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Biomedical subjects

G Amoretti

Publications and source records attributed to G Amoretti.

At least 19 recordsLinked to original sources
PubMed2006

Hidden order and low-energy excitations in NpO2.

We investigate the nature of the hidden order parameter in the ordered phase of NpO2, which had been identified with a staggered arrangement of Gamma5 magnetic multipoles. By analyzing the existing experimental data, we show that the most likely driving order parameter is not provided by octupoles, as usually assumed, but rather by the rank-5 triakontadipoles. Calculations of the coupled dynamics of spins, Gamma5 quadrupoles, and Gamma5 triakontadipoles in the ordered phase enable us to analyze the resulting structure of low-energy excitations. We show that the powder inelastic neutron scattering cross section should contain, in addition to the already-observed peak at 6.5 meV, a second weaker peak at about 14 meV.

Journal Article↗
PubMed2006

High-temperature slow relaxation of the magnetization in Ni10 magnetic molecules.

We investigate a family of molecular crystals containing noninteracting Ni10 magnetic molecules. We find slow relaxation of the magnetization below a temperature as high as 17 K and we show that this behavior is not associated with an anisotropy energy barrier. Ni10 has a characteristic magnetic energy spectrum structured in dense bands, the lowest of which makes the crystal opaque to phonons of energy below about 1 meV. We ascribe the nonequilibrium behavior to the resulting resonant trapping of these low-energy phonons. Trapping breaks up spin relaxation paths leading to a novel kind of slow magnetic dynamics which occurs in the lack of anisotropy, magnetic interactions and quenched disorder.

Journal Article↗
PubMed2005

Molecular engineering of antiferromagnetic rings for quantum computation.

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows the engineering of its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.

Journal Article↗
PubMed2005

NMR as a probe of the relaxation of the magnetization in magnetic molecules.

We investigate the time autocorrelation of the molecular magnetization M(t) for three classes of magnetic molecules (antiferromagnetic rings, grids, and nanomagnets), in contact with the phonon heat bath. For all three classes, we find that the exponential decay of the fluctuations of M(t) is characterized by a single characteristic time tau(T,B) for not too high temperature T and field B. This is reflected in a nearly single-Lorentzian shape of the spectral density of the fluctuations. We show that such fluctuations are effectively probed by NMR, and that our theory explains the recent phenomenological observation by Baek et al. [Phys. Rev. B 70, 134434 (2004)] that the Larmor-frequency dependence of 1/T(1) data in a large number of AFM rings fits to a single-Lorentzian form.

Journal Article↗
PubMed2004

S mixing and quantum tunneling of the magnetization in molecular nanomagnets.

The role of S mixing in the quantum tunneling of the magnetization in nanomagnets has been investigated. We show that the effect on the tunneling frequency is huge and that the discrepancy (more than 3 orders of magnitude in the tunneling frequency) between spectroscopic and relaxation measurements in Fe(8) can be resolved if S mixing is taken into account.

Journal Article↗
PubMed2004

Quantum magneto-oscillations in a supramolecular Mn(II)-[3 x 3] grid.

The magnetic grid molecule Mn(II)-[3 x 3] has been studied by high-field torque magnetometry at 3He temperatures. At fields above 5 T, the torque versus field curves exhibit an unprecedented oscillatory behavior. A model is proposed which describes these magneto-oscillations well.

Journal Article↗
PubMed2000

Magnetic-octupole order in neptunium dioxide?

The phase transition occurring at 25 K in NpO2, discovered almost 50 years ago, is the most long-lasting mystery in the physics of actinide compounds. Theories based on magnetic or electric-quadrupole order lead inevitably to fundamental, qualitative inconsistencies with observations. We show that the phenomenology of NpO2 can be understood if the order parameter is assumed to be a magnetic octupole of gamma(2) ( xyz) symmetry. NpO2 is the first compound for which indications of an octupolar phase transition have been found.

Journal Article↗
PubMed2000

Field-dependent energy scales in URu(2)Si(2).

