Visible Angle Research Articles

TVGeAN: Tensor Visibility Graph-Enhanced Attention Network for Versatile Multivariant Time Series Learning Tasks

This paper introduces Tensor Visibility Graph-enhanced Attention Networks (TVGeAN), a novel graph autoencoder model specifically designed for MTS learning tasks. The underlying approach of TVGeAN is to combine the power of complex networks in representing time series as graphs with the strengths of Graph Neural Networks (GNNs) in learning from graph data. TVGeAN consists of two new main components: TVG which extend the capabilities of visibility graph algorithms in representing MTSs by converting them into weighted temporal graphs where both the nodes and the edges are tensors. Each node in the TVG represents the MTS observations at a particular time, while the weights of the edges are defined based on the visibility angle algorithm. The second main component of the proposed model is GeAN, a novel graph attention mechanism developed to seamlessly integrate the temporal interactions represented in the nodes and edges of the graphs into the core learning process. GeAN achieves this by using the outer product to quantify the pairwise interactions of nodes and edges at a fine-grained level and a bilinear model to effectively distil the knowledge interwoven in these representations. From an architectural point of view, TVGeAN builds on the autoencoder approach complemented by sparse and variational learning units. The sparse learning unit is used to promote inductive learning in TVGeAN, and the variational learning unit is used to endow TVGeAN with generative capabilities. The performance of the TVGeAN model is extensively evaluated against four widely cited MTS benchmarks for both supervised and unsupervised learning tasks. The results of these evaluations show the high performance of TVGeAN for various MTS learning tasks. In particular, TVGeAN can achieve an average root mean square error of 6.8 for the C-MPASS dataset (i.e., regression learning tasks) and a precision close to one for the SMD, MSL, and SMAP datasets (i.e., anomaly detection learning tasks), which are better results than most published works.

Optimal Placement of UAVs to Provide Surveillance Coverage for a Ground Vehicle in a Collaborative Search-and-Rescue Operation

A drone-truck combined search-and-rescue operation involves a ground vehicle and a swarm of unmanned aerial vehicles (UAVs), where the UAVs provide surveillance coverage to guide the ground vehicle to navigate through the environment and carry out the search and rescue, and the ground vehicle functions as a service hub for carrying and recharging the UAVs. An effective strategy for providing persistent UAV surveillance coverage around the ground vehicle consists of initially forming the UAV swarm coverage and then controlling the UAV formation to follow the ground vehicle. This paper focuses on the formation of coverage and presents a method for planning an optimal placement of the UAVs to form seamless surveillance coverage around the ground vehicle. The optimization problem is formulated to determine the number and positions of UAVs that minimize the energy consumption in deploying and collecting those UAVs, subject to a set of constraints in UAV positioning, communication, and coverage, specifically the available number of UAVs, allowable range of UAV altitude, allowable energy consumption for deploying and collecting each UAV, communication ranges of UAVs and ground vehicle, safety distance between UAVs for collision and interference avoidance, and seamless coverage. A bi-layer optimization procedure is developed, with an outer layer searching through the allowable numbers of UAVs and an inner layer searching for the optimal positions for each specific number of UAVs. The optimal number and positions of UAVs are chosen by comparing among the solutions for different numbers of UAVs. A simulation study is carried out to validate the proposed optimization formulation and solution approach, where the simulation settings of UAVs, particularly the critical parameters including the UAV energy constants, visibility angle, altitude, and communication range, use the representative values presented in the cited literature. The simulation results show that the proposed approach is effective in planning the optimal number and positions of UAVs to provide seamless surveillance coverage for a ground vehicle. The next step of research will set priorities on comprehending the complexity of the solution space and enhancing the global optimality of the solution.

