Despite the wide spread need for optical cross-section data on single spore bio-aerosols, available databases are sparse and unreliable. Information reported is based on short path measurements on high concentration media containing particle clusters. This represents an upper bound to the single spore cross-section. Measurements on single spore aerosolized media demand long path lengths and moderate particle concentration. Transmittance measurements need to be in the single scatter limit as well. These requirements are often difficult to meet. We present a procedure that leads to aerosol extinction and backscatter cross-sections in a straightforward manner. Transmittance measurements of thin films of bio-aerosols are used to obtain the bulk refractive index. This result and the measured size distribution can be used in a T-matrix calculation to yield the desired cross-sections. To illustrate this technique, infrared cross-sections are obtained for Bacillus globigii.
Pulsed-photoacoustic spectroscopy in the near IR portion of the optical spectrum was used as a local technique for quantitative monitoring of tissue hemoglobin concentration and its oxygenation state. A pulsed, tunable optical source coupled to a 1mm-diameter optical fiber cable was used to deliver optical energy to the tissue under study. The fiber was placed either on the exterior surface or inserted into the tissue. An ultrasonic signal was produced in the tissue as a result of the absorbed light pulse energy. Since the rate of conversion of laser light energy to heat was rapid and the laser pulse as much shorter than the tissue thermal- diffusion length, the ultrasonic signal amplitude was proportional to the energy absorbed. Spectra of absorbing compounds were obtained by measuring the variation in the acoustic signal with source wavelength. In contrast with near-IR spectroscopic techniques that measure diffuse light transmission and assume knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient, the photoacoustic response is produced directly by light absorption. Light scattering merely modifies the spatial distribution of the absorbed energy. Our studies demonstrate that photoacoustic spectra obtained both in vitro and in vivo allow determination of relative changes in the concentration of oxy- and de- oxyhemoglobin.
Pulsed-photoacoustic spectroscopy (PPAS) is an in-situ technique used for quantitative monitoring of brain-tissue hemoglobin concentration and its oxygenation state. In contrast to most spectroscopic techniques that measure infrared absorption PPAS does not require knowledge of the pathlength of light traveling through tissues in order to determine the absorption coefficient and hence the concentration of absorbing species. The photoacoustic response (PAR) is produced by light absorption. Light scattering modifies the spatial distribution of the absorption. PPAS uses a pulsed, tunable optical source coupled to a 1 mm diameter fiber optic cable to transmit optical energy to the tissue. The fiber can be placed on the exterior surface or inserted into the tissue. An ultrasonic signal is produced by light absorbed in the tissue. Since the rate of conversion of laser light to heat is rapid and the laser pulse much shorter than the tissue thermal-diffusion length, the ultrasonic signal amplitude is proportional to the energy absorbed. Spectra of absorbing compounds can be obtained by measuring the variation in the acoustic signal with source wavelength. Our studies demonstrate that acoustic spectra obtained both in-vitro and in-vivo allows relative changes in the concentration of oxy- and de-oxyhemoglobin to b45e determined.
Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been successfully applied to investigate the surface structure and the electron density of states of organic conductors and superconductors. The structural nature of organic conductors and superconductors makes their transport properties susceptible to one-dimensional effects. Low- dimensionality effects in the electrical conductivity of these materials are investigated using scanning tunneling microscopy at room and low temperatures. Effects such as charge density waves and Peierls instabilities are directly observed with the STM. The consequences of low- dimensionality in the electrical conductivity of these materials will be presented.
Conference Committee Involvement (3)
Technologies for Synthetic Environments: Hardware-in-the-Loop XVIII
2 May 2013 | Baltimore, Maryland, United States
Technologies for Synthetic Environments: Hardware-in-the-Loop XVII
25 April 2012 | Baltimore, Maryland, United States
Technologies for Synthetic Environments: Hardware-in-the-Loop XVI
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