Showing papers by "Ikerbasque published in 2009"
TL;DR: The main experimental results and their connections with devices such as light-emitting diodes and electronic memory devices are summarized, and the scientific and technological issues that make organic spintronics a young but exciting field are outlined.
Abstract: Organic semiconductors are characterized by a very low spin–orbit interaction, which, together with their chemical flexibility and relatively low production costs, makes them an ideal materials system for spintronics applications. The first experiments on spin injection and transport occurred only a few years ago, and since then considerable progress has been made in improving performance as well as in understanding the mechanisms affecting spin-related phenomena. Nevertheless, several challenges remain in both device performance and fundamental understanding before organic semiconductors can compete with inorganic semiconductors or metals in the development of realistic spintronics applications. In this article we summarize the main experimental results and their connections with devices such as light-emitting diodes and electronic memory devices, and we outline the scientific and technological issues that make organic spintronics a young but exciting field.
717 citations
TL;DR: In this paper, the authors examined the health implications of policies aimed at tackling climate change and provided evidence that mitigation strategies can have substantial benefits for both health and climate protection, which offers the possibility of policy choices that are potentially both more cost effective and socially attractive than are those that address these priorities independently.
437 citations
TL;DR: This study lays the foundations of a psycholinguistic approach to speech recognition in adverse conditions that draws upon the distinction between energetic masking and informational masking, and proposes a model of speech recognition that addresses not only the mapping between sensory input and lexical representations, but also the way in which this mapping interfaces with general cognition and non-linguistic processes.
217 citations
TL;DR: In this paper, the authors show that a single graphene layer possesses a double Rydberg series of even and odd symmetry image-potential states and argue that the widely discussed interlayer band in graphite is a consequence of the intersheet hybridization of the first even imagepotential state.
Abstract: Using combined ``$\text{LDA}+\text{image}$ potential'' calculations we show that below the vacuum level a single graphene layer possesses a double Rydberg series of even $({n}^{+})$ and odd $({n}^{\ensuremath{-}})$ symmetry image-potential states and argue that the widely discussed interlayer band in graphite is a consequence of the intersheet hybridization of the first even image-potential state. In light of the present results, the unoccupied electronic states with nearly-free-electron properties in carbon nanotubes, fullerenes, and fullerites can be understood to originate from the image-potential states of graphene.
141 citations
TL;DR: In this article, a low-field minimum of the martensitic transformation temperature versus magnetic-field curves is observed for single and polycrystalline Ni-Mn-Ga alloys.
Abstract: We study the magnetic-field influence on the martensitic transformation temperatures and the accompanying anomaly in the resistivity by extensive measurements of the temperature dependencies of resistivity of several Ni-Mn-Ga and Ni-Fe-Ga alloys. A low-field minimum of the martensitic transformation temperature versus magnetic-field curves is observed for single and polycrystalline Ni-Mn-Ga alloys. This minimum is confirmed by magnetization loop measurements showing a magnetic anisotropy contribution to the ordinary Clausius-Clapeyron relationship which describes the martensitic transformation. This minimum did not appear for Ni-Fe-Ga polycrystalline alloys because in this case the difference in the magnetic anisotropy of relevant phases is small. We did not find any systematic behavior of the magnetoresistance related to the phase in which it is measured. In the vicinity of the martensitic transformation, the magnetoresistance exhibits a peaklike behavior which is explained in terms of the combined influence of the zero-field resistivity anomaly at the transition and the magnetic-field-induced shift of the transformation temperature.
105 citations
TL;DR: The results of the present visual-world experiment confirm the assumption of a primary organizational principle based on association for abstract words, different from the semantic similarity principle proposed for concrete words, and provide the first piece of evidence in support of this view obtained from healthy participants.
96 citations
TL;DR: Central composite design (CCD) using RSM with three variables namely redox mediator (HBT), dye (RB5) and enzyme (laccase) concentrations was used in this study to optimise significant correlation between the effects of these variables on the decolouration of RB5.
82 citations
TL;DR: SDS‐PAGE showed that laccases were the only enzymes present in the extracellular fluid, which allowed the production of high titres of laccase, which was obtained almost pure (only needed to be ultra‐filtrated).
