Angle Resolution Research Articles

Critical Angle Refractometry for Lossy Media with a Priori Known Extinction Coefficient

Critical angle refractometry is an established technique for determining the refractive index of liquids and solids. For transparent samples, the critical angle refractometry precision is limited by incidence angle resolution. For lossy samples, the precision is also affected by reflectance measurement error. In the present study, it is demonstarted that reflectance error can be practically eliminated, provided that the sample’s extinction coefficient is a priori known with sufficient accuracy (typically, better than 5%) through an independent measurement. Then, critical angle refractometry can be as precise with lossy media as with transparent ones.

Mapping a duck: geological features and region definitions on comet 67P/Churyumov-Gerasimenko

The data from the Rosetta mission have permitted a reconstruction of the shape of comet 67P/Churyumov-Gerasimenko and an identification of the terrains and features forming the surface. The peculiar shape of the comet has made it challenging to project these geological features onto an unambiguous frame. As a result, the geological maps published to date are created on top of comet images, making them dependent on the viewing angle and image resolution. To overcome this limitation, we present an integrated set of geological maps of the northern hemisphere of the comet, displayed in an unambiguous projection. The new maps combine the geological landmarks published in previous studies in a single framework and are completed with newly identified features. We have located the landmarks on OSIRIS images projected onto the surface of a three-dimensional shape model of the comet. For each region, the geological maps are displayed in the Quincuncial adaptive closed Kohonen (QuACK) map projection. The QuACK map solves the spatial ambiguity issues and reduces the shape and area distortions of classical global projections, which particularly affect the polar regions. The outcome of this research is a set of individual geological maps that are displayed both on top of OSIRIS images and in the QuACK map projection. These maps are analysed and grouped by similarities in terrain and morphology to find common characteristics that allow expanding our knowledge of the formation processes of comets. Based on this analysis, the north-south dichotomy is confirmed, and a redefinition of the regional boundaries is proposed for the Anubis-Atum and Aker-Babi frontiers. This research fills the gap in the field of mapping comet 67P/Churyumov-Gerasimenko and provides an innovative method for treating the surface of highly irregular bodies.

Real-World Outcomes of Intravitreal Aflibercept for Neovascular Age-Related Macular Degeneration: A Large-Scale Postmarketing Surveillance in Korea.

PurposeTo investigate the efficacy and safety of intravitreal aflibercept (IVT-AFL) in Asian patients with neovascular age-related macular degeneration (nAMD) in a real-world clinical setting.Patients and MethodsIn this analysis of a prospective, regulatory, postmarketing surveillance study for IVT-AFL, 3115 patients with nAMD were included and followed for 8 months. The mean changes in best-corrected visual acuity (BCVA) and central retinal thickness (CRT) were analyzed using last observation carried forward method. A post hoc subgroup analysis and a multivariate logistic regression analysis were also performed to assess factors related to treatment outcomes.ResultsMean BCVA improved from 0.62 to 0.51 logarithm of minimum angle resolution and mean CRT decreased from 383.3 to 289.7 μm, with a mean of 3.4 injections during the 8-month follow-up. In the subgroup analysis, patients who had received 3 initial monthly doses had significantly better anatomical improvements than those treated as needed. Patients with confirmed polypoidal choroidal vasculopathy (PCV) had significantly better anatomical improvements and better visual recovery than those with other types of nAMD. The multivariate regression analysis demonstrated that age, injection number, PCV, and baseline BCVA were significantly associated with higher odds of gaining 3 lines at 8 months, and sex, injection number, PCV, and baseline CRT were associated with CRT ≤250 µm at 8 months. No new safety findings were identified.ConclusionIVT-AFL was effective and well tolerated in a real-world setting with a large number of Asian patients with nAMD. Number of injections and PCV were important determinants for improved treatment outcomes.

