Self-starting capability of a Darrieus turbine

Darrieus-type vertical axis wind turbines have a number of potential advantages for small-scale and domestic applications. For such applications, the issues of cost and reliability are paramount and hence simplicity of design of the structure, the generator, and any control system is vital. A particular concern relating to Darrieus turbines is their potential to self-start. If, as has been suggested by several authors, they require external assistance to start then much of their advantage is lost. The purpose of the study described here is, therefore, to investigate their starting performance through the development and validation of computational simulation and to determine the parameters that govern the capability to self-start. A case study is presented based upon the use of the widely used and well documented, symmetrical NACA 0012 turbine blade profile. It is shown that a lightly loaded, three-bladed rotor always has the potential to self start under steady wind conditions, whereas the starting of a two-bladed device is dependent upon its initial starting orientation

Collapse of an ecological network in Ancient Egypt

The dynamics of ecosystem collapse are fundamental to determining how and why biological communities change through time, as well as the potential effects of extinctions on ecosystems. Here we integrate depictions of mammals from Egyptian antiquity with direct lines of paleontological and archeological evidence to infer local extinctions and community dynamics over a 6000-year span. The unprecedented temporal resolution of this data set enables examination of how the tandem effects of human population growth and climate change can disrupt mammalian communities. We show that the extinctions of mammals in Egypt were nonrandom, and that destabilizing changes in community composition coincided with abrupt aridification events and the attendant collapses of some complex societies. We also show that the roles of species in a community can change over time, and that persistence is predicted by measures of species sensitivity, a function of local dynamic stability. Our study is the first high-resolution analysis of the ecological impacts of environmental change on predator-prey networks over millennial timescales, and sheds light on the historical events that have shaped modern animal communities

Alcohol Discrimination and Preferences in Two Species of Nectar-Feeding Primate

Recent reports suggest that dietary ethanol, or alcohol, is a supplemental source of calories for some primates. For example, slow lorises (Nycticebus coucang) consume fermented nectars with a mean alcohol concentration of 0.6% (range: 0.0–3.8%). A similar behaviour is hypothesized for aye-ayes (Daubentonia madagascariensis) based on a single point mutation (A294V) in the gene that encodes alcohol dehydrogenase class IV (ADH4), the first enzyme to catabolize alcohol during digestion. The mutation increases catalytic efficiency 40-fold and may confer a selective advantage to aye-ayes that consume the nectar of Ravenala madagascariensis. It is uncertain, however, whether alcohol exists in this nectar or whether alcohol is preferred or merely tolerated by nectarivorous primates. Here, we report the results of a multiple-choice food preference experiment with two aye-ayes and a slow loris. We conducted observer-blind trials with randomized, serial dilutions of ethanol (0–5%) in a standard array of nectar- simulating sucrose solutions. We found that both species can discriminate varying concentrations of alcohol; and further, that both species prefer the highest available concentrations. These results bolster the hypothesized adaptive function of the A294V mutation in ADH4, and a connection with fermented foods, both in aye-ayes and the last common ancestor of African apes and humans

The Bandwidth of Transient Yaw Effects on Vehicle Aerodynamics

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, the unsteady wakes from other vehicles and as a result of traversing through the stationary wakes of road side obstacles. There is increasing concern about potential differences in aerodynamic behaviour measured in steady flow wind tunnel conditions and that which occurs for vehicles on the road. It is possible to introduce turbulence into the wind tunnel environment (e.g. by developing active turbulence generators) but on-road turbulence is wide ranging in terms of both its intensity and frequency and it would be beneficial to better understand what aspects of the turbulence are of greatest importance to the aerodynamic performance of vehicles. There has been significant recent work on the characterisation of turbulent airflow relevant to road vehicles. The simulation of this time-varying airflow is now becoming possible in wind tunnels and in CFD. Less is known about the range of turbulence length scales and intensities that are significant to the performance of vehicles. It is only necessary to simulate (experimentally or computationally) the Venn intersection of the range of conditions experienced and the range that are important to the vehicle's performance. The focus of this work is on transient yaw fluctuations. Time-resolved simulations of simple two dimensional parametric geometries subjected to yaw transients at a range of different time scales were conducted using Exa Powerflow. The effects of model geometry, Reynolds number yaw fluctuation amplitude and superposition were investigated. It was found that, in general, the flow could be treated as quasi-steady for reduced frequencies below 0.3 (based on model length and freestream velocity), which is consistent with theory. The most significant changes were observed in a critical reduced frequency range between ω R = 0.3 and ω R = 1.5 (scales of 4-20 vehicle lengths, or periods of 0.6 to 3s for a vehicle at 30 m/s). Higher frequencies will have significant effects, but these were observed to show little sensitivity to frequency above the critical range. Small physical features on real vehicles will add importance to smaller, but not larger, scales. The dynamic effects were largely independent of Reynolds number, including for near-inviscid conditions, indicating that the sources of the non-quasi-steady response were not viscous in origin. Increasing yaw amplitude or combining multiple frequency components did not have a summative impact suggesting that it may not be possible to describe vehicle response to transient conditions using linear concepts such as transfer or admittance functions

