1,482 research outputs found
Importance of second-order piezoelectric effects in zincblende semiconductors
We show that the piezoelectric effect that describes the emergence of an
electric field in response to a crystal deformation in III-V semiconductors
such as GaAs and InAs has strong contributions from second-order effects that
have been neglected so far. We calculate the second-order piezoelectric tensors
using density functional theory and obtain the piezoelectric field for
[111]-oriented InGaAs quantum wells of realistic dimensions and
concentration . We find that the linear and the quadratic piezoelectric
coefficients have the opposite effect on the field, and for large strains the
quadratic terms even dominate. Thus, the piezoelectric field turns out to be a
rare example of a physical quantity for which the first- and second-order
contributions are of comparable magnitude.Comment: 4 pages, 3 figures, Submitted to Phys. Rev. Let
Field water dynamics in integrated systems in the Brazilian.
Agroforestry systems were established as a viable option for Brazilian farmers in recent decades. Shading is expected to affect the system?s microclimate and thus it is likely to alter water fluxes to the atmosphere via evapotranspiration. In this study we measured the evapotranspiration (ET) with micro-lysimeters in four different treatments as a proxy for different land use systems at EMBRAPA Beef Cattle, the Brazilian Agricultural Research Corporation, located in Campo Grande-MS, Brasil. The four treatments are: Integrated systems with rows of Eucalypt (Eucalyptus urograndis) trees (ICLF), integrated systems without Eucalypt trees (ICL), continuous pasture (CP) and native Cerrado (Savannah) vegetation. In the ICLF and ICL plots Bracchiaria brizantha was planted and in the CP plots Brachiaria decumbens. To measure the evapotranspiration lysimeters (diameter of 10 cm and a depth of 20 cm) were inserted into the ground and weighed daily during a period of 8 weeks. Within the ICLF systems, measurements were conducted in three different distances to the tree rows. In the treatments without trees the lysimeters were distributed randomly. Results were linked to data from the microclimate, i.e. wind speed, air humidity, and global radiation
Direct Josephson coupling between superconducting flux qubits
We have demonstrated strong antiferromagnetic coupling between two
three-junction flux qubits based on a shared Josephson junction, and therefore
not limited by the small inductances of the qubit loops. The coupling sign and
magnitude were measured by coupling the system to a high-quality
superconducting tank circuit. Design modifications allowing to continuously
tune the coupling strength and/or make the coupling ferromagnetic are
discussed.Comment: REVTeX 4, 4 pages, 5 figures; v2: completely rewritten, added
finite-temperature results and proposals for ferromagnetic galvanic couplin
The Aladin2 experiment: sensitivity study
Aladin2 is an experiment devoted to the first measurement of variations of Casimir energy in a rigid body. The main short-term scientific motivation relies on the possibility of the first demonstration of a phase transition influenced by vacuum fluctuations while, in the long term and in the mainframe of the cosmological constant problem, it can be regarded as the first step towards a measurement of the weight of vacuum energy. In this paper, after a presentation of the guiding principle of the measurement, the experimental apparatus and sensitivity studies on final cavities will be presented
Principals of the theory of light reflection and absorption by low-dimensional semiconductor objects in quantizing magnetic fields at monochromatic and pulse excitations
The bases of the theory of light reflection and absorption by low-dimensional
semiconductor objects (quantum wells, wires and dots) at both monochromatic and
pulse irradiations and at any form of light pulses are developed. The
semiconductor object may be placed in a stationary quantizing magnetic field.
As an example the case of normal light incidence on a quantum well surface is
considered. The width of the quantum well may be comparable to the light wave
length and number of energy levels of electronic excitations is arbitrary. For
Fourier-components of electric fields the integral equation (similar to the
Dyson-equation) and solutions of this equation for some individual cases are
obtained.Comment: 14 page
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