178,365 research outputs found
Integral boundary conditions in F.E.M approaches with the minimization of constitutive error
No full textA method based on the minimization of the constitutive error has been successfully applied to finite element formulations of Maxwell equations. Error based techniques present a number of appealing characteristics, including the possibility of providing an estimation of the error distribution and to split the equation system in two decoupled subsystems. However, except for very simple cases, a direct numerical translation of the boundary conditions can cause a number of drawbacks: on one side the lack of symmetry and positive definition of the matrix, on the other side the impossibility of splitting the unknowns. This paper is aiming to discuss the problem and to propose a technique to effectively impose a wide class of boundary conditions within the framework of error based formulations. To show the performance of the technique, some examples are proposed
Electromagnetic analysis with Equivalent Models of Complex Conducting Structures
No full textComplex conducting structures, whenever they are not the focus of interest of the electromagnetic analysis, are approximated by means of equivalent simplified models. Composite materials can be treated as homogeneous anisotropic media. Complex 3D structures can be approximated by means of 2D axisymmetric models or lumped parameter systems. The material properties or the parameters of the equivalent models are determined in such a way as to preserve the interaction with the remaining structures. Upper and lower bounds are established for electromagnetic quantities of interest for plates with circular holes and quasi-axisymmetric structures in fusion device
A standardized protocol for continuous subcutaneous insulin infusion in the peripartum period in women with type 1 diabetes
No full textObjectives and methods. Metabolic control must be optimized to prevent maternal-neonatal complications during and after delivery. The primary aim of this study was to provide a standardized protocol for continuous subcutaneous insulin infusion (CSII), with or without real-time continuous glucose monitoring (RT-CGM), during delivery in pregnant type 1 diabetic women. This procedure was based on a retrospective multicenter observational study in which CSII was used around the time of delivery by women already instructed on its use during pregnancy. Three basal insulin rates were established, depending on the capillary blood glucose level (CBG): profile A, last basal rate in use before delivery; profile B, half of profile A; profile C, 0.1-0.2 U/h, for CBG < 70 mg/dl, activated just before anesthesia or at the beginning of active labor. An alternative intravenous insulin protocol (IVP) was applied in case of complications or sudden metabolic deterioration. Primary outcomes were CBG in the target range (70-140 mg/dl) throughout delivery and the percentages of women managed with the IVP. Results. The study comprised 65 pregnant women with diabetes: 56 (86%) had cesarean section, 9 (14%) spontaneous/ induced vaginal delivery. Mean CBG was 102 ± 31 mg/dl at time 0; 109 ± 42 mg/dl at 30 min; 120 ± 48 mg/dl at 60 min; 99 ± 34 mg/dl at 24 h. Mean basal rate during delivery was 0.6 ± 0.4 U/h (profile B). Mean CBG was lower in the RT-CGM group than with CSII alone: 80 ± 14 mg/dl vs 111 ± 32 mg/dl at 0 min (p < 0.01); 79 ± 11 mg/dl vs 109 ± 42 mg/dl at 30 min (p < 0.02); 98 ± 20 mg/dl vs 125 ± 51 mg/dl at 60 min (p = ns). There were 11 cases (17%) of neonatal hypoglycemia, 9 of them transient. No women had to switch to IVP. No major differences were observed in relation to the delivery procedure. Conclusions. CSII is feasible and safe during delivery in selected women who have been appropriately instructed. RT-CGM can help achieve better maternal peripartu
An ionic conduction mechanism for the AgI doped glasses of the system Ag2O-B2O3
No full textIn this paper it is proposed that, as long as the glasses of the system Ag2O-B2O3-AgI are demixed on a very fine scale into a silver borate matrix and AgI microdomains, their activation energy for electrical conduction can be considered an average value of the two phases present. These values are taken to be equal to those of silver iodide and of the corresponding undoped silver borate In this light it is expected that, in the compositional range considered the following relation holds: E-sigma/E-sigma ma = R; where E-sigma and E-sigma ma are the activation energies, respectively, of the doped and undoped glass and R is the fraction of Ag+ added as Ag2O. Deviations from this 'ideal' behaviour are attributed to the presence, at the boundary of the two phases, of Ag+ in mixed neighbour sites, that is, surrounded by negatively charged structural units of both phases. This approach appears to be successful in explaining the compositional dependence of both E-sigma and the glass transformation temperature, T-g, of the studied system
Analysis of Stress Induced by Plasma Disruption on Vacuum Vessel through Multi-physics Modeling.
No full textThe analysis of the stresses induced on the vacuum vessel (VV)
of a Tokamak and its internal components by the plasma instabilities,
such as plasma disruptions, also following a Vertical Displacement Event
(VDE) is one of the major concern in the Tokamak design. So the
availability of a fast simulation tool for evaluating different design
options, also able to perform parametric analysis, is highly attractive
to define the project requirements and to verify the conceptual design.
To respond to this wish, a methodology based on the multi-physics
modeling capability offered by the Comsol® software platform was
developed. It consists in coupled simulations based on the data sharing
between two 2D axisymmetric model, everyone coupled with a corresponding
3D model, shifted each other of 10 degrees.
In the 2D axisymmetric model of every couple, the magnetic and
electric fields generated by the plasma VDE and disruption, are
calculated imposing the plasma time evolution as input. In the
corresponding 3D model only the mechanical structures are present and on
them the Electric and Magnetic fields are extruded, determining so the
induced currents diffusion in the passive conductors. Then the resulting
Lorentz's forces are imposed as body loads on the mechanical structures,
so a linear stress analysis can be carried out after the constraints
assignment. The same procedure is followed with the second couple of
2D/3D models for check purposes, comparing some proper physical
quantities, such as the total induced current flowing on the VV. In this
paper the methodology is presented by reporting the simulation of a
double null plasma VDE, lasting c.a. 100 ms, followed by a full 5.5 MA
plasma current quench in about 40 ms
Improvement of Plasma Identification in Tokamak devices with dynamical informations
No full textFast and reliable identification of plasma parameters in tokamak reactors is an issue of primary importance for the effectiveness of plasma position control action. A number of different measurement techniques are available, but the magnetic ones play the major role. Anyway, the magnetic field depends also on the currents induced in the confinement structures, which are very difficult to deal with. In this paper a new approach to the identification problem is proposed, based on the electromagnetic dynamical behavior of the system. The currents induced in the passive structures are considered and in addition, advantage is taken by the knowledge of the time derivative of the electrical state variable
Effects of Dynamical Information in Identification Problems in Electromagnetics
No full textThe identification of currents from external magnetic
measurements is an inverse problem frequently encountered in a
number of applications. This inverse problem can be regularized
with SVD decomposition, but other information coming from the
dynamical behavior of the system can be beneficial. In the paper
such an approach is analyzed and compared to classical methods
An error-based approach to the solution of full Maxwell Equations
No full textAim of this paper is to extend the error based approach to the study of general electromagnetic problems in 3D geometries in which the displacement currents may not be neglected. The unknown variables are the three-component vector potential A and W defined as the time integrals of -E and H, respectively. These potentials are constrained to satisfy initial, boundary and interface conditions. Since in this way the Maxwell equations are automatically satisfied, the solution is obtained via minimization of a global error functional which approaches zero when the constitutive equations are satisfie
ACCURATE COMPUTATION OF ELECTROMAGNETIC-FIELDS IN THE PRESENCE OF CONDUCTING AND MAGNETIC MATERIALS
No full text- …
