1,297 research outputs found
Murex medic field evaluation.
Trials: 90GE113, 90MO62, 90WH87, 90ME72, 90NO115, 90A24, 90AB17, 90AL35
Locations: Geraldton, New Norcia, Wongan Hills, Merredin, Southern Brook, Avondale, Katanning, Tenderden.
The selection SEP29.1 was outstanding for both dry matter production and seed yield over a wide range of sites varying in both rainfall and soil type. On the basis of these trials, six lines have been selected for further evaluation in 1991.
They are: SEP29.1 SEP26.2.7 GRC69 GRC87.1 87F01.28 87FB2.36
Trials 90A25 and 90NO116
Redlegged earthmite field experiments.
Very low levels of redlegged earthmite and only minor damage to test varieties was recorded in this trial. Damage ratings were recorded at 3, 4 and 5 weeks after sowing and plant yields at 3, 5 and 7 weeks, but the trial was then abandoned due to minimal responses.
90NO116 - This trial was abandoned soon after sowing due to massive germination of contaminant clover present in the paddock and negligible levels of redlegged earthmite
Nonlinear wave propagation and reconnection at magnetic X-points in the Hall MHD regime
The highly dynamical, complex nature of the solar atmosphere naturally
implies the presence of waves in a topologically varied magnetic environment.
Here, the interaction of waves with topological features such as null points is
inevitable and potentially important for energetics. The low resistivity of the
solar coronal plasma implies that non-MHD effects should be considered in
studies of magnetic energy release in this environment. This paper investigates
the role of the Hall term in the propagation and dissipation of waves, their
interaction with 2D magnetic X-points and the nature of the resulting
reconnection. A Lagrangian remap shock-capturing code (Lare2d) is used to study
the evolution of an initial fast magnetoacoustic wave annulus for a range of
values of the ion skin depth in resistive Hall MHD. A magnetic null-point
finding algorithm is also used to locate and track the evolution of the
multiple null-points that are formed in the system. Depending on the ratio of
ion skin depth to system size, our model demonstrates that Hall effects can
play a key role in the wave-null interaction. In particular, the initial
fast-wave pulse now consists of whistler and ion-cyclotron components; the
dispersive nature of the whistler wave leads to (i) earlier interaction with
the null, (ii) the creation of multiple additional, transient nulls and, hence,
an increased number of energy release sites. In the Hall regime, the relevant
timescales (such as the onset of reconnection and the period of the oscillatory
relaxation) of the system are reduced significantly, and the reconnection rate
is enhanced.Comment: 13 pages, 10 figure
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
Drawing inspiration from nature to develop anti-fouling coatings: the development of biomimetic polymer surfaces and their effect on bacterial fouling
The development of self-cleaning biomimetic surfaces has the potential to be of great benefit to human health, in addition to reducing the economic burden on industries worldwide. Consequently, this study developed a biomimetic wax surface using a moulding technique which emulated the topography of the self-cleaning Gladiolus hybridus (Gladioli) leaf. A comparison of topographies was performed for unmodified wax surfaces (control), biomimetic wax surfaces, and Gladioli leaves using optical profilometry and scanning electron microscopy. The results demonstrated that the biomimetic wax surface and Gladioli leaf had extremely similar surface roughness parameters, but the water contact angle of the Gladioli leaf was significantly higher than the replicated biomimetic surface. The self-cleaning properties of the biomimetic and control surfaces were compared by measuring their propensity to repel Escherichia coli and Listeria monocytogenes attachment, adhesion, and retention in mono-and co-culture conditions. When the bacterial assays were carried out in monoculture, the biomimetic surfaces retained fewer bacteria than the control surfaces. However, when using co-cultures of the bacterial species, only following the retention assays were the bacterial numbers reduced on the biomimetic surfaces. The results demonstrate that such surfaces may be effective in reducing biofouling if used in the appropriate medical, marine, and industrial scenarios. This study provides valuable insight into the anti-fouling physical and chemical control mechanisms found in plants, which are particularly appealing for engineering purposes
Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X-ray Tail
We propose a model for the hard X-ray (> 10 keV) emission observed from the
supernova remnant Cas A. Lower hybrid waves are generated in strong (mG)
magnetic fields, generally believed to reside in this remnant, by shocks
reflected from density inhomogeneities. These then accelerate electrons to
energies of several tens of keV. Around 4% of the x-ray emitting plasma
electrons need to be in this accelerated distribution, which extends up to
electron velocities of order the electron Alfven speed, and is directled along
magnetic field lines. Bremsstrahlung from these electrons produces the observed
hard x-ray emission. Such waves and accelerated electrons have been observed in
situ at Comet Halley, and we discuss the viability of the extrapolation from
this case to the parameters relevant to Cas A.Comment: 20 pages, 3 figures, aasTeX502, accepted in Ap
On the Nature of MeV-blazars
Broad-band spectra of the FSRQ (flat-spectrum-radio quasars) detected in the
high energy gamma-ray band imply that there may be two types of such objects:
those with steep gamma-ray spectra, hereafter called MeV-blazars, and those
with flat gamma-ray spectra, GeV-blazars. We demonstrate that this difference
can be explained in the context of the ERC (external-radiation-Compton) model
using the same electron injection function. A satisfactory unification is
reachable, provided that: (a) spectra of GeV-blazars are produced by internal
shocks formed at the distances where cooling of relativistic electrons in a jet
is dominated by Comptonization of broad emission lines, whereas spectra of
MeV-blazars are produced at the distances where cooling of relativistic
electrons is dominated by Comptonization of near-IR radiation from hot dust;
(b) electrons are accelerated via a two step process and their injection
function takes the form of a double power-law, with the break corresponding to
the threshold energy for the diffusive shock acceleration. Direct predictions
of our model are that, on average, variability time scales of the MeV-blazars
should be longer than variability time scales of the GeV-blazars, and that both
types of the blazar phenomenon can appear in the same object.Comment: Accepted for publication in the Astrophysical Journa
On Collisionless Electron-Ion Temperature Equilibration in the Fast Solar Wind
We explore a mechanism, entirely new to the fast solar wind, of electron
heating by lower hybrid waves to explain the shift to higher charge states
observed in various elements in the fast wind at 1 A.U. relative to the
original coronal hole plasma. This process is a variation on that previously
discussed for two temperature accretion flows by Begelman & Chiueh. Lower
hybrid waves are generated by gyrating minor ions (mainly alpha-particles) and
become significant once strong ion cyclotron heating sets in beyond 1.5 R_sun.
In this way the model avoids conflict with SUMER electron temperature
diagnostic measurements between 1 and 1.5 R_sun. The principal requirement for
such a process to work is the existence of density gradients in the fast solar
wind, with scale length of similar order to the proton inertial length. Similar
size structures have previously been inferred by other authors from radio
scintillation observations and considerations of ion cyclotron wave generation
by global resonant MHD waves.Comment: 32 pages including 11 figures, 4 tables, accepted by Ap
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