1,004 research outputs found
Thermoelectric relations in the conformal limit in Dirac and Weyl semimetals
In the Fermi liquid description of metals, electrical and thermoelectric
transport coefficients are linked by robust relations which can be challenged
by strong interactions or when the electron liquid enters a different regime.
These relations have been very powerful in the characterisation of novel
materials. We show that Dirac and Weyl semimetals at zero doping and zero
temperature (the conformal limit) have a very singular behavior due to a
quantum anomaly. Away from this point, a Mott relation can be established
Interfacial mechanism in the anomalous Hall effect of Co/BiO bilayers
Oxide interfaces are a source of spin-orbit coupling which can lead to novel
spin-to-charge conversion effects. In this work the contribution of the
BiO interface to the anomalous Hall effect of Co is experimentally
studied in Co/BiO bilayers. We evidence a variation of 40% in the AHE
of Co when a BiO capping layer is added to the ferromagnet. This strong
variation is attributed to an additional source of asymmetric transport in
Co/BiO bilayers that originates from the Co/BiO interface and
contributes to the skew scattering.Comment: 7 pages, 4 figure
Error estimation in IBM Quantum Computers
One of the main important features of the noisy intermediate-scale quantum
(NISQ) era is the correct evaluation and consideration of errors. In this
paper, we analyze the main sources of errors in current (IBM) quantum computers
and we present a useful tool (TED-qc) designed to facilitate the total error
probability expected for any quantum circuit. We propose this total error
probability as the best way to estimate the fidelity in the NISQ era, mainly
because we do not have to compare our quantum calculations with any classical
one. In order to contrast the robustness of our tool we compute the total error
probability that may occur in three different quantum models: 1) the
four-electron Ising model, 2) the Quantum-Phase Estimation (QPE) and 3) the
Grover's algorithm. For each model, we compute a statistically significant
sample size for both the expectation value of the related observable and the
fidelity, comparing them with the value calculated in the simulator as a
function of the error probability. The analysis is satisfactory in more than
the of the cases. In addition, we study how the error mitigation
techniques are able to eliminate the noise induced during the measurement.Comment: 9 pages, 8 figure
A Definition of the Magnetic Transition Temperature Using Valence Bond Theory
Macroscopic magnetic properties are analyzed using Valence Bond theory. Commonly the critical temperature TC for magnetic systems is associated with a maximum in the energy-based heat capacity Cp(T). Here a more broadly applicable definition of the magnetic transition temperature TC is described using the spin moment expectation value (i.e., applying the spin exchange density operator) instead of energy. Namely, the magnetic capacity Cs(T) reflects variation in the spin multiplicity as a function of temperature, which is shown to be related to ∂[χT(T)]/∂T. Magnetic capacity Cs(T) depends on long-range spin interactions that are not relevant in the energy-based heat capacity Cp(T). Differences between Cs(T) and Cp(T) are shown to be due to spin order/disorder within the crystal that can be monitored via a Valence Bond analysis of the corresponding magnetic wave function. Indeed the concept of the Boltzmann spin-alignment order is used to provide information about the spin correlation between magnetic units. As a final illustration, the critical temperature is derived from the magnetic capacity for several molecular magnets presenting different magnetic topologies that have been experimentally studied. A systematic shift between the transition temperatures associated with Cs(T) and Cp(T) is observed. It is demonstrated that this shift can be attributed to the loss of long-range spin correlation. This suggests that the magnetic capacity Cs(T) can be used as a predictive tool for the magnetic topology and thus for the synthetic chemists
Contribution of Driving Efficiency to Vehicle-to-Building
[EN] Energy consumption in the transport sector and buildings are of great concern. This research aims to quantify how eco-routing, eco-driving and eco-charging can increase the amount
of energy available for vehicle-to-building. To do this, the working population was broken into
social groups (freelancers, local workers and commuters) who reside in two cities with different
climate zones (Alcalá de Henares-Spain and Jaén-Spain) since the way of using electric vehicles is
different. An algorithm based on the Here® application program interface and neural networks was
implemented to acquire data of the stochastic usage of EVs of each social group. Finally, an increase
in the amount of energy available for vehicle-to-building was assessed thanks to the algorithm.
The results per day were as follows. Owing to the algorithm proposed a reduction ranging from
0.6 kWh to 2.2 kWh was obtained depending on social groups. The proposed algorithm facilitated
an increase in energy available for vehicle-to-building ranging from 13.2 kWh to 33.6 kWh depending
on social groups. The results show that current charging policies are not compatible with all social
groups and do not consider the renewable energy contribution to the total electricity demand.S
Estudio cinético del proceso de devolatilización de biomasa lignocelulósica mediante análisis termogravimétrico para tamaños de partÃcula de 2 a 19 mm
Con el objetivo de proporcionar herramientas que mejoren el diseño de los sistemas de gasificación/combustión de biomasa, y los modelos cinético-quÃmicos de dichos procesos, se presenta un estudio de la cinética quÃmica asociada al proceso de devolatilización de biomasa mediante pruebas de termogravimetrÃa utilizando tamaños de partÃcula que varÃan de 2 a 19 mm, y tasas de calentamiento de 10, 15 y 20 K/min. El desarrollo de este trabajo se justifica debido a que no hay resultados disponibles en la bibliografÃa que estudien tamaños superiores a 1 mm.Mediante el ajuste de los puntos experimentales utilizando un modelo de primer orden se determinan los parámetros de las constantes cinéticas (forma de Arrhenius). El estudio muestra que la energÃa de activación es directamente proporcional a la tasa de calentamiento y al tamaño de partÃcula, se comprueba que el proceso de descomposición térmica de la biomasa se da a temperaturas más altas con el aumento del tamaño de las partÃculas, debido a la importancia que toman los procesos de transferencia calor y masa. Los parámetros cinéticos calculados pueden ser utilizados en los modelos dimensionales del proceso de gasificación-combustión de biomasa, considerando el tamaño de las partÃculas intrÃnseco en la cinética
Disentangling categorical relationships through a graph of co-occurrences
The mesoscopic structure of complex networks has proven a powerful level of description to understand the linchpins of the system represented by the network. Nevertheless, themapping of a series of relationships between elements, in terms of a graph, is sometimes not straightforward. Given that all the information we would extract using complex network tools depend on this initial graph, it is mandatory to preprocess the data to build it on in the most accurate manner. Here we propose a procedure to build a network, attending only to statistically significant relations between constituents. We use a paradigmatic example of word associations to show the development of our approach. Analyzing the modular structure of the obtained network we are able to disentangle categorical relations, disambiguating words with success that is comparable to the best algorithms designed to the same end.We acknowledge financia support through Grant No. FIS2009-13364-C02-01, Holopedia (Grant No. TIN2010-21128-C02-01), MOSAICO (Grant No. FIS2006-01485), PRODIEVO (Grant No. FIS2011-22449), and Complexity-NET RESINEE, all of them from Ministerio de Educación y Ciencia in Spain,
as well as support from Research Networks MODELICO-CM (Grant No. S2009/ESP-1691) and MA2VICMR (Grant No. S2009/TIC-1542) from Comunidad de Madrid, and Network 2009-SGR-838 from Generalitat de Catalunya
- …