Long-term prognosis of polypoidal choroidal vasculopathy with a 5-year remission after an initial combination therapy

PurposeTo investigate the visual prognosis of patients with polypoidal choroidal vasculopathy (PCV) with a 5-year remission after an initial combination therapy involving photodynamic therapy (PDT) and intravitreal ranibizumab (IVR) or aflibercept injection (IVA). MethodsMedical records of 69 consecutive patients with PCV treated with PDT with IVR/IVA were retrospectively reviewed, and 17 eyes were identified with a 5-year remission after the initial combination therapy. The eyes that did not require additional treatment during the 1st–5th year were assigned to the remission group and the eyes requiring additional treatment during the 1st–5th year were assigned to the recurrence group. ResultsDuring the 7-year follow-up, the mean logarithm of the minimal angle resolution best-corrected visual acuity (logMAR BCVA) significantly improved from 0.39±0.27 to 0.17±0.38 (p=2.9 × 10−4) in the remission group, whereas the mean logMAR BCVA was maintained throughout the follow-up period (0.58±0.27 to 0.60±0.48) in the recurrence group. In the remission group, only two (11.8%) of the 17 eyes experienced recurrence during the 5th–7th year. Comparison of baseline characteristics between the two groups revealed that a higher proportion of female (p=0.012), better baseline BCVA (p=3.1 × 10−3), and lower risk allele frequency in ARMS2 A69S (p=0.029) were observed in the remission group. ConclusionsThe combination therapy showed a favourable outcome for PCV over a 7-year follow-up, especially in the eyes without recurrence during the 1st–5th year. Physicians should be careful of recurrent exudation in the eyes without recurrence during the 1st–5th years, although the recurrence rate was low.

Direction finding for coherent sources with deep hybrid neural networks

ABSTRACT In this paper, an intelligent direction finding (DF) architecture based on hybrid neural network is proposed. Firstly, the array outputs of DF system are multiplied by the corresponding ideal array manifold and a high-dimensional preprocessed feature vector is derived. In the next, the preprocessed feature is straightly fed into the auto-encoder. The auto-encoder outputs are then used as the input of the cascaded deep residual neural network in order to extract spatial spectral of sources. Finally, the direction-of-arrival (DOA) results are derived according to the locations of the normalised spectral peaks. There are two advantages with our proposed network architecture. One is the DF estimation accuracy is independent on the array aperture size when the number of elements is fixed. And the other is that the proposed network structure and processing procedures can be directly generalised into unknown scenarios but having higher angle resolution capacity at the same time. Finally, extensive numerical experiments illustrate the correctness and potential advantages of the proposed deep hybrid neural network.

Ion distribution functions in magnetotail reconnection: global hybrid-Vlasov simulation results

Abstract. We present results of noon–midnight meridional plane global hybrid-Vlasov simulations of the magnetotail ion dynamics under a steady southward interplanetary magnetic field using the Vlasiator model. The simulation results show magnetotail reconnection and formation of earthward and tailward fast plasma outflows. The hybrid-Vlasov approach allows us to study ion velocity distribution functions (VDFs) that are self-consistently formed during the magnetotail evolution. We examine the VDFs collected by virtual detectors placed along the equatorial magnetotail within earthward and tailward outflows and around the quasi-steady X line formed in the magnetotail at X≈-14RE. This allows us to follow the evolution of VDFs during earthward and tailward motion of reconnected flux tubes as well as study signatures of unmagnetized ion motion in the weak magnetic field near the X line. The VDFs indicate actions of Fermi-type and betatron acceleration mechanisms, ion acceleration by the reconnection electric field, and Speiser-type motion of ions near the X line. The simulated VDFs are compared and show good agreement with VDFs observed in the magnetotail by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. We find that the VDFs become more gyrotropic but retain transverse anisotropy and counterstreaming ion beams when being convected earthward. The presented global hybrid-Vlasov simulation results are valuable for understanding physical processes of ion acceleration during magnetotail reconnection, interpretation of in situ observations, and for future mission development by setting requirements on pitch angle and energy resolution of upcoming instruments.

Resonant-type inertial impact piezoelectric motor based on a cam locking mechanism.

