Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted ...Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted on problems in middle-aged people have focused on visual disorders without taking into account all the ocular morbidities that may affect this segment of the population, hence the present study, the aim of which is to determine the proportions of different eye diseases in people aged 40 and over. Materials and Methods: This was a descriptive cross-sectional study carried out in the ophthalmology department covering the period from January 1 to December 31, 2020. Results: In total, we collected 828 patients aged 40 and over out of 1811 patients who received ophthalmological consultation during the study period, representing 45.72%. The most represented age group was 40 - 50 years, with an average age of 58.84 years and a maximum of 93 years. There were slightly more women (62.3%) than men (37.7%). The main reasons for consultation were decreased visual acuity (26.4%) and pruritus (19.9%). The main eye diseases diagnosed were cataracts (23%), allergic conjunctivitis (21.1%), and bacterial conjunctivitis (14.2%). Discussions: The predominance of cataracts in the diagnosed diseases confirms the literature data, according to which the main eye morbidities in middle-aged and elderly people are cataracts, glaucoma, and age-related macular degeneration. Conclusion: It is crucial to have a mastery of these epidemiological data of eye diseases in order to adapt the technical platforms of eye care structures to the needs of different segments of the population.展开更多
Urban environments have challenging characteristics for bird acoustic communication.High levels of anthropogenic noise,as well as vegetation structure(e.g.,in urban parks),can potentially affect the song frequency cha...Urban environments have challenging characteristics for bird acoustic communication.High levels of anthropogenic noise,as well as vegetation structure(e.g.,in urban parks),can potentially affect the song frequency characteristics of several bird species.An additional factor such as the abundance of conspecific and heterospecific vocalizing birds may play an important role in determining the structure of bird songs.In this study,we analyzed whether noise levels,vegetation percentage,and abundance of conspecifics and heterospecifics influence the song characteristics of three syntopic songbird species:House Finch(Haemorhous mexicanus),Rufouscollared Sparrow(Zonotrichia capensis),and House Sparrow(Passer domesticus)living in urban sites.We recorded songs of these species and measured the peak frequency and entropy of their songs at 14 sites in the city of San Cristobal de Las Casas,Chiapas,Mexico.We found that the song peak frequency of House Finch and House Sparrow's songs was negatively related to the vegetation.The peak frequency of neither of the three species correlated with the average noise level.However,the abundances of conspecific and heterospecific were related to the peak frequency of the three species'songs.The entropy of the House Finch and House Sparrow songs was positively and negatively related,respectively,to noise levels.House Sparrow song entropy was negatively related to the percentage of vegetation.Song entropy of House Finches was negatively associated to conspecific and House Sparrow abundance.Song entropy of Rufous-collared Sparrows was positively related to conspecific abundance.In conclusion,the song peak frequency and song entropy of the three songbird species were differentially related to urban noise,vegetation,and conspecific and heterospecific abundance,suggesting these factors influence bird song characteristics.展开更多
The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were i...The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.展开更多
Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting t...Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.展开更多
A wide passband frequency selective surface(FSS)is proposed using a five-layer stacked structure.The proposed structure applies four layers of dielectric plates and five layers of metal patches to provide a passband a...A wide passband frequency selective surface(FSS)is proposed using a five-layer stacked structure.The proposed structure applies four layers of dielectric plates and five layers of metal patches to provide a passband and exhibits more stable frequency responses and lower insertion loss under wide-angle oblique incidence compared with the typical three-layer metal-dielectric structure.According to the simulation results,the proposed FSS can achieve a passband range of 1.7-2.7 GHz with an insertion loss of less than 0.5 d B and a relative bandwidth of 44.1%,and it can preserve stable transmission characteristics with the incident angle ranging from 0°to 45°.展开更多
Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flo...Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flood frequency analysis(FFA)and flood susceptibility mapping cannot be overstated.This study focuses on the Haora River basin in Tripura,a region prone to frequent flooding due to a combination of natural and anthropogenic factors.This study evaluates the suitability of the Log-Pearson Type Ⅲ(LP-Ⅲ)and Gumbel Extreme Value-1(EV-1)distributions for estimating peak discharges and delineates floodsusceptible zones in the Haora River basin,Tripura.Using 40 years of peak discharge data(1984-2023),the LP-Ⅲ distribution was identified as the most appropriate model based on goodness-of-fit tests.Flood susceptibility mapping,integrating 16 thematic layers through the Analytical Hierarchy Process,identified 8%,64%,and 26%of the area as high,moderate,and low susceptibility zones,respectively,with a model success rate of 0.81.The findings highlight the need for improved flood management strategies,such as enhancing river capacity and constructing flood spill channels.These insights are critical for designing targeted flood mitigation measures in the Haora basin and other flood-prone regions.展开更多
Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Dopple...Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.展开更多
As modern electromagnetic environments are more and more complex,the anti-interference performance of the synchronization acquisition is becoming vital in wireless communications.With the rapid development of the digi...As modern electromagnetic environments are more and more complex,the anti-interference performance of the synchronization acquisition is becoming vital in wireless communications.With the rapid development of the digital signal processing technologies,some synchronization acquisition algorithms for hybrid direct-sequence(DS)/frequency hopping(FH)spread spectrum communications have been proposed.However,these algorithms do not focus on the analysis and the design of the synchronization acquisition under typical interferences.In this paper,a synchronization acquisition algorithm based on the frequency hopping pulses combining(FHPC)is proposed.Specifically,the proposed algorithm is composed of two modules:an adaptive interference suppression(IS)module and an adaptive combining decision module.The adaptive IS module mitigates the effect of the interfered samples in the time-domain or the frequencydomain,and the adaptive combining decision module can utilize each frequency hopping pulse to construct an anti-interference decision metric and generate an adaptive acquisition decision threshold to complete the acquisition.Theory and simulation demonstrate that the proposed algorithm significantly enhances the antiinterference and anti-noise performances of the synchronization acquisition for hybrid DS/FH communications.展开更多
We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for.Instead of employing a phase discriminator and a phase lockin...We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for.Instead of employing a phase discriminator and a phase locking loop in the conventional active phase control scheme,the passive phase noise cancellation is realized by feeding double-trip beat-note frequency to the driver of the acoustic optical modulator at the local site.This passive scheme exhibits fine robustness and reliability,making it suitable for long-distance and noisy fiber links.An optical regeneration station is used in the link for signal amplification and cascaded transmission.The phase noise cancellation and transfer instability of the 972-km link is investigated,and transfer instability of 1.1×10^(-19)at 10^(4)s is achieved.This work provides a promising method for realizing optical frequency distribution over thousands of kilometers by using fiber links.展开更多
Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than t...Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.展开更多
To ensure frequency stability in power systems with high wind penetration,the doubly-fed induction generator(DFIG)is often used with the frequency fast response control(FFRC)to participate in frequency response.Howeve...To ensure frequency stability in power systems with high wind penetration,the doubly-fed induction generator(DFIG)is often used with the frequency fast response control(FFRC)to participate in frequency response.However,a certain output power suppression amount(OPSA)is generated during frequency support,resulting in the frequency modulation(FM)capability of DFIG not being fully utilised,and the system’s unbalanced power will be increased during speed recovery,resulting in a second frequency drop(SFD)in the system.Firstly,the frequency response characteristics of the power system with DFIG containing FFRC are analysed.Then,based on the analysis of the generation mechanism of OPSA and SFD,a combined wind-storage FM control strategy is proposed to improve the system’s frequency response characteristics.This strategy reduces the effect of OPSA and improves the FM capability of DFIG by designing the fuzzy logic of the coefficients of FFRC according to the system frequency index in the frequency support stage.During the speed recovery stage,the energy storage(ES)active power reference value is calculated according to the change of DFIG rotor speed,and the ES output power is dynamically adjusted to reduce the SFD.Finally,taking the IEEE 39-bus test system as an example,real-time digital simulation verification was conducted based on the RTLAB OP5707 simulation platform.The simulation results showthat theproposedmethodcan improve theFMcapabilityofDFIG,reduce the SFDunder thepremise of guaranteeing the rapid rotor speed recovery,and avoid the overshooting phenomenon so that the systemfrequency can be quickly restored to a stable state.展开更多
Background:Optimal patterns of accrual of recommended levels of physical activity(PA)for prevention of hypertension and obesity are not known.The overall aim of this study was to investigate whether different patterns...Background:Optimal patterns of accrual of recommended levels of physical activity(PA)for prevention of hypertension and obesity are not known.The overall aim of this study was to investigate whether different patterns of accumulation of PA are differentially associated with hypertension and obesity in Australian women over 21 years.Specifically,we investigated whether,for the same weekly volume of PA,the number of sessions(frequency)and vigorousness of PA(intensity)were associated with a reduction in the occurrence of hypertension and obesity in women.Methods:Data from the 1973-1978 and 1946-1951 cohorts of the Australian Longitudinal Study on Women's Health were analyzed(n=20,588;12%-16%with a Bachelor's or higher degree).Self-reported PA,hypertension,height,and weight were collected using mail surveys every 3 years from 1998/2000 to 2019/2021.Generalized Estimating Equation models with a 3-year lag model were used to investigate the association of PA volume(metabolic equivalent min/week)(none;33-499;500-999;≥1000,weekly frequency(none;1-2 times;3-4times;5-7 times;≥8 times),and the proportion of vigorous PA to total volume of PA(none;0%;1%-33%;34%-66%;67%-100%)with odds of hypertension and obesity from 2000 to 2021.Results:The cumulative incidence of hypertension was 6%in the 1973-1978 and 23%in the 1946-1951 cohort;27%of women in the 1973-1978;and 15%in the 1946-1951 cohort developed obesity over the period.Overall,a higher volume of PA was associated with reduced odds of hypertension and obesity.When the volume of PA was considered,the odds of hypertension did not vary according to the frequency or intensity of PA.However,increased proportion of vigorous PA to the total volume of PA was associated with a small additional reduction in the risk of obe sity.Conclusion:PA volume appears to be more important than the pattern of accumulation for the prevention of hypertension and obesity.Incorporating more sessions,particularly of vigorous-intensity PA,may provide extra benefits for the prevention of obesity.展开更多
Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence.However,little attention has been given to temporal-like correlations,such as quantum ...Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence.However,little attention has been given to temporal-like correlations,such as quantum temporal steering(TS),in this context.In this work,we investigate TS in a frequency-modulated two-level system coupled to a zero-temperature reservoir in both the weak and strong coupling regimes.We analyze the impact of various frequency-modulated parameters on the behavior of TS and non-Markovian.The results demonstrate that appropriate frequency-modulated parameters can enhance the TS of the two-level system,regardless of whether the system is experiencing Markovian or non-Markovian dynamics.Furthermore,a suitable ratio between modulation strength and frequency(i.e.,all zeroes of the 0th Bessel function J_(0)(δ/?))can significantly enhance TS in the strong coupling regime.These findings indicate that efficient and effective manipulation of quantum TS can be achieved through a frequency-modulated approach.展开更多
Macrosomia is defined as a term birth weight greater than or equal to 4000 grams, or greater than the 90 percentile of intrauterine growth curves. Excessive weight has harmful consequences for the newborn and is a maj...Macrosomia is defined as a term birth weight greater than or equal to 4000 grams, or greater than the 90 percentile of intrauterine growth curves. Excessive weight has harmful consequences for the newborn and is a major health concern. Objectives: To determine the frequency of neonatal macrosomia, describe risk factors and neonatal and maternal complications. Materials and methods: This was a cross-sectional study carried out between January and December 2022, involving newborns whose birth weight was greater than or equal to 4000 grams admitted to the neonatology unit of the Labe regional hospital. Results: 591 deliveries were recorded, 15 of which were macrosomic, representing a frequency of 2.54%. The average age of the women was 30.26 years. History of fetal macrosomia and diabetes was 93.33 and 71.43% respectively. The mean gestational age was 38.71 ± 0.75 SA, the mean antenatal consultation was 3 ± 0.8 and the mode of delivery was caesarean section (66.67%). Third-trimester ultrasound was performed in 53.33% of cases. Macrosomic newborns were male in 80% of cases. Neonatal complications were asphyxia (60%), hypoglycemia (20%) and hypocalcemia (13.33%). Factors associated with neonatal macrosomia were diabetes (P < 0.001), history of macrosomia (P Conclusion: this study shows that the frequency of neonatal macrosomia is 2.54% with high neonatal morbidity among newborns hospitalized in the neonatology unit of the Labé regional hospital. Screening for macrosomia risk factors during pregnancy is essential to prevent perinatal complications.展开更多
Introduction: Mechanical complications after osteosynthesis are spontaneous and harmful modifications of the joint compromising the consolidation process. The aim of this study is to report on the frequency of these c...Introduction: Mechanical complications after osteosynthesis are spontaneous and harmful modifications of the joint compromising the consolidation process. The aim of this study is to report on the frequency of these complications and their management in the Orthopaedic-Traumatology Department of CHU Ignace Deen. Patients and Methods: we conducted a retrospective descriptive and analytical cross-sectional study from January 2017 to December 2022. It focused on the records of patients hospitalized and treated in the department for a mechanical complication after osteosynthesis. Results: The frequency of mechanical complications was 1.2%, with an average age of 44.2 years and a sex ratio of 3.2 in favor of men. Non-compliance with postoperative instructions, non-compliance with surgical technique, postoperative infection and early loading were the main contributing factors. Disassembly of the screw-plate was the most common cause in 6 cases (35.5%), with a mean delay of 4.1 months. Revision osteosynthesis was carried out using screw plates in 8 cases (47.1%). Conclusion: Mechanical complications of osteosynthesis are less frequent traumatic conditions in our department. Several factors contribute to their occurrence.展开更多
Future inter-satellite clock comparison on high orbit will require optical time and frequency transmission technology between moving objects.Here,we demonstrate robust optical frequency transmission under the conditio...Future inter-satellite clock comparison on high orbit will require optical time and frequency transmission technology between moving objects.Here,we demonstrate robust optical frequency transmission under the condition of variable link distance.This variable link is accomplished by the relative motion of a single telescope fixed on the experimental platform to a corner-cube reflector(CCR)installed on a sliding guide.Two acousto–optic modulators with different frequencies are used to separate forward signal from backward signal.With active phase noise suppression,when the CCR moves back and forth at a constant velocity of 20 cm/s and an acceleration of 20 cm/s^(2),we achieve the best frequency stability of 1.9×10^(-16) at 1 s and 7.9×10^(-19) at 1000 s indoors.This work paves the way for future studying optical frequency transfer between ultra-high-orbit satellites.展开更多
Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal ...Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal radiation source for frequency comb and dual-comb operation.The systematic evaluation of phase noise characteristics of terahertz QCL frequency comb and dual-comb sources is of great importance for high precision measurements.In this work,we present detailed measurements and analysis of the phase noise characteristics of terahertz QCL frequency comb and dual-comb sources emitting around 4.2 THz with repetition frequencies of~6.2 GHz.The measurement results for the current noise of the direct current(DC)sources(that are used to electrically pump the terahertz QCLs)indicate that at 100 Hz,the current noise for DC-1 and DC-2 is 0.3895 and 0.0982 nA/Hz1/2,respectively.Such levels of current noise can be safely disregarded.The phase noise of radio frequency(RF)generators(that are employed for injection locking and phase locking),intermode beatnotes,and dual-comb signals with and without phase-locked loop(PLL)are all measured and compared.The experimental results show that in the free-running mode,the phase noise of the intermode beatnote signals is always lower than that of the dual-comb sig-nals across all frequencies.Additionally,the phase noise induced by the RF generators is negligible.By employing the phase lock-ing technique,the phase noise of the intermode beatnote and dual-comb signals in the low offset frequency band can be signifi-cantly suppressed.At an offset frequency of 100 Hz,the measured phase noise values of the dual-comb line without and with phase locking are 15.026 and-64.801 dBc/Hz,respectively.展开更多
Blades are one of the important components on aircraft engines.If they break due to vibration failure,the normal operation of the entire engine will be offected.Therefore,it is necessary to measure their natural frequ...Blades are one of the important components on aircraft engines.If they break due to vibration failure,the normal operation of the entire engine will be offected.Therefore,it is necessary to measure their natural frequency before installing them on the engine to avoid resonance.At present,most blade vibration testing systems require manual operation by operators,which has high requirements for operators and the testing process is also very cumbersome.Therefore,the testing efficiency is low and cannot meet the needs of efficient testing.To solve the current problems of low testing efficiency and high operational requirements,a high-precision and high-efficiency automatic test system is designed.The testing accuracy of this system can reach ±1%,and the testing efficiency is improved by 37% compared to manual testing.Firstly,the influence of compression force and vibration exciter position on natural frequency test is analyzed by amplitude-frequency curve,so as to calibrate servo cylinder and fourdimensional motion platform.Secondly,the sine wave signal is used as the excitation to sweep the blade linearly,and the natural frequency is determined by the amplitude peak in the frequency domain.Finally,the accuracy experiment and efficiency experiment are carried out on the developed test system,whose results verify its high efficiency and high precision.展开更多
Raman lasers are essential in atomic physics,and the development of portable devices has posed requirements for time-division multiplexing of Raman lasers.We demonstrate an innovative gigahertz frequency hopping appro...Raman lasers are essential in atomic physics,and the development of portable devices has posed requirements for time-division multiplexing of Raman lasers.We demonstrate an innovative gigahertz frequency hopping approach of a slave Raman laser within an optical phase-locked loop(OPLL),which finds practical application in an atomic gravimeter,where the OPLL frequently switches between near-resonance lasers and significantly detuned Raman lasers.The method merges the advantages of rapid and extensive frequency hopping with the OPLL’s inherent low phase noise,and exhibits a versatile range of applications in compact laser systems,promising advancements in portable instruments.展开更多
The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the...The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.展开更多
文摘Although eye problems can occur at any age, they are often common from the age of 40. Eye diseases with a prevalence associated with age and aging will continue to increase in the coming years. Most studies conducted on problems in middle-aged people have focused on visual disorders without taking into account all the ocular morbidities that may affect this segment of the population, hence the present study, the aim of which is to determine the proportions of different eye diseases in people aged 40 and over. Materials and Methods: This was a descriptive cross-sectional study carried out in the ophthalmology department covering the period from January 1 to December 31, 2020. Results: In total, we collected 828 patients aged 40 and over out of 1811 patients who received ophthalmological consultation during the study period, representing 45.72%. The most represented age group was 40 - 50 years, with an average age of 58.84 years and a maximum of 93 years. There were slightly more women (62.3%) than men (37.7%). The main reasons for consultation were decreased visual acuity (26.4%) and pruritus (19.9%). The main eye diseases diagnosed were cataracts (23%), allergic conjunctivitis (21.1%), and bacterial conjunctivitis (14.2%). Discussions: The predominance of cataracts in the diagnosed diseases confirms the literature data, according to which the main eye morbidities in middle-aged and elderly people are cataracts, glaucoma, and age-related macular degeneration. Conclusion: It is crucial to have a mastery of these epidemiological data of eye diseases in order to adapt the technical platforms of eye care structures to the needs of different segments of the population.
