ABSTRACT
Terahertz (THz) imaging is in its early stages of development but already the potential clinical impact of this new imaging modality is clear. From cancer research to DNA analysis THz technology is improving or even making possible imaging of hitherto inaccessible phenomena. In this paper we present a short review of THz imaging from the point of view of biomedical engineering. We discuss the current state of the art in terms of THz imaging systems; describe current applications, future potential and our own approaches to harnessing this novel technology. We draw attention to open problems in the area with respect to the limitations of the technology before concluding with descriptions of our future work in the area.
ABSTRACT
This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S(1/2) state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-alpha photons have been measured as a function of laser intensity (from 1 to 340 MW/cm(2)) and laser detuning around the 1S(1/2)-2S(1/2) two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S(1/2), 2P(1/2), and 2P(3/2) states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-alpha photons are modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma. From the measurements it is deduced that collective effects are important above a critical charge density of 3x10(8) ions/cm(3). An asymmetry is observed in the line profile of the total ion yield as a function of laser detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate resonant 2S(1/2) state of the photoionization process.
ABSTRACT
In an attempt to determine the risk of sauna bathing after heavy exercise, the responses of 10 clinically normal adult males (mean age 44 years) were observed and recorded for 26 min. during recovery from a standard, heavy exercise task on two separate days. On one of the 2d, recovery was interrupted by a 10-min (min 6-16) exposure to intense, dry heat (70-74 degrees C, 3-6% R.H.). The higher heart rate and rectal temperature during the treatment (min 6-16) and post treatment (min 16-26) phases on the experimental day were indicative of the expected response to the heat stress. Systolic blood pressure did not differ on experimental and control days during either phase of recovery, while diastolic blood pressure decreased during the heat exposure. Double product was higher during treatment and post-treatment phases on the experimental day indicating an increased myocardial O2 need in response to the heat. ECG (CM5) changes were limited to increased J-point displacement during the treatment phase on the experimental day, with S-T segment flattening (0.08 s) in one case, and prolongation of the Q-T interval (corrected for rate) with reduction in T-wave amplitude. The prolongation of electrical systole and T-wave flattening were not observed during exercise at comparable and higher heart rates and may be associated with reduced subendocardial perfusion. We concluded that sauna bathing of short duration after exercise represents a tenable risk for clinically normal males.
