642 research outputs found
Assessments of fodder values of 3 indigenous and 1 exotic woody plant species in the highlands of central Ethiopia
Leaves and twigs of indigenous woody plant species are used as a source of supplemental animal feed in the mountainous landscapes of central Ethiopia. A study was carried out from 2004 to 2006 to assess the nutritional value of three indigenous and one exotic species, based on the chemical composition, tannin contents, in vitro dry matter digestibility, and digestible energy. The species studied were Hagenia abyssinica (Bruce) J.F. Gmel., Dombeya torrida (J.F. Gmel.) P. Bamps, Buddleja polystachya Fres., and Chamaecytisus palmensis (Christ) Bisby & K. Nicholls. The first three are indigenous, and the last one is an exotic species. The Na content of the foliage and flower bud in the four species was much lower than the minimum requirement for ruminants, while other micro- and macronutrients were within the recommended range of nutrient concentrations in animal feeds. On the other hand, the crude protein content of the foliage and flower bud in the four fodder species was higher than the minimum required level. The foliage and flower bud in vitro dry matter digestibility of H. abyssinica and C. palmensis was 70% and 71%, respectively. The digestible energy of the foliage of H. abyssinica and C. palmensis was significantly higher than the digestible energy of D. torrida and B. polystachya. Therefore, the foliage and flower bud of most of those species can be used as sources of supplemental fodder with a proper feeding management scheme
Hard x-ray photon-in-photon-out spectroscopy with lifetime resolution â of XAS, XES, RIXSS and HERFD
Spectroscopic techniques that aim to resolve the electronic configuration and local coordination of a central
atom by detecting inner-shell radiative decays following photoexcitation using hard X-rays are presented. The
experimental setup requires an X-ray spectrometer based on perfect crystal Bragg optics. The possibilities arising from
non-resonant (X-Ray Emission Spectroscopy - XES) and resonant excitation (Resonant Inelastic X-Ray Scattering
Spectroscopy â RIXSS, High-Energy-Resolution Fluorescence Detected (HERFD) XAS) are discussed when the
instrumental energy broadenings of the primary (beamline) monochromator and the crystal spectrometer for x-ray
emission detection are on the order of the core hole lifetimes of the intermediate and final electronic states. The small
energy bandwidth in the emission detection yields line-sharpened absorption features. In transition metal compounds,
electron-electron interactions as well as orbital splittings and fractional population can be revealed. Combination with
EXAFS spectroscopy enables to extent the k-range beyond unwanted absorption edges in the sample that limit the
EXAFS range in conventional absorption spectroscopy
High-resolution Mn K-edge x-ray emission and absorption spectroscopy study of the electronic and local structure of the three different phases in Nd0.5Sr0.5MnO3
Nd0.5Sr0.5MnO3 is particularly representative of mixed-valent manganites since their three characteristic macroscopic phases (charge-ordered insulator, ferromagnetic-metallic, and paramagnetic insulator) appear at different temperatures.We here report a complete x-ray emission and absorption spectroscopy (XES-XAS) study of Nd0.5Sr0.5MnO3 as a function of temperature to investigate the electronic and local structure changes of the Mn atom in these three phases. Compared with the differences in the XES-XAS spectra between Nd0.5Sr0.5MnO3 and the single-valent reference compounds NdMnO3 (Mn3+) and Sr/CaMnO3 (Mn4+), only modest changes have been obtained across the magnetoelectrical transitions. The XES spectra, including both the Mn Kα and KÎČ emission lines, have mainly shown a subtle decrease in the local spin density accompanying the passage to the ferromagnetic-metallic phase. For the same phase, the small intensity variations in the pre-edge region of the high-resolution XAS spectra reflect an increase of the p-d mixing. The analysis of these XAS spectra imply a charge segregation between the two different Mn sites far from one electron, being in intermediate valences Mn+3.5±Ύ/2(ÎŽ < 0.2 eâ) for all the phases. Our results indicate that the spin, charge, and geometrical structure of the Mn atom hardly change among the three macroscopic phases demonstrating the strong competition between the ferromagnetic conductor and the charge-0rdered insulator behaviors in the manganites
The Nature of the Radiative Hydrodynamic Instabilities in Radiatively Supported Thomson Atmospheres
Atmospheres having a significant radiative support are shown to be
intrinsically unstable at luminosities above a critical fraction Gamma_crit ~
0.5-0.85 of the Eddington limit, with the exact value depending on the boundary
conditions. Two different types of absolute radiation-hydrodynamic
instabilities of acoustic waves are found to take place even in the electron
scattering dominated limit. Both instabilities grow over dynamical time scales
and both operate on non radial modes. One is stationary and arises only after
the effects of the boundary conditions are taken into account, while the second
is a propagating wave and is insensitive to the boundary conditions. Although a
significant wind can be generated by these instabilities even below the
classical Eddington luminosity limit, quasi-stable configurations can exist
beyond the Eddington limit due to the generally reduced effective opacity.