Virtual Mirrors: Non-Line-of-Sight Imaging Beyond the Third Bounce

Non-line-of-sight (NLOS) imaging methods are capable of reconstructing complex scenes that are not visible to an observer using indirect illumination. However, they assume only third-bounce illumination, so they are currently limited to single-corner configurations, and present limited visibility when imaging surfaces at certain orientations. To reason about and tackle these limitations, we make the key observation that planar diffuse surfaces behave specularly at wavelengths used in the computational wave-based NLOS imaging domain. We call such surfaces virtual mirrors. We leverage this observation to expand the capabilities of NLOS imaging using illumination beyond the third bounce, addressing two problems: imaging single-corner objects at limited visibility angles, and imaging objects hidden behind two corners. To image objects at limited visibility angles, we first analyze the reflections of the known illuminated point on surfaces of the scene as an estimator of the position and orientation of objects with limited visibility. We then image those limited visibility objects by computationally building secondary apertures at other surfaces that observe the target object from a direct visibility perspective. Beyond single-corner NLOS imaging, we exploit the specular behavior of virtual mirrors to image objects hidden behind a second corner by imaging the space behind such virtual mirrors, where the mirror image of objects hidden around two corners is formed. No specular surfaces were involved in the making of this paper.

On inverse construction of isoptics and isochordal-viewed curves

Given a regular closed curve α in the plane, a ϕ-isoptic of α is a locus of points from which pairs of tangent lines to α span a fixed angle ϕ. If, in addition, the chord that connects the two points delimiting the visibility angle is of constant length ℓ, then α is said to be (ϕ,ℓ)-isochordal viewed. Some properties of these curves have been studied, yet their full classification is not known. We approach the problem in an inverse manner, namely that we consider a ϕ-isoptic curve c as an input and construct a curve whose ϕ-isoptic is c. We provide thus a sufficient condition that constitutes a partial solution to the inverse isoptic problem. In the process, we also study a relation of isoptics to multihedgehogs. Moreover, we formulate conditions on the behavior of the visibility lines so as their envelope is a (ϕ,ℓ)-isochordal-viewed curve with a prescribed ϕ-isoptic c. Our results are constructive and offer a tool to easily generate this type of curves. In particular, we show examples of (ϕ,ℓ)-isochordal-viewed curves whose ϕ-isoptic is not circular. Finally, we prove that these curves allow the motion of a regular polygon whose vertices lie along the (ϕ,ℓ)-isochordal-viewed curve.

Generation of periodic nanobumps through a double-scan method with femtosecond lasers

Ultrafast laser surface structuring is a promising technique for precisely controlling the surface functions of materials. Nanoripples, the typical laser-induced periodic surface structures, are effective at regulating surface colors, but only in one view direction. To overcome this issue, effective methods for fabricating other types of structures are needed. In this study, we successfully form periodic nanobump structures using a simple double-scan approach, in which the same surface is subjected to two consecutive laser scans with different polarization directions. The formation behavior of these intriguing nanostructures is investigated in relation to laser parameters such as peak laser fluence, overlapping ratio, and polarization angle between two scans. The formation mechanism is hypothesized and confirmed. The obtained nanobumps exhibit exceptional optical performance compared to nanoripples by enhancing the visibility angle, hence expanding the possible applications of the ultrafast laser surface structuring technique.

Change in the structure of the focal spot at the focus of a large solar furnace from the visible angle of the Sun

In this work, for the first time, the coincidence of the proposed theoretical foundations of the methodology for calculating the dimension and energy characteristics of an optical image is shown, in contrast to the previously known to substantiate the separate consideration of the apparent angular size of the Sun 2γ from the accuracy parameters of manufacturing the SCS BLB (γ+Δα). On the example of a comparative assessment of operational measurements with the calculated ones during the past eclipses, where changes in the value of 2γ took place while the value of Δα was constant. These comparative estimates of theoretical and experimental results were carried out during partial solar eclipses that took place on August 1, 2008 and December 26, 2019.

Quantitative Anatomic Analysis and Clinical Application of Lumbar Spinous Process Split Laminotomy.

To investigate the feasibility and safety of lumbar spinous process split laminotomy by quantitative anatomic analysis. Nine fresh adult human cadaveric specimens (including 45 lumbar segments) were divided into 3 groups randomly. The simulated operations and anatomic measurements were performed to evaluate the visibility angle and surgical corridor at different retraction widths (8 mm, 10 mm, and 12 mm). By measuring the width causing bony fracture in 45 lumbar segments, the safety margin of retraction width was determined. The findings of lumbar spinous process split laminotomy in one typical case were presented. At 8 mm retraction width, there was not enough surgical corridor for the operation procedures. At 10 mm and 12 mm retraction width, all operation procedures could be conducted smoothly. The 12 mm group presented a larger surgical corridor and shorter operative time compared with the 10 mm group. The imaging examination confirmed no bony fracture and articular capsule impairment. The visibility angle and exposure extent increased in proportion to the retraction width. The retraction width that resulted in the bony fracture ranged from 12.34 mm to 16.82 mm, with an average of (14.56 ± 1.73) mm. The positions of fracture were in the pedicle of the vertebral arch (68.9%), the lamina (26.7%), and the vertebral body (4.4%). The retraction width of 10 mm-12 mm is safe and effective. The micromanipulations such as tumor resection, nervous exploration, dural suture, etc. can be conducted smoothly via the surgical corridor. In addition, the retraction width of 12.34~16.82 mm could serve as a safety margin for surgical planning. Our findings may provide a quantitative reference for clinical application of lumbar spinous process split laminotomy.

