11,855 research outputs found
Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals
We report on the thermally activated flux flow dependency on the doping
dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using
the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found
clearly that irrespective of the doping ratio, magnetoresistivity showed a
distinct tail just above the Tc, offset associated with the thermally activated
flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature
dependence of the activation energy follows the relation U(T, B)=U_0 (B)
(1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence
of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the
exponent {\alpha} is changed from a low value to a high value at a crossover
field of B=~2T, indicating the transition from collective to plastic pinning in
the crystals. Finally, it is suggested that the 3D vortex phase is the dominant
phase in the low-temperature region as compared to the TAFF region in our
series samples
Steering effects on growth instability during step-flow growth of Cu on Cu(1,1,17)
Kinetic Monte Carlo simulation in conjunction with molecular dynamics
simulation is utilized to study the effect of the steered deposition on the
growth of Cu on Cu(1,1,17). It is found that the deposition flux becomes
inhomogeneous in step train direction and the inhomogeneity depends on the
deposition angle, when the deposition is made along that direction. Steering
effect is found to always increase the growth instability, with respect to the
case of homogeneous deposition. Further, the growth instability depends on the
deposition angle and direction, showing minimum at a certain deposition angle
off-normal to (001) terrace, and shows a strong correlation with the
inhomogeneous deposition flux. The increase of the growth instability is
ascribed to the strengthened step Erlich Schwoebel barrier effects that is
caused by the enhanced deposition flux near descending step edge due to the
steering effect.Comment: 5 page
Quasiparticle Interference on the Surface of Topological Crystalline Insulator Pb(1-x)Sn(x)Se
Topological crystalline insulators represent a novel topological phase of
matter in which the surface states are protected by discrete point
group-symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy
is one possible realization of this phase which undergoes a topological phase
transition upon changing the lead content. We used scanning tunneling
microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe
the surface states on (001) PbSnSe in the topologically
non-trivial (x=0.23) and topologically trivial (x=0) phases. We observed
quasiparticle interference with STM on the surface of the topological
crystalline insulator and demonstrated that the measured interference can be
understood from ARPES studies and a simple band structure model. Furthermore,
our findings support the fact that PbSnSe and PbSe have
different topological nature.Comment: 5 pages, 4 figure
Non-Gaussian errors of baryonic acoustic oscillations
We revisit the uncertainty in baryon acoustic oscillation (BAO) forecasts and
data analyses. In particular, we study how much the uncertainties on both the
measured mean dilation scale and the associated error bar are affected by the
non-Gaussianity of the non-linear density field. We examine two possible
impacts of non-Gaussian analysis: (1) we derive the distance estimators from
Gaussian theory, but use 1000 N-Body simulations to measure the actual errors,
and compare this to the Gaussian prediction, and (2) we compute new optimal
estimators, which requires the inverse of the non-Gaussian covariance matrix of
the matter power spectrum. Obtaining an accurate and precise inversion is
challenging, and we opted for a noise reduction technique applied on the
covariance matrices. By measuring the bootstrap error on the inverted matrix,
this work quantifies for the first time the significance of the non-Gaussian
error corrections on the BAO dilation scale. We find that the variance (error
squared) on distance measurements can deviate by up to 12% between both
estimators, an effect that requires a large number of simulations to be
resolved. We next apply a reconstruction algorithm to recover some of the BAO
signal that had been smeared by non-linear evolution, and we rerun the
analysis. We find that after reconstruction, the rms error on the distance
measurement improves by a factor of ~1.7 at low redshift (consistent with
previous results), and the variance ({\sigma}^2) shows a change of up to 18%
between optimal and sub-optimal cases (note, however, that these discrepancies
may depend in detail on the procedure used to isolate the BAO signal). We
finally discuss the impact of this work on current data analyses.Comment: 13 pages, 11 figures, MNRAS accepte
Spectroscopy of a narrow-line laser cooling transition in atomic dysprosium
The laser cooling and trapping of ultracold neutral dysprosium has been
recently demonstrated using the broad, open 421-nm cycling transition.
