10,639 research outputs found
On the second moment of the number of crossings by a stationary Gaussian process
Cram\'{e}r and Leadbetter introduced in 1967 the sufficient condition
to have a
finite variance of the number of zeros of a centered stationary Gaussian
process with twice differentiable covariance function . This condition is
known as the Geman condition, since Geman proved in 1972 that it was also a
necessary condition. Up to now no such criterion was known for counts of
crossings of a level other than the mean. This paper shows that the Geman
condition is still sufficient and necessary to have a finite variance of the
number of any fixed level crossings. For the generalization to the number of a
curve crossings, a condition on the curve has to be added to the Geman
condition.Comment: Published at http://dx.doi.org/10.1214/009117906000000142 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Solar Photovoltaic and Thermal Energy Systems: Current Technology and Future Trends
Solar systems have become very competitive solutions for residential, commercial, and industrial applications for both standalone and grid connected operations. This paper presents an overview of the current status and future perspectives of solar energy (mainly photovoltaic) technology and the required conversion systems. The focus in the paper is put on the current technology, installations challenges, and future expectations. Various aspects related to the global solar market, the photovoltaic (PV) modules cost and technology, and the power electronics converter systems are addressed. Research trends and recommendations for each of the PV system sectors are also discussed.Junta de AndalucÃa P11-TIC-7070Ministerio de Ciencia e Innovación TEC2016-78430-
Rice formulae and Gaussian waves
We use Rice formulae in order to compute the moments of some level
functionals which are linked to problems in oceanography and optics: the number
of specular points in one and two dimensions, the distribution of the normal
angle of level curves and the number of dislocations in random wavefronts. We
compute expectations and, in some cases, also second moments of such
functionals. Moments of order greater than one are more involved, but one needs
them whenever one wants to perform statistical inference on some parameters in
the model or to test the model itself. In some cases, we are able to use these
computations to obtain a central limit theorem.Comment: Published in at http://dx.doi.org/10.3150/10-BEJ265 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Las construcciones geométricas en torno al lugar geométrico de la parábola influenciado por el Geogebra
El escrito presenta un extracto de algunas de las actividades que estamos elaborando en un trabajo de investigación, acerca de la incidencia de las construcciones geométricas en la génesis instrumental de la parábola. Nuestro trabajo está dirigido a docentes de matemática de una universidad privada de Lima. Los objetivos son analizar cómo la condición geométrica de dicha curva se transforma en instrumento cuando los sujetos dirigen sus acciones a la resolución de los problemas con actividades geométricas y cómo dichas acciones contribuyen al proceso de aprendizaje de algunos contenidos geométricos haciendo uso del Geogebra que movilizan como herramienta mediadora. Las actividades se fundamentan teniendo en cuenta aspectos del Enfoque Instrumental y la TeorÃa Antropológica de lo Didáctico, para analizar los esquemas y las técnicas que los profesores construyeron o movilizaron durante las tareas propuestas
The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics
The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future
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