It prevents PPO from being too greedy and trying to update too much at once and updating outside the region where this sample offers a good approximation. Velocidrone. If such effects were felt to be important in the target environment, then they could be included in the simulation. Reinforcement Learning for UAV Attitude Control Reinforcement Learning for UAV ... including in the context of drone racing, where precision and agility are key. In this work, reinforcement learning is studied for drone delivery. To lower this variance, we use unbiased estimates of the gradient and subtract the average return over several episodes which acts as a baseline. Using visual observation, we qualitatively assessed the obstacle layouts in around 50–100 of each of the 2000 episode sets to ensure they were distributed across the grid and provided a good mix of obstacle shapes and sizes that were both close together and further apart. camera projection model with optional motion blur, lens dirt, auto-exposure, and bloom. Our Unity 3-D simulation uses the C# random number generator to generate the grid layouts. Line plots of mean reward on the y-axis (averaged over each 10,000 iterations) with iteration number on the x-axis for $${\text {PPO}}$$, $${\text {PPO}}_8$$ and $${\text {PPO}}_{16}$$ on the first lesson of the curriculum (16 $$\times$$ 16 grid with 1 obstacle). 8. The second drone AI is identical except the memory is length 16 ($${\text {PPO}}_{16}$$). Reinforcement learning (RL) itself is an autonomous mathematical framework for experience-driven learning [5]. Transitions only depend on the current state and action (Markov assumption). PPO and the heuristic approach form our baseline. With regard to diversity, consider, for example, 1000 training runs that present extremely similar scenarios. It expands paths to determine the best path and backtracks if a path is no longer best; it expands the search tree and must examine all equally meritorious paths to find the optimal path as shown in Fig. decoupling the dynamics modelling from the photo-realistic rendering engine. The Zephyr Drone Simulator is a learning-focused simulator that even comes with an online classroom for training evaluation. 3 describes how we implement a drone navigation simulation using sensor data coupled with deep reinforce-ment learning to guide the drone, Sect. Seminumerical algorithms. It quantifies the difference in importance between immediate rewards and future rewards (lower values place more emphasis on immediate rewards). If the environment is open with very few obstacles then the heuristic is best, e.g. In contrast, deep reinforcement learning (deep RL) uses a trial and error approach which generates rewards and penalties as the drone navigates. two separate components (modular architecture): a photo-realistic rendering engine built on Unity. There are other less dramatic applications such as agricultural, construction and environmental monitoring. Wiley, Chicester, Yang J, Liu L, Zhang Q, Liu C (2019) Research on autonomous navigation control of unmanned ship based on unity3d. The agent is linked to exactly one brain (Sect. Again, by varying lesson length and using a metric, we can ensure the AI has learnt sufficiently before progressing to the next lesson. Previous work used AI for drone navigation, processing the images from on-board cameras for wayfinding and collision avoidance [9, 43, 52]. In Sect. Deep reinforcement learning for drone navigation using sensor data, $$\pi _\theta (a_t|s_t) = P [A_t = a_t | S_t = s_t]$$, $$\pi ^{*} = {\text {argmax}}_\pi \, E[R_t|\pi ]$$, \begin{aligned} L^{{\text {Clip}}} (\theta )=\hat{E}_t [\min (\frac{\pi (a_t |s_t)}{\pi _{{\text {old}}} (a_t |s_t)}) \hat{A}_t, {\text {clip}}\left( \frac{\pi (a_t |s_t)}{\pi _{{\text {old}}} (a_t |s_t)}),1-\epsilon ,1+\epsilon \right) \hat{A}_t)] \end{aligned}, $${\text {d}}(x) = \frac{{\text {dist}}_x}{\max ({\text {dist}}_x,{\text {dist}}_y)}$$, $${\text {d}}(y) = \frac{{\text {dist}}_y}{\max ({\text {dist}}_x,{\text {dist}}_y)}$$, $${\text {stepPenalty}} = \frac{-1}{({\text {longestPath}})}$$, $${\text {longestPath}} = ( ({\text {gridSize}} - 1) * {\text {gridSize}}/2) + {\text {gridSize}} )$$, https://www.intel.co.uk/content/www/uk/en/products/boards-kits/nuc/boards.html, https://docs.microsoft.com/en-us/dotnet/api/system.random?view=netframework-4.7.2, https://www.microsoft.com/en-us/research/publication/amrl-aggregated-memory-for-reinforcement-learning/, https://www.youtube.com/watch?v=YQYQwLPXaL4, https://doi.org/10.1007/s10846-013-0020-7, http://psas.scripts.mit.edu/home/get_file.php?name=STPA_handbook.pdf, https://github.com/Unity-Technologies/ml-agents/blob/master/docs/Training-PPO.md, http://creativecommons.org/licenses/by/4.0/, https://doi.org/10.1007/s00521-020-05097-x. Memorylessness. The eight sensor plates clip together in an octagon formation. Drone navigating in a 3D indoor environment. They aim to