Signal detection/processing, systems

Nuclear spin relaxation is considered here using a semi-classical approach, i.e., the relaxing spin system is treated quantum mechanically, while the thermal bath or lattice is treated classically. Relaxation is a process by which a spin system is restored to its equilibrium state, and the return to equilibrium can be monitored by its relaxation rates, which determine how the NMR signals detected from the spin system evolve as a function of time. The Redfield relaxation theory36 based on a density matrix formalism can provide... 

Fig-1 Schematic view of the overall olfactory processing in insects. Pheromones and other semiochemicals are detected by specialized sensilla on the antennae, where the chemical signal is transduced into nervous activity. The olfactory receptor neurons in the semiochemi-cal-detecting sensilla are connected directly to the antennal lobe. Here the semiochemical-derived electrical signals are processed and sent out (through projection neurons) to the protocerebrum. Olfactory information is then integrated with other stimulus modalities, a decision is made, and the motor system is told what to do... 

Figure 3.40 shows the layout of a typical Raman analyzer that uses fiber optics for process application. In a Raman process system, light is filtered and delivered to the sample via excitation fiber. Raman-scattered light is collected by collection fibers in the fiber-optic probe, filtered, and sent to the spectrometer via return fiber-optical cables. A charge-coupled device (CCD) camera detects the signal and provides the Raman spectrum. To take advantage of low-noise CCD cameras and to minimize fluorescence interference, NIR diode lasers are used in process instruments. 

The baroreflex system consists of mechanosensitive receptors in the aorta and carotid sinus that detect changes in blood pressure. The receptors give rise to afferent nerve fibers that relay impulses to the CNS. Within the CNS, the afferent signals are processed and ultimately transmitted to efferent sympathetic and parasympathetic fibers to the vasculature and heart. Increases in blood pressure will increase baro-receptors activity leading to an inhibition of sympathetic impulses to the blood vessels (thereby relaxing them) and to the heart (decreasing heart rate and contractility). In addition, parasympathetic activity to the heart is increased leading to a reduction in heart rate and possibly contractility. 

Odor and taste perception permits recognition and discrimination between a large number of different molecules. The detection mechanism is based on the processing of signals from several neurons in an array processing system, and does not require the presence of specific receptor proteins. The same mechanism has been proposed for the action of eye irritant molecules and studies have been made to correlate the absorption behavior of eye irritant compounds in the lipid matrix not only by hydrophobicity, but through a more complicated procedure related to phase transition phenomena in the lipid matrix. 

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