基金the Consejo Nacional de Humanidades,Ciencias y Tecnologías (CONAHCYT)of Mexico for providing funding for graduate studies of X.D.L. (No.001283)El Colegio de la Frontera Sur for PATM graduate fellowship for fieldwork。
文摘Urban environments have challenging characteristics for bird acoustic communication.High levels of anthropogenic noise,as well as vegetation structure(e.g.,in urban parks),can potentially affect the song frequency characteristics of several bird species.An additional factor such as the abundance of conspecific and heterospecific vocalizing birds may play an important role in determining the structure of bird songs.In this study,we analyzed whether noise levels,vegetation percentage,and abundance of conspecifics and heterospecifics influence the song characteristics of three syntopic songbird species:House Finch(Haemorhous mexicanus),Rufouscollared Sparrow(Zonotrichia capensis),and House Sparrow(Passer domesticus)living in urban sites.We recorded songs of these species and measured the peak frequency and entropy of their songs at 14 sites in the city of San Cristobal de Las Casas,Chiapas,Mexico.We found that the song peak frequency of House Finch and House Sparrow's songs was negatively related to the vegetation.The peak frequency of neither of the three species correlated with the average noise level.However,the abundances of conspecific and heterospecific were related to the peak frequency of the three species'songs.The entropy of the House Finch and House Sparrow songs was positively and negatively related,respectively,to noise levels.House Sparrow song entropy was negatively related to the percentage of vegetation.Song entropy of House Finches was negatively associated to conspecific and House Sparrow abundance.Song entropy of Rufous-collared Sparrows was positively related to conspecific abundance.In conclusion,the song peak frequency and song entropy of the three songbird species were differentially related to urban noise,vegetation,and conspecific and heterospecific abundance,suggesting these factors influence bird song characteristics.
基金financially supported by the Major Projects in Aviation Engines and Gas Turbines (Grant No.2019-VI-0020-0136)the National Key Research and Development Program of China (Grant Nos.2022YFB3705101&2022YFB3705102)+1 种基金the National Natural Science Foundation of China (Grant No.U1708253)the Fundamental Research Funds for the Central Universities,China (Grant No.N2302005)。
文摘The low frequency electromagnetic casting(LFEC)was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot.The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation.The results show that the average grain size decreases after application of LFEC.At the same time,the fraction of equiaxed grains increases compared with the ingots that without LFEC.In addition,the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency.When the current frequency increases from 5 Hz to 20 Hz,the average grain size decreases from 5.39 mm to 4.74 mm,and the fraction of equiaxed grains increases from 41.21%to 55.24%.The distribution of Lorentz force,melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software.It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency,thus the melt flow velocity and heat transfer in the melt are promoted.It can facilitate the heterogenous nucleation in the melt,resulting in grain refinement,and further preventing hot cracking of large size ingots.
基金Science and Technology Project of Aerospace Information Research Institute,Chinese Academy of Sciences(Y910340Z2F)Science and Technology Project of BBEF(E3E2010201)。
文摘Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.
基金supported by ZTE Industry-University-Institute Cooperation Funds under Grant No.IA20220800001。
文摘A wide passband frequency selective surface(FSS)is proposed using a five-layer stacked structure.The proposed structure applies four layers of dielectric plates and five layers of metal patches to provide a passband and exhibits more stable frequency responses and lower insertion loss under wide-angle oblique incidence compared with the typical three-layer metal-dielectric structure.According to the simulation results,the proposed FSS can achieve a passband range of 1.7-2.7 GHz with an insertion loss of less than 0.5 d B and a relative bandwidth of 44.1%,and it can preserve stable transmission characteristics with the incident angle ranging from 0°to 45°.
文摘Flooding remains one of the most destructive natural disasters,posing significant risks to both human lives and infrastructure.In India,where a large area is susceptible to flood hazards,the importance of accurate flood frequency analysis(FFA)and flood susceptibility mapping cannot be overstated.This study focuses on the Haora River basin in Tripura,a region prone to frequent flooding due to a combination of natural and anthropogenic factors.This study evaluates the suitability of the Log-Pearson Type Ⅲ(LP-Ⅲ)and Gumbel Extreme Value-1(EV-1)distributions for estimating peak discharges and delineates floodsusceptible zones in the Haora River basin,Tripura.Using 40 years of peak discharge data(1984-2023),the LP-Ⅲ distribution was identified as the most appropriate model based on goodness-of-fit tests.Flood susceptibility mapping,integrating 16 thematic layers through the Analytical Hierarchy Process,identified 8%,64%,and 26%of the area as high,moderate,and low susceptibility zones,respectively,with a model success rate of 0.81.The findings highlight the need for improved flood management strategies,such as enhancing river capacity and constructing flood spill channels.These insights are critical for designing targeted flood mitigation measures in the Haora basin and other flood-prone regions.
文摘Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.