Abstract: In this paper an eco-friendly strategy for the removal of synthetic dyes from aqueous solutions was proposed. Thus, in a first step the dyes were adsorbed onto sunflower seed shells (SS) by using a batch technique. Subsequently, in a second step, these dyed SS were used as support-substrates to produce laccase by the white-rot fungus Trametes pubescens under semi-solid-state conditions. The effect of inducer addition on laccase production was studied. The optimum conditions (addition of both 0.5 mM Cu +2 and 50 μM tannic acid on the 3 rd day of cultivation) led to a maximum laccase activity of 30272 U/L. Further, the system was efficiently scaled-up to laboratory bioreactors producing a maximum activity of 40172 U/L together with a total decolouration of the adsorbed dye. In addition, SDS-PAGE showed that laccases were the only enzymes present in the extracellular fluid. Therefore, apart from dye removal this approach allowed the production of high titres of laccase, which was obtained almost pure (only needed to be ultrafiltrated).
77 citations
TL;DR: In this paper, the analysis of the magnetocaloric effect (MCE) in a thin film of Ni-Mn-Ga alloy sputter deposited on alumina substrate is reported.
Abstract: In this letter, the analysis of the magnetocaloric effect (MCE) in a thin film of Ni–Mn–Ga alloy sputter deposited on alumina substrate is reported. This film has 0.4 μm thickness and exhibits merged martensitic and ferromagnetic transitions. The temperature dependence of the dc magnetization under different constant applied magnetic fields has been measured. The calculated MCE effect under applied magnetic fields up to 60 kOe shows the feasibility of these materials to be implemented in refrigeration system for functional microsystems. In addition, the shift of the martensitic transformation temperature, as a function of the applied magnetic field, has been determined.
58 citations
TL;DR: Sr2CrSbO6 was synthesized by the conventional solid-state reaction process as mentioned in this paper and the structure at room temperature and phase transitions at high and low-temperature.
47 citations
TL;DR: It was found that the use of CDH could be a promising alternative to the utilisation of the expensive and poisonous chemical mediators such as HOBT although much research on this topic remains still to be done.
TL;DR: In this paper, the authors describe a possible implementation of state transfer through bosonic atoms trapped in optical lattices or polaritons in on-chip coupled cavities, and show that the state transfer between two sites in two-dimensional lattices can result in quantum interference due to the different numbers of intermediate sites in different paths.
Abstract: We show how to perfectly transfer, without state initialization and remote collaboration, arbitrary functions in interacting boson lattices. We describe a possible implementation of state transfer through bosonic atoms trapped in optical lattices or polaritons in on-chip coupled cavities. Significantly, a family of Hamiltonians, both linear and nonlinear, is found which are related to the Bose-Hubbard model and that enable the perfect transfer of arbitrary functions. It is shown that the state transfer between two sites in two-dimensional lattices can result in quantum interference due to the different numbers of intermediate sites in different paths. The signature factor in nuclear physics can be useful to characterize this quantum interference.
TL;DR: In this paper, the authors studied spin relaxation due to spin-orbit coupling disorder and the resulting abilities of spin manipulation in low-dimensional electron structures and showed that the spin relaxation reveals quantum effects when the spatial scale of the randomness is smaller than the electron wavelength.
Abstract: Disorder in spin-orbit (SO) coupling is an important feature of real low-dimensional electron structures. We study spin relaxation due to such a disorder as well as resulting abilities of spin manipulation. The spin relaxation reveals quantum effects when the spatial scale of the randomness is smaller than the electron wavelength. Due to the disorder in SO coupling, a time-dependent external electric field generates a spatially random spin-dependent perturbation. The resulting electric dipole spin resonance in a two-dimensional electron gas leads to spin injection in a frequency range of the order of the Fermi energy. These effects can be important for possible applications in spintronics.
TL;DR: In this paper, a metamaterial composed of an array of discrete quantum absorbers inside a one-dimensional waveguide that implements a high-efficiency microwave photon detector is developed.
Abstract: We develop the theory of a metamaterial composed of an array of discrete quantum absorbers inside a one-dimensional waveguide that implements a high-efficiency microwave photon detector. A basic design consists of a few metastable superconducting nanocircuits spread inside and coupled to a one-dimensional waveguide in a circuit QED setup. The arrival of a {\it propagating} quantum microwave field induces an irreversible change in the population of the internal levels of the absorbers, due to a selective absorption of photon excitations. This design is studied using a formal but simple quantum field theory, which allows us to evaluate the single-photon absorption efficiency for one and many absorber setups. As an example, we consider a particular design that combines a coplanar coaxial waveguide with superconducting phase qubits, a natural but not exclusive playground for experimental implementations. This work and a possible experimental realization may stimulate the possible arrival of "all-optical" quantum information processing with propagating quantum microwaves, where a microwave photodetector could play a key role.
