248 research outputs found
Explicit Torque and Back EMF Expressions for Slotless Surface Permanent Magnet Machines with Different Magnetization Patterns
No full textSlotless permanent magnet machines are attractive in some modern drive and power generation fields, where the cogging torque and additional losses need to be minimized or removed. The stator slotless design can be combined with different surface permanent magnet (SPM) rotor topologies. In this paper, explicit analytical expressions are derived to analytically compute the slotless machine torque and no-load back Electro-Motive Force in the case of segmented SPM rotor with parallel, radial, or Halbach-array magnetization patterns. The expressions are found by solving the magnetic field due to the slotless stator winding and to the permanent magnet blocks; the latter modeled through equivalent surface current densities. The accuracy of the method is successfully assessed by comparison with the finite-element analys is (FEA). The proposed formulas are an effective alternative to
the FEA to quickly compare different design solutions as well as to optimize them. Application examples are provided in which the presented method is adopted to define the machine cross section that maximizes the torque density
A New Method for Determining the Leakage Inductances of a Nine-Phase Synchronous Machine From No-Load and Short-Circuit Tests
No full textThe accurate determination of stator leakage inductances is presently an open issue in the analysis and testing of multi-
phase electric machines. Calculation methods are available, which involve complicated and often poorly precise three-dimensional (3-D) analyses. Experimental determination techniques, using measurements on the wound stator with the rotor removed, are also possible, but quite impractical, as they need to be performed during machine manufacturing or require rotor withdrawal. In this paper, a new approach is proposed to determine all the stator self- and mutual leakage inductances of a nine-phase synchronous machine based on a minimal set (a couple) of magnetostatic finite-
element (FE) simulations, and on the measurements taken during no-load and short-circuit routine tests. The procedure is applied to a wound-field salient pole nine-phase synchronous generator for validation, showing good accordance with the results obtained from measurements on the machine with the rotor removed. A discussion is also proposed on the possibility to extend the presented procedure to other multiphase topologie
On the analytical determination of the complex relative permeance function for slotted electrical machines
No full textThe complex relative permeance function is a suitable tool to predict the air gap magnetic field in slotted stator electrical machines. In the literature, the complex permeance function is usually identified by means of numerical techniques based on complex approaches such as conformal mapping or subdomain method. In this paper, an alternative approach is proposed. This method is based on solving the magnetostatic Laplace equation over a portion of the slotted air gap by imposing appropriate boundary conditions in the slot opening region. Such boundary condition tries to represent the theoretical trend of the magnetic field divergence near the corner-shaped ferromagnetic regions. The Carter theory for the slot fringing effect is also used. A fully analytical formulation for the complex relative permeance function is obtained, and its accuracy is assessed by comparison with Finite Element Analysis (FEA)
Study of the mechanism of action of new molecules endowed with antitumoral activity
No full textThe microtubule system of eukaryotic cells is a critical element in a variety of fundamental cellular processes such as cell proliferation, mitotic spindle formation, maintenance of cell shape, regulation of motility, cell signaling, secretion, and intracellular transport. The important role of microtubules dynamic in mitosis progression and thus in cell proliferation, made them an attractive target for cancer therapy. Many chemically diverse compounds bind and affect tubulin-microtubule system, altering polymerization and dynamics during the particularly vulnerable mitotic stage of the cell cycle, causing alteration in the spindle organization with a delay or block at the metaphase-anaphase transition during mitosis.
