Experimental development of a fire management model for Jarrah (Eucalyptus Marginata Donn ex Sm.) forest.

Accumulations of flammable fuel and seasonal hot, dry weather has ensured that fire is an important environmental factor which has shaped jarrah forest ecosystems of south-west Western Australia. Today, fire impacts on all aspects of jarrah forest management, including timber and water production, recreation and wildlife conservation. Fire management involves controlling destructive wildfires and applying prescribed fires over a wide range of burning conditions to achieve a variety of protection, production and conservation objectives. A sound scientific understanding of the behaviour, physical impacts and long term ecological and commercial effects of fire is essential to planning and implementing fire regimes and suppression activities pertinent to current and foreseeable management. Existing forest fire behaviour guides developed in the 1960s from small low intensity experimental fires set under mild conditions perform adequately over the low fire intensity range, but are deficient at predicting the behaviour of moderate and high intensity fires burning under warm, dry conditions. Another shortcoming is that they do not attempt to predict physical impacts of fire which give rise to ecological responses or commercial losses. This thesis describes laboratory and field experiments designed to model the behaviour and some important physical impacts of fire in jarrah forest over a wide range of potential burning conditions. Fire behaviour and fire impact models were developed for a standardjarrah. forest fuel type; the structure, composition, dynamics and combustion properties of which were studied in detail. Most variation in equilibrium headfire rate of spread on level terrain was best explained by the product of a power function in wind speed and a power function in fuel moisture content. Headfire rate of spread was independent of the quantity of fuel per unit area. Forced convection and flame contact appeared to be the primary mechanisms for flame spread in wind driven fires which burnt across then down into the eucalypt litter fuel bed. Conversely, the rate of spread of zero wind fires and backfires was directly related to the quantity of fuel burnt, suggesting that radiation was the primary mechanism for flame spread in this situation. The transition from a fire spreading primarily by radiation to one spreading primarily by convection occurred at a wind speed of 3 - 4 km h-1. For zero wind conditions, rate of spread and slope were best related by an exponential equation form and fire shape was described by a power function in wind speed. Flame size was a function of rate of spread, fuel quantity consumed and fuel moisture content. Immediate physical impacts of fire on vegetation and soil were examined in three zones and coupled with fire behaviour variables and factors affecting heat transfer by fitted regression models. Impact above the flames (crown scorch height), was dependent on flame height, fire intensity and the season in which the fire occurred. Impacts in the flames (stem damage and mortality), were dependent on the quantity of fuel consumed, fire intensity and bark thickness. Soil heating was a function of the quantity of fuel consumed, soil moisture and fuel moisture. A soil heating index was developed which allows numerical characterisation of fire-induced soil heating. The fire behaviour and fire impact models developed by this thesis provide a scientifically based system for using fire as a tool for multiple use forest management

Jet Breaks in Short Gamma-Ray Bursts. I: The Uncollimated Afterglow of GRB 050724

We report the results of the \chandra observations of the \swift-discovered short Gamma-Ray Burst GRB 050724. \chandra observed this burst twice, about two days after the burst and a second time three weeks later. The first \chandra pointing occurred at the end of a strong late-time flare. About 150 photons were detected during this 49.3 ks observation in the 0.4-10.0 keV range. The spectral fit is in good agreement with spectral analysis of earlier \swift XRT data. In the second \chandra pointing the afterglow was clearly detected with 8 background-subtracted photons in 44.6 ks. From the combined \swift XRT and \chandra-ACIS-S light curve we find significant flaring superposed on an underlying power-law decay slope of $\alpha$=0.98$^{+0.11}_{-0.09}$. There is no evidence for a break between about 1 ks after the burst and the last \chandra pointing about three weeks after the burst. The non-detection of a jet break places a lower limit of 25$^{\circ}$ on the jet opening angle, indicating that the outflow is less strongly collimated than most previously-reported long GRBs. This implies that the beaming corrected energy of GRB 050724 is at least $4\times 10^{49}$ ergs.Comment: 7 pages, ApJ acceped, scheduled for December 20, 2006, ApJ, 65

Swift Observations of GRB 050603: An afterglow with a steep late time decay slope

