A. Di Napoli

A model of anisotropic grain-oriented steel

In this work the magnetic flux distribution in the grain-oriented steel core transformer is investigated with the finite element method. A mathematical model (Model II) is obtained for the reluctivity tensor. The model, optimized by means of experimental values of the B-H curve, predicts different directions of the magnetization field, not just along the rolling and transverse directions of the material. The results are the flux maps, as well as the reactance values and the electrodynamic forces on the windings. These results, obtained by means of the isotropic model and the anisotropic first model [1], are compared with the experimental ones.

Papillary carcinoma of the thyroid : Low expression of NCAM (CD56) is associated with downregulation of VEGF-D production by tumour cells

The expression of NCAM was investigated in tissue sections of 61 cases of papillary carcinoma and in 14 lymph node metastases using immunohistochemistry. Tumour cells of 18 primary tumours were not stained, whereas in the remaining 43 cases, NCAM was expressed in less than 5% tumour cells. Similar results were obtained when NCAM expression was evaluated at the RNA level. Reduced expression of NCAM is an early event since 6/15 cases (40%) of micro‐carcinoma were NCAM‐negative. NCAM‐positive tumour cells were more often located at the invasion front of the tumour. It has been reported that NCAM expression may affect lymphangiogenesis. In tissue sections immunostained for podoplanin, it was found that lymphatic vessels were extremely rare inside the body of the tumour, and were mostly associated with foci of chronic inflammation and/or of reparative fibrosis. Lymphangiogenesis is sustained by VEGF‐C, VEGF‐D, and FGF2. Analysis of micro‐dissected samples of the tumour and of the paired normal thyroid tissue revealed that RNA transcripts for VEGF‐D were significantly less numerous in the tumour tissue (p = 0.001). The potential role of NCAM in tumour cell biology was investigated by silencing the NCAM gene in the TPC1 thyroid papillary carcinoma cell line. It was found that NCAM down‐regulation caused a significant reduction (p < 0.05) in the expression of both VEGF‐C and VEGF‐D mRNAs. In addition, NCAM‐silenced TPC‐1 cells were more adhesive to different extracellular matrix components, and were less efficient in cell migration (59% reduction; p < 0.05) and invasiveness (68% reduction). These latter results confirm that modifications of NCAM expression cause profound alterations in the adhesive and migratory properties of tumour cells, but are in apparent discrepancy with the observation that loss of NCAM is usually associated with increased tumour invasiveness in vivo. Copyright

Combination of finite and boundary elements for magnetic field analysis

A procedure is proposed which utilizes combined Finite Elements Method and Boundary Elements Method for magnetic field analysis. Given a region constituted by sub-regions, some of which require a dense discretization, the field analysis is carried out by using the Finite Elements Method, and the Boundary Elements Method is used for the other sub-regions which require a large discretization. The procedure is applied for studying the magnetic field due to a coil and the obtained results are compared with the values given by formulas known in the scientific literature[5].

Electrostatic and Electromagnetic Field Computation for the H.V. Resistive Divider Design

In this paper, the behaviour of the elec trostatic and electromagnetic field of a resistive divi der for H.V. measurements was studied using the finite element technique.

An Approach to DC Motor Modeling and Parameter Calculation Using Finite Element Analysis and Tensor Mathematics

This paper presents a general approach to DC motor modeling, using the finite element technique for maggnetic analysis, and tensor manipulation of network parameters to simulate the machine to the desired degree of complexity. Winding types and saturation of magnetic materials are taken into account. By including electrical and mechanical dynamic behaviour in the equations of state, this approach compactly manipulates the generalized machine mathematical modelto calculate transient response.

Analysis of eddy-current contribution to the magnetic field in squirrel-cage induction machines

The study of the dynamic behaviour of an asynchronous squirrel-cage machine from the electric and magnetic fields, cannot be carried out if we neglect the consequence of the eddy-currents in rotor bars. In this paper first the electric and magnetic field of an asynchronous machine have been considered, and the diffusion equation has been discretized by means of the finite element method. Taking into account the winding connections and effecting a suitable variable transformation, the machine equation has been written in the input-state- -output form. The achieved model enables to study of the electric and mechanical machine transient-state, also considering the effect of an uneven current distribution in the rotor windings.

Induction machine equivalent network parameters computation from electrical and magnetic fields analysis

In this paper a numerical method suitable for analyzing the electric and magnetic dynamic behaviour in an induction machine at any operating condition is presented. Such study is carried out by using finite-elements method and the state variables approach. Since the iron permeability varies with time at any point and the currents in the windings are not a-priori known in the time domain, the dynamic behaviour of the machine was analyzed and the relations between voltage and current at unit terminals were deduced from the field equation. To carry out such analysis an induction machine was taken under investigation and, by neglecting the eddy currents in the conductors and the ferromagnetic non-linearity, net work parameters were computed both referring to the phase machine model and to the generalized machine mathematical one. Then the presence of the non-linearity and the mechanical equation were taken into account and the slip-torque characteristic was determined.

Time-analysis of leakage flux of a slot-bar and computation of equivalent network parameters

This paper analyzes the magnetic field analysis generated in a slot-bar, also taking into account the eddy currents, using the finite-elements method and the state-variables approach. After indicating the formulation of the procedure, the Authors mention the resulting possibility of building the equivalent network of the slot-bar, by through the determining the transfer function of the system.

Saturation effect on the magnetic field distribution in tooth region of electric machines

The time analysis of magnetic field in the rotor teeth of an alternator is carried out taking in account the saturation effects in the iron parts and eddy current in the rotor winding. It is supposed that magnetic field is produced by a step current impressed to the rotor slot-bar and by stator three phase sinusoidal linear distribution of current density. The method used for this investigation is the finite-element method with the state-variables approach.

Computing procedure of mutual reactances in multiwinding transformers

A general computing procedure is described for determining the equivalent network of a transformer with two or more concentric windings divided into multiaxial coils. The magnetic field of a transformer is considered and the equations are discretized by means of the finite element method. Taking into account the winding connections the machine equations are written such that the machine mutual reactances can be calculated simultaneously. A three-phase multiwinding transformer is considered, the mutual reactance values of which have been measured. The average discrepancies between the calculated and measured values are less than 10-15 percent.