5,058 research outputs found
Suppression of backward scattering of Dirac fermions in iron pnictides Ba(FeRuAs)
We report electronic transport of Dirac cones when Fe is replaced by Ru,
which has an isoelectronic electron configuration to Fe, using single crystals
of Ba(FeRuAs). The electronic transport of parabolic bands is
shown to be suppressed by scattering due to the crystal lattice distortion and
the impurity effect of Ru, while that of the Dirac cone is not significantly
reduced due to the intrinsic character of Dirac cones. It is clearly shown from
magnetoresistance and Hall coefficient measurements that the inverse of average
mobility, proportional to cyclotron effective mass, develops as the square root
of the carrier number (n) of the Dirac cones. This is the unique character of
the Dirac cone linear dispersion relationship. Scattering of Ru on the Dirac
cones is discussed in terms of the estimated mean free path using experimental
parameters.Comment: 6 pages, 3 figures, To be published in Phys. Rev.
Dimension Distortion by Right Coset Projections in the Heisenberg Group
We study the family of vertical projections whose fibers are right cosets of
horizontal planes in the Heisenberg group, . We prove lower
bounds for Hausdorff dimension distortion of sets under these mappings, with
respect to the Euclidean metric and also the natural quotient metric which we
show behaves like the Euclidean metric in this context. Our bounds are sharp in
a large part of the dimension range, and we give conjectural sharp lower bounds
for the remaining range. Our approach also lets us improve the known almost
sure lower bound for the standard family of vertical projections in
for
Tuberculous meningitis in children: reducing the burden of death and disability
Tuberculous meningitis disproportionately affects young children. As the most devastating form of tuberculosis, it is associated with unacceptably high rates of mortality and morbidity even if treated. Challenging to diagnose and treat, tuberculous meningitis commonly causes long-term neurodisability in those who do survive. There remains an urgent need for strengthened surveillance, improved rapid diagnostics technology, optimised anti-tuberculosis drug therapy, investigation of new host-directed therapy, and further research on long-term functional and neurodevelopmental outcomes to allow targeted intervention. This review focuses on the neglected field of paediatric tuberculous meningitis and bridges current clinical gaps with research questions to improve outcomes from this crippling disease
A natural-norm Successive Constraint Method for inf-sup lower bounds
We present a new approach for the construction of lower bounds for the inf-sup stability constants required in a posteriori error analysis of reduced basis approximations to affinely parametrized partial differential equations. We combine the âlinearizedâ inf-sup statement of the natural-norm approach with the approximation procedure of the Successive Constraint Method (SCM): the former (natural-norm) provides an economical parameter expansion and local concavity in parameterâa small(er) optimization problem which enjoys intrinsic lower bound properties; the latter (SCM) provides a systematic optimization frameworkâa Linear Program (LP) relaxation which readily incorporates continuity and stability constraints. The natural-norm SCM requires a parameter domain decomposition: we propose a greedy algorithm for selection of the SCM control points as well as adaptive construction of the optimal subdomains. The efficacy of the natural-norm SCM is illustrated through numerical results for two types of non-coercive problems: the Helmholtz equation (for acoustics, elasticity, and electromagnetics), and the convectionâdiffusion equation.United States. Air Force Office of Scientific Research (Grant No. FA 9550-07-1-0425
Unary Pushdown Automata and Straight-Line Programs
We consider decision problems for deterministic pushdown automata over a
unary alphabet (udpda, for short). Udpda are a simple computation model that
accept exactly the unary regular languages, but can be exponentially more
succinct than finite-state automata. We complete the complexity landscape for
udpda by showing that emptiness (and thus universality) is P-hard, equivalence
and compressed membership problems are P-complete, and inclusion is
coNP-complete. Our upper bounds are based on a translation theorem between
udpda and straight-line programs over the binary alphabet (SLPs). We show that
the characteristic sequence of any udpda can be represented as a pair of
SLPs---one for the prefix, one for the lasso---that have size linear in the
size of the udpda and can be computed in polynomial time. Hence, decision
problems on udpda are reduced to decision problems on SLPs. Conversely, any SLP
can be converted in logarithmic space into a udpda, and this forms the basis
for our lower bound proofs. We show coNP-hardness of the ordered matching
problem for SLPs, from which we derive coNP-hardness for inclusion. In
addition, we complete the complexity landscape for unary nondeterministic
pushdown automata by showing that the universality problem is -hard, using a new class of integer expressions. Our techniques have
applications beyond udpda. We show that our results imply -completeness for a natural fragment of Presburger arithmetic and coNP lower
bounds for compressed matching problems with one-character wildcards
The lowest eigenvalue of Jacobi random matrix ensembles and Painlev\'e VI
We present two complementary methods, each applicable in a different range,
to evaluate the distribution of the lowest eigenvalue of random matrices in a
Jacobi ensemble. The first method solves an associated Painleve VI nonlinear
differential equation numerically, with suitable initial conditions that we
determine. The second method proceeds via constructing the power-series
expansion of the Painleve VI function. Our results are applied in a forthcoming
paper in which we model the distribution of the first zero above the central
point of elliptic curve L-function families of finite conductor and of
conjecturally orthogonal symmetry.Comment: 30 pages, 2 figure
Silver and Palladium Complexes of a Bis(benzimidazolin-2-ylidene)pyridine Pincer Ligand
Reaction of 2,6-bis(3-butylbenzimidazol-1-ium)pyridine dibromide with silVer oxide affords a dinuclear complex of the type [L2Ag2]2+ [L ) 2,6-bis(3-butylbenzimidazolin-2-ylidene)pyridine]. 1H NMR spectroscopic studies suggest that the dinuclear structure is also present in solution. Transmetalationof the silVer-NHC complex with PdCl2(CH3CN)2 yields a mononuclear palladium complex of the type [LPdCl]+, with a chelating C,N,C pincer ligand
The TIANSHAN Radio Experiment for Neutrino Detection
An antenna array devoted to the autonomous radio-detection of high energy
cosmic rays is being deployed on the site of the 21 cm array radio telescope in
XinJiang, China. Thanks in particular to the very good electromagnetic
environment of this remote experimental site, self-triggering on extensive air
showers induced by cosmic rays has been achieved with a small scale prototype
of the foreseen antenna array. We give here a detailed description of the
detector and present the first detection of extensive air showers with this
prototype.Comment: 37 pages, 15 figures. Astroparticle Physics (in press
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