Andrea Stella

Andrea Stella
University of Padova | UNIPD · Department of Industrial Engineering

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403
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Publications

Publications (403)
Article
A method for the computation of the induction field in presence of open and closed passive conductors has been developed. It solves uniquely the inverse problem to determine the eddy currents needed in the passive conductors to produce a given flux. The method has been applied to the case of the RFX experimental machine to the induction field insid...
Article
To investigate the effects of the interaction between adenosine receptors and renal nerves on urinary sodium excretion and glomerular filtration rate. The effects on water and sodium excretion and glomerular filtration rate of A1 [2-chloro-N6-cyclopentyl-adenosine (CCPA)] and A2 [2-hesinyl-5'-N-ethyl-carboxamido-adenosine (2HE-NECA)] adenosine agon...
Book
Mi dispace non ho il pdf del libro, che oltre tutto è esaurito presso l'editore. Posso suggerire il nuovo testo "Elettrotecnica" (2 volumi) che lo sostituisce a Padova, con primo autore G. Chitarin ed edito da Esculapio. Credo che l'editore sia disponibile a inviare un saggio a destinatorio referenziato. mg
Article
To verify the existence of ipsilateral reno-renal reflexes we studied the effect of surgical denervation of one kidney on the ipsilateral efferent renal nerve activity (ERNA), in the absence of contralateral afferent renal nerve activity. Thus the ipsilateral renal denervation was performed 1 h later than the contralateral renal denervation. The ex...
Article
The effects of recombinant human erythropoietin (rHuEPO) administration on blood pressure and urinary albumin excretion were studied in normotensive Wistar-Kyoto rats (WKY), in spontaneously hypertensive rats (SHR), and in SHR rats treated with an angiotensin converting enzyme inhibitor (SHR-ACEi). Rats were housed in metabolic cages and treated wi...
Article
1. Afferent nerve fibres sensitive to changes in the renal chemical environment have been found in the rat. To verify the existence of these fibres in the rabbit and their response pattern, afferent renal nerve activity was recorded during pelvic perfusions with NaCl solutions at different concentrations. 2. The experiments were carried out in 13 a...
Article
To evaluate the interaction between renal nerves, the atrial natriuretic peptide (ANP), and the renin-angiotensin system (RAS), electrical stimulation of renal nerves was performed in spontaneously hypertensive rats (SHR) and in their normotensive controls, Wistar Kyoto rats (WKY), before and after pharmacologic treatment with (a) a neutral endopep...
Article
The experiments were performed to study the role of the renal nerves and the reno-renal reflexes in the control of water and sodium excretion in spontaneously hypertensive rats (SHR) compared to their normotensive controls, Wistar Kyoto (WKY) rats. Unilateral renal denervation in anaesthetized animals produced a slight, progressive decrease in arte...
Article
The paper presents a method for the reconstruction of an axisymmetric configuration of magnetic field. The reconstruction procedure is based on a multipolar series expansion of the magnetic field and requires a number of experimental measurements of magnetic field and flux. The accuracy and efficiency of the procedure is analysed and compared with...
Article
In ten sino-aortic denervated, vagotomized and anaesthetized cats, renal efferent nerves were stimulated for 30 s with trains of constant current pulses at frequencies in the range 5 - 30 Hz. The arterial pressure, heart rate, urine flow rate (electronic drop counter) and renal blood flow (electromagnetic technique) were recorded. Subsequent comput...
Article
The purpose of this study was to analyze mode of presentation, surgical treatment, and early and long-term results of a series of extracranial internal carotid artery aneurysms (EICAA). A retrospective analysis was performed on all cases treated for EICAA in a single institution from March 1974 to March 1995. Patient follow-up was obtained by a sur...
Article
To investigate the effects of the interaction between adenosine receptors and renal nerves on renin release. The effects on renin secretion of A1 (2-chloro-N6-cyclopentiladenosine) and A2 (2-hexynil-5'-N-ethyl-carboxamido-adenosine) adenosine-receptor agonists were studied in two groups of anaesthetized rats, each with one kidney surgically denerva...
Article
Full-text available
The reversed field pinch (RFP) magnetic confinement requires both toroidal and poloidal components for the magnetic field induction. As in tokamaks, the former is provided by the toroidal and poloidal components for the the ohmic heating (OH) winding and the equilibrium field (EF) winding. The two induction field components have similar amplitudes,...
