Two new eudesmane sesquiterpenes, 2alpha-hydroxy pterodontic acid (1) and pterodolide [3alpha-(2-methyl-2,3-epoxy)-butyric-4alpha-acetoxy-8beta-ethoxy eudesma-7(11)-en-8alpha,12-olide (2), along with five known compounds (3-7) were isolated from the aerial parts of Laggera pterodonta. Their structures were elucidated on the basis of spectroscopic methods. The immunosuppressive activity of the isolated compounds was investigated.

The increasing demand for ultrasonic flow meter (UFM) is due to the absence of moving, protruding parts projecting into the measured flow, transient response, high accuracy and wide range, so that it becomes important in flow measurement. By analyzing the error sources and magnitude of measurements in water, considering the uncertainty caused by sound speed profile and standard length, comprehensively. This research proposes a method to trace the transit time to standard length. Firstly, based on the servo driving and automatic displacement control, a facility which can provide displacement with a minimum displacement step of 10μm, is designed, and has been precisely calibration by laser interferometer. The error function of water temperature uniformity on transit time measurement is evaluated by theoretical model. A high-precision constant system is developed to control the temperature gradient in water better than 5mK, and the Anton Paar MKT50 platinum wire resistance thermometer is being used as the temperature standard. Assuming that the ultrasonic waveform does not change during propagation in water. The transit time for multiple reflections between fixed stainless steel protective layer and movable reflector is measured. The time difference between two different reflections of same wave can be obtained by high-precision cross-correlation algorithm, and the center frequency of the first five cycles are calculated through Hilbert transform. Through the linear increasing experiments, the effects of reflection times, path length and test temperature to the measurement of transit time are compared.