721 research outputs found
Navigation and autonomy of soaring unmanned aerial vehicles
The use of Unmanned Aerial Vehicles (UAV) has exploded over the last decade with the constant need to reduce costs while maintaining capability. Despite the relentless development of electronics and battery technology there is a sustained need to reduce the size and weight of the on-board systems to free-up payload capacity.
One method of reducing the energy storage requirement of UAVs is to utilise naturally occurring sources of energy found in the atmosphere. This thesis explores the use of static and semi-dynamic soaring to extract energy from naturally occurring shallow layer cumulus convection to improve range, endurance and average speed.
A simulation model of an X-Models XCalibur electric motor-glider is used in combination with a refined 4D parametric atmospheric model to simulate soaring flight. The parametric atmospheric model builds on previous successful models with refinements to more accurately describe the weather in northern Europe. The implementation of the variation of the MacCready setting is discussed. Methods for generating efficient trajectories are evaluated and recommendations are made regarding implementation.
For micro to small UAVs to be able to track the desired trajectories a highly accurate Attitude Heading Reference System (AHRS) is needed. Detailed analysis of the practical implementation of advanced attitude determination is used to enable optimal execution of the trajectories generated. The new attitude determination methods are compared to existing Kalman and complimentary type filters. Analysis shows the methods developed are capable of providing accurate attitude determination with extremely low computational requirements, even during extreme manoeuvring. The new AHRS techniques reduce the need for powerful on-board microprocessors. This new AHRS technique is used as a foundation to develop a robust navigation filter capable of providing improved drift performance, over traditional filters, in the temporary absence of global navigation satellite information.
All these algorithms have been verified by flight tests using a mixture of manned and unmanned aerial vehicles and avionics developed specifically for this thesis
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Inter- and intra-specimen variability masks reliable temperature control on shell Mg/Ca ratios in laboratory and field cultured Mytilus edulis and Pecten maximus (bivalvia).
yesThe Mg/Ca ratios of biogenic calcite is commonly
seen as a valuable palaeo-proxy for reconstructing
past ocean temperatures. The temperature dependence of
Mg/Ca ratios in bivalve calcite has been the subject of contradictory
observations. The palaeoceanographic use of a
geochemical proxy is dependent on initial, rigorous calibration
and validation of relationships between the proxy
and the ambient environmental variable to be reconstructed.
Shell Mg/Ca ratio data are reported for the calcite of two bivalve
species, Mytilus edulis (common mussel) and Pecten
maximus (king scallop), which were grown in laboratory
culturing experiments at controlled and constant aquarium
seawater temperatures over a range from 10 to 20 C.
Furthermore, Mg/Ca ratio data of laboratory- and fieldgrown
M. edulis specimens were compared. Only a weak,
albeit significant, shell Mg/Ca ratioÂżtemperature relationship
was observed in the two bivalve species: M. edulis
(r2=0.37, p<0.001 for laboratory-cultured specimens and
r2=0.50, p<0.001 for field-cultured specimens) and P. maximus
(r2=0.21, p<0.001 for laboratory-cultured specimens
only). In the two species, shell Mg/Ca ratios were not found
to be controlled by shell growth rate or salinity. The Mg/Ca
ratios in the shells exhibited a large degree of variability
among and within species and individuals. The results suggest
that the use of bivalve calcite Mg/Ca ratios as a temperature
proxy is limited, at least in the species studied to
date. Such limitations are most likely due to the presence
of physiological effects on Mg incorporation in bivalve calcite.
The utilization is further limited by the great variability
both within and among shells of the same species that were
precipitated under the same ambient condition
Development of an autonomous control system for a small fixed pitch helicopter
The indoor test bed of the Autonomous Systems
Laboratory has been used to create a control system for a
small fixed pitch helicopter. This paper outlines the challenges
posed by such a vehicle and the control system designed to
overcome them. The control system utilized a visual tracking
system to obtain state information without onboard hardware.
Matlab/Simulink environment was used to facilitate rapid
prototyping control development. An autopilot consisting of
multi-channel PID controllers was implemented for flight tests.
