Biomedical subjects

L Marrelli

Publications and source records attributed to L Marrelli.

14 recordsLinked to original sources

PubMed2006

Active-feedback control of the magnetic boundary for magnetohydrodynamic stabilization of a fusion plasma.

Stable operation with control on magnetohydrodynamic modes has been obtained in the modified reversed field experiment employing a set of 192 feedback controlled saddle coils. Improvements of plasma temperature, confinement (twofold), and pulse length (threefold) and, as a consequence of the magnetic fluctuation reduction, strong mitigation of plasma-wall interaction and mode locking are reported.

Journal Article↗

PubMed2006

Transport barrier inside the reversal surface in the chaotic regime of the reversed-field pinch.

Magnetic field lines and the corresponding particle orbits are computed for a typical chaotic magnetic field provided by a magnetohydrodynamics numerical simulation of the reversed-field pinch. The m = 1 modes are phase locked and produce a toroidally localized bulging of the plasma which increases particle transport. The m = 0 and m = 1 modes produce magnetic chaos implying poor confinement. However, they also allow for the formation of magnetic islands which induce transport barriers inside the reversal surface.

Journal Article↗

PubMed2005

Bilirubin removal from albumin-containing solution by adsorption on polymer resin.

Adsorption equilibrium of bilirubin onto polymeric resins is studied. Solutions containing albumin are used in order to simulate the behavior of systems for removal of albumin-bound substances from blood, serum or dialysis fluids. The effect of albumin pre-loading on the resin is also analysed. Results are explained by a chemically based model that accounts for binding reaction between albumin and bilirubin in the liquid phase. Thermodynamic equilibria and physical models are essential tools for designing adsorption columns aimed at detoxification treatments.

Adsorption↗

PubMed2005

Rheological characterization of an artificial synovial fluid.

Rheological measurements on two classes of artificial synovial fluids have been carried out in the attempt to get a suitable but cheap lubricant for wear tests of prosthetic materials. Fluids of both classes are solutions of hyaluronic acid (HA) that, for one class, is dissolved into a simple Ringer solution whereas, for the other class, into a mixture of human serum and Ringer solution. Similar rheological properties have been observed for both classes of fluids. Experimental results have been interpreted by two classical models that are commonly used in the literature to describe the rheological behavior of colloidal systems and of polymer solutions with high entanglement density, respectively. The quality of correlations shows that, at high HA concentrations, entangled structures are largely present and cannot be neglected.

Biocompatible Materials↗

PubMed2004

Measurements of the MHD dynamo in the quasi-single-helicity reversed-field pinch.

The first experimental study of the MHD dynamo in a quasi-single-helicity (QSH) reversed-field pinch toroidal plasma is presented. In QSH plasmas, a dominant wave number appears in the velocity fluctuation spectrum. This velocity component extends throughout the plasma volume and couples with magnetic fluctuations to produce a significant MHD dynamo electric field. The narrowing of the velocity fluctuation spectrum and the single-mode character of the dynamo are features predicted by theory and computation, but only now are observed in experiment.

Journal Article↗

PubMed2004

Feedback stabilization of multiple resistive wall modes.

Active feedback stabilization of multiple independent resistive wall modes is experimentally demonstrated in a reversed-field pinch plasma. A reproducible simultaneous suppression of several nonresonant resistive wall modes is achieved. Coupling of different modes due to the limited number of the feedback coils is observed in agreement with theory. The feedback stabilization of nonresonant RWMs also has an effect on tearing modes that are resonant in the central plasma, leading to a significant prolongation of the discharge pulse.

Journal Article↗

PubMed2004

Particle-transport analysis in reversed field pinch helical states.

This Letter reports the result of a numerical study of particle transport in self-organized single helicity (SH) and quasi-SH reversed field pinch plasmas. Our code, benchmarked against experimental data, predicts a large improvement in particle transport for SH compared to the standard multiple helicity states. The contribution of neoclassical effects is noted. An estimate of the ambipolar electric field in helical states and in fully stochastic magnetic fields is given.

Journal Article↗

PubMed2004

Observations of multiple magnetic islands in the core of a reversed field pinch.

We describe in this Letter the first measurement of multiple islands in the core of a reversed field pinch (RFP). These islands appear with current profile modification leading to magnetic fluctuation reduction in the Madison symmetric torus RFP. Magnetic island widths decrease to an unprecedented level, reducing the overlap of adjacent islands and allowing distinct islands to appear. The structures are observed in multichord measurements of soft-x-ray emissivity. The soft-x-ray data is validated with Poincaré reconstructions of the magnetic field structure in the core.

