547 research outputs found
Dependence of vortex phase transitions in mesoscopic BSCCO superconductor at tilted magnetic fields
A micron sized single crystal of the superconductor BSCCO was studied using
silicon mechanical micro-oscillators at various tilt angles of the dc magnetic
field with respect to the c axis of the sample. Different phases of the vortex
matter were detected by measuring changes in the value and sign of the
oscillator resonant frequency variation with temperature. We could explain the
change in the sign of this variation at high temperatures as the transition
from the 2D liquid of decoupled pancakes to a reversible 3D vortex lattice. The
data indicates that this transition only depends on the magnetic field
perpendicular to the superconducting layers while the dissipation involved in
this process depends on the component parallel to them.Comment: 4 pages, 4 figure
Latent-heat and non-linear vortex liquid at the vicinity of the first-order phase transition in layered high-Tc superconductors
In this work we revisit the vortex matter phase diagram in layered
superconductors solving still open questions by means of AC and DC local
magnetic measurements in the paradigmatic BiSrCaCuO
compound. We show that measuring with AC magnetic techniques is mandatory in
order to probe the bulk response of vortex matter, particularly at
high-temperatures where surface barriers for vortex entrance dominate. From the
-evolution of the enthalpy and latent-heat at the transition we
find that, contrary to previous reports, the nature of the dominant interlayer
coupling is electromagnetic in the whole temperature range. By studying the
dynamic properties of the phase located at , we reveal
the spanning in a considerable fraction of the phase diagram of a non-linear
vortex phase suggesting bulk pinning might play a role even in the liquid
vortex phase.Comment: arXiv admin note: substantial text overlap with arXiv:1212.456
Anisotropic response of the moving vortex lattice in superconducting MoGe amorphous films
We have performed magnetic susceptibility measurements in MoGe
amorphous thin films biased with an electrical current using anisotropic coils.
We tested the symmetry of the vortex response changing the relative orientation
between the bias current and the susceptibility coils. We found a region in the
DC current - temperature phase diagram where the dynamical vortex structures
behave anisotropically. In this region the shielding capability of the
superconducting currents measured by the susceptibility coils is less effective
along the direction of vortex motion compared to the transverse direction. This
anisotropic response is found in the same region where the peak effect in the
critical current is developed. On rising temperature the isotropic behavior is
recovered.Comment: 10 pages, 4 figure
Measurement of mesoscopic High- superconductors using Si mechanical micro-oscillators
In a superconducting mesoscopic sample, with dimensions comparable to the
London penetration depth, some properties are qualitatively different to those
found in the bulk material. These properties include magnetization, vortex
dynamics and ordering of the vortex lattice. In order to detect the small
signals produced by this kind of samples, new instruments designed for the
microscale are needed. In this work we use micromechanical oscillators to study
the magnetic properties of a BiSrCaCuO disk with a
diameter of 13.5 microns and a thickness of 2.5 microns. The discussion of our
results is based on the existence and contribution of inter and intra layer
currents.Comment: 4 pages, 6 figure
Chlamydia psittaci genotype B in a pigeon (Columba livia) inhabiting a public place in San José, Costa Rica
Human chlamydiosis is a zoonotic disease of avian origin caused by Chlamydia psittaci. The highest infection rates have been detected in parrots (Psittacidae) and pigeons (Columbiformes), the latter most frequently carry the genotypes B and E. These genotypes have been shown to also infect humans. Because pigeons (Columba livia) cohabit with humans in urban areas, C. psittaci present in the dust from dry feces of infected pigeons may be transmitted by inhalation and represent a significant public health problem. Between 2012 and 2013 a total of 120 fecal samples were collected from pigeons at four public places (Plaza de la Cultura, Parque Morazán, Parque Central de Guadalupe, Plaza de las Garantías Sociales) in San José, Costa Rica. A nested polymerase chain reaction (PCR) was used to amplify a region of the outer membrane protein A gene of C. psittaci. Only one sample was positive in PCR and the positive sample was further subjected to sequencing and genotyping. Sequencing identified this sample as C. psittaci genotype B. This study is the first report to show the presence of this organism in pigeons of Costa Rica, and shows that the infected pigeons may represent a significant risk for humans who visit public places that are inhabited by pigeons
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