1,499 research outputs found
Assessment of probability of detection of delaminations in fiber-reinforced composites
Delamination is one of the critical defects in composite materials and structures. An ultrasonic C-scan imaging technique which maps out the acoustic impedance mismatched areas with respect to the sample coordinates, is particularly well suited for detecting and characterizing delaminations in composites. To properly interpret the results, it is necessary to correlate the indications with the detection limits and probability of detection (POD) of the ultrasonic C-scan imaging technique. The baseline information on the assessment of POD of delaminations in composite materials and structures is very beneficial to the evaluation of spacecraft materials. In this study, we review the principle of POD, describe the laboratory set-up and procedure, and present the experimental results as well as assessment of POD of delaminations in fiber reinforced composite panels using ultrasonic C-scan techniques
Topological defects in flat nanomagnets: the magnetostatic limit
We discuss elementary topological defects in soft magnetic nanoparticles in
the thin-film geometry. In the limit dominated by magnetostatic forces the
low-energy defects are vortices (winding number n = +1), cross ties (n = -1),
and edge defects with n = -1/2. We obtain topological constraints on the
possible composition of domain walls. The simplest domain wall in this regime
is composed of two -1/2 edge defects and a vortex, in accordance with
observations and numerics.Comment: 3 pages, eps figures. Proceedings of MMM 0
Two universal results for Wilson loops at strong coupling
We present results for Wilson loops in strongly coupled gauge theories. The
loops may be taken around an arbitrarily shaped contour and in any field theory
with a dual IIB geometry of the form M x S^5. No assumptions about
supersymmetry are made. The first result uses D5 branes to show how the loop in
any antisymmetric representation is computed in terms of the loop in the
fundamental representation. The second result uses D3 branes to observe that
each loop defines a rich sequence of operators associated with minimal surfaces
in S^5. The action of these configurations are all computable. Both results
have features suggesting a connection with integrability.Comment: 1+12 pages. LaTeX. No figure
Lagrangian Symmetries of Chern-Simons Theories
This paper analyses the Noether symmetries and the corresponding conservation
laws for Chern-Simons Lagrangians in dimension . In particular, we find an
expression for the superpotential of Chern-Simons gravity. As a by-product the
general discussion of superpotentials for 3rd order natural and quasi-natural
theories is also given.Comment: 16 pages in LaTeX, some comments and references added. to appear in
Journal of Physics A: Mathematical and Genera
Effect of food experience on overall satisfaction: comparison between first-time and repeat visitors to Malaysia
The attractiveness of food as tourism product has partly derived from the gastronomic aspect. The ingredients, the preparations, the end products, and the eating circumstances are cultural, educational, and entertaining. However, there is little research empirically demonstrates
if there is a difference between first-time and repeat visitors in terms of food experience at destination, or how the various food experience attributes influence visitors’ overall satisfaction while visiting a destination. Hence, this study was undertaken to address the gap. Data were
collected via on-site survey questionnaire administrated to a random sample of visitors at the Kuala Lumpur International Airport (KLIA) and various touristic areas around Kuala Lumpur. The results indicated significant differences between first-time and repeat visitors in terms of their food experience. In addition, multiple regression analysis revealed that traditional food preparation was an important factor to tourists’ overall satisfaction for both first-time and repeat visitors. In sum, the study is the first to examine the effect of food experience attributes on first time and repeat visitors separately
Quantization and Corrections of Adiabatic Particle Transport in a Periodic Ratchet Potential
We study the transport of an overdamped particle adiabatically driven by an
asymmetric potential which is periodic in both space and time. We develop an
adiabatic perturbation theory after transforming the Fokker-Planck equation
into a time-dependent hermitian problem, and reveal an analogy with quantum
adiabatic particle transport. An analytical expression is obtained for the
ensemble average of the particle velocity in terms of the Berry phase of the
Bloch states. Its time average is shown to be quantized as a Chern number in
the deterministic or tight-binding limit, with exponentially small corrections.
In the opposite limit, where the thermal energy dominates the ratchet
potential, a formula for the average velocity is also obtained, showing a
second order dependence on the potential.Comment: 8 page
Tunneling in Squeezing Ground
A criterion for identifying the squeezing potential of tunnel is proposed. Tunneling conditions, classified as slightly or non-squeezing, moderately squeezing and highly squeezing, were identified by relating the strength-stress (σcm/Po ) ratio to the development of plastic zone extent and the amount of tunnel closure. Actual case histories of tunneling in Taiwan show that this criterion predicts the tunnel performance quite well. This enables the identification of tunneling conditions expected which require special considerations in support design and excavation-support procedures
Conditional linearizability criteria for a system of third-order ordinary differential equations
We provide linearizability criteria for a class of systems of third-order
ordinary differential equations (ODEs) that is cubically semi-linear in the
first derivative, by differentiating a system of second-order quadratically
semi-linear ODEs and using the original system to replace the second
derivative. The procedure developed splits into two cases, those where the
coefficients are constant and those where they are variables. Both cases are
discussed and examples given
Carrier dynamics and coherent acoustic phonons in nitride heterostructures
We model generation and propagation of coherent acoustic phonons in
piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode
structure and compute the time resolved reflectivity signal in simulated
pump-probe experiments. Carriers are created in the InGaN wells by ultrafast
pumping below the GaN band gap and the dynamics of the photoexcited carriers is
treated in a Boltzmann equation framework. Coherent acoustic phonons are
generated in the quantum well via both deformation potential electron-phonon
and piezoelectric electron-phonon interaction with photogenerated carriers,
with the latter mechanism being the dominant one. Coherent longitudinal
acoustic phonons propagate into the structure at the sound speed modifying the
optical properties and giving rise to a giant oscillatory differential
reflectivity signal. We demonstrate that coherent optical control of the
differential reflectivity can be achieved using a delayed control pulse.Comment: 14 pages, 11 figure
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