A novel method of strain - bending moment calibration for blade testing

A new method of interpreting strain data in full scale static and fatigue tests has been implemented as part of the Offshore Renewable Energy Catapult's ongoing development of biaxial fatigue testing of wind turbine blades. During bi-axial fatigue tests, it is necessary to be able to distinguish strains arising from the flapwise motion of the blade from strains arising from the edgewise motion. The method exploits the beam-like structure of blades and is derived using the equations of beam theory. It offers several advantages over the current state of the art method of calibrating strain gauges

Integrating the Theory of Sampling into Underground Mine Grade Control Strategies

Grade control in underground mines aims to deliver quality tonnes to the process plant via the accurate definition of ore and waste. It comprises a decision-making process including data collection and interpretation; local estimation; development and mining supervision; ore and waste destination tracking; and stockpile management. The foundation of any grade control programme is that of high-quality samples collected in a geological context. The requirement for quality samples has long been recognised, where they should be representative and fit-for-purpose. Once a sampling error is introduced, it propagates through all subsequent processes contributing to data uncertainty, which leads to poor decisions and financial loss. Proper application of the Theory of Sampling reduces errors during sample collection, preparation, and assaying. To achieve quality, sampling techniques must minimise delimitation, extraction, and preparation errors. Underground sampling methods include linear (chip and channel), grab (broken rock), and drill-based samples. Grade control staff should be well-trained and motivated, and operating staff should understand the critical need for grade control. Sampling must always be undertaken with a strong focus on safety and alternatives sought if the risk to humans is high. A quality control/quality assurance programme must be implemented, particularly when samples contribute to a reserve estimate. This paper assesses grade control sampling with emphasis on underground gold operations and presents recommendations for optimal practice through the application of the Theory of Sampling

Optimized pulses for the control of uncertain qubits

Constructing high-fidelity control fields that are robust to control, system, and/or surrounding environment uncertainties is a crucial objective for quantum information processing. Using the two-state Landau-Zener model for illustrative simulations of a controlled qubit, we generate optimal controls for \pi/2- and \pi-pulses, and investigate their inherent robustness to uncertainty in the magnitude of the drift Hamiltonian. Next, we construct a quantum-control protocol to improve system-drift robustness by combining environment-decoupling pulse criteria and optimal control theory for unitary operations. By perturbatively expanding the unitary time-evolution operator for an open quantum system, previous analysis of environment-decoupling control pulses has calculated explicit control-field criteria to suppress environment-induced errors up to (but not including) third order from \pi/2- and \pi-pulses. We systematically integrate this criteria with optimal control theory, incorporating an estimate of the uncertain parameter, to produce improvements in gate fidelity and robustness, demonstrated via a numerical example based on double quantum dot qubits. For the qubit model used in this work, post facto analysis of the resulting controls suggests that realistic control-field fluctuations and noise may contribute just as significantly to gate errors as system and environment fluctuations.Comment: 38 pages, 15 figures, RevTeX 4.1, minor modifications to the previous versio

Time-optimal CNOT between indirectly coupled qubits in a linear Ising chain

We give analytical solutions for the time-optimal synthesis of entangling gates between indirectly coupled qubits 1 and 3 in a linear spin chain of three qubits subject to an Ising Hamiltonian interaction with equal coupling $J$ plus a local magnetic field acting on the intermediate qubit. The energy available is fixed, but we relax the standard assumption of instantaneous unitary operations acting on single qubits. The time required for performing an entangling gate which is equivalent, modulo local unitary operations, to the $\mathrm{CNOT}(1, 3)$ between the indirectly coupled qubits 1 and 3 is $T=\sqrt{3/2} J^{-1}$, i.e. faster than a previous estimate based on a similar Hamiltonian and the assumption of local unitaries with zero time cost. Furthermore, performing a simple Walsh-Hadamard rotation in the Hlibert space of qubit 3 shows that the time-optimal synthesis of the $\mathrm{CNOT}^{\pm}(1, 3)$ (which acts as the identity when the control qubit 1 is in the state $\ket{0}$, while if the control qubit is in the state $\ket{1}$ the target qubit 3 is flipped as $\ket{\pm}\rightarrow \ket{\mp}$) also requires the same time $T$.Comment: 9 pages; minor modification