To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed with the IRAM 30 m and the SMT 10 m telescopes a systematic study of Galactic interstellar 18 O/ 17 O ratios toward a sample of 421 molecular clouds, covering a galactocentric distance range of ∼1 -22 kpc. The results presented in this paper are based on the J=2-1 transition and encompass 364 sources showing both C 18 O and C 17 O detections. The previously suggested 18 O/ 17 O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of 18 O/ 17 O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18 O/ 17 O = (0.12 ± 0.02)R GC + (2.38 ± 0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J=1-0 measurement, ratios are systematically lower. This should be caused by larger optical depths of C 18 O 2-1 lines, w.r.t the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C 18 O/C 17 O is positively correlated with 13 CO/C 18 O. After considering optical depth effects with C 18 O J=2-1 reaching typically an optical depth of ∼0.5, corrected 18 O/ 17 O ratios from the J=1-0 and J=2-1 lines become consistent. A good numerical fit to the data is provided by the MWG-12 model, including both rotating stars and novae.

It is important to monitor the iced condition for operating wind turbine blades. However, most sensors are difficult to be used in this quite cold and lightweight environment. Although the fiber bragg grating (FBG) is a good candidate for the case. With the change of the temperature, the thermal expansion coefficient and thermo-optical coeffecient of FBG material will affect the accuracy of characteristics of FBG sensor. Aiming at the application of fiber optic sensor in low temperature environment and ultrathin requirement, the low temperature characteristics of FBG sensor with free arc shape package has been studied. The low temperature calibration experiments of two packaged FBG samples are tested from -35°C ~20°C in a constant temperature freezer with alcohol tank. The effects of low temperature characteristics of two FBGs packaged with free straight and arc shape tubes are compared. The results show that arc shape can effectively reduce the repeatability error and improve its accuracy due to providing possible low temperature contracting of the optical fibers. Flat arc shape makes it possible to package ultrathin FBG temperature sensor.

In this paper, a method based on fibre Bragg gratings (FBGs) is proposed to detect ice in vibrating beam-like mechanical structures. For this, two points of an optical fibre, with a pretensioned FBG sensor in the middle, are glued on the upper surface of a cantilever beam. The fibre is placed in a way that the central fibre section containing the FBG remain unglued and loose when the cantilever is placed at the most upward bending position. This way, the vibrating beam and dangling FBG are constructed into a bowstring structure. To validate the method, ice is induced on the upper surface of the cantilever beam by applying a freezing spray in laboratory. Results point out that when no ice is present in the vibrating beam, the FBG response shows a quasi-sine wave response with a flat-bottom section, which indicates the condition of the loose FBG. On the contrary, when ice cumulated on top of the cantilever, the ice induces a gluing effect that bonds the FBG to the vibrating beam, so that its strain response corresponds to an almost undistorted sine wave. By analysing the shape of the time-domain and frequency-domain strain response of the FBG, an effective method for ice detection is demonstrated.

A method to fabricate and package long period fiber gratings using glass fiber-reinforced composites is proposed. Experimental results validate the capabilities of the manufactured sensor to measure lateral pressure applied to the optical fiber.

The progress of material technology makes the structural deformation of composites more complex and more difficult to monitor. The distributed optical fiber sensor has a wide monitoring range and can continuously obtain the strain data of the structure in space for structural deformation reconstruction. In this paper, the optical frequency domain reflectometer (OFDR) and distributed optical fiber sensor are used as measurement tools to design the deformation reconstruction experiment of a cantilever beam with constant cross section. Based on the Ko theory, the strain signals collected by the distributed optical fiber sensors are converted into displacement signals, and the deformation reconstruction of the cantilever beam is carried out, and then compared and analyzed with the actual measured values. The experiment verifies the effectiveness of using distributed fiber optic sensors for cantilever beam bending deformation based on Ko theory, which provides a favorable reference for structural health monitoring.