A mixed FEM and lumped-parameter dynamic model for evaluating the modal properties of planetary gearboxes

Planetary gearboxes are extensively used in mechatronic applications due to their compactness and high reduction ratios. The complex kinematic of such systems and the requirement of low-vibration-gears suggest studying these gearboxes with appropriate dynamic models. To this purpose, a planar lumped parameter model with 18 degrees of freedom was implemented. Model parameters such as the stiffness of the bearings and the gear meshes were calculated using dedicated FEM simulations. Two different gearbox configurations were simulated and experimentally tested. The compared results showed a good agreement. The main goal of the research was to assess the validity of such methodology for the prediction of the system eigenfrequencies. Additionally, from a kinematic analysis of the gearbox it was possible to individuate the self-excitation frequencies. The overlapping of these self-excited frequencies with the eigenfrequencies of the system was individuated as the major cause of the gearbox noise.     

XPS investigations of the proton exchange membrane fuel cell active layers aging: Characterization of the mitigating role of an anodic CO contamination on cathode degradation

This paper presents new results from XPS quantitative characterizations of cathode catalyst layers aged in a PEMFC with an anode operated under pure hydrogen and air and with 5 ppm CO contaminated hydrogen. Both oxygen rich and oxygen poor zones of the cathode catalyst layer were analyzed in order to show up heterogeneous degradation linked with gas distribution. The detailed chemical XPS analysis of the aged samples demonstrates in particular that in our operating conditions, the catalyst layer aging is mainly attributed to the oxidation of the carbon catalyst-support. A loss of the Nafion^® ionomer in the cathode is also highlighted by XPS. Furthermore, the characterization of the cathodic catalyst layer chemical composition when CO is introduced in the anode side shows that the catalyst layer degradation is lower. These results are in agreement with the experimental-modeling work by Franco et al. [1] demonstrating that anodic CO contamination decreases the reverse proton pumping effect between the cathode and the anode and enhances the PEMFC durability.     

MinerAlert: an hybrid approach for web mining detection

Journal of Computer Virology and Hacking Techniques - The introduction of new memory-based crypto-mining techniques and the rise of new web technologies like WebAssembly, made the use of browsers...     

Study of horizontal sonic gas jets in gas–solid fluidized beds

Existing jet penetration correlations have all been developed for sub‐sonic gas jets and have been found to perform poorly when employed in sonic and supersonic regimes. In the present study, triboelectric probes were used to measure both the penetration depth and expansion angle of sonic gas jets. Experiments were conducted using nozzles of different size and geometry, different particle types, different injection gases, and different fluidization velocities. All these data were used to develop a new, general correlation to predict the penetration depth of sonic gas jets. The effects of these variables on jet expansion angle were also studied.     

A Mixed Convex/Nonconvex Distributed Localization Approach for the Deployment of Indoor Positioning Services

In this paper the indoor wireless localization problem is addressed both from the theoretical and application standpoints. The main result of the paper is on the theoretical side: the topological definition of regular and irregular nodes is introduced, and formal results are presented to support regularity as a desirable network property for the attainment of precise node localization. In force of this definition, a mixed convex/non—convex optimization approach has been derived for the solution of the positioning problem. The two procedures, suitably combined, allow the achievement of better convergence towards the best positioning of a multitude of blind wireless nodes. A completely decentralized, partially asynchronous algorithm is presented, which proceeds locally on each node based on the sole knowledge of the distances measured from, and of the estimated positions of the connected nodes only. Its repeated asynchronous application on each nodes guarantees the convergence of the algorithm to the positioning of the whole network, even in presence of a limited number of peripheral reference points. Indeed, no global information is required for the proper functioning of the algorithm. Simulations of relevant case studies have been performed to qualify the proposed scheme in realistic conditions, and the results are presented.     

Resource allocation in satellite networks: certainty equivalent approaches versus sensitivity estimation algorithms

In this paper, we consider a resource allocation problem for a satellite network, where variations of fading conditions are added to those of traffic load. Since the capacity of the system is finite and divided in finite discrete portions, the resource allocation problem reveals to be a discrete stochastic programming one, which is typically NP‐hard. We propose a new approach based on the minimization over a discrete constraint set using an estimation of the gradient, obtained through a ‘relaxed continuous extension’ of the performance measure. The computation of the gradient estimation is based on the infinitesimal perturbation analysis technique, applied on a stochastic fluid model of the network. No closed‐forms of the performance measure, nor additional feedback concerning the state of the system, and very mild assumptions on the probabilistic properties about the statistical processes involved in the problem are requested. Such optimization approach is compared with a dynamic programming algorithm that maintains a perfect knowledge about the state of the satellite network (traffic load statistics and fading levels). The comparison shows that the sensitivity estimation capability of the proposed algorithm allows to maintain the optimal resource allocation in dynamic conditions and it is able to provide even better performance than the one reached by employing the dynamic programming approach. Copyright © 2004 John Wiley & Sons, Ltd.     

Mortality from tuberculosis in Spain from 1970 to 1993: changes in epidemiological trends during the acquired immune-deficiency syndrome epidemic

SETTING: Spain has the highest rates in Europe of the acquired immune-deficiency syndrome (AIDS), and probably a high rate of dual human immunodeficiency virus (HIV)/tuberculosis infection. OBJECTIVE: To determine the trends of tuberculosis mortality in Spain from 1970 to 1993, and to draw conclusions about the effects of the AIDS epidemic on these trends. DESIGN: Official population figures and data on deaths from tuberculosis were used to calculate specific tuberculosis mortality rates by age and sex (per 100000 population). Causes of death from tuberculosis were grouped according to the International Classification of Diseases. RESULTS: The crude death rate decreased from 10.28 to 1.84, with an annual mean decrease of 8.1% (95% confidence interval 7.5% to 8.7%). No changes in mortality from tuberculosis of the central nervous system (CNS) have been recorded since 1982, and none in mortality from other tuberculosis and in the age group 20-49 years since 1986. Mortality was higher among males and in the older age groups. The peak observed in the 1970s, due to the excess of deaths from CNS tuberculosis in children under the age of 5 years, has disappeared. CONCLUSION: Between 1970 and 1993, tuberculosis mortality in Spain decreased, although an excess of deaths occurred in young adults and from extra-pulmonary tuberculosis, coinciding with the AIDS epidemic.     

Elastic and anelastic properties of Marval 18 steel

Marval 18 is a precipitation hardened steel with particularly high hardness and low creep, presently used for constructing parts of the interferometers for the detection of gravitational waves in the experiments VIRGO and LIGO. The elastic moduli have been measured in samples subjected to the same treatments as the parts of the interferometer VIRGO. In addition, the anelastic spectra of samples subjected to different thermal treatments have been measured between 50 and 350 K. It is found that, in the absence of plastic deformation, the elastic energy loss coefficient under flexural vibrations around 1 kHz can vary by more than one order of magnitude depending on the thermal treatments, and is dominated by the thermoelastic effect. The main reason for such strong variations is supposed to be the dependence of the thermal conductivity on the average sizes and distances between the precipitate particles.