Removing Orbital Debris with Lasers

Orbital debris in low Earth orbit (LEO) are now sufficiently dense that the use of LEO space is threatened by runaway collisional cascading. A problem predicted more than thirty years ago, the threat from debris larger than about 1 cm demands serious attention. A promising proposed solution uses a high power pulsed laser system on the Earth to make plasma jets on the objects, slowing them slightly, and causing them to re-enter and burn up in the atmosphere. In this paper, we reassess this approach in light of recent advances in low-cost, light-weight modular design for large mirrors, calculations of laser-induced orbit changes and in design of repetitive, multi-kilojoule lasers, that build on inertial fusion research. These advances now suggest that laser orbital debris removal (LODR) is the most cost-effective way to mitigate the debris problem. No other solutions have been proposed that address the whole problem of large and small debris. A LODR system will have multiple uses beyond debris removal. International cooperation will be essential for building and operating such a system.Comment: 37 pages, 15 figures, in preparation for submission to Advances in Space Researc

The half-lives of some short lived low Z nuclei formed by photonuclear reactions

The half-lives of several members of the mirror nuclei series have been measured, using improved scintillation counter detectors and a cycling apparatus which progams the synchrotron beam and several subsequent gated detectors in sequence repetitively. By the use of beta-ray energy discrimination, least squares fitting of decay curves, and by careful correction for background activities, the improved values listed in Table A were found

The influence of large predators on the feeding ecology of two African mesocarnivores: the black-backed jackal and the brown hyaena

Interactions between apex and mesopredators and their impacts on prey populations have been well documented, while the influence of apex predators such as lions on carrion availability and the subsequent impacts at lower trophic levels are not fully understood. Here we assess dietary overlap between two sympatric carnivores (brown hyaena, Parahyaena brunnea, and black-backed jackal, Canis mesomelas) in neighbouring reserves with and without apex predators (lions, Panthera leo,and wild dog, Lycaon pictus). We investigate whether apex predators facilitate niche partitioning between mesocarnivores by creating additional scavenging opportunities through predatory activity. We found that brown hyaena density was higher in the area with apex predators, while black-backed jackal density was higher in the area without apex predators. Black-backed jackal scats contained broadly similar dietary items at both sites, while large mammal remains occurred significantly more frequently in brown hyaena scats collected inthe presence of apex predators. In the absence of apex predators there was a markedly higher degree of overlap between brown hyaena and jackal diets, suggesting increased levels of inter-specific competition. Our results suggest that apex predators potentially reduce levels of inter-specific competition for food between mesocarnivores by providing additional scavenging opportunities for specialist scavengers such as brown hyaena

Autofluorescence lifetime augmented reality as a means for real-time robotic surgery guidance in human patients.

Due to loss of tactile feedback the assessment of tumor margins during robotic surgery is based only on visual inspection, which is neither significantly sensitive nor specific. Here we demonstrate time-resolved fluorescence spectroscopy (TRFS) as a novel technique to complement the visual inspection of oral cancers during transoral robotic surgery (TORS) in real-time and without the need for exogenous contrast agents. TRFS enables identification of cancerous tissue by its distinct autofluorescence signature that is associated with the alteration of tissue structure and biochemical profile. A prototype TRFS instrument was integrated synergistically with the da Vinci Surgical robot and the combined system was validated in swine and human patients. Label-free and real-time assessment and visualization of tissue biochemical features during robotic surgery procedure, as demonstrated here, not only has the potential to improve the intraoperative decision making during TORS but also other robotic procedures without modification of conventional clinical protocols

A South African perspective on factors that impact on the adoption and meaningful use of health information technologies

Objective: Various benefits are associated with the adoption and meaningful use of health information technologies (HITs) in the healthcare sector. Despite the associated advantages with the adoption and use of HITs, the South African healthcare sector has been slow to adopt HITs, such as electronic record systems. The purpose of this study was to identify factors that should be addressed to encourage the adoption and meaningful use of HITs in the South African healthcare landscape.Design: A three-round Delphi study was conducted to identify such factors.Setting and subjects: The Delphi panel included 21 participants who were considered to be suitably knowledgeable about the acceptance and significant use of HITs in the context of the South African healthcare setting.Results: A total of 58 factors were uncovered by the participants. Consensus was reached on 42 factors that were considered to have a direct to significant impact on the adoption and meaningful use of HITs in the South African healthcare sector.Conclusion: The results of this study highlight factors that should be addressed to encourage the adoption and meaningful use of HITs in South Africa’s healthcare setting. These results indicate that a wide range of factors need to be addressed and involve a multitude of stakeholders.Keywords: health information technology, adoption, meaningful use, South Africa, Delphi stud

Plasma generation and plume expansion for a transmission-mode microlaser ablation plasma thruster

An end-to-end model is presented of the transient plume created by a microlaser ablation plasma thruster. In this article, we describe a model of the plasma generation and expansion for a micro-laser plasma thruster operated in transmission-mode (T-mode). The laser ablation and plasma formation processes are modeled using a kinetic ablation model. This procedure provides boundary conditions at the target surface for the plume model that is based on a particle computational approach. The present study considers a 2.5–8 W diode-based laser irradiating a poly-vinyl chloride target for a pulse length of 3–10 ms. Laser beam shape full width at half maximum at the target is about 25×25 μm. The plume simulations reveal many details of the multicomponent plasma expansion. The results are compared with experimentally obtained plume signatures. Generally good agreement between experimental and calculated flux profiles is found. © 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69665/2/JAPIAU-96-1-49-1.pd