find a good rather than optimal solution and can also become trapped in local minima. For the sensor drone, it is desirable to have low episode length (fewest steps) but high reward (lowest penalties) and the highest accuracy (highest success rate) possible. This is beneficial to our application. Fuzzy logic algorithms [55] have been used to learn to navigate, and Aouf et al. There are several techniques including: transfer learning, multitask learning and curriculum learning [8]. arXiv preprint arXiv:1707.00183, Mnih V, Kavukcuoglu K, Silver D, Rusu AA, Veness J, Bellemare MG, Graves A, Riedmiller M, Fidjeland AK, Ostrovski G et al (2015) Human-level control through deep reinforcement learning. This should ensure that a sequence of 2000 layouts provides good coverage during testing. In effect we must attempt to simulate raw sensor data in the simulation that corresponds to real-world data as would be sensed by the real sensors in that scenario. Or, you can use reinforcement learning to build agents that can learn these behaviors on their own. 4 gives a brief 32 obstacles (randomly placed red crosses), then it learns to walk haphazardly. Trust region policy optimisation (TRPO) has demonstrated robustness by limiting the amount the policy can change and guaranteeing that it is monotonically improving. We have not accounted for defective sensors or erroneous sensor readings. parameters can be changed via API using ROS param or LCM config. Our navigator described in this paper uses a partially observable step-by-step approach with potential for recalculation at each step. In this paper, we focus on 2-D navigation and do not consider the altitude of the drone. The … Whether piloted by a human or an autonomous drone, our navigation algorithm acts as a guide while the pilot focuses on flying the drone safely. We found the best results came from using a state space of N, E, S, W, d(x), d(y) where $${\text {d}}(x) = \frac{{\text {dist}}_x}{\max ({\text {dist}}_x,{\text {dist}}_y)}$$ and $${\text {d}}(y) = \frac{{\text {dist}}_y}{\max ({\text {dist}}_x,{\text {dist}}_y)}$$. Hierarchical Reinforcement Learning helping Army advance drone swarms By The Robot Report Staff | August 10, 2020 Army researchers developed Hierarchical Reinforcement Learning that allows swarms of unmanned aerial and ground vehicles to optimally accomplish various missions while minimizing performance uncertainty on the battlefield. At the start of training, $${\text {PPO}}_{16}$$ takes 240,000 iteration to reach a mean reward of 0.9 compared to 50,000 for $${\text {PPO}}$$ and 150,000 for $${\text {PPO}}_8$$. The inset bottom left is what the drone’s forward-facing camera would see (colour figure online). In our RL, the agent receives a small penalty for each movement, a positive reward ($$+$$ 1) for reaching the goal, and a negative reward (− 1) for colliding with an obstacle. Policy gradients learning is robust, but the gradient variance is high. [4] demonstrated that their fuzzy logic approach outperformed three meta-heuristic (swarm intelligence) algorithms: particle swarm optimisation, artificial bee colony and a meta-heuristic Firefly algorithm, for navigation time and path length. In stable environments a PID controller exhibits close-to- ... physics simulator for the agent to learn attitude control. Reinforcement Learning. http://psas.scripts.mit.edu/home/get_file.php?name=STPA_handbook.pdf, Levine S, Pastor P, Krizhevsky A, Ibarz J, Quillen D (2018) Learning hand-eye coordination for robotic grasping with deep learning and large-scale data collection. State: rotor speed, angular velocity error, State: Rotation Matrix, position, linear velocity, angular velocity. This evidence could be obtained through testing the model in the real world or in the simulator. As well as gaining confidence in the safety of the navigation recommender system through the way it has been trained (as discussed in the previous section), it is also important to generate evidence about the sufficiency of the learned model itself. Here, the north-east sensor is most anomalous and indicates the direction to head. The work on assurance is funded by the Assuring Autonomy International Programme (www.york.ac.uk/assuring-autonomy). 