TL;DR: The relationship between sample structure and data in volume-scanning backscattering mode near-field optical microscopy is investigated in this article, where the three-dimensional structure of a dielectric sample is encoded in the phase and amplitude of the scattered field and an approximate reconstruction of the sample structure may be obtained.
Abstract: The relationship between sample structure and data in volume-scanning backscattering mode near-field optical microscopy is investigated It is shown that the three-dimensional structure of a dielectric sample is encoded in the phase and amplitude of the scattered field and that an approximate reconstruction of the sample structure may be obtained
TL;DR: In this article, a metamaterial composed of an array of discrete quantum absorbers inside a one-dimensional waveguide that implements a high-efficiency microwave photon detector is developed, where the arrival of a propagating quantum microwave field induces an irreversible change in the population of the internal levels of the absorbers due to a selective absorption of photon excitations.
Abstract: We develop the theory of a metamaterial composed of an array of discrete quantum absorbers inside a one-dimensional waveguide that implements a high-efficiency microwave photon detector. A basic design consists of a few metastable superconducting nanocircuits spread inside and coupled to a one-dimensional waveguide in a circuit QED setup. The arrival of a propagating quantum microwave field induces an irreversible change in the population of the internal levels of the absorbers, due to a selective absorption of photon excitations. This design is studied using a formal but simple quantum field theory, which allows us to evaluate the single-photon absorption efficiency for one and many absorber setups. As an example, we consider a particular design that combines a coplanar coaxial waveguide with superconducting phase qubits, a natural but not exclusive playground for experimental implementations. This work and a possible experimental realization may stimulate the possible arrival of 'all-optical' quantum information processing with propagating quantum microwaves, where a microwave photodetector could play a key role.
TL;DR: In this article, a supersymmetric and Lorentz covariant version of the Matrix model equations were derived for multiple D-particle (D0-brane) systems in curved type IIA superspace.
TL;DR: In this article, the spin-electric interactions and magnetoelectric properties of triangular rare-earth molecular nanoclusters are investigated by the example of Dy3 and the effective spinelectric Hamiltonian is derived on the base of a developed quantum-mechanical model of the cluster spin structure.
Abstract: Spin-electric interactions and magnetoelectric properties of triangular rare-earth molecular nanoclusters are investigated by the example of Dy3. The effective spin-electric Hamiltonian is derived on the base of a developed quantum-mechanical model of the cluster spin structure. It is shown that a toroidal (anapole) moment is induced in such clusters with magnetic field exceeding some threshold value or with crossed electric and magnetic fields (or an electric current). Due to the considerable relaxation time of the state with non-zero toroidal moment, it is possible to observe the non-equilibrium quantum linear magnetoelectric effect.
06 Sep 2009
TL;DR: Surprisingly few misperceptions were due solely to energetic masking by the noise, suggesting that speech and noise “react” in complex ways which are not well-described by traditional masking concepts.
Abstract: Listeners make mistakes when communicating under adverse conditions, with overall error rates reasonably well-predicted by existing speech intelligibility metrics. However, a detailed examination of confusions made by a majority of listeners is more likely to provide insights into processes of normal word recognition. The current study measured the rate at which robust misperceptions occurred for highly-confusable words embedded in noise. In a second experiment, confusions discovered in the first listening test were subjected to a range of manipulations designed to help identify their cause. These experiments reveal that while majority confusions are quite rare, they occur sufficiently often to make large-scale discovery worthwhile. Surprisingly few misperceptions were due solely to energetic masking by the noise, suggesting that speech and noise “react” in complex ways which are not well-described by traditional masking concepts.
TL;DR: In this paper, it was shown that there always exists a complete set of orthogonal states, which can be employed to perform the exact state transmission, where a density matrix in one information processor A at time t = 0 is exactly equal to that in another processor B at a later time.
