Component lifetime modelling

There are two approaches to component lifetime modelling. The first one uses a reliability prediction method as described in the (military) handbooks with the appropriate models and parameters. The advantages are: (a) It takes into account all possible failure mechanisms. \ud (b) It is easy to use. \ud \ud The disadvantages are: (a) It assumes a constant failure rate which is often not the case (infant mortality). \ud (b) It contains no designable parameters and therefore it cannot be used for built-in reliability. \ud \ud The second approach is to model the different degradation mechanisms and to incorporate this into an (existing) circuit simulator. Here we have also advantages and disadvantages which are mostly complementary to those of the first method

Pionium lifetime corrections

Pionium lifetime corrections are evaluated in the frameworks of constrained Bethe-Salpeter equation and chiral perturbation theory. Corrections of order $O(\alpha)$ are calculated with respect to the conventional lowest-order formula, in which the strong interaction amplitude has been calculated to two-loop order with charged pion masses. The total correction is found to be of the order of $(6.1\pm 2.0)$.Comment: 9 pages, Latex. Uses Dubna98.sty. Talk given at the Int. Workshop "Hadronic Atoms and Positronium in the Standard Model", Dubna, 26-31 May 1998. To appear in the Proceeding

Lifetime of Kaonium

The kaon--antikaon system is studied in both the atomic and the strongly interacting sector. We discuss the influence of the structures of the $f_0(980)$ and the $a_0(980)$ mesons on the lifetime of kaonium. The strong interactions are generated by vector meson exchange within the framework of the standard $SU(3)_V\times SU(3)_A$ invariant effective Lagrangian. In the atomic sector, the energy levels and decay widths of kaonium are determined by an eigenvalue equation of the Kudryavtsev--Popov type, with the strong interaction effects entering through the complex scattering length for $K\bar K$ scattering and annihilation. The presence of two scalar mesons, $f_0(980)$ and $a_0(980)$, leads to a ground state energy for the kaonium atom that is shifted above the point Coulomb value by a few hundred eV. The effect on the lifetime for the kaonium decay into two pions is much more dramatic. This lifetime is reduced by two orders of magnitude from $0.8\times 10^{-16}$ sec for annihilation in a pure Coulomb field down to $3.1\times 10^{-18}$ sec when the strong interactions are included. The analysis of the two photon decay width of the $f_0(980)$ suggests a generalization of the molecular picture which reduces the lifetime of kaonium still further to $1.1\times 10^{-18}\textrm{sec}$.Comment: 33 pages, 12 figures;3 new figures and new comment concerning the a

Theory and it ab initio calculation of radiative lifetime of excitons in semiconducting carbon nanotubes

We present theoretical analysis and first-principles calculation of the radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic lifetime of the order of 10 ps is computed for the lowest optically active bright excitons. The intrinsic lifetime is however a rapid increasing function of the exciton momentum. Moreover, the electronic structure of the nanotubes dictates the existence of dark excitons nearby in energy to each bright exciton. Both effects strongly influence measured lifetime. Assuming a thermal occupation of bright and dark exciton bands, we find an effective lifetime of the order of 10 ns at room temperature, in good accord with recent experiments.Comment: 12 pages, 3 figure

BS-ISO helical gear fatigue life estimation and wear quantitative features analysis

Original article can be found at: http://www3.interscience.wiley.com/ Copyright Blackwell Publishing. DOI: 10.1111/j.1475-1305.2008.00457.xLack of representative theoretical models for gear wear causes difficulties in their useful lifetime prediction. Critical operating parameters, such as loading and lubrication, affect the wear process in a very complex manner and lead the theoretical modelling to an imperfect zone of assumptions. Complexities in gear wear mathematical modelling allow the researchers to use approximations for useful lifetime calculations. On the basis of modelling approximations and assumptions, organizations, such as American Gear Manufacturers' Association (AGMA) and British Standards (BS), provide gear useful lifetime formulations. In these formulations, the useful lifetime values are estimated by means of experimentation that is controlled with known gear operating conditions and physical dimensions. However, for useful lifetime estimation and validation, these standards have not considered any experimental approach that represents the actual gear wear. In this paper, an effort is made to validate the competency of standard's gear useful lifetime formulation. For this purpose, an approach that is able to provide an idea about actual gear wear is used. During the effort, BS-ISO 6336-2 standard formulation is used for helical gear useful lifetime estimation under linear pitting fatigue conditions. The used formulation is validated by using wear quantitative feature analysis that is able to provide actual gear wear quantitative trends. The obtained wear quantitative trends fairly validate the lifetime estimation of BS-ISO 6336-2 standard.Peer reviewe

Making Your Nest Egg Last a Lifetime

Media attention on retirement security generally focuses on the need to save enough to enjoy a comfortable retirement. However, accumulating a nest egg is no longer the only significant challenge – the other is managing one’s nest egg in retirement. In contrast to previous birth cohorts who often received a lifetime income from a defined benefit pension plan, in today’s 401(k) world retirees must choose how to convert their accumulated savings into a monthly paycheck. One straightforward solution to the drawdown challenge is an immediate annuity, which turns a lump sum of income into a lifelong payment stream. However, for various reasons, such annuities have not proven broadly popular. Therefore, this brief examines several alternatives. All such strategies involve a trade-off between maximizing consumption and minimizing the risk of running out of money. Calculating the optimal strategy is really hard – maybe impossible. But, despite the complexity of the problem, some strategies are clearly superior to others...

Lifetime-Extended MCP-PMT

In order to develop a long-lifetime MCP-PMT under high rates of circumstance, we investigated the degradation of the quantum efficiency (QE) of PMT's with a multialkali photocathode. We found that not only positive ions, but also neutral residual gases would damage the photocathode resulting in an enhancement of the work function; their countermeasures were established in newly manufactured square-shaped MCP-PMT's with 4 or 4x4 multi-anodes. The performances of the PMT's were measured: QE was stable up to an integrated amount of anode output charge of 2-3 C/cm^2, while keeping other basic performances steady, such as the time resolution for single photons of ~40 ps, a photoelectron collection efficiency (CE) of 60%, a multiplication gain (G) of a few x 10^6, and dark counts of 20-300 Hz. The causes of QE degradation are discussed.Comment: 14 pages, 7 figure

Reduction of Statistical Power Per Event Due to Upper Lifetime Cuts in Lifetime Measurements

A cut on the maximum lifetime in a lifetime fit not only reduces the number of events, but also, in some circumstances dramatically, decreases the statistical significance of each event. The upper impact parameter cut in the hadronic B trigger at CDF, which is due to technical limitations, has the same effect. In this note we describe and quantify the consequences of such a cut on lifetime measurements. We find that even moderate upper lifetime cuts, leaving event numbers nearly unchanged, can dramatically increase the statistical uncertainty of the fit result.Comment: Changes to latest revision: added DOI link, took the opportunity to correct some minor typos added one small clarificatio