telescope, using the IRS instrument at moderate resolution (R ∼ 600), covering the range of ∼10-37 μm. Our sample includes early, mid and late O supergiants and dwarfs. We explore for the first time their mid-IR spectral morphology in a quantitative way. We use NLTE expanding atmosphere models to help with line identifications, analyse profile contributions and line-formation regions. The O supergiants present a rich emission line spectra. The most intense features are from hydrogen-6 α, 7 α and 8 αthat have non-negligible contributions of He I or He II lines, depending on the spectral type. The spectrum of early O supergiants is a composite of HI and He II lines, He I lines being absent. On the other hand, late O supergiants present features composed mainly by HI and He I lines. All emission lines are formed throughout the stellar wind. We found that O dwarfs exhibit a featureless mid-IR spectrum. Two stars of our sample exhibit very similar mid-IR features, despite having a very different optical spectral classification. The analysis of O-type stars based on mid-IR spectra alone to infer spectral classes or to estimate physical parameters may thus be prone to substantial errors. Our results may therefore inform spectroscopic observations of massive stars located in heavily obscured regions and help establish an initial framework for observations of massive stars using the Mid-Infrared Instrument on the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

This paper presents the sharpest near-IR images of the massive cluster R136 to date, based on the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode. The crowded stellar population in the core of the R136 starburst compact cluster remains still to be characterized in terms of individual luminosities, age, mass and multiplicity. SPHERE/VLT and its high contrast imaging possibilities open new windows to make progress on these questions. Stacking-up a few hundreds of short exposures in J and Ks spectral bands over a field of view (FoV) of 10:9" × 12:3" centered on the R 136a1 stellar component, enabled us to carry a refined photometric analysis of the core of R136. We detected 1110 and 1059 sources in J and Ks images respectively with 818 common sources. Thanks to better angular resolution and dynamic range, we found that more than 62.6% (16.5%) of the stars, detected both in J and Ks data, have neighbours closer than 0.2" (0.1"). The closest stars are resolved down to the full width at half maximum (FWHM) of the point spread function (PSF) measured by Starfinder. Among resolved and/or detected sources R 136a1 and R 136c have optical companions and R 136a3 is resolved as two stars (PSF fitting) separated by 59 ± 2 mas. This new companion of R136a3 presents a correlation coefficient of 86% in J and 75% in Ks. The new set of detected sources were used to re-assess the age and extinction of R136 based on 54 spectroscopically stars that have been recently studied with HST slit-spectroscopy (Crowther et al. 2016, MNRAS, 458, 624) of the core of this cluster. Over 90% of these 54 sources identified visual companions (closer than 0.200). We found the most probable age and extinction for these sources are 1:8-0:8+1:2 Myr, AJ = (0:45 ± 0:5) mag and AK = (0:2 ± 0:5) mag within the photometric and spectroscopic error-bars. Additionally, using PARSEC evolutionary isochrones and tracks, we estimated the stellar mass range for each detected source (common in J and K data) and plotted the generalized histogram of mass (MF with error-bars). Using SPHERE data, we have gone one step further and partially resolved and studied the initial mass function covering mass range of (3-300) M⊙ at the age of 1 and 1.5 Myr. The density in the core of R136 (0.1-1.4 pc) is estimated and extrapolated in 3D and larger radii (up to 6 pc). We show that the stars in the core are still unresolved due to crowding, and the results we obtained are upper limits. Higher angular resolution is mandatory to overcome these difficulties. [ABSTRACT FROM AUTHOR]

We report on the in situ measured evolution of the spectral complex refractive index of a prototypical conjugated polymer, a phenyl-substituted poly(para-phenylenevinylene) copolymer (Ph-PPV, “Super Yellow”), during electrochemical p- and n-type doping. We find that the real part of the refractive index is lowered in a significant and continuous fashion over essentially the entire visible range with doping, as exemplified by a drop in the peak value at ∼480 nm from 2.1 for pristine Ph-PPV to 1.8 at a p-type doping concentration of 0.2 dopants per repeat unit and an n-type doping concentration of 0.6 dopants per repeat unit. The imaginary part features a concomitant distinct bleaching of the high-energy π–π* transition and the emergence of a low-energy polaron band. Interestingly, we observe that the optical response of Ph-PPV to p-type and n-type doping is highly asymmetric, with the former resulting in much stronger changes and a distinct blue-shift of all optical transitions. We tentatively attribute this difference in response to larger effective size of the p-type polaron compared to the n-type polaron. We anticipate that the presented results should be of value for the rational design of emerging optical devices that utilize the doping capacity of conjugated polymers. [ABSTRACT FROM AUTHOR]

