1,721,032 research outputs found
Homogenization and exact controllability for problems with imperfect interface
No full textThe first aim of this paper is to study, by means of the periodic unfolding method, the homogenization of elliptic problems with source terms converging in a space of functions less regular than the usual L-2, in an s-periodic two component composite with an imperfect transmission condition on the interface. Then we exploit this result to describe the asymptotic behaviour of the exact controls and the corresponding states of hyperbolic problems set in composites with the same structure and presenting the same condition on the interface. The exact controllability is developed by applying the Hilbert Uniqueness Method, introduced by J. -L. Lions, which leads us to the construction of the exact controls as solutions of suitable transposed problem
A gap in the essential spectrum of a cylindrical waveguide with a periodic perturbation of the surface
No full textIt is proved that small periodic singular perturbation of a cylindrical waveguide surface may
open a gap in the continuous spectrum of the Dirichlet problem for the Laplace operator. If the
perturbation period is long and the caverns in the cylinder are small, the gap certainly opens
Is there an association between childhood obesity and dental caries? A clinic-statistic study.
No full textA note on the exact boundary controllability for an imperfect transmission problem
No full textIn this note, we consider a hyperbolic system of equations in a domain made up of two components. We prescribe a homogeneous Dirichlet condition on the exterior boundary and a jump of the displacement proportional to the conormal derivatives on the interface. This last condition is the mathematical interpretation of an imperfect interface. We apply a control on the external boundary and, by means of the Hilbert Uniqueness Method, introduced by J. L. Lions, we study the related boundary exact controllability problem. The key point is to derive an observability inequality by using the so called Lagrange multipliers method, and then to construct the exact control through the solution of an adjoint problem. Eventually, we prove a lower bound for the control time which depends on the geometry of the domain, on the coefficients matrix and on the proportionality between the jump of the solution and the conormal derivatives on the interface
Asymptotic Behavior of a Bingham Flow in Thin Domains with Rough Boundary
No full textWe consider an incompressible Bingham flow in a thin domain with rough boundary, under the action of given external forces and with no-slip boundary condition on the whole boundary of the domain. In mathematical terms, this problem is described by non linear variational inequalities over domains where a small parameter ε denotes the thickness of the domain and the roughness periodicity of the boundary. By using an adapted linear unfolding operator we perform a detailed analysis of the asymptotic behavior of the Bingham flow when ε tends to zero. We obtain the homogenized limit problem for the velocity and the pressure, which preserves the nonlinear character of the flow, and study the effects of the microstructure in the corresponding effective equations. Finally, we give the interpretation of the limit problem in terms of a non linear Darcy law
Estimates in homogenization of degenerate elliptic equations by spectral method
No full textWe study the homogenization of elliptic equations stated in L2-space with degenerate weight. Both coefficients of
the differential operator and the weight are ε-periodic and highly oscillating as ε tends to zero. Under minimal hypotheses on
the coefficients and the weight we prove estimates of order ε and ε2 for L2-norm of the difference between the exact solution
and its appropriate approximations by L2-norm of the right-side function. The spectral method based on Bloch decomposition
is used. In the case of nonunique solution provided that the weight is not regular we consider estimates for any of so-called
variational solutions
Optimal control problem stated in a locally periodic rough domain: a homogenization study
No full textWe study the asymptotic behaviour of a linear optimal control problem posed on a locally periodic rapidly oscillating domain. We consider an (Formula presented.) -cost functional constrained by a Poisson problem having a mixed boundary condition: we assume a homogeneous Neumann condition on the oscillating part of the boundary and a homogeneous Dirichlet condition on the remaining part
Homogenization results for a coupled system of reaction–diffusion equations
No full textThe macroscopic behavior of the solution of a coupled system of partial differential equations arising in the modeling of reaction–diffusion processes in periodic porous media is analyzed. Our mathematical model can be used for studying several metabolic processes taking place in living cells, in which biochemical species can diffuse in the cytosol and react both in the cytosol and also on the organellar membranes. The coupling of the concentrations of the biochemical species is realized via various properly scaled nonlinear reaction terms. These nonlinearities, which model, at the microscopic scale, various volume or surface reaction processes, give rise in the macroscopic model to different effects, such as the appearance of additional source or sink terms or of a non-standard diffusion matrix
Immediate dentin sealing in indirect restorations of dental fractures in paediatric dentistry
Full text linkAIM:
At present, two different clinical procedures to ensure the adherence of indirect tooth restorations to the dental tissues are available: a traditional method based on a delayed dentin sealing (DDS) and an innovative approach that contemplates an immediate dentin sealing (IDS). In this study the authors highlight the advantages of the latter method (IDS), decribing the operating phases of this procedure used in paediatric dentistry to perform indirect restorations of dental fractures.
MATERIALS AND METHODS:
The operating phases of indirect composite restorations of dental fractures in paediatric patients are described, introducing an innovative procedure that recommends the immediate application of the dental adhesive (IDS) on the exposed dentin before the subsequent operating phases of tooth preparation, dental impression and adhesive cementation of the restoration.
RESULTS:
The immediate application of the dental adhesive (IDS) on the freshly cut exposed dentin, before taking the dental impression, protects the dental pulp from bacterial contamination and prevents post-operative sensitivity. At the same time, this procedure provides an ideal substrate for formation of a hybrid layer with excellent adhesion properties.
CONCLUSION:
Both methods (DDS and IDS) allow the formation of an adequate hybrid layer to seal the dentin in the interdiffusion area, although SEM images of samples treated with the two methods reveal clear ultrastructural differences between the different interface
Conservative treatment of a recto-urethral fistula due to salvage HIFU for local recurrence of prostate cancer, 5 years after radical prostatectomy and external beam radiotherapy
No full textRecto-urethral fistula is one of the most serious complications caused by high-intensity-focused ultrasound used as salvage treatment for recurrence of prostate cancer after brachytherapy or external beam radiotherapy (EBRT). We report the case of a recto-urethral fistula in a 68-year-old patient, who previously had undergone radical prostatectomy and EBRT for prostate cancer (pT3 N0 Mx). The fistula was treated conservatively by an indwelling Foley catheter, without the creation of an intestinal diversion. The fistula was assessed initially by a retrograde and a CT scan of the pelvis with contrast medium and reassessed periodically by means of retrograde urethrograms. To date, 24 months after this episode, no evidence of recurrence of the fistula has been found
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