1,721,086 research outputs found
Thermodynamics of high frequency nonlinear vibrations
No full textIn the field of vibrations of complex structures, energy methods like SEA and a series of mid-frequency methods, represent an important resource for computational analysis. All these methods are based in general on a linear formulation of the elastic problem. However, when nonlinearities are present, for example related to clearance or stiffening of joints, these methods, in principle, cannot be applied. This paper, on the basis of a theory presented recently by one of the authors, proposes a foundation of a new energy method able to deal with nonlinearities when studying the energy exchange between subsystems. The idea relies on the concept of a thermodynamic vibroacoustic temperature, that can be directly defined when introducing the entropy of a vibrating structure. The theory is introduced in general, and examples of calculation of the power flow between nonlinear resonators are presented introducing stiffening and clearences for systems with many degrees of freedom
Biomimetic customized composite scaffolds and translational models for the bone regenerative medicine using CAD-CAM technology
No full textNature produces soft and hard materials exhibiting remarkable functional properties by controlling the hierarchical assembly of simple molecular building blocks from the nano- to the macro-scale. Biogenic materials are nucleated in defined nano–micro-dimensioned sites inside the biological environments, in which chemistry can be spatially controlled, in order to monitor the size, shape, and structural organization of biomaterials. With the development of nanotechnology, this strategy employing natural material genesis has attracted attention in designing bioinspired materials at the nanoscale dimensions. In this contest, biomimetic nanostructured hydroxyapatite is a promising biomaterial for bone tissue engineering because this material exhibits excellent biological properties. However, hydroxyapatite is still limited as bone substitute due to the brittleness of the material. Hence, a widespread approach is the creation of hybrid materials with an inorganic or organic bioactive phase mimicking functional bony units and a polymeric phase of a consistency permitting the device to be manipulated to achieve an anatomically compatible shape and allowing surface adsorption of molecules that play active roles in the biological environment. Recently, many studies were developed in order to prepare and test new bioengineered custom-made composite scaffold materials using a combination of CAD/CAM technology to restore full-thickness defects of the bone. Modern 3D printing techniques allow dimensioning of the external volume according to the surgical defect, thus simplifying the surgery and reducing biological morbidity. The use of CAD/CAM technology and the novel composite, biomimetic, and resorbable scaffolds are the promising way to interpret the need of bone regenerative medicine
Damage diagnostic technique combining machine learning approach with a sensor swarm
Full text linkA Model-free approach is particularly valuable for Structural Health Monitoring because real structures are often too complex to be modelled accurately, requiring anyhow a large quantity of sensor data to be processed. In this context, this paper presents a machine learning technique that analyses data acquired by swarm of a sensor. The proposed algorithm uses unsupervised learning and is based on the use principal component analysis and symbolic data analysis: PCA extracts features from the acquired data and use them as a template for clustering. The algorithm is tested with numerical experiments. A truss bridge is modelled by a finite element model, and structural response is produced in healthy and several damaged scenarios. The present research shows also the importance of considering a sufficient number of measurements points along the structure, i.e. the swarm of sensors. This technology, which nowadays is easily attainable with the application of optical Fiber Bragg Grating strain sensors. The difficulties related to the early stage damage detection in complex structures can be skipped, especially when ambient, narrow band, moving loads are considered, enhancing the prediction capabilities of the proposed algorithm
Silica xerogels as a delivery system for the controlled release of different molecular weight heparins.
No full textIn this work, we investigated a sol-gel derived silica matrix as a delivery system for the prolonged release of different molecular weight heparins, which allows the glycosaminoglicons to retain their whole biological activity. Several xerogels were obtained by embedding different molecular weight heparins into matrices prepared by using different amount of NH4OH as a catalyst during gel formation. Gel synthesis parameters, drug release properties, and xerogels surface area were evaluated. Unfractionated, low and oligo-molecular weight heparins were embedded into xerogels and the effect of the molecular weight on the release kinetics and the retained biological activity has been investigated. The results show that the surface area of the matrix is a determinant parameter affecting drug release kinetics. This structural feature can be modified by varying the catalyst tetraethoxysilane molar ratio used during the matrix synthesis. In most cases release kinetics fitted the Higuchi diffusive model and a lower diffusion rate was observed from silica matrices characterized by a smaller surface area. In the case of matrices with lower surface area, loaded with unfractionated heparin, zero order kinetics was observed. In this paper, we have defined a heparin release silica xerogel system and we have pointed out how modulation of its synthesis parameters allows adjusting the release of heparin according to therapeutic needs
Bioactive Inorganic Matrices for the Local Delivery of Platinum-based Prodrugs in the Treatment of Bone Tumors
No full textVibration energy harvesting for cars: semi-active piezo controllers
Full text linkEnergy harvesting represents one of the recent challenging subjects related to vibration and control. The scale of energy harvesters and storage can involve a wide power range, and the scale of some milliwatt is the elective field of piezoelectric applications. This paper investigates the power frontiers of the piezoelectric-based harvesters applied to automotive units. The analysis, supported by experimental data, aims at estimating the upper bound of the specific power of this technology for powering small devices on board cars. Passive optimally tuned piezoelectric harvester and semi-active controlled ones are compared, based on a new control strategy named VFC-Variational Feedback Control, recently developed by the authors. This new technique makes it possible to increase the total energy storage drained from car vibrations. However, the real advantage for their use relies on a sharp balance between the harvested power and the costs for the additional hardware mass transport. Numerical simulations of circuitry and experimental vibration data provides references to assess the energy convenience in installing this type of devices on board
Connectivity in waves and vibrations: One-to-six, one-to-all, all-to-all and random connections
Full text linkThis paper develops a theory of propagation based on connectivity templates. Connectivity describes how the elastic connections distribute. A visual counterpart is the structure of the stiffness matrix. D'Alembert equation refers to classical elasticity based on closest neighbors connectivity and is characterized by propagation of waves, which can be classified as one-to-six, since each particle of the scheme is connected only with two other particles for each direction. However, very different connectivity schemes can be introduced, e.g. a one-to-all connectivity scheme, in which one particle can be connected with a cluster of particles, or all-to-all where each particle is connected with any other. Moreover, connections are not instantaneous: the information flows is delayed due to the connection length. Waves exhibit unbelievable behaviour changing the system connectivity. Nondissipative structures shows damping. Energy can propagate backwards in respect to wave direction. Waves can stop or localize at some points. Negative mass effect can emerge. These effects will be discussed in the present paper
Electrospun collagen/hyaluronic acid nanofibers improve osteoblastic differentiation onto titanium surfaces
No full textSafe and secure control of swarms of vehicles by small-world theory
Full text linkThe present paper investigates a new paradigm to control a swarm of moving individual vehicles, based on the introduction of a few random long-range communications in a queue dominated by short-range car-following dynamics. The theoretical approach adapts the small-world theory, originally proposed in social sciences, to the investigation of these networks. It is shown that the controlled system exhibits properties of higher synchronization and robustness with respect to communication failures. The considered application to a vehicle swarm shows how safety and security of the related traffic dynamics are strongly increased, diminishing the collision probability even in the presence of a hacker attack to some connectivity channels
- …
