465 research outputs found
TALOS Dome Migration: Preliminary Results
Ice divide-dome migration is a key parameter in mass balance studies and in the interpretation of ice cores. The stability of the dome and position of the ice divide must be known to accurately interpret ice core records and to complete mass balance studies. Models of depth-age relationships for deep ice cores are sensitive to migration of the dome position (Anandakrishnan et al., 1994). The evolution of an ice divide is driven by the accumulation-rate history, its spatial pattern and conditions at ice-sheet boundaries (e.g. Frezzotti et al., 2004; Hindmarsh, 1996; Nereson et al., 1998). Ice divide migration is also important in determining the input parameter of large Antarctic drainage basins. Due to the very low slope (less than a decimetre per km) of East Antarctic domes and to surface morphology (e.g. sastrugi), it is very difficult to determine the summit point of a dome and its migration in time. In 2004 a new ice coring project, TALDICE (Talos Dome Ice
Core Project), started at TD to recover 1550 m of ice spanning the last 120 000 years (Frezzotti et al., 2004). This paper discusses preliminary findings on the present and past morphology of Talos Dome based on detailed snow accumulation data, radar-derived isochrons and ice velocity measurements in the last 10 years
The Frontier Mountain meteorite gap (Antarctica)
The Frontier Mountain blue ice field is an important Antarctic meteorite trap which has yielded 472 meteorite specimens since its discovery in 1984. Remote sensing analyses and field campaigns from 1993 to 1999 have furnished new glaciological data on ice flow, ice thickness, bedrock topography, ice ablation and surface mass transport by wind, along with detailed descriptions of the field situation at the trap. This solid set of data combined with an updated meteorite distribution map and terrestrial ages available from literature allows us to better describe the nature of the concentration mechanism. In particular, we observe that the meteorite trap forms in a blue ice field i) located upstream of an absolute and a shallow subice barriers; ii) characterized by compressive ice flow with horizontal velocities decreasing from 100 to <10 cm a-1 on approaching the obstacle; iii) undergoing mean ablation rates of 6.5 cm a-1; iv) nourished by a limited snow accumulation zone extending ~20 km upstream of the blue ice area. We also draw the following conclusions: i) the origin of the meteorite trap can be explained according to the present-day glaciological situation; ii) the meteorite concentration develops according to the general principles of the “ice flow model”; iii) the accumulation model can be described as “stagnant ice or slow-moving ice against an absolute and submerged barriers”, according to the descriptive schemes present in literature; iv) the Frontier Mountain ice field is an effective trap for meteorites weighing more than ~200 g; for smaller masses, the combination of wind and glacial drift may remove meteorites in less than a few tens of ka; v) although the activation age of the FM trap is not yet constrained, we infer that one of the most important findsite may be as old as 50 ka, i.e. older than the Last Glacial Maximum
Non-perturbative Test of the Witten-Veneziano Formula from Lattice QCD
We compute both sides of the Witten-Veneziano formula using lattice
techniques. For the one side we perform dedicated quenched simulations and use
the spectral projector method to determine the topological susceptibility in
the pure Yang-Mills theory. The other side we determine in lattice QCD with
dynamical Wilson twisted mass fermions including for the first time
also the flavour singlet decay constant. The Witten-Veneziano formula
represents a leading order expression in the framework of chiral perturbation
theory and we also employ leading order chiral perturbation theory to relate
the flavor singlet decay constant to the relevant decay constant parameters in
the quark flavor basis and flavor non-singlet decay constants. After taking the
continuum and the SU chiral limits we compare both sides and find good
agreement within uncertainties.Comment: 30 pages, 7 figures, version accepted for publicatio
Climate variability along latitudinal and longitudinal transects in East Antarctica
AbstractIn the framework of the International Trans-Antarctic Scientific Expedition (ITASE) programme, France and Italy carried out a traverse along one west–east and two north–south transects in East Antarctica from November 2001 to January 2002. Eighteen shallow snow–firn cores were drilled, and surface snow samples were collected every 5km along the traverse. Firn temperatures were measured in boreholes down to 30 m. The cores were analyzed for β radioactivity to obtain snow accumulation-rate data. The surface snow samples were analyzed for δ18O to correlate isotopic values with borehole temperatures. Multiple regression analysis shows a global near-dry-adiabatic lapse rate and a latitudinal lapse rate of 1.05˚C(˚ lat. S)–1, in the Dome C drainage area. Analysis of firn temperatures reveals a super-adiabatic lapse rate along the ice divide between Talos Dome and the Southern Ocean coast, and in some sectors along the ice divide between the Astrolabe Basin and D59. Snow accumulation rates and firn temperatures show warmer temperatures and higher accumulation values close to the ice divides extending from Talos Dome and Dome C to the Southern Ocean. The spatial pattern of data is linked with a katabatic-wind-source basin and moisture-source region
Light quark masses and pseudoscalar decay constants from Nf=2 Lattice QCD with twisted mass fermions
We present the results of a lattice QCD calculation of the average up-down
and strange quark masses and of the light meson pseudoscalar decay constants
with Nf=2 dynamical fermions. The simulation is carried out at a single value
of the lattice spacing with the twisted mass fermionic action at maximal twist,
which guarantees automatic O(a)-improvement of the physical quantities. Quark
masses are renormalized by implementing the non-perturbative RI-MOM
renormalization procedure. Our results for the light quark masses are
m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +-
9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +-
3.1 MeV and the ratio fK/fpi=1.227 +- 0.009 +- 0.024. From this ratio, by using
the experimental determination of Gamma(K-> mu nu (gamma))/Gamma(pi -> mu nu
(gamma)) and the average value of |Vud| from nuclear beta decays, we obtain
|Vus|=0.2192(5)(45), in agreement with the determination from Kl3 decays and
the unitarity constraint.Comment: 20 pages, 5 figure
Going chiral: overlap versus twisted mass fermions
We compare the behavior of overlap fermions, which are chirally invariant,
and of Wilson twisted mass fermions at full twist in the approach to the chiral
limit. Our quenched simulations reveal that with both formulations of lattice
fermions pion masses of O(250 MeV) can be reached in practical applications.
Our comparison is done at a fixed value of the lattice spacing a=0.123 fm. A
number of quantities are measured such as hadron masses, pseudoscalar decay
constants and quark masses obtained from Ward identities. We also determine the
axial vector renormalization constants in the case of overlap fermions.Comment: 22 pages, 10 figure
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