AIM:To compare objective dry retinoscopy and subjective refraction measurements in patients with mild keratoconus(KCN)and quantify any differences.METHODS:This cross-sectional study was done on 68 eyes of 68 patients ...AIM:To compare objective dry retinoscopy and subjective refraction measurements in patients with mild keratoconus(KCN)and quantify any differences.METHODS:This cross-sectional study was done on 68 eyes of 68 patients diagnosed with mild KCN.Objective dry retinoscopy using autorefractometer and subjective refraction measurements were performed.Sphere,cylinder,J0,J45,and spherical equivalent values were compared between the two techniques.RESULTS:The mean age of 68 patients with mild KCN was 21.32±5.03y(12–35y).There were 37(54.4%)males.Objective refraction yielded significantly more myopic sphere(-1.44 D vs-0.57 D),higher cylinder magnitude(-2.24 D vs-1.48 D),and more myopic spherical equivalent(-2.56 D vs-1.31 D)compared to subjective refraction(all P<0.05).The mean differences were-0.87 D for sphere,-0.76 D for cylinder,and-1.25 D for spherical equivalent.No significant differences were found for J0 and J45 values,indicating agreement in astigmatism axis(P>0.05).CONCLUSION:In patients with mild KCN,objective dry retinoscopy overestimates the degree of myopia and astigmatism compared to subjective refraction.The irregular cornea in KCN likely impacts objective measurements.Subjective refraction allows compensation for irregularity,providing a more accurate correction.When determining refractive targets,the tendency of objective methods to overcorrect should be considered.展开更多
AIM:To compare the subjective refraction data with autorefraction findings in high astigmatisms.METHODS:In a cross-sectional study,sampling was done from in different geographic regions in Iran using a multistage rand...AIM:To compare the subjective refraction data with autorefraction findings in high astigmatisms.METHODS:In a cross-sectional study,sampling was done from in different geographic regions in Iran using a multistage random cluster sampling method.All study participants underwent cycloplegic auto-refraction and subjective refraction using the red-green test.RESULTS:In this study,277 eyes of 158 students aged 8 to 15y were analyzed.According to the results,the mean difference between subjective refraction and autorefraction in measuring sphere,cylinder,spherical equivalent,J0,and J45 was-0.18±0.76,-0.36±0.40,-0.36±0.79,0.15±0.20,and 0.05±0.21 respectively.The correlation of these two refraction methods in measuring the aforementioned indices was 0.963,0.898,0.960,0.931,and 0.948 respectively.The 95%limits of agreement of the two methods in measuring the above indices were-1.66 to 1.31,-1.14 to 0.42,-1.91 to 1.19,-0.24 to 0.54,and-0.36 to 0.47 respectively.The agreement between the two methods decreased with increasing cylinder power,and the best agreement was found in myopic individuals.CONCLUSION:The measurements obtained by autorefractometer have a significantly higher cylinder average compared to subjective refraction.However,in the cylinder range of 4–5 diopters,the values of J0 and J45 do not have a high correlation.展开更多
The emergent metagrating,with its unique and flexible beam shaping capabilities,offers new paths to efficient modulation of acoustic waves.In this work,an acoustic metagrating is demonstrated for high-efficiency and w...The emergent metagrating,with its unique and flexible beam shaping capabilities,offers new paths to efficient modulation of acoustic waves.In this work,an acoustic metagrating is demonstrated for high-efficiency and wide-angle anomalous refraction.It is shown that the normal reflection and transmission can be totally suppressed by properly modulating the amplitude and phase characteristics of the metagrating supercells for high-efficiency anomalous refraction.The anomalous refraction behavior is achieved in the wide range of incident angles from 28°to 78°,and the efficiency of-1st order diffraction is higher than 90%by finely designing the metagrating structure.The anomalous refraction behaviors are verified experimentally at incidence angle of 28°,45°,and 78°,respectively.The demonstrated metagrating is anticipated to possess efficient wide-angle composite wavefront engineering applications in such fields as communications.展开更多
AIM:To compare relative peripheral refraction(RPR)in Chinese school children with different refractive errors using multispectral refraction topography(MRT).METHODS:A total of 713 eyes of primary school children[172 e...AIM:To compare relative peripheral refraction(RPR)in Chinese school children with different refractive errors using multispectral refraction topography(MRT).METHODS:A total of 713 eyes of primary school children[172 emmetropia(E),429 low myopia(LM),80 moderate myopia(MM),and 32 low hypermetropia(LH)]aged 10 to 13y were analyzed.RPRs were measured using MRT without mydriasis.MRT results showed RPR at 0-15°(RPR 0-15),15°-30°(RPR 15-30),and 30°-45°(RPR 30-45)annular in the inferior(RPR-I),superior(RPR-S),nasal(RPR-N),and temporal(RPR-T)quadrants.Spherical equivalent(SE)was detected and calculated using an autorefractor.RESULTS:There were significant differences of RPR 15-30 between groups MM[0.02(-0.12;0.18)]and LH[-0.13(-0.36;0.12)](P<0.05),MM and E[-0.06(-0.20;0.10)](P<0.05),and LM[-0.02(-0.15;0.15)]and E(P<0.05).There were also significant differences of RPR 30-45 between groups MM[0.45(0.18;0.74)]and E[0.29(-0.09;0.67)](P<0.05),and LM[0.44(0.14;0.76)]and E(P<0.001).RPR values increased from the hyperopic to medium myopic group in each annular.There were significant differences of RPR-S between groups MM[-0.02(-0.60;0.30)]and E[-0.44(-0.89;-0.04)](P<0.001),and LM[-0.28(-0.71;0.12)]and E(P<0.05).There were also significant differences of RPR-T between groups MM[0.37(0.21;0.78)]and LH[0.14(-0.52;0.50)](P<0.05),LM[0.41(0.06;0.84)]and LH(P<0.05),and LM and E[0.29(-0.10;0.68),P<0.05].A Spearman’s correlation analysis showed a negative correlation between RPR and SE in the 15°-30°(P=0.005),30°-45°(P<0.05)annular(P=0.002),superior(P<0.001),and temporal(P=0.001)quadrants.CONCLUSION:Without pupil dilation,values for RPR 15-30,30-45,RPR-S,and T shows significant differences between myopic eyes and emmetropia,and the differences are negatively correlated with SE.展开更多
The article develops coordinate-invariant methods to calculate reflection and refraction of plane monochromatic waves at the plane boundary between two isotropic and an isotropic and an anisotropic medium. The vectori...The article develops coordinate-invariant methods to calculate reflection and refraction of plane monochromatic waves at the plane boundary between two isotropic and an isotropic and an anisotropic medium. The vectorial wave equation for the electric field is used to determine polarization vectors to known refraction vectors and this is applied to uniaxial media. Then it is shortly shown how the boundary conditions can be derived using the Heaviside step function and its derivatives which are the delta function and its derivatives. As preparation to the anisotropic case, there are calculated in coordinate-invariant way the amplitude relations for the reflection and refraction between two isotropic media and then in analogous way, the case of reflection and refraction between an isotropic and an anisotropic medium. This is then specialized for perpendicular incidence. It is shown that negative refraction such as discussed in last twenty-five years is impossible.展开更多
Elastic metamaterials with unusual elastic properties offer unprecedented ways to modulate the polarization and propagation of elastic waves.However,most of them rely on the resonant structural components,and thus are...Elastic metamaterials with unusual elastic properties offer unprecedented ways to modulate the polarization and propagation of elastic waves.However,most of them rely on the resonant structural components,and thus are frequency-dependent and unchangeable.Here,we present a reconfigurable 2D mechanism-based metamaterial which possesses transformable and frequency-independent elastic properties.Based on the proposed mechanism-based metamaterial,interesting functionalities,such as ternarycoded elastic wave polarizer and programmable refraction,are demonstrated.Particularly,unique ternary-coded polarizers,with 1-trit polarization filtering and 2-trit polarization separating of longitudinal and transverse waves,are first achieved.Then,the strong anisotropy of the proposed metamaterial is harnessed to realize positive-negative bi-refraction,only-positive refraction,and only-negative refraction.Finally,the wave functions with detailed microstructures are numerically verified.展开更多
