A new method to calibrate ionospheric pulse dispersion for UHE cosmic ray and neutrino detection using the Lunar Cherenkov technique

UHE particle detection using the lunar Cherenkov technique aims to detect nanosecond pulses of Cherenkov emission which are produced during UHE cosmic ray and neutrino interactions in the Moon's regolith. These pulses will reach Earth-based telescopes dispersed, and therefore reduced in amplitude, due to their propagation through the Earth's ionosphere. To maximise the received signal to noise ratio and subsequent chances of pulse detection, ionospheric dispersion must therefore be corrected, and since the high time resolution would require excessive data storage this correction must be made in real time. This requires an accurate knowledge of the dispersion characteristic which is parameterised by the instantaneous Total Electron Content (TEC) of the ionosphere. A new method to calibrate the dispersive effect of the ionosphere on lunar Cherenkov pulses has been developed for the LUNASKA lunar Cherenkov experiments. This method exploits radial symmetries in the distribution of the Moon's polarised emission to make Faraday rotation measurements in the visibility domain of synthesis array data (i. e. instantaneously). Faraday rotation measurements are then combined with geomagnetic field models to estimate the ionospheric TEC. This method of ionospheric calibration is particularly attractive for the lunar Cherenkov technique as it may be used in real time to estimate the ionospheric TEC along a line-of-sight to the Moon and using the same radio telescope.Comment: 4 pages, 2 figures, Proceedings of ARENA 2010, Nantes, France; doi:10.1016/j.nima.2010.10.12

Beyond technology and finance: pay-as-you-go sustainable energy access and theories of social change

Two-thirds of people in sub-Saharan Africa lack access to electricity, a precursor of poverty reduction and development. The international community has ambitious commitments in this regard, e.g. the UN's Sustainable Energy for All by 2030. But scholarship has not kept up with policy ambitions. This paper operationalises a sociotechnical transitions perspective to analyse for the first time the potential of new, mobileenabled, pay-as-you-go approaches to financing sustainable energy access, focussing on a case study of pay-as-you-go approaches to financing solar home systems in Kenya. The analysis calls into question the adequacy of the dominant, two-dimensional treatment of sustainable energy access in the literature as a purely financial/technology, economics/ engineering problem (which ignores sociocultural and political considerations) and demonstrates the value of a new research agenda that explicitly attends to theories of social change – even when, as in this paper, the focus is purely on finance. The paper demonstrates that sociocultural considerations cut across the literature's traditional two-dimensional analytic categories (technology and finance) and are material to the likely success of any technological or financial intervention. It also demonstrates that the alignment of new payas- you-go finance approaches with existing sociocultural practices of paying for energy can explain their early success and likely longevity relative to traditional finance approaches

Operational experience and design recommendations for teleoperated flight hardware

Teleoperation (remote manipulation) will someday supplement/minimize astronaut extravehicular activity in space to perform such tasks as satellite servicing and repair, and space station construction and servicing. This technology is being investigated by NASA with teleoperation of two space-related tasks having been demonstrated at the Oak Ridge National Lab. The teleoperator experiments are discussed and the results of these experiments are summarized. The related equipment design recommendations are also presented. In addition, a general discussion of equipment design for teleoperation is also presented

Simultaneous Dual Frequency Observations of Giant Pulses from the Crab Pulsar

Simultaneous measurements of giant pulses from the Crab pulsar were taken at two widely spaced frequencies using the real-time detection of a giant pulse at 1.4 GHz at the Very Large Array to trigger the observation of that same pulse at 0.6 GHz at a 25-m telescope in Green Bank, WV. Interstellar dispersion of the signals provided the necessary time to communicate the trigger across the country via the Internet. About 70% of the pulses are seen at both 1.4 GHz and 0.6 GHz, implying an emission mechanism bandwidth of at least 0.8 GHz at 1 GHz for pulse structure on time scales of one to ten microseconds. The arrival times at both frequencies display a jitter of 100 microseconds within the window defined by the average main pulse profile and are tightly correlated. This tight correlation places limits on both the emission mechanism and on frequency dependent propagation within the magnetosphere. At 1.4 GHz the giant pulses are resolved into several, closely spaced components. Simultaneous observations at 1.4 GHz and 4.9 GHz show that the component splitting is frequency independent. We conclude that the multiplicity of components is intrinsic to the emission from the pulsar, and reject the hypothesis that this is the result of multiple imaging as the signal propagates through the perturbed thermal plasma in the surrounding nebula. At both 1.4 GHz and 0.6 GHz the pulses are characterized by a fast rise time and an exponential decay time which are correlated. The pulse broadening with its exponential decay form is most likely the result of multipath propagation in intervening ionized gas.Comment: LaTeX, 18 pages, 7 figures, accepted for publication in The Astrophysical Journa

