Biomedical subjects

F Bouquet

Publications and source records attributed to F Bouquet.

At least 19 recordsLinked to original sources

PubMed2002

Specific heat of single crystal MgB2: a two-band superconductor with two different anisotropies.

Heat-capacity measurements of a 39 microg MgB2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence, and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the smaller gap being isotropic, that carrying the larger gap having an anisotropy of approximately 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2.

Journal Article↗

PubMed2001

Specific heat of Mg11B2: evidence for a second energy gap.

Measurements of the specific heat of Mg11B2 from 1 to 50 K, in magnetic fields to 9 T, give the Debye temperature, Theta = 1050 K, the coefficient of the normal-state electron contribution, gamma(n) = 2.6 mJ mol(-1) K-2, and a discontinuity in the zero-field specific heat of 133 mJ mol(-1) K-1 at T(c) = 38.7 K. The estimated value of the electron-phonon coupling parameter, lambda = 0.62, could account for the observed T(c) only if the important phonon frequencies are unusually high relative to Theta. At low T, there is a strongly field-dependent feature that suggests the existence of a second energy gap, about 4 times smaller than the major gap.

Journal Article↗

PubMed2001

An unusual phase transition to a second liquid vortex phase in the superconductor YBa2Cu3O7.

A magnetic field penetrates a superconductor through an array of 'vortices', each of which carries one quantum of flux that is surrounded by a circulating supercurrent. In this vortex state, the resistivity is determined by the dynamical properties of the vortex 'matter'. For the high-temperature copper oxide superconductors (see ref.1 for a theoretical review), the vortex phase can be a 'solid', in which the vortices are pinned, but the solid can 'melt' into a 'liquid' phase, in which their mobility gives rise to a finite resistance. (This melting phenomenon is also believed to occur in conventional superconductors, but in an experimentally inaccessible part of the phase diagram.) For the case of YBa2Cu3O7, there are indications of the existence of a critical point, at which the character of the melting changes. But neither the thermodynamic nature of the melting, nor the phase diagram in the vicinity of the critical point, has been well established. Here we report measurements of specific heat and magnetization that determine the phase diagram in this material to 26 T, well above the critical point. Our results reveal the presence of a reversible second-order transition above the critical point. An unusual feature of this transition-namely, that the high-temperature phase is the less symmetric in the sense of the Landau theory-is in accord with theoretical predictions of a transition to a second vortex-liquid phase.

Journal Article↗

PubMed1998

[Ethical evaluation of biomedical research].

Every human behaviour, therefore also biomedical research, implies a reference, either implicit or explicit, to ethic values. The expression "biomedical research" attains to the domain of two distinct fields, the scientific and the technical one and this distinction is important for its ethic implications. In fact, it was the great progress in the biotechnologies that in the early 70's stimulated the birth of a new discipline known as bioethics, that from its very start was meant to be the meeting point between culturers of the biological sciences and those of human sciences. Among the paradigms adopted by bioethics, those of Beauchamp and Childress, which refer to the principles of "beneficence" (well doing), "non maleficence" (not wrong doing), autonomy and justice, are still of great importance. Bioethics proposed to establish an inequivocal and shared language and to develop adequate and rigorous procedures of analysis. So, at various levels, international, national and local, those interesting tools of the trade, which are the ethics committees, have arose. In order for an ethic committee to function, one must guarantee from the start, the conditions of autonomy and representativeness of different knowledges and cultural options that characterize our complex society. It is also necessary that an ethics committee, rather than assuming a prescriptive role, should promote attention and reflection on the ethical aspects of biomedical research.

Bioethics↗

PubMed1997

Use of the fractal dimension for the analysis of electroencephalographic time series.

Electroencephalogram (EEG) traces corresponding to different physiopathological conditions can be characterized by their fractal dimension, which is a measure of the signal complexity. Generally this dimension is evaluated in the phase space by means of the attractor dimension or other correlated parameters. Nevertheless, to obtain reliable values, long duration intervals are needed and consequently only long-term events can be analysed; also much calculation time is required. To analyse events of brief duration in real-time mode and to apply the results obtained directly in the time domain, thus providing an easier interpretation of fractal dimension behaviour, in this work we optimize and propose a new method for evaluating the fractal dimension. Moreover, we study the robustness of this evaluation in the presence of white or line noises and compare the results with those obtained with conventional spectral methods. The non-linear analysis carried out allows us to investigate relevant EEG events shorter than those detectable by means of other linear and non-linear techniques, thus achieving a better temporal resolution. An interesting link between the spectral distribution and the fractal dimension value is also pointed out.

Algorithms↗

PubMed1997

Endozepine stupor in children.

Recurring episodes of stupor in adults have been shown to be related to increased levels of endozepines, which are endogenous ligands for the GABAA receptors. We report here two children presenting with recurrent episodes of stupor associated with fast EEG activity who had increased levels of endozepine-4 in plasma. Mass spectroscopy did not reveal commercially available benzodiazepines. Interictal endozepine-4 levels were normal. In one of the patients, administration of flumazenil (0.25 mg i.v.), a benzodiazepine inverse agonist, induced improvement of consciousness and attenuation of EEG fast activity. In conclusion, children presenting with recurrent episodes of stupor and EEG fast activity should be evaluated for endozepine levels and can be effectively treated with i.v. flumazenil.

Carrier Proteins↗

PubMed1992

Coeliac disease, epilepsy, and cerebral calcifications. The Italian Working Group on Coeliac Disease and Epilepsy.

There have been anecdotal reports of an association between coeliac disease and epilepsy with cerebral calcifications that resemble those of the Sturge-Weber syndrome. A series of patients who had epilepsy with calcifications, in whom coeliac disease (CD) was incidentally observed, prompted us to study this association. 43 patients (15 male, age range 4.6-30.7 years) were selected from two series. 31 patients with cerebral calcifications of unexplained origin and epilepsy (series A) underwent intestinal biopsy. 12 patients with CD and epilepsy (series B) underwent computed tomography. Antibodies to gluten, folic acid serum concentrations, were measured, and HLA typing was done in most patients. 24 of the series A patients were identified as having CD on the basis of a flat intestinal mucosa (15/22 with a high concentration of serum antigluten), and 5 series B patients showed cerebral calcifications, giving a total of 29 cases with the combination of CD, epilepsy, and cerebral calcifications (CEC). In 27 of these CEC patients, calcifications were located in the parieto-occipital regions. Only 2 of the series A patients had gastrointestinal symptoms at the time of intestinal biopsy; most patients had recurrent diarrhoea, anaemia, and other symptoms suggestive of CD in the first 3 years of life. The epilepsy in CEC patients was poorly responsive to antiepileptic drugs. Gluten-free diet beneficially affected the course of epilepsy only when started soon after epilepsy onset. Cases of "atypical Sturge-Weber syndrome" (characterised by serpiginous cerebral calcifications and epilepsy without facial port-wine naevus) should be reviewed, and CD should be ruled out in all cases of epilepsy and cerebral calcifications of unexplained origin.

Adolescent↗

PubMed1991

Coeliac disease, folic acid deficiency and epilepsy with cerebral calcifications.

Two cases of focal occipital epilepsy with cerebral calcifications poorly responsive to antiepileptic treatment are described. In both cases coeliac disease was diagnosed and folic acid deficiency documented. A gluten-free diet and a brief supplementation with folic acid lead to a complete EEG and clinical normalization in one case and to a significant improvement of EEG and seizure control in the other.

Adult↗

PubMed1988