Acoustic emission(AE)localization algorithms based on homogeneous media or single-velocity are less accurate when applied to the triaxial localization experiments.To the end,a robust triaxial localization method of AE...Acoustic emission(AE)localization algorithms based on homogeneous media or single-velocity are less accurate when applied to the triaxial localization experiments.To the end,a robust triaxial localization method of AE source using refraction path is proposed.Firstly,the control equation of the refraction path is established according to the sensor coordinates and arrival times.Secondly,considering the influence of time-difference-of-arrival(TDOA)errors,the residual of the governing equation is calculated to estimate the equation weight.Thirdly,the refraction points in different directions are solved using Snell’s law and orthogonal constraints.Finally,the source coordinates are iteratively solved by weighted correction terms.The feasibility and accuracy of the proposed method are verified by pencil-lead breaking experiments.The simulation results show that the new method is almost unaffected by the refraction ratio,and always holds more stable and accurate positioning performance than the traditional method under different ratios and scales of TDOA outliers.展开更多
AIM:To evaluate the refraction difference value(RDV)variations in children and adolescents with different refractive errors and analyze its correlation with refractive development.METHODS:Participants aged 4-16y with ...AIM:To evaluate the refraction difference value(RDV)variations in children and adolescents with different refractive errors and analyze its correlation with refractive development.METHODS:Participants aged 4-16y with different refractive statuses(hyperopia,emmetropia,myopia)underwent comprehensive eye examinations,including spherical equivalent(SE)refraction,axial length(AL),total RDV(TRDV),and RDVs at various eccentricities(0°-15°,15°-30°,30°-45°)and quadrants(inferior,superior,nasal,temporal).Statistical analysis involved one-way ANOVA for group comparisons and Pearson correlation for examining relationships between SE/AL and RDVs.Paired t-tests compared quadrant-specific RDVs within groups.RESULTS:Significant difference was found in TRDV(P<0.001),RDV15°-30°(P=0.033),RDV30°-45°(P<0.001),RDV-inferior(RDV-I,P<0.001)and RDV-temporal(RDV-T,P<0.001)among hyperopia,emmetropia and myopia group.Pearson correlation analysis revealed a negative correlation of SE with TRDV(P=0.001),RDV30°-45°(P=0.004),RDV-I(P=0.047),and RDV-T(P<0.001).The differences between RDV-superior(RDV-S)and RDV-I were statistically significant in all groups(P<0.001 for all)and between RDV-T and RDV-nasal(RDV-N)were statistically significant in hyperopia group(P<0.001).Within the premyopic group,the analysis revealed a negative correlation of SE with RDV-I(P=0.009).Pearson correlation analysis revealed a positive correlation of AL with TRDV(P=0.036),RDV15°-30°(P=0.004),RDV30°-45°(P<0.001),RDV-S(P=0.003),RDV-I(P<0.001),RDV-T(P<0.001),RDV-N(P=0.022),while revealed a negative correlation of AL with RDV0-15°(P=0.018).CONCLUSION:Our study indicates TRDV,RDV30°-45°,RDV-I,RDV-T may relate to refractive development,and a negative correlation between SE and RDV-I in pre-myopic children.展开更多
AIM: To compare the results of noncycloplegic photorefraction, cycloplegic photorefraction and cycloplegic refraction in preschool and non-verbal children.METHODS: One hundred and ninety-six eyes of 98children(50 fema...AIM: To compare the results of noncycloplegic photorefraction, cycloplegic photorefraction and cycloplegic refraction in preschool and non-verbal children.METHODS: One hundred and ninety-six eyes of 98children(50 females, 48 males) were included in the study. Firstly, non-cycloplegic photorefraction was achieved with Plusoptix A09; secondly, cycloplegic photorefraction was carried out with Plusoptix A09 after10 min cyclopentolate. Finally, 30 min after instillation of twice cyclopentolate, cycloplegic refraction was obtained with autorefraction and/or standard retinoscopy. Spheric equivalent, spheric power, cylindric power and cylindrical axis measurements were statistically compared.RESULTS: The mean age was 28.8±18.5mo(range12-72mo). The differences in spherical equivalent, spheric power and cylindrical power measured by the three methods were found statistically significant(P 【0.05).The spherical equivalent and spheric power measured by cycloplegic photorefraction were statistically higher than the measurements of the other methods(P 【0.05). The cylindrical power measured by cycloplegic refraction was statistically lower than the measurements of the photorefraction methods(P 【0.05). There was no significant difference in cylindrical axis measurements between three methods(P 】0.05).CONCLUSION: For the determination of refractive errors in children, the Plusoptix A09 measurements give incorrect results after instillation of cyclopentolate.Additionally, the cylindrical power measured by Plusoptix A09 with or without cycloplegia is higher. However, the non-cycloplegic Plusoptix A09 measures spheric equivalent and spheric power similar to cycloplegic refraction measurements in preschool and non-verbal children.展开更多
AIM:To evaluate the accuracy of spherical equivalent(SE) estimates of a double-pass system and to compare it with retinoscopy,subjective refraction and a table mounted autorefractor.METHODS:Non-cycloplegic refraction ...AIM:To evaluate the accuracy of spherical equivalent(SE) estimates of a double-pass system and to compare it with retinoscopy,subjective refraction and a table mounted autorefractor.METHODS:Non-cycloplegic refraction was performed on 125 eyes of 65 healthy adults(age 23.5±3.0 years) from October 2010 to January 2011 using retinoscopy,subjective refraction,autorefraction(Auto kerato refractometer TOPCON KR-8100,Japan) and a double pass system(Optical Quality Analysis System,OQAS,Visiometrics S.L.,Spain).Nine consecutive measurements with the double-pass system were performed on a subgroup of 22 eyes to assess repeatability.To evaluate the trueness of the OQAS instrument,the SE laboratory bias between the double pass system and the other techniques was calculated.RESULTS:The SE mean coefficient of repeatability obtained was 0.22D.Significant correlations could be established between the OQAS and the SE obtained with retinoscopy(r=0.956,P【0.001),subjective refraction(r=0.955,P【0.001) and autorefraction(r=0.957,P【0.001).The differences in SE between the double-pass system and the other techniques were significant(P【0.001),but lacked clinical relevance except for retinoscopy;Retinoscopy gave more hyperopic values than the double-pass system-0.51±0.50D as well as the subjective refraction-0.23±0.50D;More myopic values were achieved by means of autorefraction 0.24±0.49D. CONCLUSION:The double-pass system provides accurate and reliable estimates of the SE that can be used for clinical studies.This technique can determine the correct focus position to assess the ocular optical quality.However,it has a relatively small measuring range in comparison with autorefractors(-8.00 to +5.00D),and requires prior information on the refractive state of the patient.展开更多
Dynamic nonlinearities of C70/toluene solution are measured and analysed by an improved picosecond timeresolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters ...Dynamic nonlinearities of C70/toluene solution are measured and analysed by an improved picosecond timeresolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters are determined by the five-level model, which is adopted to interpret the experimental data. The change of refraction index per unit density of the excited state obtained by a numerically simulation is a critical factor to determine the nonlinear behaviour of C70 in picosecond time regime.展开更多