Phase and Intensity Distributions of Individual Pulses of PSR B0950+08

The distribution of the intensities of individual pulses of PSR B0950+08 as a function of the longitudes at which they appear is analyzed. The flux density of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of 13) due to the passage of the radiation through the interstellar plasma (interstellar scintillation). The intensities of individual pulses can exceed the amplitude of the mean pulse profile, obtained by accumulating 770 pulses, by more than an order of magnitude. The intensity distribution along the mean profile is very different for weak and strong pulses. The differential distribution function for the intensities is a power law with index n = -1.1 +- 0.06 up to peak flux densities for individual pulses of the order of 160 Jy

Book Reviews

Reviews of the following books: The Penobscot Dance of Resistence: Tradition in the History of a People by Pauleena MacDougall; Maine’s Visible Black History: The First Chronicle of its People by H. H. Price and Gerald E.Talbot; Borderland Smuggling: Patriots, Loyalists, and Illicit Trade in the Northeast, 1783-1820 by Joshua M. Smith

Hamilton's principle: why is the integrated difference of kinetic and potential energy minimized?

I present an intuitive answer to an often asked question: why is the integrated difference K-U between the kinetic and potential energy the quantity to be minimized in Hamilton's principle? Using elementary arguments, I map the problem of finding the path of a moving particle connecting two points to that of finding the minimum potential energy of a static string. The mapping implies that the configuration of a non--stretchable string of variable tension corresponds to the spatial path dictated by the Principle of Least Action; that of a stretchable string in space-time is the one dictated by Hamilton's principle. This correspondence provides the answer to the question above: while a downward force curves the trajectory of a particle in the (x,t) plane downward, an upward force of the same magnitude stretches the string to the same configuration x(t).Comment: 7 pages, 4 figures. Submitted to the American Journal of Physic

Healthcare for truck drivers: Assessing accessibility and appropriateness of South African Roadside Wellness Centres

Background Truck drivers occupy a pivotal role in the economies of southern Africa, due to limited rail, water and other forms of transport of goods. The occupational nature of truck driving limits access to healthcare. North Star Alliance (North Star) offers a tailored primary healthcare service for truck drivers along the sub-Saharan trucking corridor. Objectives The overall objective of this study was to explore truck drivers’ views regarding access to, and appropriateness of, selected South African North Star Roadside Wellness Centres (RWCs) coupled with understanding their health-seeking behaviour. Methods We conducted semi-structured interviews with two groups of purposively-sampled truck drivers: 24 who accessed North Star RWCs and 22 who knew about the centres but did not use them. The interviews explored access, health-seeking behaviour, and healthcare experiences. Additional information on risk perceptions emerged. Qualitative data were organised into four themes: client satisfaction, health-seeking behaviour, risk perception and behaviour, and service delivery strengthening. Results The majority of those interviewed were older (36–65 years old), South African, with secondary education, employed full-time, in stable relationships, and having children. Overall users were satisfied with RWC locations, operating hours, infrastructure, and healthcare worker attitudes. Half of the non-users did not access routine healthcare anywhere. Non-users primarily did not access the RWCs because they did not know the operating times and preferred local facilities. Both groups used traditional healers and pharmacies. RWC users accessed traditional healers and pharmacies for services not available to them at the RWCs. Both groups reported not using private general practitioners or specialists. Both groups provided recommendations for strengthening the service delivery model including an increased focus on non-communicable diseases and occupationally-required health services including vaccinations. Conclusion Comprehensive care packages delivered through accessible satellite facilities should form the foundation of service delivery models for truck drivers and other mobile populations

Anomalous Radio-Wave Scattering from Interstellar Plasma Structures

This paper considers scattering screens that have arbitrary spatial variations of scattering strength transverse to the line of sight, including screens that are spatially well confined, such as disks and filaments. We calculate the scattered image of a point source and the observed pulse shape of a scattered impulse. The consequences of screen confinement include: (1) Source image shapes that are determined by the physical extent of the screen rather than by the shapes of much-smaller diffracting microirregularities. These include image elongations and orientations that are frequency dependent. (2) Variation with frequency of angular broadening that is much weaker than the trademark \nu^{-2} scaling law (for a cold, unmagnetized plasma), including frequency-independent cases; and (3) Similar departure of the pulse broadening time from the usually expected \nu^{-4} scaling law. We briefly discuss applications that include scattering of pulses from the Crab pulsar by filaments in the Crab Nebula; image asymmetries from Galactic scattering of the sources Cyg X-3, Sgr A*, and NGC 6334B; and scattering of background active galactic nuclei by intervening galaxies. We also address the consequences for inferences about the shape of the wavenumber spectrum of electron density irregularities, which depend on scaling laws for the image size and the pulse broadening. Future low-frequency (< 100 MHz) array observations will also be strongly affected by the Galactic structure of scattering material. Our formalism is derived in the context of radio scattering by plasma density fluctuations. It is also applicable to optical, UV and X-ray scattering by grains in the interstellar medium.Comment: 21 pages, LaTeX2e with AASTeX-4.0, 6 PostScript figures, accepted by ApJ, revised version has minor changes to respond to referee comments and suggestion