Polarization nuclei

XENIOPHYTE The triploid tissue found in the endosperm of the angiosperms formed as the result of the fusion of a sperm nucleus with two polar nuclei in the embryo sac, at the same time the egg is fertilized. 

The embryo develops from a zygote formed by fusion of a sperm nucleus originating from the pollen and an egg cell. The fertilized egg is surrounded in the gynmosperms by a nutritive layer or endosperm which is haploid and is derived from the same game-tophyte tissue that produced the egg. In angiosperms two sperm nuclei form one of these fertilizes the egg, while the other fuses with two haploid polar nuclei derived from the female gametophyte. (The polar nuclei are formed by the same mitotic divisions that formed the egg.) From this develops a 3n triploid endosperm. 

Under continuous uv irradiation, the observed steady-state polarization (whether by cw or by FT spectrometers) may be substantially modified by various nuclear relaxation processes. For example, Closs and Czeropski (35,36) have demonstrated that CIDNP can be transferred from a group of polarized nuclei to another group not originally polarized. Both the dipolar and the scalar relaxation mechanisms (of the nuclear Overhauser effects) can be operative. The extremely interesting case of intramolecular dipolar nuclear cross relaxation reported by Closs and Czeropski (35) involves the thermal reaction of... 

The transfer of magnetization from an abundant spin (/), to a dilute one (S), by CP is widely used in numerous pulse sequences in solid-state NMR. The process of CP occurs through the tendency of the magnetization to flow from highly polarized nuclei to nuclei with lower polarizations when the two are brought into contact. CP improves the signal-to-noise... 

Fig. 97.—A, Immature angiospermous ovule B, same, after embryo-sac e.s). has matured to form the female gametophyte nucellus nuc) outer integument (0. int) inner integument (t. int) embryo sac e.s.) micropyle mic) chalaza ch) funiculus (/) synergids s) ovum (0) polar nuclei p) antipodals a) C, fertilized and matured angiospermous ovule (seed). Note that the nucellus nuc) has been pushed out by the encroachment of the embryo sac, in which endosperm has formed by the fusion of the two polar nuclei with the second sperm nucleus from the pollen tube which has later divided to form numerous nuclei scattered about in the protoplasm of the embryo sac and accumulated protoplasm and laid down walls, within which nourishment was stored embryo em) from fertilized ovum testa t) from outer integument tegmen te) from maturation of inner. integument micropyle mic) hilum or scar (h), after funiculus became detached.

When studying a new sample, a sample containing a nucleus with which you are not familiar, or a sample about which you have some suspicion, you should try to estimate the S/N so that you will not be taken by total surprise when you get no signal at all. This task is considerably easier for solution samples than solids because the line broadening mechanisms are more predictable and you do not have to worry about losing intensities to satellite transitions as you might for quadru-polar nuclei in solids. The most likely circumstance under... 

While the main recent advance in NMR has been the development of multidimensional spectroscopy, novel catalytic applications include in situ studies and two-dimensional (2D) solid-state techniques such as correlation spectroscopy, spin diffusion, and quadrupole nutation. Completely new techniques have appeared, such as multiple-quantum spin counting, and old ones have developed in quite unexpected directions. For example, cross-polarization, a 20-year-old experiment, has recently been applied to quadmpolar nuclei to yield important new information on heterogeneous catalysts. Magic-angle spinning (MAS) of quadru-polar nuclei has been extended to methods in which the sample is spun about two different angles either simultaneously or sequentially (DOR and DAS). These experiments have been made possible by the significant advances in NMR instrumentation in the last decade. 

The classical RADOP experiments are described by H.-J. Kluge in Part B, Chapter 17. Their sensitivity is based on the detection of the asymmetry in the radioactive jS-decay, which provides an inherent spin detector for polarized nuclei. A combination of fast-beam spectroscopy with the RADOP... 

Here are the zero angle scattering amplitudes on the polarized nuclei for neutrons polarized parallel and antiparallel to the A x / axis, respectively, z is the target length, and N is the density of nuclei in the target. 

As mentioned above, the true endosperm is derived from two polar nuclei of the ovule and one male nucleus. It is therefore at least a triploid tissue. 

B. van den Brandt, P. Hautle, J. A. Konter, F. Kurdzesau, F. M. Piegsa and J.-P. Urrego-Blanco, Polarized Nuclei From Fundamental Nuclear Physics to Applications in Neutron Scattering and Magnetic Resonance Imaging , in AIP Conference Proceedings, American Institute of Physics, 2008, vol. 980, PSPTR 2007, p. 312. 

S.E. Ashbrook and S. Wimperis, High-Resolution NMR of Quadm-polar Nuclei in Solids The Satellite-Transition Magic Angle Spinning (STMAS) Experiment , p. 53... 

R 363 H. Glattli, Polarized Nuclei for Neutron Science Recent Applications and Perspectives , Nucl.Instrum.Meth., A, 2004,529,194... 

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