Spin transport in carbon nanotubes with magnetic vacancy-defects

in Physical Review. B, Condensed Matter and Materials Physics (2010), 81(16),

The spin-polarized electron transport properties of metallic carbon nanotubes containing vacancies are investigated using first-principles and nonequilibrium Green’s function techniques. Reconstructed ... [more ▼]

The spin-polarized electron transport properties of metallic carbon nanotubes containing vacancies are investigated using first-principles and nonequilibrium Green’s function techniques. Reconstructed mono- and trivacancies, containing carbon atoms with unsaturated bonds, behave like quasilocalized magnetic impurities. However, in conventional ab initio simulations, these magnetic defects are artificially repeated periodically (supercell method) and are thus incorrectly coupled by long range interactions. Consequently, a technique based on an open system with an isolated magnetic impurity is used here to accurately describe the local magnetic properties of these defects, revealing spin-dependent conductances in tubes, which could be exploited in spintronic nanodevices. [less ▲]

The spin-flip amplitude in the impact-parameter representation

in European Physical Journal. Special Topics (2008)

The impact-parameter representation of the spin-flip amplitude of hadron elastic scattering is examined in different unitarisation schemes, taking the Born term of the spin-flip amplitude from the Dubna ... [more ▼]

The impact-parameter representation of the spin-flip amplitude of hadron elastic scattering is examined in different unitarisation schemes, taking the Born term of the spin-flip amplitude from the Dubna Dynamical Model (DDM). It is shown that the basic properties of the unitarisation schemes are independent of the functional form used for unitarisation but heavily depend on the asymptotic value of the unitarised amplitude. [less ▲]

Spin-orbit alignment in planetary systems: what can we learn from resolved debris disks?

Scientific conference (2011, May 17)

Since the first detection of the spectroscopic transit of a hot Jupiter by Queloz et al. (2000), the Rossiter-McLaughlin effect, which allows the measurement of the sky-projected angle between the stellar ... [more ▼]

Since the first detection of the spectroscopic transit of a hot Jupiter by Queloz et al. (2000), the Rossiter-McLaughlin effect, which allows the measurement of the sky-projected angle between the stellar rotation axis and a planet's orbit axis, has been investigated for a large number of planetary systems. These observations have lead to the detection of spin-orbit misalignments for many hot Jupiters, and even of retrograde orbits in some cases (e.g., Triaud et al. 2010). Such misalignments are generally interpreted as the signature of either Kozai migration, or of planet-planet scattering followed by inward migration of the planet (e.g., Morton & Johnson 2011). However, it has recently been proposed that circumstellar disks themselves might not be aligned with the stellar spin axis due to either to early stellar encounters (Bate et al. 2010) or to magnetosphere-disk interactions (Lai et al. 2011). In this talk, I discuss how resolved debris disks may be used to settle this question, in particular by measuring the position angle of oblate stellar photospheres deformed by rapid rotation using spectro-interferometric measurements within the Brackett-gamma line. The method is illustrated by our recent study of Fomalhaut with VLTI/AMBER (Le Bouquin et al. 2009), which confirms the spin-orbit alignment with a high accuracy for the first time in a debris disk system. Possible implications on the nature of the dust grains composing the Fomalhaut debris disk will also be discussed. [less ▲]

The spin-orbit alignment of the Fomalhaut planetary system probed by optical long baseline interferometry

in Astronomy and Astrophysics (2009), 498

Aims. We discuss the spin-orbit orientation of the Fomalhaut planetary system composed of a central A4V star, a debris disk, and a recently discovered planetary companion. Methods: We use spectrally ... [more ▼]

Aims. We discuss the spin-orbit orientation of the Fomalhaut planetary system composed of a central A4V star, a debris disk, and a recently discovered planetary companion. Methods: We use spectrally resolved, near-IR long baseline interferometry to obtain precise spectro-astrometric measurements across the Br-gamma absorption line. The achieved astrometric accuracy of ±3 muas and the spectral resolution R=1500 from the AMBER/VLTI instrument allow us to spatially and spectrally resolve the rotating photosphere. Results: We find a position angle PA(star)=65° ± 3° for the stellar rotation axis, perpendicular to the literature measurement for the disk position angle (PA(disk)=156.0 ° ± 0.3°). This is the first time such a test could be performed for a debris disk, and in a non-eclipsing system. Additionally, our measurements suggest unexpected backward-scattering properties for the circumstellar dust grains. Conclusions: Our observations validate the standard scenario for star and planet formation in which the angular momentum of the planetary systems are expected to be colinear with the stellar spins. Based on observations collected at the VLTI (ESO Paranal, Chile), with the 082.C-0376 program from the AMBER Guaranteed Time of the Osservatorio Astrofisico di Arcetri (INAF, Italy). [less ▲]

