Abstract. Optical-resolution photoacoustic microscopy ͑OR-PAM͒ is a novel imaging technology for visualizing optically absorbing superficial structures in vivo with lateral spatial resolution determined by optical focusing rather than acoustic detection. Since scanning of the illumination spot is required, OR-PAM imaging speed is limited by both scanning speed and laser pulse repetition rate. Unfortunately, lasers with high repetition rates and suitable pulse durations and energies are not widely available and can be cost-prohibitive and bulky. We are developing compact, passively Q-switched fiber and microchip laser sources for this application. The properties of these lasers are discussed, and pulse repetition rates up to 100 kHz are demonstrated. OR-PAM imaging was conducted using a previously developed photoacoustic probe, which enabled flexible scanning of the focused output of the lasers. Phantom studies demonstrate the ability to image with lateral spatial resolution of 7±2 m with the microchip laser system and 15± 5 m with the fiber laser system. We believe that the high pulse repetition rates and the potentially compact and fiber-coupled nature of these lasers will prove important for clinical imaging applications where real-time imaging performance is essential.
The creation of a road network can lead to the fragmentation and reduction of the connectivity of the ecological habitat. The study of urban ecological networks under threat from rapidly developing road networks is of great significance in understanding the changes in urban ecological processes and in constructing a reasonable ecological network. Spatial syntax is a linear space analysis method based on graph theory. Taking Wuhan city as an example and adopting spatial syntax to quantify road network threat factors, two resistance surfaces are established based on land use type assignment and overlapping road network threat factor assignment. The ecological environment under two scenarios is constructed by combining the MSPA (Morphological Spatial Pattern Analysis) method and MCR (Minimal Cumulative Resistance) model to comprehensively evaluate the network. Results demonstrate that spatial syntax can effectively describe the spatial characteristics of the road network. The average resistance value of the study area increases by 15.94%, the length of corridor increases by 37.9 km, the energy consumption of biological and material exchanges increases, and the resistance increases. To a certain extent, the model reflects the impact of road network threats on ecological processes. The results are useful in identifying the impact of human activities on ecological processes and provide a reference point for the construction of urban ecological security patterns.
Langasite-type crystals, including La3Ga5.5Nb0.5O14 (LGN), and La3Ga5.5Ta0.5O14(LGT) with disordered structure, and Ca3TaGa3Si2O14 (CTGS) and Ca3NbGa3Si2O14 (CNGS) with ordered structure, were grown using the Czochralski method. Resistivity was studied as a function of temperature. Temperature coefficients of frequency (TCFs) for different cuts were investigated in the above crystals at elevated temperatures, which were found to be ±11 ppm K−1 and ±6.0 ppm K−1 up to 400 °C for LGN (YXl)1.5° and LGT (YXl) − 20° cuts, respectively, in thickness shear mode, while the TCF was found to be 21 ppm K−1 up to 800 °C for CTGS (YXl) − 20° and CNGS (YXl) − 20°. Furthermore, the dielectric and electromechanical behaviour of the above crystals with low TCF cuts as a function of temperature were studied. It was observed that CTGS and CNGS crystals with an ordered structure possessed temperature independent dielectric and electromechanical behaviour up to 800 °C, making CTGS and CNGS potential candidates for high temperature sensor applications.
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