Asymmetric mass distribution

The thus obtained fission half lives are depicted in the lower part of Figure 8.11. Their distribution as a function of the fragment mass A2 resembles quite well the asymmetric mass distribution. Cluster radioactive decays correspond to the broad peaks around A2 = 20, 30 (200, 210). The confrontation of the calculated fission half lives with experiments is depicted in Figure 8.12. One notices "nearly quantitative" agreement over 20 orders of magnitude, which is—for an ab-initio calculation—remarkable ... 

There is, however, an interesting exception in the figure, namely Md, which shows a neutron yield of about 2 rather than an extrapolated value of 4. The nucleus of Md is the only nucleus among those shown in Fig. 4.20 with a symmetric yield distribution as seen in O Fig. 4.16. (The fermium isotopes with A = 254, 256, and 257 (N = 154, 156, and 157) shown also in Fig. 4.20 have an asymmetric mass distribution (see Fig. 4.16)). Unfortunately, no values of prompt neutron emission are known for the other isotopes with Z > 100 that show a symmetric mass distribution ( Fig. 4.16). 

Chain yields in very asymmetric mass distribution. Recently, using the mass separator Lohengrin briefly presented above, it has become possible to measure yields of the light fission fragments down to very low values. Four fission reactions studied are shown in Fig. 4.23. 

Figure 1.29 shows that fission products range over masses from about 75 to 165, which correspond to elements Ge to Dy. Most probable nuclides are grouped into two distinct mass regions (the asymmetric mass distribution), as also shown in Figure 1.30. 

Increase of symmetric fission is also observed at lower atomic numbers Z. It prevails at Z < 85, and at Z = 89 ( Ac) symmetric and asymmetric fission have nearly the same probability, which results in three maxima in the mass distribution. Three maxima are also observed in the fission of Ra by 11 MeV protons or by y rays. 

As an example, the mass distribution of the products obtained by the bombardment of with " Ar is plotted in Fig. 8.24. The curve is explained by superposition of the processes described above only few nucleons are transferred by quasielastic reactions (a), and many nucleons by deeply inelastic processes (b). Fusion followed by fission of highly excited products leads to a broad distribution of fission products around l/2(y4i + A2), where A and Ai are the mass numbers of and Ar, respectively (c), and asymmetric fission of heavy products of low excitation energy gives two small maxima (d). 

The photoelectron spectra of the mass-selected j-triazine (1,3,5-triazme, denoted Tz) cluster anions, Tz ( = 1-6), were obtained at various photon energies to investigate the electronic character of the clusters. This study provides the first direct observation of an isolated molecular anion of azabenzene, Tz. From the photoelectron spectrum taken at 1064 nm, the electron affinity (EA) of Tz was determined to be 0.03 eV. By examining the effect of the Jahn-Teller distortion in Tz, active vibrations associated with photodetachment were identified. A series of Ar-solvated clusters of Tz were also studied, which provided indirect evidence of asymmetric charge distribution in Tz caused by the Jahn-Teller distortion <2003JCP4320>. 

Schematic representations of all of the measured mass-yield distributions (normalized to 200% fragment yield) for SF of the trans-Bk isotopes are shown in Fig. 18.13 (Hoffinan and Lane 1995). It is interesting to observe rather sudden changes from asymmetric to symmetric fission as reflected by the mass distributions changing from asymmetric to symmetric mass distributions as the neutron number increases toward N 160 for the elements Fm Z = 100), No (Z= 102), andRf(Z= 104).

The Gaussian distribution is symmetrical with respect to the mean value 0 and, consequently, application to asymmetrical molar-mass distributions of polydisperse polymers is not possible. However, the composition of petroleum fractions the Gaussian distribution is acceptable and in many practical cases the lower integration limit is — oo and this complete symmetry results in other difficulties. 

If it concerns a rotation in the case of the movement of the body, then its inhomogeneity leads to a so-called imbalance. Depending on the number of revolutions n = tS/2ir and the mass distribution asymmetrical to the rotation axis... 

A series of aliphatic polyesters, characterised by asymmetric oligomer distributions, heteroterminated linear chains, and cyclic oligomers, were studied using MALDI. Structural characterisation results were compared with those from fast atom bombardment mass spectrometry, electrospray ionisation mass spectrometry, NMR and end-group titration. MALDI molecular weight determination was contrasted with those from GPC and NMR. 23 refs. 

The power of ROA for assigning ACs of chiral compounds has been previously demonstrated, including two very challenging cases. The first case was that of bromo-chlorofluoromethane, the simplest chiral molecule that is used as an example to illustrate chirality or asymmetric carbon atoms, which was assigned as (+)-S and The second case involved the AC of chirally deuterated neopentane, a chemically inert saturated hydrocarbon, which represents the archetype of all molecules that are chiral as a result of a dissymmetric mass distribution. This compound was assigned as (R)-[ Hi, H2, H3]-neopentane by ROA combined with quantum chemical computations. ... 

The observed width of the distribution functions in mass number of the fission products indicates that the spherons that lie in the plane of the fissure are essentially randomly distributed between the two daughter nuclei, as discussed below for asymmetric fission. 

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

The Td point group behaves as expected and offers no special problems. Of course, % - 0 for CH4, CH3C1, and CH2ClBr. For an asymmetric center (point group Cj), % is a quantitative measure of how chiral is the distribution of the property in question, taken to be simply atomic mass in all these examples. Thus, % is -0.0052 for (Rj-CHDCIBr, +0.0052 for (5>CHDClBr, +0.041 for (Rj-CHFCIBr, and -0.041 for (5j-CHFClBr. In terms of other chirality... 

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