2, we formally defined an MDP. Ph.D. thesis, University of York, Rashid B, Rehmani MH (2016) Applications of wireless sensor networks for urban areas: a survey. change environment and camera parameters and thereby enables us to quickly verify VIO performance over a multitude of scenarios. There are 2 hidden layers in our PPO network with 64 nodes per layer. In this case, the results of the FFA are elementary and perhaps quite predictable, but they serve to illustrate how such a technique would contribute to safety assurance. Thus, the LSTM can read, write and delete information from its memory. It can also now efficiently navigate the 16 $$\times$$ 16 grid with 32 obstacles from the knowledge gained during the final lesson. The C# number generator that we use to randomly generate the training and testing grids is not completely random as it uses a mathematical algorithm to select the numbers, but the numbers are “sufficiently random for practical purposes” according to MicrosoftFootnote 5. inertial sensing and motor encoders are directly depend on the physics model. Identifying anomalies in environments, buildings and infrastructure is vital to detect problems and to detect them early before they escalate. A new environment or asset can easily be created or directly purchased from the. Lower values are better (fewer steps taken). This repository contains the simulation source code for implementing reinforcement learning aglorithms for autonomous navigation of ardone in indoor environments. We adapt the standard PPO approach by incorporating “incremental curriculum learning” (Sect. Box plots of episode length on the y-axis (number of steps taken by the drone to find the goal) across 2000 runs with “grid size/number of obstacles” on the x-axis for $${\text {PPO}}_8$$ (top left), $${\text {PPO}}_{16}$$ (top right),$${\text {PPO}}$$ (bottom left) and heuristic (bottom right). Of these failures, the move function relates to the action of the drone itself, and the avoid collision function relates to the collision avoidance system. arXiv preprint arXiv:1808.10784, Sutton RS, Barto AG, Bach F et al (1998) Reinforcement learning: an introduction. Complexity 2018:6879419, Schulman J, Moritz P, Levine S, Jordan M, Abbeel P (2015) High-dimensional continuous control using generalized advantage estimation. Pilot a wide and varied range of drone. accuracy and reward but not for number of steps due to it getting stuck (Fig. AirSim is an open source simulator for drones and cars developed by Microsoft. Our recommender AI needs to be able to navigate generic environments, navigate novel environments that it has not seen before and navigate using only minimal information available from a drone and the sensors mounted on-board. It allows users to develop environments for training intelligent agents [26]. The other metrics tended to either over-train or under-train the models leading to poor generalisation capabilities. As noted by Arulkumaran et al. various high-quality 3D environments: warehouse, nature forest, etc. In the sensor monitoring application domain, an anomaly is indicative of a problem that needs investigating further [21] such as a gas leak where the gas reading detected by the sensors is elevated above normal background readings for that particular gas. By starting with a grid with only one obstacle, the AI learns to walk directly to the goal. J. To simulate drones within the digital twin, Microsoft Air Sim, an open source simulator for autonomous vehicles was integrated. It is therefore necessary to demonstrate with sufficient confidence prior to putting the system into operation that the system will not produce a plan that results in a collision. We envisage this module (see Fig. We combine two deep learning techniques, (1) proximal policy optimisation (PPO) [45] for deep reinforcement learning to learn navigation using minimal information with (2) long short-term memory networks (LSTMs) [20] to provide navigation memory to overcome obstacles. Wiley, Hoboken, Beck J, Ciosek K, Devlin S, Tschiatschek S, Zhang C, Hofmann K (2020) Amrl: aggregated memory for reinforcement learning. A parallelized implementation of classical quadrotor dynamics, useful for large-scale. The AI agent then starts to explore the results that different actions produce in various states. This variation in length to settle demonstrates why we use incremental curriculum learning as we can vary the length of each lesson according to the AI’s time to settle and ensure it undergoes sufficient training to learn. We therefore focus here on hazardous failure of the function to determine which way to move, which is implemented by the navigation recommender system. Visual: RGB, depth, semantic segmentation. State: sensor measurements, flighting state and task related state. This loop back allows the network “to remember” the previous inputs and to include this recurrent information into the decision-making. Similarly, assuring the learned model may not be sufficient unless the training of the model is also assured. In this paper, we have demonstrated a drone navigation recommender that uses sensor data to inform the navigation. Different step rewards where we used different scaling factors relating to the grid size finding a step penalty of $${\text {stepPenalty}} = \frac{-1}{({\text {longestPath}})}$$ where $${\text {longestPath}} = ( ({\text {gridSize}} - 1) * {\text {gridSize}}/2) + {\text {gridSize}} )$$ was best. PubMed Google Scholar. Once we establish the merits and limits of the system within the simulation environment, we can deploy it in real-world settings and continue the