AIM:To compare the subjective refraction data with non-cycloplegic auto-refraction findings in the geriatric population above 60 years of age according to the different crystalline lens conditions.METHODS:This report ...AIM:To compare the subjective refraction data with non-cycloplegic auto-refraction findings in the geriatric population above 60 years of age according to the different crystalline lens conditions.METHODS:This report is a part of the Tehran Geriatric Eye Study(TGES)that was conducted from January 2019 to January 2020 on elderly population 60 years of age and above in Tehran.The samples were selected by multistage stratified random cluster sampling.Of 3791 individual invitees,3310(response rate:87.3%)participated in this study.All study participants underwent non-cycloplegic autorefraction(auto-refractometer/keratometer Nidek ARK-510)and subjective refraction.RESULTS:Regarding the sphere,eyes with mixed cataract had the worst limits of agreement(LoA:-1.24 to 0.87)and the best agreement was related to the pseudophakic eyes(LoA:-0.83 to 0.54).The highest(0.27±0.31 D)and lowest(0.21±0.27 D)differences between the two methods regarding the cylinder power were observed in eyes with cortical cataract and normal eyes,respectively.The worst LoA between the two methods in measuring the cylinder power was related to the eyes with mixed cataract(LoA:-0.44 to 0.96).Regarding the J0(horizontal/vertical components of astigmatism),the mean values of J0 obtained by auto-refraction were tended more toward against the rule direction in all crystalline lens conditions,and the two methods had the greatest difference in cortical cataract cases(0.05±0.17 D).Regarding the J45(oblique components of astigmatism),the lowest(0±0.11 D)and highest(-0.01±0.12 D)differences were observed in normal eyes and eyes with cortical cataract,respectively.CONCLUSION:The auto-refractometer/keratometer Nidek ARK-510 results in the elderly with different phakic and pseudophakic conditions do not correspond well with subjective refraction findings.This discrepancy in spherical findings is more pronounced in individuals with mixed cataract than in other cases.展开更多
The 1D τ-p inversion algorithm is widely employed to generate starting models with most computer programs that implement refraction tomography. However, this algorithm emphasizes the vertical resolution of many layer...The 1D τ-p inversion algorithm is widely employed to generate starting models with most computer programs that implement refraction tomography. However, this algorithm emphasizes the vertical resolution of many layers, and as a result, it frequently fails to detect even large lateral variations in seismic velocities, such as the decreases that are indicative of shear zones. This study presents a case that demonstrates the failure of the 1D τ-p inversion algorithm to define or even detect a major shear zone that is 50 m or ten stations wide. Furthermore, the majority of refraction tomography programs parameterize the seismic velocities within each layer with vertical velocity gradients. By contrast, the 2D generalized reciprocal method （GRM） inversion algorithms emphasize the lateral resolution of individual layers. This study demonstrates the successful detection and definition of the 50-m wide shear zone with the GRM inversion algorithms. The existence of the shear zone is corroborated by a 2D analysis of the head wave amplitudes and by numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, a 1D analysis of the head wave amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients, occurs in the weathered layers. While all seismic refraction operations should aim to provide as accurate depth estimates as is practical, the major conclusion reached in this study is that refraction inversion algorithms that emphasize the lateral resolution of individual layers generate more useful results for geotechnical and environmental applications. The advantages of the improved lateral resolution are obtained with 2D profiles in which the structural features can be recognized from the magnitudes of the variations in the seismic velocities. Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features that do not display any intrinsic variation or ＂signature＂ in seismic velocities.展开更多
Topological photonics provides a strategy that makes light transmission immune to structural-defects-induced backward scattering.Leveraging this,topological negative refraction enables robust,reflectionless light defl...Topological photonics provides a strategy that makes light transmission immune to structural-defects-induced backward scattering.Leveraging this,topological negative refraction enables robust,reflectionless light deflection,but directly controlling the refraction direction remains challenging.We demonstrate continuously tunable topological negative refraction at the interface between a one-way waveguide state and a free-space beam,overcoming the limitations of fixed refraction angles in conventional systems.The key insight is the ability to adjust the wavevector of the incident one-way waveguide state.Through manipulating the Bloch wavevector of the waveguide states in momentum space,we achieve a transition from negative to positive refraction.The unidirectional nature of these states prevents backscattering from defects,ensuring immunity to imperfections.As a prototypical demonstration,we achieve dynamic steering of refraction beams from-38°to+12°through active magnetic bias control.Our findings provide an exotic pathway for photon manipulation and a promising route toward topological photonics applications.展开更多
BACKGROUND Myopia,as one of the common ocular diseases,often occurs in adolescence.In addition to the harm from itself,it may also lead to serious complications.Thus,prevention and control of myopia are attracting mor...BACKGROUND Myopia,as one of the common ocular diseases,often occurs in adolescence.In addition to the harm from itself,it may also lead to serious complications.Thus,prevention and control of myopia are attracting more and more attention.Previous research revealed that single-focal glasses and orthokeratology lenses(OK lenses)played an important part in slowing down myopia and preventing high myopia.AIM To compare the clinical effects of OK lenses and frame glasses against the increase of diopter in adolescent myopia and further explore the mechanism of the OK lens.METHODS Changes in diopter and axial length were collected among 70 adolescent myopia patients(124 eyes)wearing OK lenses for 1 year(group A)and 59 adolescent myopia patients(113 eyes)wearing frame glasses(group B).Refractive states of their retina were inspected through multispectral refraction topography.The obtained hyperopic defocus was analyzed for the mechanism of OK lenses on slowing down the increase of myopic diopter by delaying the increase of ocular axis length and reducing the near hyperopia defocus.RESULTS Teenagers in groups A and B were divided into low myopia(0 D--3.00 D)and moderate myopia(-3.25 D--6.00 D),without statistical differences among gender and age.After 1-year treatment,the increase of diopter and axis length and changes of retinal hyperopic defocus amount of group A were significantly less than those of group B.According to the multiple linear analysis,the retinal defocus in the upper,lower,nasal,and temporal directions had almost the same effect on the total defocus.The amount of peripheral retinal defocus(15°-53°)in group A was significantly lower than that in group B.CONCLUSION Multispectral refraction topography is progressive and instructive in clinical prevention and control of myopia.展开更多
Underwater navigation system is an indispensable part for autonomous underwater vehicles.Due to the indiscernibility of satellite signal,however,the underwater navigation problem is quite challenging,and a satellite-f...Underwater navigation system is an indispensable part for autonomous underwater vehicles.Due to the indiscernibility of satellite signal,however,the underwater navigation problem is quite challenging,and a satellite-free navigation scheme should be looked for.Polarization navigation,inspired by insects’capability of autonomous homing and foraging,is an alternative solution to satellite navigation with great application potential.Underwater polarization provides an indirect sun compass to animals for orientation determination.However,it is difficult to apply terrestrial solar-tracking methodologies in underwater situations due to the refraction of polarized skylight at the air–water interface.To resolve this issue,an underwater solar-tracking algorithm is developed based on the underwater refraction-polarization pattern inside the Snell’s window.By employing Snell’s law and Fresnel refraction formula to decouple the refractive ray bending and polarization deflection,the celestial polarization pattern is obtained based on underwater measurement.To further improve the accuracy,the degree of polarization is employed as a weight factor for E-vector.A long-lasting underwater experiment was conducted to validate the effectiveness of the proposed approach,and the results showed the root-mean-square errors of solar zenith and azimuth employing this algorithm were 0.3°and 1.3°,respectively.Our experimental results show that the refraction-polarization pattern inside the Snell’s window exhibits immense potential to improve the solar-tracking accuracy for underwater navigation.展开更多
