2,715 research outputs found
Dynamical description of the buildup process in resonant tunneling: Evidence of exponential and non-exponential contributions
The buildup process of the probability density inside the quantum well of a
double-barrier resonant structure is studied by considering the analytic
solution of the time dependent Schr\"{o}dinger equation with the initial
condition of a cutoff plane wave. For one level systems at resonance condition
we show that the buildup of the probability density obeys a simple charging up
law, where is the
stationary wave function and the transient time constant is exactly
two lifetimes. We illustrate that the above formula holds both for symmetrical
and asymmetrical potential profiles with typical parameters, and even for
incidence at different resonance energies. Theoretical evidence of a crossover
to non-exponential buildup is also discussed.Comment: 4 pages, 2 figure
Magnetic Field Probing of an SU(4) Kondo Resonance in a Single Atom Transistor
Semiconductor nano-devices have been scaled to the level that transport can
be dominated by a single dopant atom. In the strong coupling case a Kondo
effect is observed when one electron is bound to the atom. Here, we report on
the spin as well as orbital Kondo ground state. We experimentally as well than
theoretically show how we can tune a symmetry transition from a SU(4) ground
state, a many body state that forms a spin as well as orbital singlet by
virtual exchange with the leads, to a pure SU(2) orbital ground state, as a
function of magnetic field. The small size and the s-like orbital symmetry of
the ground state of the dopant, make it a model system in which the magnetic
field only couples to the spin degree of freedom and allows for observation of
this SU(4) to SU(2) transition.Comment: 12 pages, 10 figures, accepted for publication in Physical Review
Letter
A methodological proposal and tool support for the HL7 standards compliance in the development of health information systems
Health information systems are increasingly complex, and their development is presented as a challenge for software development companies offering quality, maintainable and interoperable products. HL7 (Health level 7) International, an international non-profit organization, defines and maintains standards related to health information systems. However, the modelling languages proposed by HL7 are far removed from standard languages and widely known by software engineers. In these lines, NDT is a software development methodology that has a support tool called NDT-Suite and is based, on the one hand, on the paradigm of model-driven engineering and, on the other hand, in UML that is a widely recognized standard language. This paper proposes an extension of the NDT methodology called MoDHE (Model Driven Health Engineering) to offer software engineers a methodology capable of modelling health information systems conforming to HL7 using UML domain models
A proto brown dwarf candidate in Taurus
Aims. We search for brown dwarfs at the Class 0/I evolutionary stage, or proto brown dwarfs.
Methods. We present a multi wavelength study, ranging from optical at 0.8 μm to radio wavelengths at 6 cm, of a cool, very faint, and red multiple object, SSTB213 J041757, detected by Spitzer toward the Barnard 213 dark cloud, in Taurus.
Results. The SED of SSTB213 J041757 displays a clear excess at long wavelengths resembling that of a Class I object. The mid-IR source has two possible counterparts, A and B, in the near-IR and optical images, and the 350 μm observations detect clear extended emission, presumably from an envelope around the two sources. The position of A & B in the (Ic− J) versus (J − [3.6]) colour-colour diagram is consistent with them being Galactic sources and not extragalactic contaminants. A proper-motion study confirms this result for A, while it is inconclusive for B. The temperature and mass of the two possible central objects, according to COND evolutionary models, range between 1550−1750 K and 3−4 M_(Jupiter), and 950−1300 K and 1−2 M_(Jupiter), for A and B, respectively. The integrated SED provides bolometric temperatures and luminosities of 280 K and 0.0034 L_⊙, assuming that the emission at wavelengths > 5 μm is associated with component A, and 150 K and 0.0033 L_⊙, assuming that the emission at wavelengths > 5 μm is associated with component B, which would imply the SSTB213 J041757 object has a luminosity well below the luminosity of other very low luminosity objects discovered up to date.
