3,745 research outputs found
Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsOF
The electrical resistivity, crystalline structure and electronic properties
calculated from the experimentally measured atomic positions of the compound
SmFeAsOF have been studied up to pressures ~20GPa. The
correlation between the pressure dependence of the superconducting transition
temperature (Tc) and crystallographic parameters on the same sample shows
clearly that a regular FeAs tetrahedron maximizes Tc, through
optimization of carrier transfer to the FeAs planes as indicated by the
evolution of the electronic band structures.Comment: 15pages, 4 figure
Quantum critical point and superconducting dome in the pressure phase diagram of o-TaS3
We measure the electrical resistance of o-TaS3 between 1K and 300K under
pressures up to 20GPa. We observe a gradual decrease of the charge density wave
transition temperature with increasing pressure P following a mean-field
quantum fluctuation power law with a quantum critical point at a pressure Pc =
11.5GPa. Around the quantum critical point we observe a superconducting dome
with a maximum superconducting transition temperature Tc = 3.1K. Such dome is
similar to superconducting domes around other types of order suggesting that
the QCP is directly responsible for the enhancement of superconductivity
through a universal mechanism still not well understood.Comment: To be published in PRB as a Rapid Communication. 11 pages with 4
figure
Large lianas as hyperdynamic elements of the tropical forest canopy
Lianas (woody vines) are an important component of lowland tropical forests.
We report large liana and tree inventory and dynamics data from Amazonia over periods
of up to 24 years, making this the longest geographically extensive study of liana ecology
to date. We use these results to address basic questions about the ecology of large lianas
in mature forests and their interactions with trees. In one intensively studied site we find
that large lianas (≥10 cm diameter) represent ,5% of liana stems, but 80% of biomass of
well-lit upper canopy lianas. Across sites, large lianas and large trees are both most successful
in terms of structural importance in richer soil forests, but large liana success may
be controlled more by the availability of large tree supports rather than directly by soil
conditions. Long-term annual turnover rates of large lianas are 5–8%, three times those of
trees. Lianas are implicated in large tree mortality: liana-infested large trees are three times
more likely to die than liana-free large trees, and large lianas are involved in the death of
at least 30% of tree basal area. Thus large lianas are a much more dynamic component of
Amazon forests than are canopy trees, and they play a much more significant functional
role than their structural contribution suggests
A short note on the nested-sweep polarized traces method for the 2D Helmholtz equation
We present a variant of the solver in Zepeda-N\'u\~nez and Demanet (2014),
for the 2D high-frequency Helmholtz equation in heterogeneous acoustic media.
By changing the domain decomposition from a layered to a grid-like partition,
this variant yields improved asymptotic online and offline runtimes and a lower
memory footprint. The solver has online parallel complexity that scales
\emph{sub linearly} as , where is
the number of volume unknowns, and is the number of processors, provided
that . The variant in Zepeda-N\'u\~nez and Demanet
(2014) only afforded . Algorithmic scalability is a
prime requirement for wave simulation in regimes of interest for geophysical
imaging.Comment: 5 pages, 5 figure
Strong, Weak and Branching Bisimulation for Transition Systems and Markov Reward Chains: A Unifying Matrix Approach
We first study labeled transition systems with explicit successful
termination. We establish the notions of strong, weak, and branching
bisimulation in terms of boolean matrix theory, introducing thus a novel and
powerful algebraic apparatus. Next we consider Markov reward chains which are
standardly presented in real matrix theory. By interpreting the obtained matrix
conditions for bisimulations in this setting, we automatically obtain the
definitions of strong, weak, and branching bisimulation for Markov reward
chains. The obtained strong and weak bisimulations are shown to coincide with
some existing notions, while the obtained branching bisimulation is new, but
its usefulness is questionable
Unconscious Learning. Conditioning to Subliminal Visual Stimuli.
Se analizó el papel de la consciencia en el condicionamiento pavloviano mediante dos experimentos en los que se utilizaron, como estímulos condicionados (ECs), palabras neutras visualmente enmascaradas y, como estímulo incondicionado (EI), un shock eléctrico. El intervalo inter-estímulo se estableció individualmente. Se utilizó un umbral de detección en el Experimento 1 y un umbral de identificación en el Experimento 2. La principal variable dependiente fue la respuesta de conductancia de la piel. Los resultados mostraron que la respuesta condicionada (RC) fue adquirida por el 58% de los sujetos que percibieron los estímulos por encima del umbral de identificación, por el 50% de los sujetos que percibieron los estímulos por debajo del umbral de detección y por el 11% de los sujetos que percibieron los estímulos por debajo del umbral de identificación, pero por encima del umbral de detección. Estos resultados sugieren que la conciencia de la contingencia EC-EI no es condición necesaria para adquirir una RC del sistema nervioso autónomo
A useful form of the recurrence relation between relativistic atomic matrix elements of radial powers
Recently obtained recurrence formulae for relativistic hydrogenic radial
matrix elements are cast in a simpler and perhaps more useful form. This is
achieved with the help of a new relation between the and the
terms ( is a Dirac matrix and are constants) in the
atomic matrix elements.Comment: 7 pages, no figure
Using genetic algorithms to generate test sequences for complex timed systems
The generation of test data for state based specifications is a computationally expensive process. This problem is magnified if we consider that time con- straints have to be taken into account to govern the transitions of the studied system. The main goal of this paper is to introduce a complete methodology, sup- ported by tools, that addresses this issue by represent- ing the test data generation problem as an optimisa- tion problem. We use heuristics to generate test cases. In order to assess the suitability of our approach we consider two different case studies: a communication protocol and the scientific application BIPS3D. We give details concerning how the test case generation problem can be presented as a search problem and automated. Genetic algorithms (GAs) and random search are used to generate test data and evaluate the approach. GAs outperform random search and seem to scale well as the problem size increases. It is worth to mention that we use a very simple fitness function that can be eas- ily adapted to be used with other evolutionary search techniques
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