The study is done using a rigorous numerical linear analysis of a gray plane
parallel atmosphere under the Eddington approximation. We also present more
simplified analytical explanations.Comment: 18 Pages, 7 figures, uses emulateapj5.sty, accepted to Ap
A metamorphic inorganic framework that can be switched between eight single-crystalline states
The design of highly flexible framework materials requires organic linkers, whereas inorganic materials are more robust but inflexible. Here, by using linkable inorganic rings made up of tungsten oxide (P8W48O184) building blocks, we synthesized an inorganic single crystal material that can undergo at least eight different crystal-to-crystal transformations, with gigantic crystal volume contraction and expansion changes ranging from â2,170 to +1,720âĂ
3 with no reduction in crystallinity. Not only does this material undergo the largest single crystal-to-single crystal volume transformation thus far reported (to the best of our knowledge), the system also shows conformational flexibility while maintaining robustness over several cycles in the reversible uptake and release of guest molecules switching the crystal between different metamorphic states. This material combines the robustness of inorganic materials with the flexibility of organic frameworks, thereby challenging the notion that flexible materials with robustness are mutually exclusive
Determination of Nucleosynthetic Yields of Supernovae and Very Massive Stars from Abundances in Metal-Poor Stars
(Abridged) We determine the yields of Na to Ni for Type II supernovae (SNe
II) and the yield patterns of the same elements for Type Ia supernovae (SNe Ia)
and very massive (>100 M_sun) stars (VMS) using a phenomenological model of
stellar nucleosynthesis and the data on a number of stars with -4<[Fe/H]<-3, a
single star with [Fe/H]=-2.04, and the sun. We consider that there are two
distinct kinds of SNe II: the high-frequency SNe II(H) and the low-frequency
SNe II(L). We also consider that VMS were the dominant first-generation stars
formed from big bang debris. The yield patterns of Na to Ni for SNe II(H),
II(L), and Ia and VMS appear to be well defined. It is found that SNe II(H)
produce almost none of these elements, that SNe II(L) can account for the
entire solar inventory of Na, Mg, Si, Ca, Ti, and V, and that compared with SNe
II(L), VMS underproduce Na, Al, V, Cr, and Mn, overproduce Co, but otherwise
have an almost identical yield pattern. A comparison is made between the yield
patterns determined here from the observational data and those from ab initio
models of nucleosynthesis in SNe II and VMS. The evolution of the other
elements relative to Fe is shown to involve three distinct stages, the earliest
of which is directly related to the problems of early aggregation and
dispersion of baryonic matter. It is argued that the VMS contributions should
represent the typical composition of dispersed baryonic matter in the universe.Comment: 33 pages, 14 postscript figures, to appear in Ap
Local Radiative Hydrodynamic and Magnetohydrodynamic Instabilities in Optically Thick Media
We examine the local conditions for radiative damping and driving of short
wavelength, propagating hydrodynamic and magnetohydrodynamic (MHD) waves in
static, optically thick, stratified equilibria. We show that so-called strange
modes in stellar oscillation theory and magnetic photon bubbles are intimately
related and are both fundamentally driven by the background radiation flux
acting on compressible waves. We identify the necessary criteria for unstable
driving of these waves, and show that this driving can exist in both gas and
radiation pressure dominated media, as well as pure Thomson scattering media in
the MHD case. The equilibrium flux acting on opacity fluctuations can drive
both hydrodynamic acoustic waves and magnetosonic waves unstable. In addition,
magnetosonic waves can be driven unstable by a combination of the equilibrium
flux acting on density fluctuations and changes in the background radiation
pressure along fluid displacements. We briefly describe the conditions under
which these instabilities might be manifested in both main sequence stellar
envelopes and accretion disks.Comment: 55 pages, revised version accepted for publication by ApJ. New
appendix added justifying WKB analysi
The Structure of the Homunculus. III. Forming a Disk and Bipolar Lobes in a Rotating Surface Explosion
We present a semi-analytic model for shaping the nebula around eta Carinae
that accounts for the simultaneous production of bipolar lobes and an
equatorial disk through a rotating surface explosion. Material is launched
normal to the surface of an oblate rotating star with an initial kick velocity
that scales approximately with the local escape speed. Thereafter, ejecta
follow ballistic orbital trajectories, feeling only a central force
corresponding to a radiatively reduced gravity. Our model is conceptually
similar to the wind-compressed disk model of Bjorkman & Cassinelli, but we
modify it to an explosion instead of a steady line-driven wind, we include a
rotationally-distorted star, and we treat the dynamics somewhat differently.
Continuum-driving avoids the disk inhibition that normally operates in
line-driven winds. Our model provides a simple method by which rotating hot
stars can simultaneously produce intrinsically bipolar and equatorial mass
ejections, without an aspherical environment or magnetic fields. Although
motivated by eta Carinae, the model may have generic application to other LBVs,
B[e] stars, or SN1987A's nebula. When near-Eddington radiative driving is less
influential, our model generalizes to produce bipolar morphologies without
disks, as seen in many PNe.Comment: ApJ accepted, 9 page
Spectroscopic and adsorptive studies of a thermally robust pyrazolato-based PCP
The pyrazolato-based PCP [Ni8(OH)4(OH2)2(PBP)6] (NiPBP, H2PBP = 4,4\u2019-bis(1H-pyrazol-4-yl)biphenyl), whose 3-D architecture is built upon octametallic hydroxo clusters reciprocally connected by the organic spaces, is a very promising candidate for gas adsorption applications, owing to its remarkable thermal stability (up to 400 \ub0C in air) and its high void volume (70%). As such, NiPBP was selected as a proof-of-concept material to demonstrate how an optimized set of solid state techniques can concur to create a comprehensive and coherent picture, relating (average and local) structural features to adsorptive properties. To this aim, the response of NiPBP toward different gases, retrieved by gas adsorption measurements (N2 at 77 K, in the low pressure region; H2 at 77 K, in the high pressure region), was explained in terms of local-level details, as emerged by coupling electronic, X-ray (absorption and emission), and variable temperature IR spectroscopy
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