Abstract: We consider an exact state transmission, where a density matrix in one information processor A at time t=0 is exactly equal to that in another processor B at a later time. We demonstrate that there always exists a complete set of orthogonal states, which can be employed to perform the exact state transmission. Our result is very general in the sense that it holds for arbitrary media between the two processors and for any time interval. We illustrate our results in terms of models of spin, fermionic, and bosonic chains. This complete set can be used as a basis to study the perfect state transfer which is associated with degenerate subspaces of this set of states. Interestingly, this formalism leads to a proposal of perfect state transfer via adiabatic passage, which does not depend on the specific form of the driving Hamiltonian.
TL;DR: The continuum mechanics of quantum many-body systems in the linear response regime is developed, showing that this equation of motion is exact for systems consisting of a single particle, and for all systems at sufficiently high frequency, and that it leads to an excitation spectrum that has the correct integrated strength.
Abstract: We develop the continuum mechanics of quantum many-body systems in the linear response regime. The basic variable of the theory is the displacement field, for which we derive a closed equation of motion under the assumption that the time-dependent wave function in a locally comoving reference frame can be described as a geometric deformation of the ground-state wave function. We show that this equation of motion is exact for systems consisting of a single particle, and for all systems at sufficiently high frequency, and that it leads to an excitation spectrum that has the correct integrated strength. The theory is illustrated by simple model applications to one- and two-electron systems.
TL;DR: In this paper, the existence of a long-lived collective excitation corresponding to coherent charge density fluctuations between the boron $\ensuremath{\sigma}$ and the σ-pi$ bands was demonstrated, and a sine-like oscillating dispersion was found for energies below 0.5 eV.
Abstract: We present ab initio time-dependent density-functional theory calculation results for low-energy collective electron excitations in ${\text{MgB}}_{2}$. The existence of a long-lived collective excitation corresponding to coherent charge density fluctuations between the boron $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ bands ($\ensuremath{\sigma}\ensuremath{\pi}$ mode) is demonstrated. This mode has a sine-like oscillating dispersion for energies below 0.5 eV. At even lower energy we find another collective mode ($\ensuremath{\sigma}\ensuremath{\sigma}$ mode). We show the strong impact of local-field effects on dielectric functions in ${\text{MgB}}_{2}$. These effects account for the long $q$-range behavior of the modes. We discuss the physics that these collective excitations bring to the energy region typical for lattice vibrations.
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TL;DR: In this article, the main dynamic parameters of the spin polarized current induced magnetic vortex oscillations in nanopillars, such as the range of current density, where a vortex steady oscillations exist, the oscillation frequency and orbit radius, were calculated.
Abstract: We calculated the main dynamic parameters of the spin polarized current induced magnetic vortex oscillations in nanopillars, such as the range of current density, where a vortex steady oscillations exist, the oscillation frequency and orbit radius. We accounted for both the non-linear vortex frequency and non-linear vortex damping. To describe the vortex excitations by the spin polarized current we used a generalized Thiele approach to motion of the vortex core as a collective coordinate. All the calculation results are represented via the free layer sizes, saturation magnetization, Gilbert damping and the degree of the spin polarization of the fixed layer. Predictions of the developed model can be checked experimentally.
TL;DR: In this article, the spin dynamics of high-mobility two-dimensional electrons in GaAs/AlGaAs quantum wells grown along the [001] and [110] directions by time-resolved Faraday rotation at low temperatures were investigated.
Abstract: We investigate the spin dynamics of high-mobility two-dimensional electrons in GaAs/AlGaAs quantum wells grown along the [001] and [110] directions by time-resolved Faraday rotation at low temperatures. In measurements on the (001)-grown structures without external magnetic fields, we observe coherent oscillations of the electron-spin polarization about the effective spin-orbit field. In nonquantizing magnetic fields applied normal to the sample plane, the cyclotron motion of the electrons rotates the effective spin-orbit field. This rotation leads to fast oscillations in the spin polarization about a nonzero value and a strong increase in the spin dephasing time in our experiments. These two effects are absent in the (110)-grown structure due to the different symmetry of its effective spin-orbit field. The measurements are in excellent agreement with our theoretical model.
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TL;DR: In this article, the authors consider the existence of traveling wave solutions, including standing waves, to configurational forces, describing diffusionless phase transformations of solid materials, e.g., steel, and phase transitions due to interface motion by interface diffusion.
