423 research outputs found
Aluminium and Acacia plant growth on coal mine dumps
Colonising native and introduced plant species present on old abandoned dumps in the Collie coal field in south-west Western Australia provide a potential resource for rehabilitation. Coal waste dumps are more acidic than the surrounding forest soils, indicating a potentially toxic presence of aluminium. Some plants exhibit tolerance, and may accumulate, avoid or exclude aluminium. Excluders restrict translocation of the metal bound in root cells. Evolution of tolerance to metal stress may be comparatively rapid and although aluminium has many adverse affects on growth, plants tolerant of its presence also tend to be drought tolerant, an advantage for survival on dumps over dry summers.
Progeny of a dump population of Acacia decurrens are contrasted with a non-dump population. Seedlings were subjected to varied concentrations of aluminium in solution and harvested at 10 weeks. A. decurrens tolerated low levels of applied aluminium but severe effects on growth were observed at 500 ppm. Plants of dump origin failed to produce greater plant biomass than non-dump plants. However, dump origin plants took up less total aluminium than non-dump plants, indicating an avoidance mechanism. Dump progeny held more of the absorbed aluminium within roots, translocating lower quantities to foliage, suggesting an exclusion mechanism. Decreased tissue nitrogen, phosphorus and calcium coincided with increased aluminium supplied. Calcium decline was the most severe. Trace element and manganese concentrations increased with added aluminium.
Despite an inability to out-perform non-dump progeny, the pattern of nutrient uptake indicates a real difference between the two accessions. In the long run survivors are likely to persist and reproduce if they have successfully avoided uptake of deleterious elements beyond the root systems. It is therefore recommended that collection of seed for use on coal-mine rehabilitation sites should be made from established plants growing on dumps
Large-space shell-model calculations for light nuclei
An effective two-body interaction is constructed from a new Reid-like
potential for a large no-core space consisting of six major shells and is used
to generate the shell-model properties for light nuclei from =2 to 6. (For
practical reasons, the model space is partially truncated for =6.) Binding
energies and other physical observables are calculated and compare favorably
with experiment.Comment: prepared using LaTex, 21 manuscript pages, no figure
Some investigations into non passive listening
Our knowledge of the function of the auditory nervous system is based upon a wealth of data obtained, for the most part, in anaesthetised animals. More recently, it has been generally acknowledged that factors such as attention profoundly modulate the activity of sensory systems and this can take place at many levels of processing. Imaging studies, in particular, have revealed the greater activation of auditory areas and areas outside of sensory processing areas when attending to a stimulus. We present here a brief review of the consequences of such non-passive listening and go on to describe some of the experiments we are conducting to investigate them. In imaging studies, using fMRI, we can demonstrate the activation of attention networks that are non-specific to the sensory modality as well as greater and different activation of the areas of the supra-temporal plane that includes primary and secondary auditory areas. The profuse descending connections of the auditory system seem likely to be part of the mechanisms subserving attention to sound. These are generally thought to be largely inactivated by anaesthesia. However, we have been able to demonstrate that even in an anaesthetised preparation, removing the descending control from the cortex leads to quite profound changes in the temporal patterns of activation by sounds in thalamus and inferior colliculus. Some of these effects seem to be specific to the ear of stimulation and affect interaural processing. To bridge these observations we are developing an awake behaving preparation involving freely moving animals in which it will be possible to investigate the effects of consciousness (by contrasting awake and anaesthetized), passive and active listening
Background-free detection of trapped ions
We demonstrate a Doppler cooling and detection scheme for ions with low-lying
D levels which almost entirely suppresses scattered laser light background,
while retaining a high fluorescence signal and efficient cooling. We cool a
single ion with a laser on the 2S1/2 to 2P1/2 transition as usual, but repump
via the 2P3/2 level. By filtering out light on the cooling transition and
detecting only the fluorescence from the 2P_3/2 to 2S1/2 decays, we suppress
the scattered laser light background count rate to 1 per second while
maintaining a signal of 29000 per second with moderate saturation of the
cooling transition. This scheme will be particularly useful for experiments
where ions are trapped in close proximity to surfaces, such as the trap
electrodes in microfabricated ion traps, which leads to high background scatter
from the cooling beam
Optimum electrode configurations for fast ion separation in microfabricated surface ion traps
For many quantum information implementations with trapped ions, effective
shuttling operations are important. Here we discuss the efficient separation
and recombination of ions in surface ion trap geometries. The maximum speed of
separation and recombination of trapped ions for adiabatic shuttling operations
depends on the secular frequencies the trapped ion experiences in the process.