Abstract. As most stars are born in a clustered mode, young massive star clusters are the best places to find and study the formation and evolution of massive stars. R136 is one of the most massive nearby clusters in the LMC. It contains at least 72 known O and Wolf-Rayet stars. These young stars are usually embedded in dust and gas so that correcting the local extinction plays an important role to estimate their mass from their luminosity. The extinction is derived for 26 O stars in different HST filters using TLUSTY model atmospheres of O stars. We derived the stellar masses, and hence the Mass Function (MF), using HST multi-color photometry. In parallel, we simulated series of R136-like clusters using the NBODY6 code to test the segregation scenario for R136. We could check whether massive stars are preferentially formed in the cluster core or formed homogeneously. By comparing the surface brightness profiles (SBP) of simulated clusters mimicking R136 with HST data, we could determine which scenario best represents R136. We present here a method that we used to connect the results of the NBODY6 simulations to R136 HST imaging data. The results of these studies bring a new insight to the understanding of R136 and similar clusters, pending future VLT and E-ELT high-contrast imaging observations at the diffraction limit at visible and IR wavelengths. [ABSTRACT FROM AUTHOR]

We present a spectroscopic analysis of Hubble Space Telescope/Cosmic Origins Spectrograph observations of three massive stars in the low metallicity dwarf galaxies IC 1613 and WLM. These stars, were previously observed with Very Large Telescope (VLT)/X-shooter by Tramper et al., who claimed that their mass-loss rates are higher than expected from theoretical predictions for the underlying metallicity. A comparison of the far ultraviolet (FUV) spectra with those of stars of similar spectral types/luminosity classes in the Galaxy, and the Magellanic Clouds provides a direct, model-independent check of the mass-loss-metallicity relation. Then, a quantitative spectroscopic analysis is carried out using the non-LTE (NLTE) stellar atmosphere code CMFGEN. We derive the photospheric and wind characteristics, benefiting from a much better sensitivity of the FUV lines to wind properties than Ha. Iron and CNO abundances are measured, providing an independent check of the stellar metallicity. The spectroscopic analysis indicates that Z/Z⊙ = 1/5, similar to a Small Magellanic Cloud-type environment, and higher than usually quoted for IC 1613 and WLM. The mass-loss rates are smaller than the empirical ones by Tramper et al., and those predicted by the widely used theoretical recipe by Vink et al. On the other hand, we show that the empirical, FUV-based, mass-loss rates are in good agreement with those derived from mass fluxes computed by Lucy. We do not concur with Tramper et al. that there is a breakdown in the mass-loss-metallicity relation. [ABSTRACT FROM AUTHOR]

A simple lamination technique for conductive and semitransparent fabrics on top of organic photovoltaic cells is presented. Conductive fabrics consisted of metal wires woven in a fabric with polymeric fibers. The lamination of this conductive fabric with help of a high conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate formulation results in well aligned low resistive metal wires as top electrode. Semitransparent flexible organic photovoltaic cells were processed with laminated fabrics as top electrode and sputtered layers of aluminum doped zinc oxide and Ag as bottom electrode. The organic photovoltaic cells showed similar performance when illuminated through the bottom or top electrode. Optical simulations were performed to investigate light scattering effects of the fabric. Results are very promising for photovoltaic and lightning devices as well as for all kinds of devices where semitransparent, highly conductive, and non-vacuum processed electrode materials are needed. [ABSTRACT FROM AUTHOR]

Striatal-enriched protein tyrosine phosphatase (STEP) has been described as a regulator of multiple kinases and glutamate receptor subunits critical for synaptic plasticity. Published behavioral and biochemical characterization from the founder line of STEP knockout (KO) mice revealed superior cognitive performance, with enhanced phosphorylation of substrates such as ERK, Fyn and GluN2B; suggesting that inhibitors of STEP may have potential as therapeutic agents for the treatment of neuropsychiatric disorders. The objectives of this work aimed to replicate and extend the previously reported behavioral consequences of STEP knockout. Consistent with previous reported data, STEP KO mice demonstrated exploratory activity levels and similar motor coordination relative to WT littermate controls as well as intact memory in a Y-maze spatial novelty test. Interestingly, KO mice demonstrated deficits in pre-pulse inhibition as well as reduced seizure threshold relative to WT controls. Immunohistochemical staining of brains revealed the expected gene-dependent reduction in STEP protein confirming knockout in the mice. The present data confirm expression and localization of STEP and the absence in KO mice, and describe functional downstream implications of reducing STEP levels in vivo. [ABSTRACT FROM AUTHOR]

