7,395 research outputs found
Screening of pair fluctuations in superconductors with coupled shallow and deep bands: a route to higher temperature superconductivity
A combination of strong Cooper pairing and weak superconducting fluctuations
is crucial to achieve and stabilize high-Tc superconductivity. We demonstrate
that a coexistence of a shallow carrier band with strong pairing and a deep
band with weak pairing, together with the Josephson-like pair transfer between
the bands to couple the two condensates, realizes an optimal multicomponent
superconductivity regime: it preserves strong pairing to generate large gaps
and a very high critical temperature but screens the detrimental
superconducting fluctuations, thereby suppressing the pseudogap state.
Surprisingly, we find that the screening is very efficient even when the
inter-band coupling is very small. Thus, a multi-band superconductor with a
coherent mixture of condensates in the BCS regime (deep band) and in the
BCS-BEC crossover regime (shallow band) offers a promising route to higher
critical temperatures.Comment: 8 pages, 1 figure, including supplemental material
Quantum Key Distribution using Continuous-variable non-Gaussian States
In this work we present a quantum key distribution protocol using
continuous-variable non-Gaussian states, homodyne detection and post-selection.
The employed signal states are the Photon Added then Subtracted Coherent States
(PASCS) in which one photon is added and subsequently one photon is subtracted.
We analyze the performance of our protocol, compared to a coherent state based
protocol, for two different attacks that could be carried out by the
eavesdropper (Eve). We calculate the secret key rate transmission in a lossy
line for a superior channel (beam-splitter) attack, and we show that we may
increase the secret key generation rate by using the non-Gaussian PASCS rather
than coherent states. We also consider the simultaneous quadrature measurement
(intercept-resend) attack and we show that the efficiency of Eve's attack is
substantially reduced if PASCS are used as signal states.Comment: We have included an analysis of the simultaneous quadrature
measurement attack plus 2 figures; we have also clarified some point
Semiclassical Tunneling of Wavepackets with Real Trajectories
Semiclassical approximations for tunneling processes usually involve complex
trajectories or complex times. In this paper we use a previously derived
approximation involving only real trajectories propagating in real time to
describe the scattering of a Gaussian wavepacket by a finite square potential
barrier. We show that the approximation describes both tunneling and
interferences very accurately in the limit of small Plank's constant. We use
these results to estimate the tunneling time of the wavepacket and find that,
for high energies, the barrier slows down the wavepacket but that it speeds it
up at energies comparable to the barrier height.Comment: 23 pages, 7 figures Revised text and figure
Geometric combinatorial algebras: cyclohedron and simplex
In this paper we report on results of our investigation into the algebraic
structure supported by the combinatorial geometry of the cyclohedron. Our new
graded algebra structures lie between two well known Hopf algebras: the
Malvenuto-Reutenauer algebra of permutations and the Loday-Ronco algebra of
binary trees. Connecting algebra maps arise from a new generalization of the
Tonks projection from the permutohedron to the associahedron, which we discover
via the viewpoint of the graph associahedra of Carr and Devadoss. At the same
time that viewpoint allows exciting geometrical insights into the
multiplicative structure of the algebras involved. Extending the Tonks
projection also reveals a new graded algebra structure on the simplices.
Finally this latter is extended to a new graded Hopf algebra (one-sided) with
basis all the faces of the simplices.Comment: 23 figures, new expanded section about Hopf algebra of simplices,
with journal correction
Penetrability of chloride ions in concrete protected by an acrylic painting
In order do decrease the penetrability of chloride ions in concrete the use of paintings based on polymers can be a good solution. The use of acrylic paintings is recommended because they have good resistance to ultraviolet radiation. It is important to quantify the decrease of chloride ions penetrability obtained by the use of this kind of paintings. The durability of the polymeric paintings is another aspect that needs to be analysed. In this study an acrylic painting was used to
protect the concrete and decrease the penetrability of chloride ions. The concrete used was a C12/15, with a cement content of 280 kg/m3 and a water-cement ratio of 0.60. The acrylic painting was applied in concrete specimens 28 days after casting. In order to have a better protection we applied two coats separated by 5 hours. The penetrability of chloride ions was
measured following the ASTM standard C 1202 â 94. Before the penetrability tests, some specimens were exposed to UV radiation. The exposition to the light occurred by cycles consisting of alternating periods of 8 hours of UV radiation at 60 ÂșC and 16 hours without UV radiation at 50 ÂșC. Three kinds of exposition were made consisting on 5, 10 and 15 cycles. The results showed always a high penetrability of chloride ions. This occurred because a poor concrete
was used. The protection by an acrylic painting decreases the penetrability of chloride ions. The charge passed decreased about 32 %. However, is not possible to achieve low chloride ions penetrability only with the use of acrylic paintings. It is necessary also the use of a good concrete
with low porosity. After the exposition to the UV radiation the penetrability of chlorides ions did not increase. It seems that the UV radiation does not affect the properties of the acrylic painting
Turing Patterns And Apparent Competition In Predator-prey Food Webs On Networks.
Reaction-diffusion systems may lead to the formation of steady-state heterogeneous spatial patterns, known as Turing patterns. Their mathematical formulation is important for the study of pattern formation in general and plays central roles in many fields of biology, such as ecology and morphogenesis. Here we show that Turing patterns may have a decisive role in shaping the abundance distribution of predators and prey living in patchy landscapes. We extend the original model proposed by Nakao and Mikhailov [Nat. Phys. 6, 544 (2010)] by considering food chains with several interacting pairs of prey and predators distributed on a scale-free network of patches. We identify patterns of species distribution displaying high degrees of apparent competition driven by Turing instabilities. Our results provide further indication that differences in abundance distribution among patches can be generated dynamically by self organized Turing patterns and not only by intrinsic environmental heterogeneity.8605620
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