We report the results of Swift observations of the Gamma Ray Burst GRB 050603. With a V magnitude V=18.2 about 10 hours after the burst the optical afterglow was the brightest so far detected by Swift and one of the brightest optical afterglows ever seen. The Burst Alert Telescope (BAT) light curves show three fast-rise-exponential-decay spikes with $T_{90}$=12s and a fluence of 7.6$\times 10^{-6}$ ergs cm$^{-2}$ in the 15-150 keV band. With an $E_{\rm \gamma, iso} = 1.26 \times 10^{54}$ ergs it was also one of the most energetic bursts of all times. The Swift spacecraft began observing of the afterglow with the narrow-field instruments about 10 hours after the detection of the burst. The burst was bright enough to be detected by the Swift UV/Optical telescope (UVOT) for almost 3 days and by the X-ray Telescope (XRT) for a week after the burst. The X-ray light curve shows a rapidly fading afterglow with a decay index $\alpha$=1.76$^{+0.15}_{-0.07}$. The X-ray energy spectral index was $\beta_{\rm X}$=0.71\plm0.10 with the column density in agreement with the Galactic value. The spectral analysis does not show an obvious change in the X-ray spectral slope over time. The optical UVOT light curve decays with a slope of $\alpha$=1.8\plm0.2. The steepness and the similarity of the optical and X-ray decay rates suggest that the afterglow was observed after the jet break. We estimate a jet opening angle of about 1-2$^{\circ}$Comment: 14 pages, accepted for publication in Ap

Redshift Filtering by Swift Apparent X-ray Column Density

We remark on the utility of an observational relation between the absorption column density in excess of the Galactic absorption column density, $\Delta N_{\rm H} = N_{\rm H, fit} - N_{\rm H, gal}$, and redshift, z, determined from all 55 Swift-observed long bursts with spectroscopic redshifts as of 2006 December. The absorption column densities, $N_{\rm H, fit}$, are determined from powerlaw fits to the X-ray spectra with the absorption column density left as a free parameter. We find that higher excess absorption column densities with $\Delta N_{\rm H} > 2\times 10^{21}$ cm$^{-2}$ are only present in bursts with redshifts z$<$2. Low absorption column densities with $\Delta N_{\rm H} < 1\times 10^{21}$ cm$^{-2}$ appear preferentially in high-redshift bursts. Our interpretation is that this relation between redshift and excess column density is an observational effect resulting from the shift of the source rest-frame energy range below 1 keV out of the XRT observable energy range for high redshift bursts. We found a clear anti-correlation between $\Delta N_{\rm H}$ and z that can be used to estimate the range of the maximum redshift of an afterglow. A critical application of our finding is that rapid X-ray observations can be used to optimize the instrumentation used for ground-based optical/NIR follow-up observations. Ground-based spectroscopic redshift measurements of as many bursts as possible are crucial for GRB science.Comment: revised version including updates and the referee's comments, accepted for publication in the Astronomical Journal, 12 pages, 2 figures, 2 tables - v3 contains an update on the reference lis

Polymer of intrinsic microporosity (PIM-7) coating affects triphasic palladium electrocatalysis

A film of the polymer of intrinsic microporosity PIM-7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water-insoluble microcrystalline anthraquinone is immobilised directly into the PIM-7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM-7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano-palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM-7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM-7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial “gas management” layer

Swift XRT Observations of the Afterglow of XRF 050416A

Swift discovered XRF 050416A with the BAT and began observing it with its narrow field instruments only 64.5 s after the burst onset. Its very soft spectrum classifies this event as an X-ray flash. The afterglow X-ray emission was monitored up to 74 days after the burst. The X-ray light curve initially decays very fast, subsequently flattens and eventually steepens again, similar to many X-ray afterglows. The first and second phases end about 172 and 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index Gamma ~ 3.0 during the initial steep decay, to a harder emission with Gamma ~ 2.0 during the following evolutionary phases. The spectra show intrinsic absorption in the host galaxy. The consistency of the initial photon index with the high energy BAT photon index suggests that the initial phase of the X-ray light curve may be the low-energy tail of the prompt emission. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with empirical relations between the source rest-frame peak energy and the collimation-corrected energy of the burst. The standard uniform jet model can give a possible description of the XRF 050416A X-ray afterglow for an opening angle larger than a few tens of degrees, although numerical simulations show that the late time decay is slightly flatter than expected from on-axis viewing of a uniform jet. A structured Gaussian-type jet model with uniform Lorentz factor distribution and viewing angle outside the Gaussian core is another possibility, although a full agreement with data is not achieved with the numerical models explored.Comment: Accepted for publication on ApJ; replaced with revised version: part of the discussion moved in an appendix; 11 pages, 6 figures; abstract shortened for posting on astro-p