AIM:To characterize peripheral refraction and its relationship with myopia development in a selected group of male teenage Chinese students.METHODS:This 2-year prospective cohort study randomly enrolled 85 non-myopic ...AIM:To characterize peripheral refraction and its relationship with myopia development in a selected group of male teenage Chinese students.METHODS:This 2-year prospective cohort study randomly enrolled 85 non-myopic boys(age,14-16 y)from the Experimental Class of Air Force in China.Cycloplegic peripheral refraction was examined at 0°,±10°,and±20°along the horizontal visual field in the right eye at the baseline and 2-year follow-up.RESULTS:The incidence of myopia at the 2-year followup was 15.29%(13/85).The baseline central refraction(CR)and peripheral refraction at±10°were significantly lower in students who developed myopia than in those who did not(P<0.05).Relative peripheral refraction(RPR)did not differ between students with and without myopia(P>0.05).At the 2-year follow-up,the RPR at±10°and 20°nasal was significantly more hyperopic in the myopic group than in the non-myopic group.Multiple linear regression analysis indicated that the change in CR was significantly correlated with the changes in RPR at 20°nasal,10°nasal,and 20°temporal.Multivariate Logistic regression analysis indicated that the baseline CR[odds ratio(OR):0.092,95%confidence interval(CI):0.012-0.688,P=0.020]and the baseline RPR at 10°nasal(OR:0.182,95%CI:0.042-0.799,P=0.024)were significantly correlated with incident myopia(Omnibus test,χ=10.20,P=0.006).CONCLUSION:CR change is significantly correlated with changes in RPR,and students who develop myopia have more relative peripheral hyperopia.More baseline CR and relative peripheral hyperopia at 10°nasal are protective of myopia onset.展开更多
Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPSdenied environments. Starlight...Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPSdenied environments. Starlight refraction compensates for the significant along-track position error that occurs from only using gravity gradients and benefits from integration in terms of improved accuracy in radial and cross-track position estimates. The between-epoch differencing of gravity gradients is employed to eliminate slowly varying measurement biases and noise near the orbit revolution frequency. The refraction angle measurements are directly used and its Jacobian matrix derived from an implicit observation equation. An information fusion filter based on a sequential extended Kalman filter is developed for the orbit determination. Truth-model simulations are used to test the performance of the algorithm, and the effects of differencing intervals and orbital heights are analyzed. A semi-simulation study using actual gravity gradient data from the Gravity field and steady-state Ocean Circulation Explorer（GOCE） combined with simulated starlight refraction measurements is further conducted, and a three-dimensional position accuracy of better than 100 m is achieved.展开更多
AIM:To investigate the differences in retinal refraction difference values(RDVs)of adult patients with myopic anisometropia compared with those without myopic anisometropia,and to investigate the relationship between ...AIM:To investigate the differences in retinal refraction difference values(RDVs)of adult patients with myopic anisometropia compared with those without myopic anisometropia,and to investigate the relationship between ocular biometric measurements and relative peripheral refraction.METHODS:This clinical observation study included 130 patients with myopia(-0.25 to-10.00 D)between October 2022 and January 2023 aged between 18 and 40y.The patients were divided into anisometropia(n=63;difference in binocular anisometropia≥1.00 D)and non-anisometropia(n=67;difference in binocular anisometropia<1.00 D)groups accordingly.Ocular biometric measurements were performed by optical biometrics and corneal topography to assess the steep keratometry(Ks),flap keratometry(Kf),axial length(AL),corneal astigmatism(CYL;Ks-Kf),surface regularity index(SRI),surface asymmetry index(SAI),and central corneal thickness(CCT).The RDV was measured at five retinal areas from the fovea to 53 degrees(RDV-0-10,RDV-10-20,RDV-20-30,RDV-30-40,and RDV-40-53),the total RDV(TRDV)of 53 degrees,and four regions,including RDV-superior,RDV-inferior,RDV-temporal,and RDV-nasal.An analysis of Spearman correlation was carried out to examine the correlation between RDV and the spherical equivalent(SE)and ocular biological parameters.RESULTS:Within RDV-20-53,both groups showed relative hyperopic defocus,and the increase in RDV corresponds to the increase in eccentricity.In the myopic anisometropia group,the TRDV,RDV-20-53,RDV-superior,and more myopic eyes had significantly higher RDVtemporal values than less myopic eyes.(P<0.05).In the non-anisometropia group,there was no significant difference in the RDV between the more and less myopic eyes at different eccentricities(P>0.05).There was a negative correlation between SE and TRDV(r=-0.205,P=0.001),RDV-20-53(r=-0.281,-0.183,-0.176,P<0.05),RDV-superior(r=-0.251,P<0.001),and RDV-temporal(r=-0.230,P<0.001),a negative correlation between CYL and RDV-10-30(r=-0.147,-0.180,P<0.05),and a negative correlation between SRI and RDV-0-20(r=-0.190,-0.170,P<0.05).AL had a positive correlation with RDV-20-30(r=0.164,P=0.008)and RDV-temporal(r=0.160,P=0.010).CONCLUSION:More myopic eyes in patients with myopic anisometropia show more peripheral hyperopic defocus.Diopter and corneal morphology may affect peripheral retinal defocus.展开更多
Sinkholes and cavities can represent serious hazards to human safety and urban infrastructures,cause roadbed subsidence,and so on.It is therefore essential to evaluate various sinkholes in different depths and sizes t...Sinkholes and cavities can represent serious hazards to human safety and urban infrastructures,cause roadbed subsidence,and so on.It is therefore essential to evaluate various sinkholes in different depths and sizes to assess the risk of collapse.This paper evaluates the effect of different cavities on Rayleigh-wave propagation and body(P)wave refraction.Rayleigh(R)wave propagation is analyzed according to the classical multi-channel analysis of surface waves(MASW)method also considering the R-wave backscattering.Synthetic seismic traces are computed by means of finite element modeling(FEM)for cavity and intrusion at different depths and sizes.Furthermore,field acquisition data is used to verify the detection effect of a cavity on R-and P-waves.The results show that the presence of backscattered R-waves and the changes in the R-wave velocity spectrum can help in cavity identification.Additional possible evidence is represented by significant changes in the refraction travel times over the cavity location.It can be concluded that the field data are in good agreement with the synthetic,and it could be effective to consider the results of both R-and P-wave analysis in order to efficiently identify the cavities.展开更多
文摘AIM:To compare objective dry retinoscopy and subjective refraction measurements in patients with mild keratoconus(KCN)and quantify any differences.METHODS:This cross-sectional study was done on 68 eyes of 68 patients diagnosed with mild KCN.Objective dry retinoscopy using autorefractometer and subjective refraction measurements were performed.Sphere,cylinder,J0,J45,and spherical equivalent values were compared between the two techniques.RESULTS:The mean age of 68 patients with mild KCN was 21.32±5.03y(12–35y).There were 37(54.4%)males.Objective refraction yielded significantly more myopic sphere(-1.44 D vs-0.57 D),higher cylinder magnitude(-2.24 D vs-1.48 D),and more myopic spherical equivalent(-2.56 D vs-1.31 D)compared to subjective refraction(all P<0.05).The mean differences were-0.87 D for sphere,-0.76 D for cylinder,and-1.25 D for spherical equivalent.No significant differences were found for J0 and J45 values,indicating agreement in astigmatism axis(P>0.05).CONCLUSION:In patients with mild KCN,objective dry retinoscopy overestimates the degree of myopia and astigmatism compared to subjective refraction.The irregular cornea in KCN likely impacts objective measurements.Subjective refraction allows compensation for irregularity,providing a more accurate correction.When determining refractive targets,the tendency of objective methods to overcorrect should be considered.