Влияние величины угла косоглазия, возраста пациентов, дозировки препарата на эффективность лечения содружественного косоглазия у детей методом хемоденервации ботулиническим токсином типа А

Purpose. To evaluate strabismus angle, patient's age, drug dosage on its treatment effectiveness in children using method of chemodenervation with botulinum toxin type A. Material and methods. The study involved 50 children (100 eyes), the average age of which was 4.33±2.75 years (from one year of life to 12.8 years), of which 27 boys (54%) and 23 girls (46%). The studies were carried out from 2016 to 2020 based on Voyno-Yasenetsky Scientific and Practical Center of Specialized Care or Children and Pirogov Russian National Research Medical University, Moscow. The observation period was 6 months. All patients were treated for concomitant strabismus by injecting BT-A into the oculomotor muscles through transconjunctival route, using specially designed forceps to isolate the oculomotor muscles, a syringe and a G27 needle (0.4×12.5 mm). Results. The success rate of the treatment of strabismus by chemodenervation using BT-A was 99.14% 6 months after the onset of treatment and was higher in children with a smaller angle of strabismus. The dosage of BT-A from 2 to 4 units gave the maximum effect when the angle of strabismus was more than 15°. Most of patients in the study group (75.49%) responded to therapy from the first month after chemodenervation. An analysis of data comparing the effectiveness of treatment in different age groups showed that the age of patients did not have a significant effect on the outcome of treatment – the outcome of treatment was more dependent on the initial angle of strabismus. Conclusion. Treatment of concomitant strabismus in children by chemodenervation of the extraocular oculomotor muscles with botulinum toxin type A can effectively eliminate the visible angle of concomitant strabismus and is an alternative to traditional surgical methods for treating children with this type of pathology. Key words: concomitant strabismus; botulinum toxin type A; chemodenervation, treatment efficacy

Case Report: The efficacy of early phacoemulsification in the intraocular pressure control in primary angle closure glaucoma associated with cataract in a young female

Glaucoma is a leading cause of irreversible blindness worldwide. Among different types of glaucoma, irreversible bilateral visual impairment is more common in primary angle closure glaucoma (PACG) patients. PACG and cataract often coexist and are both more prevalent among the elderly population, being rare in children and young adults. Here, we discuss the case of a 39-year-old Caucasian woman with unilateral PACG associated with cataract. The patient presented with a several-day history of left sided headache, decreased and blurred vision as well as pain and redness of the left eye (LE). She reported similar episodes in the previous year. Visual acuity (VA) of the LE was limited to counting fingers and intra-ocular pressure (IOP) of the LE was 42 mmHg. Anterior segment examination of the LE revealed: edematous cornea, a peripheral anterior chamber depth corresponding to Van Herick’s grade 0, mid-dilated pupil and lens opacities with visible glaukomflecken. Gonioscopic evaluation revealed iridotrabecular contact for 360º, no visible angle structures and a flat–mild convex iris contour. Spectral domain optical coherence tomography suggested only a thinning of neuro-retinal rim at the lower pole. Following treatment of the initial symptoms, phacoemulsification with intra-ocular lens implant was performed. IOP improved and no IOP-lowering medication was required. The patient was monitored for VA, IOP, field of vision changes, and optic disc evaluation every six months for 2 years and no glaucomatous change occurred. The patient also denied ocular symptoms during this period. This case supports the effectiveness of early phacoemulsification in the IOP control in patients with PACG.