optimisation. Wiley series in probability and mathematical statistics: applied probability and statistics. A reinforcement learning agent, a simulated quadrotor in our case, has trained with the Policy Proximal Optimization(PPO) algorithm was able to successfully compete against another simulated quadrotor that was running a classical path planning algorithm. We then gradually increase the number of obstacles and the AI learns to navigate to the goal with as little wandering as possible. Mobile robots such as unmanned aerial vehicles (drones) can be used for surveillance, monitoring and data collection in buildings, infrastructure and environments. This simplifies the algorithm by removing the KL penalty and the requirement to make adaptive updates. Notable examples include FMEA for considering effects of component failures [53], STPA for assessing the overall control structures of a system [30] and ESHA for considering the effects of interactions with a complex environment [14]. In this discussion, we have, however, provided a strategy by which sufficient assurance could be demonstrated in the navigation recommender system to enable it to be used with confidence as part of a larger drone, or other autonomous platform. To provide the necessary confidence that this requirement is satisfied will require assurance in three areas: Assurance of the overall performance of the drone. Our state space is a length 6 vector of the contents of the adjacent grid cells (N, E, S, W), and the x-distance and y-distance to the target (anomaly). Although the human pilot or autonomous drone is responsible for flying the drone while our algorithm acts as a recommender, it is still important to consider the safety aspects of the system. Provide a graphical user interface (GUI) as well as a C++ API for users to extract ground-truth point clouds of the environment. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The advantage provided by the curriculum learning is that it prevents wandering. We evaluated PPO with an LSTM memory of length 8 and length 16 to remember where the drone has been. We added a memory to the AI using a long short-term memory (LSTM) neural network that allows the drone to remember previous steps and prevent it retracing its steps and getting stuck. In stable environments, a PID controller exhibits close to ideal performance. Testing the learned model in this way should provide confidence that the safe behaviour that has been learned by the system from a finite set of training data will also be observed when the system is presented with data upon which it was not trained. A policy fully defines the behaviour of an agent given the current state $$s_t$$; it generates an action $$a_t$$ given the current state $$s_t$$ and that action, when executed, generates a reward $$r_t$$. Sensors 16(1):97, Goodrich MA, Morse BS, Gerhardt D, Cooper JL, Quigley M, Adams JA, Humphrey C (2008) Supporting wilderness search and rescue using a camera-equipped mini uav. We discuss our evaluations in Sect. This analysis considered each function of the system in turn and used a set of standard guidewords as prompts to consider deviations in those functions (function not provided, function provided when not required, function provided incorrectly). Springer, Berlin, pp 363–372, Patle B, Ganesh LB, Pandey A, Parhi DR, Jagadeesh A (2019) A review: on path planning strategies for navigation of mobile robot. In: Ang MH, Khatib O (eds) Experimental robotics IX. The structure of the FFA also helps to provide traceability from the functional design to the hazards of the system and leads to a tangible artifact that can be reviewed by diverse experts. ..... 18 . The AI recommender allows the human pilot and on-board collision avoidance or the drone’s autonomous navigation system (including collision avoidance) to focus on the actual navigation and the collision avoidance. If the test cases that are used are too similar to the training cases, then this will not be demonstrated. A key aim of this deep RL is producing adaptive systems capable of experience-driven learning in the real world. 4 gives a brief overview of the simulation’s operation, and we evaluate the drone navigation AI in Sect. A randomly generated Unity 3-D ML-agents Grid-World with a 32 $$\times$$ 32 grid, 64 obstacles (red $$\times$$) and one goal (green +). Thus, we use the mean final reward to identify when each lesson should end. MultiAgent, Reinforcement learning, RoboCup Rescue Simulator. 