Abstract: A process for sampling aldehydes and ketones contained in diluted exhaust gases from thermal combustion engines uses a sampling unit that has a specific trapping circuit and a simulation circuit that simulates the specific trapping circuit. The specific trapping circuit and the simulation circuit are arranged in parallel. The diluted gases are passed for some time in the simulation circuit (5) before they are passed into specific trapping circuit wherein aldehydes and ketones are trapped.

Abstract: The present invention is a system for specific pollutants contained in diluted exhaust gases from thermal combustion engines, comprising a first module (1) which samples aldehyde and ketone emissions and a second module (2) which samples hydrocarbon emissions. The system according to the invention further comprises a control which coordinates the sampling(s) with predetermined working phases of the thermal engine. The first module (1) comprises a circuit (3) for trapping the aldehydes and the ketones contained in the diluted exhaust gases and a dilution air sampling circuit (4).

Abstract: A tunable monochromator selects a narrow range of wavelengths from a broadband source of radiation, such as a synchrotron X-ray source, visible light, etc. Wavelength selectivity is obtained by Bragg reflection from crystal surfaces or by diffraction gradings, prisms, etc. The inventive apparatus maintains proper orientation of two rotary members, at least one of which is typically a wavelength selective member. The apparatus allows the angles of incidence and reflection to be changed, thus changing the wavelength selected without changing the output angle or height. Two wavelength selective members can be used, or a detector probe may be positioned relative to a single wavelength selective member, or a desired polarization can be obtained with the use of a single wavelength selective member and a quarter wavelength plate. Other devices employing the .theta.-2.theta. principle, including variable delay lines, can be realized with the device.