Context. According to the magnetospheric accretion model, hot spots form on the surface of classical T Tauri stars (CTTSs) in regions where accreting disk material impacts the stellar surface at supersonic velocity, generating a shock. Aims. We investigate the dynamics and stability of postshock plasma that streams along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. Methods. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model considers the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction (including the effects of heat flux saturation). We explore different configurations and strengths of the magnetic field. Results. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic field. In the case of weak magnetic fields (plasma β ≳ 1 in the postshock region), a large component of B may develop perpendicular to the stream at the base of the accretion column, which limits the sinking of the shocked plasma into the chromosphere and perturbs the overstable shock oscillations induced by radiative cooling. An envelope of dense and cold chromospheric material may also develop around the shocked column. For strong magnetic fields (β < 1 in the postshock region close to the chromosphere), the field configuration determines the position of the shock and its stand-off height. If the field is strongly tapered close to the chromosphere, an oblique shock may form well above the stellar surface at the height where the plasma β ≈ 1. In general, we find that a nonuniform magnetic field makes the distribution of emission measure vs. temperature of the postshock plasma at T > 106 K lower than when there is uniform magnetic field. Conclusions. The initial magnetic field strength and configuration in the region of impact of the stream are expected to influence the chromospheric absorption and, therefore, the observability of the shock-heated plasma in the X-ray band. In addition, the field strength and configuration also influence the energy balance of the shocked plasma with its emission measure at T > 106 K, which is lower than expected for a uniform field. The above effects contribute to underestimating the mass accretion rates derived in the X-ray band. [ABSTRACT FROM AUTHOR]

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Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do not show evidence of such periodicity. Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere could disrupt the shock structure influencing the observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromosphere, taking optically thin radiation losses and thermal conduction into account. We investigated the effects of several perturbation types, such as clumps in the accretion stream or chromospheric fluctuations, and also explored a wide range of plasma-β values. Results. In the case of a weak magnetic field, the post-shock region shows chaotic motion and mixing, smoothing out the perturbations and retaining a global periodic signature. On the other hand, a strong magnetic field confines the plasma in flux tubes, which leads to the formation of fibrils that oscillate independently. Realistic values for the amplitude, length, and time scales of the perturbation are capable of bringing the fibril oscillations out of phase, suppressing the periodicity of the emission. Conclusions. The strength of a locally uniform magnetic field in YSO accretion shocks determines the structure of the post-shock region, namely, whether it will be somewhat homogeneous or if it will split up to form a collection of fibrils. In the second case, the size and shape of the fibrils is found to depend strongly on the plasma-β value but not on the perturbation type. Therefore, the actual value of the protostellar magnetic field is expected to play a critical role in the time dependence of the observable emission. [ABSTRACT FROM AUTHOR]

The structure and dynamics of young stellar object (YSO) accretion shocks depend strongly on the local magnetic field strength and configuration, as well as on the radiative transfer effects responsible for the energy losses. We present the first 3D YSO shock simulations of the interior of the stream, assuming a uniform background magnetic field, a clumpy infalling gas, and an acoustic energy flux flowing at the base of the chromosphere. We study the dynamical evolution and the post-shock structure as a function of the plasma-beta (thermal pressure over magnetic pressure). We find that a strong magnetic field (~hundreds of Gauss) leads to the formation of fibrils in the shocked gas due to the plasma confinement within flux tubes. The corresponding emission is smooth and fully distinguishable from the case of a weak magnetic field (~tenths of Gauss) where the hot slab demonstrates chaotic motion and oscillates periodically. [ABSTRACT FROM PUBLISHER]

In order to improve the understanding of the physics of ac-cretion shocks around young stellar objects, we have performed a three dimensional simulation of a radiative shock generated in a laser installation. We depict the 3D structure of such a shock. Radiation hydrodynamics is modeled with the HERACLES code; then, radiative transfer post-processing is performed with the IRIS code. [ABSTRACT FROM AUTHOR]

