1,554 research outputs found
Bose-Glass behaviour in Bi_{2}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{8} crystals with columnar defects: experimental evidence for variable-range hopping
We report on vortex transport in Bi_{2}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{8}
crystals irradiated at different doses of heavy ions. We show evidence of a
flux-creep resistivity typical of a variable-range vortex hopping mechanism as
predicted by Nelson and Vinokur.Comment: 5 pages LaTeX2e (uses elsart.cls), 1 Encapsulated PostScript figur
A portable platform for accelerated PIC codes and its application to GPUs using OpenACC
We present a portable platform, called PIC_ENGINE, for accelerating
Particle-In-Cell (PIC) codes on heterogeneous many-core architectures such as
Graphic Processing Units (GPUs). The aim of this development is efficient
simulations on future exascale systems by allowing different parallelization
strategies depending on the application problem and the specific architecture.
To this end, this platform contains the basic steps of the PIC algorithm and
has been designed as a test bed for different algorithmic options and data
structures. Among the architectures that this engine can explore, particular
attention is given here to systems equipped with GPUs. The study demonstrates
that our portable PIC implementation based on the OpenACC programming model can
achieve performance closely matching theoretical predictions. Using the Cray
XC30 system, Piz Daint, at the Swiss National Supercomputing Centre (CSCS), we
show that PIC_ENGINE running on an NVIDIA Kepler K20X GPU can outperform the
one on an Intel Sandybridge 8-core CPU by a factor of 3.4
Metal-to-insulator crossover and pseudogap in single-layer compound BiSrCuO single crystals in high magnetic fields
The in-plane and the out-of-plane
magneto-transport in magnetic fields up to 28 T has been investigated in a
series of high quality, single crystal, hole-doped La-free Bi2201 cuprates for
a wide doping range and over a wide range of temperatures down to 40 mK. With
decreasing hole concentration going from the overdoped (p=0.2) to the
underdoped (p=0.12) regimes, a crossover from a metallic to and insulating
behavior of is observed in the low temperature normal state,
resulting in a disorder induced metal insulator transition. In the zero
temperature limit, the normal state ratio of the
heavily underdoped samples in pure Bi2201 shows an anisotropic 3D behavior, in
striking contrast with that observed in La-doped Bi2201 and LSCO systems. Our
data strongly support that that the negative out-of-plane magnetoresistance is
largely governed by interlayer conduction of quasiparticles in the
superconducting state, accompanied by a small contribution of normal state
transport associated with the field dependent pseudogap. Both in the optimal
and overdoped regimes, the semiconducting behavior of persists even
for magnetic fields above the pseudogap closing field . The method
suggested by Shibauchi \textit{et al.} (Phys. Rev. Lett. \textbf{86}, 5763,
(2001)) for evaluating is unsuccessful for both under- and overdoped
Bi2201 samples. Our findings suggest that the normal state pseudogap is not
always a precursor of superconductivity.Comment: 11 pages, 8 figures, published in PRB Nov 200
ULF/ELF electromagnetic fields produced in a conducting medium of infinite extent by linear current sources of infinite length
A previous analysis of a linear current source of finite length embedded in a conducting medium of infinite extent is extended to linear current sources of (1) infinite length and (2) semi-infinite length. Electric and magnetic field expressions are derived, and the results are numerically evaluated for frequencies in the ULF/ELF bands. For convenience, some of the results are presented in a dimensionless form. A comparison is made between the electromagnetic fields produced by linear current sources of finite and infinite length, and it is shown that there is a relative enhancement in the electric field near the source of finite length. It is also found that an optimum frequency exists for the electric field produced by a linear current source of infinite length at which the field amplitude is a maximum at a fixed observation point. Some practical applications of our results are suggested
ULF/ELF electromagnetic fields generated along the sea floor interface by a straight current source of infinite length
Propagation of ULF/ELF electromagnetic fields along the seafloor interface (assumed to be a plane boundary separating two semi-infinite conducting media) is considered. Earlier expressions for the electromagnetic fields generated by a straight current source of infinite length are applied to the sea/seabed interface. The field components are calculated numerically and are compared to the field components in seawater of infinite extent. At the seafloor boundary, the fields can propagate longer distances because of the lower seabed conductivities. The new horizontal component of the magnetic field generated as a result of the existence of the sea/seabed interface becomes larger than the vertical component of the magnetic field at large distances; it is also more sensitive to the conductivity of the seabed at low frequencies. The results indicate that there is an optimal frequency at which two of the field components have a maximum field intensity at a certain distance from the source. Some practical applications are discussed
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