Conclusions. With these characteristics, SSTB213 J041757 seems to be a promising, and perhaps double, proto brown dwarf candidate
AES depth profile and photoconductive studies of AgInS2 thin films prepared by co-evaporation
In this study, thin films of AgInS2 with chalcopyrite-type tetragonal structure were grown by means of a procedure based on the sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process. The effect of the growth temperature and the proportion of the evaporated Ag mass in relation to the evaporated In mass (mAg/mIn) on the phase and homogeneity in the chemical composition were researched through X-ray diffraction measurements and Auger electrons spectroscopy. These measurements evidenced that the conditions for preparing thin films containing only the AgInS2 phase, grown with tetragonal chalcopyrite-type structure and good homogeneity of the chemical composition in the entire volume, are a temperature of 500 ºC and a 0.89 mAg/mIn proportion.En este trabajo se crecieron películas delgadas de AgInS2 con estructura tetragonal tipo calcopirita usando un procedimiento basado en la evaporación secuencial de precursores metálicos en presencia de azufre elemental, en un proceso en dos etapas. Se investigó el efecto de la temperatura de crecimiento y la proporción de la masa de Ag evaporada a la masa de In evaporada (mAg/mIn) sobre la fase y la homogeneidad en la composición química a través de medidas de difracción de rayos X y espectroscopía de electrones Auger. Estas medidas mostraron que las condiciones para preparar películas delgadas que contengan únicamente la fase AgInS2, crecidas con estructura tipo calcopirita tetragonal y buena homogeneidad de la composición química en todo el volumen son temperatura de 500 °C y proporción mAg/mIn 0.89. Las medidas de fotocorriente de transiente indicaron que el transporte eléctrico es afectado por procesos de recombinación, vía transiciones banda a banda y transiciones asistidas por trampas
Estudios de perfiles de profundidad AES y fotoconductividad de películas delgadas de AgInS2 preparadas por co-evaporación
In this study, thin films of AgInS2 with chalcopyrite-type tetragonalstructure were grown by means of a procedure based on the sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process. The effect of the growth temperature and the proportion of the evaporated Ag mass in relation to the evaporated In mass (mAg/mIn) on the phase and homogeneity in the chemical composition were researched through X-ray diffraction measurements and Auger electrons spectroscopy. These measurements evidenced that the conditions for preparing thin films containing only the AgInS2 phase, grown with tetragonal chalcopyrite-type structure and good homogeneity of thechemical composition in the entire volume, are a temperature of 500 ºC and a 0.89 mAg/mIn proportionEn este trabajo se crecieron películas delgadas de AgInS2 con estructura tetragonal tipo calcopirita usando un procedimiento basado en la evaporación secuencial de precursores metálicos en presencia de azufre elemental, en un proceso en dos etapas. Se investigó el efecto de la temperatura de crecimiento y la proporción de la masa de Ag evaporada a la masa de In evaporada (mAg/mIn) sobre la fase y la homogeneidad en la composición química a través de medidas de difracción de rayos X y espectroscopía de electrones Auger. Estas medidas mostraron que las condiciones parapreparar películas delgadas que contengan únicamente la fase AgInS2, crecidas con estructura tipo calcopirita tetragonal y buena homogeneidad de la composición química en todo el volumen son temperatura de 500 °C y proporción mAg/mIn 0.89. Las medidas de fotocorriente de transiente indicaron que el transporte eléctrico es afectado por procesos de recombinación, vía transiciones banda a banda y transiciones asistidas por trampas
Strain control of superlattice implies weak charge-lattice coupling in LaCaMnO
We have recently argued that manganites do not possess stripes of charge
order, implying that the electron-lattice coupling is weak [Phys Rev Lett
\textbf{94} (2005) 097202]. Here we independently argue the same conclusion
based on transmission electron microscopy measurements of a nanopatterned
epitaxial film of LaCaMnO. In strain relaxed regions, the
superlattice period is modified by 2-3% with respect to the parent lattice,
suggesting that the two are not strongly tied.Comment: 4 pages, 4 figures It is now explained why the work provides evidence
to support weak-coupling, and rule out charge orde
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