Higher secular frequencies during the transportation processes can be achieved
by optimising trap geometries. We show how two different arrangements of
segmented static potential electrodes in surface ion traps can be optimised for
fast ion separation or recombination processes. We also solve the equations of
motion for the ion dynamics during the separation process and illustrate
important considerations that need to be taken into account to make the process
adiabatic
The Effects of Disorder on the Quantum Hall State
A disorder-averaged Hartree-Fock treatment is used to compute the density of
single particle states for quantum Hall systems at filling factor . It
is found that transport and spin polarization experiments can be simultaneously
explained by a model of mostly short-range effective disorder. The slope of the
transport gap (due to quasiparticles) in parallel field emerges as a result of
the interplay between disorder-induced broadening and exchange, and has
implications for skyrmion localization.Comment: 4 pages, 3 eps figure
Disarmed anthrax toxin delivers antisense oligonucleotides and siRNA with high efficiency and low toxicity
Inefficient cytosolic delivery and vector toxicity contribute to the limited use of antisense oligonucleotides (ASOs) and siRNA as therapeutics. As anthrax toxin (Atx) accesses the cytosol, the purpose of this study was to evaluate the potential of disarmed Atx to deliver either ASOs or siRNA. We hypothesized that this delivery strategy would facilitate improved transfection efficiency while eliminating the toxicity seen for many vectors due to membrane destabilization. Atx complex formation with ASOs or siRNA was achieved via the in-frame fusion of either Saccharomyces cerevisiae GAL4 or Homo sapien sapien PKR (respectively) to a truncation of Atx lethal factor (LFn), which were used with Atx protective antigen (PA). Western immunoblotting confirmed the production of: LFN-GAL4, LFn-PKR and PA which were detected at ~ 45.9 kDa, ~ 37 kDa, and ~ 83 kDa respectively and small angle neutron scattering confirmed the ability of PA to form an annular structure with a radius of gyration of 7.0 ± 1.0 nm when placed in serum. In order to form a complex with LFn-GAL4, ASOs were engineered to contain a double-stranded region, and a cell free in vitro translation assay demonstrated that no loss of antisense activity above 30 pmol ASO was evident. The in vitro toxicity of both PA:LFn-GAL4:ASO and PA:LFn-PKR:siRNA complexes was low (IC50 > 100 μg/mL in HeLa and Vero cells) and subcellular fractionation in conjunction with microscopy confirmed the detection of LFn-GAL4 or LFn-PKR in the cytosol. Syntaxin5 (Synt5) was used as a model target gene to determine pharmacological activity. The PA:LFn-GAL4:ASO complexes had transfection efficiency approximately equivalent to Nucleofection® over a variety of ASO concentrations (24 h post-transfection) and during a 72 h time course. In HeLa cells, at 200 pmol ASO (with PA:LFN-GAL4), 5.4 ± 2.0% Synt5 expression was evident relative to an untreated control after 24 h. Using 200 pmol ASOs, Nucleofection® reduced Synt5 expression to 8.1 ± 2.1% after 24 h. PA:LFn-GAL4:ASO transfection of non- or terminally-differentiated THP-1 cells and Vero cells resulted in 35.2 ± 19.1%, 36.4 ± 1.8% and 22.9 ± 6.9% (respectively) Synt5 expression after treatment with 200 pmol of ASO and demonstrated versatility. Nucleofection® with Stealth RNAi™ siRNA reduced HeLa Synt5 levels to 4.6 ± 6.1% whereas treatment with the PA:LFn-PKR:siRNA resulted in 8.5 ± 3.4% Synt5 expression after 24 h (HeLa cells). These studies report for the first time an ASO and RNAi delivery system based upon protein toxin architecture that is devoid of polycations. This system may utilize regulated membrane back-fusion for the cytosolic delivery of ASOs and siRNA, which would account for the lack of toxicity observed. High delivery efficiency suggests further in vivo evaluation is warranted
Skymrion lattice melting in the quantum Hall system
The melting and magnetic disordering of the skyrmion lattice in the quantum
Hall system at filling factor are studied. A
Berezinskii-Kosterlitz-Thouless renormalization group theory is employed to
describe the coupled magnetic and translational degrees of freedom. The
non-trivial magnetic properties of the skyrmion system stem from the in-plane
components of the non-collinear magnetization in the vicinity of skyrmions,
which are described by an antiferromagnetic XY model. In a Coulomb gas
formulation the `particles' are the topological defects of the XY model
(vortices) and of the lattice (dislocations and disclinations). The latter
frustrate the antiferromagnetic order and acquire fractional vorticity in order
to minimize their energy. We find a number of melting/disordering scenarios for
various lattice types. While these results do not depend on a particular model,
we also consider a simple classical model for the skyrmion system. It results
in a rich T=0 phase diagram. We propose that the triangular and square skyrmion
lattices are generically separated by a centered rectangular phase in the
quantum Hall system.Comment: 15 pages with 5 figures. Minor revisions. Important reference to M.
Rao, S. Sengupta, and R. Shankar, Phys. Rev. Lett. 79, 3998 (1997) adde
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
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