Atmospheric effects on interferometric synthetic aperture radar(InSAR) measurements are quantitatively studied based on a tandem pair of SAR data and a month-long continuous GPS tracking data obtained at six stations....Atmospheric effects on interferometric synthetic aperture radar(InSAR) measurements are quantitatively studied based on a tandem pair of SAR data and a month-long continuous GPS tracking data obtained at six stations. Differential atmospheric signals extracted from the SAR data for two selected areas show apparent power law characteristics. The RMS values of the signals are 2.04 and 3.66 rad respectively for the two areas. These differential delays can potentially cause in the two areas peak-to-peak deformation errors of 3.64 and 6.52cm, respectively, at the 95% confidence level and Gaussian distribution. The respective potential peak-to-peak DEM errors are 123 and 221 m. The GPS tropospheric total zenith delays estimate indicates that a peak-to-peak error of about 7.8cm can potentially be caused in a SAR interferogram with only 1 d interval at the 95% confidence level. The error increases to about 9.6cm for 10 d interval. The potential peak-to-peak DEM and deformation errors estimated from GPS total zenith delay measurements are however quite similar to those estimated from InSAR data. This provides us with a useful tool to pre-estimate the potential atmospheric effects in a SAR interferogram before we order the SAR images. Nevertheless, the results reveal that even in a small area the atmospheric delays can obscure centimetre level ground displacements and introduce a few hundred meters of errors to derived DEM.展开更多
Purpose： Posttraumatic arthritis （PTA） may develop years after acetabular fracture, hindering joint function and causing significant chronic musculoskeletal pain. Given the delayed onset of PTA, few studies have as...Purpose： Posttraumatic arthritis （PTA） may develop years after acetabular fracture, hindering joint function and causing significant chronic musculoskeletal pain. Given the delayed onset of PTA, few studies have assessed outcomes of delayed total hip arthroplasty （THA） in acetabular fracture patients. This study systematically reviewed the literature for outcomes of THA in patients with PTA and prior acetabular fracture. Methods： Pubmed, EMBASE, SCOPUS, and Cochrane library were searched for articles containing the keywords ＂acetabular＂, ＂fracture＂, ＂arthroplasty＂, and ＂post traumatic arthritis＂ published between 1995 and August 2017. Studies with less than 10 patients, less than 2 years of follow-up, conference abstracts, and non-English language articles were excluded. Data on patient demographics, surgical characteristics, and outcomes of delayed THA, including implant survival, complications, need for revision, and functional scores, was collected from eligible studies. Results： With 1830 studies were screened and data from 10 studies with 448 patients were included in this review, The median patient age on date of THA was 51.5 years, ranging from 19 to 90 years. The median time from fracture to THA was 37 months, with a range of 27-74 months. Mean follow-up times ranged from 4 to 20 years, The mean Harris hip scores （HHS） improved from 41.5 pre-operatively, to 87.6 post-operatively, The most prevalent postoperative complications were heterotopic ossification （28% -63%）, implant loosening （1%-24%）, and infection （0%-16%）. The minimum 5-year survival of implants ranged from 70% to 100%. Revision rates ranged from 2% to 32%. Conclusion： Despite the difficulties associated with performing THA in patients with PTA from previous acetabular fracture （including soft tissue scarring, existing hardware, and acetabular bone loss） and the relatively high complication rates, THA in patients with VIA following prior acetabular fracture leads to significant improvement in pain and function at 10-year follow-up. Further high quality randomized controlled studies are needed to confirm the outcomes after delayed THA in these patients.展开更多
