49,513 research outputs found
Hydrogen as a Source of Flux Noise in SQUIDs
Superconducting qubits are hampered by flux noise produced by surface spins
from a variety of microscopic sources. Recent experiments indicated that
hydrogen (H) atoms may be one of those sources. Using density functional theory
calculations, we report that H atoms either embedded in, or adsorbed on, an
a-Al2O3(0001) surface have sizeable spin moments ranging from 0.81 to 0.87 uB
with energy barriers for spin reorientation as low as ~10 mK. Furthermore, H
adatoms on the surface attract gas molecules such as O2, producing new spin
sources. We propose coating the surface with graphene to eliminate H-induced
surface spins and to protect the surface from other adsorbates.Comment: 12 pages, 4 figure
Fabrication and characterizations of proton-exchanged LiNbO3 waveguides fabricated by inductively coupled plasma technique
This Letter reports the use of an inductively coupled plasma technique for fabrication of proton-exchanged (PE) LiNbO3 (LN) waveguides. Planar and stripe waveguides have been formed in Y-cut LN which are difficult to obtain with the conventional molten acid method due to the occurrence of surface damage. Secondary ion mass spectrometry, scanning electron microscopy, and infrared absorption spectrum characterization results revealed that a uniform vertical PE profile with a single low order crystal phase has been directly obtained as a result of this unique process. X-ray photoelectron spectroscopy characterization of the treated surface revealed the existence of NbO as the cause for a sometimes darkened surface and confirms the ability to completely restore the surface to LN by oxygen plasma treatment. Atomic force microscopy measurement confirms that good surface quality has been maintained after regeneration of the surface to LN
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On the exceptional damage-tolerance of gradient metallic materials
An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse macro-scale to nano-scale (CG → NG) and vice versa (NG → CG), with the measured crack-resistance R-curves compared to the corresponding behavior in uniform nano-grained (NG) and coarse-grained (CG) materials. It is found that the gradient structures display a much-improved combination of high strength and toughness compared to uniform grain-sized materials. However, based on J-integral measurements in the gradient materials, the crack-initiation toughness is far higher for cracks grown in the direction of the coarse-to-nano grained gradient than vice versa, a result which we ascribe primarily to excessive crack-tip blunting in the coarse-grained microstructure. Both gradient structures, however, display marked rising R-curve behavior with exceptional crack-growth toughnesses exceeding 200 MPa.m½
Possible dibaryons in the quark cluster model
In the framework of RGM, the binding energy of one channel
() and are studied in the
chiral SU(3) quark cluster model. It is shown that the binding energies of the
systems are a few tens of MeV. The behavior of the chiral field is also
investigated by comparing the results with those in the SU(2) and the extended
SU(2) chiral quark models. It is found that the symmetry property of the
system makes the contribution of the relative kinetic energy
operator between two clusters attractive. This is very beneficial for forming
the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very
important role on binding. The S-wave phase shifts and the corresponding
scattering lengths of the systems are also given.Comment: LeTex with 2 ps figure
Position-Based Multi-Agent Dynamics for Real-Time Crowd Simulation (MiG paper)
Exploiting the efficiency and stability of Position-Based Dynamics (PBD), we
introduce a novel crowd simulation method that runs at interactive rates for
hundreds of thousands of agents. Our method enables the detailed modeling of
per-agent behavior in a Lagrangian formulation. We model short-range and
long-range collision avoidance to simulate both sparse and dense crowds. On the
particles representing agents, we formulate a set of positional constraints
that can be readily integrated into a standard PBD solver. We augment the
tentative particle motions with planning velocities to determine the preferred
velocities of agents, and project the positions onto the constraint manifold to
eliminate colliding configurations. The local short-range interaction is
represented with collision and frictional contact between agents, as in the
discrete simulation of granular materials. We incorporate a cohesion model for
modeling collective behaviors and propose a new constraint for dealing with
potential future collisions. Our new method is suitable for use in interactive
games.Comment: 9 page
Optical properties of in the normal state
We present the optical reflectance and conductivity spectra for non-oxide
antiperovskite superconductor at different temperatures. The
reflectance drops gradually over a large energy scale up to 33,000 cm,
with the presence of several wiggles. The reflectance has slight temperature
dependence at low frequency but becomes temperature independent at high
frequency. The optical conductivity shows a Drude response at low frequencies
and four broad absorption features in the frequency range from 600 to
33,000 . We illustrate that those features can be well understood from
the intra- and interband transitions between different components of Ni 3d
bands which are hybridized with C 2p bands. There is a good agreement between
our experimental data and the first-principle band structure calculations.Comment: 4 pages, to be published in Phys. Rev.
Tourism boycotts and animosity: a study of seven events
The impacts of tourism boycotts on a destination’s tourist economy can be vast, yet few studies have examined such events. This paper explores the effects of tourism boycotts by analysing seven events involving Chinese tourism boycotts during the past decade.
The findings show that boycotts can significantly decrease visitor numbers. Also, non-political animosity boycotts and political animosity boycotts differ in their intensity and impact; the former are found to exert immediate short-term impacts, whereas the latter tend to have enduring effects. These results are based on local projection techniques using narratively identified boycott events and are robust to several specifications. This paper highlights tourism boycotts as a key risk factor in destination management
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