Stereoselective Synthesis of (E)-α,β-Dehydroamino Acid Esters. -The presented method gives access to the E-isomers of α,β-dehydroamino acid esters in high yields and is complementary to the existing methods for the preparation of the thermodynamically more stable Z-isomers. The E/Z ratio depends on the reaction conditions as well as on the substituents and protecting groups on the substrates. The best results are obtained by using NaI as additive for aryl-substituted substrates and MgBr 2 ·Et 2 O or ZnCl2 for alkyl-substituted substrates. -(YASUMO, Y.; HAMADA, M.; YAMADA, T.; SHINADA, T.; OHFUNE*, Y.; Eur.

With recent advances in millimeter-wave technology, including the availability of high-power sources in this band, it has become necessary to understand the biological implications of this energy for human beings. This paper gives the millimeter-wave absorption efficiency for the human body with and without clothing. Ninety to ninety-five percent of the incident energy may be absorbed in the skin with dry clothing, with or without an intervening air gap, acting as an impedance transformer. On account of the submillimeter depths of penetration in the skin, superficial SAR'S as high as 65-357 W/Kg have been calculated for power density of incident radiation corresponding to the ANSI guideline of 5 mW/cm2. Becanse most of the millimeter-wave absorption is in the region of the cutaneous thermal receptors (O.1-1.0 mm), the sensations of absorbed energy are likely to be similar to those of IR. For the latter, threshold of heat perception is near 0.67 mW/cm2, with power densities on the order of 8.7 mW/cm2 likely to cause sensations of "very warm to hot" with a latency of 1.0+ 0.6 s. Calculations are made for thresholds of hearing of pulsed millimeter waves. Pulsed energy densities of 143-579 pJ/cm2 are obtained for the frequency band 30-300 GHz. These are 8-28 times larger than the threshold for microwaves below 3 GHz. The paper also points to the need for evaluation of ocular effects of millimeter-wave irradiation because of high SAR'S in the cornea.

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We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function of height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively.

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A comparative, computational study of the modeling of transcranial magnetic stimulation (TMS) and electroconvulsive therapy (ECT) is presented using a human head model. The magnetic fields from a typical TMS coil of figure-eight type is modeled using the Biot-Savart law. The TMS coil is placed in a position used clinically for treatment of depression. Induced current densities and electric field distributions are calculated in the model using the impedance method. The calculations are made using driving currents and wave forms typical in the clinical setting. The obtained results are compared and contrasted with the corresponding ECT results. In the ECT case, a uniform current density is injected on one side of the head and extracted from the equal area on the opposite side of the head. The area of the injected currents corresponds to the electrode placement used in the clinic. The currents and electric fields, thus, produced within the model are computed using the same three-dimensional impedance method as used for the TMS case. The ECT calculations are made using currents and wave forms typical in the clinic. The electrical tissue properties are obtained from a 4-Cole-Cole model. The numerical results obtained are shown on a two-dimenaional cross section of the model. In this study, we find that the current densities and electric fields in the ECT case are stronger and deeper penetrating than the corresponding TMS quantities but both methods show biologically interesting current levels deep inside the brain.

The existing cell phone certification process uses a plastic model of the head called the Specific Anthropomorphic Mannequin (SAM), representing the top 10% of U.S. military recruits in 1989 and greatly underestimating the Specific Absorption Rate (SAR) for typical mobile phone users, especially children. A superior computer simulation certification process has been approved by the Federal Communications Commission (FCC) but is not employed to certify cell phones. In the United States, the FCC determines maximum allowed exposures. Many countries, especially European Union members, use the "guidelines" of International Commission on Non-Ionizing Radiation Protection (ICNIRP), a non governmental agency. Radiofrequency (RF) exposure to a head smaller than SAM will absorb a relatively higher SAR. Also, SAM uses a fluid having the average electrical properties of the head that cannot indicate differential absorption of specific brain tissue, nor absorption in children or smaller adults. The SAR for a 10-year old is up to 153% higher than the SAR for the SAM model. When electrical properties are considered, a child's head's absorption can be over two times greater, and absorption of the skull's bone marrow can be ten times greater than adults. Therefore, a new certification process is needed that incorporates different modes of use, head sizes, and tissue properties. Anatomically based models should be employed in revising safety standards for these ubiquitous modern devices and standards should be set by accountable, independent groups.

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