30,290 research outputs found
Obtaining a class of Type N pure radiation metrics using invariant operators
We develop further the integration procedure in the generalised invariant
formalism, and demonstrate its efficiency by obtaining a class of Petrov type N
pure radiation metrics without any explicit integration, and with comparatively
little detailed calculations. The method is similar to the one exploited by
Edgar and Vickers when deriving the general conformally flat pure radiation
metric. A major addition to the technique is the introduction of non-intrinsic
elements in generalised invariant formalism, which can be exploited to keep
calculations manageable.Comment: This work was presented in July 2004, in the Gr17 meeting held in
Dublin-Irelan
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
Towards a new determination of the QCD Lambda parameter from running couplings in the three-flavour theory
We review our new strategy and current status towards a high precision
computation of the Lambda parameter from three-flavour simulations in QCD. To
reach this goal we combine specific advantages of the Schr\"odinger functional
and gradient flow couplings.Comment: 7 pages, 3 figures; Proceedings of the 32nd International Symposium
on Lattice Field Theory; 23-28 June, 2014, Columbia University, New Yor
I-V curves of Fe/MgO (001) single- and double-barrier tunnel junctions
In this work, we calculate with ab initio methods the current-voltage
characteristics for ideal single- and double-barrier Fe/MgO (001) magnetic
tunnel junctions. The current is calculated in the phase-coherent limit by
using the recently developed SMEAGOL code, combining the nonequilibrium Green
function formalism with density-functional theory. In general we find that
double-barrier junctions display a larger magnetoresistance, which decays with
bias at a slower pace than their single-barrier counterparts. This is explained
in terms of enhanced spin filtering from the middle Fe layer sandwiched in
between the two MgO barriers. In addition, for double-barrier tunnel junctions,
we find a well defined peak in the magnetoresistance at a voltage of V=0.1 V.
This is the signature of resonant tunneling across a majority quantum well
state. Our findings are discussed in relation to recent experiments
The -parameter in 3-flavour QCD and by the ALPHA collaboration
We present results by the ALPHA collaboration for the -parameter in
3-flavour QCD and the strong coupling constant at the electroweak scale,
, in terms of hadronic quantities computed on the CLS gauge
configurations. The first part of this proceedings contribution contains a
review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields
the -parameter in units of a low energy scale, . We
then discuss how to determine this scale in physical units from experimental
data for the pion and kaon decay constants. We obtain MeV which translates to
using perturbation theory to match between 3-, 4- and 5-flavour QCD.Comment: 21 pages. Collects contributions of A. Ramos, S. Sint and R. Sommer
to the 34th annual International Symposium on Lattice Field Theory; LaTeX
input encoding problem fixe
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