Benefits of emissive display (OLED TV) from a visual perception

OLED TVs have clear picture quality with a perfect visible angle, perfect black luminance and boast faster response times than LCD TVs. Therefore, the study major contents are Benefits of emitting devices (OLED TV) in terms of visual perception. The first study, we investigated the effects of the peripheral vision luminance level (PVL) and field of view (FOV) on the display brightness perceived by the observer. The results revealed that the lower the black luminance of the display and the smaller the viewing field of the peak luminance image, the higher the relative brightness perceived by the HVS. This result shows the Benefits of OLED TVs that implement perfect black in terms of visual perceived brightness. The second study compared the effects of 4K organic light‐emitting diode (OLED) and liquid‐crystal display (LCD) TVs on human visual task performance when viewing moving pictures. From the results obtained, it was determined that OLED TVs exhibit superior characteristics for hit rate and false alarm rate compared with LCD TVs (non‐emissive‐type). Thus, this study confirms that OLED TVs, given their ultrafast response time characteristics, are superior in terms of moving picture images to LCD TVs.

Case Report: The efficacy of early phacoemulsification in the intraocular pressure control in primary angle closure glaucoma associated with cataract in a young female

Glaucoma is a leading cause of irreversible blindness in the world, second only to cataract. Among different types of glaucoma, irreversible bilateral visual impairment is more common in primary angle closure glaucoma (PACG) patients. PACG and cataract often coexist and are both more prevalent among the elderly population, being rare in children and young adults. Here, we discuss the case of a 39-year-old Caucasian woman with unilateral PACG associated with cataract. The patient presented with a several-day history of left sided headache, decreased and blurred vision as well as pain and redness of the left eye (LE). She reported similar episodes in the previous year. Visual acuity (VA) of the LE was limited to counting fingers and intra-ocular pressure (IOP) of the LE was 42 mmHg. Anterior segment examination of the LE revealed: edematous cornea, a peripheral anterior chamber depth corresponding to Van Herick’s grade 0, mid-dilated pupil and lens opacities with visible glaukomflecken. Gonioscopic evaluation revealed iridotrabecular contact for 360º, no visible angle structures and a flat–mild convex iris contour. The digital image of the optic disc suggested only a thinning of neuro-retinal rim at the lower pole. Following treatment of the initial symptoms, phacoemulsification with intra-ocular lens implant was performed. IOP improved and no IOP-lowering medication was required. The patient was monitored for VA, IOP, field of vision changes, and optic disc evaluation every six months for 2 years and no glaucomatous change occurred. The patient also denied ocular symptoms during this period. This case supports the effectiveness of early phacoemulsification in the IOP control in patients with PACG.

INDICATOR FOR URGENCY ASSESSMENT IN ERGONOMIC INTERVENTION OF WOOD HARVESTING MACHINES

ABSTRACT Many studies on ergonomics in forestry operations are punctual and assess ergonomic variables in isolation, with each result being obtained on a specific scale. Thus, the objective of this study was to improve an ergonomic indicator through a classification according to the urgency of the ergonomic intervention, to improve its practicality of application in forest harvesting machines. This research was carried out in planted forests of a company in Southern Brazil, and based on ergonomic evaluations of a feller buncher, a skidder, a forest processor, harvesters, and forwarder machines during the day and night shifts. Vibration, noise, heat, illumination, repeatability, postures, and visibility angles were measured. The results of the ergonomic assessments were standardized by adapting the ergonomic Degree of Compliance (V) method calculated with the legislation norms, having a value between 0 and 1, and the higher the value, the greater the compliance with effective norms and guidelines. It was proposed to classify the degree of ergonomic urgency in different colors. The skidder showed the worst degrees of compliance, requiring emergency corrective measures, with an emphasis on vibrations (V 0.0 and 0.1), noise (V 0.2) and visibility in the lateral plane (V 0.0) in both shifts worked due to shocks and bumps in the machine’s movements and visibility difficulty in the operation, in addition to illumination (V 0.6) at night and heat (V 0.8) in the daytime. The forestry processor showed the best ergonomic performance without any urgencies but emphasizing care with noise (V 0.7 and 0.8) and the daily dose of vibration (V 0.8 and 0.7) in both shifts. The classification by a color scale made it possible to better interpret the indicators and facilitate the practical application of corrective ergonomic interventions.

