Use of Navigation Beacons to Support Lunar Vehicle Operations

To support a wide variety of lunar missions in a condensed regime, solutions are needed outside of the use of Earth-based orbit determination. This research presents an alternate approach to in-situ navigation through the use of beacons, similar to that used on Earth as well as under technology development efforts. An overview of the current state of navigation aids included as well as discussion of the Lunar Node 1 payload being built at NASA/Marshall Space Flight Center. Expected navigation results of this beacon payload for planned operation from the lunar surface are provided. Applications of navigation beacons to multiple stages of the proposed human lunar landing architecture are given, with initial analysis showing performance gains from the use of this technology. This work provides a starting point for continued analysis and design, laying out the foundation of how navigation beacons can be incorporated into the architecture to enable continued analysis, design, and future expanded capability

Model Predictive Control (MPC) of quadrotors using LPV techniques

This Thesis objective was to apply Model predictive control (MPC) on a quadcopters using linear parameter varying (LPV) techniques. In order to do so the non-linear mathematical model of the quadcopter was put in the Linear Parameter Varying (LPV) form in order to be able to use the most basic Model Predictive Control (MPC) strategy, developed for linear systems. After applying the MPC strategy, the aim was to make the quadcopter track a given trajectory. Different trajectories were tested and validated. Initially, the most important step was to define the coordinate frames that are used to control the quadcopter and to establish the mathematical model of a quadcopter. Once the mathematical model of the quadcopter is developed, the next step was to design the controller. The controller was split into two sub controllers. One controller is responsible for the position variables x, y, z. This position controller controls the position variables by using the state feedback linearization method. Moreover, the attitude controller was used to control the angles using the LPV-MPC control strategy. The proposed strategy turned out to be a success in controlling the quadcopter. All the Quadcopter’s six degrees of freedom are tracked with very small errors. In tracking the x, y, z reference velocity values, one can observe strong overshoot at the beginning of the test period. That can be explained by the fact that the quadcopter starts its journey from quite a long distance away from the trajectory. However, once it reaches the path that it needs to follow, the velocities of the quadcopter stabilize and track the reference values very smoothly. Everything was done keeping in mind that the LPV-MPC controller needs time to push the state angles towards its reference values. Therefore, the attitude controller must work at a higher frequency compared to the position controlle

Phase Synthesis Using Coupled Phase-Locked Loops

Phase Synthesis is a fundamental operation in Smart Antennas and other Phased Array systems based on beamforming. There are increasing commercial applications for Integrated Phased Arrays due to their low cost, size and power and also because the RF and digital signal processing can be performed on the same chip. These low cost beamforming applications have augmented interest in Coupled Phase Locked Loop (CPLL) systems for Phase Synthesis. Previous work on the implementation of Phase Synthesis systems using Coupled PLLs for low cost beamforming had the constraint of a limited phase range of ±90°. The idea behind the thesis is that this phase synthesis range can be increased to ±180° through the use of PLLs employing Phase Frequency Detectors(PFDs), which is a significant improvement over conventional coupled-PLL systems. This work presents the detailed design and measurement results for a phase synthesizer using Coupled PLLs for achieving phase shift in the range of ±180°. Several Coupled PLL architectures are investigated and their advantages and limitations are evaluated in terms of frequency controllability, phase difference synthesis control and phase noise of the systems. A two-PLL system implementation using off the shelf components is presented, which generates a steady-state phase difference in the range ±180° using an adjustable DC control current. This is the proof of concept for doing an IC design for a Coupled Phase Locked Loop system. Commercial applications in the Wireless Medical Telemetry Service (WMTS) band motivate the design of a CPLL system in the 608-614 MHz band. The design methodology is presented which shows the flowchart of the IC design process from the system design specifications to the transistor level design. MATLAB simulations are presented to model the system performance quickly. VerilogA modeling of the CPLL system is performed followed by the IC design of the system and each block is simulated under different process and temperature corners. The transistor level design is then evaluated for its performance in terms of phase difference synthesis and phase noise and compared with the initial MATLAB analysis and improved iteratively. The CPLL system is implemented in IBM 130nm CMOS process and consumes 40mW of power from a 1.2V supply with a phase noise performance of -88 dBc/Hz for 177° phase generation

Transitional services for adolescents with epilepsy in the UK: A survey

AbstractPurposeTo survey the current transitional epilepsy services in tertiary paediatric neurology centres in the UK within the principles of transitional care for young people with epilepsy.MethodsAn online web-based questionnaire was sent to the lead epilepsy clinicians in tertiary paediatric neurology centres on behalf of the British Paediatric Epilepsy Group, the specialist epilepsy group of the British Paediatric Neurology Association (BPNA). A transition clinic was defined as a ‘clinic or service that provided joint paediatric and adult supervision of care from paediatric to adult services’.ResultsTwenty-three centres were approached of which18 responded and 15 of which provided auditable data. The clinics were held between three and 12 times per year, mostly in the afternoon and sited equally between the paediatric and adult centre. Approximately three to five new, and three to eight follow up patients were seen in each clinic. Most clinics accepted new referrals with a minimum age of 14 and a maximum of 20 years. Most young people were seen only once in a transition clinic before then being promoted into the adult epilepsy service. Very few clinics accepted direct referrals from the GP. Adult, slightly more than the paediatric team provided out-of-hospital advice after the young person was seen in the transition clinic.ConclusionsYoung people with epilepsy are a challenging, but interesting group and their care at this time may have a potentially irreversible impact on their life. Their progress from paediatric to adult services should be a dynamic, gradual and smoothly transitioned process to optimise their care. Although recommended by the National Institute for Health and Clinical Excellence (NICE) and the National Services Framework (NSF), the findings of this survey would suggest an un-met need of this population

