3,464 research outputs found
Detection of Radial Bolt-Hole Cracks Using Sampled CW Ultrasonic Doppler-Shift Techniques
Recently there has been considerable interest in detecting radial cracks under fasteners in the wings of C-5A aircraft. Generally, detection is accomplished using the pulse-echo method, reflections from cracks being detected in real time. In the present study, cracks are detected by observing the ·Doppler-shifted frequency. A sample having a radial crack is mounted on a rotating platform in a water bath. A focused transducer transmits a tone burst such that only the shear mode propagates tangential to the hole in the metal. This transducer receives a Doppler-shifted reflected signal whenever a moving crack is in the field of view of the incident beam. The received signal is heterodyned, filtered, and displayed on a low-frequency spectrum analyzer. Merits and limitations of the technique are discussed
Stability and topology of scale-free networks under attack and defense strategies
We study tolerance and topology of random scale-free networks under attack
and defense strategies that depend on the degree k of the nodes. This situation
occurs, for example, when the robustness of a node depends on its degree or in
an intentional attack with insufficient knowledge on the network. We determine,
for all strategies, the critical fraction p_c of nodes that must be removed for
disintegrating the network. We find that for an intentional attack, little
knowledge of the well-connected sites is sufficient to strongly reduce p_c. At
criticality, the topology of the network depends on the removal strategy,
implying that different strategies may lead to different kinds of percolation
transitions.Comment: Accepted in PR
A geometrically-exact Finite Element Method for micropolar continua with finite deformations
Micropolar theory is a weakly non-local higher-order continuum theory based on the inclusion of independent (micro-)rotational degrees of freedom. Subsequent introduction of couple-stresses and an internal length scale mean the micropolar continuum is therefore capable of modelling size effects. This paper proposes a non-linear Finite Element Method based on the spatial micropolar equilibrium equations, but using the classical linear micropolar constitutive laws defined in the reference configuration. The method is verified rigorously with the Method of Manufactured Solutions, and quadratic Newton-Raphson convergence of the minimised residuals is demonstrated
Crystallization and X-ray diffraction analysis of the DNA-remodelling protein DnaD from Bacillus subtilis
Crystallization and preliminary X-ray diffraction analysis of the two domains of DnaD from B. subtilis is reported
Observation of Irregular Labyrinthine Magnetic Domains with Dendritic Edges in a Co-Rich CoCu Alloyed Film
Universal trend of the information entropy of a fermion in a mean field
We calculate the information entropy of single-particle states in
position-space and momentum-space for a nucleon in a nucleus, a
particle in a hypernucleus and an electron in an atomic cluster. It
is seen that and obey the same approximate functional form as
functions of the number of particles, ({\rm or}
in all of the above many-body systems in position- and momentum- space
separately. The net information content is a slowly varying
function of of the same form as above. The entropy sum is
invariant to uniform scaling of coordinates and a characteristic of the
single-particle states of a specific system. The order of single-particle
states according to is the same as their classification according to
energy keeping the quantum number constant. The spin-orbit splitting is
reproduced correctly. It is also seen that enhances with
excitation of a fermion in a quantum-mechanical system. Finally, we establish a
relationship of with the energy of the corresponding single-particle
state i.e. . This relation holds for all the
systems under consideration.Comment: 9 pages, latex, 6 figure
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