81,370 research outputs found
(13)C NMR investigation of the superconductor MgCNi_3 up to 800K
We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et
al., Nature (411), 54 (2001)). We found that both the uniform spin
susceptibility and the spin fluctuations show a strong enhancement with
decreasing temperature, and saturate below ~50K and ~20K respectively. The
nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for
isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that
grows with decreasing magnetic field.Comment: Accepted for publication in Physical Review Letter
A Template for Implementing Fast Lock-free Trees Using HTM
Algorithms that use hardware transactional memory (HTM) must provide a
software-only fallback path to guarantee progress. The design of the fallback
path can have a profound impact on performance. If the fallback path is allowed
to run concurrently with hardware transactions, then hardware transactions must
be instrumented, adding significant overhead. Otherwise, hardware transactions
must wait for any processes on the fallback path, causing concurrency
bottlenecks, or move to the fallback path. We introduce an approach that
combines the best of both worlds. The key idea is to use three execution paths:
an HTM fast path, an HTM middle path, and a software fallback path, such that
the middle path can run concurrently with each of the other two. The fast path
and fallback path do not run concurrently, so the fast path incurs no
instrumentation overhead. Furthermore, fast path transactions can move to the
middle path instead of waiting or moving to the software path. We demonstrate
our approach by producing an accelerated version of the tree update template of
Brown et al., which can be used to implement fast lock-free data structures
based on down-trees. We used the accelerated template to implement two
lock-free trees: a binary search tree (BST), and an (a,b)-tree (a
generalization of a B-tree). Experiments show that, with 72 concurrent
processes, our accelerated (a,b)-tree performs between 4.0x and 4.2x as many
operations per second as an implementation obtained using the original tree
update template
Higgs triplets at like-sign linear colliders and neutrino mixing
We study the phenomenology of the type-II seesaw model at a linear e^-e^-
collider. We show that the process e^-e^- \rightarrow alpha^-beta^- (alpha,
beta = e, mu, tau being charged leptons) mediated by a doubly charged scalar is
very sensitive to the neutrino parameters, in particular the absolute neutrino
mass scale and the Majorana CP-violating phases. We identify the regions in
parameter space in which appreciable collider signatures in the channel with
two like-sign muons in the final state are possible. This includes Higgs
triplet masses beyond the reach of the LHC.Comment: 8 pages, 6 figure
Pomeranchuk effect and spin-gradient cooling of Bose-Bose mixtures in an optical lattice
We theoretically investigate finite-temperature thermodynamics and
demagnetization cooling of two-component Bose-Bose mixtures in a cubic optical
lattice, by using bosonic dynamical mean field theory (BDMFT). We calculate the
finite-temperature phase diagram, and remarkably find that the system can be
heated from the superfluid into the Mott insulator at low temperature,
analogous to the Pomeranchuk effect in 3He. This provides a promising many-body
cooling technique. We examine the entropy distribution in the trapped system
and discuss its dependence on temperature and an applied magnetic field
gradient. Our numerical simulations quantitatively validate the spin-gradient
demagnetization cooling scheme proposed in recent experiments.Comment: 9 pages, 8 figure
Suppressing longitudinal double-layer oscillations by using elliptically polarized laser pulses in the hole-boring radiation pressure acceleration regime
It is shown that well collimated mono-energetic ion beams with a large
particle number can be generated in the hole-boring radiation pressure
acceleration regime by using an elliptically polarized laser pulse with
appropriate theoretically determined laser polarization ratio. Due to the
effect, the double-layer charge separation region is
imbued with hot electrons that prevent ion pileup, thus suppressing the
double-layer oscillations. The proposed mechanism is well confirmed by
Particle-in-Cell simulations, and after suppressing the longitudinal
double-layer oscillations, the ion beams driven by the elliptically polarized
lasers own much better energy spectrum than those by circularly polarized
lasers.Comment: 6 pages, 5 figures, Phys. Plasmas (2013) accepte
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