11,087 research outputs found
Higher Order Acoustoelastic Lamb Wave Propagation in Stressed Plates
Residual stresses can be generated during fabrication processes, such as, welding, forging, rolling etc[1-3] . They have obvious influence on the performance of the material, like cracking and corrosion. To better control residual stresses, the initial distribution of them in materials must be clear. Ultrasonic methods can be used as a good tool for residual stress detection, and this approach is non-destructive and costs are modest. Methods which utilize longitudinal critically refracted (LCR) waves are receiving increased attention and it can be used on thick material. However, there have only been a limited number of studies which consider the acoustoelastic effect for thin plate materials which generate Lamb waves[4] . This paper reports a study in which a numerical model[5-6] is used to investigate the Lamb wave dispersion curves under loading that induce stresses. The effects of stress on various Lamb modes are discussed and those which appear to be most sensitive are identified. It is found that when the stress’s direction is the same with wave propagation direction in a 1 mm thick aluminum plate the A0 mode is the most sensitive to the applied stress
Kaluza-Klein dimensional reduction and Gauss-Codazzi-Ricci equations
In this paper we imitate the traditional method which is used customarily in
the General Relativity and some mathematical literatures to derive the
Gauss-Codazzi-Ricci equations for dimensional reduction. It would be more
distinct concerning geometric meaning than the vielbein method. Especially, if
the lower dimensional metric is independent of reduced dimensions the
counterpart of the symmetric extrinsic curvature is proportional to the
antisymmetric Kaluza-Klein gauge field strength. For isometry group of internal
space, the SO(n) symmetry and SU(n) symmetry are discussed. And the
Kaluza-Klein instanton is also enquired.Comment: 15 page
ELID grinding of silicon wafers: a literature review
Silicon wafers are the most widely used substrates for fabricating integrated circuits. There have been continuous demands for higher quality silicon wafers with lower prices, and it becomes more and more difficult to meet these demands using current manufacturing processes. In recent years, research has been done on electrolytic in-process dressing (ELID) grinding of silicon wafers to explore its potential to become a viable manufacturing process. This paper reviews the literature on ELID grinding, covering its set-ups, wheel dressing mechanism, and experimental results. It also discusses the technical barriers that have to be overcome before ELID grinding can be used in manufacturing
Outflow and dense gas emission from massive Infrared Dark Clouds
Infrared Dark Clouds are expected to harbor sources in different, very young
evolutionary stages. To better characterize these differences, we observed a
sample of 43 massive Infrared Dark Clouds, originally selected as candidate
high-mass starless cores, with the IRAM 30m telescope covering spectral line
tracers of low-density gas, high-density gas, molecular outflows/jets and
temperature effects. The SiO(2-1) observations reveal detections toward 18
sources. Assuming that SiO is exclusively produced by sputtering from dust
grains, this implies that at least in 40% of this sample star formation is
on-going. A broad range of SiO line-widths is observed (between 2.2 and
65km/s), and we discuss potential origins for this velocity spread. While the
low-density tracers 12CO(2-1) and 13CO(1-0) are detected in several velocity
components, the high-density tracer H13CO+(1--0) generally shows only a single
velocity component and is hence well suited for kinematic distance estimates of
IRDCs. Furthermore, the H13CO+ line-width is on average 1.5 times larger than
that of previously observed NH3(1,1). This is indicative of more motion at the
denser core centers, either due to turbulence or beginning star formation
activity. In addition, we detect CH3CN toward only six sources whereas CH3OH is
observed toward approximately 40% of the sample. Estimates of the CH3CN and
CH3OH abundances are low with average values of 1.2x10^{-10} and 4.3x10^{-10},
respectively. These results are consistent with chemical models at the earliest
evolutionary stages of high-mass star formation. Furthermore, the CH3OH
abundances compare well to recently reported values for low-mass starless
cores.Comment: 22 pages (ApJ referee style), 7 figures, accepted for Ap
Jet-hadron correlations in STAR
Advancements in full jet reconstruction have made it possible to use jets as
triggers in azimuthal angular correlations to study the modification of
hard-scattered partons in the medium created in ultrarelativistic heavy-ion
collisions. This increases the range of parton energies accessible in these
analyses and improves the signal-to-background ratio compared to dihadron
correlations. Results of a systematic study of jet-hadron correlations in
central Au-Au collisions at sqrt(s_NN) = 200 GeV are indicative of a broadening
and softening of jets which interact with the medium. Furthermore, jet-hadron
correlations suggest that the suppression of the associated hadron yield at
high-pT is balanced in large part by low-pT enhancement.Comment: 4 pages, 2 figures, proceedings for Quark Matter 201
Jet Studies in STAR via 2+1 Correlations
This paper reports analysis on jet-medium interactions and di-jet surface
emission bias at RHIC, based on a new multi-hadron correlation technique called
\texttt{2+1} where back-to-back high hadron triggers work as proxy of
di-jets. In contrast with traditional correlations with single triggers, the
associated hadron distributions and spectra at both trigger sides show no
evident modification from d+Au to central Au+Au collisions. This observation
stands for both cases when triggers pairs are symmetric(5GeV/ vs.
4GeV/) or asymmetric(10GeV/ vs. 4GeV/).Comment: DIS 2011 conference proceeding
Neutrino masses, leptogenesis and dark matter in hybrid seesaw
We suggest a hybrid seesaw model where relatively ``light''right-handed
neutrinos give no contribution to the neutrino mass matrix due to a special
symmetry. This allows their Yukawa couplings to the standard model particles to
be relatively strong, so that the standard model Higgs boson can decay
dominantly to a left and a right-handed neutrino, leaving another stable
right-handed neutrino as cold dark matter. In our model neutrino masses arise
via the type-II seesaw mechanism, the Higgs triplet scalars being also
responsible for the generation of the matter-antimatter asymmetry via the
leptogenesis mechanism.Comment: 4 page
Photon-meson transition form factors of light pseudoscalar mesons
The photon-meson transition form factors of light pseudoscalar mesons , , and are systematically calculated in a
light-cone framework, which is applicable as a light-cone quark model at low
and is also physically in accordance with the light-cone pQCD approach
at large . The calculated results agree with the available experimental
data at high energy scale. We also predict the low behaviors of the
photon-meson transition form factors of , and , which are measurable in process via Primakoff
effect at JLab and DESY.Comment: 22 Latex pages, 7 figures, Version to appear in PR
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