An Acoustic Emission Study for Monitoring Anterior Cruciate Ligament Failure Under Tension

The analysis of the acoustic signals produced during anterior cruciate ligament (ACL) failure could be useful in understanding its behavior. The purpose of the present study was to evaluate the role of coupling conditions of the sensors and to determine the value of newly introduced acoustic emission (AE) parameters. Seven femur-ACL-tibia complex (FATC) specimens were fixed in a universal tensile testing machine and load was applied. Different coupling conditions were applied in two groups of specimens. The load-time curve was monitored, with the simultaneous recording of the acoustic signals and the failure mode. During ACL tear, detectable changes in the load-time curve occurred linked to changes in the macroscopic sequence of events and the measured AE parameters irrespective the coupling conditions. AE provides information on the determination of the moment (or load) when crucial irreversible damage occurs. Furthermore, specific AE indices exhibit changes throughout the testing, and imply shift of the failure mechanisms.     

Stability analysis of phase fitted variational integrators

In the present work, we discuss the benefits, limitations and restrictions for the high order phase fitted variational integrators, derived specifically for the numerical integration of systems with oscillatory solutions. To do that, we study linear stability properties of these methods using the eigenvalues of the amplification matrix. The obtained stability region verifies their good behavior, when used for the numerical solution of highly oscillatory problems. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantumchromodynamic corrections for ΔF=2 processes in the presence of a heavy top quark

We calculate the QCD corrections to the ΔS=2 and ΔB=2 transition amplitudes for the casem _t ?m _w and extrapolate the results tom _t ?m _w , where they join smoothly with the low mass calculations,m _t ?m _w . We present explicit formulas for the corrections with numerical results summarized in tables and figures and compare them with earlier calculations. We arrive at a QCD corrected effective Hamiltonian which must hold for all ranges ofm _t .     

S 3 flavor symmetry and leptogenesis

We consider leptogenesis in a minimal S₃ extension of the standard model with an additional Z₂ symmetry in the leptonic sector. It is found that the CP phase appearing in the mass matrix of the left-handed neutrinos is the same as that for the CP asymmetries responsible for leptogenesis. Because of the discrete S₃ x Z₂ flavor symmetries, the CP asymmetries are strongly suppressed. To obtain a realistic size of the baryon number asymmetry in the universe, we therefore have to assume that resonant enhancement of the CP asymmetries takes place, and that three degenerate right-handed neutrino masses of O(10) TeV are present. Arrival of the final proofs: 22 November 2005 PACS: 11.30.Hv, 12.15.Ff, 14.60.Pq     

Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.     

Local approximations for maximum partial subgraph problem

We deal with MAXH₀-FREE PARTIAL SUBGRAPH. We mainly prove that 3-locally optimum solutions achieve approximation ratio (δ₀+1)/(B+2+ν₀), where B=max_v∈Vd_G(v), δ₀=min_v∈V(H0)d_H0(v) and ν₀=(|V(H₀)|+1)/δ₀. Next, we show that this ratio rises up to 3/(B+1) when H₀=K₃. Finally, we provide hardness results for MAXK₃-FREE PARTIAL SUBGRAPH.     

Rupture of anterior cruciate ligament monitored by acoustic emission

The scope of this study is to relate the acoustic emission (AE) during rupture of human soft tissue (anterior cruciate ligament, ACL) to the mechanisms leading to its failure. The cumulative AE activity highlights the onset of serious damage, while other parameters, show repeatable tendencies, being well correlated with the tissue's mechanical behavior. The frequency content of AE signals increases throughout the experiment, while other indices characterize between different modes of failure. Results of this preliminary study show that AE can shed light into the failure process of this tissue, and provide useful data on the ACL reconstruction.     

On frequency estimations in phase fitted variational integrators for the general N-body problem

In the present work, the advantages of high order variational integrator methods are combined with phase lag properties for the numerical integration of the general N-body problem. Expressing the action integral at any intermediate points along the curve segment using a discrete Lagrangian that depends only on the end points of the interval, high order integrators can be obtained by defining the discrete Lagrangian in any time segment as a weighted sum on intermediate points, whose expressions for positions and velocities use Galerkin interpolation techniques. When oscillatory behavior is taken into account, the methods derived use trigonometric interpolation functions that depend on a frequency, which needs to be estimated. For that, using phase lag analysis, a new way to derive methods has been developed, that uses frequency estimation for each body at every time step. Results on special cases of the N-body problem show more stable orbits and less energy error when compared with the linear interpolation scheme. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)