Article
Parietal characteristics of small aortic aneurysms predictive of increased risk of rupture are unknown. Prospective morphologic evaluation was performed in 135 consecutive cases of small (< 5 cm) abdominal aortic aneurysm. Twelve cases (9%) were found to be ruptured and sent for emergency surgery. The remaining 123 patients were evaluated with ultr...
Article
The RFX magnetic measurement system consists of 508 probes installed outside the vacuum vessel and allows an accurate measurement of the fundamental quantities of the experiment, such as the toroidal current, the poloidal and toroidal voltage and flux, the average toroidal field at the wall, the vertical field through the shell and the field error...
Chapter
Full-text available
RFX is equipped with an original fast protection central system named SGPR, particularly designed to perform the fast protection of the device during the pulse phase. It is interfaced with all sub-systems in which dangerous faults for the machine integrity can arise and develop very quickly, namely within 2 ms. SGPR is a logic machine, including a...
Chapter
Full-text available
The commissioning of the RFX power supplies and their integration with the machine windings were performed in steps of increasing complexity; the target was to start the experiments with plasma in the final configuration of all systems, tested up to the performances required for first operation. After a brief description of RFX circuits and operati...
Chapter
Full-text available
The Reverse Field Pinch experiment RFX has been operating since the end of 1991. The paper, after a brief description of the load assembly, presents the most significant aspects of the assembly phase and discusses methods and results of the final tests, carried out before producing the first plasma. Finally, the machine behaviour during the first e...
Article
Mechanoreceptors and chemoreceptors have been identified inside the kidney, but their functional role is still largely unclear. The aim of this study was to investigate whether changes in urine output could modify the discharge rate of renal afferent fibers. Experiments were performed in anesthetized cats in which afferent renal nerve activity (ARN...
Conference Paper
Full-text available
The paper presents the application and the first results of a plasma shape identification code used in the RFX experiment. This code has been specifically developed for machines provided with a stabilizing shell and with magnetic probes placed outside the vacuum vessel. In RFX, as in all the present-generation RFP machines, no steady-state magnetic...
Conference Paper
Full-text available
RFX, the largest RFP machine, has air-core poloidal windings. A tree-shaped earthing geometry has been adopted for all the machine components, to avoid electrical loops. Nevertheless, during the first operation phase a number of accidental contacts occurred, which caused loops currents high enough to distort plasma equilibrium. These loops could be...
Article
Inflammatory aneurysms (IAs) have peculiar macroscopic and histological aspects which make them very different from nonspecific aneurysms (NSAs). These morphological differences seem to be determined by significant modifications of the extracellular matrix. Extracellular matrix protein component concentrations were determined biochemically in infra...
Article
Of 779 patients undergoing repair of abdominal aortic aneurysms over a 7-year period (1984–1990), 40 (5.1%) had gross features of inflammatory abdominal aortic aneurysms (IAAAs). Twenty IAAAs were assessed by CT scan preoperatively and postoperatively to evaluate the outcome of the inflammatory layer of the aneurysm in 19 cases. Complete postoperat...
Article
RFX is a magnetic confinement toroidal machine based on the reversed field pinch (RFP) concept. A study of the magnetic configurations with null-field points (X-points) has been performed in order to analyze the feasibility of operating RFX with a magnetic divertor. A reasonable solution has been found by means of an optimization procedure that tak...
Article
We conducted a retrospective review of all patients undergoing repair of abdominal aortic aneurysm at or above the proximal anastomosis of a previous infrarenal aortic graft between 1986 and 1991. Infected grafts and patients with suprarenal aneurysms present at the time of the original graft were excluded. Twenty-one patients, 19 men and two women...
Article
This paper deals with the problem of internal overvoltages within large coils due to fast-rising surges. Numerical simulations are performed on a lumped-parameter equivalent circuit, representing a coil of the magnetic system of a thermo-nuclear fusion experiment. Inductances and capacitances are computed through numerical methods which ensure a go...
Article
Arterial lesions in patients with neurofibromatosis are rarely described and in most cases are stenotic. The aneurysmal changes reported in the literature are usually characterized by multiple microaneurysms due to the dysplastic lesions of the artery. We report a case of a single aneurysm of the inferior hilar branch of the left renal artery of a...
