1,459 research outputs found
Two-step phase changes in cubic relaxor ferroelectrics
The field-driven conversion between the zero-field-cooled frozen relaxor
state and a ferroelectric state of several cubic relaxors is found to occur in
at least two distinct steps, after a period of creep, as a function of time.
The relaxation of this state back to a relaxor state under warming in zero
field also occurs via two or more sharp steps, in contrast to a one-step
relaxation of the ferroelectric state formed by field-cooling. An intermediate
state can be trapped by interrupting the polarization. Giant pyroelectric noise
appears in some of the non-equilibrium regimes. It is suggested that two
coupled types of order, one ferroelectric and the other glassy, may be required
to account for these data.Comment: 27 pages with 8 figures to appear in Phys. Rev.
Aging in the Relaxor Ferroelectric PMN/PT
The relaxor ferroelectric
(PbMnNbO)(PbTiO), ,
(PMN/PT(90/10)) is found to exhibit several regimes of complicated aging
behavior. Just below the susceptibility peak there is a regime exhibiting
rejuvenation but little memory. At lower temperature, there is a regime with
mainly cumulative aging, expected for simple domain-growth. At still lower
temperature, there is a regime with both rejuvenation and memory, reminiscent
of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging
regimes. This qualitative aging behavior is reminiscent of that seen in
reentrant ferromagnets, which exhibit a crossover from a domain-growth
ferromagnetic regime into a reentrant spin glass regime at lower temperatures.
These striking parallels suggest a picture of competition in PMN/PT (90/10)
between ferroelectric correlations formed in the domain-growth regime with
glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also
found to exhibit frequency-aging time scaling of the time-dependent part of the
out-of-phase susceptibility for temperatures 260 K and below. The stability of
aging effects to thermal cycles and field perturbations is also reported.Comment: 8 pages RevTeX4, 11 figures; submitted to Phys. Rev.
Beyond school-related learning : parent-child homework talk as a morality building activity
Family interactions constitute an arena for children's moral development: it is indeed through ordinary talk, and shared, task-oriented activities that children are socialized into moral orders and culturally informed ways of thinking and acting. Drawing on a video-based study on the everyday life of 19 middle-class families and adopting a discourse analytic approach, the paper sheds light on the socializing function of a domestic activity: homework. We illustrate that, when it unfolds as a family activity, the issues at stake go far beyond its school-oriented goals: homework provides âethical affordancesâ that make relevant moral talk whereby parents introduce children to some unquestioned principles such as homework must be done neatly and it is part of the child's duties. We contend that, by participating in morally loaded homework interactions, children are socialized not only into a school-aligned cultural list concerning what is right and what is wrong about homework, but moreover into a constitutive, taken-for-granted pillar of human sociality: the moral assessability of human conduct, i.e., its being subject to evaluations informed by the âright vs. wrongâ category. Implications for teacher training and parent education programs are discussed in the conclusion
steam turbine control valve and actuation system modeling for dynamics analysis
Abstract The paper describes a study conducted on Steam Turbine control valve and actuation systems, which rule the machine final power production and rotational speed. A dynamic model developed in the Matlab/Simulink environment is proposed to support the analysis of the operational stability of the hydro-mechanical system as well as the failure modes that it may face during operation. The model was validated through specific field tests conducted on the actuation system at a cogeneration plant in Nuovo Pignone, Florence. The proposed work also underlines the requirements that new actuation technologies should fulfil in order to meet control valve system performance criteria
When school language and culture enter the home : testing children as a âschool-alignedâ parental activity
Since Bronfenbrennerâs claims on the ecology of human development, an
impressive amount of research has explored the ways in which childrenâs
primary social worlds (i.e., family and school) connect and potentially create an osmotic ecological milieu. In the building of the so-called âfamilyschool partnershipâ, homework plays a crucial role. Being a school activity
carried out inside the home, it is a key site for implementing parental involvement and a crucial occasion where cultural models of âgood parentâ and
âgood pupilâ are instantiated. This video-based, conversation analytic study
shows a specific activity taking place while parents assist their children with
homework: testing. The analysis shows that parents deploy a âschool-likeâ
interactive conduct by reproducing the standards, morality, and linguistic
practices of the school. In so doing, they comply with the contemporary
model of âgood parent as school partnerâ and socialize their children into
the culture of the school by turning them into âgood pupilsâ.
