Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites (more than 120 in orbit to date). Moreover, they can offer a cost-effective ...solution for interplanetary journey, as proved by the recent ESA SMART-1 mission to the Moon. The main limiting factor of the HETs lifetime is the erosion of the annular channel ceramics walls. In order to provide a better understanding of the energy deposition on the insulated walls, a laser irradiation study has been carried out on a PPS100-ML thruster during its run in the PIVOINE-2G ground test facility (CNRS Orléans, France). Two distinct approaches have been followed: continuous wave fiber laser irradiation (generation of thermal defects) and nanosecond pulsed laser ablation (generation of topological defects). The irradiated zones have been monitored in situ by IR thermography and optical emission spectroscopy and further investigated ex situ by scanning electron microscopy and profilometry.
Longevity is the amount of time breeding females stay active in a herd by avoiding death or culling because of illness or reproductive failure. This is a trait of economic relevance in commercial ...small ruminant breeding herds as it affects lifetime reproductive output. The purpose of this study was to determine if breed of meat goat influences breeding doe survival rates and cumulative reproductive performance under semi-intensive management.
Boer (n = 132), Kiko (n = 92) and Spanish (n = 79) does were evaluated for longevity trends and cumulative kid production. The herd was managed on humid subtropical pasture. Does had the chance to complete 2 to 6 production years. Survival curves were analyzed for 2 culling methods. The actual culling practice removed does after two failures to wean a kid. An alternative culling protocol removed doe records after the first failure to wean a kid. Kid production traits analyzed across herd life were the total number of kids weaned and cumulative kid weight weaned to the 2-, 3-, and 5-year stayability endpoints. Most (82%) doe exits were illness-related under the actual culling method. Reproductive failure represented 51% of doe exits under the alternative culling protocol. Boer does had greater survival declines (P < 0.01) from 2 to 6 years of herd life compared with Kiko and Spanish under both culling protocols. Boer does had lower stayability rates (P < 0.01) at each year endpoint for both culling protocols. Under the alternative protocol, over 50% of Boer does failed to complete 2 years, whereas over 50% of Kiko and Spanish does successfully completed 4 years. Boer does had lower (P < 0.01) total number of kids weaned and cumulative weight weaned through each stayability endpoint compared with Kiko and Spanish.
Boer does had low stayability and cumulative kid production rates compared with Kiko and Spanish does. Poor health was the primary driver of does exiting the herd. Kiko and Spanish does did not differ for longevity and lifetime performance indicators.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Soda lime silicate oxide glasses are studied to perform coloration thanks to gold nanoparticles’ crystallization. This precipitation is conducted by chemical reduction of gold ions with stannous or ...antimony oxides as reducing agents. A control of the rendered coloration between blank to red shades has been obtained using Sb
2
O
3
agent and appropriate thermal treatments. The glasses remain colorless while heating up to 450 °C. Structural glasses evolution is studied by MAS NMR spectroscopy of
29
Si and
23
Na nuclei to investigate the silicate network polymerization change and the modification of sodium/oxygen bond length versus nucleation state and growth of Au nanoparticles. A clear decrease of the Q
2
species part is observed with nanoparticles growth confirmed by the evolution of chemical shift for
23
Na resonance. A slight network polymerization is then showed independently of the only thermal treatment. This structural change could be induced by the antimony oxidation and change towards higher coordinations. Finally, the glasses chemical durability has been studied by leaching tests and shows lower alteration for colored glass. The optical spectroscopy applied to colored glasses has given rise to plasmon resonance phenomena at around 600 nm which is the typical surface plasmon resonance of gold for a refractive medium index of 1.5, with a shift of the resonance towards the higher wavelengths with increasing thermal treatment temperature. This shift is modelized by Drude and MIE approaches and confirms the trend observed by UV-visible measurement with an increasing absorption at the SPR correlated to a typical Ostwald growth mechanism according to the increase of the annealing temperature.
Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites and for interplanetary missions. The main limiting factor of the HET ...lifetime is the erosion of the annular channel ceramic walls. Erosion monitoring has been performed in the laboratory using optical emission spectroscopy (OES) measurements and data treatment based on the coronal model and the actinometric hypothesis. This study uses laser ablation of the ceramic wall in a running HET in order to introduce controlled amounts of sputtered material in the thruster plasma. The transient laser-induced breakdown plasma expands orthogonally in a steady-state plasma jet created by the HET discharge. The proposed spectroscopic method involves species from both plasmas (B, Xe, Xe+). The optical emission signal is correlated to the ablated volume (measured by profilometry) leading to the first direct validation of the actinometric hypothesis in this frame and opening the road for calibration of in-flight erosion monitoring based on the OES method.
► First laser ablation study in a running Hall Effect Thruster. ► Optical emission spectroscopy used to validate the actinometric hypothesis. ► Opens the way for absolute calibration of in-flight erosion monitoring.
Chemical disorder can be characterized in silicate glasses using spectral editing in (29)Si solid-state NMR. Resonances of the Q(n)(mX) (i.e. Si(OX)(m)(OSi)(n-m)) molecular motifs, which strongly ...overlap in the (29)Si solid-state NMR spectra of silicate glasses, can be separated and quantified using 2 to n-quantum filters in INADEQUATE-like experiments, without prior knowledge of assigned chemical shifts, offering a new probe for the microscopic origins of residual entropy in glassy materials.
Over the years, solid-state nuclear magnetic resonance (NMR) spectroscopy has become an important tool for materials science, with its local point of view that is highly complementary to the ...structural information provided by diffraction techniques, electron microscopy, and molecular modeling, for example. As compared to other interactions that determine the spectral expression of the local structure of the observed nuclei in solid-state NMR experiments, the
J coupling, characteristic of the chemical bonds, has received far less attention because of its being generally so small that it is masked in the line-widths. Nevertheless, the scalar or isotropic part of
J couplings, which is not averaged by magic angle spinning (MAS), can be evidenced in many systems, and exploited to unequivocally characterize the extended coordination sphere. In a first step we describe the different experiments that permit the observation and the measurement of
J couplings, even when dealing with quadrupolar nuclei. We then present new and recently-published results that illustrate the state of the art of NMR methodologies based on or intended for measuring
J couplings in solids and the novel perspectives that they open towards better understanding of ordered and disordered materials at the subnanometric scale, a length scale that is otherwise difficult to access.
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