5,061 research outputs found
Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite
We report on unusual magnetic properties observed in the nanofluid
room-temperature ferromagnetic graphite (with an average particle size of
l=10nm). More precisely, the measured magnetization exhibits a low-temperature
anomaly (attributed to manifestation of finite size effects below the quantum
temperature) as well as pronounced temperature oscillations above T=50K
(attributed to manifestation of the hard-sphere type pair correlations between
ferromagnetic particles in the nanofluid)
Comparación de la eficacia y seguridad diagnóstica entre el estudio isotópico hepatobiliar y la ecografía en la colecistitis aguda
Hemos estudiado en 67 pacientes con el diagnóstico de colecistitis aguda (CA) confirmado mediante intervención quirúrgica precoz, la sensibilidad diagnóstica del estudio isotópico con HIDA comparándola con la de la ecografía. El estudio se llevó a cabo de forma retrospectiva. La sensibilidad del estudio isotópico (97%) ha sido claramente superior a la de la ecografía (82%), aunque esta última ofrece ventajas en cuanto a la rapidez y economía de valor indudable. Asimismo hemos intentado establecer la seguridad de ambas técnicas en el diagnóstico de la coledocolitiasis asociada a la CA, que en nuestro estudio ha mostrado una incidencia alta (26%), siendo mala para ambas técnicas; la sensibilidad en este caso para la ecografía ha sido del 50% mientras que para el HIDA ha sido del 12,5%. Por tanto creemos conveniente realizar como primer estudio diagnóstico para la confirmación de la sospecha clínica de CA una ecografía abdominal, reservando la escintigrafía para los casos, por otra parte numéricamente apreciables, en que persista la duda diagnóstica. Asimismo recomendamos la realización de colangiografía intraoperatoria debido a la deficiente fiabilidad que ambas exploraciones han demostrado en la detección de coledocolitiasis en los pacientes con C
Dynamic ordering of driven vortex matter in the peak effect regime of amorphous MoGe films and 2H-NbSe2 crystals
Dynamic ordering of driven vortex matter has been investigated in the peak
effect regime of both amorphous MoGe films and 2H-NbSe2 crystals by mode
locking (ML) and dc transport measurements. ML features allow us to trace how
the shear rigidity of driven vortices evolves with the average velocity.
Determining the onset of ML resonance in different magnetic fields and/or
temperatures, we find that the dynamic ordering frequency (velocity) exhibits a
striking divergence in the higher part of the peak effect regime.
Interestingly, this phenomenon is accompanied by a pronounced peak of dynamic
critical current. Mapping out field-temperature phase diagrams, we find that
divergent points follow well the thermodynamic melting curve of the ideal
vortex lattice over wide field and/or temperature ranges. These findings
provide a link between the dynamic and static melting phenomena which can be
distinguished from the disorder induced peak effect.Comment: 9 pages, 6 figure
Fermiology and transport properties of the half-metallic itinerant ferromagnet CoS: influence of spin orbit coupling
Electronic structure calculations were performed on the compound CoS, an
itinerant ferromagnet whose magnetic properties can be understood in terms of
spin fluctuation theory. We have identified nesting features in the Fermi
surface of the compound, active for long wavelength spin fluctuations. The
electronic structure of the material is close to a half-metal. We show the
importance of introducing spin-orbit coupling (SOC) in the calculations, that
partially destroys the half-metallicity of the material. By means of transport
properties calculations, we have quantified the influence of SOC in the
conductivity at room temperature, with an important decrease comparing to the
GGA alone conductivity. SOC also helps to understand the negative 0 of the
material, whose conductivity varies by a few percent with the introduction of
small perturbations in the states around the Fermi level.Comment: 8 pages, 8 figure
AC loss in ReBCO pancake coils and stacks of them: modelling and measurement
Many applications of ReBCO coated conductors contain stacks of pancake coils.
