Showing papers by "Université Paris-Saclay published in 1996"

Central motor loop oscillations in parkinsonian resting tremor revealed by magnetoencephalography.

Abstract: A variety of clinical and experimental findings suggest that parkinsonian resting tremor results from the involuntary activation of a central mechanism normally used for the production of rapid voluntary alternating movements. However, such central motor loop oscillations have never been directly demonstrated in parkinsonian patients. Using magnetoencephalography, we recorded synchronized and tremor-related neuromagnetic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seven patients suffering from early-stage idiopathic Parkinson's disease (PD). Single equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions (magnetic field tomography, MFT) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor in PD is accompanied by rhythmic subsequent electrical activation at the diencephalic level and in lateral premotor, somatomotor, and somatosensory cortex. Tremor-evoked magnetic activity can be attributed to source generators that were previously described for voluntary movements. The interference of such slow central motor loop oscillations with voluntary motor activity may therefore constitute a pathophysiologic link between tremor and bradykinesia in PD.

Tuning and test of fragmentation models based on identified particles and precision event shape data

Abstract: Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

First-Principles Calculation of the Anomalous Perpendicular Anisotropy in a Co Monolayer on Au(111).

Abstract: We perform fully relativistic spin-polarized local spin density calculations for Au covered Co monolayer on Au(111). In accord with a trend observed in experiments we obtain an enhancement of perpendicular magnetic anisotropy as a function of the Au coverage. The close relationship found between the anisotropies of orbital magnetic moments and the anisotropy energies leads to an interpretation of our results in terms of familiar perturbation theory. By using this framework the anomalous behavior of the magnetic anisotropy energies can be well explained due to changes in the sp-d hybridization at the interface of Co monolayer and Au cap.

Evidence for distinct vascular and tubular urea transporters in the rat kidney.

Abstract: Facilitated urea transport has been demonstrated in several mammalian tissues, including those of the collecting ducts and red blood cells. Two urea transporters have been recently cloned: UT2, expressed in rabbit inner medullary collecting ducts, and HUT11, expressed in human erythrocytes. Because of significant identity (63%) between these two transporters, and because HUT11 is also expressed in the human kidney, they could represent the same transporter with species-related differences in their-sequences. In the study presented here, two different cDNA fragments, corresponding to the rat equivalents (rUT2 and rUT11) of the two previously cloned urea transporters, were isolated by reverse transcription-polymerase chain reaction. These rat probes were used for Northern analysis of RNA extracted from rat tissues. From the following findings, the results show that rUT2 and rUT11 are two distinct urea transporters: (1) The two cDNA fragments isolated in the rat exhibit different sequences; (2) The mRNA for rUT2 is found exclusively in the kidney, with two transcripts (3.2- and 4.4-kilobase (kb)), whereas rUT11 (only one transcript, 4.2 kb) is present in the brain, spleen, kidney, and testis; (3) in the kidney, the inner stripe of the outer medulla expresses rUT11 mRNA and the short transcript of rUT2, whereas the inner medulla expresses rUT11 and the two rUT2 transcripts; (4) In hydronephrotic kidneys that have completely lost their tubular epithelium but have intact vasculature, rUT2 transcripts are no longer expressed, whereas expression of rUT11 is intensified; (5) Experimental chronic alterations in urine concentrating activity induced different changes in the expression of rUT2 and rUT11.

Femtosecond laser excitation dynamics of the semiconductor-metal phase transition in VO2

Abstract: We have measured the subpicosecond optical response of a solid‐state, semiconductor‐to‐metal phase transition excited by femtosecond laser pulses. We have determined the dynamic response of the complex refractive index of polycrystalline VO2 thin‐films by making pump‐probe optical transmission and reflection measurements at 780 nm. The phase transition was found to be largely prompt with the optical properties very close to the high‐temperature metallic state being attained within about 5 ps. The equilibration of the metallic state after femtosecond excitation was modeled by non‐exponentially decaying perturbations in the metallic state electron density and collision frequency. The decay of both these plasma parameters was well fit by a 1/√t time dependence. This indicated that a diffusion process governed the equilibration of the metallic phase of VO2.

Gene therapy in lung transplantation: feasibility of ex vivo adenovirus-mediated gene transfer to the graft.