Polymer of Intrinsic Microporosity (PIM-7) Coating Affects Triphasic Palladium Electrocatalysis

A film of the polymer of intrinsic microporosity PIM-7 is coated onto a glassy carbon electrode and the resulting effects on electron transfer reactions are studied for three different types of processes: (i) aqueous solution based, (ii) solid state surface immobilised, and (iii) electrocatalytic processes on electrodeposited palladium. The effects on reactivity for hydroquinone oxidation in aqueous phosphate buffer are shown to be linked to microporosity causing a slightly lower rate of mass transport without detrimental effects on electron transfer and reaction kinetics. Next, water-insoluble microcrystalline anthraquinone is immobilised directly into the PIM-7 film and shown to give a chemically reversible reduction process, which is enhanced in the presence of PIM-7, when compared to the case of anthraquinone immobilised directly onto bare glassy carbon. Electrodeposition of a film of nano-palladium is demonstrated to give catalytically active electrodes for the reduction/oxidation of protons/hydrogen, the reduction of oxygen, and for the oxidation of formic acid and methanol. With the PIM-7 film applied onto palladium, a mechanical stabilisation effect occurs. In addition, both the hydrogen insertion and the hydrogen evolution reactions as well as formic acid oxidation are enhanced. Effects are discussed in terms of PIM-7 beneficially affecting the interfacial reaction under triphasic conditions. The microporous polymer acts as an interfacial “gas management” layer.</p

The Swift X-ray flaring afterglow of GRB 050607

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected Gamma-Ray Burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early lightcurve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the Fast Rise, Exponential Decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of approximately 25,peaking for 30 seconds at a count rate of approximately 30 counts s-1, and it presented hints of addition short time scale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short time scale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.Comment: 23 pages, 5 figures, Accepted by the Astrophysical Journa

Leveraging Space-based Data from the Nearest Solar-type Star to Better Understand Stellar Activity Signatures in Radial Velocity Data

Stellar variability is a key obstacle in reaching the sensitivity required to recover Earth-like exoplanetary signals using the radial velocity (RV) detection method. To explore activity signatures in Sun-like stars, we present SolAster, a publicly distributed analysis pipeline10 that allows for comparison of space-based measurements with ground-based disk-integrated RVs. Using high-spatial-resolution Dopplergrams, magnetograms, and continuum filtergrams from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO), we estimate "Sun-as-a-star" disk-integrated RVs due to rotationally modulated flux imbalances and convective blueshift suppression, as well as other observables such as unsigned magnetic flux. Comparing these measurements with ground-based RVs from the NEID instrument, which observes the Sun daily using an automated solar telescope, we find a strong relationship between magnetic activity indicators and RV variation, supporting efforts to examine unsigned magnetic flux as a proxy for stellar activity in slowly rotating stars. Detrending against measured unsigned magnetic flux allows us to improve the NEID RV measurements by ∼20% (∼50 cm s−1 in a quadrature sum), yielding an rms scatter of ∼60 cm s−1 over five months. We also explore correlations between individual and averaged spectral line shapes in the NEID spectra and SDO-derived magnetic activity indicators, motivating future studies of these observables. Finally, applying SolAster to archival planetary transits of Venus and Mercury, we demonstrate the ability to recover small amplitude (&lt;50 cm s−1) RV variations in the SDO data by directly measuring the Rossiter–McLaughlin signals

Unusual Central Engine Activity in the Double Burst GRB 110709B

The double burst, GRB 110709B, triggered Swift/BAT twice at 21:32:39 UT and 21:43:45 UT, respectively, on 9 July 2011. This is the first time we observed a GRB with two BAT triggers. In this paper, we present simultaneous Swift and Konus-WIND observations of this unusual GRB and its afterglow. If the two events are from the same physical origin, their different time-dependent spectral evolution suggest they must belong to different episodes of the central engine, which may be a magnetar-to-BH accretion system