5,428 research outputs found
Oxygen Transfer on Substituted ZrO2, Bi2O3, and CeO2 Electrolytes with Platinum Electrodes II. A-C Impedance Study
An equivalent electrical circuit that describes the electrode processes on different electrolytes, using porous Pt electrodes,is given. Diffusional processes are important and have to be presented by Warburg components in the circuit. Theoverall electrode process is rate limited by diffusion of atomic oxygen on the electrode surface for stabilized zirconia andsubstituted ceria (low PO2). On stabilized bismuth sesquioxide diffusion of atomic oxygen on the electrolyte surface is ratelimiting at high PO2 while at low PO2 another process, probably diffusion of electronic species in the electrolyte, is dominant.One of these processes plays a role too on substituted ceria at high PO2, where a charge transfer process is dominant. Theseresults are consistent with the mechanisms developed in part I of this paper
Variation and Distribution of Glucosinolates in 42 Cultivars of Brassica oleracea Vegetable Crops
Brassica vegetables are known to contain glucosinolates that are precursors for bioactive compounds like isothiocyanates that have been shown to play an important role in human health. This study reports the results of a screening of 11 Brassica oleracea crops consisting of 42 cultivars (6 white cabbage, 5 red cabbage, 7 Brussels sprouts, 2 kale, 1 tronchuda, 3 oxheart cabbage, 2 kohlrabi, 6 broccoli, 5 cauliflower, 3 romanesco and 2 Savoy cabbage). All these cultivars were cultivated under the same conditions on a single location in the same season. The variation found in the level of glucosinolates is expected to be mainly due to the genetic variation. A large variation was observed in the level and profile of glucosinolates. Total glucosinolates varied from 14 to 625 µmol/100 g fresh weight. Glucoraphanin, the precursor of the isothiocyanate sulforophane, varied from 0 to 141 µmol/100 g fresh weight. Within broccoli glucoraphanin varied from 27 to 141 µmol/100 g fresh weight. Glucoiberin that is structurally related to glucoraphanin varied from 6 to 397 µmol/100 g fresh weight. Within broccoli glucoiberin varied from 21 to 397 µmol/100 g fresh weigh
Differences in Thermal Stability of Glucosinolates in Five Brassica Vegetables
The thermal stability of individual glucosinolates within five different Brassica vegetables was studied at 100°C for different incubation times up to 120 minutes. Three vegetables that were used in this study were Brassica oleracea (red cabbage, broccoli and Brussels sprouts) and two were Brassica rapa (pak choi and Chinese cabbage). To rule out the influence of enzymatic breakdown, myrosinase was inactivated prior to the thermal treatments. The stability of three glucosinolates that occurred in all five vegetables (gluconapin, glucobrassicin and 4-methoxyglucobrassicin) varied considerably between the different vegetables. The degradation could be modeled by first order kinetics. The rate constants obtained varied between four to twenty fold between the five vegetables. Brussels sprouts showed the highest degradation rates for all three glucosinolates. The two indole glucosinolates were most stable in red cabbage, while gluconapin was most stable in broccoli. These results indicate the possibilities for plant breeding to select for cultivars in which glucosinolates are more stable during processin
The Dual Frequency Anisotropic Magneto-Optical Trap
The cloud of cold atoms produced by a Magneto-Optical Trap is known to
exhibit instabilities. We examine in this paper in which limits it could be
possible to realize an experimental trap similar to the configurations studied
theoretically, i.e. mainly traps where one direction is privileged. We study
the static behavior of an anisotropic trap, where anisotropy results
essentially from the use of two different laser frequencies for the arms of the
trap. Such a trap has very surprising behaviors, in particular the cloud
disappears for some laser frequencies, while it exists for smaller and larger
frequencies. A model is build to explain these behaviors. We show in particular
that, to reproduce the experimental observations, the model has to take into
account the cross saturation effects. Moreover, the couplings between the
different directions cannot be neglected
Phase-space description of the magneto-optical trap
An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is
derived, without any approximations. It is shown that the atomic density is
described by a Vlasov-Fokker-Planck equation, coupled with two simple
differential equations describing the trap beam propagation. The analogy of
such a system with plasmas is discussed. This set of equations is then
simplified through some approximations, and it is shown that corrective terms
have to be added to the models usually used in this context
Isotropic Light vs Six-Beam Molasses for Doppler Cooling of Atoms From Background Vapor - Theoretical Comparison
We present a 3D theoretical comparison between the radiation-pressure forces
exerted on an atom in an isotropic light cooling scheme and in a six-beam
molasses. We demonstrate that, in the case of a background vapor where all the
space directions of the atomic motion have to be considered, the mean cooling
rate is equal in both configurations. Nevertheless, we also point out what
mainly differentiates the two cooling techniques: the force component
orthogonal to the atomic motion. If this transverse force is always null in the
isotropic light case, it can exceed the radiation-pressure-force longitudinal
component in the six-beam molasses configuration for high atomic velocities,
hence reducing the velocity capture range.Comment: 10 pages, 8 figure
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