630 research outputs found
Increased aeolian activity during humidity shifts as recorded in a raised bog in south-west Sweden during the past 1700 years
International audienceAnalyses of testate amoebae and aeolian sediment influx (ASI) were used to reconstruct effective humidity changes and aeolian activity in the coastal zone of south-west Sweden. Cores were taken from an ombrotrophic peat sequence from the Undarsmosse bog. Since both types of analysis were carried out on the same core, a direct comparison between humidity fluctuations in the bog and aeolian activity was possible, potentially providing detailed information on atmospheric circulation changes in this region. Relatively wet bog surface conditions occurred from around 1500 to 1230 and 770 to 380 cal. yrs BP, whereas dry conditions dominated from ca. 1630 to 1530, 1160 to 830 and 300 to 50 cal. yrs BP. The transitions between these phases occurred within 60?100 years and are characterised by a major change in the testate amoebae assemblages. A watertable reconstruction was used to study the hydrological changes at the bog surface in more detail. ASI peak events were reconstructed around 1450, 1150, 850 and after 370 cal. yrs BP. Most interestingly, these aeolian activity peaks started during the recorded hydrological transitions, regardless of the direction of these shifts. Our results therefore suggest that humidity shifts in this region were associated with temporary intensifications of atmospheric circulation during the past 1700 years. Several ASI peaks apparently coincide with reduced solar activity, possibly suggesting a solar related cause for some of the observed events
Vertical zonation of testate amoebae in the Elatia Mires, northern Greece : palaeoecological evidence for a wetland response to recent climate change or autogenic processes?
The Elatia Mires of northern Greece are unique ecosystems of high conservation value. The mires are climatically marginal and may be sensitive to changing hydroclimate, while northern Greece has experienced a significant increase in aridity since the late twentieth century. To investigate the impact of recent climatic change on the hydrology of the mires, the palaeoecological record was investigated from three near-surface monoliths extracted from two sites. Testate amoebae were analysed as sensitive indicators of hydrology. Results were interpreted using transfer function models to provide quantitative reconstructions of changing water table depth and pH. AMS radiocarbon dates and 210Pb suggest the peats were deposited within the last c. 50 years, but do not allow a secure chronology to be established. Results from all three profiles show a distinct shift towards a more xerophilic community particularly noted by increases in Euglypha species. Transfer function results infer a distinct lowering of water tables in this period. A hydrological response to recent climate change is a tenable hypothesis to explain this change; however other possible explanations include selective test decay, vertical zonation of living amoebae, ombrotrophication and local hydrological change. It is suggested that a peatland response to climatic change is the most probable hypothesis, showing the sensitivity of marginal peatlands to recent climatic change
N2′→P3′ Phosphoramidate Glycerol Nucleic Acid as a Potential Alternative Genetic System
The long-term fate of permafrost peatlands under rapid climate warming
Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms
Search for Neutral Higgs Bosons in e+e- Collisions at sqrt(s) ~189GeV
A search for neutral Higgs bosons has been performed with the OPAL detector
at LEP, using approximately 170 pb-1 of e+e- collision data collected at
sqrt(s)~189GeV. Searches have been performed for the Standard Model (SM)
process e+e- to H0Z0 and the MSSM processes e+e- to H0Z0, A0h0. The searches
are sensitive to the b b-bar and tau antitau decay modes of the Higgs bosons,
and also to the MSSM decay mode h0 to A0A0. OPAL search results at lower
centre-of-mass energies have been incorporated in the limits we set, which are
valid at the 95% confidence level. For the SM Higgs boson, we obtain a lower
mass bound of 91.0 GeV. In the MSSM, our limits are mh>74.8GeV and mA>76.5GeV,
assuming tan(beta)>1, that the mixing of the scalar top quarks is either zero
or maximal, and that the soft SUSY-breaking masses are 1 TeV. For the case of
zero scalar top mixing, we exclude values of tan(beta) between 0.72 and 2.19.Comment: 38 pages, 15 figures, submitted Euro. Phys. J.
