185 research outputs found
Scale relativity and fractal space-time: theory and applications
In the first part of this contribution, we review the development of the
theory of scale relativity and its geometric framework constructed in terms of
a fractal and nondifferentiable continuous space-time. This theory leads (i) to
a generalization of possible physically relevant fractal laws, written as
partial differential equation acting in the space of scales, and (ii) to a new
geometric foundation of quantum mechanics and gauge field theories and their
possible generalisations. In the second part, we discuss some examples of
application of the theory to various sciences, in particular in cases when the
theoretical predictions have been validated by new or updated observational and
experimental data. This includes predictions in physics and cosmology (value of
the QCD coupling and of the cosmological constant), to astrophysics and
gravitational structure formation (distances of extrasolar planets to their
stars, of Kuiper belt objects, value of solar and solar-like star cycles), to
sciences of life (log-periodic law for species punctuated evolution, human
development and society evolution), to Earth sciences (log-periodic
deceleration of the rate of California earthquakes and of Sichuan earthquake
replicas, critical law for the arctic sea ice extent) and tentative
applications to system biology.Comment: 63 pages, 14 figures. In : First International Conference on the
Evolution and Development of the Universe,8th - 9th October 2008, Paris,
Franc
Comparative population structure of <i>Plasmodium malariae</i> and <i>Plasmodium falciparum</i> under different transmission settings in Malawi
<b>Background:</b> Described here is the first population genetic study of Plasmodium malariae, the causative agent of quartan malaria. Although not as deadly as Plasmodium falciparum, P. malariae is more common than previously thought, and is frequently in sympatry and co-infection with P. falciparum, making its study increasingly important. This study compares the population parameters of the two species in two districts of Malawi with different malaria transmission patterns - one seasonal, one perennial - to explore the effects of transmission on population structures.
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<b>Methods:</b> Six species-specific microsatellite markers were used to analyse 257 P. malariae samples and 257 P. falciparum samples matched for age, gender and village of residence. Allele sizes were scored to within 2 bp for each locus and haplotypes were constructed from dominant alleles in multiple infections. Analysis of multiplicity of infection (MOI), population differentiation, clustering of haplotypes and linkage disequilibrium was performed for both species. Regression analyses were used to determine association of MOI measurements with clinical malaria parameters.
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<b>Results:</b> Multiple-genotype infections within each species were common in both districts, accounting for 86.0% of P. falciparum and 73.2% of P. malariae infections and did not differ significantly with transmission setting. Mean MOI of P. falciparum was increased under perennial transmission compared with seasonal (3.14 vs 2.59, p = 0.008) and was greater in children compared with adults. In contrast, P. malariae mean MOI was similar between transmission settings (2.12 vs 2.11) and there was no difference between children and adults. Population differentiation showed no significant differences between villages or districts for either species. There was no evidence of geographical clustering of haplotypes. Linkage disequilibrium amongst loci was found only for P. falciparum samples from the seasonal transmission setting.
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<b>Conclusions:</b> The extent of similarity between P. falciparum and P. malariae population structure described by the high level of multiple infection, the lack of significant population differentiation or haplotype clustering and lack of linkage disequilibrium is surprising given the differences in the biological features of these species that suggest a reduced potential for out-crossing and transmission in P. malariae. The absence of a rise in P. malariae MOI with increased transmission or a reduction in MOI with age could be explained by differences in the duration of infection or degree of immunity compared to P. falciparum
Structure functions for the three nucleon system
The spectral functions and light-cone momentum distributions of protons and
neutrons in 3He and 3H are given in terms of the three-nucleon wave function
for realistic nucleon-nucleon interactions. To reduce computational complexity,
separable expansions are employed for the nucleon-nucleon potentials. The
results for the light-cone momentum distributions suggest that they are not
very sensitive to the details of the two-body interaction, as long as it has
reasonable short-range repulsion. The unpolarised and polarised structure
functions are examined for both 3He and 3H in order to test the usefulness of
3He as a neutron target. It is found that the measurement of the spin structure
function of polarised 3H would provide a very clear test of the predicted
change in the polarised parton distributions of a bound proton.Comment: 30 pages, REVTeX, 11 figure
Rotation measure variations for 20 millisecond pulsars
We report on variations in the mean position angle of the 20 millisecond
pulsars being observed as part of the Parkes Pulsar Timing Array (PPTA)
project. It is found that the observed variations are dominated by changes in
the Faraday rotation occurring in the Earth's ionosphere. Two ionospheric
models are used to correct for the ionospheric contribution and it is found
that one based on the International Reference Ionosphere gave the best results.