Abstract: Lung transplantation is associated with complications such as reperfusion injury and graft rejection. Gene therapy targeted to the graft offers a promising approach to the prevention of these complications. Because adenovirus vectors can transfer genes in vivo to the lung vasculature, we evaluated the feasibility of adenovirus-mediated gene transfer to the lung graft in a porcine model of left lung allotransplantation. Following removal of the donor lung, an adenovirus vector encoding the β-galactosidase (β-Gal) gene was injected ex vivo into the lumen of the upper lobe pulmonary artery of the graft. After 2 hr of incubation at 10°C, the lung graft was implanted into the recipient animal. Three days later, the animals were sacrificed and the lung graft was evaluated for β-Gal activity. No β-Gal activity was detected in the left lower lobe used as a control. In contrast, β-Gal activity was detected in endothelial cells of the left upper lobe pulmonary circulation, and was also observed in airway a...

Large enhancement of deuteron polarization with frequency modulated microwaves

Abstract: We report a large enhancement of 1.7 in deuteron polarization up to values of 0.6 due to frequency modulation of the polarizing microwaves in a two liter polarized target using the method of dynamic nuclear polarization. This target was used during a deep inelastic polarized muon-deuteron scattering experiment at CERN. Measurements of the electron paramagnetic resonance absorption spectra show that frequency modulation gives rise to additional microwave absorption in the spectral wings. Although these results are not understood theoretically, they may provide a useful testing ground for the deeper understanding of dynamic nuclear polarization.

Nuclear and Gamma-Ray Production by Supernova Ejecta

Abstract: Early Universe lto appear in ~~e A9tr0phy9id Journal ( 9 9 ) The fastest ejecta of supernova explosions propagate as a precursor to the main supernova shock wave, and can be quite energetic. The spectrum of such fast ejecta is estimated based on recent analytic and numerical supernova models, and found to be a power law having a cutoff at an energy of order 10 MeV/nucl, the precise value of which depends on the supernova mass and energetic. With cutoffs in this range there can be significant flux with energies above the thresholds for 7-ray and Li, Be, and B production. These nuclear interactions should inevitably accompany the passage of prompt supernova ejecta through the surrounding medium. The fast particle composition is that of the outermost layers of the progenitor; if the progenitor experienced significant loss of its envelope to a companion or by mass loss, then the composition is nonsolar, and in particular, metal-rich. Such a composition and spectrum of fast particles is required to explain the recent COMPTEL observations of 7-ray emission in Orion. Supernova ejecta from one progenitor having lost a large amount of mass are shown to quantitatively account for the Orion 7 rays, and to imply the presence of other, weaker lines and of a supernova explosion in Orion in the last <104 years. Implications for this mechanism as a mode of nucleosynthesis, and as a potential supernova diagnostic, are discussed. Model dependence and uncertainties are noted, and the need is shown for accurate measurements of 7-ray and spallation production cross sections at energies near threshold. Subject headings: acceleration of particles—gamma rays: theory—nuclear reactions, nucleosynthesis, abundances—supernovae: general

Nuclear and Gamma-ray Production by Supernova Ejecta

Abstract: The fastest ejecta of supernova explosions propagate as a precursor to the main supernova shock wave, and can be quite energetic. The spectrum of such fast ejecta is estimated based on recent analytic and numerical supernova models, and found to be a power law having a cutoff at an energy of order 10 MeV/nucl, the precise value of which depends on the supernova mass and energetics. With cutoffs in this range there can be significant flux with energies above the thresholds for $\gamma$-ray and Li, Be, and B production. These nuclear interactions should inevitably accompany the passage of prompt supernova ejecta through the surrounding medium. The fast particle composition is that of the outermost layers of the progenitor; if the progenitor experienced significant loss of its envelope to a companion or by mass loss, then the composition is nonsolar, and in particular, metal-rich. Such a composition and spectrum of fast particles is required to explain the recent COMPTEL observations of $\gamma$-ray emission in Orion. Supernova ejecta from one progenitor having lost a large amount of mass are shown to quantitatively account for the Orion $\gamma$ rays, and to imply the presence of other, weaker lines and of a supernova explosion in Orion in the last $\la 10^4$ years. Implications for this mechanism as a mode of nucleosynthesis, and as a potential supernova diagnostic, are discussed. Model dependences and uncertainties are noted, and the need is shown for accurate measurements of $\gamma$-ray and spallation production cross sections at energies near threshold.

Relativistic Raman instability shifted by half‐plasma frequency

Abstract: A new nonlinear Raman instability in underdense plasma is investigated theoretically Unlike the usual linear Raman instabilities which grow exponentially in time, this instability takes a finite amount of time to diverge The explosion time t∞ depends on the initial level of the perturbation A general set of equations for spatio‐temporal evolution of the forward nonlinear Raman scattering is derived and its temporal evolution is studied in detail This new instability results in the generation of forward Raman radiation shifted by half the plasma frequency for laser intensities of order or exceeding 1018 W/cm2, something that has been recently observed [A Modena (private communication, 1995)]