A Study on GPS Data Tracking Method for KOMPSAT Spacecraft Orbit Control

The Global Positioning System (GPS) is becoming more attractive navigation means for LEO spacecraft due to the data accuracy and convenience for utilization. The anomalies such as serious variations of Dilution-Of-Precision (DOP), loss of infrequent 3-dimensional position fix, and deterioration of instantaneous accuracy of position and velocity data could be observed, which have not been appeared during the ground testing. It may cause lots of difficulty for the processing of the orbit control algorithm using the GPS data. In this paper, the characteristics of the GPS data were analyzed according to the configuration of GPS receiver such as position fix algorithm and mask angle using GPS navigation data obtained from the first Korea Multi-Purpose Satellite (KOMPSAT). The problem in orbit tracking using GPS data, including the infrequent deterioration of the accuracy, and an efficient algorithm for its countermeasures has also been introduced. The reliability and efficiency of the modified algorithm were verified by analyzing the effect of the results between algorithm simulation using KOMPSAT flight data and ground simulator

A Study on Thermal Modeling and Heat Load Mitigation for Satellite Electronic Components

Since most of the satellite components are using various EEE (Electrical, Electronic and Electromechanical) parts, the reliability of EEE parts acts very important in the satellite system. There are many factors that influence the reliability of EEE parts in the satellite system. Excessively dissipated heat can cause the failure of EEE parts and consequently, leading to a failure of total satellite system. In this paper, the thermal modeling using nodal network was compared with that using plate modeling to find out which one is the most suitable methodology. For a comparison, KOMPSAT- 1 SAR was modeled by two different modeling and the result was discussed. There was almost no difference in the numerical results between the two modeling methods. However, while it took much more time to perform thermal analysis using the nodal network modeling method, and the debugging was more difficult in the plate modeling method when the error is occurred. The computation time was considerably reduced by developing and implementing the input file format transfer code when using nodal network modeling method. It was found that the nodal network modeling method is suitable for the complicated components, such as SAR or transponder, because of its simple debugging ability. Excessive heat load was expected on some EEE parts of SAR such as high heat-dissipated diodes, transistors, and inductors due to increased power requirements of KOMPSAT-2 satellite system. The methods for the mitigation of heat load were studied through the design change of housing or the layout change of high power parts

METABOLIC RATES (SMR, RMR, AMR, AND MMR) OF Oplegnathus fasciatus ON DIFFERENT TEMPERATURE AND SALINITY SETTINGS

The metabolic rate of aquatic animals is closely related to oxygen concentration and influenced by internal and external factors. Despite its high value as marine fish species in South Korea, information on rock bream Oplegnathus fasciatus metabolism is scarcely available. This study observed the standard metabolic rate (SMR), routine metabolic rate (RMR), and active metabolic rate (AMR) of rock bream Oplegnathus fasciatus subjected to different temperature settings. Another observation was performed to find out the maximum metabolic rate (MMR) on rock bream subjected to different salinity settings. Fish (TL: 26.86 ± 0.29 cm and BW: 469.40 ± 38.21 g for SMR, RMR, and AMR measurement; TL: 26.7 ± 0.4 cm and BW: 451.0 ± 44.4 g for MMR measurement) were observed using respirometer (dimension = 30 cm × 20 cm × 20 cm; volume: 10.4 L) inside a recirculation systems. SMR, RMR, and AMR were measured at 15°C, 20°C, and 25°C. Meanwhile, MMR was measured at 15, 25, and 35 psu. The results showed that SMR, RMR, and AMR increased linearly by increasing the temperatures (SMR: 58.7 ± 3.2, 102.7 ± 4.3, and 157.1 ± 4.1 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively; RMR: 66.0 ± 8.6, 112.6 ± 10.2, and 175.2 ± 21.3 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively; AMR: 73.4 ± 7.4, 122.0 ± 6.3, and 196.7 ± 15.4 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively), whilst MMR decreased by lowering salinity (48.5 ± 5.2, 61.1 ± 5.5, and 89.3 ± 14.7 mg O2/kg/hour at salinity of 15, 25, and 35 psu, respectively)