In this study we evaluated the antiproliferative activity of seven series of novel tubulin polymerization inhibitors deriving from three classes of colchicine site binders: combretastatin-A4, chalcones and pyrroloquinolinones. Furthermore we investigated on the inhibitory effects on tubulin polimerization, cell cycle alteration, and apoptosis induction in in vitro and in vivo models and described a possible mechanism of action. The studied compounds, showed antiproliferative activity derived from a interference with microtubule assembly similar or higher than the reference compounds. As general mechanisms of action, the interaction of such compounds with tubulin, induces cell cycle arrest in the G2/M phase, with increased expression of cyclin B1 and phosphorylation of cdc25c, that trigger to apoptosis in a time- and concentration-dependent manner with activation of caspase-3 and cleavage of PARP and reduction of Bcl-2 prosurvival protein. Moreover, several compounds was effective against cancer cell lines, characterized by high expression of glycoprotein-P and multidrug resistance-associated protein, resistant to chemotherapy drugs such as vinblastine, doxorubucine and taxol. Prelimary experiment carried out in vivo models of tumor xenograft showed a significative reduction of tumor growth suggesting a potential clinical applications for these compounds.Nelle cellule eucariotiche i microtubuli costituiscono un elemento cruciale nella regolazione di molteplici processi cellulari, tra cui la proliferazione, la formazione del fuso mitotico, il mantenimento della forma cellulare, la regolazione della motilità, il signaling cellulare, i processi di secrezione e trasporto intracellulare. Il ruolo fondamentale di tale struttura citoscheletrica nella progressione mitotica e di conseguenza nella proliferazione cellulare rende i microtubuli un ottimo target per la terapia antitumorale. Molti composti aventi struttura chimica differente sono in grado di legare il sistema tubulina-microtubuli, alterandone la polimerizzazione e la dinamica, in particolare durante la fase mitotica del ciclo cellulare, destabilizzando l'organizzazione del fuso mitotico, ritardando o bloccando la transizione metafase-anafase.
In questo studio è stata valutata l'attività antiproliferativa di sette serie di nuovi inibitori della polimerizzazione della tubulina, derivati da 3 classi di composti che legano i microtubuli a livello del sito di legame della colchicina:
combretastatina-A4, calconi e pirrolochinolinoni. In particolare, è stato studiato in modelli in vitro e in vivo l'effetto di tali inibitori sulla polimerizzazione della tubulina, sul ciclo cellulare e sull'attivazione dell'apoptosi per la descrizione di un possibile meccanismo d'azione. I composti testati hanno mostrato attività antiproliferativa comparabile o superiore rispetto ai composti di riferimento.
Per quanto riguarda il meccanismo d'azione, in generale, l'interazione di tali composti con la tubulina induce un blocco del ciclo cellulare in fase G2/M con l'aumento dell'espressione della ciclina B1 e la fosforilazione di Cdc25c. Tale arresto della progressione mitotica porta all'attivazione del processo apoptotico in modo tempo- e concentrazione- dipendente con la attivazione di caspase-3, il taglio proteolitico di PARP e la riduzione delle proteine Bcl-2 antiapoptotiche.
Inoltre, alcuni composti hanno mostrato elevata efficacia nell'indurre citotossicità in cellule tumorali multidrug resistant, esprimenti la licoproteina-P e le pompe di efflusso MDR, resistenti a chemioterapici quali vinblastina, doxorubucina e tassolo. Esperimenti preliminari, svolti in modelli murini di xenotrapianto, hanno mostrato una significativa riduzione della crescita tumorale, suggerendo una possibile applicazione clinica per alcuni dei composti studiati
A sizing equation for slotless surface-mounted radially-magnetized permanent-magnet machines
No full textSlotless surface permanent-magnet (SPM) machines are attractive for many applications where it is important to minimize the cogging torque and or the eddy-current losses due to slotting effects. The design of these machines is often approached through Finite Element Analysis (FEA) simulations interfaced to design optimization programs, leading to a significant computational burden. In this paper, a compact but accurate sizing equation is established linking machine maximum torque to the main design data. The sizing equation can be used for a fast first-attempt sizing of the machine with no need for FEA simulations and no need for complicated magnetic field solutions. The proposed sizing approach is based on an explicit fully-analytical expression of machine torque, which is validated by FEA simulations
Analytical Computation of End-Coil Leakage Inductance of Round-Rotor Synchronous Machines Field Winding
