3,630 research outputs found
Physical weathering by glaciers enhances silicon mobilisation and isotopic fractionation
Glacial meltwaters export substantial quantities of dissolved and dissolvable amorphous silicon (DSi and ASi), providing an essential nutrient for downstream diatoms. Evidence suggests that glacially exported DSi is isotopically light compared to DSi in non-glaciated rivers. However, the isotopic fractionation mechanisms are not well constrained, indicating an important gap in our understanding of processes in the global Si cycle. We use rock crushing experiments to mimic subglacial physical erosion, to provide insight into subglacial isotope fractionation. Isotopically light DSi (ÎŽ30SiDSi) released following initial dissolution of freshly ground mineral surfaces (down to â2.12â±â0.02 â°) suggests mechanochemical reactions induce isotopic fractionation, explaining the low ÎŽ30SiDSi composition of subglacial runoff. ASi with a consistent isotopic composition is present in all mechanically weathered samples, but concentrations are elevated in samples that have undergone more intense physical grinding. These experiments illustrate the critical role of physical processes in driving isotopic fractionation and biogeochemical weathering in subglacial environments. Understanding perturbations in high latitude Si cycling under climatic change will likely depend on the response of mechanochemical weathering to increased glacial melt
The Road Towards the ILC: Higgs, Top/QCD, Loops
The International Linear e+e- Collider (ILC) could go into operation in the
second half of the upcoming decade. Experimental analyses and theory
calculations for the physics at the ILC are currently performed. We review
recent progress, as presented at the LCWS06 in Bangalore, India, in the fields
of Higgs boson physics and top/QCD. Also the area of loop calculations,
necessary to achieve the required theory precision, is included.Comment: 7 pages, 1 figure. Plenary talk given at the LCWS06 March 2006,
Bangalore, India. Top part slightly enlarged, references adde
Lepton Flavor Violation in Supersymmetric SO(10) Grand Unified Models
The study for lepton flavor violation combined with the neutrino oscillation
may provide more information about the lepton flavor structure of the grand
unified theory. In this paper, we study two lepton flavor violation processes,
and , in the context of supersymmetric SO(10)
grand unified models. We find the two processes are both of phenomenological
interest. In particular the latter may be important in some supersymmetric
parameter space where the former is suppressed. Thus, Z-dacay may offer another
chance for looking for lepton flavor violation.Comment: 26 pages, 10 figure
Silicon isotopes in Arctic and sub-Arctic glacial meltwaters:The role of subglacial weathering in the silicon cycle
Glacial environments play an important role in high-latitude marine nutrient cycling, potentially contributing signiïŹcant ïŹuxes of silicon (Si) to the polar oceans, either as dissolved silicon (DSi) or as dissolvable amorphous silica (ASi). Silicon is a key nutrient in promoting marine primary productivity, contributingto atmosphericCO2 removal.We present the current understanding of Si cycling in glacial systems,focusingontheSiisotope(ÎŽ30Si)composition of glacial meltwaters. We combine existing glacial ÎŽ30Si data with new measurements from 20 subArctic glaciers, showing that glacial meltwaters consistently export isotopically light DSi compared with non-glacial rivers (+0.16â° versus +1.38â°). Glacial ÎŽ30SiASi composition ranges from â0.05â° to â0.86â° but exhibits low seasonal variability. Silicon ïŹuxes and ÎŽ30Si composition from glacial systems are not commonly included in global Si budgets and isotopic mass balance calculations at present. We discuss outstanding questions, including the formation mechanism of ASi and the export of glacial nutrients from fjords. Finally, we provide a contextual framework for the recent advances in our understanding of subglacial Si cycling and highlight critical research avenues for assessing potential future changes in these environments
Lepton flavor violation two-body decays of quarkoniums
In this paper we firstly study various model-independent bounds on lepton
flavor violation (LFV) in processes of , and
two-body decays, then calculate their branch ratios % By using the constraints
from other ways, we obtain %the indirect bounds of in models of the leptoquark, violating
MSSM and topcolor assisted technicolor(TC2) models.Comment: 14 pages, 4 figures, submitted to PR
Lepton flavor conserving Z -> l^+ l^-$ decays in the general two Higgs doublet model
We calculate the new physics effects to the branching ratios of the lepton
flavor conserving decays Z -> l^+ l^- in the framework of the general two Higgs
Doublet model. We predict the upper limits for the couplings