Little or no significant long-term variation in interstellar RM was found with
limits typically about 0.1 rad m yr in absolute value. In a few
cases, apparently significant RM variations over timescales of a few 100 days
or more were seen. These are unlikely to be due to localised magnetised regions
crossing the line of sight since the implied magnetic fields are too high. Most
probably they are statistical fluctuations due to random spatial and temporal
variations in the interstellar electron density and magnetic field along the
line of sight.Comment: Accepted for publication in Astrophysics & Space Scienc
ama1 Genes of Sympatric Plasmodium vivax and P. falciparum from Venezuela Differ Significantly in Genetic Diversity and Recombination Frequency
BACKGROUND: We present the first population genetic analysis of homologous loci from two sympatric human malaria parasite populations sharing the same human hosts, using full-length sequences of ama1 genes from Plasmodium vivax and P. falciparum collected in the Venezuelan Amazon. METHODOLOGY/PRINCIPAL FINDINGS: Significant differences between the two species were found in genetic diversity at the ama1 locus, with 18 distinct haplotypes identified among the 73 Pvama1 sequences obtained, compared to 6 unique haplotypes from 30 Pfama1 sequences, giving overall diversity estimates of h = 0.9091, and h = 0.538 respectively. Levels of recombination were also found to differ between the species, with P. falciparum exhibiting very little recombination across the 1.77 kb sequence. In contrast, analysis of patterns of nucleotide substitutions provided evidence that polymorphisms in the ama1 gene of both species are maintained by balancing selection, particularly in domain I. The two distinct population structures observed are unlikely to result from different selective forces acting upon the two species, which share both human and mosquito hosts in this setting. Rather, the highly structured P. falciparum population appears to be the result of a population bottleneck, while the much less structured P. vivax population is likely to be derived from an ancient pool of diversity, as reflected in a larger estimate of effective population size for this species. Greatly reduced mosquito transmission in 1997, due to low rainfall prior to the second survey, was associated with far fewer P. falciparum infections, but an increase in P. vivax infections, probably due to hypnozoite activation. CONCLUSIONS/SIGNIFICANCE: The relevance of these findings to putative competitive interactions between these two important human pathogen species is discussed. These results highlight the need for future control interventions to employ strategies targeting each of the parasite species present in endemic areas
Timing stability of millisecond pulsars and prospects for gravitational-wave detection
Analysis of high-precision timing observations of an array of approx. 20
millisecond pulsars (a so-called "timing array") may ultimately result in the
detection of a stochastic gravitational-wave background. The feasibility of
such a detection and the required duration of this type of experiment are
determined by the achievable rms of the timing residuals and the timing
stability of the pulsars involved. We present results of the first long-term,
high-precision timing campaign on a large sample of millisecond pulsars used in
gravitational-wave detection projects. We show that the timing residuals of
most pulsars in our sample do not contain significant low-frequency noise that
could limit the use of these pulsars for decade-long gravitational-wave
detection efforts. For our most precisely timed pulsars, intrinsic
instabilities of the pulsars or the observing system are shown to contribute to
timing irregularities on a five-year timescale below the 100 ns level. Based on
those results, realistic sensitivity curves for planned and ongoing timing
array efforts are determined. We conclude that prospects for detection of a
gravitational-wave background through pulsar timing array efforts within five
years to a decade are good.Comment: 21 pages, 5 figures, submitted to MNRA
Observations and Modelling of Relativistic Spin Precession in PSR J1141-6545
Observations of the binary pulsar PSR J1141-6545 using the Parkes radio
telescope over 9.3 years show clear time-variations in pulse width, shape and
polarization. We interpret these variations in terms of relativistic precession
of the pulsar spin axis about the total angular momentum vector of the system.
