Influence of the sample geometry on the vortex matter in superconducting microstructures

The dependence of the vortex penetration and expulsion on the geometry of mesoscopic superconductors is reported. Hall magnetometry measurements were performed on a superconducting Al square and triangle. The stability of the vortex patterns imposed by the sample geometry is discussed. The field-temperature $H-T$ diagram has been reconstructed showing the transitions between states with different vorticity. We have found that the vortex penetration is only weakly affected by the vortex configuration inside the sample while the expulsion is strongly controlled by the stability of the vortex patterns. A qualitative explanation for this observation is given.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.

Short-Term cost impact of compliance with clinical practice guidelines for initial sarcoma treatment

Background: The impact of compliance to clinical practice guidelines (CPG) on outcomes and/or costs of care has not been completely clarified.Objective: To estimate relationships between medical expenditures and compliance to CPG for initial sarcoma treatment.Research design: Selected cohorts of patients diagnosed with sarcoma in 2005 and 2006, and treated at the University hospital and/or the cancer centre of the Rhône-Alpes region, France (n=90). Main outcome measurements were: patient characteristics, compliance with CPG, health outcomes, and costs. Data were mainly extracted from patient records. The logarithm of treatment costs was modelled using linear and Tobit regressions.Results: Rates of compliance with CPG were 86%, 66%, 88%, 89%, and 95% for initial diagnosis, primary surgical excision, wide surgical excision, chemotherapy, and radiotherapy, respectively. Total average costs reached €24,439, with €1,784, €11,225, €10,360, and €1,016 for diagnosis, surgery (primary and wide surgical excisions), chemotherapy, and radiotherapy, respectively. Compliance of diagnosis with CPG decreased the cost of diagnosis, whereas compliance of primary surgical excision increased the cost of chemotherapy. Compliance of chemotherapy with CPG decreased the cost of radiotherapy.Conclusion: Since chemotherapy is one of the major cost drivers, these results support that compliance with guidelines increases medical care expenditures in short term.Oncology; Sarcoma; Cost; Clinical guidelines; Efficacy; Medical Practices; Government Policy; Regulation; Public Health

Nucleation of superconductivity in a mesoscopic triangle

The nucleation of superconductivity in a mesoscopic equilateral triangle is studied experimentally by transport measurements and theoretically by using the linearized Ginzburg-Landau equation. The voltage and current leads, intrinsic to transport measurements. give rise to a broadening of the resistive transition R(T). However, by choosing the right resistance criterion to determine the experimental superconducting/normal phase boundary T-c(H) and by reducing the coupling between the triangle and the contacts, achieved by changing the shape of the contacts, this influence can be minimized. From the theoretical study, we found that the trigonal symmetry of the sample has a profound effect on the superconducting state in the presence of a magnetic field H leading, in particular. to the formation of antivortices in symmetry-consistent states. A good agreement between the theory and the experimental T-c(H) data is observed. (C) 2001 Elsevier Science B.V. All rights reserved.status: publishe

Controlled multiple reversals of a ratchet effect

A single particle confined in an asymmetric potential demonstrates an anticipated ratchet effect by drifting along the 'easy' ratchet direction when subjected to non-equilibrium fluctuations(1-3). This well-known effect can, however, be dramatically changed if the potential captures several interacting particles. Here we demonstrate that the inter-particle interactions in a chain of repelling particles captured by a ratchet potential can, in a controllable way, lead to multiple drift reversals, with the drift sign alternating from positive to negative as the number of particles per ratchet period changes from odd to even. To demonstrate experimentally the validity of this very general prediction, we performed transport measurements on a. c.-driven vortices trapped in a superconductor by an array of nanometre-scale asymmetric traps. We found that the direction of the vortex drift does undergo multiple reversals as the vortex density is increased, in excellent agreement with the model predictions. This drastic change in the drift behaviour between single- and multiparticle systems can shed some light on the different behaviour of ratchets and biomembranes(4) in two drift regimes: diluted ( single particles) and concentrated ( interacting particles).status: publishe

Ginzburg-Landau description of confinement and quantization effects in mesoscopic superconductors