提出了一种无需气象数据,直接用对流层天顶总延迟(zenith total delay,ZTD)推导大气可降水量(precipitable water vapor,PWV)的新方法。该方法从GPS反演大气水汽的反演方程出发,基于最小二乘法建立ZTD推算PWV的模型。结果表明,就BJFS测...提出了一种无需气象数据,直接用对流层天顶总延迟(zenith total delay,ZTD)推导大气可降水量(precipitable water vapor,PWV)的新方法。该方法从GPS反演大气水汽的反演方程出发,基于最小二乘法建立ZTD推算PWV的模型。结果表明,就BJFS测站而言,模型推算的PWV与GPS反演的PWV的均方根(root mean square,RMS)值为4.5 mm,两者存在一个微小的系统偏差,但相关系数高达0.982。在不研究其数值大小只研究其趋势变化时,可以用模型直接推算PWV,这可为气象学短期预报提供一定参考。展开更多
文摘Atmospheric effects on interferometric synthetic aperture radar(InSAR) measurements are quantitatively studied based on a tandem pair of SAR data and a month-long continuous GPS tracking data obtained at six stations. Differential atmospheric signals extracted from the SAR data for two selected areas show apparent power law characteristics. The RMS values of the signals are 2.04 and 3.66 rad respectively for the two areas. These differential delays can potentially cause in the two areas peak-to-peak deformation errors of 3.64 and 6.52cm, respectively, at the 95% confidence level and Gaussian distribution. The respective potential peak-to-peak DEM errors are 123 and 221 m. The GPS tropospheric total zenith delays estimate indicates that a peak-to-peak error of about 7.8cm can potentially be caused in a SAR interferogram with only 1 d interval at the 95% confidence level. The error increases to about 9.6cm for 10 d interval. The potential peak-to-peak DEM and deformation errors estimated from GPS total zenith delay measurements are however quite similar to those estimated from InSAR data. This provides us with a useful tool to pre-estimate the potential atmospheric effects in a SAR interferogram before we order the SAR images. Nevertheless, the results reveal that even in a small area the atmospheric delays can obscure centimetre level ground displacements and introduce a few hundred meters of errors to derived DEM.
文摘Purpose： Posttraumatic arthritis （PTA） may develop years after acetabular fracture, hindering joint function and causing significant chronic musculoskeletal pain. Given the delayed onset of PTA, few studies have assessed outcomes of delayed total hip arthroplasty （THA） in acetabular fracture patients. This study systematically reviewed the literature for outcomes of THA in patients with PTA and prior acetabular fracture. Methods： Pubmed, EMBASE, SCOPUS, and Cochrane library were searched for articles containing the keywords ＂acetabular＂, ＂fracture＂, ＂arthroplasty＂, and ＂post traumatic arthritis＂ published between 1995 and August 2017. Studies with less than 10 patients, less than 2 years of follow-up, conference abstracts, and non-English language articles were excluded. Data on patient demographics, surgical characteristics, and outcomes of delayed THA, including implant survival, complications, need for revision, and functional scores, was collected from eligible studies. Results： With 1830 studies were screened and data from 10 studies with 448 patients were included in this review, The median patient age on date of THA was 51.5 years, ranging from 19 to 90 years. The median time from fracture to THA was 37 months, with a range of 27-74 months. Mean follow-up times ranged from 4 to 20 years, The mean Harris hip scores （HHS） improved from 41.5 pre-operatively, to 87.6 post-operatively, The most prevalent postoperative complications were heterotopic ossification （28% -63%）, implant loosening （1%-24%）, and infection （0%-16%）. The minimum 5-year survival of implants ranged from 70% to 100%. Revision rates ranged from 2% to 32%. Conclusion： Despite the difficulties associated with performing THA in patients with PTA from previous acetabular fracture （including soft tissue scarring, existing hardware, and acetabular bone loss） and the relatively high complication rates, THA in patients with VIA following prior acetabular fracture leads to significant improvement in pain and function at 10-year follow-up. Further high quality randomized controlled studies are needed to confirm the outcomes after delayed THA in these patients.
文摘提出了一种无需气象数据,直接用对流层天顶总延迟(zenith total delay,ZTD)推导大气可降水量(precipitable water vapor,PWV)的新方法。该方法从GPS反演大气水汽的反演方程出发,基于最小二乘法建立ZTD推算PWV的模型。结果表明,就BJFS测站而言,模型推算的PWV与GPS反演的PWV的均方根(root mean square,RMS)值为4.5 mm,两者存在一个微小的系统偏差,但相关系数高达0.982。在不研究其数值大小只研究其趋势变化时,可以用模型直接推算PWV,这可为气象学短期预报提供一定参考。