Narrow-line magneto-optical trapping of Dy on longer wavelength transitions
would enable the preparation of ultracold Dy samples suitable for loading
optical dipole traps and subsequent evaporative cooling. We have identified the
closed 741-nm cycling transition as a candidate for the narrow-line cooling of
Dy. We present experimental data on the isotope shifts, the hyperfine constants
A and B, and the decay rate of the 741-nm transition. In addition, we report a
measurement of the 421-nm transition's linewidth, which agrees with previous
measurements. We summarize the laser cooling characteristics of these
transitions as well as other narrow cycling transitions that may prove useful
for cooling Dy.Comment: 6+ pages, 5 figures, 5 table
A performance comparison of the contiguous allocation strategies in 3D mesh connected multicomputers
The performance of contiguous allocation strategies can be significantly affected by the distribution of job execution times. In this paper, the performance of the existing contiguous allocation strategies for 3D mesh multicomputers is re-visited in the context of heavy-tailed distributions (e.g., a Bounded Pareto distribution). The strategies are evaluated and compared using simulation experiments for both First-Come-First-Served (FCFS) and Shortest-Service-Demand (SSD) scheduling strategies under a variety of system loads and system sizes. The results show that the performance of the allocation strategies degrades considerably when job execution times follow a heavy-tailed distribution. Moreover, SSD copes much better than FCFS scheduling strategy in the presence of heavy-tailed job execution times. The results also show that the strategies that depend on a list of allocated sub-meshes for both allocation and deallocation have lower allocation overhead and deliver good system performance in terms of average turnaround time and mean system utilization
Asynchronous Graph Pattern Matching on Multiprocessor Systems
Pattern matching on large graphs is the foundation for a variety of
application domains. Strict latency requirements and continuously increasing
graph sizes demand the usage of highly parallel in-memory graph processing
engines that need to consider non-uniform memory access (NUMA) and concurrency
issues to scale up on modern multiprocessor systems. To tackle these aspects,
graph partitioning becomes increasingly important. Hence, we present a
technique to process graph pattern matching on NUMA systems in this paper. As a
scalable pattern matching processing infrastructure, we leverage a
data-oriented architecture that preserves data locality and minimizes
concurrency-related bottlenecks on NUMA systems. We show in detail, how graph
pattern matching can be asynchronously processed on a multiprocessor system.Comment: 14 Pages, Extended version for ADBIS 201
One-Dimensional Confinement and Enhanced Jahn-Teller Instability in LaVO
Ordering and quantum fluctuations of orbital degrees of freedom are studied
theoretically for LaVO in spin-C-type antiferromagnetic state. The
effective Hamiltonian for the orbital pseudospin shows strong one-dimensional
anisotropy due to the negative interference among various exchange processes.
This significantly enhances the instability toward lattice distortions for the
realistic estimate of the Jahn-Teller coupling by first-principle LDA+
calculations, instead of favoring the orbital singlet formation. This explains
well the experimental results on the anisotropic optical spectra as well as the
proximity of the two transition temperatures for spin and orbital orderings.Comment: 4 pages including 4 figure
Vertically-aligned graphene flakes on nanoporous templates: Morphology, thickness, and defect level control by pre-treatment
© 2014 National Institute for Materials Science. Various morphologies of the vertically-aligned graphene flakes were fabricated on the nanoporous templates treated with metal ions in solutions, as well as coated with a thin gold layer and activated in the low-temperature Ar plasma. The thickness and level of structural defects in the graphene flakes could be effectively controlled by a proper selection of the pre-treatment method. We have also demonstrated that various combinations of the flake thickness and defect levels can be obtained, and the morphology and density of the graphene pattern can be effectively controlled. The result obtained could be of interest for various applications requiring fabrication of large graphene networks with controllable properties
- …