Planetary Rover Inertial Navigation Applications: Pseudo Measurements and Wheel Terrain Interactions

Accurate localization is a critical component of any robotic system. During planetary missions, these systems are often limited by energy sources and slow spacecraft computers. Using proprioceptive localization (e.g., using an inertial measurement unit and wheel encoders) without external aiding is insufficient for accurate localization. This is mainly due to the integrated and unbounded errors of the inertial navigation solutions and the drifted position information from wheel encoders caused by wheel slippage. For this reason, planetary rovers often utilize exteroceptive (e.g., vision-based) sensors. On the one hand, localization with proprioceptive sensors is straightforward, computationally efficient, and continuous. On the other hand, using exteroceptive sensors for localization slows rover driving speed, reduces rover traversal rate, and these sensors are sensitive to the terrain features. Given the advantages and disadvantages of both methods, this thesis focuses on two objectives. First, improving the proprioceptive localization performance without significant changes to the rover operations. Second, enabling adaptive traversability rate based on the wheel-terrain interactions while keeping the localization reliable. To achieve the first objective, we utilized the zero-velocity, zero-angular rate updates, and non-holonomicity of a rover to improve rover localization performance even with the limited available sensor usage in a computationally efficient way. Pseudo-measurements generated from proprioceptive sensors when the rover is stationary conditions and the non-holonomic constraints while traversing can be utilized to improve the localization performance without any significant changes to the rover operations. Through this work, it is observed that a substantial improvement in localization performance, without the aid of additional exteroceptive sensor information. To achieve the second objective, the relationship between the estimation of localization uncertainty and wheel-terrain interactions through slip-ratio was investigated. This relationship was exposed with a Gaussian process with time series implementation by using the slippage estimation while the rover is moving. Then, it is predicted when to change from moving to stationary conditions by mapping the predicted slippage into localization uncertainty prediction. Instead of a periodic stopping framework, the method introduced in this work is a slip-aware localization method that enables the rover to stop more frequently in high-slip terrains whereas stops rover less frequently for low-slip terrains while keeping the proprioceptive localization reliable

Evaluation of the Benefits of Zero Velocity Update in Decentralized EKF-Based Cooperative Localization Algorithms for GNSS-Denied Multi-Robot Systems

This paper proposes the cooperative use of zero velocity update (ZU) in a decentralized extended Kalman filter (DEKF) based localization algorithm for multi-robot systems. The filter utilizes inertial measurement unit (IMU), ultra-wideband (UWB), and odometry velocity measurements to improve the localization performance of the system in the presence of a GNSS-denied environment. The contribution of this work is to evaluate the benefits of using ZU in a DEKF-based localization algorithm. The algorithm is tested with real hardware in a video motion capture facility and a Robot Operating System (ROS) based simulation environment for unmanned ground vehicles (UGV). Both simulation and real-world experiments are performed to show the effectiveness of using ZU in one robot to reinstate the localization of other robots in a multi-robot system. Experimental results from GNSS-denied simulation and real-world environments show that using ZU with simple heuristics in the DEKF significantly improves the 3D localization accuracy.Comment: 18 pages, preprint version, the manuscript is accepted for publication in NAVIGATION, the Journal of the Institute of Navigation. Submitted:10-11-2022, Revised: 21-04-2023, Accepted:23-06-202

Organizational support for intrapreneurship and its interaction with human capital to enhance innovative performance

This study explores the impacts of the internal supportive environment for intrapreneurial activities on firms’ innovative performance and the moderating role of human capital in this relationship by making use of a questionnaire study covering 184 manufacturing firms in Turkey. As for the individual direct effects of the dimensions of Organizational Support (OS), Management Support for Idea Generation and Tolerance for Risk Taking are found to exert positive effects on innovative performance. Availability of a Performance Based Reward System and Free Time have no impact on innovativeness, while Work Discretion has a negative one. As for the role of Human Capital (HC), it is found to be an important driver of innovative performance especially when the OS is limited. However, when the levels of both HC and OS are high, innovative performance does not further increase, probably reaching a temporary performance ceiling. Managerial and further research implications are provided

The effects of streptozotocin-induced diabetes on ghrelin expression in rat testis: biochemical and immunohistochemical study

Introduction. Ghrelin is a hormone which has effects on the secretion of growth hormone, gastrointestinal system, cardiovascular system, cell proliferation and reproductive system. The present study we focused on the relation between ghrelin and GHS-R1a gene expression and the regulation of their expression in the testes of diabetic rats. Material and methods. 40 male Wistar albino rats were divided into four groups: control, and sampled 4, 8 and 12 weeks after induction of diabetes by streptozotocin (STZ) intraperitoneal injection (40 mg/kg). The rats were decapitated under ketamine anesthesia and their testes were removed. Blood was obtained from heart and serum follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone levels were measured by ELISA. Tissue ghrelin and GHS-R mRNA levels were determined by qRT-PCR, while ghrelin protein expression was studied by immunohistochemistry. Histopathological damage scores were also assessed. Results. Eight weeks after diabetes induction serum FSH level was increased, whereas LH and testosterone concentrations decreased. The ghrelin and GHS-R1a gene expression and ghrelin immunohistochemistry score first tended to increase after first four weeks of diabetes, and then tended to decrease. Ghrelin-immunopositive cells were detected in Leydig cells in all groups of rats, however, not in the germinal epithelium. Congestion of vessels and hemorrhage, formation of the vacuoles in spermatogonia and spermatocytes, desquamation of spermatids in the lumen and disorganization of seminiferous tubule germinal epithelium were observed in testis of all the diabetic rats. In addition, mean testicular biopsy score and mean seminiferous tubule diameter were getting lower in diabetic animals. Conclusion. Our results suggest that diabetes affects ghrelin expression in rat testis.

Heart Rate Variability in Children with Tricyclic Antidepressant Intoxication

The aim of this study was to evaluate HRV in children requiring intensive care unit stays due to TCA poisoning between March 2009 and July 2010. In the time-domain nonspectral evaluation, the SDNN (P<0.001), SDNNi (P<0.05), RMSDD (P<0.01), and pNN50 (P<0.01) were found to be significantly lower in the TCA intoxication group. The spectral analysis of the data recorded during the first 5 minutes after intensive care unit admission showed that the values of the nLF (P<0.05) and the LF/HF ratio (P=0.001) were significantly higher in the TCA intoxication group, while the nHF (P=0.001) values were significantly lower. The frequency-domain spectral analysis of the data recorded during the last 5 minutes showed a lower nHF (P=0.001) in the TCA intoxication group than in the controls, and the LF/HF ratio was significantly higher (P<0.05) in the intoxication group. The LF/HF ratio was higher in the seven children with seizures (P<0.001). These findings provided us with a starting point for the value of HRV analysis in determining the risk of arrhythmia and convulsion in TCA poisoning patients. HRV can be used as a noninvasive testing method in determining the treatment and prognosis of TCA poisoning patients

Calibration Quality Analysis of Phased Array Antennas

A phased array antenna (PAA) system can be calibrated by using several methods. In general, the aim of this calibration is to guarantee that the systematic errors are diminished. Still there can be residual errors due to the random errors in the system. These residual errors may decrease the correction accuracy of the calibration. This correction accuracy can be quantified as a quality factor. In this paper, quality of the Rotating Electric-Field Vector (REV) calibration method is examined with a statistical approach. Also, a statistical approach for PAA error analysis is developed for this purpose. This approach is used for the first time for a specific calibration method

Interferon alpha might be an alternative therapeutic choice for refractory Neuro-Behçet's disease

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