Context. For most astronomical objects, radiation is the only probe of their physical properties. Therefore, it is important to have the most elaborate theoretical tool to interpret observed spectra or images, thus providing invaluable information to build theoretical models of the physical nature, the structure, and the evolution of the studied objects. Aims. We present IRIS, a new generic three-dimensional (3D) spectral radiative transfer code that generates synthetic spectra, or images. It can be used as a diagnostic tool for comparison with astrophysical observations or laboratory astrophysics experiments. Methods. We have developed a 3D short-characteristic solver that works with a 3D nonuniform Cartesian grid.We have implemented a piecewise cubic, locally monotonic, interpolation technique that dramatically reduces the numerical diffusion effect. The code takes into account the velocity gradient effect resulting in gradual Doppler shifts of photon frequencies and subsequent alterations of spectral line profiles. It can also handle periodic boundary conditions. This first version of the code assumes local thermodynamic equilibrium (LTE) and no scattering. The opacities and source functions are specified by the user. In the near future, the capabilities of IRIS will be extended to allow for non-LTE and scattering modeling. Results. IRIS has been validated through a number of tests.We provide the results for the most relevant ones, in particular a searchlight beam test, a comparison with a 1D plane-parallel model, and a test of the velocity gradient effect. Conclusions. IRIS is a generic code to address a wide variety of astrophysical issues applied to different objects or structures, such as accretion shocks, jets in young stellar objects, stellar atmospheres, exoplanet atmospheres, accretion disks, rotating stellar winds, cosmological structures. It can also be applied to model laboratory astrophysics experiments, such as radiative shocks produced with high power lasers. [ABSTRACT FROM AUTHOR]

Aims. We aim to constrain the properties and evolutionary status of early and mid-spectral type supergiants (from O4 to O7.5). These posses the highest mass-loss rates among the O stars, and exhibit conspicuous wind profiles. Methods. Using the non-LTE wind code cmfgen we simultaneously analyzed the FUV-UV and optical spectral range to determine the photospheric properties and wind parameters. We derived effective temperatures, luminosities, surface gravities, surface abundances, mass-loss rates, wind terminal velocities, and clumping filling factors. Results. The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive stars to older stars with lower initial masses. O4 supergiants cluster around the 3 Myr isochrone and are more massive than 60 M☉, while the O5 to O7.5 stars have masses in the range 50-40 M☉ and are 4 ± 0.3 Myr old. The surface chemical composition is typical of evolved O supergiants (nitrogen-rich, carbon- and oxygen-poor). While the observed ranges of carbon and nitrogen mass-fractions are compatible with those expected from evolutionary models for the measured stellar masses, the N/C ratios as a function of age are inconsistent with the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. We question the efficiency of rotational mixing as a function of age for these stars and suggest that another mechanism may be needed to explain the observed abundance patterns. Mass-loss rates derived with clumped-models range within a factor of three of the theoretical mass-loss rates. The corresponding volume-filling factors associated with small-scale clumping are 0.05 ± 0.02. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators. [ABSTRACT FROM AUTHOR]

Advances in laser and Z-pinch technology, coupled with the development of plasma diagnostics, and the availability of high-performance computers, have recently stimulated the growth of high-energy density laboratory astrophysics. In particular, a number of experiments have been designed to study radiative shocks and jets with the aim of shedding new light on physical processes linked to the ejection and accretion of mass by newly born stars. Although general scaling laws are powerful tools to link laboratory experiments with astrophysical plasmas, the phenomena modeled are often too complicated for simple scaling to remain relevant. Nevertheless, the experiments can still give important insights into the physics of astrophysical systems and can be used to provide the basic experimental validation of numerical simulations in regimes of interest to astrophysics. We will illustrate the possible links between laboratory experiments, numerical simulations, and astrophysics in the context of stellar jets. First we will discuss the propagation of stellar jets in a cross-moving interstellar medium and the scaling to Z-pinch produced jets. Our second example focuses on slab-jets produced at the Prague Asterix Laser System laser installation and their practical applications to astrophysics. Finally, we illustrate the limitations of scaling for radiative shocks, which are found at the head of the most rapid stellar jets. [ABSTRACT FROM AUTHOR]