The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations

in Monthly Notices of the Royal Astronomical Society (2011), 414

We present observations of the Rossiter-McLaughlin effect for the transiting exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the orientations of the planetary orbits with respect to the ... [more ▼]

We present observations of the Rossiter-McLaughlin effect for the transiting exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the orientations of the planetary orbits with respect to the host stars' rotation axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde orbits and be well aligned, having sky-projected spin orbit angles consistent with zero: {\lambda} = -4.7 \pm 4.0{\deg}, {\lambda} = 15 + 33{\deg}/-43{\deg} and {\lambda} = -9.7 +9.0{\deg}/-7.7{\deg}, respectively. The host stars have Teff < 6250 K and conform with the trend of cooler stars having low obliquities. WASP-38b is a massive planet on a moderately long period, eccentric orbit so may be expected to have a misaligned orbit given the high obliquities measured in similar systems. However, we find no evidence for a large spin-orbit angle. By contrast, WASP-1b joins the growing number of misaligned systems and has an almost polar orbit, {\lambda} = -79 +4.5{\deg}/-4.3{\deg}. It is neither very massive, eccentric nor orbiting a hot host star, and therefore does not share the properties of many other misaligned systems. [less ▲]

Spin-orbit misalignement for the transiting planet HD 80606b

Report (2009)

A global Markov Chain Monte Carlo analysis of published eclipse photometry and radial velocities is presented for the transiting planet HD 80606b. Despite the lack of a complete transit light curve, the ... [more ▼]

A global Markov Chain Monte Carlo analysis of published eclipse photometry and radial velocities is presented for the transiting planet HD 80606b. Despite the lack of a complete transit light curve, the size of the planet is measured with a good level of precision (R_p = 1.04 +0.05-0.09 R_Jup), while the orbital parameters are refined. This global analysis reveals that the orbital axis of the planet is significatively inclined relative to the spin axis of the host star (Beta = -59 +18-28 deg), providing a compelling evidence that HD 80606b owes its peculiar orbit to the Kozai migration mechanism. [less ▲]

Spinal Cord

in Dulbecco, R. (Ed.) Encyclopedia of Human Biology (1991)

Spinal cord compression due to C4 vertebral arch osteochondroma.

in Orthopaedics & Traumatology: Surgery & Research (2010)

Osteochondromas are usually benign bone tumors found on the metaphysis of long bones. These tumors are rarely located on the spine especially at cervical level. This report presents the case of a 23-year ... [more ▼]

Osteochondromas are usually benign bone tumors found on the metaphysis of long bones. These tumors are rarely located on the spine especially at cervical level. This report presents the case of a 23-year-old man who had previously developed tetraparesis at the age of 13 after infectious myelitis. Recent severe clinical neurological deterioration revealed the diagnosis of osteochondroma arising in the C4 vertebral arch compressing the spinal cord and associated with syringomyelia. Of note in his past history was a treated hip localization. The patient underwent complete surgical excision of the osteochondroma. Postoperative outcome was good with slow clinical recovery from the spinal cord compression. We report this rare cause of spinal cord compression and other cases reported in the literature. [less ▲]

The spinal cord ependymal region: A stem cell niche in the caudal central nervous system

in Frontiers in Bioscience : A Journal and Virtual Library (2011), (16), 1044-1059

In the brain, specific signalling pathways localized in highly organized regions called niches, allow the persistence of a pool of stem and progenitor cells that generate new neurons and glial cells in ... [more ▼]

In the brain, specific signalling pathways localized in highly organized regions called niches, allow the persistence of a pool of stem and progenitor cells that generate new neurons and glial cells in adulthood. Much less is known on the spinal cord central canal niche where a sustained adult neurogenesis is not observed. Here we review our current knowledge of this caudal niche in normal and pathological situations. Far from being a simple layer of homogenous cells, this region is composed of several cell types localized at specific locations, expressing characteristic markers and with different morphologies and functions. We further report on a screen of online geneexpression databases to better define this spinal cord niche. Several genes were found to be preferentially expressed within or around the central canal region (Bmp6, CXCR4, Gdf10, Fzd3, Mdk, Nrtn, Rbp1, Shh, Sox4, Wnt7a) some of which by specific cellular subtypes. In depth characterization of the spinal cord niche constitutes a framework to make the most out of this endogenous cell pool in spinal cord disorders. [less ▲]

Spinal cord injury and its treatment:current management and experimental perspectives

in Advances and Technical Standards in Neurosurgery (2012), 38