基金supported in part by the National Natural Science Foundation of China (NSFC) under Grants 62131005, 62071096in part by the Fundamental Research Funds for the Central Universities under Grant 2242022k60006+1 种基金in part by the National NSFC under Grant U19B2014in part by the Natural Science Foundation of Sichuan under Grant 2022NSFSC0495
文摘As modern electromagnetic environments are more and more complex,the anti-interference performance of the synchronization acquisition is becoming vital in wireless communications.With the rapid development of the digital signal processing technologies,some synchronization acquisition algorithms for hybrid direct-sequence(DS)/frequency hopping(FH)spread spectrum communications have been proposed.However,these algorithms do not focus on the analysis and the design of the synchronization acquisition under typical interferences.In this paper,a synchronization acquisition algorithm based on the frequency hopping pulses combining(FHPC)is proposed.Specifically,the proposed algorithm is composed of two modules:an adaptive interference suppression(IS)module and an adaptive combining decision module.The adaptive IS module mitigates the effect of the interfered samples in the time-domain or the frequencydomain,and the adaptive combining decision module can utilize each frequency hopping pulse to construct an anti-interference decision metric and generate an adaptive acquisition decision threshold to complete the acquisition.Theory and simulation demonstrate that the proposed algorithm significantly enhances the antiinterference and anti-noise performances of the synchronization acquisition for hybrid DS/FH communications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12103059,12033007,12303077,and 12303076)the Fund from the Xi’an Science and Technology Bureau,China(Grant No.E019XK1S04)the Fund from the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.1188000XGJ).
文摘We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for.Instead of employing a phase discriminator and a phase locking loop in the conventional active phase control scheme,the passive phase noise cancellation is realized by feeding double-trip beat-note frequency to the driver of the acoustic optical modulator at the local site.This passive scheme exhibits fine robustness and reliability,making it suitable for long-distance and noisy fiber links.An optical regeneration station is used in the link for signal amplification and cascaded transmission.The phase noise cancellation and transfer instability of the 972-km link is investigated,and transfer instability of 1.1×10^(-19)at 10^(4)s is achieved.This work provides a promising method for realizing optical frequency distribution over thousands of kilometers by using fiber links.
基金supports from the National Natural Science Foundation of China(12074123,12174108)the Foundation of‘Manufacturing beyond limits’of Shanghai‘Talent Program'of Henan Academy of Sciences.
文摘Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.
基金funded by Jilin Province Science and Technology Development Plan Projects(20230508157RC)the National Natural Science Foundation of China(U2066208).
文摘To ensure frequency stability in power systems with high wind penetration,the doubly-fed induction generator(DFIG)is often used with the frequency fast response control(FFRC)to participate in frequency response.However,a certain output power suppression amount(OPSA)is generated during frequency support,resulting in the frequency modulation(FM)capability of DFIG not being fully utilised,and the system’s unbalanced power will be increased during speed recovery,resulting in a second frequency drop(SFD)in the system.Firstly,the frequency response characteristics of the power system with DFIG containing FFRC are analysed.Then,based on the analysis of the generation mechanism of OPSA and SFD,a combined wind-storage FM control strategy is proposed to improve the system’s frequency response characteristics.This strategy reduces the effect of OPSA and improves the FM capability of DFIG by designing the fuzzy logic of the coefficients of FFRC according to the system frequency index in the frequency support stage.During the speed recovery stage,the energy storage(ES)active power reference value is calculated according to the change of DFIG rotor speed,and the ES output power is dynamically adjusted to reduce the SFD.Finally,taking the IEEE 39-bus test system as an example,real-time digital simulation verification was conducted based on the RTLAB OP5707 simulation platform.The simulation results showthat theproposedmethodcan improve theFMcapabilityofDFIG,reduce the SFDunder thepremise of guaranteeing the rapid rotor speed recovery,and avoid the overshooting phenomenon so that the systemfrequency can be quickly restored to a stable state.