An approach to the Ginzburg-Landau problem for superconducting regular polygons is developed making use of an analytical gauge transformation for the vector potential A which gives A(n)=0 for the normal component along the boundary line of different symmetric polygons. As a result the corresponding linearized Ginzburg-Landau equation reduces to an eigenvalue problem in the basis set of functions obeying Neumann boundary condition. Such basis sets are found analytically for several symmetric structures. The proposed approach allows for accurate calculations of the order parameter distributions at low calculational cost (small basis sets) for moderate applied magnetic fields. This is illustrated by considering the nucleation of superconductivity in squares, equilateral triangles and rectangles, where vortex patterns containing antivortices are obtained on the T-c-H phase boundary. The calculated phase boundaries are compared with the experimental T-c(H) curves measured for squares, triangles, disks, rectangles, and loops. The stability of the symmetry consistent solutions against small deviations from the phase boundary line deep into the superconducting state is investigated by considering the full Ginzburg-Landau functional. It is shown that below the nucleation temperature symmetry-switching or symmetry-breaking phase transitions can take place. The symmetry-breaking phase transition has the same structure as the pseudo-Jahn-Teller instability of high symmetry nuclear configurations in molecules. The existence of these transitions is predicted to be strongly dependent on the size of the samples. (c) 2005 American Institute of Physics.status: publishe

Electrochemical chloride extraction of a beam polluted by chlorides after 40 years in the sea

A beam element, naturally polluted by chlorides after 40 years of a marine tidal exposure, has been treated by electrochemical chloride extraction. The chloride profiles, before and after treatment, show that free chlorides are extrated with an efficiency of 70 % close to the steel, 50 % in the intermediate cover and only 5 % at the concrete surface. From the electrochemical characterizations (before, after, 1, 2 and 17 months after treatment), the steel potential values can, semehow, indicate a passivity of the rebars, but, this phenomenon is not confirmed by the corrosion current values. Chloride content, 17 months after treatment, continue to decrease on the first cm of the cover

Electrochemical chloride extraction of a beam polluted by chlorides after 40 years in the sea

A beam element, naturally polluted by chlorides after 40 years of a marine tidal exposure, has been treated by electrochemical chloride extraction. The chloride profiles, before and after treatment, show that free chlorides are extracted with an efficiency of 70 % close to the steel, 50% in the intermediate cover and only 5% at the concrete surface. From the electrochemical characterizations (before, after, 1, 2 and 17 months after treatment), the steel potential values can, somehow, indicate a passivity of the rebars, but, this phenomenon is not confirmed by the corrosion current values. Chloride content, 17 months after treatment, continue to decrease on the first cm of the cover

Electrochemical chloride extraction of a beam polluted by chlorides after 40 years in the sea

A beam element, naturally polluted by chlorides after 40 years of a marine tidal exposure, has been treated by electrochemical chloride extraction. The chloride profiles, before and after treatment, show that free chlorides are extracted with an efficiency of 70 % close to the steel, 50% in the intermediate cover and only 5% at the concrete surface. From the electrochemical characterizations (before, after, 1, 2 and 17 months after treatment), the steel potential values can, somehow, indicate a passivity of the rebars, but, this phenomenon is not confirmed by the corrosion current values. Chloride content, 17 months after treatment, continue to decrease on the first cm of the cover

Vortex ratchet effects in films with a periodic array of antidots

The vortex ratchet effect has been studied in Al films patterned with square arrays of submicron antidots. We have investigated the transport properties of two sets of samples: (i) asymmetrical antidots where vortices are driven by an unbiased ac current and (ii) symmetrical antidots where in addition to the ac drive a dc bias was used. For each sample, the rectified dc voltage is measured as a function of drive amplitude and frequency, magnetic field, and temperature. As unambiguously shown by our data, the voltage rectification in the asymmetric antidots is induced by the intrinsic asymmetry in the pinning potential created by the antidots, whereas the rectification in the symmetric antidots is induced by the dc bias. In addition, the experiments reveal interesting collective phenomena in the vortex ratchet effect. At fields below the first matching field (H-1), the dc-voltage-ac-drive characteristics present two rectification peaks, which is interpreted as an interplay between the one-dimensional motion of weakly pinned incommensurate vortex rows and the two-dimensional motion of the whole vortex lattice. We also discuss the different dynamical regimes controlling the motion of interstitial and trapped vortices at fields higher than H-1 and their implications for the vortex ratchet effect.10 pages, 8 figuresstatus: publishe