Failsafe strategies and gain scheduling were both investigated
and implemented with the use of a graphical user interface. A
number of flight tests were conducted and the results are
provided. The future work of the laboratory is also covered
Geometry of Frictionless and Frictional Sphere Packings
We study static packings of frictionless and frictional spheres in three
dimensions, obtained via molecular dynamics simulations, in which we vary
particle hardness, friction coefficient, and coefficient of restitution.
Although frictionless packings of hard-spheres are always isostatic (with six
contacts) regardless of construction history and restitution coefficient,
frictional packings achieve a multitude of hyperstatic packings that depend on
system parameters and construction history. Instead of immediately dropping to
four, the coordination number reduces smoothly from as the friction
coefficient between two particles is increased.Comment: 6 pages, 9 figures, submitted to Phys. Rev.
Situationally edited empathy: an effect of socio-economic structure on individual choice
Criminological theory still operates with deficient models of the offender as agent, and of social influences on the agentâs decision-making process. This paper takes one âemotionâ, empathy, which is theoretically of considerable importance in influencing the choices made by agents; particularly those involving criminal or otherwise harmful action. Using a framework not of rational action, but of ârationalised actionâ, the paper considers some of the effects on individual psychology of social, economic, political and cultural structure. It is suggested that the climate-setting effects of these structures promote normative definitions of social situations which allow unempathic, harmful action to be rationalised through the situational editing of empathy. The âcrime is normalâ argument can therefore be extended to include the recognition that the uncompassionate state of mind of the criminal actor is a reflection of the self-interested values which govern non-criminal action in wider society
Chiral fermion mass and dispersion relations at finite temperature in the presence of hypermagnetic fields
We study the modifications to the real part of the thermal self-energy for
chiral fermions in the presence of a constant external hypermagnetic field. We
compute the dispersion relation for fermions occupying a given Landau level to
first order in g'^2, g^2 and g_phi^2 and to all orders in g'B, where g' and g
are the U(1)_Y and SU(2)_L couplings of the standard model, respectively, g_phi
is the fermion Yukawa coupling, and B is the hypermagnetic field strength. We
show that in the limit where the temperature is large compared to sqrt{g'B},
left- and right-handed modes acquire finite and different B-dependent masses
due to the chiral nature of their coupling with the external field. Given the
current bounds on the strength of primordial magnetic fields, we argue that the
above is the relevant scenario to study the effects of magnetic fields on the
propagation of fermions prior and during the electroweak phase transition.Comment: 11 pages 4 figures, published versio
Nonlinear dynamics of a bistable piezoelectric-composite energy harvester for broadband application
The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or âsnap-throughâ, is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2âmW, comparing well with the needs of typical wireless senor node applications
Induction of antibodies by Staphylococcus aureus nasal colonization in young children
AbstractIn order to develop novel antlstaphylococcal strategies, understanding the determinants of carriage and how humans respond to Staphylococcus aureus exposure is essential. Here, the primary S. aureus-specific humoral immune response and its association with nasal colonization was studied in young children. Sera from 57 colonized or non-colonized children, serially collected at birth and at 6, 14 and 24 months, were analysed for IgG, IgA and IgM binding to 19 staphylococcal proteins, using flow cytometry-based technology. The antibody responses showed extensive inter-individual variability. On average, the levels of antistaphylococcal IgA and IgM increased from birth until the age of 2 years (p <0.05), whereas the levels of IgG decreased (p <0.001). Placentally transferred maternal IgG did not protect against colonization. In colonized children, IgG and IgA levels for a number of proteins were higher than in non-colonized children. At both 14 and 24 months, the levels of IgG against chemotaxis inhibitory protein of S. aureus (at 24 months; median fluorescence intensity, 4928 vs. 24, p <0.05), extracellular fibrinogen-binding protein (987 vs. 604, p <0.05), and iron-responsive surface determinant H (62 vs. 5, p <0.05) were significantly higher in colonized children. The levels of IgA against CHIPS, IsdH and IsdA were higher (p <0.05). Therefore, CHIPS, Efb, IsdA and IsdH seem to play a role in nasal colonization of young children
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