Radiation radiofrequency

If the source emits radiofrequency radiation consisting of two frequencies, v and v, of the same amplitude then 

For our purposes we can neglect the imaginary part of Equation (3.16), i sin27ivt, and then it is apparent that f t) is a sum of cosine waves, as we had originally supposed. Fourier transformation allows us to go from f t) to F(v) by the relationship 

A computer digitizes the time domain spectmm f(t) and carries out the Fourier transformation to give a digitized F(v). Then digital-to-analogue conversion gives the frequency domain spectmm F(v) in the analogue form in which we require it. 

In the case of a radio operating in the FM wavelength band, or indeed any wavelength band, the aerial receives a signal which contains all the transmitted frequencies. What the radio does is, effectively, to Fourier transform the signal so that we can tune in to any of the frequencies without interference from any others. 

If the radiofrequency spectmm is due to emission of radiation between pairs of states - for example nuclear spin states in NMR spectroscopy - the width of a line is a consequence of the lifetime, t, of the upper, emitting state. The lifetime and the energy spread, AE, of the upper state are related through the uncertainty principle (see Equation 1.16) by 

---

A MBER spectrometer is shown schematically in figure C1.3.1. The teclmique relies on using two inhomogeneous electric fields, the A and B fields, to focus the beam. Since the Stark effect is different for different rotational states, the A and B fields can be set up so that a particular rotational state (with a positive Stark effect) is focused onto the detector. In MBER spectroscopy, the molecular beam is irradiated with microwave or radiofrequency radiation in the... 

From the Heisenberg uncertainty principle as stated in Equation (1.16) estimate, in cm and Hz, the wavenumber and frequency spread of pulsed radiation with a pulse length of 30 fs, typical of a very short pulse from a visible laser, and of 6 ps, typical of pulsed radiofrequency radiation used in a pulsed Fourier transform NMR experiment. 

Main advances in ESR spectroscopy have recently come about by adding new dimensions to basic ID ESR [1015]. Dimensions such as time and radiofrequency radiation have either created new spectroscopies or enriched one-dimensional forms. Examples are pulsed ESR and ENDOR. 

Investigations of the cellular effects of radiofrequency radiation provide evidence of damage to various types of avian and mammalian cells. These effects involve radiofrequency interactions with cell membranes, especially the plasma membrane. Effects include alterations in membrane cation transport, Na+/K+-ATPase activity, protein kinase activity, neutrophil precursor membrane receptors, firing rates and resting potentials of neurons, brain cell metabolism, DNA and RNA synthesis in glioma cells, and mitogenic effects on human lymphocytes (Cleary 1990). 

Some radiation is helpful and necessary, as in the case of sunlight, which allows us to see the world. The nonionizing radiation of the sun warms us, but too much ultraviolet radiation can cause sunburn or cancer depending on our individual sensitivity. There is clearly a dose - response relationship between exposure and effect, with individual sensitivity playing an important role. Microwave and radiofrequency radiation are incredibly useful in heating and transmitting information. 

Guidance on Occupational and Public Exposure Resulting from Diagnostic Nuclear Medicine Procedures Practical Guidance on the Evaluation of Human Exposures to Radiofrequency Radiation... 

Heat inducible gene expression systems can be activated by a variety of technologies, all via the production of hyperthermia. Technologies used in clinical applications of hyperthermia include simple approaches, such as water baths, or more sophisticated methods, such as microwave or radiofrequency radiations and ultrasound (Gemer and Cetas, 1993). The magnitude of heat shock promoter activity induction is dependent on both the time of exposure to hyperthermia and the hyperthermic temperature (Gemer et al., 2000). HSP promoter activity is activated by temperature in a species-specific manner. In flies, HSP promoter activity is activated by temperatures over 30 °C (Lindquist, 1986). In human cells, temperatures of 40 °C and above are required to activate HSP promoters (Gemer et al., 2000). 

Calcium Ion Efflux Induction in Brain Tissue by Radiofrequency Radiation... 

The experimental results suggest that radiofrequency radiation may be useful as an investigative tool to learn more about the electrical properties of the central nervous system. 

In the ENDOR methods, the spin system is irradiated by a microwave field to partially saturate the EPR transition while simultaneously sweeping the sample with radiofrequency radiation through nuclear resonance transitions (Makinen, 1998 Makinen et al. 1998). ENDOR provides a means of precisely measuring the hyperfine interaction (Ahf) between electron and nuclear spins. Within the strong-field approximation, the observed A f is given by Eq. 1.16 ... 

---