Over the nine years, the pulse width at the 50% level has changed by more than
a factor of three. Large variations have also been observed in the 1400-MHz
mean flux density. The pulse polarization has been monitored since 2004 April
using digital filterbank systems and also shows large and systematic variations
in both linear and circular polarization. Position angle variations, both
across the pulse profile and over the data span, are complex, with major
differences between the central and outer parts of the pulse profile. Modelling
of the observed position angle variations by relativistic precession of the
pulsar spin axis shows that the spin-orbit misalignment angle is about 110 deg
and that the precessional phase has passed through 180 deg during the course of
our observations. At the start of our observations, the line-of-sight impact
parameter was about 4 deg in magnitude and it reached a minimum very close to 0
deg around early 2007, consistent with the observed pulse width variations. We
have therefore mapped approximately one half of the emission beam, showing that
it is very asymmetric with respect to the magnetic axis. The derived
precessional parameters imply that the pre-supernova star had a mass of about 2
Msun and that the supernova recoil kick velocity was relatively small. With the
reversal in the rate of change of the impact parameter, we predict that over
the next decade we will see a reversed "replay" of the variations observed in
the past decade.Comment: 45 pages, 19 figures, 6 tables, accepted by Astrophysical Journa
WALLABY Early Science - II. The NGC 7232 galaxy group
We report on neutral hydrogen (HI) observations of the NGC 7232 group with
the Australian Square Kilometre Array Pathfinder (ASKAP). These observations
were conducted as part of the Wide-field ASKAP L-Band Legacy All-sky Blind
surveY (WALLABY) Early Science program with an array of 12 ASKAP antennas
equipped with Phased Array Feeds, which were used to form 36 beams to map a
field of view of 30 square degrees. Analyzing a subregion of the central beams,
we detect 17 HI sources. Eleven of these detections are identified as galaxies
and have stellar counterparts, of which five are newly resolved HI galaxy
sources. The other six detections appear to be tidal debris in the form of HI
clouds that are associated with the central triplet, NGC 7232/3, comprising the
spiral galaxies NGC 7232, NGC7232B and NGC7233. One of these HI clouds has a
mass of M_HI ~ 3 x 10^8 M_sol and could be the progenitor of a long-lived tidal
dwarf galaxy. The remaining HI clouds are likely transient tidal knots that are
possibly part of a diffuse tidal bridge between NGC 7232/3 and another group
member, the lenticular galaxy IC 5181.Comment: 18 pages (including appendix), 9 figures, accepted for publication in
MNRA
Ionospheric Modelling using GPS to Calibrate the MWA. II : Regional ionospheric modelling using GPS and GLONASS to estimate ionospheric gradients
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Publications of the Astronomical Society of Australia (PASA), after peer review and technical editing by the publisher. The version of record is available on line at https://doi.org/10.1017/pasa.2016.22 COPYRIGHT: © Astronomical Society of Australia 2016.We estimate spatial gradients in the ionosphere using the Global Positioning System (GPS) and GLONASS (Russian global navigation system) observations, utilising data from multiple GPS stations in the vicinity of Murchison Radio-astronomy Observatory (MRO). In previous work the ionosphere was characterised using a single-station to model the ionosphere as a single layer of fixed height and this was compared with ionospheric data derived from radio astronomy observations obtained from the Murchison Widefield Array (MWA). Having made improvements to our data quality (via cycle slip detection and repair) and incorporating data from the GLONASS system, we now present a multi-station approach. These two developments significantly improve our modelling of the ionosphere. We also explore the effects of a variable-height model. We conclude that modelling the small-scale features in the ionosphere that have been observed with the MWA will require a much denser network of Global Navigation Satellite System (GNSS) stations than is currently available at the MRO.Peer reviewe
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