A new resonant-type inertial impact piezoelectric motor based on a cam locking mechanism was designed, assembled, and tested. The motor is composed of a stator, a rotor, and other auxiliary components. The cam clamping foot of the stator in contact with the inner surface of the rotor forms a cam locking mechanism, which can make the resonant vibration of the stator effective in a half cycle. By receiving sinusoidal signals, the stator generates bending deformation due to the regular deformation of the piezoelectric plate, which drives the cam clamping foot to move and subsequently causes the rotor to rotate. COMSOL5.4 finite element analysis software was used to design the structure of the piezoelectric motor, and an experimental device was built to evaluate and verify the performance of the motor. The maximum no-load speed of the prototype reached 21.61 rpm and the maximum load torque of the motor was 84 N mm under a driving voltage of 360Vp-p and a driving frequency of 388Hz. The motor achieved a net efficiency of 5.6% under a preload torque of 2 N mm with the same condition. The maximum resolution of the motion angle of the new motor prototype was 0.0748° with a driving voltage of 160Vp-p and the same frequency.

Midinfrared Dispersion Relations in InP -Based Photonic Crystal Slabs Revealed by Fourier-Transform Angle-Resolved Reflection Spectroscopy

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create novel functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However, the techniques cannot be applied to the mid- and long-wavelength infrared regions due to the limited sensitivity of infrared detectors. Here, we propose an alternative approach to measuring infrared dispersion relations. We construct a high-precision angle-resolved setup compatible with a Fourier-transform spectrometer with an angle resolution as high as 0.3 degrees. Hence, the reflection spectra are mapped to the 2D photonic band structures of In(Ga,Al)As/InP based PC slabs, which are designed as mid-infrared PC surface-emitting lasers. We identify complex PC modes with the aid of polarization selection rules derived by the group theory. Spectral analysis makes it possible to evaluate the mode quality (Q) factors. Therefore, angle-resolved reflection is a useful way of optimizing 2D PC parameters for mid-infrared devices.

Bionic target localization method based on range-azimuth joint dictionary

The traditional underwater sonar system usually achieve high angle resolution by increasing array aperture and the number of array elements, but this method will inevitably lead to complex system and high cost. Given that big brown bats have obtained surprisingly high resolution using a simple system, this paper proposes a bionic target localization method. First, a range-azimuth joint dictionary was constructed based on the bionic system of multi-harmonic emission and double random array reception. Then, the coherence characteristic of the dictionary was analyzed and the range and azimuth of the target were estimated, and at last the experimental verification was completed. The results show that the bionic range-azimuth joint estimation based on sparse signal representation can achieve high-precision target localization under the condition of echo high aliasing.

(Invited) Progress in Using Carbon Nanotube Spectra for Mechanical Strain Sensing

A characteristic property of semiconducting single-wall carbon nanotubes (SWCNTs) is distinct near-infrared photoluminescence following excitation by visible light. Theory and experiment show that these optical emission peaks shift predictably in wavelength as nanotubes are compressed or stretched along their axis. We are exploiting this effect in a powerful new method intended for measuring mechanical strain in critical infrastructure components such as airframes, pressurized vessels, pipelines, support beams, etc. The method involves applying a dilute dispersion of nanotubes in a polymeric host onto the surface of the specimen to form a sub-micron thick film in which SWCNTs act as strain sensors. This layer is overcoated with a transparent protective top coat such as a polyurethane varnish. Subsequent strains in the substrate are transmitted to the nanotubes by load transfer. The substrate strain magnitude and direction are then measured by illuminating the surface at any point of interest with a small visible laser beam and spectrally analyzing the resulting near-IR nanotube emission. Single-point measurements currently provide strain magnitude resolution of ca. 50 microstrain, strain angle resolution of ca. 5 degrees, and spatial resolution of ca. 50 mm. Each reading takes less than one second, allowing compilation of strain maps from scanned data. Unlike digital image correlation, which is currently the only commercial non-contact strain technology, the new method can measure strains accumulated when the specimen is not under observation. It thus has the potential for routine use in industrial structural health monitoring as well as in testing and development laboratories. Results will be presented showing strain measurements in metallic, plastic, and concrete specimens. We will also describe recent progress in adapting the technology to camera-based measurements using spectrally resolved fluorescence imaging.

