962 research outputs found
Critical loads of sulphur and nitrogen for surface waters in Northern Ireland
A survey of 140 surface waters (lakes, streams and reservoirs) across Northern Ireland was carried out in March 2000. One site was selected to represent each 10km OS NI grid square in Northern Ireland using a map of freshwater sensitivity to identify the most acid sensitive water body in each grid squar
Spatial variability of nitrate concentration in lakes in Snowdonia, North Wales, UK
International audienceAt a regional scale, high nitrate (NO3?) concentrations in upland surface waters generally occur in tandem with high nitrogen (N) deposition levels. However, significant differences in the patterns of surface water NO3? concentration have been observed within areas of similar N deposition yet relatively few studies have been undertaken which examine within-region variation of NO3? concentrations. A study of 76 lakes in Snowdonia, north Wales, an area of high deposition and sensitive catchments, was undertaken to assess variation in surface water NO3? concentration across a 20 x 20 km grid square and to identify catchments vulnerable to NO3? leaching. Nitrate concentrations vary considerably, particularly during winter when values range from 0.7 to 70 ?eq l-1. Although retention by vegetation and soil microbes in summer reduces the amount of NO3? reaching the lakes, 37 % of sites are characterised by NO3? concentrations greater then 4 ?eq l-1. The elevated concentrations occurring in summer suggests that N breakthrough has occurred. By examining the ratio of NO3? to total strong acid anions, it is shown that NO3? contributes significantly to freshwater acidity, particularly during the winter. Redundancy analysis shows that NO3? leaching is greatest, both in winter and summer, in catchments with high proportions of bare rock where soil and vegetation cover is limited. Nitrogen cycling in these catchments, generally at higher altitudes, may no longer be governed by seasonal biological controls. They are likely to be saturated with respect to nitrogen (i.e. incapable of further N retention) as a result of the elevated deposition levels in the area. The contribution of NO3? to acidity is also greatest at these sites. In winter, significant positive relationships are also evident between NO3? concentration and soil pH and coniferous woodland. The study demonstrates the importance of catchment factors in modifying the relationship between N deposition and N leaching in upland catchments
Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos
We suggest that recent neutrino puzzles that are the solar and atmospheric
neutrino deficits as well as the possible neutrino oscillations reported by the
LSND experiment and the possibility of massive neutrinos providing the hot
component of the cosmological dark matter, can all be naturally explained by
assuming existence of a mirror world described by an ``electroweak'' gauge
symmetry , with the breaking scale larger by about factor
of 30 than the scale of the standard model. An interesting
aspect of this model is that the sterile neutrinos arise from the hidden mirror
sector of the theory and thus their lightness is more natural than in the usual
neutrino mass scenarios. The needed pattern of the neutrino mass matrix in this
model is obtained by assuming a conserved ZKM-type global lepton number , which is violated by Planck scale effects. One implication
of our proposal is that bulk of the dark matter in the universe is a warm dark
matter consisting of few KeV mass particles rather than the 100 GeV range
particles of the currently popular cold dark matter scenarios.Comment: 10 pages, Latex, no figure
Magnetic fields in the early universe in the string approach to MHD
There is a reformulation of magnetohydrodynamics in which the fundamental
dynamical quantities are the positions and velocities of the lines of magnetic
flux in the plasma, which turn out to obey equations of motion very much like
ideal strings. We use this approach to study the evolution of a primordial
magnetic field generated during the radiation-dominated era in the early
Universe. Causality dictates that the field lines form a tangled random
network, and the string-like equations of motion, plus the assumption of
perfect reconnection, inevitably lead to a self-similar solution for the
magnetic field power spectrum. We present the predicted form of the power
spectrum, and discuss insights gained from the string approximation, in
particular the implications for the existence or not of an inverse cascade.Comment: 12 pages, 2 figure
The Age Of Globular Clusters In Light Of Hipparcos: Resolving the Age Problem?
We review five independent techniques which are used to set the distance
scale to globular clusters, including subdwarf main sequence fitting utilizing
the recent Hipparcos parallax catalogue. These data together all indicate that
globular clusters are farther away than previously believed, implying a
reduction in age estimates. This new distance scale estimate is combined with a
detailed numerical Monte Carlo study designed to assess the uncertainty
associated with the theoretical age-turnoff luminosity relationship in order to
estimate both the absolute age and uncertainty in age of the oldest globular
clusters. Our best estimate for the mean age of the oldest globular clusters is
now Gyr, with a one-sided, 95% confidence level lower limit of
9.5 Gyr. This represents a systematic shift of over 2 compared to our
earlier estimate, due completely to the new distance scale---which we emphasize
is not just due to the Hipparcos data. This now provides a lower limit on the
age of the universe which is consistent with either an open universe, or a
flat, matter dominated universe (the latter requiring H_0 \le 67 \kmsmpc).
