522 research outputs found
Developing frameworks for studies on sedimentary fluxes and budgets in changing cold environments
Geomorphic processes that are responsible for the transfer of sediments and landform change are highly dependent on climate and vegetation cover. It is anticipated that climate change will have a major impact on the behaviour of Earth surface systems and that the most profound changes will occur in high-latitude and high-altitude cold environments. Collection, comparison and evaluation of data from a range of different high-latitude and high-altitude cold environments are required to permit greater understanding of sedimentary fluxes in cold environments. The focus of the I.A.G./A.I.G. SEDIBUD (Sediment Budgets in Cold Environments) Programme is the analysis of source-to-sink fluxes and sediment budgets in changing cold environments. Establishing contemporary sediment fluxes in a diversity of cold environments will form a baseline for modelling. At a minimum, baseline information from defined SEDIBUD test sites must consist of measures of mean annual precipitation, stream discharge, suspended load, conductivity/TDS and dominant catchment processes. Reports from ongoing studies on sedimentary fluxes and budgets in three selected study sites in Arctic Canada, sub-Arctic Iceland and sub-Arctic Norway are presented and discussed in the context of effects of climate change on process rates and sediment budgets in sensitive cold environments. Comparable datasets and coordinated data collection and data exchange will be of use for the individual studies at the different study sites. In addition, comparable data sets and data exchange will help to improve our understanding of existing relationships between contemporary climate and sedimentary fluxes and will enable larger-scale integrated investigations on effects of climate change in changing cold environments
Consequences of permafrost degradation for Arctic infrastructure - Bridging the model gap between regional and engineering scales
Infrastructure built on perennially frozen ice-rich ground relies heavily on thermally stable subsurface conditions. Climate-warming-induced deepening of ground thaw puts such infrastructure at risk of failure. For better assessing the risk of large-scale future damage to Arctic infrastructure, improved strategies for model-based approaches are urgently needed.
We used the laterally coupled 1D heat conduction model CryoGrid3 to simulate permafrost degradation affected by linear infrastructure. We present a case study of a gravel road built on continuous permafrost (Dalton highway, Alaska) and forced our model under historical and strong future warming conditions (following the RCP8.5 scenario). As expected, the presence of a gravel road in the model leads to higher net heat flux entering the ground compared to a reference run without infrastructure and thus a higher rate of thaw. Further, our results suggest that road failure is likely a consequence of lateral destabilisation due to talik formation in the ground beside the road rather than a direct consequence of a top-down thawing and deepening of the active layer below the road centre. In line with previous studies, we identify enhanced snow accumulation and ponding (both a consequence of infrastructure presence) as key factors for increased soil temperatures and road degradation. Using differing horizontal model resolutions we show that it is possible to capture these key factors and their impact on thawing dynamics with a low number of lateral model units, underlining the potential of our model approach for use in pan-Arctic risk assessments.
Our results suggest a general two-phase behaviour of permafrost degradation: an initial phase of slow and gradual thaw, followed by a strong increase in thawing rates after the exceedance of a critical ground warming. The timing of this transition and the magnitude of thaw rate acceleration differ strongly between undisturbed tundra and infrastructure-affected permafrost ground. Our model results suggest that current model-based approaches which do not explicitly take into account infrastructure in their designs are likely to strongly underestimate the timing of future Arctic infrastructure failure.
By using a laterally coupled 1D model to simulate linear infrastructure, we infer results in line with outcomes from more complex 2D and 3D models, but our model's computational efficiency allows us to account for long-term climate change impacts on infrastructure from permafrost degradation. Our model simulations underline that it is crucial to consider climate warming when planning and constructing infrastructure on permafrost as a transition from a stable to a highly unstable state can well occur within the service lifetime (about 30 years) of such a construction. Such a transition can even be triggered in the coming decade by climate change for infrastructure built on high northern latitude continuous permafrost that displays cold and relatively stable conditions today.publishedVersio
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
Production of Y(1S) Mesons from chib Decays in pp(bar) Collisions at sqrt(s)=1.8 TeV
We have reconstructed the radiative decays and in collisions
at TeV, and measured the fraction of mesons
that originate from these decays. For mesons with
GeV/, the fractions that come from and
decays are and
, respectively. We have derived the fraction of
directly produced mesons to be .Comment: 13 Pages, 2 figure
Measurement of the Decay Amplitudes of B0 --> J/psi K* and B0s --> J/psi phi Decays
A full angular analysis has been performed for the pseudo-scalar to
vector-vector decays, B0 --> J/psi K* and B_s --> J/psi phi, to determine the
amplitudes for decays with parity-even longitudinal and transverse polarization
and parity-odd transverse polarization. The measurements are based on 190 B0
candidates and 40 B_s candidates collected from a data set corresponding to 89
inverse pb of pbarp collisions at root(s) = 1.8 TeV at the Fermilab Tevatron.
In both decays the decay amplitude for longitudinal polarization dominates and
the parity-odd amplitude is found to be small.Comment: 7 pages, 3 figures, 1 tabl
Search for the Supersymmetric Partner of the Top-Quark in Collisions at
We report on a search for the supersymmetric partner of the top quark (stop)
produced in events using of
collisions at recorded with the Collider Detector at
Fermilab. In the case of a light stop squark, the decay of the top quark into
stop plus the lightest supersymmetric particle (LSP) could have a significant
branching ratio. The observed events are consistent with Standard Model production and decay. Hence, we set limits on the branching ratio of
the top quark decaying into stop plus LSP, excluding branching ratios above 45%
for a LSP mass up to 40 {\rm GeV/c}.Comment: 11 pages, 4 figure
Measurement of the Helicity of W Bosons in Top Quark Decays
We use the transverse momentum spectrum of leptons in the decay chain t-->bW
with W-->l nu to measure the helicity of the W bosons in the top quark rest
frame. Our measurement uses a ttbar sample isolated in 106 +/- 4 inverse
picobarns of data collected in ppbar collisions at sqrt(s)=1.8 TeV with the CDF
detector at the Fermilab Tevatron. Assuming a standard V--A weak decay, we find
that the fraction of W's with zero helicity in the top rest frame is F_0 = 0.91
+/- 0.37 (stat) +/- 0.13 (syst), consistent with the standard model prediction
of F_0=0.70 for a top mass of 175 GeV/c**2.Comment: Submitted to PRL. 8 pages, 2 figure
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