基金supported by a National Health and Medical Research Council(NHMRC)Investigator Grant(APP2008702)supported by the National Council for Scientific and Technological Developments-CNPq(process number 308772/2022-9)。
文摘Background:Optimal patterns of accrual of recommended levels of physical activity(PA)for prevention of hypertension and obesity are not known.The overall aim of this study was to investigate whether different patterns of accumulation of PA are differentially associated with hypertension and obesity in Australian women over 21 years.Specifically,we investigated whether,for the same weekly volume of PA,the number of sessions(frequency)and vigorousness of PA(intensity)were associated with a reduction in the occurrence of hypertension and obesity in women.Methods:Data from the 1973-1978 and 1946-1951 cohorts of the Australian Longitudinal Study on Women's Health were analyzed(n=20,588;12%-16%with a Bachelor's or higher degree).Self-reported PA,hypertension,height,and weight were collected using mail surveys every 3 years from 1998/2000 to 2019/2021.Generalized Estimating Equation models with a 3-year lag model were used to investigate the association of PA volume(metabolic equivalent min/week)(none;33-499;500-999;≥1000,weekly frequency(none;1-2 times;3-4times;5-7 times;≥8 times),and the proportion of vigorous PA to total volume of PA(none;0%;1%-33%;34%-66%;67%-100%)with odds of hypertension and obesity from 2000 to 2021.Results:The cumulative incidence of hypertension was 6%in the 1973-1978 and 23%in the 1946-1951 cohort;27%of women in the 1973-1978;and 15%in the 1946-1951 cohort developed obesity over the period.Overall,a higher volume of PA was associated with reduced odds of hypertension and obesity.When the volume of PA was considered,the odds of hypertension did not vary according to the frequency or intensity of PA.However,increased proportion of vigorous PA to the total volume of PA was associated with a small additional reduction in the risk of obe sity.Conclusion:PA volume appears to be more important than the pattern of accumulation for the prevention of hypertension and obesity.Incorporating more sessions,particularly of vigorous-intensity PA,may provide extra benefits for the prevention of obesity.
基金Project supported by the National Natural Science Foundation of China(Grant No.62375140)。
文摘Various strategies have been proposed to harness and protect space-like quantum correlations in different models under decoherence.However,little attention has been given to temporal-like correlations,such as quantum temporal steering(TS),in this context.In this work,we investigate TS in a frequency-modulated two-level system coupled to a zero-temperature reservoir in both the weak and strong coupling regimes.We analyze the impact of various frequency-modulated parameters on the behavior of TS and non-Markovian.The results demonstrate that appropriate frequency-modulated parameters can enhance the TS of the two-level system,regardless of whether the system is experiencing Markovian or non-Markovian dynamics.Furthermore,a suitable ratio between modulation strength and frequency(i.e.,all zeroes of the 0th Bessel function J_(0)(δ/?))can significantly enhance TS in the strong coupling regime.These findings indicate that efficient and effective manipulation of quantum TS can be achieved through a frequency-modulated approach.
文摘Macrosomia is defined as a term birth weight greater than or equal to 4000 grams, or greater than the 90 percentile of intrauterine growth curves. Excessive weight has harmful consequences for the newborn and is a major health concern. Objectives: To determine the frequency of neonatal macrosomia, describe risk factors and neonatal and maternal complications. Materials and methods: This was a cross-sectional study carried out between January and December 2022, involving newborns whose birth weight was greater than or equal to 4000 grams admitted to the neonatology unit of the Labe regional hospital. Results: 591 deliveries were recorded, 15 of which were macrosomic, representing a frequency of 2.54%. The average age of the women was 30.26 years. History of fetal macrosomia and diabetes was 93.33 and 71.43% respectively. The mean gestational age was 38.71 ± 0.75 SA, the mean antenatal consultation was 3 ± 0.8 and the mode of delivery was caesarean section (66.67%). Third-trimester ultrasound was performed in 53.33% of cases. Macrosomic newborns were male in 80% of cases. Neonatal complications were asphyxia (60%), hypoglycemia (20%) and hypocalcemia (13.33%). Factors associated with neonatal macrosomia were diabetes (P < 0.001), history of macrosomia (P Conclusion: this study shows that the frequency of neonatal macrosomia is 2.54% with high neonatal morbidity among newborns hospitalized in the neonatology unit of the Labé regional hospital. Screening for macrosomia risk factors during pregnancy is essential to prevent perinatal complications.
文摘Introduction: Mechanical complications after osteosynthesis are spontaneous and harmful modifications of the joint compromising the consolidation process. The aim of this study is to report on the frequency of these complications and their management in the Orthopaedic-Traumatology Department of CHU Ignace Deen. Patients and Methods: we conducted a retrospective descriptive and analytical cross-sectional study from January 2017 to December 2022. It focused on the records of patients hospitalized and treated in the department for a mechanical complication after osteosynthesis. Results: The frequency of mechanical complications was 1.2%, with an average age of 44.2 years and a sex ratio of 3.2 in favor of men. Non-compliance with postoperative instructions, non-compliance with surgical technique, postoperative infection and early loading were the main contributing factors. Disassembly of the screw-plate was the most common cause in 6 cases (35.5%), with a mean delay of 4.1 months. Revision osteosynthesis was carried out using screw plates in 8 cases (47.1%). Conclusion: Mechanical complications of osteosynthesis are less frequent traumatic conditions in our department. Several factors contribute to their occurrence.
基金Project supported by the National Key Research and Development Program of China(Grant No.2020YFB0408300)the National Natural Science Foundation of China(Grant No.62175246)+2 种基金the Natural Science Foundation of Shanghai,China(Grant No.22ZR1471100)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.YIPA2021244)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0300701).
