From E_8 to F via T

We argue that T-duality and F-theory appear automatically in the E_8 gauge bundle perspective of M-theory. The 11-dimensional supergravity four-form determines an E_8 bundle. If we compactify on a two-torus, this data specifies an LLE_8 bundle where LG is a centrally-extended loopgroup of G. If one of the circles of the torus is smaller than sqrt(alpha') then it is also smaller than a nontrivial circle S in the LLE_8 fiber and so a dimensional reduction on the total space of the bundle is not valid. We conjecture that S is the circle on which the T-dual type IIB theory is compactified, with the aforementioned torus playing the role of the F-theory torus. As tests we reproduce the T-dualities between NS5-branes and KK-monopoles, as well as D6 and D7-branes where we find the desired F-theory monodromy. Using Hull's proposal for massive IIA, this realization of T-duality allows us to confirm that the Romans mass is the central extension of our LE_8. In addition this construction immediately reproduces the conjectured formula for global topology change from T-duality with H-flux.Comment: 25 pages, 4 eps figure

Identification of host odour attractants for tsetse flies. Final report 1986-1990

Tsetse flies, Glossina spp., are blood-feeding insects and vectors of trypanosomes, microorganisms which cause sleeping sickness in man and a similar disease, "nagana" in domestic animals. The economic importance of trypanosomiasis is the constraint it imposes on orderly rural development in Africa, leading to under-exploitation of infested land and over-exploitation and degradation of trypanosomiasis-free areas. Traps and targets which attract tsetse flies and kill them could provide environmentally-acceptable, appropriate technology for monitoring and control of tsetse in Africa. Unbaited devices providing only visual attraction have proved effective in monitoring and control of riverine species of tsetse, but not the savannah species found in the fly belt of Malawi, Mozambique, Zambia and Zimbabwe covered by the EDF Regional Tsetse and Trypanosomiasis Control Project (RTTCP). Previously, collaborative was begun between glossinologists of the Zimbabwe Department of Veterinary Services (DVS) and UK Tsetse Research Laboratory (TRL) and chemists at NRI. This brought together the experience of the DVS in the field, the experience of TRL in laboratory bioassay work, and the experience of NRI in using gas chromatography linked to electroantennography (GC-EAG) and chemical techniques to detect and identify insect behaviour-modifying chemicals. Tsetse attractants produced by host animals were identified and synthesised, and dispensing systems for these compounds devised. Traps and targets impregnated with insecticide, baited with these lures were shown to provide effective control of the savannah tsetse species, G. pallidipes and G. m. morsitans

Amplitude to phase conversion of InGaAs pin photo-diodes for femtosecond lasers microwave signal generation

When a photo-diode is illuminated by a pulse train from a femtosecond laser, it generates microwaves components at the harmonics of the repetition rate within its bandwidth. The phase of these components (relative to the optical pulse train) is known to be dependent on the optical energy per pulse. We present an experimental study of this dependence in InGaAs pin photo-diodes illuminated with ultra-short pulses generated by an Erbium-doped fiber based femtosecond laser. The energy to phase dependence is measured over a large range of impinging pulse energies near and above saturation for two typical detectors, commonly used in optical frequency metrology with femtosecond laser based optical frequency combs. When scanning the optical pulse energy, the coefficient which relates phase variations to energy variations is found to alternate between positive and negative values, with many (for high harmonics of the repetition rate) vanishing points. By operating the system near one of these vanishing points, the typical amplitude noise level of commercial-core fiber-based femtosecond lasers is sufficiently low to generate state-of-the-art ultra-low phase noise microwave signals, virtually immune to amplitude to phase conversion related noise.Comment: 7 pages, 6 figures, submitted to Applied Physics

Embodying our values in our teaching practices: Building open and critical discourse through computer mediated communication

Computer mediated communication—including web pages, email and web-based bulletin boards—was used to support the development of a cooperative learning community among students in a web-based distance education unit for practicing science and mathematics educators. The students lived in several Australian states and a number of Pacific Rim countries. They reported increased satisfaction with their studies, decreased feelings of isolation, and better support for their learning processes. This article describes the iterative processes of research and design involved in developing and refining the unit, which was based in a social constructivist/constructionist conception of teaching and learning, between 1997 and 1999. Issues and implications for others planning to develop web-based teaching units, including the time and energy commitment involved, and the challenges of credibly assessing online participation, are also considered