Synthesis and Applications of Antimicrobial and UV Protected Polymeric glass coatings

polymeric materials along with nanoparticles are widely used to protect from microbial propagation. In humid environments, enclosed edifice is amongst the foremost propagation substrates aimed at microorganisms. Antimicrobial coatings could help to stop microbial proliferation or, reduce the number of microorganisms growing on inside buildings. This paper deals with inhibition of Escherichia coli bacteria by TiO2 and silver nano-particles doping along with poly acrylate-based copolymers. Coated glass was characterized for FTIR, antimicrobial activity, UV Visible Spectroscopy and water contact angle for hydrophobicity and SEM analysis for surface morphology. The disk diffusion method was used for bacterial inhibition. Results revealed that developed material has good adhesion with glass and shows transparency, hydrophobicity and antibacterial activity. Which shows that coating material can be used for significant antibacterial coatings to protect window glass table ware glass doors etc. further these coatings are transparent, UV radiation protected and hydrophobic in nature which also enhance the self-cleaning effects. In addition, the coating has photocatalytic activity due to the presence of TiO2 and showed momentous antibacterial events after 2,4 and 6 hrs and this efficiency would be increased by improving formulation composition.

Reactive 3D deployment of a flying robotic network for surveillance of mobile targets

The paper considers deploying a flying robotic network to monitor mobile targets in an area of interest for a specific time period. Each flying robot carries a battery with limited initial energy and a camera with a fixed visible angle. When the energy consumption of a flying robot depends on its altitude, minimizing the energy consumption and maximizing the number of covered targets are two contradictory goals because to have a larger coverage area, a flying robot needs to fly higher, which leads to more energy consumption. Thus, there should be a balance between them. A constrained optimization problem accounting these two objectives is formulated subject to some energy and connectivity constraints. A control system containing a movement decision maker (MDM) is designed. A decentralized navigation algorithm implemented on each robot is proposed. The algorithm navigates each flying robot to a new position in 3D space that contributes more to the coverage. The performance of the proposed approach against some baseline methods is validated by extensive simulations.

Experimental prototype for visual support in the calibration of the precision indicator lights of approach slope, for a landing track using a drone

The use of calibration methods for visual aids systems in airports guarantees aviation safety with new alternatives and precision methods. The article shows the implementation of an experimental prototype for the support of visual aid in the calibration of precision indicator lights by means of a drone to improve the approach slopes of aircraft. In each of the experimental tests the following activities were developed: a) execute the program that contains the code to perform the process of emulation / calibration of the lights, b) connect the model of the lights to the Arduino and be connected to the portable equipment, c) perform the drone calibration process each time a flight plan is made, d) connect the mobile device to the drone’s remote control to integrate them into the wireless network (Wi-Fi), e) on the device mobile the application is executed to configure the flight plan and f) the emulation / calibration is performed with the model of the lights. Obtain the best visibility angles according to the effective percentages of experimentation that indicate the accuracy of the experimental system proposed through a mobile application. In addition, this article proposes a methodology for the calibration of the Precision Approach Path Indicator (PAPI) lights through wireless devices. The proposed methodology establishes the basic conditions for the development of the process of supervision, monitoring and calibration of the PAPI lighting system of any track in Colombia according to the regulations on luminous visual aids.

ОСОБЕННОСТИ ТРАНСФОРМАЦИИ И ИНВЕРСИИ ГРАВИТАЦИОННОГО ПОЛЯ С ПРИМЕНЕНИЕМ ДИСПЕРСИОННОГО И РЕГРЕССИОННОГО АНАЛИЗОВ

The Purpose of the paper is to study the possibilities of regression and variance analyses under quantitative interpretation of gravitational anomalies. Methods. On example of the Ulanbaatar and Nalaikh intermountain depressions (Mongolia) the application possibilities of the principal component method and the pseudo-inverse algorithm under the transformation and inversion of gravitational fields are considered. Results. The quantitative characteristics of the thickness of loose deposits of the structures under investigation are obtained through regression and variance analyses. The maximum thickness of the deposits of the Ulanbaatar depression is 100-200 m whereas the Nalaikh depression is 600 m. The obtained estimates are confirmed by the results of investigated depression gravitational field inversion by other methods. Conclusions. The transformation and inversion results of the gravitational field of sedimentary deposits of low thickness (100-200 m) when replacing infinite length rectangular prisms by the parallelepipeds limited along the strike vary insignificantly and remain within the initial limits (while maintaining the magnitude of the lack of density). The depression filled with the sediments of great thickness features a significant increase in this characteristic (from 600 m to 900 m) while maintaining the lack of sediment density. Such variations in the sedimentary thickness of the studied objects can be explained by the magnitude of the visibility angle of individual geometric bodies approximating precipitation lenses. It is found that the application of the method of principal components of the variance analysis in the identification of the regional and local (residual) components of the gravitational field and the inversion of the anomalous gravity field using a pseudo-inverse algorithm of the regression research method are quite possible and effective.

