Quantifying stream phosphorus dynamics and total suspended sediment export in forested watersheds in Vermont

Globally the quantity of reactive phosphorus (P) in soils, streams and groundwater has greatly increased throughout the 20th and early 21st centuries. This phenomenon is problematic in Vermont, evidenced by the repeated cyanobacteria blooms in shallow bays in Lake Champlain. While many studies have focused on P dynamics in agricultural watersheds, there is limited information on P dynamics in forested watersheds. Current remediation plans under the Lake Champlain total maximum daily loads (TMDL) call for substantial reductions in P loadings from forested areas of the basin. However, the lack of information and knowledge regarding forest P dynamics limits management and remediation plans. This study was conducted in three small forested watersheds, ranging in size from 2.5 to 8.3 square kilometers that have been managed under varying practices, including logging and maple sugaring. All three watersheds drain into Missisquoi Bay, a shallow bay in Lake Champlain that consistently has seasonal algal blooms. Streams in the forested watersheds were instrumented with turbidity sensors and pressure transducers to measure stage. A rating curve was developed during field visits to relate stage to discharge. Water samples were collected from May through November 2017 using ISCO Automated Samplers. A total of twenty storm events were captured, along with periodic baseflow sampling, and these data were used to characterize P concentrations and calculate seasonal P loadings. Results indicate that there is a strong positive relationship between turbidity, total suspended sediment and total phosphorus concentrations (R2 ranging from 0.64 to 0.83). The results of this project provide insight into transport of P and total suspended sediment within forested catchments of Lake Champlain tributaries. In particular, the research shows that fluxes in total phosphorus are linked to fluxes in total suspended sediment and that the overall monthly totals of P being exported from forested catchments are low, relative to urban, suburban and agricultural areas

Book review: enduring time by Lisa Baraitser

In Enduring Time, Lisa Baraitser offers a generous and expansive rumination on experiences of time's suspension - delaying, waiting, repeating, persisting – that attends to their potential capacity to offer conditions for political action. This is a thought-provoking and stirring engagement with living the elongated present, writes Ryan Ross, that will contribute to emergent debates on temporality across the humanities

Book review: public inquiries: wrong route on Bloody Sunday by Louis Blom-Cooper

In Public Inquiries: Wrong Route on Bloody Sunday, Sir Louis Blom-Cooper QC argues that for much of the twentieth century public inquiries have been ill-focused and mishandled, with a particular focus on the Bloody Sunday Inquiry, chaired by Lord Saville. While the book’s insights are occasionally hampered by the recurrent emphasis placed on the individual influence of Lord Saville, it is impressive when advocating for a more focused role for public inquiries in contemporary Britain, finds Ryan Ross

Nielsen's Arcadia: The Case of the Flute Concerto

In this essay I suggest that there are distinct patterns pertaining to the Flute Concerto involving the idea of ‘Arcadia’ as it contrasts an idyllic past with a troubled present. In my analysis, I argue that his positioning of simple themes with relation to their surroundings in the concerto’s two movements suggests a process-driven search for an Arcadian ideal. As such, and far from simply being merely an interesting work with several beautiful moments, the concerto is an important access point both for further understanding Nielsen’s creative approach to form and his late-period preoccupation with the idea of simplicity

Nielsen\u27s Arcadia: The Case of the Flute Concerto

In this essay I suggest that there are distinct patterns pertaining to the Flute Concerto involving the idea of ‘Arcadia’ as it contrasts an idyllic past with a troubled present. In my analysis, I argue that his positioning of simple themes with relation to their surroundings in the concerto’s two movements suggests a process-driven search for an Arcadian ideal. As such, and far from simply being merely an interesting work with several beautiful moments, the concerto is an important access point both for further understanding Nielsen’s creative approach to form and his late-period preoccupation with the idea of simplicit

“Blaspheming Beethoven?”: The Altered BACH Motive in Vaughan Williams’s Fourth Symphony

Vaughan Williams’s Fourth Symphony (1934) has elicited much discussion regarding its aesthetic nature and sources of inspiration. Early critics associated the work’s dissonances with a concession to continental European musical modernism, or with a depiction of the political tensions of 1930s Europe. More recent commentaries have noted its references to Beethoven, one of which the composer admitted to in print. These commentators have argued either that these references constitute a continuation of the Beethovenian tradition in the twentieth century, or that they present a critique of the German composer. This essay adds a new argument in favor of the latter position. First, it examines Vaughan Williams’s writings, which reveal respect for Beethoven’s stature, sharp antipathy toward his aesthetic, and a tendency to negatively measure him against Johann Sebastian Bach. Next, it considers one of the main recurring motives of Vaughan Williams’s Fourth Symphony, a slightly altered musical BACH cipher, through the lens of these writings. It concludes that the use and placement of this motive at the points in the Fourth Symphony which most strongly recall Beethoven are intentionally mischievous, and echo musically Vaughan Williams’s Bach-aided digs at Beethoven in prose