基金Supported by Shahid Beheshti University of Medical Sciences.
文摘AIM:To compare the subjective refraction data with autorefraction findings in high astigmatisms.METHODS:In a cross-sectional study,sampling was done from in different geographic regions in Iran using a multistage random cluster sampling method.All study participants underwent cycloplegic auto-refraction and subjective refraction using the red-green test.RESULTS:In this study,277 eyes of 158 students aged 8 to 15y were analyzed.According to the results,the mean difference between subjective refraction and autorefraction in measuring sphere,cylinder,spherical equivalent,J0,and J45 was-0.18±0.76,-0.36±0.40,-0.36±0.79,0.15±0.20,and 0.05±0.21 respectively.The correlation of these two refraction methods in measuring the aforementioned indices was 0.963,0.898,0.960,0.931,and 0.948 respectively.The 95%limits of agreement of the two methods in measuring the above indices were-1.66 to 1.31,-1.14 to 0.42,-1.91 to 1.19,-0.24 to 0.54,and-0.36 to 0.47 respectively.The agreement between the two methods decreased with increasing cylinder power,and the best agreement was found in myopic individuals.CONCLUSION:The measurements obtained by autorefractometer have a significantly higher cylinder average compared to subjective refraction.However,in the cylinder range of 4–5 diopters,the values of J0 and J45 do not have a high correlation.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2023YFB3811400 and 2022YFB3806000)the National Natural Science Foundation of China(Grant No.12074314)+1 种基金the Science and Technology New Star Program of Shaanxi Province,China(Grant No.2023KJXX-148)the Fundamental Research Funds for the Central Universities。
文摘The emergent metagrating,with its unique and flexible beam shaping capabilities,offers new paths to efficient modulation of acoustic waves.In this work,an acoustic metagrating is demonstrated for high-efficiency and wide-angle anomalous refraction.It is shown that the normal reflection and transmission can be totally suppressed by properly modulating the amplitude and phase characteristics of the metagrating supercells for high-efficiency anomalous refraction.The anomalous refraction behavior is achieved in the wide range of incident angles from 28°to 78°,and the efficiency of-1st order diffraction is higher than 90%by finely designing the metagrating structure.The anomalous refraction behaviors are verified experimentally at incidence angle of 28°,45°,and 78°,respectively.The demonstrated metagrating is anticipated to possess efficient wide-angle composite wavefront engineering applications in such fields as communications.
基金Supported by the Shenzhen Science and Technology Program (No.JCYJ20210324142800001).
文摘AIM:To compare relative peripheral refraction(RPR)in Chinese school children with different refractive errors using multispectral refraction topography(MRT).METHODS:A total of 713 eyes of primary school children[172 emmetropia(E),429 low myopia(LM),80 moderate myopia(MM),and 32 low hypermetropia(LH)]aged 10 to 13y were analyzed.RPRs were measured using MRT without mydriasis.MRT results showed RPR at 0-15°(RPR 0-15),15°-30°(RPR 15-30),and 30°-45°(RPR 30-45)annular in the inferior(RPR-I),superior(RPR-S),nasal(RPR-N),and temporal(RPR-T)quadrants.Spherical equivalent(SE)was detected and calculated using an autorefractor.RESULTS:There were significant differences of RPR 15-30 between groups MM[0.02(-0.12;0.18)]and LH[-0.13(-0.36;0.12)](P<0.05),MM and E[-0.06(-0.20;0.10)](P<0.05),and LM[-0.02(-0.15;0.15)]and E(P<0.05).There were also significant differences of RPR 30-45 between groups MM[0.45(0.18;0.74)]and E[0.29(-0.09;0.67)](P<0.05),and LM[0.44(0.14;0.76)]and E(P<0.001).RPR values increased from the hyperopic to medium myopic group in each annular.There were significant differences of RPR-S between groups MM[-0.02(-0.60;0.30)]and E[-0.44(-0.89;-0.04)](P<0.001),and LM[-0.28(-0.71;0.12)]and E(P<0.05).There were also significant differences of RPR-T between groups MM[0.37(0.21;0.78)]and LH[0.14(-0.52;0.50)](P<0.05),LM[0.41(0.06;0.84)]and LH(P<0.05),and LM and E[0.29(-0.10;0.68),P<0.05].A Spearman’s correlation analysis showed a negative correlation between RPR and SE in the 15°-30°(P=0.005),30°-45°(P<0.05)annular(P=0.002),superior(P<0.001),and temporal(P=0.001)quadrants.CONCLUSION:Without pupil dilation,values for RPR 15-30,30-45,RPR-S,and T shows significant differences between myopic eyes and emmetropia,and the differences are negatively correlated with SE.
文摘The article develops coordinate-invariant methods to calculate reflection and refraction of plane monochromatic waves at the plane boundary between two isotropic and an isotropic and an anisotropic medium. The vectorial wave equation for the electric field is used to determine polarization vectors to known refraction vectors and this is applied to uniaxial media. Then it is shortly shown how the boundary conditions can be derived using the Heaviside step function and its derivatives which are the delta function and its derivatives. As preparation to the anisotropic case, there are calculated in coordinate-invariant way the amplitude relations for the reflection and refraction between two isotropic media and then in analogous way, the case of reflection and refraction between an isotropic and an anisotropic medium. This is then specialized for perpendicular incidence. It is shown that negative refraction such as discussed in last twenty-five years is impossible.
