1,721,026 research outputs found
Limiting equations in the problem of total stability.
No full textThis paper concerns the relationship between total stability properties of a differential equation and the same properties of its limiting equations. Two different concepts of total stability are discussed
A survey on stability for stochastic differential equations
No full textThis article presents a brief survey on the use of Lyapunov method for stochastic differential equations. Sufficient conditions extending Lyapunov theory for ordinary differential equations to stochastic stability in probability are given
An Application of Reduction Principle to Stability
No full textIn problemi di modellizzazione è importante ricavare informazioni sui sistemi perturbati a partire dal sistema originale imperturbato.
E' quini importante il trasferimento di proprietà di stabilità da varietà invarianti all’intero spazio. Problema affrontato in questa conferenza nel caso della stabilità asintotica, con applicazione a problemi di biforcazione
On the ordinal and absolute stability properties.
No full textThis paper concerns absolute stability (in the sense of T. Ura) for compact sets with respect to an autonomous dynamical system. In particular, properties which have intrinsic absolute character are individuated (in the sense that if a compact set has such a property, then it has the same property for each degree). It is shown that asymptotic stability as well as total stability are intrinsic absolute properties
A two-step approach to surface functionalize Ti dental implants
Full text linkFor enhancing the osseointegration aptitude of Ti dental implant, titanium oxide (TiO2) - hydroxyapatite (HA) bi-layered coatings were deposited by means of a two-step process on commercial-grade-IV Ti substrates with different pristine morphologies and topographies (machined, sandblasted, and sandblasted/acid etched). Firstly, dense, compact and crystalline titania was deposited as an inter-layer via Low Pressure Metal-Organic Chemical Vapor Deposition. Then a suitably discontinuous HA upper layer was deposited by means of spray pyrolysis. The thermal treatment at 600°C was assessed as the most suitable, both for material features and for bioactivity.
The novelty of this work is that this synergic two-step approach allows the co-existence of both TiO2 and HA ceramics on the implant surface, in order to increase the surface bioactivity and improve the short(HA)- and long(TiO2)-term implant service-life.
The relationship between material processing and functional properties was investigated and evaluated. The electrochemical and tribocorrosive behavior (in artificial saliva) of the functionalized surfaces as well as their metallic ion release (in lactic acid) appeared improved with respect to the uncoated ones. The (nano)hardness of the coated materials was higher than that of bare substrates. In agreement with industrial practice, HA-coating adhesion was qualitatively assessed by tape test. As expected, different results were obtained for different morphologies of substrate surfaces: machined surfaces showed reduced HA retention, while HA coatings better adhered to sandblasted and sandblasted/acid etched substrates. Useful information was obtained by wettability analysis. Freshly prepared surfaces always showed hydrophilicity, and even superhydrophilicity in the case of pure titania coatings. Exposure to air induced gradual wettability decreasing due to atmospheric hydrocarbon contamination. To maintain high-energy surfaces, two industrial-scalable strategies were positively set-up, either storing the samples in distilled water or radiating the contaminated samples by UV.
Acellular in-vitro bioactivity was evaluated testing the growth rate of bone-like apatite after immersion in Dulbecco’s Phosphate Buffer Saline (DPBS) solution at 37°C. The results showed that a bone-like apatite layer was effectively formed on the TiO2 – HA functionalized substrates, giving significant results just after 30 minutes incubation in DPBS. Higher HA nucleation rate was, furthermore, detected on the solely TiO2 coated samples when compared to bare Ti substrates, confirming their improved bioactivity. Finally, according to ISO 10993-5:2009, cell viability confirmed the safety of the samples in terms of cytotoxicity
Limiting processes in the stability problem.
No full textThis paper gives some relationship between stability properties of general processes and the same properties of their limiting processes. The obtained results concern asymptotic stability and total stability
First integrals and stability properties
No full textStability properties of equilibrium for a differential system satisfying a Lipschitz condition uniform on the time. Unconditional stability results are obtained when uniform asymptotic stability occurs with respect to the solutions for which a first integral assumes a fixed appropriate value. A complete discussion is given in a particular case frequently appearing in the applications
Time dependent forces and stability of equilibrium for holonomic systems
No full textThis paper concerns some results on stability of the equilibrium position of holonomic mechanical systems subject to a generalized conservative force and a dissipative one by means of families of Lyapunov functions. The most interesting results concern the case in which the generalized conservative force is the product of a conservative force and a function f(t) periodic in t. In this case we obtain asymptotic stability even if when there is instability for f(t)=1
First and invariant integrals in stability problems
No full textThe relationship between conditional and unconditional asymptotic stability properties of the null solution of a differential system satisfying a Lipschitz condition, uniform on the time, are considered. The conditional properties are given on an invariant manifold defined by a first integrals. The results are illustrated by their applications to a bifurcation problem
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