ECPC-ICP: A 6D Vehicle Pose Estimation Method by Fusing the Roadside Lidar Point Cloud and Road Feature.

In the vehicle pose estimation task based on roadside Lidar in cooperative perception, the measurement distance, angle, and laser resolution directly affect the quality of the target point cloud. For incomplete and sparse point clouds, current methods are either less accurate in correspondences solved by local descriptors or not robust enough due to the reduction of effective boundary points. In response to the above weakness, this paper proposed a registration algorithm Environment Constraint Principal Component-Iterative Closest Point (ECPC-ICP), which integrated road information constraints. The road normal feature was extracted, and the principal component of the vehicle point cloud matrix under the road normal constraint was calculated as the initial pose result. Then, an accurate 6D pose was obtained through point-to-point ICP registration. According to the measurement characteristics of the roadside Lidars, this paper defined the point cloud sparseness description. The existing algorithms were tested on point cloud data with different sparseness. The simulated experimental results showed that the positioning MAE of ECPC-ICP was about 0.5% of the vehicle scale, the orientation MAE was about 0.26°, and the average registration success rate was 95.5%, which demonstrated an improvement in accuracy and robustness compared with current methods. In the real test environment, the positioning MAE was about 2.6% of the vehicle scale, and the average time cost was 53.19 ms, proving the accuracy and effectiveness of ECPC-ICP in practical applications.

Unusual electronic structure of Dirac material BaMnSb2 revealed by angle-resolved photoemission spectroscopy* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300600, 2018YFA0305602, 2016YFA0300300, and 2017YFA0302900), the National Natural Science Foundation of China (Grant Nos. 11974404, 11888101, 11922414, and 11404175), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant Nos. XDB33000000

High resolution angle resolved photoemission measurements and band structure calculations are carried out to study the electronic structure of BaMnSb2. All the observed bands are nearly linear that extend to a wide energy range. The measured Fermi surface mainly consists of one hole pocket around Γ and a strong spot at Y which are formed from the crossing points of the linear bands. The measured electronic structure of BaMnSb2 is unusual and deviates strongly from the band structure calculations. These results will stimulate further efforts to theoretically understand the electronic structure of BaMnSb2 and search for novel properties in this Dirac material.

Mathematical Analysis and Micro-Spacing Implementation of Acoustic Sensor Based on Bio-Inspired Intermembrane Bridge Structure.

A biomimetic study on the auditory localization mechanism of Ormia ochracea was performed to improve the localization ability of small acoustic systems. We also present a microscale implementation of an acoustic localization device inspired by the auditory organ of the parasitic O. ochracea. The device consists of a pair of circular membranes coupled together with an elastic beam. The coupling serves to amplify the difference in magnitude and phase between the two membranes’ responses as the incident angle of the sound changes, allowing directional information to be deduced from the coupled device response. The research results show that the intermembrane bridge structure improves the sound source localization and directional weak acoustic signal acquisition of sound detectors. The recognition rate of the phase difference and amplitude ratio was greatly improved. The theoretical resolution of the incident angle of the sound source can reach 2° at a phase difference recognition rate of 5°. The sound source’s optimal identification frequency range for the coupling device based on the intermembrane bridge bionic structure is 300 Hz to 1500 Hz.

High-Precision Automatic Calibration Modeling of Point Light Source Tracking Systems.

