A portable thermal lens spectrometer with a precise focusing system was developed. Astigmatism of the reflected excitation beam from the microchip was used for depth direction focusing. For width direction focusing, the scattering effect of the transmitted probe beam by a microchannel edge was used. The focusing system was evaluated with a 250 microm wide x 50 microm deep microchannel. Focusing resolutions for depth and width directions were 1 and 10 microm, respectively. The repeatability of the thermal lens signal (40 microM xylenecyanol solution) was proved to be approximately 1% coefficient of variance when using these focusing methods. The limit of detection for a xylenecyanol solution was 30 nM, and the absorbance was 4.7 x 10(-6) AU. The sensitivity was 20-100 times higher than that obtained by spectrophotometry. In consequence, a practical thermal lens spectrometer was realized.

The so-called “spontaneous,” background, or “basal” time series of electroencephalographic (EEG) data from rat olfactory cortex are compared with those generated by a model of the ol-factory system, denoted KIII, composed of nonlinear coupled second order ODEs with feedback delay. Each ODE (KO) represents a neural mass having either excitatory or inhibitory output to the ODEs to which it connects. Connected mutually inhibitory or mutually excitatory pairs represent populations of similar neurons interacting to form one structure (KI set). A connected set (KII set) of excitatory and inhibitory KI sets (KIe and KIi) represents the activity of a gross structure in the olfactory system (the olfactory bulb—OB, anterior olfactory nucleus—AON, and prepyriform cortex—PPC or PC). The set of KII sets connected with dispersion-delay feedback pathways (KIII set) form a model of the first central stage of olfactory perceptual processing upon olfactory stimulation, with transition on receptor input from a self-sustained basal state of activity to an induced burst. Both basal and stimulated states are studied using amplitude histograms, power spectra, attractor reconstruction, visual inspection of traces, and correlation. A comparison shows that the two systems are similar, having broad spectra, correlation functions that rapidly go to zero, and gaussian amplitude histograms. Activity is nearly periodic and higher amplitude in the excited state and aperiodic, lower amplitude in the basal state with close to 1/f falloff. Cross spectra between OB and PPC show wide frequency bands of coherent high frequency activity in both the model and rat. The excited state nearly periodic frequencies differ between the KIII model and rat (30–60 Hz in KIII, 50–100 Hz in rat EEG), because the KIII model was developed for the cat and the rabbit, which have lower frequencies than the rat. These benchmarks may be used to evaluate the physiological validity of the output produced by a proposed model, as all components of the system and its connectivity were derived from or evaluated by physiological data.

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A reflective thermal lens detection device was developed for realizing a portable and sensitive detector for a microsystem. An aluminum mirror was formed on the main plate of a microchip, and a reflected probe beam was detected with a single pick-up unit. The background signal due to light absorption of the aluminum mirror was 60 times reduced when the microchannel and the mirror were separated with an interval of 600 microm. The tilt angle of the microchip significantly affected the precision of the measurement. Then a quadrant photodiode was used to detect the center of gravity of the reflected probe beam to regulate the tilt angle within +/-0.05 degrees , and this value was enough to achieve 1% CV (coefficient of variance) precision in the measurements. The limit of detection (LOD) was 60 nM for xylene cyanol solution, and the absorbance was 9.4 x 10(-6) AU. About 40 times higher sensitivity was obtained in comparison with a spectrophotometer.