Journal Article↗

PubMed2003

Net proton charge of beta- and kappa-casein in concentrated aqueous electrolyte solutions.

Titration experiments have been carried out in order to measure the net proton charge of beta- and kappa-casein in NaCl solutions at 0.1 M and 1 M salt concentrations, at 4 degrees C, in the pH range between 5.5 and 10.5. Experimental data are compared with model values calculated through pK(a)'s of titrable groups neglecting the electrostatic perturbation term (deltapK(a)) in order to evaluate the magnitude of the error caused by this approximation and to delimit its effectiveness. At both ionic strengths, the agreement is good for kappa-casein in the pH range [5.5, 9.5], while errors of up to 2 charges are observed for beta-casein in the same range. These deviations are likely to be caused by strong electrostatic effects induced by the high density of negative charges of beta-casein 1-21 peptide. In order to account for these electrostatic effects, the net proton charge on this peptide is evaluated through a model based on the counterion condensation theory developed for the titration of polyelectrolytes with different types of ionizable groups.

Animals↗

PubMed2002

ALEX (artificial liver for extracorporeal xenoassistance): a new bioreactor containing a porcine autologous biomatrix as hepatocyte support. Preliminary results in an ex vivo experimental model.

Long-term maintenance of viability and expression of differentiated hepatocyte function is crucial for bioartificial liver support. We developed a new bioreactor design (ALEX), associated with a new extracellular autologous hepatocyte biomatrix (Porcine Autologous Biomatrix - PBM) support. To test this new bioreactor, we compared it to a standard BAL (BioArtificial Liver) cartridge in a ex vivo model using human plasma added to bilirubin, ammonium and lidocaine. A pathology study was performed on both bioreactors. The results suggest that ALEX allows a maximal contact between the perfusing plasma and the liver cells and a proper hepatocyte support by a cell-to-matrix attachment. ALEX is a suitable cell support bioreactor, guaranteeing long-term maintenance of the metabolic activity of hepatocytes when compared to a standard BAL cartridge.

Ammonia↗

PubMed2001

Quasistationary magnetic fluctuation control in the reversed field pinch: a proof of principle experiment.

We present the results of the first successful experiments aimed to control in a quasistationary way the magnetic fluctuation dynamics in a reversed field pinch (RFP) device. This is done by the application of an oscillating poloidal electric field to the plasma edge. Although the additional power input is negligible, a stationary positive effect on the electron temperature is obtained. Temperature increases up to 50% over the standard values. This experiment demonstrates that in principle a stationary current profile and magnetic fluctuation control technique is feasible in the RFP.

Journal Article↗

PubMed2000

Quasi-single-helicity reversed-field-pinch plasmas

The reversed field pinch (RFP) is a configuration for plasma magnetic confinement. It has been traditionally viewed as dominated by a bath of MHD instabilities producing magnetic chaos and high energy transport. We report experimental results which go beyond this view. They show a decrease of magnetic chaos and the formation of a coherent helical structure in the plasma, whose imaging and temperature profile are provided for the first time. These quasi-single-helicity states are observed both transiently and in stationary conditions. The last case is consistent with a theoretically predicted bifurcation. Our results set a new frame for improving confinement in high current nonchaotic RFP's.

Journal Article↗

PubMed1976

Kinetic analysis of penicillin production by semicontinuous fermenters.

The relationships between the specific rate of nutrient consumption and biomass growth and between the specific rate of penicillin production and oxygen concentration in the broth are analyzed. The functional dependencies which have been obtained from the experimental data of industrial fermenters are used with the mass balances to develop a model of the behavior of semicontinous operations. The proposed model allows one to study the influence of some operational parameters. The obtained results agree with the data of industrial processes.

Bacteria↗

PubMed1976

The influence of oxygen concentration and of specific rate of growth on the kinetics of penicillin production.

The role of fundamental parameters in the conduction of penicillin semicontinuous fermentations is analyzed. Biomass concentration, penicillin production, and main nutrient consumption are particularly studied. Furthermore, the conduction of the operation is simulated with regard to conditions of constant specific rate of growth and of constant oxygen concentration in the broth. An intermediate condition is also considered.

Bacteria↗