To realize high-precision and high-frequency unattended site calibration and detection of satellites, automatic direction adjustment must be implemented in mirror arrays. This paper proposes a high-precision automatic calibration model based on a novel point light source tracking system for mirror arrays. A camera automatically observes the solar vector, and an observation equation coupling the image space and local coordinate systems is established. High-precision calibration of the system is realized through geometric error calculation of multipoint observation data. Moreover, model error analysis and solar tracking verification experiments are conducted. The standard deviations of the pitch angle and azimuth angle errors are 0.0176° and 0.0305°, respectively. The root mean square errors of the image centroid contrast are 2.0995 and 0.8689 pixels along the x- and y-axes, respectively. The corresponding pixel angular resolution errors are 0.0377° and 0.0144°, and the comprehensive angle resolution error is 0.0403°. The calculated model values are consistent with the measured data, validating the model. The proposed point light source tracking system can satisfy the requirements of high-resolution, high-precision, high-frequency on-orbit satellite radiometric calibration and modulation transfer function detection.

Scaled Wigner distribution using fractional instantaneous autocorrelation

The traditional Wigner distribution (WD) is extended to a novel one inspired by the definition of fractional bispectrum, giving rise to a scaled version with respect to the frequency variable, termed as the scaled Wigner distribution (SWD). A natural magnification effect characterized by a factor k on the frequency axis enables the SWD to have flexibility to be used in cross-term reduction. Some essential properties of this variation generalize very nicely and simply the classical results for the WD, and it enjoys a computational complexity in the order of O(kN2) comparable to O(N2) of the WD. The SWD does not use localization windows, but its resolutions depend on the factor k. Comparison of the detection performance (i.e. cross-term reduction, time–frequency resolution, angle or distance resolution) of SWD and WD for multicomponent linear frequency-modulated (LFM) signals processing is then observed by exploring the factor k selection results on two kinds of bi-component cases, including the one with a different frequency rate and the other one with the same frequency rate but having a different initial frequency. Correctness of the derived results and the SWD’s superiority in the instantaneous frequency estimation of noisy LFM signals compared with the WD are illustrated through simulations, and finally further discussions point out some promising future research directions and perspectives.

Technical note: A sensitivity analysis from 1 to 40 GHz for observing the Arctic Ocean with the Copernicus Imaging Microwave Radiometer

Abstract. The Copernicus Imaging Microwave Radiometer (CIMR) is one of the high-priority missions for the expansion of the Copernicus program within the European Space Agency (ESA). It is designed to respond to the European Union Arctic policy. Its channels, incidence angle, precision, and spatial resolutions have been selected to observe the Arctic Ocean with the recommendations expressed by the user communities. In this note, we present the sensitivity analysis that has led to the choice of the CIMR channels. The famous figure from Wilheit (1979), describing the frequency sensitivity of passive microwave satellite observations to ocean parameters, has been extensively used for channel selection of microwave radiometer frequencies on board oceanic satellite missions. Here, we propose to update this sensitivity analysis, using state-of-the-art radiative transfer simulations for different geophysical conditions (Arctic, mid-latitude, tropics). We used the Radiative Transfer Model (RTM) from Meissner and Wentz (2012) for the ocean surface, the Round Robin Data Package of the ESA Climate Change Initiative (Pedersen et al., 2019) for the sea ice, and the RTM from Rosenkranz (2017) for the atmosphere. The sensitivities of the brightness temperatures (TBs) observed by CIMR as a function of sea surface temperature (SST), sea surface salinity (SSS), sea ice concentration (SIC), ocean wind speed (OWS), total column water vapor (TCWV), and total column liquid water (TCLW) are presented as a function of frequency between 1 and 40 GHz. The analysis underlines the difficulty to reach the user requirements with single-channel retrieval, especially under cold ocean conditions. With simultaneous measurements between 1.4 and 36 GHz onboard CIMR, applying multi-channel algorithms will be facilitated, to provide the user community with the required ocean and ice information under arctic environments.

