7,221 research outputs found
Behavioural compensation by drivers of a simulator when using a vision enhancement system
Technological progress is suggesting dramatic changes to the tasks of the driver, with the general aim of making driving environment safer. Before any of these technologies are implemented, empirical research is required to establish if these devices do, in fact, bring about the anticipated improvements. Initially, at least, simulated driving environments offer a means of conducting this research. The study reported here concentrates on the application of a vision enhancement (VE) system within the risk homeostasis paradigm. It was anticipated, in line with risk homeostasis theory, that drivers would compensate for the reduction in risk by increasing speed. The results support the hypothesis although, after a simulated failure of the VE system, drivers did reduce their speed due to reduced confidence in the reliability of the system
Adding value to milk by increasing its protein and CLA contents
End of project reportThe mid-summer milk protein study was undertaken on 34 commercial dairy farms in 2005 to evaluate the influence of dietary and management variables on milk protein content in mid-season. Data on grass composition, genetic merit of the herds and milk protein content were collected and analysed by multiple regression. Both calving date and genetic merit for milk protein content were significantly associated with milk protein content and were used as adjustment factors when evaluating the association between measures of grass quality and milk protein content. Milk protein content was associated with grass OMD (P = 0.04) and NDF content (P = 0.02) but not with CP content (P = 0.80). It is concluded that herds calving earlier, with a greater genetic merit for milk protein content and consuming better quality pasture would have greater milk protein contents in mid-season
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Predicting pilot error on the flight deck: Validation of a new methodology and a multiple methods and analysts approach to enhancing error prediction sensitivity
The Human Error Template (HET) is a recently developed methodology for predicting designed induced pilot error. This article describes a validation study undertaken to compare the performance of HET against three contemporary Human Error Identification (HEI) approaches when used to predict pilot errors for an approach and landing task and also to compare individual analyst error predictions to an approach to enhancing error prediction sensitivity: the multiple analysts and methods approach, whereby multiple analyst predictions using a range of HEI technique are pooled. The findings indicate that, of the four methodologies used in isolation, analysts using the HET methodology offered the most accurate error predictions, and also that the multiple analysts and methods approach was more successful overall in terms of error prediction sensitivity than the three other methods but not the HET approach. The results suggest that when predicting design induced error, it is appropriate to use domain specific approaches and also a toolkit of different HEI approaches and multiple analysts in order to heighten error prediction sensitivity
Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures
We show that large amplitude, coherent acoustic phonon wavepackets can be
generated and detected in InGaN/GaN epilayers and heterostructures
in femtosecond pump-probe differential reflectivity experiments. The amplitude
of the coherent phonon increases with increasing Indium fraction and unlike
other coherent phonon oscillations, both \textit{amplitude} and \textit{period}
are strong functions of the laser probe energy. The amplitude of the
oscillation is substantially and almost instantaneously reduced when the
wavepacket reaches a GaN-sapphire interface below the surface indicating that
the phonon wavepackets are useful for imaging below the surface. A theoretical
model is proposed which fits the experiments well and helps to deduce the
strength of the phonon wavepackets. Our model shows that localized coherent
phonon wavepackets are generated by the femtosecond pump laser in the epilayer
near the surface. The wavepackets then propagate through a GaN layer changing
the local index of refraction, primarily through the Franz-Keldysh effect, and
as a result, modulate the reflectivity of the probe beam. Our model correctly
predicts the experimental dependence on probe-wavelength as well as epilayer
thickness.Comment: 11 pages, 14 figure
Development of a generic activities model of command and control
This paper reports on five different models of command and control. Four different models are reviewed: a process model, a contextual control model, a decision ladder model and a functional model. Further to this, command and control activities are analysed in three distinct domains: armed forces, emergency services and civilian services. From this analysis, taxonomies of command and control activities are developed that give rise to an activities model of command and control. This model will be used to guide further research into technological support of command and control activities
Carrier dynamics and coherent acoustic phonons in nitride heterostructures
We model generation and propagation of coherent acoustic phonons in
piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode
structure and compute the time resolved reflectivity signal in simulated
pump-probe experiments. Carriers are created in the InGaN wells by ultrafast
pumping below the GaN band gap and the dynamics of the photoexcited carriers is
treated in a Boltzmann equation framework. Coherent acoustic phonons are
generated in the quantum well via both deformation potential electron-phonon
and piezoelectric electron-phonon interaction with photogenerated carriers,
with the latter mechanism being the dominant one. Coherent longitudinal
acoustic phonons propagate into the structure at the sound speed modifying the
optical properties and giving rise to a giant oscillatory differential
reflectivity signal. We demonstrate that coherent optical control of the
differential reflectivity can be achieved using a delayed control pulse.Comment: 14 pages, 11 figure
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Soldering Small Beads to Fine Wires
One method suggested for soldering small beads to fine wires using a torch to heat the bead, flux, and magnesia brick did not prove entirely satisfactory in this case. It was found the brick would draw heat away from the bead and flux at too fast a rate resulting in a poor weld, a rough surface, and an excessive accumulation of flux on the bead. Secondly, removal of the depleted flux presented a problem when the welding was done on the surface of the brick
Excitonic effects on coherent phonon dynamics in single wall carbon nanotubes
We discuss how excitons can affect the generation of coherent radial
breathing modes in ultrafast spectroscopy of single wall carbon nanotubes.
Photoexcited excitons can be localized spatially and give rise to a spatially
distributed driving force in real space which involves many phonon wavevectors
of the exciton-phonon interaction. The equation of motion for the coherent
phonons is modeled phenomenologically by the Klein-Gordon equation, which we
solve for the oscillation amplitudes as a function of space and time. By
averaging the calculated amplitudes per nanotube length, we obtain
time-dependent coherent phonon amplitudes that resemble the homogeneous
oscillations that are observed in some pump-probe experiments. We interpret
this result to mean that the experiments are only able to see a spatial average
of coherent phonon oscillations over the wavelength of light in carbon
nanotubes and the microscopic details are averaged out. Our interpretation is
justified by calculating the time-dependent absorption spectra resulting from
the macroscopic atomic displacements induced by the coherent phonon
oscillations. The calculated coherent phonon spectra including excitonic
effects show the experimentally observed symmetric peaks at the nanotube
transition energies in contrast to the asymmetric peaks that would be obtained
if excitonic effects were not included.Comment: submitted to Phys. Rev. B on 7 May 2013, revised on 17 July and 13
August 2013, published 30 August 201
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