基金supported by the National Key R&D Program of China(No.2021YFE0110900)the National Natural Science Foundation of China(Nos.U22B2078 and 11991033)。
文摘Elastic metamaterials with unusual elastic properties offer unprecedented ways to modulate the polarization and propagation of elastic waves.However,most of them rely on the resonant structural components,and thus are frequency-dependent and unchangeable.Here,we present a reconfigurable 2D mechanism-based metamaterial which possesses transformable and frequency-independent elastic properties.Based on the proposed mechanism-based metamaterial,interesting functionalities,such as ternarycoded elastic wave polarizer and programmable refraction,are demonstrated.Particularly,unique ternary-coded polarizers,with 1-trit polarization filtering and 2-trit polarization separating of longitudinal and transverse waves,are first achieved.Then,the strong anisotropy of the proposed metamaterial is harnessed to realize positive-negative bi-refraction,only-positive refraction,and only-negative refraction.Finally,the wave functions with detailed microstructures are numerically verified.
基金the National Natural Science Foundation of China (Nos.52304123 and 52104077)the Postdoctoral Fellowship Program of CPSF (No.GZB20230914)+1 种基金the China Postdoctoral Science Foundation (No.2023M730412)the National Key Research and Development Program for Young Scientists (No.2021YFC2900400)。
文摘Acoustic emission(AE)localization algorithms based on homogeneous media or single-velocity are less accurate when applied to the triaxial localization experiments.To the end,a robust triaxial localization method of AE source using refraction path is proposed.Firstly,the control equation of the refraction path is established according to the sensor coordinates and arrival times.Secondly,considering the influence of time-difference-of-arrival(TDOA)errors,the residual of the governing equation is calculated to estimate the equation weight.Thirdly,the refraction points in different directions are solved using Snell’s law and orthogonal constraints.Finally,the source coordinates are iteratively solved by weighted correction terms.The feasibility and accuracy of the proposed method are verified by pencil-lead breaking experiments.The simulation results show that the new method is almost unaffected by the refraction ratio,and always holds more stable and accurate positioning performance than the traditional method under different ratios and scales of TDOA outliers.
文摘AIM:To evaluate the refraction difference value(RDV)variations in children and adolescents with different refractive errors and analyze its correlation with refractive development.METHODS:Participants aged 4-16y with different refractive statuses(hyperopia,emmetropia,myopia)underwent comprehensive eye examinations,including spherical equivalent(SE)refraction,axial length(AL),total RDV(TRDV),and RDVs at various eccentricities(0°-15°,15°-30°,30°-45°)and quadrants(inferior,superior,nasal,temporal).Statistical analysis involved one-way ANOVA for group comparisons and Pearson correlation for examining relationships between SE/AL and RDVs.Paired t-tests compared quadrant-specific RDVs within groups.RESULTS:Significant difference was found in TRDV(P<0.001),RDV15°-30°(P=0.033),RDV30°-45°(P<0.001),RDV-inferior(RDV-I,P<0.001)and RDV-temporal(RDV-T,P<0.001)among hyperopia,emmetropia and myopia group.Pearson correlation analysis revealed a negative correlation of SE with TRDV(P=0.001),RDV30°-45°(P=0.004),RDV-I(P=0.047),and RDV-T(P<0.001).The differences between RDV-superior(RDV-S)and RDV-I were statistically significant in all groups(P<0.001 for all)and between RDV-T and RDV-nasal(RDV-N)were statistically significant in hyperopia group(P<0.001).Within the premyopic group,the analysis revealed a negative correlation of SE with RDV-I(P=0.009).Pearson correlation analysis revealed a positive correlation of AL with TRDV(P=0.036),RDV15°-30°(P=0.004),RDV30°-45°(P<0.001),RDV-S(P=0.003),RDV-I(P<0.001),RDV-T(P<0.001),RDV-N(P=0.022),while revealed a negative correlation of AL with RDV0-15°(P=0.018).CONCLUSION:Our study indicates TRDV,RDV30°-45°,RDV-I,RDV-T may relate to refractive development,and a negative correlation between SE and RDV-I in pre-myopic children.
文摘AIM: To compare the results of noncycloplegic photorefraction, cycloplegic photorefraction and cycloplegic refraction in preschool and non-verbal children.METHODS: One hundred and ninety-six eyes of 98children(50 females, 48 males) were included in the study. Firstly, non-cycloplegic photorefraction was achieved with Plusoptix A09; secondly, cycloplegic photorefraction was carried out with Plusoptix A09 after10 min cyclopentolate. Finally, 30 min after instillation of twice cyclopentolate, cycloplegic refraction was obtained with autorefraction and/or standard retinoscopy. Spheric equivalent, spheric power, cylindric power and cylindrical axis measurements were statistically compared.RESULTS: The mean age was 28.8±18.5mo(range12-72mo). The differences in spherical equivalent, spheric power and cylindrical power measured by the three methods were found statistically significant(P 【0.05).The spherical equivalent and spheric power measured by cycloplegic photorefraction were statistically higher than the measurements of the other methods(P 【0.05). The cylindrical power measured by cycloplegic refraction was statistically lower than the measurements of the photorefraction methods(P 【0.05). There was no significant difference in cylindrical axis measurements between three methods(P 】0.05).CONCLUSION: For the determination of refractive errors in children, the Plusoptix A09 measurements give incorrect results after instillation of cyclopentolate.Additionally, the cylindrical power measured by Plusoptix A09 with or without cycloplegia is higher. However, the non-cycloplegic Plusoptix A09 measures spheric equivalent and spheric power similar to cycloplegic refraction measurements in preschool and non-verbal children.
基金Spanish Ministry of Education and Science(No.DPI2008-06455-C02-01)European Union and the Spanish Agency for International Cooperation(AECI)(No.D/030286/10)
文摘AIM:To evaluate the accuracy of spherical equivalent(SE) estimates of a double-pass system and to compare it with retinoscopy,subjective refraction and a table mounted autorefractor.METHODS:Non-cycloplegic refraction was performed on 125 eyes of 65 healthy adults(age 23.5±3.0 years) from October 2010 to January 2011 using retinoscopy,subjective refraction,autorefraction(Auto kerato refractometer TOPCON KR-8100,Japan) and a double pass system(Optical Quality Analysis System,OQAS,Visiometrics S.L.,Spain).Nine consecutive measurements with the double-pass system were performed on a subgroup of 22 eyes to assess repeatability.To evaluate the trueness of the OQAS instrument,the SE laboratory bias between the double pass system and the other techniques was calculated.RESULTS:The SE mean coefficient of repeatability obtained was 0.22D.Significant correlations could be established between the OQAS and the SE obtained with retinoscopy(r=0.956,P【0.001),subjective refraction(r=0.955,P【0.001) and autorefraction(r=0.957,P【0.001).The differences in SE between the double-pass system and the other techniques were significant(P【0.001),but lacked clinical relevance except for retinoscopy;Retinoscopy gave more hyperopic values than the double-pass system-0.51±0.50D as well as the subjective refraction-0.23±0.50D;More myopic values were achieved by means of autorefraction 0.24±0.49D. CONCLUSION:The double-pass system provides accurate and reliable estimates of the SE that can be used for clinical studies.This technique can determine the correct focus position to assess the ocular optical quality.However,it has a relatively small measuring range in comparison with autorefractors(-8.00 to +5.00D),and requires prior information on the refractive state of the patient.