In order to reduce their high AC loss, it is necessary to understand the loss
mechanisms. In this article, we measure and simulate the AC loss and the
critical current, I_c, in stacks of pancake coils ("pancakes"). We construct
stacks of up to 4 pancakes and we measure them by electrical means. We also
obtain the anisotropic field dependence of J_c from I_c measurements of the
tape. This J_c is the only input to the simulations, together with the coil
dimensions. After validating our computations with the measurements, we
simulate stacks of many pancakes, up to 32. We found that the AC loss in a
stack of (four) pancakes is very high, two orders of magnitude larger than for
a single tape. A double pancake behaves as a single one with double width but a
stack of more pancakes is very different. Finally, we found that a 2-strand
Roebel cable reduces the AC loss in a stack of pancakes but not in a single
pancake. In conclusion, the AC loss in stacks of pancakes is too high. However,
our simulations are useful to predict the AC loss and optimise the coil design,
reducing the AC loss.Comment: 34 pages, 18 figures. All figures are modified; figures 3, 7 and 10
are new. Text thoroughly revised and extende
Manifestation of finite temperature size effects in nanogranular magnetic graphite
In addition to the double phase transition (with the Curie temperatures
T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the
magnetization is observed in the bulk magnetic graphite (with an average
granular size of L=10nm), which is attributed to manifestation of the size
effects below the quantum temperature. The best fits of the high-temperature
data (using the mean-field Curie-Weiss and Bloch expressions) produced
reasonable estimates for the model parameters, such as defects mediated
effective spin exchange energy J=12meV (which defines the intragranular Curie
temperature T_C) and proximity mediated interactions between neighboring grains
(through potential barriers created by thin layers of non-magnetic graphite)
with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie
temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and
characteristic length, respectively
Current profiles and AC losses of a superconducting strip with elliptic cross-section in perpendicular magnetic field
The case of a hard type II superconductor in the form of strip with elliptic
cross-section when placed in transverse magnetic field is studied. We approach
the problem in two steps, both based on the critical-state model. First we
calculate numerically the penetrated current profiles that ensure complete
shielding in the interior, without assuming an a priori form for the profiles.
In the second step we introduce an analytical approximation that asumes that
the current profiles are ellipses. Expressions linking the sample magnetization
to the applied field are derived covering the whole range of applied fields.
The theoretical predictions are tested by the comparison with experimental data
for the imaginary part of AC susceptibility.Comment: 12 pages; 3 figure
Kinematic evaluation of physical impairments of an elite Paralympic karateka
Karate is a Japanese martial art that counts millions of practitioners worldwide and that is spreading also in Paralympic competitions, requiring accurate categories definition for disabled athletes. The aim of the study is to present kinematic data of an elite Paralympic karateka, in comparison with able-bodied athletes. The authors also aim to promote a better classification within the discipline, based on objective biomechanical evaluations of physical impairments. A male black belt Paralympic karateka (age: 36 y; body weight: 75.5 kg; height: 173 cm) with lower limbs impairments was evaluated. The athlete had been performing high level karate for 20 years before the disability took place. After the post-operative rehabilitation, he attended 3/4 sessions of para- karate training per week. He performed a standardized sequence of movements, involving a sequence of offensive and defensive techniques, (kata) from traditional Shotokan karate. Joints and body Center of Mass (CoM) kinematics were collected with an optoelectronic motion capture system and compared with those obtained in two groups of able-bodied (elite and amateurs) athletes from a previous study1. Knee angular range of motion (RoM) and peak angular velocity were obtained. Coordinates of CoM were estimated, using the Segmental Centroid Method2, along with CoM average velocity and acceleration. To assess differences between Paralympic karateka and able-bodied groups, the one-sample t-test was performed. The sequence performed by the karateka lasted more than in both able-bodied groups. CoM average velocity and acceleration decreased in comparison with elite karateka. Knees range of movement and peak angular velocity were similar to amateur but lower than elite athletes. Results show that the physical impairments negatively affected the function of lower limbs in the Paralympic athlete. Fundamental skills in karate elite performance (dynamic balance control and joint RoM and angular velocity) were reduced
Monoids of intervals of simple refinement monoids and non-stable K-Theory of multiplier algebras
We show that the representation of the monoid of intervals of a simple refinement monoid in terms of affine semicontinuous functions, given by Perera in 2001, fails to be faithful in the case of strictly perforated monoids. We give some potential applications of this result in the context of monoids of intervals and K-Theory of multiplier rings
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