文摘Future inter-satellite clock comparison on high orbit will require optical time and frequency transmission technology between moving objects.Here,we demonstrate robust optical frequency transmission under the condition of variable link distance.This variable link is accomplished by the relative motion of a single telescope fixed on the experimental platform to a corner-cube reflector(CCR)installed on a sliding guide.Two acousto–optic modulators with different frequencies are used to separate forward signal from backward signal.With active phase noise suppression,when the CCR moves back and forth at a constant velocity of 20 cm/s and an acceleration of 20 cm/s^(2),we achieve the best frequency stability of 1.9×10^(-16) at 1 s and 7.9×10^(-19) at 1000 s indoors.This work paves the way for future studying optical frequency transfer between ultra-high-orbit satellites.
基金supported by the Innovation Program for Quantum Science and Technology (2023ZD0301000)the National Science Fund for Distinguished Young Scholars (62325509)+3 种基金the National Natural Science Foundation of China (62235019,61875220,61927813,61991430,62035005,62105351,62275258,62035014,and 62305364)Science and Technology Commission of Shanghai Municipality (21ZR1474600)the"From 0 to 1"Innovation Program of the Chinese Academy of Sciences (ZDBS-LY-JSC009)the CAS Project for Young Scientists in Basic Research (YSBR-069).
文摘Frequency combs with equally spaced frequency lines show great potentials for applications in spectroscopy,imag-ing,communications,and so on.In the terahertz frequency region,the quantum cascade laser(QCL)is an ideal radiation source for frequency comb and dual-comb operation.The systematic evaluation of phase noise characteristics of terahertz QCL frequency comb and dual-comb sources is of great importance for high precision measurements.In this work,we present detailed measurements and analysis of the phase noise characteristics of terahertz QCL frequency comb and dual-comb sources emitting around 4.2 THz with repetition frequencies of~6.2 GHz.The measurement results for the current noise of the direct current(DC)sources(that are used to electrically pump the terahertz QCLs)indicate that at 100 Hz,the current noise for DC-1 and DC-2 is 0.3895 and 0.0982 nA/Hz1/2,respectively.Such levels of current noise can be safely disregarded.The phase noise of radio frequency(RF)generators(that are employed for injection locking and phase locking),intermode beatnotes,and dual-comb signals with and without phase-locked loop(PLL)are all measured and compared.The experimental results show that in the free-running mode,the phase noise of the intermode beatnote signals is always lower than that of the dual-comb sig-nals across all frequencies.Additionally,the phase noise induced by the RF generators is negligible.By employing the phase lock-ing technique,the phase noise of the intermode beatnote and dual-comb signals in the low offset frequency band can be signifi-cantly suppressed.At an offset frequency of 100 Hz,the measured phase noise values of the dual-comb line without and with phase locking are 15.026 and-64.801 dBc/Hz,respectively.
基金supported by the National Natural Science Foundation of China (No.51975293)Aeronautical Science Foundation of China (No.2019ZD052010)Postgraduate Research & Practice Innovation Program of NUAA (No.xcxjh20230502)。
文摘Blades are one of the important components on aircraft engines.If they break due to vibration failure,the normal operation of the entire engine will be offected.Therefore,it is necessary to measure their natural frequency before installing them on the engine to avoid resonance.At present,most blade vibration testing systems require manual operation by operators,which has high requirements for operators and the testing process is also very cumbersome.Therefore,the testing efficiency is low and cannot meet the needs of efficient testing.To solve the current problems of low testing efficiency and high operational requirements,a high-precision and high-efficiency automatic test system is designed.The testing accuracy of this system can reach ±1%,and the testing efficiency is improved by 37% compared to manual testing.Firstly,the influence of compression force and vibration exciter position on natural frequency test is analyzed by amplitude-frequency curve,so as to calibrate servo cylinder and fourdimensional motion platform.Secondly,the sine wave signal is used as the excitation to sweep the blade linearly,and the natural frequency is determined by the amplitude peak in the frequency domain.Finally,the accuracy experiment and efficiency experiment are carried out on the developed test system,whose results verify its high efficiency and high precision.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2021YFA0718300 and 2021YFA1400900)the National Natural Science Foundation of China(Grant Nos.11920101004,11934002,and 92365208)+1 种基金Science and Technology Major Project of Shanxi(Grant No.202101030201022)Space Application System of China Manned Space Program.
文摘Raman lasers are essential in atomic physics,and the development of portable devices has posed requirements for time-division multiplexing of Raman lasers.We demonstrate an innovative gigahertz frequency hopping approach of a slave Raman laser within an optical phase-locked loop(OPLL),which finds practical application in an atomic gravimeter,where the OPLL frequently switches between near-resonance lasers and significantly detuned Raman lasers.The method merges the advantages of rapid and extensive frequency hopping with the OPLL’s inherent low phase noise,and exhibits a versatile range of applications in compact laser systems,promising advancements in portable instruments.
基金the National Natural Science Foun-dation of China(Grant Nos.91963201 and 12174163)the 111 Project(Grant No.B20063).
文摘The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.