基金Project supported by the National Natural Science Fundation of China(Grant No.90922007)
文摘Dynamic nonlinearities of C70/toluene solution are measured and analysed by an improved picosecond timeresolved pump-probe system based on a nonlinear imaging technique with phase object. The photophysical parameters are determined by the five-level model, which is adopted to interpret the experimental data. The change of refraction index per unit density of the excited state obtained by a numerically simulation is a critical factor to determine the nonlinear behaviour of C70 in picosecond time regime.
基金Supported by National Institute for Medical Research Development(NIMAD)affiliated with the Iranian Ministry of Health and Medical Education(No.963660).
文摘AIM:To compare the subjective refraction data with non-cycloplegic auto-refraction findings in the geriatric population above 60 years of age according to the different crystalline lens conditions.METHODS:This report is a part of the Tehran Geriatric Eye Study(TGES)that was conducted from January 2019 to January 2020 on elderly population 60 years of age and above in Tehran.The samples were selected by multistage stratified random cluster sampling.Of 3791 individual invitees,3310(response rate:87.3%)participated in this study.All study participants underwent non-cycloplegic autorefraction(auto-refractometer/keratometer Nidek ARK-510)and subjective refraction.RESULTS:Regarding the sphere,eyes with mixed cataract had the worst limits of agreement(LoA:-1.24 to 0.87)and the best agreement was related to the pseudophakic eyes(LoA:-0.83 to 0.54).The highest(0.27±0.31 D)and lowest(0.21±0.27 D)differences between the two methods regarding the cylinder power were observed in eyes with cortical cataract and normal eyes,respectively.The worst LoA between the two methods in measuring the cylinder power was related to the eyes with mixed cataract(LoA:-0.44 to 0.96).Regarding the J0(horizontal/vertical components of astigmatism),the mean values of J0 obtained by auto-refraction were tended more toward against the rule direction in all crystalline lens conditions,and the two methods had the greatest difference in cortical cataract cases(0.05±0.17 D).Regarding the J45(oblique components of astigmatism),the lowest(0±0.11 D)and highest(-0.01±0.12 D)differences were observed in normal eyes and eyes with cortical cataract,respectively.CONCLUSION:The auto-refractometer/keratometer Nidek ARK-510 results in the elderly with different phakic and pseudophakic conditions do not correspond well with subjective refraction findings.This discrepancy in spherical findings is more pronounced in individuals with mixed cataract than in other cases.
文摘The 1D τ-p inversion algorithm is widely employed to generate starting models with most computer programs that implement refraction tomography. However, this algorithm emphasizes the vertical resolution of many layers, and as a result, it frequently fails to detect even large lateral variations in seismic velocities, such as the decreases that are indicative of shear zones. This study presents a case that demonstrates the failure of the 1D τ-p inversion algorithm to define or even detect a major shear zone that is 50 m or ten stations wide. Furthermore, the majority of refraction tomography programs parameterize the seismic velocities within each layer with vertical velocity gradients. By contrast, the 2D generalized reciprocal method （GRM） inversion algorithms emphasize the lateral resolution of individual layers. This study demonstrates the successful detection and definition of the 50-m wide shear zone with the GRM inversion algorithms. The existence of the shear zone is corroborated by a 2D analysis of the head wave amplitudes and by numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, a 1D analysis of the head wave amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients, occurs in the weathered layers. While all seismic refraction operations should aim to provide as accurate depth estimates as is practical, the major conclusion reached in this study is that refraction inversion algorithms that emphasize the lateral resolution of individual layers generate more useful results for geotechnical and environmental applications. The advantages of the improved lateral resolution are obtained with 2D profiles in which the structural features can be recognized from the magnitudes of the variations in the seismic velocities. Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features that do not display any intrinsic variation or ＂signature＂ in seismic velocities.
基金National Natural Science Foundation of China(12434016,12474380)Science and Technology Project of Guangdong(2020B010190001)+1 种基金National Key Research and Development Program of China(2023YFA1406900)Natural Science Foundation of Guangdong Province(2025A1515010714)。
文摘Topological photonics provides a strategy that makes light transmission immune to structural-defects-induced backward scattering.Leveraging this,topological negative refraction enables robust,reflectionless light deflection,but directly controlling the refraction direction remains challenging.We demonstrate continuously tunable topological negative refraction at the interface between a one-way waveguide state and a free-space beam,overcoming the limitations of fixed refraction angles in conventional systems.The key insight is the ability to adjust the wavevector of the incident one-way waveguide state.Through manipulating the Bloch wavevector of the waveguide states in momentum space,we achieve a transition from negative to positive refraction.The unidirectional nature of these states prevents backscattering from defects,ensuring immunity to imperfections.As a prototypical demonstration,we achieve dynamic steering of refraction beams from-38°to+12°through active magnetic bias control.Our findings provide an exotic pathway for photon manipulation and a promising route toward topological photonics applications.
文摘BACKGROUND Myopia,as one of the common ocular diseases,often occurs in adolescence.In addition to the harm from itself,it may also lead to serious complications.Thus,prevention and control of myopia are attracting more and more attention.Previous research revealed that single-focal glasses and orthokeratology lenses(OK lenses)played an important part in slowing down myopia and preventing high myopia.AIM To compare the clinical effects of OK lenses and frame glasses against the increase of diopter in adolescent myopia and further explore the mechanism of the OK lens.METHODS Changes in diopter and axial length were collected among 70 adolescent myopia patients(124 eyes)wearing OK lenses for 1 year(group A)and 59 adolescent myopia patients(113 eyes)wearing frame glasses(group B).Refractive states of their retina were inspected through multispectral refraction topography.The obtained hyperopic defocus was analyzed for the mechanism of OK lenses on slowing down the increase of myopic diopter by delaying the increase of ocular axis length and reducing the near hyperopia defocus.RESULTS Teenagers in groups A and B were divided into low myopia(0 D--3.00 D)and moderate myopia(-3.25 D--6.00 D),without statistical differences among gender and age.After 1-year treatment,the increase of diopter and axis length and changes of retinal hyperopic defocus amount of group A were significantly less than those of group B.According to the multiple linear analysis,the retinal defocus in the upper,lower,nasal,and temporal directions had almost the same effect on the total defocus.The amount of peripheral retinal defocus(15°-53°)in group A was significantly lower than that in group B.CONCLUSION Multispectral refraction topography is progressive and instructive in clinical prevention and control of myopia.
