341 research outputs found
Intrinsic Josephson Effects in the Magnetic Superconductor RuSr2GdCu2O8
We have measured interlayer current transport in small sized RuSr2GdCu2O8
single crystals. We find a clear intrinsic Josephson effect showing that the
material acts as a natural
superconductor-insulator-ferromagnet-insulator-superconductor superlattice. So
far, we detected no unconventional behavior due to the magnetism of the RuO2
layers.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
A Transport and Microwave Study of Superconducting and Magnetic RuSr2EuCu2O8
We have performed susceptibility, thermopower, dc resistance and microwave
measurements on RuSr2EuCu2O8. This compound has recently been shown to display
the coexistence of both superconducting and magnetic order. We find clear
evidence of changes in the dc and microwave resistance near the magnetic
ordering temperature (132 K). The intergranular effects were separated from the
intragranular effects by performing microwave measurements on a sintered
ceramic sample as well as on a powder sample dispersed in an epoxy resin. We
show that the data can be interpreted in terms of the normal-state resistivity
being dominated by the CuO2 layers with exchange coupling to the Ru moments in
the RuO2 layers. Furthermore, most of the normal-state semiconductor-like
upturn in the microwave resistance is found to arise from intergranular
transport. The data in the superconducting state can be consistently
interpreted in terms of intergranular weak-links and an intragranular
spontaneous vortex phase due to the ferromagnetic component of the
magnetization arising from the RuO2 planes.Comment: 20 pages including 6 figures in pdf format. To be published in Phys.
Rev.
Decoupling of superconducting layers in magnetic superconductor RuSr_{2}GdCu_{2}O_{8}
We propose the model for magnetic properties of the magnetic superconductor
RuSrGdCuO, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line , on
which the Josephson coupled superconducting planes are decoupled, i.e. , is calculated as a function of the exchange energy . As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field , Josephson plasma frequency, etc. is realized
near (or by crossing) the line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSrGdCuO with possible weak ferromagnetic order in the RuO
planes.Comment: 12 pages, 3 figs embede
Evidence for Possible Phase-Separations in RuSr2(Gd,Ce)2Cu2O10-delta
An unusual thermal-magnetic hysteresis was observed between a minor magnetic
transition around 120 K and the main one at 80 K in superconducting
RuSr2(R,Ce)2Cu2O10-delta (Ru1222R) samples, where R = Gd or Eu, down to a
submicron length-scale. The observation suggests a possible phase-separation
and is consistent with the very small but universal demagnetizing factor
observed, which is difficult to reconcile with the canted spin-structure
previously proposed. In such a scenario, the unusual superconducting properties
of the Ru-based cuprates can also be understood naturally.Comment: 8 pages, 3 figures, submitted to Phys. Rev. B, "Rapid Communications"
(September 26, 2001
Decoupled CuO_2 and RuO_2 layers in superconducting and magnetically ordered RuSr_2GdCu_2O_8
Comprehensive measurements of dc and ac susceptibility, dc resistance,
magnetoresistance, Hall resistivity, and microwave absorption and dispersion in
fields up to 8 T have been carried out on RuSr_2GdCu_2O_8 with the aim to
establish the properties of RuO_2 and CuO_2 planes. At ~130 K, where the
magnetic order develops in the RuO_2 planes, one observes a change in the slope
of dc resistance, change in the sign of magnetoresistance, and the appearance
of an extraordinary Hall effect. These features indicate that the RuO_2 planes
are conducting. A detailed analysis of the ac susceptibility and microwave data
on both, ceramic and powder samples show that the penetration depth remains
frequency dependent and larger than the London penetration depth even at low
temperatures. We conclude that the conductivity in the RuO_2 planes remains
normal even when superconducting order is developed in the CuO_2 planes below
\~45 K. Thus, experimental evidence is provided in support of theoretical
models which base the coexistence of superconductivity and magnetic order on
decoupled CuO_2 and RuO_2 planes.Comment: 11 pages, 11 figures, submitted to PR
Study of the crystal structure, superconducting and magnetic properties of Ru1-xFexSr2GdCu2O8
Samples of the Ru1-xFexSr2GdCu2O8 system with x = 0, 0.025, 0.05, 0.075, 0.1
and 0.2, were prepared and their structural, superconducting and magnetic
properties were studied. Rietveld refinement of the X-ray diffraction patterns
show that the Fe substitution occurs in both Ru and Cu sites. An increase of Fe
concentration produces no significant changes in the bond angle Ru-O(3)-Ru,
which is a measure of the rotation of the RuO6 octahedra around the c-axis, and
also in the bond angle Ru-O(1)-Cu, which is a measure of the canting of the
