5,253 research outputs found
Aerodynamic configuration development of the highly maneuverable aircraft technology remotely piloted research vehicle
The aerodynamic development of the highly maneuverable aircraft technology remotely piloted research vehicle (HiMAT/RPRV) from the conceptual design to the final configuration is presented. The design integrates several advanced concepts to achieve a high degree of transonic maneuverability, and was keyed to sustained maneuverability goals while other fighter typical performance characteristics were maintained. When tests of the baseline configuration indicated deficiencies in the technology integration and design techniques, the vehicle was reconfigured to satisfy the subcritical and supersonic requirements. Drag-due-to-lift levels only 5 percent higher than the optimum were obtained for the wind tunnel model at a lift coefficient of 1 for Mach numbers of up to 0.8. The transonic drag rise was progressively lowered with the application of nonlinear potential flow analyses coupled with experimental data
Design and analysis of a supersonic penetration/maneuvering fighter
The design of three candidate air combat fighters which would cruise effectively at freestream Mach numbers of 1.6, 2.0, and 2.5 while maintaining good transonic maneuvering capability, is considered. These fighters were designed to deliver aerodynamically controlled dogfight missiles at the design Mach numbers. Studies performed by Rockwell International in May 1974 and guidance from NASA determined the shape and size of these missiles. The principle objective of this study is the aerodynamic design of the vehicles; however, configurations are sized to have realistic structures, mass properties, and propulsion systems. The results of this study show that air combat fighters in the 15,000 to 23,000 pound class would cruise supersonically on dry power and still maintain good transonic maneuvering performance
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Development of a Virtual Laparoscopic Trainer using Accelerometer Augmented Tools to Assess Performance in Surgical training
Previous research suggests that virtual reality (VR) may supplement conventional training in laparoscopy. It may prove useful in the selection of surgical trainees in terms of their dexterity and spatial awareness skills in the near future. Current VR training solutions provide levels of realism and in some instances, haptic feedback, but they are cumbersome by being tethered and not ergonomically close to the actual surgical instruments for weight and freedom of use factors. In addition, they are expensive hence making them less accessible to departments than conventional box trainers. The box trainers in comparison, although more economical, lack tangible feedback and realism for handling delicate tissue structures. We have previously reported on the development of a modified digitally enhanced surgical instrument for laparoscopic training, named the Parkar Tool. This tool contains wireless accelerometer and gyroscopic sensors integrated into actual laparoscopic instruments. By design, it alleviates the need for both tethered and physically different shaped tools thereby enhancing the realism when performing surgical procedures. Additionally the software (Valhalla) has the ability to digitally record surgical motions, thereby enabling it to remotely capture surgical training data to analyse and objectively evaluate performance. We have adapted and further developed our initial single training tool method as used with a laparoscopic pyloromyotomy scenario, to an enhanced method using multiple Parkar wireless tools simultaneously, for use in several different case scenarios. This allows the use and measurement of right and left handed dexterity with the benefit of using several tasks of differing complexity. The development of a 3D tissue-surface deformations solution written in OpenGL gives us several different virtual surgical training scenario approximations to use with the instruments. The trainee can start with learning simple tasks e.g. incising tissue, grasping, squeezing and stretching tissue, to more complex procedures such as suturing, herniotomies, bowel anastomoses, as well as the original pyloromyotomy as used in the first model
Power loss in open cavity diodes and a modified Child Langmuir Law
Diodes used in most high power devices are inherently open. It is shown that
under such circumstances, there is a loss of electromagnetic radiation leading
to a lower critical current as compared to closed diodes. The power loss can be
incorporated in the standard Child-Langmuir framework by introducing an
effective potential. The modified Child-Langmuir law can be used to predict the
maximum power loss for a given plate separation and potential difference as
well as the maximum transmitted current for this power loss. The effectiveness
of the theory is tested numerically.Comment: revtex4, 11 figure
Gravitational Radiation from First-Order Phase Transitions
It is believed that first-order phase transitions at or around the GUT scale
will produce high-frequency gravitational radiation. This radiation is a
consequence of the collisions and coalescence of multiple bubbles during the
transition. We employ high-resolution lattice simulations to numerically evolve
a system of bubbles using only scalar fields, track the anisotropic stress
during the process and evolve the metric perturbations associated with
gravitational radiation. Although the radiation produced during the bubble
collisions has previously been estimated, we find that the coalescence phase
enhances this radiation even in the absence of a coupled fluid or turbulence.