At low temperature, macroscopic properties of URu(2)Si(2) display a characteristic energy scale delta(0)(B) which decreases when a magnetic field is applied, and eventually vanishes at an extrapolated value of the field of about 40 T. We have performed inelastic neutron scattering measurements of the magnetic dynamics of URu(2)Si(2) in applied fields along the c axis of intensities up to 12 T. We show that delta(0)(B) is not related to gaps in the magnetic fluctuations spectra. This provides direct evidence of the fact that two distinct energy scales govern the physics of this compound.

Journal Article↗
PubMed1996

Catecholaminergic, neuroendocrine and anxiety responses to acute psychological stress in healthy subjects: influence of alprazolam administration.

We studied the effect of alprazolam (APZ) in 12 healthy volunteers on the psychological stress-induced activation of emotion and on the pituitary-adrenal, adrenomedullary and sympathoneuronal systems. After 3 days of placebo or APZ (1 mg/day orally) administration, we examined plasma levels of adrenocorticotropic hormone, cortisol, L-3,4 dihydroxyphenylalanine, dopamine, norepinephrine (NE), epinephrine, metanephrine, normetanephrine, homovanillic acid, vanillylmandelic acid, 3-methoxy-4-hydroxy phenyglycol, urinary levels of cortisol and catecholamines, circulatory responses and state anxiety levels in subjects undergoing psychological stress based on viewing horror, violence, danger and war film clips. Film viewing produced modest rises of state anxiety levels, of plasma NE concentration and of diastolic blood pressure in both the placebo and drug groups. APZ significantly reduced anxiety levels at the beginning of the experimental session and caused a decrease of noradrenergic and dopaminergic neurotransmitter and cortisol concentrations. Our data suggest that APZ reduced anxiety related to the expectation of the event, while the circuitry between structures responsible for anxiety and peripheral sympathoneural function was still found to be partly sensitive to film viewing.

Adrenocorticotropic Hormone↗
PubMed1995

Sex hormones and pituitary function in male epileptic patients with altered or normal sexuality.

Male epileptic patients frequently complain of sexual dysfunction, particularly impotence and loss of libido. Epilepsy itself, antiepileptic drugs (AEDs), and psychosocial factors are believed to contribute to impaired sexuality. We studied luteinizing hormone (LH) pulsatile secretion, gonadotropin, and prolactin (PRL) responses to LH-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) in 37 adult male epileptic patients receiving AED monotherapy who were seizure-free and had normal EEGs. Sexuality was assessed by psychological interview. Impotence was diagnosed in 8 patients (in 2 combined with loss of sexual desire). The occurrence of hyposexuality (approximately 20%) was independent of epilepsy syndrome or AED. No change in total testosterone (T) level was observed. Free T (fT) and dihydrotestosterone (DHT) levels were lower and sex hormone binding globulin (SHBG) levels were higher in epileptic subjects than in healthy controls, but a statistically significant difference was not observed between hypo- and normosexual patients. In impotent epileptic patients, estradiol (E2) levels were significantly increased as compared with those of patients with preserved sexuality and of healthy controls. The unbalanced relation between androgen and E2 levels was emphasized by decreased T/E2, fT/E2, and DHT/E2 ratios obtained in hyposexual epileptic patients. In this group, LHRH induced blunted LH peaks. No changes were noted in LH pulsatility features. These findings of higher E2 levels and of decreased LH response to LHRH administration in some epileptic patients with impaired sexuality, may suggest they have subclinical hypogonadotropic hypogonadism.

Adult↗
PubMed1989

[Antibiotic prophylaxis in major surgery of the neck and head].

Twenty-two patients undergoing major head and neck surgery were included in a randomized trial to value the efficacy and side effects of parenteral short-term antibiotic prophylaxis of post-operative infections. Two different antibiotic regimens were compared: group A, ceftazidime i.v. (2 g) in three doses (half an hour before surgery, 8 and 16 hours, from the first dose); group B, netilmicin (100 mg) plus clindamycin (600 mg i.v.), following the same chronological schedule. Overall infection rate was 18% (4/22): all post-operative infections occurred in group A patients, including one case of wound infection and 3 mixed infections (wound infection associated with lung infection), with a significant reduction of post-operative infection rate in group B patients (p = 0.045; Fisher's exact test).

Adult↗