The aviation industry's increasing reliance on GPS to facilitate navigation and air traffic monitoring opens new attack vectors with the purpose of hijacking UAVs or interfering with air safety. We propose Crowd-GPS-Sec to detect and localize GPS spoofing attacks on moving airborne targets such as UAVs or commercial airliners. Unlike previous attempts to secure GPS, Crowd-GPS-Sec neither requires any updates of the GPS infrastructure nor of the airborne GPS receivers, which are both unlikely to happen in the near future. In contrast, Crowd-GPS-Sec leverages crowdsourcing to monitor the air traffic from GPS-derived position advertisements that aircraft periodically broadcast for air traffic control purposes. Spoofing attacks are detected and localized by an independent infrastructure on the ground which continuously analyzes the contents and the times of arrival of these advertisements. We evaluate our system with real-world data from a crowdsourced air traffic monitoring sensor network and by simulations. We show that Crowd-GPS-Sec is able to globally detect GPS spoofing attacks in less than two seconds and to localize the attacker up to an accuracy of 150 meters after 15 minutes of monitoring time.
Muscle deoxygenation in a single muscle was more heterogeneous at lower exercise workloads, and variations of the muscle deoxygenation heterogeneity between subjects were greater at lower exercise workloads.
Selective laser sintering (SLS) is an additive manufacturing technique able to rapidly create parts directly from a CAD model using a laser to selectively fuse successive layers of powder. However, defects can arise in SLS parts due to incomplete fusion of the powder layers or thermal stresses introduced by large temperature gradients during the part build. Accurate models of the SLS process are needed to ensure that high quality parts are produced and to allow new materials and designs to be used without requiring extensive experimentation. Most existing models of the SLS process are very narrowly focused, predicting the temperature history of a single powder layer after a single laser pass or examining the impact of a few processing parameters on the properties of the produced part. A model capable of predicting a complete temperature history during an entire part build does not yet exist. Therefore, a new thermal model able to simulate multiple powder layers is proposed.
A transient, three-dimensional, finite volume model is developed and implemented in ANSYS Fluent. A domain of cells representing multiple layers of an SLS build is initialized, some with the properties of air and some with the properties of powder, depending on cell location. A Gaussian heat source representing the laser is applied to the top layer of powder cells. The center of the Gaussian is varied with time along an established path to simulate the motion of the laser along the powder bed. At all times the three-dimensional heat equation is solved to produce a temperature profile of the powder bed. When the laser completes a full scan of the powder layer, the air cells directly above the powder layer are re-initialized as powder cells and re-set to an initial temperature, representing the addition of a new powder layer. The process is repeated for each new layer. Temperature history results from the model are validated against experimental data available in the literature and good agreement is obtained. As the model accounts for multiple powder layers, it can be used to simulate an entire part build and predict the impact of any of the SLS processing parameters on part quality and thus enable better control and optimization of the SLS process.
Recent research has shown that a number of existing wireless avionic systems lack encryption and are thus vulnerable to eavesdropping and message injection attacks. The Aircraft Communications Addressing and Reporting System (ACARS) is no exception to this rule with 99% of the tra c being sent in plaintext. However, a small portion of the tra c coming mainly from privately-owned and government aircraft is encrypted, indicating a stronger requirement for security and privacy by those users. In this paper, we take a closer look at this protected communication and analyze the cryptographic solution being used. Our results show that the cipher used for this encryption is a mono-alphabetic substitution cipher, broken with little e↵ort. We assess the impact on privacy and security to its unassuming users by characterizing months of real-world data, decrypted by breaking the cipher and recovering the keys. Our results show that the decrypted data leaks privacy sensitive information including existence, intent and status of aircraft owners.
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