The received satellite signal amplitude is attenuated greatly due to the strong ionospheric scintillation for lowlatitude regions, which causes the GPS tracking loop＇s loss of lock, the positioning errors to increase...The received satellite signal amplitude is attenuated greatly due to the strong ionospheric scintillation for lowlatitude regions, which causes the GPS tracking loop＇s loss of lock, the positioning errors to increase, and navigation to be interrupted. To solve the above problems, a novel signal processing algorithm is proposed based on the GPS L1 software receiver during strong ionospheric scintillation using the multi-channel intermediate frequency（IF） data sampling system. Tens of thousands of fading events are obtained based on the signal intensity measurement. The amplitude fading characteristics in the lowlatitude region are analyzed,including fading duration, time separation between fades and the numbers of signal intensity fading events. The fading thresholds are set to be 15 and 10 dB, respectively. The main fading time is very short in- 15 dB fading threshold, which generally is less than 20 ms. The main time separation between fades is less than 2 s in a single one-hour period from the time 23： 00 to 24： 00. Therefore, it has the characteristic of a short reacquisition time for the receiver designed to reduce the probability of simultaneous loss of lock for some satellites.Subsequently, the acquisition, tracking and PVT（position,velocity and time） calculations are completed by the customdesigned software receiver. The results show that the impact analysis of ionospheric scintillation on GPS amplitude attenuation in the lowlatitude region is helpful for designing the advanced tracking algorithm and to improve the robustness and accuracy of the GPS receiver.展开更多
Lu0.1Y0.9AlO3：Ce single crystals in dimensions Φ30×90 mma are successfully grown by the Czochralski method. The light output and energy resolution of the crystal in dimensions Φ14×2mm^3 are 9420 photons/M...Lu0.1Y0.9AlO3：Ce single crystals in dimensions Φ30×90 mma are successfully grown by the Czochralski method. The light output and energy resolution of the crystal in dimensions Φ14×2mm^3 are 9420 photons/MeV and 12.5% respectively. Dependence of the light output on the thickness of the sample is found and explained by the self-absorption in the range of 320-370nm and the underlying parasitic absorption around 250hm. In addition, the local enrichment of Ce ions and the presence of low-valent impurity ions may cause the deterioration of its light output. In addition, Lu0.1 Y0.9AlO3：Ce has an almost constant fluorescence decay time of 16ns in the temperature range of 80-373 K.展开更多
AIM: To evaluate the role of pentavalent Tc-99m dimercaptosuccinic acid [Tc-99m (V) DMSA] in the diagnosis of ischemic colitis. METHODS: Fourteen patients with endoscopically and histologically confirmed ischemic coli...AIM: To evaluate the role of pentavalent Tc-99m dimercaptosuccinic acid [Tc-99m (V) DMSA] in the diagnosis of ischemic colitis. METHODS: Fourteen patients with endoscopically and histologically confirmed ischemic colitis were included in the study. Tc-99m (V) DMSA scintigraphy was performed within 2 d after colonoscopy. Images were considered positive when an area of increased activity was observed in the region of interest and negative when no abnormal tracer uptake was detected. RESULTS: In 3 out of the 14 patients, Tc-99m (V) DMSA images showed moderate activity in the bowel. The scintigraphic results corresponded with the endoscopic findings. In the other 11 patients, no abnormal tracer uptake was detected in the abdomen. CONCLUSION: Besides the limited number of patients, Tc-99m (V) DMSA could not be considered as a useful imaging modality for the evaluation of ischemic colitis.展开更多
This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal perfor...This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal performance.There are many phenomenons that cause degradation to signal during transmission through the earth's atmosphere one of them is scintillation.Scintillation estimation is based on measurements of surface temperature T and relative humidity RH.Input parameter for ITU-R scintillation estimation model is the monthly average of wet part of refractivity Nwet.MATLAB software tool is employed to show the results for tropospheric scintillation in various seasons for time percentage p and frequencies ranging from 4GHz to 20 GHz.展开更多
基金The National Natural Science Foundation for Young Scholars(No.51405203)Jiangsu Overseas Research and Training Program for University Prominent Young and Middle-Aged Teachers and Presidentsthe Natural Science Foundation of Jiangsu Province(No.BK20160699)
文摘The received satellite signal amplitude is attenuated greatly due to the strong ionospheric scintillation for lowlatitude regions, which causes the GPS tracking loop＇s loss of lock, the positioning errors to increase, and navigation to be interrupted. To solve the above problems, a novel signal processing algorithm is proposed based on the GPS L1 software receiver during strong ionospheric scintillation using the multi-channel intermediate frequency（IF） data sampling system. Tens of thousands of fading events are obtained based on the signal intensity measurement. The amplitude fading characteristics in the lowlatitude region are analyzed,including fading duration, time separation between fades and the numbers of signal intensity fading events. The fading thresholds are set to be 15 and 10 dB, respectively. The main fading time is very short in- 15 dB fading threshold, which generally is less than 20 ms. The main time separation between fades is less than 2 s in a single one-hour period from the time 23： 00 to 24： 00. Therefore, it has the characteristic of a short reacquisition time for the receiver designed to reduce the probability of simultaneous loss of lock for some satellites.Subsequently, the acquisition, tracking and PVT（position,velocity and time） calculations are completed by the customdesigned software receiver. The results show that the impact analysis of ionospheric scintillation on GPS amplitude attenuation in the lowlatitude region is helpful for designing the advanced tracking algorithm and to improve the robustness and accuracy of the GPS receiver.
文摘Lu0.1Y0.9AlO3：Ce single crystals in dimensions Φ30×90 mma are successfully grown by the Czochralski method. The light output and energy resolution of the crystal in dimensions Φ14×2mm^3 are 9420 photons/MeV and 12.5% respectively. Dependence of the light output on the thickness of the sample is found and explained by the self-absorption in the range of 320-370nm and the underlying parasitic absorption around 250hm. In addition, the local enrichment of Ce ions and the presence of low-valent impurity ions may cause the deterioration of its light output. In addition, Lu0.1 Y0.9AlO3：Ce has an almost constant fluorescence decay time of 16ns in the temperature range of 80-373 K.
文摘AIM: To evaluate the role of pentavalent Tc-99m dimercaptosuccinic acid [Tc-99m (V) DMSA] in the diagnosis of ischemic colitis. METHODS: Fourteen patients with endoscopically and histologically confirmed ischemic colitis were included in the study. Tc-99m (V) DMSA scintigraphy was performed within 2 d after colonoscopy. Images were considered positive when an area of increased activity was observed in the region of interest and negative when no abnormal tracer uptake was detected. RESULTS: In 3 out of the 14 patients, Tc-99m (V) DMSA images showed moderate activity in the bowel. The scintigraphic results corresponded with the endoscopic findings. In the other 11 patients, no abnormal tracer uptake was detected in the abdomen. CONCLUSION: Besides the limited number of patients, Tc-99m (V) DMSA could not be considered as a useful imaging modality for the evaluation of ischemic colitis.
文摘This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal performance.There are many phenomenons that cause degradation to signal during transmission through the earth's atmosphere one of them is scintillation.Scintillation estimation is based on measurements of surface temperature T and relative humidity RH.Input parameter for ITU-R scintillation estimation model is the monthly average of wet part of refractivity Nwet.MATLAB software tool is employed to show the results for tropospheric scintillation in various seasons for time percentage p and frequencies ranging from 4GHz to 20 GHz.