4D flow MRI: impact of region of interest size, angulation and spatial resolution on aortic flow assessment

Objectives. In cardiovascular magnetic resonance, the 3D time-resolved phase-contrast technique, also known as 4D flow, is gaining increasing attention due to applications that exploit three-directional velocity encoding throughout the cardiac cycle. Blood flow volume assessment usually requires an expert to draw regions of interest (ROI) around the vessel cross section, whereas the errors involved in this estimation have not been thoroughly investigated. Our objective is to quantify the influence of ROI sizing, angulation and spatial resolution of the reconstructed plane employed in blood flow measurements using 4D flow. Approach. Three circular ROIs were drawn around the ascending, arch and descending aorta of healthy volunteers (n = 27) and patients with a dilated ascending aorta or bicuspid valve (n = 37). We applied systematic changes of ROI diameter (up to ±10%), tilt angle (up to ±25°) and spatial resolution (from 0.25 to 2 mm) of the reconstructed oblique planes, calculating the effects on net, forward and backward blood flow volumes. Main results. Patients had a larger ascending aorta than healthy volunteers with similar ages and male sex proportion (60 ± 15 y.o. vs 58 ± 16 y.o. and 84% vs 70%, respectively). Higher forward and backward flow volumes were observed in the ascending aorta and the aortic arch of the patients with respect to controls (p < 0.001), whereas net volumes were similar: 74.0 ± 20.8 ml versus 75.7 ± 21.8 ml (p = 0.37), respectively. The ascending aorta was the most sensitive to ROI modifications. Changes of ±10% in the ROI diameter and ±25° in tilt angles produced flow volume differences of up to 9 ml (10%) and 18 ml (15%) in controls and patients, respectively. Modifying the reconstructed planes spatial resolution produced flow volume changes below 2 ml. Significance. Since the setting of the ROI size and plane angle could produce errors that represent up to 20% of the forward and/or backward aortic flow volume, a good standardization for vessel segmentation and plane positioning is desirable.

Long-term outcomes following primary versus secondary Boston keratoprosthesis type 1 implantation

Background/aimsTo compare long-term outcomes of primary versus secondary (postgraft failure) Boston keratoprosthesis type 1 (KPro) implantation.MethodsMedical records of patients at the Centre hospitalier de l’Université de Montréal having undergone KPro...

Intelligent Reflecting Surface-Enhanced Target Detection in MIMO Radar

Motivated by the improved capacity and energy performance by intelligent reflecting surface (IRS) in multiinput-multioutput (MIMO) communication systems, we apply the IRS in the colocated MIMO radar systems to increase the received power and improve the target detection performance. To deal with this, we introduce an IRS-assisted target detection algorithm, in which the reflection optimization with practical IRS model is carried out, and then the optimal beamforming for target detection is proposed. Meanwhile, the Cramér-Rao bound (CRB) of the proposed method shows the effectiveness of utilizing the IRS in MIMO radar systems. Simulation results illustrate that the proposed method can achieve better target detection performance. With the increased number of elements in the IRS, the proposed method has better angle resolution and detection probability compared with a non-IRS-assisted MIMO radar system.

Space-Time Coding Technique for Coherent Frequency Diverse Array

Coherent frequency diverse array (FDA) radar is able to cover all directions with a stable gain by transmitting a single frequency-shifted waveform. However, it is revealed in this work that the range resolution scales linearly with the number of elements, which is limited by the fixed element number. By leveraging the relationship between the beam direction and the signal frequency, we link the sub-bands of the emitted signal to angular sectors. Based on the fact, a novel transmit diversity technique, referred to as two-dimensional (2-D) space-time coding (STC), is proposed to improve the range resolution. For a specific observation direction, the frequency band of each pulse is shifted by STC to synthesize a full bandwidth after the pulse accumulation. Furthermore, the piecewise LFM (linear frequency modulation) waveform design can be combined with the STC technique to synthesize the transmit beampattern flexibly without range resolution degradation for each pulse. Compared with the state-of-the-art technologies, the proposed STC technique has superiorities in range resolution improvement, ultra-low range sidelobe level, interference suppression, and beampattern design capability. In addition, multi-dimensional ambiguity functions are derived to assess the performance in range-angle-Doppler domain, including the range and angle resolutions, the sidelobe level (SLL) and the angular coverage. To satisfy practical demands, the general receive processing procedures are also designed. The proposed method and corresponding theoretical analysis are verified by extensive numerical results.