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The effect of visual impairment on quality of life of children aged 3-16 years
Background: It is well known that visual impairment (VI) has a detrimental effect on Quality of Life (QoL) in adults.
Little is known about the effects of VI in childhood.
Aims: To evaluate the effects of VI on QoL of children. To the authors’ knowledge, this is the first study containing
a comparison arm for children with VI.
Methods: QoL in children with VI (nÂĽ24, age 10.1362.89, 18 male, 6 female) was compared with an age-matched comparison group (nÂĽ24, age 9.8362.81, 18 male, 6 female) using the Low Vision Quality of Life Questionnaire. Factors (distance and near visual acuity and age) that could be used as predictors of QoL were assessed. These were measured with standard clinical tests.
Results: Children with VI had significantly lower QoL scores than the comparison group (p<0.001), resulting in a 35.6% reduction in total QoL score. QoL scores in children with VI were correlated with distance and near visual acuity (p<0.05). 38% of the variance could be predicted by these factors and age.
Conclusions: Consideration of the effects of this reduced QoL must be made. Further studies are needed to establish the benefit to QoL of different habilitation strategies
Evolving turbulence and magnetic fields in galaxy clusters
We discuss, using simple analytical models and MHD simulations, the origin
and parameters of turbulence and magnetic fields in galaxy clusters. Three
physically distinct regimes can be identified in the evolution of cluster
turbulence and magnetic fields. Firstly, the fluctuation dynamo will produce
microgauss-strong, random magnetic fields during cluster formation and major
mergers. Turbulent velocity of about 300 km/s can be maintained at scales
100-200 kpc. The magnetic field is intermittent, has a smaller scale of 20-30
kpc and average strength of 2 microgauss. Secondly, when major mergers end,
turbulent speed and magnetic field undergo a power-law decay, decreasing in
strength but increasing in scale by a factor of about two. Thirdly,
smaller-mass subclusters and cluster galaxies produce turbulent wakes, with
turbulent speeds and magnetic field strengths similar to those quoted above.
The velocity scales are about 200 kpc and 10 kpc respectively, and the magnetic
field scale is about 6 times smaller. Although these wakes may fill only a
small fraction of the cluster volume, their area covering factor can be close
to unity. So one can potentially reconcile observations that indicate the
coexistence of turbulence with ordered filamentary gas structures, as in the
Perseus cluster. Random Faraday rotation measure is estimated to be typically
100-200 rad/m^2, in agreement with observations. We predict detectable
synchrotron polarization from cluster radio halos at wavelengths 3-6 cm, if
observed at sufficiently high resolution (abridged).Comment: 20 pages, 9 figures, Replaced to match version accepted by MNRA
Magnetic helicity in stellar dynamos: new numerical experiments
The theory of large scale dynamos is reviewed with particular emphasis on the
magnetic helicity constraint in the presence of closed and open boundaries. In
the presence of closed or periodic boundaries, helical dynamos respond to the
helicity constraint by developing small scale separation in the kinematic
regime, and by showing long time scales in the nonlinear regime where the scale
separation has grown to the maximum possible value. A resistively limited
evolution towards saturation is also found at intermediate scales before the
largest scale of the system is reached. Larger aspect ratios can give rise to
different structures of the mean field which are obtained at early times, but
the final saturation field strength is still decreasing with decreasing
resistivity. In the presence of shear, cyclic magnetic fields are found whose
period is increasing with decreasing resistivity, but the saturation energy of
the mean field is in strong super-equipartition with the turbulent energy. It
is shown that artificially induced losses of small scale field of opposite sign
of magnetic helicity as the large scale field can, at least in principle,
accelerate the production of large scale (poloidal) field. Based on mean field
models with an outer potential field boundary condition in spherical geometry,
we verify that the sign of the magnetic helicity flux from the large scale
field agrees with the sign of alpha. For solar parameters, typical magnetic
helicity fluxes lie around 10^{47} Mx^2 per cycle.Comment: 23 pages, 27 figures, Astron. Nach
Frequency and time profiles of metric wave isolated Type I solar noise storm bursts at high spectral and temporal resolution
Type I noise storms constitute a sizeable faction of the active-Sun radio
emission component. Observations of isolated instances of such bursts, in the
swept-frequency-mode at metric wavelengths, have remained sparse, with several
unfilled regions in the frequency coverage. Dynamic spectra of the burst
radiation, in the 30 - 130 MHz band, obtained from the recently commissioned
digital High Resolution Spectrograph (HRS) at the Gauribidanur Radio
Observatory, on account of the superior frequency and time resolution, have
unravelled in explicit detail the temporal and spectral profiles of isolated
bursts. Apart from presenting details on their fundamental emission features,
the time and frequency profile symmetry, with reference to custom-specific
Gaussian distributions, has been chosen as the nodal criterion to statistically
explain the state of the source regions in the vicinity of magnetic
reconnections, the latent excitation agent that contributes to plasma wave
energetics, and the quenching phenomenon that causes damping of the burst
emission.Comment: 9 pages 7 black and white / grey-scale figures (inclusive of 3
composite). MNRAS - accepte
Non-collinear Magnetic Order in the Double Perovskites: Double Exchange on a Geometrically Frustrated Lattice
Double perovskites of the form A_2BB'O_6 usually involve a transition metal
ion, B, with a large magnetic moment, and a non magnetic ion B'. While many
double perovskites are ferromagnetic, studies on the underlying model reveal
the possibility of antiferromagnetic phases as well driven by electron
delocalisation. In this paper we present a comprehensive study of the magnetic
ground state and T_c scales of the minimal double perovskite model in three
dimensions using a combination of spin-fermion Monte Carlo and variational
calculations. In contrast to two dimensions, where the effective magnetic
lattice is bipartite, three dimensions involves a geometrically frustrated face
centered cubic (FCC) lattice. This promotes non-collinear spiral states and
`flux' like phases in addition to collinear anti-ferromagnetic order. We map
out the possible magnetic phases for varying electron density, `level
separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour)
hopping t'.Comment: 15 pages pdflatex + 19 figs, revision: removed redundant comment
A Unified treatment of small and large- scale dynamos in helical turbulence
Helical turbulence is thought to provide the key to the generation of
large-scale magnetic fields. Turbulence also generically leads to rapidly
growing small-scale magnetic fields correlated on the turbulence scales. These
two processes are usually studied separately. We give here a unified treatment
of both processes, in the case of random fields, incorporating also a simple
model non-linear drift. In the process we uncover an interesting plausible
saturated state of the small-scale dynamo and a novel analogy between quantum
mechanical (QM) tunneling and the generation of large scale fields. The steady
state problem of the combined small/large scale dynamo, is mapped to a
zero-energy, QM potential problem; but a potential which, for non-zero mean
helicity, allows tunneling of bound states. A field generated by the
small-scale dynamo, can 'tunnel' to produce large-scale correlations, which in
steady state, correspond to a force-free 'mean' field.Comment: 4 pages, 1 figure, Physical Review Letters, in pres
The effect of ambient conditions on carbon monoxide emissions from an idling gas turbine combustor
A test program employing a gas turbine combustor is outlined; the results of which quantize the effects of changes in ambient temperature and humidity on carbon monoxide emissions at simulated idle operating conditions. A comparison of the experimental results with analytical results generated by a kinetic model of the combustion process, and reflecting changing ambient conditions, is given. It is demonstrated that for a complete range of possible ambient variations, significant changes do occur in the amount of carbon monoxide emitted by a gas turbine at idle, and that the analytical model is reasonably successful in predicting changes
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