We report here the detection of a weak magnetic field of 50–100 G on the O9.7 supergiant ζ Orionis A (ζ Ori A), using spectropolarimetric observations obtained with NARVAL at the 2-m Télescope Bernard Lyot atop Pic du Midi (France). ζ Ori A is the third O star known to host a magnetic field (along with and HD 191612), and the first detection on a ‘normal’ rapidly rotating O star. The magnetic field of ζ Ori A is the weakest magnetic field ever detected on a massive star. The measured field is lower than the thermal equipartition limit (about 100 G). By fitting non-local thermodynamic equilibrium (NLTE) model atmospheres to our spectra, we determined that ζ Ori A is a star with a radius of and an age of about 5–6 Myr, showing no surface nitrogen enhancement and losing mass at a rate of about . The magnetic topology of ζ Ori A is apparently more complex than a dipole and involves two main magnetic polarities located on both sides of the same hemisphere; our data also suggest that ζ Ori A rotates in about 7.0 d and is about 40° away from pole-on to an Earth-based observer. Despite its weakness, the detected magnetic field significantly affects the wind structure; the corresponding Alfvén radius is however very close to the surface, thus generating a different rotational modulation in wind lines than that reported on the two other known magnetic O stars. The rapid rotation of ζ Ori A with respect to appears as a surprise, both stars having similar unsigned magnetic fluxes (once rescaled to the same radius); it may suggest that the subequipartition field detected on ζ Ori A is not a fossil remnant (as opposed to that of Ori C and HD 191612), but the result of an exotic dynamo action produced through magnetohydrodynamics (MHD) instabilities. [ABSTRACT FROM AUTHOR]

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We study the quantitative effects of excitation, ionization, radiation energy and pressure, on the jump conditions in hypersonic shocks in a real gas. The ionization structure and excitation energies are calculated from the local temperature and density, using the Screened Hydrogenic Model. We assume an optically thick medium and no radiation flux through the shock front. We investigate the jump conditions in different gases and propose a phenomenological description of compression for different shock velocities. We find that the excitation energy term is the dominant term in ionized gases at low velocities. Consequently, higher shock velocities than the values predicted by standard calculations in a perfect gas must be reached in order to observe the effects of radiation in the compression ratio. Our results provide constraints for the design of future radiative shock experiments on the next generation of powerful nanosecond lasers or on Z-pinches. [ABSTRACT FROM AUTHOR]

Chalcone (CHS) and stilbene (STS) synthases are related plant-specific polyketide synthases that are key enzymes in the biosynthesis of flavonoids and of stilbene phytoalexins, respectively. A phylogenetic tree constructed from 34 CHS and four STS sequences revealed that the STS formed no separate cluster but grouped with CHS from the same or related plants. This suggested that STS evolved from CHS several times independently. We attempted to simulate this by site-directed mutagenesis of an interfamily CHS/STS hybrid, which contained 107 amino acids of a CHS from Sinapis alba (N-terminal) and 287 amino acids of a STS from Arachis hypogaea. The hybrid had no enzyme activity. Three amino acid exchanges in the CHS part (Gln-100 to Glu, Val-103 to Met, Val-105 to Arg) were sufficient to obtain low STS activity, and one additional exchange (Gly-23 to Thr) resulted in 20-25% of the parent STS activity. A kinetic analysis indicated (1) that the hybrids had the same K for the substrate 4-coumaroyl-CoA but a lower V than the parent STS, and (2) that they had a different substrate preference than the parent STS and CHS. Most of the other mutations and their combinations led to enzymatically inactive protein aggregates, suggesting that the subunit folding and/or the dimerization was disturbed. We propose that STS evolved from CHS by a limited number of amino acid exchanges, and that the advantage gained by this enzyme function favored the selection of plants with improved STS activity. [ABSTRACT FROM AUTHOR]

A high signal-to-noise ratio (SNR) in31P-nuclear magnetic resonance (31P-NMR) spectroscopy can be obtained only with good B 0-field homogeneity and optimal coil sensitivity. This demands double-tumed coils with a highly sensitive31P channel and an additional1H channel for1H-magnetic resonance imaging, shimming,1H decoupling, and nuclear Overhauser enhancement (NOE). For studies on an 11.75 T magnet, we built coils derived from the four-ring birdcage design originally described by Murphy-Boesch. A comparison with conventional, single-tuned coils shows that, in spite of double tuning, there is no significant loss in31P sensitivity while the1H channel provides the requested performance. The coil design offers the advantage of circular polarization on both channels. [ABSTRACT FROM AUTHOR]

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Copyright of Zeitschrift für Anatomie und Entwicklungsgeschichte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)