|\bar{\xi}^{D}_{N,\mu\tau}| and |\bar{\xi}^{D}_{N,\tau\tau}| as 3\times 10^2
GeV and 1\times 10^2 GeV, respectively.Comment: 9 pages, 3 figure
Patterns in Microbial Assemblages Exported From the Meltwater of Arctic and Sub-Arctic Glaciers
Meltwater streams connect the glacial cryosphere with downstream ecosystems. Dissolved and particulate matter exported from glacial ecosystems originates from contrasting supraglacial and subglacial environments, and exported microbial cells have the potential to serve as ecological and hydrological indicators for glacial ecosystem processes. Here, we compare exported microbial assemblages from the meltwater of 24 glaciers from six (sub)Arctic regions - the southwestern Greenland Ice Sheet, Qeqertarsuaq (Disko Island) in west Greenland, Iceland, Svalbard, western Norway, and southeast Alaska - differing in their lithology, catchment size, and climatic characteristics, to investigate spatial and environmental factors structuring exported meltwater assemblages. We found that 16S rRNA gene sequences of all samples were dominated by the phyla Proteobacteria, Bacteroidetes, and Actinobacteria, with Verrucomicrobia also common in Greenland localities. Clustered OTUs were largely composed of aerobic and anaerobic heterotrophs capable of degrading a wide variety of carbon substrates. A small number of OTUs dominated all assemblages, with the most abundant being from the genera Polaromonas, Methylophilus, and Nitrotoga. However, 16-32% of a region's OTUs were unique to that region, and rare taxa revealed unique metabolic potentials and reflected differences between regions, such as the elevated relative abundances of sulfur oxidizers Sulfuricurvum sp. and Thiobacillus sp. at Svalbard sites. Meltwater alpha diversity showed a pronounced decrease with increasing latitude, and multivariate analyses of assemblages revealed significant regional clusters. Distance-based redundancy and correlation analyses further resolved associations between whole assemblages and individual OTUs with variables primarily corresponding with the sampled regions. Interestingly, some OTUs indicating specific metabolic processes were not strongly associated with corresponding meltwater characteristics (e.g., nitrification and inorganic nitrogen concentrations). Thus, while exported assemblage structure appears regionally specific, and probably reflects differences in dominant hydrological flowpaths, OTUs can also serve as indicators for more localized microbially mediated processes not captured by the traditional characterization of bulk meltwater hydrochemistry. These results collectively promote a better understanding of microbial distributions across the Arctic, as well as linkages between the terrestrial cryosphere habitats and downstream ecosystems
High export of dissolved silica from the Greenland Ice Sheet
Silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean. Glacial activity stimulates rock weathering, generating dissolved silica that is exported to coastal areas along with meltwater. The magnitude of the dissolved silica export from large glacial areas such as the Greenland Ice Sheet is presently poorly quantified and not accounted for in global budgets. Here we present data from two fjord systems adjacent to the Greenland Ice Sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients. Upscaled to the entire Greenland Ice Sheet, the export of dissolved silica equals 22â±â10âGmolâSiâyrâ1. When the silicate-rich meltwater mixes with upwelled deep water, either inside or outside Greenland's fjords, primary production takes place at increased silicate to nitrate ratios. This likely stimulates the growth of diatoms relative to other phytoplankton groups
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.
Bose-Einstein Correlations of Three Charged Pions in Hadronic Z^0 Decays
Bose-Einstein Correlations (BEC) of three identical charged pions were
studied in 4 x 10^6 hadronic Z^0 decays recorded with the OPAL detector at LEP.
The genuine three-pion correlations, corrected for the Coulomb effect, were
separated from the known two-pion correlations by a new subtraction procedure.
A significant genuine three-pion BEC enhancement near threshold was observed
having an emitter source radius of r_3 = 0.580 +/- 0.004 (stat.) +/- 0.029
(syst.) fm and a strength of \lambda_3 = 0.504 +/- 0.010 (stat.) +/- 0.041
(syst.). The Coulomb correction was found to increase the \lambda_3 value by
\~9% and to reduce r_3 by ~6%. The measured \lambda_3 corresponds to a value of
0.707 +/- 0.014 (stat.) +/- 0.078 (syst.) when one takes into account the
three-pion sample purity. A relation between the two-pion and the three-pion
source parameters is discussed.Comment: 19 pages, LaTeX, 5 eps figures included, accepted by Eur. Phys. J.
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