No full textThe computation of end coil leakage inductances of electric machines is a challenging task due to the complicated leakage flux 3D distribution in the winding overhang region. In this paper the problem is addressed of computing the field circuit leakage inductance of round-rotor synchronous machines. The proposed method is fully analytical and descends from the symbolical solution of Neumann integrals applied to the computation of self and mutual inductances combined with the method of mirror images to account for core effects. With respect to existing analytical approaches, the methodology requires neither numerical integral solutions nor discretizing the end-coil geometry into small straight elements. The accuracy of the proposed technique for computing the mutual inductance between two single end turns is assessed against measurements on a dedicated experimental set-up. The extension of the method to the
computation of the entire field-circuit end-coil leakage inductance is assessed by comparison with 3D finite element analysis (FEA)
Unitary permeability of gap junction channels tosecond messengers measured by FRET microscopy
No full textGap junction channels assembled from connexin protein subunits mediate intercellular transfer of ions and metabolites. Impaired channel function is implicated in several hereditary human diseases. In particular, defective permeation of cAMP or inositol-1,4,5- trisphosphate (InsP(3)) through connexin channels is associated with peripheral neuropathies and deafness, respectively. Here we present a method to estimate the permeability of single gap junction channels to second messengers. Using HeLa cells that overexpressed wild-type human connexin 26(HCx26wt) as a model system, we combined measurements of junctional conductance and fluorescence resonance energy transfer ( FRET) emission ratio of biosensors selective for cAMP and InsP3. The unitary permeabilities to cAMP (47 x 10(-3) +/- 15 x 10(-3) mu m(3)/s) and InsP(3) (60 x 10(-3) +/- 12 x 10(-3) mu m(3)/s) were similar, but substantially larger than the unitary permeability to lucifer yellow (LY; 7 +/- 3 x 10(-3) mu m(3)/s), an exogenous tracer. This method permits quantification of defects of metabolic coupling and can be used to investigate interdependence of intercellular diffusion and cross-talk between diverse signaling pathways
Investigation into Multi-Layer Fractional-Slot Concentrated Windings with Unconventional Slot-Pole Combinations
No full textFractional-slot concentrated windings (FSCWs) are an attractive option for the design of synchronous permanent-magnet machines. It is commonly assumed in the existing literature that a symmetrical three-phase FSCW is feasible only on a condition that the number of slots Z is an integer multiple of three times the maximum common divisor between Z and the number of pole pairs p. Slot-pole combinations satisfying this rule can be defined conventionally, the others unconventionally. In contrast to the common belief, this paper shows that, using a multi-layer arrangement, it is possible to synthetize a symmetrical FSCW having unconventional slot-pole combinations. A general design methodology for this purpose is presented and validated by finite element analysis. The pros and contras of FSCWs with unconventional slot-pole combinations are examined. Finally, the application of an unconventional FSCW to a shipboard surface permanent-magnet machine prototype is presented to illustrate the possible practical convenience of this kind of winding and tests on the prototype are reported for experimental validation
FEA-Assisted steady-state modelling of a spoke type IPM machine with enhanced flux weakening capability
No full textInterior permanent magnet (IPM) machines with spoke-type design are possible candidates for various applications, including vehicle traction. One of their drawback is the high demagnetizing current required in the flux weakening region to let the motor achieve high speeds. This problem can be mitigated by equipping the motor with a mechanical devices consisting of mobile rotor yokes. These move radially by centrifugal force so as to reduce the air-gap flux at high speed with no need for demagnetizing current injection. This paper addresses the problem of modeling such IPM motor to study its steady-state behavior under different operating conditions, both in the full-flux and in the flux-weakening region of the speed range. The approach uses a limited set of non-linear finite element analysis to characterize the dependency of motor flux linkages on the stator currents and rotor position. Interpolating functions are then obtained to mathematically capture this dependency and plug it into the steady-state electromechanical equations of the motor. The effectiveness and accuracy of the method are assessed through on-load measurements taken on the modelled motor both in low and high speed operation
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