Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures

We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 \mu K < T < 9 K. In the mesoscopic temperature regime, the normal metal-superconductor system shows the yet unexplained paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990)], superimposing on full Meissner screening. The logarithmic slope of the reentrant paramagnetic susceptibility chi_para(T) \propto \exp(-L/\xi_N) is limited by the condition \xi_N=n L, with \xi_N=\hbar v_F/2 \pi k_B T, the thermal coherence length and n=1,2,4. In wires with perimeters L=72 \mu m and L=130 \mu m, we observe integer multiples n=1,2,4. At the lowest temperatures, \chi_para compensates the diamagnetic susceptibility of the \textit{whole} AgNb structure.Comment: 4 pages, 4 figures (color

Diamagnetic response of cylindrical normal metal - superconductor proximity structures with low concentration of scattering centers

We have investigated the diamagnetic response of composite NS proximity wires, consisting of a clean silver or copper coating, in good electrical contact to a superconducting niobium or tantalum core. The samples show strong induced diamagnetism in the normal layer, resulting in a nearly complete Meissner screening at low temperatures. The temperature dependence of the linear diamagnetic susceptibility data is successfully described by the quasiclassical Eilenberger theory including elastic scattering characterised by a mean free path l. Using the mean free path as the only fit parameter we found values of l in the range 0.1-1 of the normal metal layer thickness d_N, which are in rough agreement with the ones obtained from residual resistivity measurements. The fits are satisfactory over the whole temperature range between 5 mK and 7 K for values of d_N varying between 1.6 my m and 30 my m. Although a finite mean free path is necessary to correctly describe the temperature dependence of the linear response diamagnetic susceptibility, the measured breakdown fields in the nonlinear regime follow the temperature and thickness dependence given by the clean limit theory. However, there is a discrepancy in the absolute values. We argue that in order to reach quantitative agreement one needs to take into account the mean free path from the fits of the linear response. [PACS numbers: 74.50.+r, 74.80.-g]Comment: 10 pages, 9 figure

Overscreening Diamagnetism in Cylindrical Superconductor-Normal Metal-Heterostructures

We study the linear diamagnetic response of a superconducting cylinder coated by a normal-metal layer due to the proximity effect using the clean limit quasiclassical Eilenberger equations. We compare the results for the susceptibility with those for a planar geometry. Interestingly, for $R\sim d$ the cylinder exhibits a stronger overscreening of the magnetic field, i.e., at the interface to the superconductor it can be less than (-1/2) of the applied field. Even for $R\gg d$, the diamagnetism can be increased as compared to the planar case, viz. the magnetic susceptibility $4\pi\chi$ becomes smaller than -3/4. This behaviour can be explained by an intriguing spatial oscillation of the magnetic field in the normal layer

Echocardiographic evaluation of partial anomalous pulmonary venous drainage

AbstractObjectives. This study was undertaken to determine the accuracy of routine echocardiography in the detection of partial anomalous pulmonary venous drainage.Background. Although there are occasional case reports of the echocardiographic appearance of partial anomalous pulmonary venous drainage, no large series have addressed the accuracy of this technique in a large cohort of patients.Methods. Between January 1983 and December 1993, 50 patients with partial anomalous pulmonary venous drainage (with or without an associated atrial septal defect as the only other significant intracardiac defect) were identified from the data base at the Hospital For Sick Children, Toronto. Routine echocardiographic reports were reviewed, and the results were compared with surgical or catheterization findings. Risk factors related to diagnostic errors were sought using a Fisher exact test, chi square analysis, ttest and Kruskal-Wallis analysis of variance.Results. Confirmation of the diagnosis was available in 45 patients whose data were subsequently used for risk factor analysis. The median age at echocardiography was 4.1 years (range 1 month to 18 years). Right-sided drainage was present in 43 patients (86%), with left-sided drainage in 7 (14%). Thirteen patients had an intact atrial septum, 7 a patent foramen ovale and 30 a secundum atrial septal defect. Right ventricular dilation was observed in 46 patients. Two had normal dimensions (two not assessed). The diagnosis was missed by echocardiography in 15 (33%) of the 45 patients with a confirmed diagnosis. Year of study and use of color flow mapping were the only significant variables related to detection rate (7% missed diagnosis with vs. 62% without the use of color flow, p < 0.0005). The median year of missed diagnosis was 1985 versus 1990 (p < 0.002). Transesophageal echocardiography accurately defined the site of drainage in all three patients in whom it was utilized.Conclusions. Two-dimensional echocardiography in conjunction with color flow mapping is a valuable tool for the diagnosis of partial anomalous pulmonary venous drainage

Testing feasibility of scalar-tensor gravity by scale dependent mass and coupling to matter

We investigate whether there are any cosmological evidences for a scalar field with a mass and coupling to matter which change accordingly to the properties of the astrophysical system it "lives in", without directly focusing on the underlying mechanism that drives the scalar field scale-dependent properties. We assume a Yukawa type of coupling between the field and matter and also that the scalar field mass grows with density, in order to overcome all gravity constraints within the solar system. We analyse three different gravitational systems assumed as "cosmological indicators": supernovae type Ia, low surface brightness spiral galaxies and clusters of galaxies. Results show that: a) a quite good fit to the rotation curves of low surface brightness galaxies only using visible stellar and gas mass components is obtained; b) a scalar field can fairly well reproduce the matter profile in clusters of galaxies, estimated by X-ray observations and without the need of any additional dark matter; c) there is an intrinsic difficulty in extracting information about the possibility of a scale-dependent massive scalar field (or more generally about a varying gravitational constant) from supernovae type Ia.Comment: 30 pages, 15 figures, to appear in Phys. Rev.

Controle do alho-macho (Sisyrinchium platense Johnst): pesquisas realizadas na Embrapa Pecuária Sul.

Efeito do uso de calcário; Efeito de roçadasbitstream/item/67073/1/CR-22-2001.pd