Representing critical reflections in teacher education

This critical action research study explores the professional growth of a middle school teacher and two teacher educators. It focuses on a professional development program in which one author (Bev) had the role of student, one of teacher (Peter), and one of the teacher's 'critical friend' (David). The program's epistemology was based on Habermas' theory of 'knowledge and human interests', emphasising the 'emancipatory' interest's potential for creating empowering learning environments. The teaching and learning roles of the participants, with their professional development and new understandings, are explored with reference to a 'critical incident' that sparked this inquiry. Narrative accounts are used to explore the sometimes conflicting meanings constructed by the authors, highlighting the complex nature of their educative discourses and problematising notions of emancipatory curriculum and student empowerment

Breaking up prolonged sitting time with walking does not affect appetite or gut hormone concentrations but does induce an energy deficit and suppresses postprandial glycaemia in sedentary adults

Breaking up periods of prolonged sitting can negate harmful metabolic effects but the influence on appetite and gut hormones is not understood and is investigated in this study. Thirteen sedentary (7 female) participants undertook three 5-h trials in random order: (i) uninterrupted sitting (SIT), (ii) seated with 2-min bouts of light-intensity walking every 20 min (SIT + LA), and (iii) seated with 2-min bouts of moderate-intensity walking every 20 min (SIT + MA). A standardised test drink was provided at the start of each trial and an ad libitum pasta test meal provided at the end of each trial. Subjective appetite ratings and plasma acylated ghrelin, peptide YY, insulin, and glucose were measured at regular intervals. Area under the curve (AUC) was calculated for each variable. AUC values for appetite and gut hormone concentrations were unaffected in the activity breaks conditions compared with uninterrupted sitting (linear mixed modelling: p > 0.05). Glucose AUC was lower in SIT + MA than in SIT + LA (p = 0.004) and SIT (p = 0.055). There was no difference in absolute ad libitum energy intake between conditions (p > 0.05); however, relative energy intake was lower in SIT + LA (39%; p = 0.011) and SIT + MA (120%; p < 0.001) than in SIT. In conclusion, breaking up prolonged sitting does not alter appetite and gut hormone responses to a meal over a 5-h period. Increased energy expenditure from activity breaks could promote an energy deficit that is not compensated for in a subsequent meal

3-D Perturbations in Conformal Turbulence

The effects of three-dimensional perturbations in two-dimensional turbulence are investigated, through a conformal field theory approach. We compute scaling exponents for the energy spectra of enstrophy and energy cascades, in a strong coupling limit, and compare them to the values found in recent experiments. The extension of unperturbed conformal turbulence to the present situation is performed by means of a simple physical picture in which the existence of small scale random forces is closely related to deviations of the exact two-dimensional fluid motion.Comment: Discussion of intermittency improved. Figure include

Improved Nearside-Farside Decomposition of Elastic Scattering Amplitudes

A simple technique is described, that provides improved nearside-farside (NF) decompositions of elastic scattering amplitudes. The technique, involving the resummation of a Legendre partial wave series, reduces the importance of unphysical contributions to NF subamplitudes, which can arise in more conventional NF decompositions. Applications are made to a strong absorption model and to a $^{16}$O + $^{12}$C optical potential at $E_{\text{lab}} = 132$ MeV.Comment: 5 pages, 2 figure

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Magnetoluminescence

Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain regions where the electromagnetic energy density greatly exceeds the plasma energy density. These sources exhibit dramatic flaring activity where the electromagnetic energy distributed over large volumes, appears to be converted efficiently into high energy particles and gamma-rays. We call this general process magnetoluminescence. Global requirements on the underlying, extreme particle acceleration processes are described and the likely importance of relativistic beaming in enhancing the observed radiation from a flare is emphasized. Recent research on fluid descriptions of unstable electromagnetic configurations are summarized and progress on the associated kinetic simulations that are needed to account for the acceleration and radiation is discussed. Future observational, simulation and experimental opportunities are briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews serie