RuO6 octahedra. On the other hand, the bond angle Cu-O(2)-Cu, which is a
measure of the buckling of the CuO2 layer, has a slight tendency to decrease
with the increase of the Fe content. We found thet both ferromagnetic and
superconducting transition temperatures are reduced with the increase of Fe
concentration. Analisys related to the decay of the superconducting and
ferromagnetic states is presented.Comment: 9 pages, 7 figure
The Superconductivity, Intragrain Penetration Depth and Meissner Effect of RuSr2(Gd,Ce)2Cu2O10+delta
The hole concentration (p)(delta), the transition temperature Tc, the
intragrain penetration depth lambda, and the Meissner effect were measured for
annealed RuSr2(Gd,Ce)2Cu2O10+delta samples. The intragrain superconducting
transition temperature Tc} varied from 17 to 40 K while the p changed by only
0.03 holes/CuO2. The intragrain superfluid-density 1/lambda^2 and the
diamagnetic drop of the field-cooled magnetization across Tc (the Meissner
effect), however, increased more than 10 times. All of these findings are in
disagreement with both the Tc vs. p and the Tc vs. 1/lambda^2 correlations
proposed for homogeneous cuprates, but are in line with a possible
phase-separation and the granularity associated with it.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev. B (May 2,
2002
Elevation and cholera: an epidemiological spatial analysis of the cholera epidemic in Harare, Zimbabwe, 2008-2009
BACKGROUND: In highly populated African urban areas where access to clean water is a challenge, water source contamination is one of the most cited risk factors in a cholera epidemic. During the rainy season, where there is either no sewage disposal or working sewer system, runoff of rains follows the slopes and gets into the lower parts of towns where shallow wells could easily become contaminated by excretes. In cholera endemic areas, spatial information about topographical elevation could help to guide preventive interventions. This study aims to analyze the association between topographic elevation and the distribution of cholera cases in Harare during the cholera epidemic in 2008 and 2009. METHODS: We developed an ecological study using secondary data. First, we described attack rates by suburb and then calculated rate ratios using whole Harare as reference. We illustrated the average elevation and cholera cases by suburbs using geographical information. Finally, we estimated a generalized linear mixed model (under the assumption of a Poisson distribution) with an Empirical Bayesian approach to model the relation between the risk of cholera and the elevation in meters in Harare. We used a random intercept to allow for spatial correlation of neighboring suburbs. RESULTS: This study identifies a spatial pattern of the distribution of cholera cases in the Harare epidemic, characterized by a lower cholera risk in the highest elevation suburbs of Harare. The generalized linear mixed model showed that for each 100 meters of increase in the topographical elevation, the cholera risk was 30% lower with a rate ratio of 0.70 (95% confidence interval=0.66-0.76). Sensitivity analysis confirmed the risk reduction with an overall estimate of the rate ratio between 20% and 40%. CONCLUSION: This study highlights the importance of considering topographical elevation as a geographical and environmental risk factor in order to plan cholera preventive activities linked with water and sanitation in endemic areas. Furthermore, elevation information, among other risk factors, could help to spatially orientate cholera control interventions during an epidemic
The Response of Paroxysmal Supraventricular Tachycardia to Overdrive Atrial and Ventricular Pacing:
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75015/1/j.1540-8167.1993.tb01227.x.pd
Maintaining Fluoroquinolone Class Efficacy: Review of Influencing Factors
Previous experience with antimicrobial resistance has emphasized the importance of appropriate stewardship of these pharmacotherapeutic agents. The introduction of fluoroquinolones provided potent new drugs directed primarily against gram-negative pathogens, while the newer members of this class demonstrate more activity against gram-positive species, including Streptococcus pneumoniae. Although these agents are clinically effective against a broad range of infectious agents, emergence of resistance and associated clinical failures have prompted reexamination of their use. Appropriate use revolves around two key objectives: 1) only prescribing antimicrobial therapy when it is beneficial and 2) using the agents(s) with optimal activity against the expected pathogens(s). Pharmacodynamic principles and properties can be applied to achieve the latter objective when prescribing agents belonging to the fluoroquinolone class. A focused approach emphasizing “correct-spectrum” coverage may reduce development of antimicrobial resistance and maintain class efficacy
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