A comparison between different optimization criteria for tuned mass dampers design

Tuned mass sampers (TMDs) are widely used strategies for vibration control in many engineering applications, so that many TMD optimization criteria have been proposed till now. However, they normally consider only TMD stiffness and damping as design variables and assume that the tuned mass is a pre-selected value. In this work a more complete approach is proposed and then also TMD mass ratio is optimized. A standard single degree of freedom system is investigated to evaluate TMD protection efficiency in case of excitation at the support. More precisely, this model is used to develop two different optimizations criteria which minimize the main system displacement or the inertial acceleration. Different environmental conditions described by various char- acterizations of the input, here modelled by a stationary filtered stochastic process, are considered. Results show that all solutions obtained considering also the mass of the TMD as design variable are more efficient if compared with those obtained without it. However, in many cases these solutions are inappropriate because the optimal TMD mass is greater than real admissible values in practical technical applications for civil and mechanical engineering. Anyway, one can deduce that there are some interesting indications for applications in some actual contexts. In fact, the results show that there are some ranges of environmental parameters ranges where results attained by the displacement criterion are compatible with real applications requiring some percent of main system mass. Finally, the present research gives promising indications for complete TMD optimization application in emerging technical contexts, as micro- mechanical devices and nano resonant beam

Singular quasilinear elliptic systems in RN\mathbb{R}^N

The existence of positive weak solutions to a singular quasilinear elliptic system in the whole space is established via suitable a priori estimates and Schauder's fixed point theorem

Energy harvesting from earthquake for vibration-powered wireless sensors

Wireless sensor networks can facilitate the acquisition of useful data for the assessment and retrofitting of existing structures and infrastructures. In this perspective, recent studies have presented numerical and experimental results about self-powered wireless nodes for structural monitoring applications in the event of earthquake, wherein the energy is scavenged from seismic accelerations. A general computational approach for the analysis and design of energy harvesters under seismic loading, however, has not yet been presented. Therefore, this paper proposes a rational method that relies on the random vibrations theory for the electromechanical analysis of piezoelectric energy harvesters under seismic ground motion. In doing so, the ground acceleration is simulated by means of the Clough-Penzien filter. The considered piezoelectric harvester is a cantilever bimorph modeled as Euler-Bernoulli beam with concentrated mass at the free-end, and its global behavior is approximated by the dynamic response of the fundamental vibration mode only (which is tuned with the dominant frequency of the site soil). Once the Lyapunov equation of the coupled electromechanical problem has been formulated, mean and standard deviation of the generated electric energy are calculated. Numerical results for a cantilever bimorph which piezoelectric layers made of electrospun PVDF nanofibers are discussed in order to understand issues and perspectives about the use of wireless sensor nodes powered by earthquakes. A smart monitoring strategy for the experimental assessment of structures in areas struck by seismic events is finally illustrated

How does a bicycle work? A new instrument to assess mechanical reasoning in school aged children

This study demonstrated that a brief interview can reveal the mechanical reasoning that could not be assessed via the Bicycle Drawing Test. This study, conducted on 190 children (6 to 11 years old), shows that mechanical reasoning improves with age. It shows correlations with spatial reasoning and motor control, and with visual reasonin

Transfusion thresholds and beyond

Comment on Liberal transfusion strategy improves survival in perioperative but not in critically ill patients. A meta-analysis of randomised trials. [Br J Anaesth. 2015

Estimation of the incidence for non-terminal events in presence of a terminal event and evaluation of covariate effects: Sub-distribution and marginal distributions based on copulas. An application to disease progression on a breast cancer trial dataset

In clinical studies, during follow-up several kinds of events related to disease progression may be observed. In the semi-competing risks setting, some events, such as death, may prevent the observation of disease progression, thus acting as competitor for the event of interest. Methods of analysis specific for semi-competing risks data referring to marginal distribution of the non-competing events constitute a recent area of methodological research which has received a great impulse in latest years. However in clinical applications the analysis is traditionally based on crude cumulative incidences, and inference on marginal distributions is seldom considered, even when the principal aim concerns the probability of observing disease progression and death occurred without progression is a \u201cnuisance\u201d. Aim of this work is making a comparative review of semi-parametric marginal and sub-distribution methods of analysis, with particular reference to marginal regression models based on copulas. More specifically, two structures were considered for marginal models: in the first one all parameters are time-dependent, while in the second one parameters vary with covariates but does not depend on time. Applications to breast cancer clinical trial data and to a simulated dataset are reported, to show the differences and the similarities among marginal and sub-distribution approaches. Results highlight that, when the competing event acts during the whole follow-up, the marginal approach became essential for the correct estimation of marginal incidences and covariate effects. Regression methods based on copulas are promising, however there is a need of refinements concerning model building strategies, and, of standardised software routine for the practical application of these methods

Synthesis of organosiloxy: Transition metal polymers

The new compound, Mo(OSiPH3)4 (where Ph is C6H5) was synthesized. An overall chemical reaction which accounts for the observed products is given by the redox approach. Results indicate that Mo(OSiPH3)4 is thermally stable up to 230 C and relatively unreactive toward most common acids and bases even at elevated temperatures. Its behavior is not unlike that of Ti(OSiPH3)4

Chloride Penetration in Circular Concrete Columns

Most of the diffusion models of chloride ions in reinforced concrete (RC) elements proposed in literature are related to an isotropic homogeneous semi-infinite medium. This assumption reduces the mathematical complexity, but it is correct only for plane RC elements. This work proposes a comparison between the diffusion model of chloride ions in RC circular columns and in RC slab elements. The durability of RC cylindric elements estimated with the circular model instead of the plane model is shown to be shorter. Finally, a guideline is formulated to properly use the standard and more simple plane model instead of the circular one to estimate the time to corrosion initiation of cylindrical RC elements

Development of improved LOX compatible laminated gasket composite Final summary report, 16 Jun. 1965 - 16 Jun. 1966

Laminated gasket composite compatible with liquid oxyge