Article
In this study we analyse the beat-by-beat dynamics of mean renal vascular resistance (MRVR) and water excretion, to graded levels of electrical stimulation of the renal efferent nerves in anesthetised sinoaortic dener-vated cats. Data is presented which demonstrates that changes in RVR are mediated via two independent mechanisms having different te...
Article
Two methods are considered for the solution of automated digital optimal design problems. The computer procedures based on these methods have been implemented and tested. The first method, based on a deterministic approach, considers a quadratic approximation of the cost function. The second, based on a stochastic approach, is derived from the simu...
Article
Reports of high mortality and amputation rates following total excision and extra-anatomic bypass for aortic graft infection have prompted the use of alternate approaches including local antibiotics, partial resection, in situ revascularization, and graft excision without revascularization. Experience with aortic graft infection was reviewed to est...
Article
Block I1 is the innermost group of Poloidal Field coils of the RFX machine. It is constituted by 6 Ohmic Heating coils and two Field Shaping coils moulded in one piece. These coils are made of copper conductors insulated with fibreglass and Kapton and impregnated with epoxy resin. During acceptance tests, the inter-turn insulation of a Field Shapin...
Article
We studied neural influences on the renal actions of atrial peptides in anaesthetized cats by comparing the response to atrial natriuretic factor (ANF) infusion in the innervated kidney and in the contralateral surgically denervated kidney. During ANF infusion arterial pressure decreased, the heart rate did not change and blood flow to both kidneys...
Article
Primary dissections of the abdominal aorta are rare (0.4-4% of aortic dissections) and in most cases are traumatic (accidental or iatrogenic) in origin. The authors describe a case of iatrogenic dissection of the abdominal aorta following arteriography. The macroscopic and histological appearance of the aortic wall was compatible with an inflammato...
Article
Full-text available
The authors present a methodological examination of several formulations developed to solve different kinds of inverse electromagnetic problems. Some general numerical formulations of the inverse problems are presented that are defined regardless of the nature of the specific electromagnetic problem. It is shown that the different approaches can be...
Article
The present study was designed to determine whether renal nerves influence the natriuretic response to an infusion of vasopressin. Experiments were performed on anaesthetized rats in which the response to vasopressin of the innervated kidney was compared with that of the contralateral surgically denervated kidney. During the vasopressin infusion th...
Conference Paper
In the reversed field pinch experiment (RFX), many kinds of transducers are used in order to measure a great deal of parameters related to the machine monitoring, control, and protection. After a description of the principal measurement requirements and of the expected noise sources, the possible physical mechanisms by which noise and signals can b...
Article
Experiments were performed in anaesthetized cats, to determine whether renal nerves interfere with the negative feedback action of angiotensin II (Ang II) on renin release. The increase in renin release from the innervated kidney in response to captopril-induced inhibition of Ang II generation was compared with the response of the contralateral den...
Article
Full-text available
A method for solving problems of electromagnetic field diffusion in axisymmetric configurations with linear conducting media is presented. The approach, which is based on lumped-parameter circuit modeling, has a number of theoretical and practical advantages in comparison with other methods currently used, particularly in dealing with problems wher...
Article
Among the major mechanisms controlling the renal release of renin, renal nerves are known to exert a direct stimulating action on juxtaglomerular cells that is mediated by beta-adrenoceptors. Activation of the renal nerves also exerts an important permissive role in order to amplify and possibly accelerate responses to stimuli affecting the vascula...
Conference Paper
Full-text available
The paper describes the development work on the design and the manufacture of the RFX Field Shaping Winding, from the preliminary analysis and the tests on prototypes to the final design. The winding consists of 16 coils, with 24 copper turns each and of diameters up to 5.5 m. The maximum current is 6.25 kA and the maximum voltage to earth is 35 kV...
Article
Full-text available
This paper presents the final design and main manufacturing aspects of the RFX Magnetizing Winding, now being manufactured by ABB. The winding is designed to store 15 Wb flux and consists of 200 copper turns wound into 40 coils. These are impregnated in groups to form 17 blocks, to satisfy mechanical requirements. The largest coils, with diameters...