Our new study also explicitly quantifies how remaining uncertainties in the
distance scale and stellar evolution models translate into uncertainties in the
derived globular cluster ages. Simple formulae are provided which can be used
to update our age estimate as improved determinations for various quantities
become available.Comment: 41 pages, including 10 eps figs, uses aaspp4.sty and flushrt.sty,
submitted to Ap.J., revised to incorporate FULL Hipparcos catalogue dat
Big Bang Nucleosynthesis Constraints on Primordial Magnetic Fields
We reanalyze the effect of magnetic fields in BBN, incorporating several
features which were omitted in previous analyses. We find that the effects of
coherent magnetic fields on the weak interaction rates and the electron
thermodynamic functions (\rhoe, \Pe, and \drhoedt ) are unimportant in
comparison to the contribution of the magnetic field energy density in BBN. In
consequence the effect of including magnetic fields in BBN is well approximated
numerically by treating the additional energy density as effective neutrino
number. A conservative upper bound on the primordial magnetic field,
parameterized as , is (). This bound can be stronger than the conventional bound coming from
the Faraday rotation measures of distant quasars if the cosmological magnetic
field is generated by a causal mechanism.Comment: Latex, 20 pages, 3 uuencoded figures appende
Spin-Flavour Oscillations and Neutrinos from SN1987A
The neutrino signal from SN1987A is analysed with respect to spin-flavour
oscillations between electron antineutrinos, , and muon
neutrinos, , by means of a maximum likelihood analysis.
Following Jegerlehner et al. best fit values for the total energy released in
neutrinos, , and the temperature of the electron antineutrino,
, for a range of mixing parameters and progenitor models are
calculated. In particular the dependence of the inferred quantities on the
metallicity of the supernova is investigated and the uncertainties involved in
using the neutrino signal to determine the neutrino magnetic moment are pointed
out.Comment: 14 pages, RevTeX, 4 figures, to appear in Physical Review
Limits on Active-Sterile Neutrino Mixing and the Primordial Deuterium Abundance
Studies of limits on active-sterile neutrino mixing derived from big bang
nucleosynthesis considerations are extended to consider the dependance of these
constraints on the primordial deuterium abundance. This study is motivated by
recent measurements of D/H in quasar absorption systems, which at present yield
discordant results. Limits on active-sterile mixing are somewhat relaxed for
high D/H. For low D/H (), no active-sterile neutrino
mixing is allowed by currently popular upper limits on the primordial He
abundance . For such low primordial D/H values, the observational inference
of active-sterile neutrino mixing by upcoming solar neutrino experiments would
imply that has been systematically underestimated, unless there is new
physics not included in standard BBN.Comment: 10 pages + 2 figures, uses revtex macros, submitted to Phys. Rev. D.
Corrected figure captions and an added referenc
Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models
We re-examine the evolution of neutrino asymmetries in several four neutrino
models. The first case involves the direct creation of by oscillations. In the second case, we consider the mass
hierarchy where oscillations generate a large and some of
this asymmetry is converted into by oscillations. We estimate the implications for BBN for a range of
cosmologically interesting values. The present paper improves on
previous published work by taking into account the finite repopulation rate and
the time dependence of the distortions to the neutrino momentum distributions.
The treatment of chemical decoupling is also improved.Comment: Expanded discussion on the sign of the neutrino asymmetr
Testing The Friedmann Equation: The Expansion of the Universe During Big-Bang Nucleosynthesis
In conventional general relativity, the expansion rate H of a
Robertson-Walker universe is related to the energy density by the Friedmann
equation. Aside from the present day, the only epoch at which we can constrain
the expansion history in a model-independent way is during Big-Bang
Nucleosynthesis (BBN). We consider a simple two-parameter characterization of
the behavior of H during BBN and derive constraints on this parameter space,
finding that the allowed region of parameter space is essentially
one-dimensional. We also study the effects of a large neutrino asymmetry within
this framework. Our results provide a simple way to compare an alternative
cosmology to the observational requirement of matching the primordial
abundances of the light elements.Comment: 18 pages, Final version to be published in Phys. Rev.
- …