336 research outputs found
La renaissance de la publicité
No full textLa crise a profondément modifié le comportement des consommateurs. La distribution et la publicité sont contraintes de s'adapter aux évolutions de la société. Claude Matricon, qui est l'un des responsables du groupe I P (Information et Publicité), dispose d'un observatoire européen de ces évolutions. Il publie deux fois par an, en mai et en décembre, une note de conjoncture qui fait autorité. En mai sont confirmés les résultats économiques et publicitaires de l'année précédente. En décembre sont présentées les estimations pour l'année en cours et les prévisions pour l'année suivante. Les équipes de Claude Matricon suivent l'évolution de 13 pays et les notes de synthèse qui sont établies sont diffusées à 3 000 exemplaires auprès des agences, des entreprises et des organismes officiels de la communication. Cette masse de données enrichie d'année en année permet à Claude Matricon de faire des prévisions très engagées dans l'article ci-dessous.Matricon Claude. La renaissance de la publicité. In: Communication et langages, n°100-101, 2ème-3ème trimestre 1994. 25e anniversaire. pp. 89-101
Near zero-energy Caroli-de Gennes-Matricon vortex states in the presence of impurities
No full textCaroli-de Gennes-Matricon (CdGM) states are localized states with a discrete
energy spectrum bound to the core of vortices in superconductors. In
topological superconductors, CdGM states are predicted to coexist with
zero-energy, chargeless states widely known as Majorana zero modes (MZMs). Due
to their energy difference, current experiments rely on scanning tunneling
spectroscopy methods to distinguish between them. This work shows that
electrostatic inhomogeneities can push trivial CdGM states arbitrarily close to
zero energy in non-topological systems where no MZM is present. Furthermore,
the BCS charge of CdGM states is suppressed under the same mechanism. Through
exploration of the impurity parameter space, we establish that these two
phenomena generally happen in consonance. Our results show that energy and
charge shifts in CdGM may be enough to imitate the spectroscopic signatures of
MZMs even in cases where the estimated CdGM level spacing (in the absence of
impurities) is much larger than the typical experimental level broadening.Comment: Revised and expanded version. 8 pages, 5 figure
Protocol for Reading Out Majorana Vortex Qubits and Testing Non-Abelian Statistics
No full textThe successful testing of non-Abelian statistics not only serves as a milestone in fundamental physics but also provides a quantum-gate operation in topological quantum computation. An accurate and efficient readout scheme of a topological qubit is an essential step toward the experimental confirmation of non-Abelian statistics. In the current work, we propose a protocol to read out the quantum state of a Majorana vortex qubit on a topological superconductor island. The protocol consists of four Majorana zero modes trapped in spatially well-separated vortex cores on the two-dimensional surface of a Coulomb blockaded topological superconductor. Our proposed measurement is implemented by a pair of weakly coupled Majorana modes separately in touch with two normal-metal leads and the readout is realized by observing the conductance-peak location in terms of the gate voltage. Using this protocol, we can further test the non-Abelian statistics of Majorana zero modes in the two-dimensional platform. A successful readout of a Majorana qubit is a crucial step toward the future application of topological quantum computation. In addition, this Coulomb-blockaded setup can distinguish Majorana zero modes from Caroli-de Gennes-Matricon modes in vortex cores.ChemE/Delft Ingenious Desig
Finite temperature effects on Majorana bound states in chiral -wave superconductors
No full textWe study Majorana fermions bound to vortex cores in a chiral -wave
superconductor at temperatures non-negligible compared to the superconducting
gap. Thermal occupation of Caroli de Gennes-Matricon states, below the full
gap, causes the free energy difference between the two fermionic parity sectors
to decay algebraically with increasing temperature. The power law acquires an
additional factor of for each bound state thermally excited. The
zero-temperature result is exponentially recovered well below the minigap
(lowest-lying CdGM level). Our results suggest that temperatures larger than
the minigap may not be disastrous for topological quantum computation. We
discuss the prospect of precision measurements of pinning forces on vortices as
a readout scheme for Majorana qubits
Vortex supercurrent inversion by frequency-symmetry conversion of Cooper pairs
No full textWe theoretically demonstrate that the vortex supercurrent can be reversed by the frequency-symmetry conversion among Cooper pairs by surface Andreev bound states. The surface of a three-dimensional superconductor pierced by a flux quantum is considered. We compare the vortex supercurrents near the surface of the spin-singlet s-wave and spin-triplet pz-wave superconductors using quasiclassical Eilenberger theory, where the surface is perpendicular to the z direction. We demonstrate that the vortex supercurrent near the surface of a pz-wave superconductor is reversed compared to those far from the surface, whereas that of an s-wave superconductor is not. The splitting of the zero-energy states caused by the interference of the surface Andreev bound states and Caroli-de Gennes-Matricon modes is demonstrated.</p