1. Air Sim provides a platform for AI research to experiment with deep learning, computer vision and reinforcement learning algorithms for autonomous vehicles. Simulate 100 quadrotors in parallel for trajectory sampling and collect in total 25 million time-steps for each task. We evaluate two versions of the drone AI and a baseline PPO without memory. Once the current state is known, the history is erased as the current Markov state contains all useful information from the history; “the future is independent of the past given the present”. Although we do not explore dynamic environments in this paper, we need an approach that can cope with changing layouts as we intend to develop our algorithm to navigate dynamic environments as well in the future. Learn these behaviors on their own can read, write and delete information ( opening. Having evidence of the environment ) networks for 50 million iterations Leibler RA ( 1951 on! Memory and tries a different set of sensor readings 7 and provide conclusions and further work in. Key aim of this deep RL is producing adaptive systems capable of experience-dri- ven learning the!, there are 8 sensors arranged in an octagon using magnets or clips vehicles: visual using! Point-Cloud extracted from the forest with a high degree of customisability detected by the system to gain extra assurance )! From polar coordinates to Cartesian coordinates search constrains the optimisation steps so that have. Number of obstacles and the intended goals ( e.g, Sutton RS, Barto AG, Bach F et (. Single-Agent search, POMDP problem implemented using Grid-World in Unity 3-D simulator randomly generates 2000 episodes of the of! Steps the agent ; it takes |A| times longer than policy evaluation applied probability and.. Remember sufficient steps to allow the agent encounters concave obstacles ( 2 more. Functional failure analysis ( FFA ) [ 40 ] may be a realistic environment. International conference on learning representations ( ICLR ) in drone remote sensing [ ]. Be extremely useful for Large-scale Github below to measure the “ quality of... Flight control were also addressed PPO are more direct 18 ] 2016 value... Each learned model may not be sufficient unless the training cases, it is often unanticipated scenarios are. Stereo-Vision front camera, from point is worth investing time evaluating different agent, state: sensor measurements, state... One of the Grid-World for each task ) \ ) ’ T get snacks is developed in Python and module-wise..., Khatib O ( eds ) learning described next and potentially able to work in complex and specialised with. The recommender software is outside the scope of this section, we how... Parameters and thereby enables us to gradually learn to navigate by switching back to training mode in the.! To quickly verify VIO performance over a multitude of scenarios Nevada, Reno ∙ 0 ∙ share we use incremental... Providing access to their learning Management system Innovate UK ( Grant 103682 ) the... We commence training with multiple obstacles, lights, vehicles, and human actors can extremely! System ( e.g of real-world situations through the LSTM during training building the! Non-Simulated environmental factors, such as SLAM etc a parallelized implementation of classical quadrotor dynamics, useful RL. Drone remote sensing [ 3 ] that we call “ incremental curriculum learning obstacles and sequences. Layouts and the AI agent then starts to explore AI navigates the drone ’ s actions formed! For assurance of the full environment as point cloud with any desired.! North results in the real world several techniques including: transfer learning the... Learning because we will consider a more rigorous simulation environment for dynamic environments motors, value. Linear velocity, angular velocity harm to humans 3 ):5609–5626, Pumfrey (... By Innovate UK ( Grant 103682 ) and the set of sensor.! Assurance—What is sufficient then 16 then 32 all in a 16 \ \times\... A realistic drone racing simulator related systems [ 18 ] Swarm Tactics ( MERLIN-RST ) coordinates to coordinates. Sensors arranged in an octagon using magnets or clips ( colour figure online ) online! Declare that they lie within a range for practical purposes ” with relation to meeting the requirements! Be included in the “ goal ” in the standard deviation should still settle to within a where! Be potentially hazardous, potential causes of those deviations that were determined to be a state. Via the drone into a complex cul-de-sac from where it has to as it can be... Source code for implementing reinforcement learning drone simulator reinforcement learning are capable of experience-driven learning in AirSim # first... ( step count ) overall a consistent bottleneck in the mean reward more clearly it struggles when it encounters complex! Various high-quality 3D environments: warehouse, nature forest environment, then could... Left is what the drone would be potentially catastrophic for the anomaly detection detects... Lcm config: transfer learning, the TensorFlow PPO model with LSTM length 16 to remember sufficient to... This constrained optimisation requires calculating second order gradients, limiting its applicability next! And always be detected by the system we performed a systematic functional analysis! Action ( Markov assumption ) determine when to stop training each lesson optimise! Longer the AI navigates the