1,262 research outputs found
Non-Destructive Evaluation—A Pivotal Technology for Qualification of Composite Aircraft Structures
Tremendous advances in composite materials and a deeper understanding of their behavior have been responsible for the increased use of composites in the development of advanced, new generation civil and military aircraft. Composites play an important role in any aircraft development programme and are strong contenders to their metal counterparts due to their significant contributions towards improving strength, stiffness, fatigue properties & weight reduction. As materials, structural design &
processing have evolved, strong emphasis is placed on effective & reliable damage detection, durability
and damage tolerance. As a consequence, Non-destructive Evaluation (NDE) has also undergone significant advances towards meeting the growing demands of quality assurance. Advanced Composites Division (ACD) of National Aerospace Laboratories (NAL), has been involved in the development of
composite structures for both civil and military aircraft for over a decade and a half. Innovative composite processing methods like co-curing/co-bonding have been successfully employed to realize airworthy structures. The role of NDE in the development of these structures has been critical and not limited to damage detection alone. On several occasions, NDE has provided valuable inputs towards
improving design and process parameters. In-spite of the complexity of the structures, stringent quality requirements and tight delivery schedules, NDE has been successful in certifying these composite structures for airworthiness. This paper discusses the implementation of key NDE techniques like ultrasonics, radiography, acoustic emission and thermography for reliable flaw detection, characterization and quality assurance of composite aircraft structures
Anomalous diffusion of optical vortices in random wavefields
We investigate the dynamic behavior of optical vortices, or phase
singularities, in random wavefields and demonstrate the direct experimental
observation of the anomalous diffusion of optical vortices. The observed
subdiffusion of optical vortices show excellent agreement with the fractional
Brownian motion, a Gaussian process. Paradoxically, the vortex displacements
are observed exhibiting a non-Gaussian heavy-tailed distribution. We also tune
the extent of subdiffusion and non-Gaussianity of optical vortex by varying the
viscoelasticity of light scattering media. This complex motion of optical
vortices is reminiscent of particles in viscoelastic environments suggesting a
vortex tracking based microrheology approach. The fractional Brownian yet
non-Gaussian subdiffusion of optical vortices may not only offer insights into
the dynamics of phase singularities, but also contribute to the understanding
certain general physics, including vortex diffusion in fluids and the
decoupling between Brownian and Gaussian
Quantum supergravity, supergravity anomalies and string phenomenology
I discuss the role of quantum effects in the phenomenology of effective
supergravity theories from compactification of the weakly coupled heterotic
string. An accurate incorporation of these effects requires a regularization
procedure that respects local supersymmetry and BRST invariance and that
retains information associated with the cut-off scale, which has physical
meaning in an effective theory. I briefly outline the Pauli-Villars
regularization procedure, describe some applications, and comment on what
remains to be done to fully define the effective quantum field theory.Comment: 30 pages, to be published in a memorial volume for Raymon
Top quark in theory
I review how the top quark is embedded in the Standard Model and some its
proposed extensions, and how it manifests itself in various hadron collider
signals.Comment: 12 page
On the renormalization group flow of f(R)-gravity
We use the functional renormalization group equation for quantum gravity to
construct a non-perturbative flow equation for modified gravity theories of the
form . Based on this equation we show that certain
gravitational interactions monomials can be consistently decoupled from the
renormalization group (RG) flow and reproduce recent results on the asymptotic
safety conjecture. The non-perturbative RG flow of non-local extensions of the
Einstein-Hilbert truncation including and interactions is investigated in detail. The inclusion of
such interactions resolves the infrared singularities plaguing the RG
trajectories with positive cosmological constant in previous truncations. In
particular, in some -truncations all physical trajectories emanate from
a Non-Gaussian (UV) fixed point and are well-defined on all RG scales. The RG
flow of the -truncation contains an infrared attractor which drives a
positive cosmological constant to zero dynamically.Comment: 55 pages, 7 figures, typos corrected, references added, version to
appear in Phys. Rev.
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