Article
Full-text available
The paper describes the development work on the design and the manufacture of the RFX Field Shaping Winding, from the preliminary analysis and the tests on prototypes to the final design. The winding consists of 16 coils, with 24 copper turns each and of diameters up to 5.5 m. The maximum current is 6.25 kA and the maximum voltage to earth is 35 kV...
Article
Full-text available
RFX is a fusion Reversed Field Pinch (RFP) experiment under construction in Padua, Italy. Its air-core magnetizing winding is part of the poloidal-field winding and is devoted to inducing the toroidal plasma current by transformer action. This is obtained by slowly charging the winding to a specified current which is then forced to deca quickly. Du...
Article
Full-text available
The RFX toroidal field winding consists of 48 coils, which can be connected in many series/parallel configurations according to the toroidal field programming required for plasma operation. For ease of maintenance each coil consists of two identical half-coils connected at the equatorial plane of the machine. To be in alignment, the half coils are...
Article
A 3-D computer code for the calculation of magnetic fields, self- and mutual-inductance coefficients, and electromagnetic forces is considered. A unique feature of this code is the presence of a number of very precise models for the calculation of the field produced by circular or noncircular coils, busbars, or any other kind of conductor of arbitr...
Article
Full-text available
A methodological approach that is based on a lumped parameter model is proposed for analyzing the dynamic electromagnetic performance of iron-free coil systems with massive conductors. This approach is particularly convenient in studying the transient current density distribution inside the turns and the transient magnetic field distribution in eve...
Chapter
This paper deals with resonance problems due to stray capacitances in large magnets, such as those used in fusion research machines or big H.V. transformers. The paper presents the method set up to investigate frequency response of the coils of the Poloidal Field System of the RFX fusion experiment. For each coil an equivalent network is first iden...
Article
Stimulation of visceral receptors with bradykinin has been shown to cause reflex increases in sympathetic nerve activity and systemic arterial pressure. In this investigation, serosal receptors of the intestine were stimulated by bradykinin in anesthetized cats to 1) compare mesenteric and renal sympathetic responses, 2) compare hemodynamic respons...
Article
The renal nerves appear to be involved in the control of cardiovascular homeostasis and volume balance both in physiological and in pathological conditions such as experimental hypertension. Anatomical and electrophysiological evidence suggests that the kidney has a diffuse sensory innervation connected with areas in the brain and spinal cord that...
Article
We have studied the role of afferent renal nerve fibres in anaesthetized cats in mediating the decrease in sodium and water excretion from the contralateral kidney caused by unilateral renal denervation. Transient denervation of one kidney obtained by cooling of the left renal nerves increases contralateral efferent renal nerve activity and decreas...
Article
The rich innervation of the kidney is distributed to all structures of renal parenchyma thus providing important anatomical support to the functional evidence that the renal nerves can control kidney functions and send signals on the kidney environment to the central nervous system. Efferent renal nerve fibres are known to influence renal haemodyna...
Article
Electrical stimulation of afferent renal nerves elicits an increase in arterial pressure and heart rate. The hypertensive response is presumably due to the widespread activation of the sympathetic nervous system leading to peripheral vasoconstriction. Interestingly, the kidney does not appear involved in this reflex excitatory response to afferent...
Article
Full-text available
The paper deals with an automatic design procedure for axisymmetric induction heating systems, which makes use of the Volume Integral eddy current formulation known as the Coupled Circuit Method. Starting from a preliminary tentative design, the position of each turn of the exciting coil is automatically adjusted, within specified boundaries, to mo...
Article
1. In anaesthetized cats, reversible nenal nerve denervation (cooling of the renal nerves on one side at 4°C for 16 min) was performed and its effects on haemodynamic and excretory functions of the ipsilateral and the contralateral kidneys were studied. 2. Renal nerve cooling did not cause any change in arterial pressure. Slight increase in blood f...
Article
Full-text available
The problem of winding design to perform a specified field synthesis is usually carried out as analytic determination of current distribution within a given region. This approach may be useful for conceptual or preliminary design, but presents severe technical difficulties from a construction point of view. A construction oriented procedure for axi...
