8,162 research outputs found
Hall conductivity as bulk signature of topological transitions in superconductors
Topological superconductors may undergo transitions between phases with
different topological numbers which, like the case of topological insulators,
are related to the presence of gapless (Majorana) edge states. In
topological insulators the charge Hall conductivity is quantized, being
proportional to the number of gapless states running at the edge. In a
superconductor, however, charge is not conserved and, therefore,
is not quantized, even in the case of a topological
superconductor. Here it is shown that while the evolves
continuously between different topological phases of a topological
superconductor, its derivatives display sharp features signaling the
topological transitions. We consider in detail the case of a triplet
superconductor with p-wave symmetry in the presence of Rashba spin-orbit (SO)
coupling and externally applied Zeeman spin splitting. Generalization to the
cases where the pairing vector is not aligned with that of the SO coupling is
given. We generalize also to the cases where the normal system is already
topologically non-trivial.Comment: 10 pages, 10 figure
Neoplasia renal con extensión a la vena cava
La neoplasia renal con extensión a la vena cava es relativamente rara (4-10%). Cualquiera que sea la terapia coadjuvante (radioterapia, hormonal, quimioterapia e inmunoterapia), la exéresis completa del trombo tumoral de la vena cava continúa siendo la mejor forma de tratamiento. El valor pronóstico de la extensión cefálica de un trombo tumoral en la vena cava inferior en enfermos con carcinoma de células renales es controvertido. Es posible conseguir una larga supervivencia después del tratamiento quirúrgico en enfermos con carcinoma de células renales localizado (supervivencia de 50%
en 5 años).
Los autores describen un caso de carcinoma de células renales con extensión a la vena cava en un enfermo del sexo masculino, de 70 años de edad. El enfermo presentaba una historia de lumbalgia derecha y edema del miembro inferior homolateral. La resonancia magnética demostró la presencia y el nivel del trombo tumoral. El enfermo fue sometido a nefrectomía radical derecha y exéresis completa del trombo tumoral de la vena cava. Renal cancer with vena cava tumour thrombus is relatively rare (4 to 10%). Because of the poor results obtained with any kind of alternative therapy (e.g. radiation, hormonal, chemotherapy and immunotherapy) operation with complete removal of the vena cava tumour thrombus continues to be the better method of treatment. The prognostic significance of the cephalic extent of an inferior vena caval tumor thrombus associated with renal cell carcinoma is controversial. Long-term survival after surgical treatment is possible in patients with localized renal cell carcinoma (survival 50% at five years).
The authors report a case of vena caval extension of renal cell carcinoma in a 70-years-old man. The patient presented with a history of right lombar pain and pedal edema. Magnetic Ressonance demonstrated the presence and the level of tumoral thrombus. The patient was submitted to a radical nefrectomy and complete removal of tumor thrombus from vena caval
Multiple Invaded Consolidating Materials
We study a multiple invasion model to simulate corrosion or intrusion
processes. Estimated values for the fractal dimension of the invaded region
reveal that the critical exponents vary as function of the generation number
, i.e., with the number of times the invasion process takes place. The
averaged mass of the invaded region decreases with a power-law as a
function of , , where the exponent . We
also find that the fractal dimension of the invaded cluster changes from
to . This result confirms that the
multiple invasion process follows a continuous transition from one universality
class (NTIP) to another (optimal path). In addition, we report extensive
numerical simulations that indicate that the mass distribution of avalanches
has a power-law behavior and we find that the exponent
governing the power-law changes continuously as a
function of the parameter . We propose a scaling law for the mass
distribution of avalanches for different number of generations .Comment: 8 pages and 16 figure
Gaussian model of explosive percolation in three and higher dimensions
The Gaussian model of discontinuous percolation, recently introduced by
Ara\'ujo and Herrmann [Phys. Rev. Lett., 105, 035701 (2010)], is numerically
investigated in three dimensions, disclosing a discontinuous transition. For
the simple-cubic lattice, in the thermodynamic limit, we report a finite jump
of the order parameter, . The largest cluster at the
threshold is compact, but its external perimeter is fractal with fractal
dimension . The study is extended to hypercubic lattices up
to six dimensions and to the mean-field limit (infinite dimension). We find
that, in all considered dimensions, the percolation transition is
discontinuous. The value of the jump in the order parameter, the maximum of the
second moment, and the percolation threshold are analyzed, revealing
interesting features of the transition and corroborating its discontinuous
nature in all considered dimensions. We also show that the fractal dimension of
the external perimeter, for any dimension, is consistent with the one from
bridge percolation and establish a lower bound for the percolation threshold of
discontinuous models with finite number of clusters at the threshold
Theory of Andreev reflection in a two-orbital model of iron-pnictide superconductors
A recently developed theory for the problem of Andreev reflection between a
normal metal (N) and a multiband superconductor (MBS) assumes that the incident
wave from the normal metal is coherently transmitted through several bands
inside the superconductor. Such splitting of the probability amplitude into
several channels is the analogue of a quantum waveguide. Thus, the appropriate
matching conditions for the wave function at the N/MBS interface are derived
from an extension of quantum waveguide theory. Interference effects between the
transmitted waves inside the superconductor manifest themselves in the
conductance. We provide results for a FeAs superconductor, in the framework of
a recently proposed effective two-band model and two recently proposed gap
symmetries: in the sign-reversed s-wave () scenario
resonant transmission through surface Andreev bound states (ABS) at nonzero
energy is found as well as destructive interference effects that produce zeros
in the conductance; in the extended s-wave ()
scenario no ABS at finite energy are found.Comment: 4 pages, 5 figure
Enhancement of the critical temperature in iron-pnictide superconductors by finite size effects
Recent experiments have shown that, in agreement with previous theoretical
predictions, superconductivity in metallic nanostructures can be enhanced with
respect to the bulk limit. Motivated by these results we study finite size
effects (FSE) in an iron-pnictide superconductor. For realistic values of the
bulk critical temperature Tc ~ 20-50K, we find that, in the nanoscale region L
~ 10 nm, Tc(L) has a complicated oscillating pattern as a function of the
system size L. A substantial enhancement of Tc with respect to the bulk limit
is observed for different boundary conditions, geometries and two microscopic
models of superconductivity. Thermal fluctuations, which break long range
order, are still small in this region. Finally we show that the differential
conductance, an experimental observable, is also very sensitive to FSE.Comment: 4 pages, 3 figure
- …