Blindness affected 45 million people globally in 2021,and moderate to severe vision loss a further 295 million.[1]The most common causes,cataract and uncorrected refractive error,are generally the easiest to treat,and...Blindness affected 45 million people globally in 2021,and moderate to severe vision loss a further 295 million.[1]The most common causes,cataract and uncorrected refractive error,are generally the easiest to treat,and are among the most cost-effective procedures in all of medicine and international development.[1-2]Thus,vision impairment is both extremely common and,in principle,readily manageable.展开更多
Schools are an important avenue to tackle the rising prevalence of uncorrected refractive error among children.School-based vision programs are an innovative approach of vision care delivery in the urban school settin...Schools are an important avenue to tackle the rising prevalence of uncorrected refractive error among children.School-based vision programs are an innovative approach of vision care delivery in the urban school setting in the United States.These programs are effective in improving vision outcomes and advancing health equity,especially among the disadvantaged school districts.While most school-based vision programs provide vision screening,eye examinations,and eyeglasses prescription to students directly in schools,different mechanisms and models have been reported.In this paper,we describe two large-scale school-based vision programs,Vision for Baltimore and Helen Keller International’s United States Vision Program,representing national and regional efforts to partner with local communities in improving access to pediatric vision care.These programs also serve as data collection platforms and provide evidence to inform public health policy and guide best practice.Collectively,these two programs showed that one in three students failed vision screening.The prevalence of uncorrected refractive error was high and the demand for eyeglasses was great among those who failed vision screening.While most of the students’uncorrected refractive errors could be addressed in the school setting,one in seven needed additional eye care.We found that schools with more socioeconomically disadvantaged students had greater needs of school-based vision program services.We hope this knowledge helps to maximize the impact of school-based vision programs and promote a system that ensures better health outcomes for all children.展开更多
This letter describes the implementation of a high-precision time and frequency transmission system using a two-way and wavelength division multiplexing scheme over 3,143.6 km of field fiber links,connecting 21 sites ...This letter describes the implementation of a high-precision time and frequency transmission system using a two-way and wavelength division multiplexing scheme over 3,143.6 km of field fiber links,connecting 21 sites between Xi’an and Beijing,China.This scheme incorporates a link noise clean-up system(LNCUS),wherein a controlled very-low-phase noise BVA oscillator acts as an internal frequency source at the relay site to effectively suppress the interference caused by the fiber link noise.Additionally,the high-stability pulse generation technology in the LNCPS provides sufficient short-term stability to significantly improve the stability of the fiber time transfer.The results indicate a time transfer stability in terms of time deviation(TDEV)of less than2.07 ps@1s,5.9 ps@100,000s,and combined uncertainty of less than 49.29 ps for the 3,143.6 km field fiber link.The results represent a significant breakthrough in achieving high-accuracy time transfer and continuous operation over ultralong-span field optical fibers exceeding 3,000 km for the first time.This enabled time transfer and synchronization services over the longest international optical fiber distance,thereby establishing a fundamental basis for constructing a nationwide high-precision time service through optical fiber networks.展开更多
An implementation of high-precision time transfer over a 1839-km field fiber loop back link between two provincial capitals of China,Xi’an and Taiyuan,is reported.Time transfer stabilities of 6.5 ps at averaging time...An implementation of high-precision time transfer over a 1839-km field fiber loop back link between two provincial capitals of China,Xi’an and Taiyuan,is reported.Time transfer stabilities of 6.5 ps at averaging time of 1 s and 4.6 ps at 40000 s were achieved.The uncertainty for the time transfer system was evaluated,showing a budget of 56.2 ps.These results stand for a significant milestone in achieving high-precision time transfer over a field fiber link spanning thousands of kilometers,signifying a record-breaking achievement for the real-field time transfer in both stability and distance,which paves the way for constructing the nationwide high-precision time service via fiber network.展开更多
It is now generally accepted that several locations in East and Southeast Asia,specifically the Republic of Korea,Japan,Singapore,China's Mainland,Hong Kong and Taiwan,have a high prevalence of myopia and potentia...It is now generally accepted that several locations in East and Southeast Asia,specifically the Republic of Korea,Japan,Singapore,China's Mainland,Hong Kong and Taiwan,have a high prevalence of myopia and potentially pathological high myopia(1-3).In fact,around 70-90%of students completing secondary schooling in these locations are now myopic(4-11),requiring some form of correction for good distance viewing.In many places,over half of the students are myopic and need correction by the end of primary school.In most of these locations,there has been a progressive development of education systems since the end of the Second World War,resulting in highly competitive systems,which produce educational outcomes that top the world in international surveys such as PISA and TIMSS(12).The data which illustrate these trends were published in recent review(2)and used as a figure in an influential news report in Nature on The Myopia Boom(1).展开更多
In this paper,we demonstrate the single-fiber and two-wavelength time transfer(SFTWTT)over a 2061 km field fiber loopback link network with a synchronous wavelength-division and time-division multiplexing access(WD-TD...In this paper,we demonstrate the single-fiber and two-wavelength time transfer(SFTWTT)over a 2061 km field fiber loopback link network with a synchronous wavelength-division and time-division multiplexing access(WD-TDMA).This system utilizes wavelength-division multiplexing to avoid the impact of backscatter.In order to achieve high-precision time transfer,time-division multiplexing access is employed.This approach facilitates multiple bidirectional comparisons between local and remote devices.A digital phase-locked loop(PLL),which matches the bandwidth of the transfer system,and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system.The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated.Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved.The precision of time transfer over a 2061 km fiber-optic network,employing a single-fiber and two-wavelength approach,has been significantly enhanced.This study presents an average time difference of 52 ps across the distance,with a system uncertainty budgeted at 41.8 ps.This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer,facilitating the development of a high-precision ground-based time service system.展开更多
文摘Blindness affected 45 million people globally in 2021,and moderate to severe vision loss a further 295 million.[1]The most common causes,cataract and uncorrected refractive error,are generally the easiest to treat,and are among the most cost-effective procedures in all of medicine and international development.[1-2]Thus,vision impairment is both extremely common and,in principle,readily manageable.