Bose-Einstein Correlations in e+e- to W+W- at 172 and 183 GeV
Bose-Einstein correlations between like-charge pions are studied in hadronic
final states produced by e+e- annihilations at center-of-mass energies of 172
and 183 GeV. Three event samples are studied, each dominated by one of the
processes W+W- to qqlnu, W+W- to qqqq, or (Z/g)* to qq. After demonstrating the
existence of Bose-Einstein correlations in W decays, an attempt is made to
determine Bose-Einstein correlations for pions originating from the same W
boson and from different W bosons, as well as for pions from (Z/g)* to qq
events. The following results are obtained for the individual chaoticity
parameters lambda assuming a common source radius R: lambda_same = 0.63 +- 0.19
+- 0.14, lambda_diff = 0.22 +- 0.53 +- 0.14, lambda_Z = 0.47 +- 0.11 +- 0.08, R
= 0.92 +- 0.09 +- 0.09. In each case, the first error is statistical and the
second is systematic. At the current level of statistical precision it is not
established whether Bose-Einstein correlations, between pions from different W
bosons exist or not.Comment: 24 pages, LaTeX, including 6 eps figures, submitted to European
Physical Journal
W+W- production and triple gauge boson couplings at LEP energies up to 183 GeV
A study of W-pair production in e+e- annihilations at Lep2 is presented,
based on 877 W+W- candidates corresponding to an integrated luminosity of 57
pb-1 at sqrt(s) = 183 GeV. Assuming that the angular distributions of the
W-pair production and decay, as well as their branching fractions, are
described by the Standard Model, the W-pair production cross-section is
measured to be 15.43 +- 0.61 (stat.) +- 0.26 (syst.) pb. Assuming lepton
universality and combining with our results from lower centre-of-mass energies,
the W branching fraction to hadrons is determined to be 67.9 +- 1.2 (stat.) +-
0.5 (syst.)%. The number of W-pair candidates and the angular distributions for
each final state (qqlnu,qqqq,lnulnu) are used to determine the triple gauge
boson couplings. After combining these values with our results from lower
centre-of-mass energies we obtain D(kappa_g)=0.11+0.52-0.37,
D(g^z_1)=0.01+0.13-0.12 and lambda=-0.10+0.13-0.12, where the errors include
both statistical and systematic uncertainties and each coupling is determined
setting the other two couplings to the Standard Model value. The fraction of W
bosons produced with a longitudinal polarisation is measured to be
0.242+-0.091(stat.)+-0.023(syst.). All these measurements are consistent with
the Standard Model expectations.Comment: 48 pages, LaTeX, including 13 eps or ps figures, submitted to
European Physical Journal
Measurements of Flavour Dependent Fragmentation Functions in Z^0 -> qq(bar) Events
Fragmentation functions for charged particles in Z -> qq(bar) events have
been measured for bottom (b), charm (c) and light (uds) quarks as well as for
all flavours together. The results are based on data recorded between 1990 and
1995 using the OPAL detector at LEP. Event samples with different flavour
compositions were formed using reconstructed D* mesons and secondary vertices.
The \xi_p = ln(1/x_E) distributions and the position of their maxima \xi_max
are also presented separately for uds, c and b quark events. The fragmentation
function for b quarks is significantly softer than for uds quarks.Comment: 29 pages, LaTeX, 5 eps figures (and colour figs) included, submitted
to Eur. Phys. J.
A Measurement of Rb using a Double Tagging Method
The fraction of Z to bbbar events in hadronic Z decays has been measured by
the OPAL experiment using the data collected at LEP between 1992 and 1995. The
Z to bbbar decays were tagged using displaced secondary vertices, and high
momentum electrons and muons. Systematic uncertainties were reduced by
measuring the b-tagging efficiency using a double tagging technique. Efficiency
correlations between opposite hemispheres of an event are small, and are well
understood through comparisons between real and simulated data samples. A value
of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is
statistical and the second systematic. The uncertainty on Rc, the fraction of Z
to ccbar events in hadronic Z decays, is not included in the errors. The
dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the
deviation of Rc from the value 0.172 predicted by the Standard Model. The
result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the
Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European
Physical Journal
Measurement of the B+ and B-0 lifetimes and search for CP(T) violation using reconstructed secondary vertices
The lifetimes of the B+ and B-0 mesons, and their ratio, have been measured in the OPAL experiment using 2.4 million hadronic Z(0) decays recorded at LEP. Z(0) --> b (b) over bar decays were tagged using displaced secondary vertices and high momentum electrons and muons. The lifetimes were then measured using well-reconstructed charged and neutral secondary vertices selected in this tagged data sample. The results aretau(B+) = 1.643 +/- 0.037 +/- 0.025 pstau(Bo) = 1.523 +/- 0.057 +/- 0.053 pstau(B+)/tau(Bo) = 1.079 +/- 0.064 +/- 0.041,where in each case the first error is statistical and the second systematic.A larger data sample of 3.1 million hadronic Z(o) decays has been used to search for CP and CPT violating effects by comparison of inclusive b and (b) over bar hadron decays, No evidence fur such effects is seen. The CP violation parameter Re(epsilon(B)) is measured to be Re(epsilon(B)) = 0.001 +/- 0.014 +/- 0.003and the fractional difference between b and (b) over bar hadron lifetimes is measured to(Delta tau/tau)(b) = tau(b hadron) - tau((b) over bar hadron)/tau(average) = -0.001 +/- 0.012 +/- 0.008
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