Conference Paper
Full-text available
This paper presents the RFX Magnetizing Winding design and describes its most significant features. Two numerical codes have been used for the magnetic design and a number of solutions, complying with the design specifications, have been obtained. The most attractive of them have been studied in detail from the electromagnetic point of view and a c...
Article
Full-text available
This paper presents the RFX Magnetizing Winding design and describes its most significant features. Two numerical codes have been used for the magnetic design and a number of solutions, complying with the design specifications, have been obtained. The most attractive of them have been studied in detail from the electromagnetic point of view and a c...
Article
Stimulation and denervation experiments have provided evidence that adrenergic mechanisms can enhance sodium and water reabsorption from the renal tubule, and that this influence is probably exerted on the entire tubular extent. Reflexes originating from cardiopulmonary and renal receptors can control adrenergic renal sodium handling, and evidence...
Article
In anesthetized cats (n = 9) renal afferent fibers were electrically stimulated for 11 min, and the response of the contralateral innervated kidney was compared with that of the ipsilateral denervated one. Before stimulation, renal blood flow, glomerular filtration rate, and water and sodium excretions were significantly lower in the innervated kid...
Article
Circulatory, secretory (renin release) and excretory (tubular sodium and water reabsorption) renal functions are known to be under neural control exerted by sympathetic fibers. Influences on circulatory and secretory functions are modulated by vagally mediated reflexes originated from low pressure (or volume) receptors in the cardiopulmonary area....
Article
Denervation of one kidney has been shown to induce a prompt decrease in sodium and water excretion from the contralateral kidney. The present study was designed to clarify whether this response is due to suppression of a tonic inhibitory renorenal reflex. Experiments were performed in anaesthetized cats in which the renal nerves of the left kidney...
Article
1. Active and cryoactivated renin (plasma renin) activity after incubation at -5 degrees C for 4 days, were measured in cat plasma sampled before and during the following procedures: suprarenal aortic stenosis, electrical stimulation of the pons and mild hypotensive haemorrhage. 2. Under all experimental conditions the values of plasma renin activi...
Conference Paper
This paper describes the JET Ohmic Heating Circuit - a switching network in the Poloidal System of the JET Machine - that connects the driving energy source to the JET Torus to induce and maintain the plasma current. The sequential operation, including the protective action, is described. The basic design aspects for all components are reviewed and...
Article
Full-text available
Anesthetized cats were subjected to two 10-min trials of head-up tilting spaced 60 min apart. Bilateral cervical vagotomy, performed after the first tilting episode, did not affect the hemodynamic response to the change in posture, but significantyly and markedly reduced the increase in renin release from the innervated kidney. After sinoaortic den...
Article
1. Anaesthetized cats were subjected to two 10 min trials of head-up tilting spaced 30 min. Arterial pressure, heart rate, blood flow to an innervated kidney and to the contralateral denervated one, and renin release from both kidneys were measured. 2. The same haemodynamic changes and comparable increases in renin release from innervated kidneys o...
Article
Experiments on Reverse Field Pinches (RFP) were formerly carried out in fast programmed devices employing insulating vessels; the program is now developing to relatively slow devices with metal liners on a larger and larger scale. Eta-Beta II is the first toroidal experiment of this kind and allows a gradual transition from the fast programming mod...
Article
The paper describes the design of Eta-Beta II, a toroidal device for the RFP configuration operation. The torus lies in the vertical plane and is supported by two aluminum alloy rings which are short circuiting elements for the magnetizing flux. The poloidal and toroidal inductors are made by windings which can be connected in series, parallel, or...
Article
In the anesthetized, moderately fluid-depleted cat (no fluid infusion during the experiment), bilateral cervical vagotomy caused a marked and prompt increase in renin release from the innervated kidney without significantly affecting renin release from the contralateral denervated kidney. This excitatory effect was a transient one, however, and dis...
Chapter
This chapter focuses on the action of angiotensins on the central nervous system as their production depends largely on the release of renin from the kidney. It reviews some of the mechanisms that play a role in the release of renin and presents some experimental data on the function of renal nerves in its release. The chapter discusses the aspects...
Article
This chapter discusses the mechanism of the sympathetic activation of renin release, the central organization of the neural control of renin release, and the reflex modulation of renin release. Evidence indicates that the sympathetic system can directly influence renin release of juxtaglomerular cells without the involvement of the vascular or macu...