Kinematic Basis for Body Specific Locomotor Mechanics and Perturbation Responses

Animals have evolved mechanical and neural strategies for locomotion in almost every environment, overcoming the complexities of their habitats using specializations in body structure and animal behavior. These specializations are created by neural networks responsible for generating and altering muscle activation. Species specific musculoskeletal anatomy and physiology determine how locomotion is controlled through the transformation of motor patterns into body movements. Furthermore, when these species specific locomotor systems encounter perturbations during running and walking their behavioral and mechanical attributes determine how stability is established during and after the perturbation. It is still not understood how species specific structural and behavioral variables contribute to locomotion in non-uniform environments. To understand how these locomotor properties produce unique gaits and stability strategies we compared three species of brachyuran crabs during normal and perturbed running. Although all crabs ran sideways, morphological and kinematic differences explained how each species produced its unique gait and stability response. Despite the differences in running behavior and perturbation response, animals tended to use locomotor resources that were in abundance during stabilizing responses. Each crab regained stability during the perturbation response by altering leg joint movements or harnessing the body\u27s momentum. These species body designs and running behavior show how slight changes in body structure and joint kinematics can produce locomotor systems with unique mechanical profiles and abilities. Understanding how evolutionary pressures have optimized animals\u27 locomotor ability to successfully move in different environments will provide a deeper understanding of how to mimic these movements through mathematical models and robotics

Unsteady loads and associated flow fields on wings exposed to high rotation-rate dynamic stall

