128 research outputs found
Guidance in the area of socio-emotional competencies for secondary students in multicultural contexts
Abstract One of the aims of Educational Guidance is social development and learning in Secondary Education students who are in multicultural contexts. An increase in socio-emotional competencies is promoted through Guidance program interventions. The Guidance Program for Socio-emotional Competencies (in Spanish, POCOSE) not only improves students' learning process and academic performance, it also favors their integration socially and at school, thus exercising a preventive function against future school failure and other risk factors, such as absenteeism, school drop-out, or violence (bullying). The broad cultural diversity which characterizes our Educational System requires identification of socioemotional competencies that are positively related to optimal learning and better socio-educational adjustment of secondary students who are in multicultural contexts, as well as identifying existing cultural differences in the process of teaching and learning these competencies. There is also a need for scientifically-validated programs for guidance and training in socio-emotional competencies, since these are an appropriate way to improve learning and socio-educational adjustment of Secondary Education students
Comparative Study of Conductivity in Mid-Voltage Cable XLPE Insulation
It is well established that space charge conditions
insulation lifetime. Because of this, space charge
formation and relaxation processes characterization has
become a very active research field, not only from an basic
science point of view, but also in order to improve
insulation performance in cable and other devices.
In the case of mid-voltage power cable, crosslinked
polyethylene is widely used as insulator. Service temperature
of such cables is around 90°C, which in the case
of the cable insulation studied is in the melting temperature
range. In previous works it has been determined that
at this temperature conductivity plays a relevant role in
the space charge relaxation process, so that the characterization
of conductive processes at service temperature
may become important in order to enhance cable insulation
performance. The aim of this work is to contribute to
a better knowledge of the conductive properties of XLPE
in both time and frequency domains
Dielectric study of the glass transition: correlation with calorimetric data
The glass transition in amorphous poly(ethylene terephthalate) is studied by
thermally stimulated depolarization currents (TSDC) and differential scanning
calorimetry (DSC). The ability of TSDC to decompose a distributed relaxation,
as the glass transition, into its elementary components is demonstrated. Two
polarization techniques, windows polarization (WP) and non-isothermal windows
polarization (NIW), are employed to assess the influence of thermal history in
the results. The Tool-Narayanaswami-Moynihan (TNM) model has been used to fit
the TSDC spectra. The most important contributions to the relaxation comes from
modes with non-linearity (x) around 0.7. Activation energies yield by this
model are located around 1eV for polarization temperature (Tp) below 50C and
they raise up to values higher than 8eV as Tp increases (up to 80C). There are
few differences between results obtained with WP and NIW but, nonetheless,
these are discussed. The obtained kinetic parameters are tested against DSC
results in several conditions. Calculated DSC curves at several cooling and
heating rates can reproduce qualitatively experimental DSC results. These
results also demonstrate that modelization of the non-equilibrium kinetics
involved in TSDC spectroscopy is a useful experimental tool for glass
transition studies in polar polymers.Comment: 13 pages, 2 tables, 10 figures; minor change
Annealing Effect on the Conductivity of XLPE Insulation in Power Cable
Conductivity () in XLPE insulation of power cables annealed at 90 ºC at
temperatures between 50 and 97 ºC has been measured. In all cases there is an initial
increase in conductivity that develops a maximum and finally decreases for long
annealing times. This maximum appears in the sample annealed 20 days when
conductivity is measured at 50 ºC and shifts gradually to higher annealing times up to
40 days when the measurement is performed at 97 ºC. A linear behavior of ln() versus
T -1/4 is observed, which implies that the transport mechanism is basically via thermally
assisted hopping conduction. Infrared spectroscopy indicates that, during annealing,
some chemical species diffuse from the semiconducting shields (SC) into the XLPE.
Thermally stimulated depolarization currents technique (TSDC) and intensity-current
measurements (I-V) point out as well the presence of this diffusion process that
becomes less significant after long annealing times. The initial increase in is
explained in terms of the increase in traps density due to the diffusion process from the
SC shields. Long term decrease in is justified by the observed decrease of diffusion
rate for long annealing times
ZnO:Co Diluted Magnetic Semiconductor or Hybrid Nanostructure for Spintronics?
We have studied the influence of intrinsic and extrinsic defects in the
magnetic and electrical transport properties of Co-doped ZnO thin films. X ray
absorption measurements show that Co substitute Zn in the ZnO structure and it
is in the 2+ oxidation state. Magnetization (M) measurements show that doped
samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found
that the values of the orbital L and spin S numbers are between 1 and 1.3 for L
and S = 3/2, in agreement with the representative values for isolated Co 2+.
The obtained negative values of the Curie-Weiss temperatures indicate the
existence of antiferromagnetic interactions between transition metal atoms.Comment: To be published in Journal of Materials Scienc
Double glass transition in polyethylene naphthalate structural relaxation by MDSC, BDS and TSDC
We present the experimental study of the primary, , and secondary,
, relaxations of the glassy polymer polyethylene naphthalate (PEN), by
Modulated Differential Scanning Calorimetry (MDSC), Thermally Stimulated
Discharge Currents (TSDC) and Broadband Dielectric Spectroscopy (BDS). Results
show how the and relaxations can be considered part of a
very broad and distributed relaxation. The relaxation is composed of
a main contribution () and two additional ones ( and
) and each elementary mode of the relaxation has its own glass
transition temperature. This scenario gives rise to an extended glass
transition mainly centered in K and K
Effect of annealing on conductivity in XLPE mid-voltage cable insulation
A new study of the electrical conductivity of crosslinked polyethylene (XLPE) mid-voltage (MV) cable insulation is presented. Its main
objective is to show the effect of annealing treatments on MV cables under actual service conditions. Complementary time domain
(absorption/resorption currents) and frequency domain (dynamic electrical analysis) techniques are applied on different laboratory
samples containing XLPE insulations: sections of XLPE insulated cable (with and without semiconducting screens) in the case of
absorption/resorption currents and, in the case of dynamic electrical analysis, a thin ribbon obtained from the cable insulation by
mechanical procedures. For annealing temperatures below a certain critical temperature, conductivity decreases both for XLPE cylinders
(cable sections from which inner and outer semiconducting screens have been removed) and for real cables (sections of cable with
semiconducting screens) but its value is smaller in the case of cables. If the annealing temperature is higher than the critical temperature,
the behaviour of conductivity is more complex. In XLPE, cylinders conductivity initially decreases with the annealing time but after some
annealing time it begins to increase, it passes over a maximum and eventually it decreases monotonically. In the case of real cable
sections, conductivity grows, tending to a saturation value, which is noticeably higher than the corresponding value of the maximum
obtained for XLPE cylinders. The experimental results are explained satisfactorily by means of the Mott equation that takes into account
hopping conduction assisted both by temperature and electric field
- …