7,090 research outputs found
Signal enhancement of the in-plane and out-of-plane Rayleigh wave components
Several groups have reported an enhancement of the ultrasonic Rayleigh wave when scanning close to a surface-breaking defect in a metal sample. This enhancement may be explained as an interference effect where the waves passing directly between source and receiver interfere with those waves reflected back from the defect. We present finite element models of the predicted enhancement when approaching a defect, along with experiments performed using electromagnetic acoustic transducers sensitive to either in-plane or out-of-plane motion. A larger enhancement of the in-plane motion than the out-of-plane motion is observed and can be explained by considering ultrasonic reflections and mode conversion at the defect
The Friedmann equation in modified entropy-area relation from entropy force
According to the formal holographic principle, a modification to the
assumption of holographic principle in Verlinder's investigation of entropy
force is obtained. A more precise relation between entropy and area in the
holographic system is proposed. With the entropy corrections to the
area-relation, we derivate Newton's laws and Einstein equation with a static
spherically symmetric holographic screen. Furthermore we derived the correction
terms to the modified Friedmann equation of the FRW universe starting from the
holographic principle and the Debye model.Comment: Mod. Phys. Lett. A26, 489-500 (2011
Fast and Exact Discrete Geodesic Computation Based on Triangle-Oriented Wavefront Propagation
Computing discrete geodesic distance over triangle meshes is one of the fundamental problems in computational geometry and computer graphics. In this problem, an effective window pruning strategy can significantly affect the actual running time. Due to its importance, we conduct an in-depth study of window pruning operations in this paper, and produce an exhaustive list of scenarios where one window can make another window partially or completely redundant. To identify a maximal number of redundant windows using such pairwise cross checking, we propose a set of procedures to synchronize local window propagation within the same triangle by simultaneously propagating a collection of windows from one triangle edge to its two opposite edges. On the basis of such synchronized window propagation, we design a new geodesic computation algorithm based on a triangle-oriented region growing scheme. Our geodesic algorithm can remove most of the redundant windows at the earliest possible stage, thus significantly reducing computational cost and memory usage at later stages. In addition, by adopting triangles instead of windows as the primitive in propagation management, our algorithm significantly cuts down the data management overhead. As a result, it runs 4-15 times faster than MMP and ICH algorithms, 2-4 times faster than FWP-MMP and FWP-CH algorithms, and also incurs the least memory usage
A systematic TMRT observational study of Galactic C/C ratios from Formaldehyde
We present observations of the C-band (4.8 GHz) and Ku-band
(14.5 GHz) K-doublet lines of HCO and the C-band
(4.6 GHz) line of HCO toward a large sample of
Galactic molecular clouds, through the Shanghai Tianma 65-m radio telescope
(TMRT). Our sample with 112 sources includes strong HCO sources from the
TMRT molecular line survey at C-band and other known HCO sources. All three
lines are detected toward 38 objects (43 radial velocity components) yielding a
detection rate of 34\%. Complementary observations of their continuum emission
at both C- and Ku-bands were performed. Combining spectral line parameters and
continuum data, we calculate the column densities, the optical depths and the
isotope ratio HCO/HCO for each source. To evaluate photon
trapping caused by sometimes significant opacities in the main isotopologue's
rotational mm-wave lines connecting our measured K-doublets, and to obtain
C/C abundance ratios, we used the RADEX non-LTE model accounting
for radiative transfer effects. This implied the use of the new collision rates
from \citet{Wiesenfeld2013}. Also implementing distance values from
trigonometric parallax measurements for our sources, we obtain a linear fit of
C/C = (5.081.10)D + (11.866.60), with a
correlation coefficient of 0.58. D refers to Galactocentric distances.
Our C/C ratios agree very well with the ones deduced from CN and
CO but are lower than those previously reported on the basis of HCO,
tending to suggest that the bulk of the HCO in our sources was formed on
dust grain mantles and not in the gas phase.Comment: 27 pages, 8 figures, 7 tables. Accepted for publication in The
Astrophysical Journa
Observation of orbital ordering and origin of the nematic order in FeSe
To elucidate the origin of nematic order in FeSe, we performed
field-dependent 77Se-NMR measurements on single crystals of FeSe. We observed
orbital ordering from the splitting of the NMR spectra and Knight shift and a
suppression of it with magnetic field B0 up to 16 T applied parallel to the
Fe-planes. There is a significant change in the distribution and magnitude of
the internal magnetic field across the orbital ordering temperature Torb while
stripe-type antiferromagnetism is absent. Giant antiferromagnetic (AFM) spin
fluctuations measured by the NMR spin-lattice relaxation are gradually
developed starting at ~ 40 K, which is far below the nematic ordering
temperature Tnem. These results demonstrate that orbital ordering is the origin
of the nematic order, and the AFM spin fluctuation is the driving mechanism of
superconductivity in FeSe under the presence of the nematic order.Comment: 6 pages, 4 figure
Dual EMAT and PEC non-contact probe: applications to defect testing
For many non-destructive testing (NDT) applications, more information and greater reliability can be gained by using different techniques for defect detection, especially when the methods are particularly sensitive to different types of defects. However, this will often lead to a much longer and more expensive test and is not always practical due to time and cost constraints. We have previously discussed initial experiments using a new dual-probe combining electromagnetic acoustic transducers (EMATs) generating and detecting ultrasonic surface waves, and a pulsed eddy current (PEC) sensor 1. This enables more reliable detection and sizing of surface and near-surface defects, with a reduced testing time compared to using two \{NDT\} techniques separately. In this paper, we present experiments using the dual-probe on samples which are more representative of real defects, for example testing for surface defects in rails. Several aluminium calibration samples containing closely spaced and angled slots have been measured, in addition to rail samples containing manufactured and real defects. The benefits of using the dual-probe are discussed
Robust optimization in HTS cable based on DEPSO and design for six sigma
The non-uniform AC current distribution among the multi-layer conductors in a high-temperature superconducting (HTS) cable reduces the current capacity and increases the AC loss. In this paper, Particle swarm optimization coupled with differential evolution operator (DEPSO) has been applied in structural optimization of HTS cables. While the existence of fluctuation in design variables or operation conditions has a great influence on the cable quality, in order to eliminate the effects of parameter perturbations in design and improve the design efficiency, a robust design method based on design for six sigma (DFSS) is applied in this paper. The optimization solutions show that the proposed optimization procedure can not only achieve a uniform current distribution, but also improve significantly the reliability and robustness of the HTS cable quality. © 2008 IEEE
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