Micromechanics of oxides - From complex scales to single crystals

Protective oxide scales shield high temperature materials from corrosion, thus ensuring safety and long material life under adverse operating conditions. Cracking and spallation of such scales can lead to fatigue crack initiation and expose the material to further oxidation. It is therefore imperative to measure the fracture properties of oxides so that they can be incorporated in the life estimation models of high temperature materials. Existing models require inputs on oxide properties such as fracture strain and elastic modulus. The established measurement methods are mainly applied for thick (several microns) scales, but for many materials such as superalloys the oxides are thinner (< 1 \ub5m), and the results would be affected by the influence of substrate and residual stresses. Focused ion beam machining (FIB) enables the preparation of micro sized specimens in the size range of these scales. \ua0In this work, a modified microcantilever geometry with partially removed substrate is proposed for testing of oxide scales. Room temperature microcantilever bending of thermally grown superalloy oxide (complex oxide with an upper layer of spinel and lower layer of Cr2O3) revealed the presence of plasticity, which is attributed to the deformation of the upper cubic spinel layer and low defect density of the volume being probed. Due to difficulties in isolating Cr2O3 from the complex oxide layer, dedicated oxidation exposures are performed on pure chromium to generate Cr2O3 which is tested using the same cantilever geometry at room temperature and 600 \ub0C. Results show lower fracture strain at 600 \ub0C in comparison to room temperature and presence of cleavage type of transgranular fracture in both cases, pointing to a need for studying cleavage fracture of Cr2O3. This was analysed using microcantilever bending of single crystal Cr2O3 to identify the preferential cleavage planes. Finally, fracture toughness was also measured through microcantilever bending and micropillar splitting. \ua0Thus, it is shown that micromechanical testing is an effective tool for measuring fracture properties of oxide scales. The fracture study of Cr2O3 scales show that it is a complex process in which the crystallographic texture also plays a role. Surface energy and fracture toughness criterion was unable to explain the fracture behaviour of single crystal Cr2O3 observed from experiments. Such a comprehensive analysis can contribute towards the development of reliable models for oxidation assisted failure

An Efficient Bandit Algorithm for Realtime Multivariate Optimization

Optimization is commonly employed to determine the content of web pages, such as to maximize conversions on landing pages or click-through rates on search engine result pages. Often the layout of these pages can be decoupled into several separate decisions. For example, the composition of a landing page may involve deciding which image to show, which wording to use, what color background to display, etc. Such optimization is a combinatorial problem over an exponentially large decision space. Randomized experiments do not scale well to this setting, and therefore, in practice, one is typically limited to optimizing a single aspect of a web page at a time. This represents a missed opportunity in both the speed of experimentation and the exploitation of possible interactions between layout decisions. Here we focus on multivariate optimization of interactive web pages. We formulate an approach where the possible interactions between different components of the page are modeled explicitly. We apply bandit methodology to explore the layout space efficiently and use hill-climbing to select optimal content in realtime. Our algorithm also extends to contextualization and personalization of layout selection. Simulation results show the suitability of our approach to large decision spaces with strong interactions between content. We further apply our algorithm to optimize a message that promotes adoption of an Amazon service. After only a single week of online optimization, we saw a 21% conversion increase compared to the median layout. Our technique is currently being deployed to optimize content across several locations at Amazon.com.Comment: KDD'17 Audience Appreciation Awar

The Road to Retirement: Bumpy or Smooth, Depends on Your Route

Defined Contribution (DC) plans are rapidly becoming the primary retirement investment vehicle for a majority of employees across the US and other markets around the globe. Asset allocation for DC plans has to strike a balance between growth and protection assets over the savings lifecycle while protecting the long-term purchasing power of the nest egg. Due to the long duration of retirement investing and various risks associated with it, implementing the right asset allocation has become critical and challenging for DC plans. The unique Risk Focused methodology presented in this paper aims to address the shortcomings of conventional Target Date Funds experienced during the 2008 financial crisis. The proposed approach addresses the cumulative impact of shortfall, sequence of returns, longevity, and market risks in determining asset allocation at different time horizons. This is accomplished by combining the term structure of risk, return, and covariance of asset classes with an explicit risk budget. The Risk Focused glide path potentially delivers comparable retirement wealth outcomes with enhanced downside protection, lower journey volatility, and attempts to facilitate a smoother journey on the road to retirement. Hence, the caption of the paper, Road to Retirement – Bumpy or Smooth, Depends on your Route