基金supported by grants from the National Natural Science Foundation of China(Nos.61751302,62003017,61627810,61833013,61973012)Science and Technology Key Innovative Project of Hangzhou,China(No.20182014B06)。
文摘Underwater navigation system is an indispensable part for autonomous underwater vehicles.Due to the indiscernibility of satellite signal,however,the underwater navigation problem is quite challenging,and a satellite-free navigation scheme should be looked for.Polarization navigation,inspired by insects’capability of autonomous homing and foraging,is an alternative solution to satellite navigation with great application potential.Underwater polarization provides an indirect sun compass to animals for orientation determination.However,it is difficult to apply terrestrial solar-tracking methodologies in underwater situations due to the refraction of polarized skylight at the air–water interface.To resolve this issue,an underwater solar-tracking algorithm is developed based on the underwater refraction-polarization pattern inside the Snell’s window.By employing Snell’s law and Fresnel refraction formula to decouple the refractive ray bending and polarization deflection,the celestial polarization pattern is obtained based on underwater measurement.To further improve the accuracy,the degree of polarization is employed as a weight factor for E-vector.A long-lasting underwater experiment was conducted to validate the effectiveness of the proposed approach,and the results showed the root-mean-square errors of solar zenith and azimuth employing this algorithm were 0.3°and 1.3°,respectively.Our experimental results show that the refraction-polarization pattern inside the Snell’s window exhibits immense potential to improve the solar-tracking accuracy for underwater navigation.
基金Supported by National Natural Science Foundation of China(No.81800854)Joint Innovation Project of National Defense Technology Innovation Zone(No.20-163-15-ZT-001-001-10)Efficiency Improvement Project of Air Force Medical University(No.2021HKYX24)。
文摘AIM:To characterize peripheral refraction and its relationship with myopia development in a selected group of male teenage Chinese students.METHODS:This 2-year prospective cohort study randomly enrolled 85 non-myopic boys(age,14-16 y)from the Experimental Class of Air Force in China.Cycloplegic peripheral refraction was examined at 0°,±10°,and±20°along the horizontal visual field in the right eye at the baseline and 2-year follow-up.RESULTS:The incidence of myopia at the 2-year followup was 15.29%(13/85).The baseline central refraction(CR)and peripheral refraction at±10°were significantly lower in students who developed myopia than in those who did not(P<0.05).Relative peripheral refraction(RPR)did not differ between students with and without myopia(P>0.05).At the 2-year follow-up,the RPR at±10°and 20°nasal was significantly more hyperopic in the myopic group than in the non-myopic group.Multiple linear regression analysis indicated that the change in CR was significantly correlated with the changes in RPR at 20°nasal,10°nasal,and 20°temporal.Multivariate Logistic regression analysis indicated that the baseline CR[odds ratio(OR):0.092,95%confidence interval(CI):0.012-0.688,P=0.020]and the baseline RPR at 10°nasal(OR:0.182,95%CI:0.042-0.799,P=0.024)were significantly correlated with incident myopia(Omnibus test,χ=10.20,P=0.006).CONCLUSION:CR change is significantly correlated with changes in RPR,and students who develop myopia have more relative peripheral hyperopia.More baseline CR and relative peripheral hyperopia at 10°nasal are protective of myopia onset.
基金supported by the National Natural Science Foundation of China (No.11002008)funded in part by Ministry of Science and Technology of China (No.2014CB845303)
文摘Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPSdenied environments. Starlight refraction compensates for the significant along-track position error that occurs from only using gravity gradients and benefits from integration in terms of improved accuracy in radial and cross-track position estimates. The between-epoch differencing of gravity gradients is employed to eliminate slowly varying measurement biases and noise near the orbit revolution frequency. The refraction angle measurements are directly used and its Jacobian matrix derived from an implicit observation equation. An information fusion filter based on a sequential extended Kalman filter is developed for the orbit determination. Truth-model simulations are used to test the performance of the algorithm, and the effects of differencing intervals and orbital heights are analyzed. A semi-simulation study using actual gravity gradient data from the Gravity field and steady-state Ocean Circulation Explorer（GOCE） combined with simulated starlight refraction measurements is further conducted, and a three-dimensional position accuracy of better than 100 m is achieved.
文摘AIM:To investigate the differences in retinal refraction difference values(RDVs)of adult patients with myopic anisometropia compared with those without myopic anisometropia,and to investigate the relationship between ocular biometric measurements and relative peripheral refraction.METHODS:This clinical observation study included 130 patients with myopia(-0.25 to-10.00 D)between October 2022 and January 2023 aged between 18 and 40y.The patients were divided into anisometropia(n=63;difference in binocular anisometropia≥1.00 D)and non-anisometropia(n=67;difference in binocular anisometropia<1.00 D)groups accordingly.Ocular biometric measurements were performed by optical biometrics and corneal topography to assess the steep keratometry(Ks),flap keratometry(Kf),axial length(AL),corneal astigmatism(CYL;Ks-Kf),surface regularity index(SRI),surface asymmetry index(SAI),and central corneal thickness(CCT).The RDV was measured at five retinal areas from the fovea to 53 degrees(RDV-0-10,RDV-10-20,RDV-20-30,RDV-30-40,and RDV-40-53),the total RDV(TRDV)of 53 degrees,and four regions,including RDV-superior,RDV-inferior,RDV-temporal,and RDV-nasal.An analysis of Spearman correlation was carried out to examine the correlation between RDV and the spherical equivalent(SE)and ocular biological parameters.RESULTS:Within RDV-20-53,both groups showed relative hyperopic defocus,and the increase in RDV corresponds to the increase in eccentricity.In the myopic anisometropia group,the TRDV,RDV-20-53,RDV-superior,and more myopic eyes had significantly higher RDVtemporal values than less myopic eyes.(P<0.05).In the non-anisometropia group,there was no significant difference in the RDV between the more and less myopic eyes at different eccentricities(P>0.05).There was a negative correlation between SE and TRDV(r=-0.205,P=0.001),RDV-20-53(r=-0.281,-0.183,-0.176,P<0.05),RDV-superior(r=-0.251,P<0.001),and RDV-temporal(r=-0.230,P<0.001),a negative correlation between CYL and RDV-10-30(r=-0.147,-0.180,P<0.05),and a negative correlation between SRI and RDV-0-20(r=-0.190,-0.170,P<0.05).AL had a positive correlation with RDV-20-30(r=0.164,P=0.008)and RDV-temporal(r=0.160,P=0.010).CONCLUSION:More myopic eyes in patients with myopic anisometropia show more peripheral hyperopic defocus.Diopter and corneal morphology may affect peripheral retinal defocus.
文摘Sinkholes and cavities can represent serious hazards to human safety and urban infrastructures,cause roadbed subsidence,and so on.It is therefore essential to evaluate various sinkholes in different depths and sizes to assess the risk of collapse.This paper evaluates the effect of different cavities on Rayleigh-wave propagation and body(P)wave refraction.Rayleigh(R)wave propagation is analyzed according to the classical multi-channel analysis of surface waves(MASW)method also considering the R-wave backscattering.Synthetic seismic traces are computed by means of finite element modeling(FEM)for cavity and intrusion at different depths and sizes.Furthermore,field acquisition data is used to verify the detection effect of a cavity on R-and P-waves.The results show that the presence of backscattered R-waves and the changes in the R-wave velocity spectrum can help in cavity identification.Additional possible evidence is represented by significant changes in the refraction travel times over the cavity location.It can be concluded that the field data are in good agreement with the synthetic,and it could be effective to consider the results of both R-and P-wave analysis in order to efficiently identify the cavities.