CAMAC booster ("CAB" system): a versatile microcomputer for high rate CAMAC data acquisition
No full textReports the present status of CAB from the points of view of hardware and software. CAB is a microprogrammable system, using fast TTL bit- slice technology, designed to improve the capabilities of a standard CAMAC data acquisition chain. It can be implemented as crate controller, branch driver, or computer to CAMAC (or GPIB to CAMAC) interface. It is well adapted to a wide range of complex applications, such as software triggering, event filtering, data compaction and formatting, equipment calibration and monitoring. The basic software includes a cross-assembler, an emulating program and an interactive debugger. Improvements are now under development. Today, more than 15 units are used in different laboratories. (0 refs)
Boundary states with elevated critical temperatures in Bardeen-Cooper-Schrieffer superconductors
No full textBardeen-Cooper-Schrieffer (BCS) theory describes a superconducting transition as a single critical point where the gap function or, equivalently, the order parameter vanishes uniformly in the entire system. We demonstrate that in superconductors described by standard BCS models, the superconducting gap survives near the sample boundaries at higher temperatures than superconductivity in the bulk. Therefore, conventional superconductors have multiple critical points associated with separate phase transitions at the boundary and in the bulk. We show this by revising the Caroli-De Gennes-Matricon theory of a superconductor-vacuum boundary and finding inhomogeneous solutions of the BCS gap equation near the boundary, which asymptotically decay in the bulk. This is demonstrated for a BCS model of almost free fermions and for lattice fermions in a tight-binding approximation. The analytical results are confirmed by numerical solutions of the microscopic model. The existence of these boundary states can manifest itself as discrepancies between the critical temperatures observed in calorimetry and transport probes.</p
Molecular simulations of G protein-coupled receptors [Elektronisk resurs] : A journey into structure-based ligand design and receptor function
No full textThe superfamily of G protein-coupled receptors (GPCRs) contains a large number of important drug targets. These cell surface receptors recognize extracellular signaling molecules, which stimulates intracellular pathways that play major roles in human physiology. Breakthroughs in structural biology have led to an exponentially increasing number of atomic resolution GPCR structures, which have provided insights into the molecular basis of ligand binding and receptor activation. However, in order to use these structures in rational drug design, computational methods able to predict ligand binding modes and affinities are required. In the first part of this thesis, molecular simulations were used to explore the potential of using structure-based approaches to discover and optimize GPCR ligands. In paper I, molecular dynamics (MD) simulations in combination with free energy perturbation (FEP) guided improvements of binding affinities for fragment-like ligands of the A2A adenosine receptor (A2AAR), which is a target for Parkinson’s disease and cancer. Two computational approaches were then explored to design selective GPCR ligands. MD/FEP was first used to guide the optimization of a weak fragment ligand for subtype selectivity. Simulations of the A1- and A2AARs led to the discovery of high affinity and selective A1AR antagonists (paper II). In the second approach, a molecular docking screen of millions of molecules was carried out against AR crystal structures with the goal to identify A1AR ligands. Structure-based optimization of two hits resulted in the discovery of potent and selective A1AR antagonists (paper III). In paper IV, the role of a binding site water in agonist binding to the A2AAR was probed by modifying the endogenous agonist adenosine. MD simulations highlighted the complexity of ligand binding and the benefits of using FEP calculations to guide ligand optimization. In the second part of the thesis, MD simulations were used to study the activation mechanism of class A GPCRs and the function of class F receptors. The allosteric communication between the orthosteric and G protein binding sites of the β2 adrenergic receptor was investigated, which revealed the roles of structural motifs in receptor activation (paper V). Finally, MD simulations of a homology model of the Frizzled 4 receptor, which is a target for the development of anticancer drugs, led to the identification of a conserved structural motif that is important for receptor signaling (paper VI). The results of the thesis show that computer simulations can be valuable tools in structure-based drug discovery and studies of GPCR function.</p
- …
