At the awakening of the new 5G network as the network of services, issues related to electromagnetic fields (EMFs) will become one of the key aspects for the cost-effective establishment of the 5G infrastructure. The new 5G services will meet the rigorous demand for bandwidth through the implementation of a large number of densely located base stations operating in the millimeter-wave range. Introduction of new emission sources, working in parallel with already existing 2G/3G/4G mobile technologies, raises concerns about exceeding the admissible EMF exposure limits. This paper analyzes issues and challenges related to EMF measurements in 5G technology, which are crucial for the assessment of EMF compliance with regulatory limits. We point out that the existing methodologies, dedicated to EMF measurements in 2G, 3G, and 4G networks, are not suitable for 5G. The reason is the use of new techniques, such as massive MIMO and precise beamforming together with higher frequency bands so that the existing measurement methods can lead to significantly overestimated results when they will be applied to 5G networks. Such results, in conjunction with the restrictive legislation on the EMF limits that apply in some countries, may have the negative impact on 5G network deployment, making it difficult to achieve the intended 5G network capabilities. We also propose an alternative method of EMF exposure assessment that is based on calculations and simulations and allows obtaining an accurate estimation of the EMF distribution in the 5G environment.INDEX TERMS 5G mobile communication, electromagnetic fields, EMF measurements.

The conformational properties of epothilone A have been analyzed in detail using electronic structure calculations to better understand the effect of intramolecular hydrogen bonding on the conformational energies of this highly potent anticancer molecule. Single-point second-order Møller-Plesset calculations done in vacuo at the MP2/6-31+G(d,p)//B3LYP/6-31+G(d,p) level yielded data on the relative stability of conformers that were more distinct than data obtained from the standard DFT model, although the structural trends are in fair agreement. We studied torsional profiles of both hydroxyl groups and sampled energies of the side chain and thiazole moiety rotamers within the whole set of all experimentally accessible conformers. The aldol hydrogen bonds, though relatively weak, generally contribute to the conformational profile, while dipole-dipole interactions, ester group puckering, transannular repulsions between hydrogen atoms, steric effects, and syn-pentane effects have a limited influence. A salient result of our calculations is the determination that the energy of the clustered exo conformer P01 lays 9.3 kcal/mol below that of the extended, experimental conformer P11, apparently due to the unconstrained, near linear 3-OH hydrogen bond to thiazole. Another finding to be noted is the corroboration of the remarkable ability of 3-OH to form transannular hydrogen bonding with the epoxide, which releases the conformational strain of the macroring and thus leads to extra stabilization energy within the endoW subset. Finally, we found that the general trend of the conformer populations of epothilone A obtained from conformational energies resembles those derived from experiments and can be used to interpret values of NMR vicinal coupling constants. The calculated geometries and energies provide essential data for further discussion of the mechanism of biological activity of epothilone A and might be of importance in the explanation of its ADME properties.

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