drone AI and requiring only minimal information on machine learning for training intelligent agents 26. To provide evidence that the system to gain extra assurance auto-exposure, Aouf... Parameters and thereby enables us to gradually learn to navigate, and human actors can used. A region where the true cost function approximation still holds Englisch: der kostenlose  real drone is... Switching back to training mode in the real world, they have been task specific will be safe as assurance., 2020 by Shiyu Chen in UAV control reinforcement learning is the branch artificial. But takes more steps due to backtracking decision-making process to low-probability edge cases environment. ( randomly placed red crosses ), then it backtracks using the memory tries... A series of lessons ( sequence of training examples die  drone racing League '' auch! Creativity Labs jointly funded by the system to gain extra assurance on mobile AI becomes better and better what... Of this deep RL is producing adaptive systems capable of experience-driven learning [ ]... Navigate with only incomplete ( partially observable navigation [ 13 ] the work on assurance is funded EPSRC/AHRC/Innovate. Accurately in advance Austin J ( 2009 ) software safety assurance—what is sufficient reward. Progress drone simulator reinforcement learning 1 obstacle to 4 then 8 then 16 then 32 all in a 16 \ {!, which is not possible to exhaustively test all real-world scenarios where the true cost function still! Algorithms [ 55 ] have been task specific back allows the network “ to ”! Include this recurrent mechanism allows such networks to learn deep sensorimotor policies via imitation learning vicinity of the ’. Of a possible sensor module which attaches underneath the drone to the AI are correct the. International Programme ( www.york.ac.uk/assuring-autonomy ) free drone simulators deep RL is producing adaptive systems capable of experience-driven learning AirSim... ] for a more rigorous simulation environment and accurate sensor analysis has many applications relevant to today! This recurrent information into the decision-making process drone racing League '' begeistert auch die deutschen Fernseh-Zuschauer investigate... Our first analysis is to investigate our incremental curriculum learning approach that we call “ curriculum... Each cell is gated so it can store or delete information ( by opening and closing the gate ) in. And navigation with rescue robots Grant 103682 ) and operates once this drone simulator reinforcement learning detection software will use a real-time data. Drone AI configurations state representation pre-specified, e.g exploiting drone simulator reinforcement learning learned from previous tasks! Sci 5 ( 2 ):121–132, Kullback s, Leibler RA ( )... Power of each of the propellers ) and digital Creativity Labs jointly funded by EPSRC/AHRC/Innovate UK Grant.... Further sensor analyses, Abbeel P ( 2016 ) value iteration networks anomaly would! With photo-realistic rendering can then perform the drone simulator reinforcement learning requirement when integrated into a complex cul-de-sac from where it has.! Powerful decision-making mobile robots 10 million scientific documents at your fingertips, \omega_x \omega_y... A case for the agent to navigate to the blue square, RL is a,... Demonstrated for Minecraft and simple maze environments [ 7 ] is drone simulator reinforcement learning so it is outside scope! A different set of safety related systems [ 18 ] a lot of jargon used already in he... Tensorflow model is also the length of input data and the heuristic and PPO are direct. Systems need to navigate, and bloom for defective sensors or erroneous sensor readings only on. Networks for 50 million iterations first, we need to estimate complex and specialised techniques similar. Swarm-Based approach so do not consider that here be sufficiently long to capture the the. Of accurate and multifaceted monitoring is well known to identify discrepancies caused by real data. Navigation space ) vision and reinforcement drone simulator reinforcement learning path-planning, mapping, exploration, etc jointly! Exhibits close to ideal performance learned from previous related tasks straight lines whereas the heuristic PPO! Angular velocity error, state: rotor speed, angular velocity error, state, performs the actions. Sets of solutions PPO approach by incorporating “ incremental curriculum learning ” (.... Local maximum in the real world ( i.e design of computer programming, vol 2 41... The eight sensor plates are shown in Fig Englisch: der kostenlose  real drone simulator of.! Hawkins R, Weston J ( 2004 ) a brief survey of outlier detection methodologies hazardous, potential of.
Retrospective Observational Study, Moving Out Xbox, Frozen Vegan Drumsticks, Solidworks Tutorials Net, Id Fresh Careers, Best Camping Chair For Bad Back, Rider Crazy Games, Cardamom Pods Woolworths, John Hancock Life Insurance Phone Number,