Keywords: homework; family-school partnership; test; parental involvement; ethnography-informed conversation analysis
A Fuzzy Logic-based Tuning Approach of PID Control for Steam Turbines for Solar Applications
Abstract This work aims at improving the control concept based on PID controller by jointly exploiting experience and knowledge on the system behaviour and artificial intelligence. A Concentrated Solar Power Plant (CSPP) system has been modelled and a stability and performance analysis has been carried out, focusing on power control loop, which is normally based on standard PID. A hybrid fuzzy PID approach is proposed to improve the steam turbine governor action and its performance are compared to the classical PID tuned according to three different approaches. Compared to the classic PID, the PID fuzzy logic controller extends the simplicity of PID and adapts the control action at actual operating condition by providing the system with a sort of "decision-making skill". The possibility to design implementable algorithms on PLC, which have stringent computational speed and memory requirements, has been explicitly taken into account in the developed work
Neural network based prediction of roughing and finishing times in a hot strip mill
The paper presents a model based on neural networks which is able to predict the time required to pass the different gauges of a roughing and finishing mill as function of some slab features and process parameters. The final aim of the work is to increase the rolling efficiency while avoiding collisions and queues that cause time and energy losses. Neural networks are suitable to this prediction task as they are particularly able to cope with unknown non linear relationships between input and output variables. Moreover they can learn from real industrial data and therefore do not require prior assumptions or mathematical modelling of the process and transferability is ensured by the possibility to use different databases coming from different rolling mills. In the paper, two different kinds of neural network- based models have been proposed, their performances have been discussed and compared.En este artĂculo se presenta un modelo basado en redes neuronales capaz de predecir el tiempo necesario para pasar las diferentes galgas de un tren desbastador y acabador en funciĂłn de ciertas caracterĂsticas del desbaste y parĂĄmetros de proceso. El objetivo final es aumentar la eficacia de la laminaciĂłn evitando colisiones y colas que provoquen pĂ©rdidas de tiempo y energĂa. Se propone utilizar para esta tarea redes neuronales por su capacidad de predicciĂłn en aquellos casos en los que existen relaciones no lineales desconocidas entre las variables de entrada y las de salida. AdemĂĄs, son capaces de aprender de datos industriales reales y, por tanto, no requieren suposiciones previas o modelos matemĂĄticos del proceso, estando la transferibilidad asegurada ya que es posible utilizar distintas bases de datos procedentes de diferentes trenes de laminaciĂłn
âDonât complain and do it properlyâ : 'Pedagogicalized parents' and the morality of doing homework
In the last decades, pedagogical studies and policies in western countries have proposed parental involvement in education as the formula for maximizing studentsâ success and increasing social equality. In the building of the family-school partnership, a crucial role is commonly attributed to parent-assisted homework. Therefore, parental involvement in homework has increased and the model of the âinvolvedâ and âpedagogically competentâ parent has become common. Analyzing video-recorded parent-child interactions during homework, this paper illustrates how parents make relevant and educate their children to moral horizons concerning homework, education, and schooling. The moral beliefs evoked by the parents in the study are significantly aligned with the school culture. Parent-assisted homework therefore becomes a particularly relevant arena for childrenâs socialization into the cultural and moral horizons of the school system. Yet a socio-pedagogical issue emerges: if the school relies heavily on the family for homework activities, what happens to those children who cannot rely on school-aligned, pedagogically competent parents
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