文摘Schools are an important avenue to tackle the rising prevalence of uncorrected refractive error among children.School-based vision programs are an innovative approach of vision care delivery in the urban school setting in the United States.These programs are effective in improving vision outcomes and advancing health equity,especially among the disadvantaged school districts.While most school-based vision programs provide vision screening,eye examinations,and eyeglasses prescription to students directly in schools,different mechanisms and models have been reported.In this paper,we describe two large-scale school-based vision programs,Vision for Baltimore and Helen Keller International’s United States Vision Program,representing national and regional efforts to partner with local communities in improving access to pediatric vision care.These programs also serve as data collection platforms and provide evidence to inform public health policy and guide best practice.Collectively,these two programs showed that one in three students failed vision screening.The prevalence of uncorrected refractive error was high and the demand for eyeglasses was great among those who failed vision screening.While most of the students’uncorrected refractive errors could be addressed in the school setting,one in seven needed additional eye care.We found that schools with more socioeconomically disadvantaged students had greater needs of school-based vision program services.We hope this knowledge helps to maximize the impact of school-based vision programs and promote a system that ensures better health outcomes for all children.
文摘This letter describes the implementation of a high-precision time and frequency transmission system using a two-way and wavelength division multiplexing scheme over 3,143.6 km of field fiber links,connecting 21 sites between Xi’an and Beijing,China.This scheme incorporates a link noise clean-up system(LNCUS),wherein a controlled very-low-phase noise BVA oscillator acts as an internal frequency source at the relay site to effectively suppress the interference caused by the fiber link noise.Additionally,the high-stability pulse generation technology in the LNCPS provides sufficient short-term stability to significantly improve the stability of the fiber time transfer.The results indicate a time transfer stability in terms of time deviation(TDEV)of less than2.07 ps@1s,5.9 ps@100,000s,and combined uncertainty of less than 49.29 ps for the 3,143.6 km field fiber link.The results represent a significant breakthrough in achieving high-accuracy time transfer and continuous operation over ultralong-span field optical fibers exceeding 3,000 km for the first time.This enabled time transfer and synchronization services over the longest international optical fiber distance,thereby establishing a fundamental basis for constructing a nationwide high-precision time service through optical fiber networks.
基金supported by the National Major Science and Technology Infrastructure Project of China,for“High Precision Ground-based Time Service System”(Grant No.2017-000052-73-01-002401)the National Natural Science Foundation of China(Grant No.12033007)。
文摘An implementation of high-precision time transfer over a 1839-km field fiber loop back link between two provincial capitals of China,Xi’an and Taiyuan,is reported.Time transfer stabilities of 6.5 ps at averaging time of 1 s and 4.6 ps at 40000 s were achieved.The uncertainty for the time transfer system was evaluated,showing a budget of 56.2 ps.These results stand for a significant milestone in achieving high-precision time transfer over a field fiber link spanning thousands of kilometers,signifying a record-breaking achievement for the real-field time transfer in both stability and distance,which paves the way for constructing the nationwide high-precision time service via fiber network.
文摘It is now generally accepted that several locations in East and Southeast Asia,specifically the Republic of Korea,Japan,Singapore,China's Mainland,Hong Kong and Taiwan,have a high prevalence of myopia and potentially pathological high myopia(1-3).In fact,around 70-90%of students completing secondary schooling in these locations are now myopic(4-11),requiring some form of correction for good distance viewing.In many places,over half of the students are myopic and need correction by the end of primary school.In most of these locations,there has been a progressive development of education systems since the end of the Second World War,resulting in highly competitive systems,which produce educational outcomes that top the world in international surveys such as PISA and TIMSS(12).The data which illustrate these trends were published in recent review(2)and used as a figure in an influential news report in Nature on The Myopia Boom(1).
基金the National Major Science and Technology Infrastructure Project of China“High Precision Ground-based Time Service System”(No.2017-000052-73-01-002401)the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.2021407)the National Natural Science Foundation of China(No.12033007)。
文摘In this paper,we demonstrate the single-fiber and two-wavelength time transfer(SFTWTT)over a 2061 km field fiber loopback link network with a synchronous wavelength-division and time-division multiplexing access(WD-TDMA).This system utilizes wavelength-division multiplexing to avoid the impact of backscatter.In order to achieve high-precision time transfer,time-division multiplexing access is employed.This approach facilitates multiple bidirectional comparisons between local and remote devices.A digital phase-locked loop(PLL),which matches the bandwidth of the transfer system,and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system.The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated.Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved.The precision of time transfer over a 2061 km fiber-optic network,employing a single-fiber and two-wavelength approach,has been significantly enhanced.This study presents an average time difference of 52 ps across the distance,with a system uncertainty budgeted at 41.8 ps.This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer,facilitating the development of a high-precision ground-based time service system.
