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R Deblock

Publications and source records attributed to R Deblock.

12 recordsLinked to original sources
PubMed2006

Emission and absorption asymmetry in the quantum noise of a Josephson junction.

We measure current fluctuations of mesoscopic devices in the quantum regime, when the frequency is of the order of or higher than the applied voltage or temperature. Detection is designed to probe separately the absorption and emission contributions of current fluctuations, i.e. the positive and negative frequencies of the Fourier transformed nonsymmetrized noise correlator. It relies on measuring the quasiparticles photon assisted tunneling current across a superconductor-insulator-superconductor junction (the detector junction) caused by the excess current fluctuations generated by quasiparticles tunneling across a Josephson junction (the source junction). We demonstrate unambiguously that the negative and positive frequency parts of the nonsymmetrized noise correlator are separately detected and that the excess current fluctuations of a voltage biased Josephson junction present a strong asymmetry between emission and absorption.

Journal Article↗
PubMed2002

Diamagnetic orbital response of mesoscopic silver rings.

We report measurements of the flux-dependent orbital magnetic susceptibility of an ensemble of 10(5) disconnected silver rings at 217 MHz. Because of the strong spin-orbit scattering rate in silver this experiment is a test of existing theories on ensemble averaged persistent currents. Below 100 mK the rings exhibit a magnetic signal with a flux periodicity of h/2e consistent with averaged persistent currents, whose amplitude is of the order of 0.3 nA. The sign of the oscillations indicates unambiguously diamagnetism in the vicinity of zero magnetic field. This sign is a priori not consistent with theoretical predictions for average persistent currents. We discuss several possible explanations of this result.

Journal Article↗
PubMed2000

Acoustoelectric effects in carbon nanotubes

We report observations of acoustoelectric effects in carbon nanotubes. We excite sound in &mgr;m long ropes of single walled carbon nanotubes suspended between two metallic contacts by applying radio-frequency electric field. The sound is detected by measuring either the dc resistance of the tubes in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. We show that, depending on the excitation power, the vibrations produce either electron heating or phase coherence breaking.

Journal Article↗
PubMed2000

Measurements of flux-dependent screening in aharonov-bohm rings

In order to investigate the effect of electronic phase coherence on screening we have measured the flux-dependent polarizability of isolated mesoscopic rings at 350 MHz. At low temperatures (below 100 mK) both the nondissipative and the dissipative parts of the polarizability exhibit flux oscillations with a period of one-half a flux quantum in a ring. The sign and amplitude of the effect are in good agreement with recent theoretical predictions. The observed positive magnetopolarizability corresponds to an enhancement of screening when time reversal symmetry is broken. The effect of electronic density and temperature are also measured.

Journal Article↗
PubMed1999

Supercurrents through single-walled carbon nanotubes

Proximity-induced superconductivity in single-walled carbon nanotubes below 1 kelvin, both in a single tube 1 nanometer in diameter and in crystalline ropes containing about 100 nanotubes, was observed. The samples were suspended between two superconducting electrodes, permitting structural study in a transmission electron microscope. When the resistance of the nanotube junction is sufficiently low, it becomes superconducting and can carry high supercurrents. The temperature and magnetic field dependence of the critical current of such junctions exhibits unusual features related to their strong one-dimensional character.

Journal Article↗
PubMed1978

[Ontogenic development of the surface of craniofacial sagittal angular sectors in man and chimpanzee].

By means of a technique for measuring surfaces by direct reading, six angular sectors have been studied (3 for the face and 3 for the skull) at various ontogenic periods of Man, common chimpanzee and dwarf chimpanzee. The growth curves have been drawn for absolute values and for relative values. They show a certain evolutive parallelism between the frontal bone and the parietal bone, and between the face and the mandible, with a special fate for the occipital bone.

Adult↗
PubMed1977

[Angles of the base of the skull in chimpanzees].

Ten angular measurements have been retained for a study of the basis of the skull for two species of chimpanzees : Pan troglodytes (83 skulls) and Pan paniscus (179 skulls). Were especially studied : growth and sexual or specific differences. Classical parameters or angles measured in reference to the horizontal vestibular axis were used. The statistical study clearly shows the phenomenom of negative rotation with an ontogenic accentuation of quadrupedia.

Animals↗
PubMed1976

[Phylogenic interest of the clivo-pterygoid angle].

The comparison between the planum-clivus angle of Man and the african Pongids shows that the closing of this angle is the result of a noticeable rotation of the clivus and a less important rotation of the planum in an opposite direction.

Anatomy, Comparative↗
PubMed1975

[Spatial variability of some lateral cranial points in chimpanzees].

The differential variability of cranial regions of chimpanzees has been studied, in the three dimensional space defined by the vestibular method, by means of the volume of the ellipsoid surrounding the scatter diagram of each lateral point. Thus the importance of the variation of a given point as a function of its position can be measured and the specific and sexual differences of this variation can be determined.

Animals↗