Proton density

Fig. 2.8.9 (a) Implementation of opposed jet device, (b) Proton density image obtained across a horizontal slice, (c) Velocity image obtained across a horizontal slice, (d) Velocity profile taken along the x axis of the cell showing the uniform extensional strain rate e such that vx — ex (adapted from Ref. [15]). 

Figure 6. The single-particle potentials of nucleons n, p and hyperons , A in baryonic matter of fixed nucleonic density pN = 0.4 fm-3, proton density pp/pN = 0.2, and varying density pz/pN = 0.0, 0.2, 0.5. The vertical lines represent the corresponding Fermi momenta of n, p, and . For the nucleonic curves, the thick lines represent the complete single-particle potentials Un, whereas the thin lines show the values excluding the contribution, i.e., U + uffi.

The different single-particle potentials involved in the previous equations are illustrated in Fig. 6, where neutron and proton densities are fixed, given by pN = 0.4 fm-3 and pp/pN = 0.2, and the density is varied. Under these conditions the T, single-particle potential is sizeably repulsive, while Ua is still attractive (see also Ref. [15]) and the nucleons are both strongly bound. The single-particle potential has a particular shape with an effective mass m /m close to 1, whereas the... 

Surface protonation at the kaolinite surfaces. The excess proton density, Th.v. at the surface hydroxyl group is displayed as a function of pH. Surface protonation is interpreted as a successive protonation of two distinct types of OH groups localized at the gibbsite and edge surfaces. The pHpzc of the edge surface is about 7.5. 

For molecular sizes that are amenable by NMR techniques, nucleic acids usually lack a tertiary fold. This fact, together with the characteristic low proton density, complicates NMR structural analysis of nucleic acids. As a result, local geometries and overall shapes of nucleic acids, whose structures have been determined by NMR, usually are poorly defined. Dipolar couplings provide the necessary long-range information to improve the quality of nucleic acid structures substantially [72]. Some examples can be found already in the literature where the successful application of dipolar couplings into structure calculation and structure refinement of DNA and RNA are reported [73-77]. 

It is important to note that even in the presence of sufficient proton density and in the case of differential isotope labeling, efficient spin-diffusion may complicate the interpretation of the NOE data and result in structures or relative orientations that are erroneous. A similar problem does not occur when using residual dipolar couplings. 

Fig. 5. Standard fast spin-echo imaging of the pelvis and the lower leg. Typical contrasts between musculature and other tissues are demonstrated. Bl = bladder, Fe = femur. Gluteus = gluteus muscle. Original recording parameters matrix 192 x 256, slice thickness 6 mm, a-c field of view (fov) = 380 mm, d-f fov = 180 mm. (a) and (d) Proton density weighting TR = 5000 ms, TE = 12 ms. (b) and (e) Ti-weighting TR = 500 ms, TE = 12 ms. (c) and (f) 7 2-weighting TR = 5000 ms, TE = 100 ms.

Compared to lipids in the subcutaneous fat layer and in the bone marrow (TiR O.S s), musculature shows a clearly slower longitudinal relaxation (Ti 1.0 s). For this reason, musculature has lost more signal intensity than fat in Ty weighted images, when compared with proton density weighting (Fig. 5a... 

Abbreviations D, self-diffusion coefficient ge, gradient-echo IR, inversion recovery IRFT, inversion recovery fourier transform MRS, magnetic resonance spectroscopy PD, proton density PFGSE, pulsed field gradient spin echo se, spin-echo. 

Abbreviations ge, gradient-echo IR, inversion recovery PD, proton density se, spin-echo. 

---