We comment on how these simulations scale and propose that the same enhancement
should be found at the Electroweak scale; this modification should make direct
detection of a first-order electroweak phase transition easier.Comment: 7 pages, 7 figure
State-to-state rotational transitions in H+H collisions at low temperatures
We present quantum mechanical close-coupling calculations of collisions
between two hydrogen molecules over a wide range of energies, extending from
the ultracold limit to the super-thermal region. The two most recently
published potential energy surfaces for the H-H complex, the so-called
DJ (Diep and Johnson, 2000) and BMKP (Boothroyd et al., 2002) surfaces, are
quantitatively evaluated and compared through the investigation of rotational
transitions in H+H collisions within rigid rotor approximation. The
BMKP surface is expected to be an improvement, approaching chemical accuracy,
over all conformations of the potential energy surface compared to previous
calculations of H-H interaction. We found significant differences in
rotational excitation/de-excitation cross sections computed on the two surfaces
in collisions between two para-H molecules. The discrepancy persists over a
large range of energies from the ultracold regime to thermal energies and
occurs for several low-lying initial rotational levels. Good agreement is found
with experiment (Mat\'e et al., 2005) for the lowest rotational excitation
process, but only with the use of the DJ potential. Rate coefficients computed
with the BMKP potential are an order of magnitude smaller.Comment: Accepted by J. Chem. Phy
Coherent Control and Entanglement in the Attosecond Electron Recollision Dissociation of D2+
We examine the attosecond electron recollision dissociation of D2+ recently
demonstrated experimentally [H. Niikura et al., Nature (London) 421, 826
(2003)] from a coherent control perspective. In this process, a strong laser
field incident on D2 ionizes an electron, accelerates the electron in the laser
field to eV energies, and then drives the electron to recollide with the parent
ion, causing D2+ dissociation. A number of results are demonstrated. First, a
full dimensional Strong Field Approximation (SFA) model is constructed and
shown to be in agreement with the original experiment. This is then used to
rigorously demonstrate that the experiment is an example of coherent pump-dump
control. Second, extensions to bichromatic coherent control are proposed by
considering dissociative recollision of molecules prepared in a coherent
superposition of vibrational states. Third, by comparing the results to similar
scenarios involving field-free attosecond scattering of independently prepared
D2+ and electron wave packets, recollision dissociation is shown to provide an
example of wave-packet coherent control of reactive scattering. Fourth, this
analysis makes clear that it is the temporal correlations between the continuum
electron and D2+ wave packet, and not entanglement, that are crucial for the
sub-femtosecond probing resolution demonstrated in the experiment. This result
clarifies some misconceptions regarding the importance of entanglement in the
recollision probing of D2+. Finally, signatures of entanglement between the
recollision electron and the atomic fragments, detectable via coincidence
measurements, are identified
State-to-State Differential and Relative Integral Cross Sections for Rotationally Inelastic Scattering of H2O by Hydrogen
State-to-state differential cross sections (DCSs) for rotationally inelastic
scattering of H2O by H2 have been measured at 71.2 meV (574 cm-1) and 44.8 meV
(361 cm-1) collision energy using crossed molecular beams combined with
velocity map imaging. A molecular beam containing variable compositions of the
(J = 0, 1, 2) rotational states of hydrogen collides with a molecular beam of
argon seeded with water vapor that is cooled by supersonic expansion to its
lowest para or ortho rotational levels (JKaKc= 000 and 101, respectively).
Angular speed distributions of fully specified rotationally excited final
states are obtained using velocity map imaging. Relative integral cross
sections are obtained by integrating the DCSs taken with the same experimental
conditions. Experimental state-specific DCSs are compared with predictions from
fully quantum scattering calculations on the most complete H2O-H2 potential
energy surface. Comparison of relative total cross sections and state-specific
DCSs show excellent agreement with theory in almost all detailsComment: 46 page
Pulse-driven near-resonant quantum adiabatic dynamics: lifting of quasi-degeneracy
We study the quantum dynamics of a two-level system driven by a pulse that
starts near-resonant for small amplitudes, yielding nonadiabatic evolution, and
induces an adiabatic evolution for larger amplitudes. This problem is analyzed
in terms of lifting of degeneracy for rising amplitudes. It is solved exactly
for the case of linear and exponential rising. Approximate solutions are given
in the case of power law rising. This allows us to determine approximative
formulas for the lineshape of resonant excitation by various forms of pulses
such as truncated trig-pulses. We also analyze and explain the various
superpositions of states that can be obtained by the Half Stark Chirped Rapid
Adiabatic Passage (Half-SCRAP) process.Comment: 21 pages, 12 figure
Easing the transition of First Year Undergraduates Through an Immersive Induction Module
Entry into higher education (HE) is recognised as a challenging time for undergraduates as they negotiate the norms and practices of new academic communities and foster relationships with peers and academics. Given the significance of this time period, our University has piloted a new four-week module that immerses students in their discipline and provides them with the academic skills and networks to support them through this period and beyond. Here we report a comprehensive evaluation examining academic and student experience of this immersive module. We explore its impact on essential aspects of the transition experience e.g. social integration, academic literacies and the sense of preparation for HE. Whilst this new approach did have positive impacts on students’ sense of integration, questions were raised around the extent to which it matched or even raised expectations, and the extent to which this prepared students for the rest of their studies
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