Visible Angle on Magnetic Resonance Imaging Can Be Considered Indicator of Postoperative Outcome in Retropubic Radical Prostatectomy

Visible Angle on Magnetic Resonance Imaging Can Be Considered Indicator of Postoperative Outcome in Retropubic Radical Prostatectomy

Viewing-angle-switching device based on array of optical micro-rods incorporated with electrophoretic material systems

We have successfully demonstrated a control device for a viewing angle that enables switching between two states, a wide-viewing angle, and a narrow-viewing angle. It is composed of a light-transmitting portion formed with an array of optical micro-rods and a shielding/transmitting changeable portion of cross stripes designed with electrophoretic material systems consisting of black particles and an optically transparent medium. When the black particles are fully dispersed in the optically transparent medium, the cross stripe portion plays the role of a non-transmitting material as the shielding portion in a similar manner to a conventional viewing angle control film. When the black particles are completely gathered electronically to one side in the optically transparent medium, in contrast, the cross stripe portion filled by the optically transparent medium can transmit incident light. These functions allow us to select electrically either of two modes between a limited viewing angle and a non-limited viewing angle. The optical properties for the limited viewing angle mode were +/−30° of the visible angle and 50% of the transmittance, and the one for the non-limited viewing mode was 58% of the transmittance. The response time from the narrow-viewing angle to wide-viewing angle was 1 s at 20 V of applied voltage.

Global Satellite Navigation Systems at High Latitudes, Visibility and Geometry

Abstract Since few years the significance of the navigation at high latitudes (60° and more), increases incessantly, e.g. northern passages between Atlantic and Pacific Waters. In these regions the user’s position can be obtained mainly from global satellite navigation systems (SNS). Nowadays (September 2016) two systems, American GPS and Russian GLONASS, are fully operational, two next, Galileo in Europe and BeiDou in China, are under construction. As the error of user’s position obtained from these systems depends on geometry factor DOP (Dilution Of Precision) among other things the knowledge of the number of satellites visible by this user above given masking elevation angle Hmin and the distributions of DOP coefficient values, GDOP in particular, is very important. The lowest and the greatest number of satellites visible in open area by the user at high latitudes for different Hmin, the percentage of satellites visible above angle H, distributions of satellites azimuths and GDOP coefficient values for different Hmin for all these four SNSs at different user’s latitudes (beginning from 60°) and other distributions are presented in the paper. All calculations were made for constellation of BeiDou 27 MEO satellites, Galileo 24 satellites, GLONASS 24 and GPS 31 satellites.

Visibility and Geometry of Global Satellite Navigation Systems Constellations

Abstract Nowadays (November 2015) there are two global fully operational satellite navigation systems, American GPS and Russian GLONASS. Two next are under construction, Galileo in Europe and BeiDou in China. As the error of observer’s position obtained from these systems depends on geometry factor DOP (Dilution Of Precision) among other things the knowledge of the number of satellites visible by this observer above given masking elevation angle Hmin and the distributions of DOP coefficient values, GDOP in particular, is very important. The lowest and the greatest number of satellites visible in open area by the observer at different latitudes for different Hmin, the percentage of satellites visible above angle H (9 intervals, each 10O wide), distributions (in per cent) of satellites azimuths (8 intervals, each 45O wide) and GDOP coefficient values (8 intervals) for Hmin = 5O for all these four systems at different observer’s latitudes (9 intervals, each wide 10O wide) are presented in the paper. Additionally the lowest elevation for which the number of satellites visible at different latitudes by the observer in open area above this angle is equal 4 or 3 and the distributions (in per cent) of GDOP coefficient values for different Hmin at observer’s latitudes 50-60O for the same four systems are showed. All calculations were made for constellation of GPS 27 satellites, GLONASS 24, Galileo 30 and BeiDou 27 MEO satellites.