3,573 research outputs found
Methodology for automated generation of multiple choice questions in self assessment
Current trends in the European Higher Education Area (EHEA) are moving towards the continuous evaluation of the students in substitution of the traditional evaluation based on a single test or exam. This fact and the increase in the number of students during last years in Engineering Schools, requires to modify evaluation procedures making them compatible with the educational and research activities. This work presents a methodology for the automatic generation of questions. These questions can be used as self assessment questions by the student and/or as queries by the teacher. The proposed approach is based on the utilization of parametric questions, formulated as multiple choice questions and generated and supported by the utilization of common programs of data sheets and word processors. Through this approach, every teacher can apply the proposed methodology without the use of programs or tools different from those normally used in his/her daily activit
Ultra-Wideband Interference Resistant System for Multi-User Communication
In the emergence of high frequency systems comes the opportunity to investigate the possibilities of ultra-wideband (UWB) techniques. These UWB capabilities give presence to higher data rates and opens a door for techniques to ensure commination security. Secure communication is vital for mission critical scenarios, environments abundant with malicious interference, and areas with congesting transmissions. Being able to have a variety of techniques available to counteract these unfavorable scenes and as well satisfy high data rates of current technology is a goal that this paper aims to contribute in. We present here an investigation into an ultra-wideband system that is resistant to interference and is capable of accommodating a plethora of users. The system exploits the high data rate capabilities of orthogonal frequency division multiplexing (OFDM), implemented with 16-ary quadrature amplitude mapping (16-QAM). An interference resistant quality is then supplied by implementing frequency-hopping spread spectrum (FHSS). The frequency hopping scheme implements orthogonal pseudo-random sequences in order to ensure not only interference resistance but also to prevent inter-user interference. The system is simulated at 5 gigahertz (GHz) and, at these frequencies, we show that bit error rate (BER) degradation is minimal among users in the presence of interference
Statistical repulsion/attraction of electrons in graphene in a magnetic field
The aim of this work is to describe the thermodynamic properties of an
electron gas in graphene placed in a constant magnetic field. The electron gas
is constituted by Bloch electrons in the long wavelength approximation. The
partition function is analyzed in terms of a perturbation expansion of the
dimensionless constant . The statistical
repulsion/attraction potential for electrons in graphene is obtained in the
respective case in which antisymmetric/symmetric states in the coordinates are
chosen. Thermodynamic functions are computed for different orders in the
perturbation expansion and the different contributions are compared for
symmetric and antisymmetric states, showing remarkable differences between them
due to the spin exchange correlation. A detailed analysis of the statistical
potential is done, showing that, although electrons satisfy Fermi statistics,
attractive potential at some interparticle distances can be found.Comment: Physica B, 201
Valley properties of doped graphene in a magnetic field
The aim of this work is to describe the electronic properties of graphene in
a constant magnetic field in the long wavelength approximation with random
binary disorder, by solving the Soven equation self-consistently. Density of
state contributions for different valleys in each sublattice sites are obtained
for different values of magnetic field strength showing remarkable differences
between K and K' valleys. A band gap is obtained by an asymmetric on-site
impurity concentration and the graphene electrons acquire an anomalous magnetic
moment, which is opposite in different valleys, which depend highly in the
interplay between the impurity band, the band edges and the broadening of the
Landau levels. In turn, magnetization as a function of B for different on-site
random impurities is computed showing that by decreasing the on-site impurity
energy values, maximum magnetization is shifted towards higher values of B
which can be used to create and manipulate polarized valley currents. Finally,
conductivity and local vertex function are obtained as a function of energy
showing that scattering contributions from A and B sublattices differ
significantly. Effective medium local two-irreducible vertex is computed
showing that scattering from sublattices A and B do not contribute equally,
which can be related to weak anti-localization. From these results, it could be
possible to explore how the valley pseudospin can be used to create polarized
currents by populating asymmetrically the sublattice sites, where the
population can be tuned with the applied magnetic field strength
- …