Stall flutter experiment in a transonic oscillating linear cascade

Two dimensional biconvex airfoils were oscillated at reduced frequencies up to 0.5 based on semi-chord and a free stream Mach number of 0.80 to simulate transonic stall flutter in rotors. Steady-state periodicity was confirmed through end-wall pressure measurements, exit flow traverses, and flow visualization. The initial flow visualization results from flutter tests indicated that the oscillating shock on the airfoils lagged the airfoil motion by as much as 80 deg. These initial data exhibited an appreciable amount of scatter; however, a linear fit of the results indicated that the greatest shock phase lag occurred at a positive interblade phase angle. Photographs of the steady-state and unsteady flow fields reveal some of the features of the lambda shock wave on the suction surface of the airfoils

A Survey on Trust Metrics for Autonomous Robotic Systems

This paper surveys the area of Trust Metrics related to security for autonomous robotic systems. As the robotics industry undergoes a transformation from programmed, task oriented, systems to Artificial Intelligence-enabled learning, these autonomous systems become vulnerable to several security risks, making a security assessment of these systems of critical importance. Therefore, our focus is on a holistic approach for assessing system trust which requires incorporating system, hardware, software, cognitive robustness, and supplier level trust metrics into a unified model of trust. We set out to determine if there were already trust metrics that defined such a holistic system approach. While there are extensive writings related to various aspects of robotic systems such as, risk management, safety, security assurance and so on, each source only covered subsets of an overall system and did not consistently incorporate the relevant costs in their metrics. This paper attempts to put this prior work into perspective, and to show how it might be extended to develop useful system-level trust metrics for evaluating complex robotic (and other) systems

Translating expert system rules into Ada code with validation and verification

The purpose of this ongoing research and development program is to develop software tools which enable the rapid development, upgrading, and maintenance of embedded real-time artificial intelligence systems. The goals of this phase of the research were to investigate the feasibility of developing software tools which automatically translate expert system rules into Ada code and develop methods for performing validation and verification testing of the resultant expert system. A prototype system was demonstrated which automatically translated rules from an Air Force expert system was demonstrated which detected errors in the execution of the resultant system. The method and prototype tools for converting AI representations into Ada code by converting the rules into Ada code modules and then linking them with an Activation Framework based run-time environment to form an executable load module are discussed. This method is based upon the use of Evidence Flow Graphs which are a data flow representation for intelligent systems. The development of prototype test generation and evaluation software which was used to test the resultant code is discussed. This testing was performed automatically using Monte-Carlo techniques based upon a constraint based description of the required performance for the system

(m-Phenyl­enedimethyl­ene)diammonium dichloride

The asymmetric unit of the title compound, C8H14N2 2+·2Cl−, contains one and a half of the dications and three chloride anions. The half molecule is completed by crystallographic twofold symmetry with two C atoms lying on the rotation axis. The two ammonium groups in each cation adopt a trans conformation with respect ot the benzene ring. The ammonium groups and chloride anions are involved in the formation of a three-dimensional N—H⋯Cl hydrogen-bonding network, which stabilizes the crystal packing

Using Both GPS L1 C/A and L1C: Strategies to Improve Acquisition Sensitivity

The upper L-Band will be the only frequency band with two different GPS civil signals available to users at the same carrier frequency with the legacy L1 C/Afcode signal and the new L1C signal. The null-to-null bandwidth of the C/A code signal is 2.046 MHz. The TMBOC modulation of the L1C signal creates bandwidth of 4.092 MHz between the outer nulls of the largest spectral lobes in the split-spectrum signal. Without the need to have two separate radio-frequency chains in the front-end of a GPS receiver, using the GPS C/A and L1C signals will improve acquisition sensitivity with limited additional complexity. This paper explores various techniques for joint acquisition of GPS L1C and L1 C/A code signals. First, the nominal received power of these two signals is discussed along with the power split parameters required for optimal combining. Next, a model for the composite C/A code and L1C signal is presented. The optimal detector for joint acquisition is then derived and simulation results provided. Finally, sub-optimal, but more efficient, techniques are proposed and their performance evaluated by comparing the detection probabilities at a fixed false alarm rate