The effect of the external lateral electric field on the luminescence intensity of InAs/GaAs quantum dots

We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications. The text was submitted by the authors in English.     

On forests, trees, elephants, and classrooms: a brief for the study of learning ecologies

The classroom intervention studies in this volume, ranging from the study of gestures to that of systemic implementation, are at very different grain sizes. A challenge is to see the forest for the trees – to see how these studies, focusing on different aspects of mathematical activity at different grain sizes, can be seen as aspects of a coherent whole. I propose an ecological metaphor for the study of mathematical activity. In ecological terms, the biosphere is comprised of interconnected and interrelated ecosystems. I argue that, analogously, there are nested and interrelated mathematical activity systems and structures in which “mathematical sense-making” plays the role of “health” in ecosystems. Moreover, what happens in the classroom environment shapes and is shaped by what happens in sub-ecologies of the classroom (e.g., sociomathematical norms, participation structures, communicational forms such as gesture, and representational tools and their use) and the larger social and organizational ecologies of which it is a part (building culture, support structures for teachers and teaching, external pressures such as testing and accountability systems etc).     

非参数自回归模型异方差的小波检验

本文讨论了非参数自回归模型异方差的检验问题.在非参数自回归模型的建模过程中,通常假定方差为常数.然而在建模前,我们应该首先检验这-假定是否成立.本文将利用小波方法来检验异方差问题.我们首先利用核估计方法定义经验小波系数,然后讨论其渐近性质.在此基础上,我们提出了异方差性检验的统计量.数值模拟结果表明,我们的方法表现良好.     

Spatially resolved measurement of femtosecond laser induced refractive index changes in transparent materials

We present a practical method to determine femtosecond laser induced refractive index changes in transparent materials. Based on an iterative Fourier transform algorithm, this technique spatially resolves the refractive index of complex structures by combining the dimensions of the modified region with the corresponding phase change extracted from far-field intensity measurements. This approach is used to characterize optical waveguides written by a femtosecond laser in borosilicate glass.     

Problematizing the didactic triangle

This paper suggests that the typical framing of the didactic triangle in the English-speaking literature is narrower than it should be, and that it should be broadened to view classroom activities from a more social/cultural perspective. A framework for examining mathematically productive classrooms is given and exemplified, with the exemplification providing a point of departure for the kinds of analytic work that might be done.