Unsupervised Hyperbolic Representation Learning via Message Passing Auto-Encoders

Most of the existing literature regarding hyperbolic embedding concentrate upon supervised learning, whereas the use of unsupervised hyperbolic embedding is less well explored. In this paper, we analyze how unsupervised tasks can benefit from learned representations in hyperbolic space. To explore how well the hierarchical structure of unlabeled data can be represented in hyperbolic spaces, we design a novel hyperbolic message passing auto-encoder whose overall auto-encoding is performed in hyperbolic space. The proposed model conducts auto-encoding the networks via fully utilizing hyperbolic geometry in message passing. Through extensive quantitative and qualitative analyses, we validate the properties and benefits of the unsupervised hyperbolic representations. Codes are available at https://github.com/junhocho/HGCAE

LOW WATER TEMPERATURE AND ITS EFFECTS ON STRESS RESPONSE OF GREY MULLETS Mugil cephalus ACCLIMATED IN FRESHWATER

Grey mullet (Mugil cephalus) can adapt to saline and freshwater. Although belonged to euryhaline species, but information regarding their stress response on low temperature. Environmental disturbance such as low water temperature may effect their physiological condition. These information can be useful for aquaculture development of this species in freshwater. Therefore, the purpose of study was to investigate the effects of low water temperature on the stress response of grey mullets Mugil cephalus acclimated in freshwater. The blood samples of experimental fish (TL: 28.2±1.1 cm, BW: 198.6±25.9 g) were collected during winter season when the water temperature of controlled rearing system was stable at 25°C and uncontrolled rearing system slowly dropped until 12°C. Their stress response on both rearing systems was observed. The results showed that low temperature affected to lower the behavior activity and increase the stress response of grey mullets. The breath frequency of grey mullet regarding their opercular movement at 12°C was 74-97 breath/min., while at 25°C it was 95-114 breath/min. Hematocrit (Ht) and hemoglobin (Hb) were shown higher values of 43.5% and 9.5 g/dL, respectively at 25°C than 12°C (28.0% and 7.1 g/dL, respectively). The tendencies of cortisol and glucose level increased with the lowering temperature, showing higher value of 264.8 ng/mL and 35.5 mg/dL in 12°C than 5.5 ng/mL and 32.7 mg/dL in 25°C. The chemical properties of blood in grey mullets showed same tendency comparing between 12°C and 25°C, there was no significant different between each temperature, except for chloride (P<0.05). Chloride value was higher at 25°C, while other blood components such as osmolality, sodium, potassium, and magnesium were showing no significant differences. However, the results showed lower values at 12°C in every blood components, except for chloride. In conclusion, lowering water temperature to 12°C had impact as stressor to the behavior and stress response of grey mullets acclimated in freshwater

Symmetric Graph Convolutional Autoencoder for Unsupervised Graph Representation Learning

We propose a symmetric graph convolutional autoencoder which produces a low-dimensional latent representation from a graph. In contrast to the existing graph autoencoders with asymmetric decoder parts, the proposed autoencoder has a newly designed decoder which builds a completely symmetric autoencoder form. For the reconstruction of node features, the decoder is designed based on Laplacian sharpening as the counterpart of Laplacian smoothing of the encoder, which allows utilizing the graph structure in the whole processes of the proposed autoencoder architecture. In order to prevent the numerical instability of the network caused by the Laplacian sharpening introduction, we further propose a new numerically stable form of the Laplacian sharpening by incorporating the signed graphs. In addition, a new cost function which finds a latent representation and a latent affinity matrix simultaneously is devised to boost the performance of image clustering tasks. The experimental results on clustering, link prediction and visualization tasks strongly support that the proposed model is stable and outperforms various state-of-the-art algorithms.Comment: 10 pages, 3 figures, ICCV 2019 accepte