Abstract: This article is concerned with the existence of traveling wave solutions, including standing waves, to some models based on configurational forces, describing respectively the diffusionless phase transformations of solid materials, e.g., Steel, and phase transitions due to interface motion by interface diffusion, e.g., Sintering. These models are recently proposed by Alber and Zhu. We consider both the order-parameter-conserved case and the non-conserved one, under suitable assumptions. Also we compare our results with the corresponding ones for the Allen-Cahn and the Cahn-Hilliard equations coupled with linear elasticity, which are models for diffusion-dominated phase transformations in elastic solids.
TL;DR: In this paper, the use of quantum interference to coherently control the transverse direction in which carriers are optically injected in a semiconductor heterostructure, and the subsequent transport and capture of these carriers is considered.
Abstract: We theoretically study the use of quantum interference to coherently control the transverse direction in which carriers are optically injected in a semiconductor heterostructure, and the subsequent transport and capture of these carriers. We consider a structure consisting of three quantum wells, where carriers can be ejected from the middle one in a given direction by coherently controlled optical pulse excitations. After traveling through the barrier, electrons are slowed down by space-charge effects, and can be captured in the side wells by emitting a phonon. If the side wells are different, the coherent control of the injection can be monitored optically. We propose a design of a AlGaAs heterostructure for a possible experimental realization of the effects considered in this paper.
01 Feb 2009
TL;DR: In this paper, the authors employ a public economic policy approach to investigate how or if at all climate adaptation should be supported by the public sector and propose ways in which government intervention could be conducted.
Abstract: Much can be learned about adaptation by applying structures and methodologies already used in other research fields. This study employs a public economic policy approach to investigate how – or if at all – adaptation should be supported by the public sector. Three different fields of adaptation activity are identified which are especially relevant for government intervention and the study proposes ways in which government intervention could be conducted. The analysis takes into account that developing regions are particularly vulnerable and they have insufficient funds to adequately adapt to climate change.
TL;DR: A universal breathing dynamics is demonstrated by using an approximate method in quantum mechanics, and under time-dependent modulations, utilizing the adiabatic approximation, bubble properties reveal memory effects.
Abstract: We study generic aspects of bubble dynamics in DNA under time-dependent perturbations, for example, temperature change, by mapping the associated Fokker-Planck equation to a quantum time-dependent Schr\"odinger equation with imaginary time. In the static case we show that the eigenequation is exactly the same as that of the $\ensuremath{\beta}$-deformed nuclear liquid drop model, without the issue of noninteger angular momentum. A universal breathing dynamics is demonstrated by using an approximate method in quantum mechanics. The calculated bubble autocorrelation function qualitatively agrees with experimental data. Under time-dependent modulations, utilizing the adiabatic approximation, bubble properties reveal memory effects.
TL;DR: In this article, laser assisted photoemission by a chirped sub-femtosecond extreme ultraviolet (XUV) pulse is considered within an exactly solvable quantum-mechanical model.
Abstract: Laser assisted photoemission by a chirped subfemtosecond extreme ultraviolet (XUV) pulse is considered within an exactly solvable quantum-mechanical model. Special emphasis is given to the energy dependence of photoexcitation cross-section. The streaked spectra are analyzed within the classical picture of initial time-momentum distribution r_ini(p,t) of photoelectrons mapped to the final energy scale. The actual time-momentum distribution in the absence of the probe laser field is shown to be a poor choice for r_ini, and a more adequate ansatz is suggested. The semiclassical theory offers a simple practically useful approximation for streaked spectra. Its limitations for sufficiently long chirped XUV pulses are established.
TL;DR: In this article, the spin density wave (SDW) state of the uniform electron gas is investigated in the exact exchange approximation of noncollinear spin density functional theory (DFT).
Abstract: The spin density wave (SDW) state of the uniform electron gas is investigated in the exact exchange approximation of noncollinear spin density functional theory (DFT). Unlike in HartreeFock theory, where the uniform paramagnetic state of the electron gas is unstable against formation of the spin density wave for all densities, in exact-exchange spin-DFT this instability occurs only for densities lower than a critical value. It is also shown that, although in a suitable density range it is possible to find a non-interacting SDW ground state Slater determinant with energy lower than the corresponding paramagnetic state, this Slater determinant is not a self-consistent solution of the Optimized Effective Potential (OEP) integral equations of noncollinear spin-DFT. A selfconsistent solution of the OEP equations which gives an even lower energy can be found using an excited-state Slater determinant where only orbitals with single-particle energies in the lower of two bands are occupied while orbitals in the second band remain unoccupied even if their energies are below the Fermi energy.