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71.
A simple cryopreservation method is described for proliferating meristem cultures of banana (Musa spp.). It relies on a 2-week preculture on media containing 0.4 M sucrose followed by rapid cooling in liquid nitrogen. Different preculture media were screened for efficient protection of banana meristems against cryopreservation. Sucrose can be replaced by both fructose and glucose without significantly affecting post-thaw survival rates. A high BA concentration (0.1 mM) in the preculture medium results in less material available for cryopreservation, but does not affect cryoprotection. Culture in liquid media significantly improved post-thaw regeneration. The optimized cryopreservation protocol was applied on 36 banana accessions belonging to 8 different genomic groups. It is shown that post-thaw regeneration frequencies (ranging between 0 and 66 percent) are highly dependent on the genomic constitution of the banana cultivar. 相似文献
72.
Bartók M Szabó PT Bartók T Szöllösi G 《Rapid communications in mass spectrometry : RCM》2000,14(6):509-514
Several ethyl pyruvate and dihydrocinchonidine adducts, formed by non-covalent interactions with alkali cations, have been identified for the first time using electrospray ionization mass and tandem mass spectrometry. This type of adduct may have an important role in asymmetric reactions of pyruvates in the presence of cinchonas. 相似文献
73.
Török B Szöllösi G Balázsik K Felföldi K Kun I Bartók M 《Ultrasonics sonochemistry》1999,6(1-2):97-103
Sonochemical chemo- and enantioselective hydrogenations over supported platinum catalysts are described. We disclose our results with respect to a sonochemical modification of the chemoselective hydrogenation of cinnamaldehyde over supported platinum catalysts, and the asymmetric hydrogenation of ethyl pyruvate promoted by various ultrasonic pretreatments. The ultrasonic pretreatment of the supported platinum catalysts was found to be highly beneficial in almost every case, improving both the catalytic activity and selectivity. The effect of additional experimental variables, such as hydrogen pressure, catalyst support, temperature and the ultrasonic insonation time were also studied. The enantioselectivity of the hydrogenation of ethyl pyruvate increased up to 97.1% ee. In the case of cinnamaldehyde hydrogenation, the selective preparation of cinnamyl alcohol became possible. The theoretical aspects of the working mechanisms in comparison with 'silent' reactions will also be provided. 相似文献
74.
Y. El Masri R. Janssens C. Michel P. Monseu J. Steyaert J. Vervier 《Zeitschrift für Physik A Hadrons and Nuclei》1975,274(2):113-119
Study of the energy levels of156Dy through the159Tb(p, 4n)156Dy reaction has revealed the existence of six states with excitation energies between 1.8 and 2.8 MeV and spins between 6 and 12. Some of them can tentatively be assigned as low-spin members of “upper” bands which are thought to be responsible for the backbending phenomenon experimentally observed in the ground-state andβ-vibrational bands of this nucleus. Others could be levels of a negative-parity octupole band. 相似文献
75.
76.
Bartók M Kele Z Sutyinszki M Bucsi I Felföldi K 《Rapid communications in mass spectrometry : RCM》2004,18(12):1352-1360
The reaction mixture for the hydrogenation of ethyl pyruvate on Pt-alumina catalyst modified with isocinchona alkaloids (alpha-ICN (I) and beta-ICN (II)) was studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). It was established that part of the chiral modifiers themselves are converted into ions of m/z 299, 305 and 309 in the course of chiral hydrogenation. The experimental data allowed the determination of the probable structure of the ions mentioned. According to ESI-MS/MS spectra the structure of the new cinchona alkaloids was assumed: tetrahydro-isocinchonines (III-VI), decahydro-isocinchonines (VII, VIII) and hydrogenated compounds of VII and VIII by scission of their C--N and C--O bonds (IX/1, IX/2, X). Fragmentation pathways are proposed for these new compounds. 相似文献
77.
Roman Barták 《Annals of Operations Research》2003,118(1-4):101-119
Global constraints provide strong filtering algorithms to reduce the search space when solving large combinatorial problems. In this paper we propose to make the global constraints dynamic, i.e., to allow extending the set of constrained variables during search. We describe a generic dynamisation technique for an arbitrary monotonic global constraint and we compare it with the semantic-based dynamisation for the alldifferent constraint. At the end we sketch a dynamisation technique for non-monotonic global constraints. A comparison with existing methods to model dynamic problems is given as well. 相似文献
78.
We describe several classes of regular partitions of dual polar spaces and determine their associated parameters and eigenvalues. We also give some general methods for computing the eigenvalues of regular partitions of dual polar spaces. 相似文献
79.
80.
Solutions for the fully compressible Navier–Stokes equations are presented for the flow and temperature fields in a cubic cavity with large horizontal temperature differences. The ideal-gas approximation for air is assumed and viscosity is computed using Sutherland's law. The three-dimensional case forms an extension of previous studies performed on a two-dimensional square cavity. The influence of imposed boundary conditions in the third dimension is investigated as a numerical experiment. Comparison is made between convergence rates in case of periodic and free-slip boundary conditions. Results with no-slip boundary conditions are presented as well. The effect of the Rayleigh number is studied. 相似文献