Biomedical subjects

R Giraud

Publications and source records attributed to R Giraud.

16 recordsLinked to original sources

PubMed2005

Very large tunneling anisotropic magnetoresistance of a (Ga,Mn)As/GaAs/(Ga,Mn)As stack.

We report the discovery of a very large tunneling anisotropic magnetoresistance in an epitaxially grown (Ga,Mn)As/GaAs/(Ga,Mn)As structure. The key novel spintronics features of this effect are as follows: (i) both normal and inverted spin-valve-like signals; (ii) a large nonhysteretic magnetoresistance for magnetic fields perpendicular to the interfaces; (iii) magnetization orientations for extremal resistance are, in general, not aligned with the magnetic easy and hard axis; (iv) enormous amplification of the effect at low bias and temperatures.

Journal Article↗

PubMed2004

Tunneling anisotropic magnetoresistance: a spin-valve-like tunnel magnetoresistance using a single magnetic layer.

We introduce a new class of spintronic devices in which a spin-valve-like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normal-metal-insulator-ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction and the two-step magnetization reversal process in this material.

Journal Article↗

PubMed2004

Sequential combined spinal-epidural anesthesia for cesarean section in a woman with a double-outlet right ventricle.

The number of women with complex cyanotic heart disease reaching childbearing age is continuously increasing. For anesthesiologists, management of this 'new' obstetric population is particularly challenging. We report the case of a parturient with a palliated double-outlet right ventricle, who underwent a cesarean section at 34 weeks with low-dose sequential combined spinal-epidural anesthesia with patient-controlled epidural postoperative analgesia. Anesthetic considerations and specific limitations of invasive monitoring are discussed, along with a review of recent literature on maternal and neonatal complications associated with pregnancies in women with cyanotic congenital heart disease.

Adult↗

PubMed2003

Quantum dynamics of atomic magnets: cotunneling and dipolar-biased tunneling.

Multispin tunneling cross relaxations in an ensemble of weakly coupled Ho3+ ions, mediated by weak anisotropic dipolar interactions, can be evidenced by ac-susceptibility measurements in a high temperature regime. Based on a four-body representation, including the rare-earth nuclear spin, two-ion tunneling mechanisms can be attributed to both dipolar-biased tunneling and cotunneling processes. The coreversal involving entangled pairs of magnetic moments is discussed with a particular emphasis, giving new evidence to elucidate the many-body quantum dynamics in dipolar spin glasses.

Journal Article↗

PubMed2001

Nuclear spin driven quantum relaxation in LiY0.998Ho0.002F4.

Staircaselike hysteresis loops of the magnetization of a LiY0.998Ho0.002F4 single crystal are observed at subkelvin temperatures and low field sweep rates. This behavior results from quantum dynamics at avoided level crossings of the energy spectrum of single Ho3+ ions in the presence of hyperfine interactions. Enhanced quantum relaxation in constant transverse fields allows the study of the relative magnitude of tunnel splittings. At faster sweep rates, nonequilibrated spin-phonon and spin-spin transitions, mediated by weak dipolar interactions, lead to magnetization oscillations and additional steps.

Journal Article↗

PubMed2000

Phonon-assisted tunneling in the quantum regime of Mn12 acetate

Longitudinal or transverse magnetic fields applied on a crystal of Mn12 acetate allows one to observe independent tunnel transitions between m = -S+p and m = S-n-p ( n = 6-10, p = 0-2 in longitudinal field and n = p = 0 in transverse field). We observe a smooth transition (in longitudinal) from coherent ground-state to thermally activated tunneling. Furthermore, two ground-state relaxation regimes show a crossover between quantum spin relaxation far from equilibrium and near equilibrium, when the environment destroys multimolecule correlations. Finally, we stress that the complete Hamiltonian of Mn12 should contain odd spin operators of low order.

Journal Article↗

PubMed1984

[Cesarean section preceding the 34th week of amenorrhea: maternal and fetal repercussions at the western university hospitals. Regional survey or 383 cesarean sections and 436 newborn infants out of 86,116 births in 5 years].

This statistical enquiry carried out in a region of France by the University Hospital Services in Obstetrics and voluntarily devoid of bibliographical references, deals with a group that are particularly pathological and thus probably explains the seriousness of the prognosis for the newborn and the frequency of maternal morbidity following these early operations. 15% of serious maternal complications with severe neonatal pathology which was often heavy and responsible for the death of the fetus in 22.4% of the cases and the late sequelae in the newborn in more than 10% of cases, mad it important to seek for the inevitable link between the pathology and the length of gestation at the time of the operation. Only one in three children were alive without any sequelae after Caesarean carried out between 28 and 31 weeks, but more than 80% were alive when the operation was performed at 34 weeks. In view of these findings the authors suggest that each case should be considered very carefully before early Caesarean section is carried out, both from the advantages and disadvantages of this means of delivery for the baby as well as for the mother. Caesarean section before 30 weeks of amenorrhoea on an infant with an estimated weight of less than 1 000 grams is seldom to be recommended in view of the poor results for the newborn and in the absence of severe maternal pathology which requires immediate evacuation of the uterus. In view of the poor statistical results that have been analysed, early Caesarean section for fetal pathology and particularly for fetal distress when there is no adequate sophisticated means of resuscitating the baby should be lowered to the minimum possible figure. The comparative study of the notes shows that pathological conditions apparently similar to one another lead to occasions for carrying out very early Caesarean section, and also show that the outlook is different from the point of view of the immediate prognosis and a late prognosis for the newborn infant in view of the delay that has occurred before extracting the baby and of the facilities available to resuscitate the baby.

Academic Medical Centers↗

PubMed1977

Treatment of hemoptysis by embolization of bronchial arteries.

One hundred and four patients presenting with either massive or repeated hemoptysis were treated by embolization of the bronchial arteries with a resorbable material (Spongel). The procedure was performed via selective catheterization of the abnormal arteries. Forty-nine patients were treated during and 55 after hemoptysis. Of the 49 patients treated during hemoptysis, immediate arrest of bleeding was affected in 41 but 6 of these patients suffered relapse two to seven months after the procedure. There was no recurrence of bleeding in the remaining 35 patients.

Adolescent↗

PubMed1975