Multi-pulse irradiation

The principles behind MAP liquid-phase and gas-phase extractions are fundamentally similar and rely on the use of microwaves to selectively apply energy to a matrix rather than to the environment surrounding it. MAP gas-phase extractions (MAP-HS) give better sensitivity than the conventional static headspace extraction method. MAP-HS may also be applied in dynamic applications. This allows the application of a prolonged, low-power irradiation, or of a multi-pulse irradiation of the sample, thus providing a means to extract all of the volatile analytes from the matrix [477]. 

If the carrier frequency of the RF pulses is close to one of the resonance transitions of the irradiated sample, the effect of the multi-pulse sequence leads to the establishment of a new time independent effective Hamiltonian Heff, now also containing the interaction of nuclear-spins with the RF field (that the effective Hamiltonian is time independent should be imderstood that it is independent of the number of the pulse interval but not independent of the time inside the definite pulse interval). A part of the dipole Hamiltonian Ha no longer commutes with the new effective Hamiltonian, which after the T2 time results in heat mixing of the quadrupole reservoir and the reservoir of the components of... 

We have implemented the principle of multiple selective excitation (pulse sequence II in fig. 1) thereby replacing the low-power CW irradiation in the preparation period of the basic ID experiment by a series of selective 180° pulses. The whole series of selective pulses at frequencies /i, /2, , / is applied for several times in the NOE build-up period to achieve sequential saturation of the selected protons. Compared with the basic heteronuclear ID experiment, in this new variant the sensitivity is improved by the combined application of sequential, selective pulses and the more efficient data accumulation scheme. Quantitation of NOEs is no longer straightforward since neither pure steady-state nor pure transient effects are measured and since cross-relaxation in a multi-spin system after perturbation of a single proton (as in the basic experiment) or of several protons (as in the proposed variant) differs. These attributes make this modified experiment most suitable for the qualitative recognition of heteronuclear dipole-dipole interactions rather than for a quantitative evaluation of the corresponding effects. 

Figure 1. a) Polarised extinction spectra of samples with Ag nanoparticles original sample and irradiated at 400 nm in the multi-shot regime (100 pulses in single spot), peak pulse intensity was 0.42 TW/cm2 b) TEM image of deformed nanoparticles after irradiation. The laser polarisation is shown as an arrow c) SAXS intensity distribution from the irradiated sample. The light ring in the centre is the shadow of the beam stop. 

The molded rubber sheets were subjected to electron beam (EB) irradiation at Elektronika 10/10 linear electron accelerator (Russia), located at the Institute of Nuclear Chemistry and Technology (Poland). The absorbed doses were 50, 122 and 198 kGy. Irradiation process was carried out in air atmosphere at room temperature. The rubber sheets were placed horizontally in the front of pulsed, scaimed beam. The total doses were obtained by multi-pass exposure (approx. 25 kGy per pass). 

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