Aerodynamics is a facet of engineering that has progressed rapidly since the discovery of flight from as early as the mid-19th century. In recent years, high manoeuvrability aircraft, high-speed helicopters, unmanned-aerial vehicles, micro-aerial vehicles and natural flyers have attracted significant interest due to their potential for military, surveillance and rescue applications. Due to economic and global demand to limit greenhouse gas emissions, the awareness of clean energy resources, such as horizontal-axis and verticalaxis wind turbines, has resulted in the rapid growth of research focusing on improving the performance and operational efficiency of such machines. Although these machines are designed for dissimilar applications, they all suffer from a common problem; the process of dynamic stall. Dynamic stall is the unsteady aerodynamic phenomenon that occurs on pitching and plunging wings due to transient fluctuations in the operating angle of attack. During the process of dynamic stall, flow separation is delayed to elevated angles of attack. Increasing the angle of attack results in growth of a vortex structure originating at the leading edge. This vortex results in increased lift, drag and moment on the wing. Increased forces and moments continue until the vortex detaches from the wing and convects into the wake. The wing proceeds into deep-stall until the incidence angle is reduced to angles permitting reattachment of the boundary layer. Dynamic stall results in increased material fatigue, cost and maintenance, and an overall decrease in performance of machine components. In contrast, natural flyers such as birds and insects have evolved to exploit the unsteady phenomenon for sustained flight. While dynamic stall has been extensively studied for helicopter applications, recent work has focused on the operation of wind turbines. Helicopter rotor blades are exposed to sinusoidal changes in the angle of attack throughout each blade rotation. Whereas, wind turbines blades are subject to multiple variations in angle of attack. In addition, stalled rotor conditions may even be used beneficially to control power output during high wind load conditions. The purpose of this thesis is to investigate the effects of dynamic stall on wings typically associated with wind turbines, helicopter and micro-aerial vehicle applications. More specifically, the thesis will focus on the study of pitching airfoils. Under the unsteady operating conditions, unsteady aerodynamic forces and flow structure development will be investigated during both pitch-up and post-stall phases of the airfoil motion. This is achieved by replicating unsteady operating conditions in both water-channel and windtunnel facilities. Particle image velocimetry and surface pressure measurements were utilised to identify key flow structure events, and the associated forces generated on wings during unsteady motion. Constant-pitch-rate motion at a Reynolds number of 20,000 was applied to similar airfoils of different thicknesses, and includes a NACA 0012 and a NACA 0021. The aim of the investigation was to determine the flow structure variation between both thick and thin airfoil profiles during dynamic stall. Separation was shown to occur at earlier stages of the dynamic stall process for the thinner airfoil section when exposed to low rotation-rate dynamic stall. Increasing the rotation rate resulted in higher inertial loads, which in turn led to delayed stall and increased force generation at higher angles of attack. Fluctuations in forces were correlated with periodic vortex shedding at the trailing edge during airfoil ramp-up. Under steady-state conditions, the presence of separation bubbles on both surfaces of the airfoil resulted in a negative lift-curve slope prior to the collapse of both bubbles and subsequent recovery of lift. Deep stall was delayed with an increased rotation rate due to the initial delay in formation of the leading-edge vortex. However, once separation of the vortex occurred, post-stall characteristics were not influenced by airfoil geometry, with both airfoils exhibiting bluff-body separated-flow characteristics. For post-stall conditions following dynamic stall, increasing the reduced frequency delayed separation in some instances up to an angle of attack of 60°. Low surface pressure on the upper surface of the airfoil was linked to vortex structure developed during dynamic stall and in post-stall conditions. The centre of pressure was shown to shift with the development of the leading-edge vortex, and move aft of the quarter-chord location during fully-separated flow conditions. The change in centre of pressure leads to increased moment, which is transferred and linked to increases in torsional loading and fatigue of rotor blades and power transmission components or rotary machines. For investigation of a boundary layer control method, a simplified leading-edge trip wire was implemented on two airfoils experiencing dynamic stall conditions. NACA 0012 and NACA 0021 airfoils were fitted with leading-edge trip wires of varying diameters, located at a fixed displacement from the airfoil leading edge. The Reynolds number was 20,000. The trip wires were shown to decrease the maximum lift, although the stall angle of attack was not observed to change with variations in the trip wire diameter. Geometric superposition was observed between the trip wire and the airfoil body when the diameter of the wire exceeded 1.6% of the airfoil chord length. This led to increases in lift and drag during the pitch-up motion. Constant-pitch-rate rotation was utilised to investigate the effects of half-saddle movement and vortex formation on the aerodynamic characteristics of a pitching flat plate. A combination of round, square and triangular leading-edge and trailing-edge extensions were alternated during testing on a flat plate with a thickness-to-chord ratio of 0.1. The Reynolds number was 20,000. The half-saddle point, located on the upper surface, was linked to leading-edge vortex attachment. Detachment of the leading-edge vortex resulted once the position of the half-saddle point reached the trailing edge of the flat plate. Similarly, the rate of aft motion of the half-saddle point was shown to increase as a function of airfoil chord length, rotation rate and free-stream velocity. No benefit to overall force generation was observed once a critical angle of attack was reached. Maximum aerodynamic efficiency was shown to occur at angles of attack significantly below the angle of attack where maximum lift force was observed. The research in the current dissertation enhances knowledge of the dynamic-stall process, and provides information that can improve methods of boundary layer control on wings exposed to dynamic stall. Moreover, research reported herein provides critical information on the deep-stall process, which occurs after the event of dynamic stall. With the information acquired in this thesis, increased awareness of dynamic stall and deepstall characteristics can be achieved and utilised for the development of blades which are lighter, perform more efficiently and require lower costs to develop and maintain.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Mechanical Engineering, 201

Contact-Aided Invariant Extended Kalman Filtering for Legged Robot State Estimation

This paper derives a contact-aided inertial navigation observer for a 3D bipedal robot using the theory of invariant observer design. Aided inertial navigation is fundamentally a nonlinear observer design problem; thus, current solutions are based on approximations of the system dynamics, such as an Extended Kalman Filter (EKF), which uses a system's Jacobian linearization along the current best estimate of its trajectory. On the basis of the theory of invariant observer design by Barrau and Bonnabel, and in particular, the Invariant EKF (InEKF), we show that the error dynamics of the point contact-inertial system follows a log-linear autonomous differential equation; hence, the observable state variables can be rendered convergent with a domain of attraction that is independent of the system's trajectory. Due to the log-linear form of the error dynamics, it is not necessary to perform a nonlinear observability analysis to show that when using an Inertial Measurement Unit (IMU) and contact sensors, the absolute position of the robot and a rotation about the gravity vector (yaw) are unobservable. We further augment the state of the developed InEKF with IMU biases, as the online estimation of these parameters has a crucial impact on system performance. We evaluate the convergence of the proposed system with the commonly used quaternion-based EKF observer using a Monte-Carlo simulation. In addition, our experimental evaluation using a Cassie-series bipedal robot shows that the contact-aided InEKF provides better performance in comparison with the quaternion-based EKF as a result of exploiting symmetries present in the system dynamics.Comment: Published in the proceedings of Robotics: Science and Systems 201