Cross-polarization build

The initial building-up of the carbon magnetization via polarization transfer is characterized with the spin-lock cross-polarization time Tcir It is sensitive to the static interactions, i.e. transfer of the polarization via static dipolar interactions (proportional to e J). Hence, the shortest TCH will have carbons a) in more rigid systems and b) with more directly attached protons, particularly the CH2 (or... 

The values of, 3C T1 and their temperature dependence are found to be very sensitive to the nature of the build-up of the carbon magnetization directly (by applying a 90° degree pulse), or indirectly by cross-polarization. The 13Clfi vs. 

Fig. 8. MIONP enhancement of nuclear spin polarization in a polycrystalline sample of pentacene doped naphthalene/ (a) Build-up curve for the enhanced spin polarization, with an MIONP repetition rate of 50 Hz (determined by the laser) the time constant for the build-up was 3730 s. TCP is an acronym for integrated cross-polarization - the authors term for their variant of the ISE. (b) 13.6 MHz single-shot H NMR spectra, taken with (top) and without bottom) MIONP enhancement (respectively, acquired at 100 K and room temperature). The top spectrum was obtained with a 10,000 s MIONP build-up time. The enormous sensitivity enhancement obtained with ONP is clear from comparing the two spectra. (Figures courtesy of K. Takeda and T. Terao, reprinted from Ref. [71], copyright 2001, with permission from Elsevier.)...

Finally, in this section, the simple Hartmann-Hahn cross polarization experiment, and in particular, the JH-19F CP build up curve was used to determine the residual JH-19F dipolar coupling constant due to motion in an ethylene/tetrafluoroethylene co-polymer.31 This curve for the crystalline... 

The build-up of signal during cross-polarization depends on two relaxation processes (Fig. 7), the cross-polarization transfer time, CH and the proton spin-lattice relaxation time in the rotating frame, Ti . Figure 7 shows that the signal intensity builds exponentially at a rate characteristic of CH> while at the same time the signal is being truncated by another exponential... 

The physical properties of polyurethanes are derived from their molecular stmcture and deterrnined by the choice of building blocks as weU as the supramolecular stmctures caused by atomic interaction between chains. The abiHty to crystalline, the flexibiHty of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, eg, polyurethane foams, other factors such as density determine the final properties. 

A sphere has a larger mass than a typical bar (L = 5D) resonating at the same frequency, and because it is equally sensitive for all directions and polarizations it has a cross-section (for the same material) that is about 75 times larger. A single sphere is also capable of determining the source direction and polarization. A spherical detector is the only detector for GWs with isotropic sky coverage and the capability of finding the location of the source. Both laser interferometers and bar detectors are unable to do this with just one detector six bar detectors would be needed to build an omni-directional observatory. 

Figure 2.10 Cylindrically symmetric hydrodynamical model of accretion flow with rotation during the early collapse phase, showing the inflow of matter in the meridional plane and the build-up of a flat rotating disk structure after about 1.05 free-fall times. Arrows indicate matter flow direction and velocity, gray lines indicate cuts of isodensity surfaces with meridional plane. Dark crosses outline locations of supersonic to subsonic transition of inflow velocity this corresponds to the position of the accretion shock. Matter falling along the polar axis and within the equatorial plane arrive within 1600 yr almost simultaneously, which results in an almost instantaneous formation of an extended initial accretion disk [new model calculation following the methods in Tscharnuter (1987), figure kindly contributed by W. M. Tscharnuter],...

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