Theory and practice of the shifted Lotka function

One of the major drawbacks of the classical Lotka function is that arguments only start from the value 1. However, in many applications one may want to start from the value 0, e.g. when including zero received citations. In this article we consider the shifted Lotka function, which includes the case of zero items. Basic results for the total number of sources, the total number of items and the average number of items per source are given in this framework. Next we give the rank-frequency function (Zipf-type function) corresponding to the shifted Lotka function and prove their exact relation. The article ends with a practical example which can be fitted by a shifted Lotka function.     

Notices

The expected number of maxima and level crossings of a continuous stationary Gaussian process and the discrete process obtained by sampling the continuous one are evaluated and compared. The ratio of these two values as a function of sampling rate for two classes of spectra is calculated. It is shown that the rule of thumb of sampling at twice the Nyquist frequency is a good one.     

Student perspectives on mentoring in a science outreach project

Abstract

The focus of this paper is an examination of mentorship relationships developed as a result of six students’ participation in a local community science centre sponsored through an NSERC/CRYSTAL project. Each year, a number of students participate in after‐school activities sponsored by the community science centre. Much of this work involves a one‐to‐one approach, with a middle years or high school student working with a professor partner. The professor acts as a mentor to the student, facilitating learning in a manner not always feasible within a school setting with large class sizes. For some students this research may be the basis of a science fair project; for others if is simply a study based on individual interest. Mentored students were interviewed about the nature of that mentorship, with the goal of describing the experience from the students’ perspective. Questions focused on the student's experience of working with a mentor, including how the mentorship relationship was formed, what the importance of the voluntary nature of mentoring was, what the benefits and challenges of working with a mentor were, how the mentorship relationship affected the level of content knowledge the student gained, and what effect the mentoring relationship had on the student's continuing interest in science. The mentorship program offers students the opportunity to work within a developing community of practice.     

Enhancing the efficiency of alternating current driven organic light-emitting devices by optimizing the operation frequency

We report efficient and bright organic light-emitting devices operated by capacitive energy coupling. In this approach, the organic layers are enclosed between sputter-deposited hafnium dioxide layers to prevent charge carrier injection. When a sinusoidal voltage signal is applied to the electrodes, the devices emit bright green light whereas no detectable emission is generated upon application of a constant voltage. The efficiency of the process depends heavily on the frequency of the applied voltage signal. By optimizing the driving scheme, a record luminous efficacy for AC driven OLEDs of 2.7 lm/W at 500 cd/m² is achieved.     

Direct structuring of C60 thin film transistors by photo-lithography under ambient conditions

Direct structuring techniques are an indispensable need for future low-cost applications of organic semiconductor materials in e.g. active matrix displays or integrated circuits. We demonstrate direct structuring of a small molecule organic semiconductor by a photo-lithography lift off process under ambient conditions. To show compatibility of this process, we fabricate organic thin film transistors (OTFT) containing the benchmark electron transporting semiconductor C60 as active material in a top-contact geometry. C60 as electron transporting semiconductor serves as good indicator for contamination and degradation caused by the structuring procedure. To disclose influences of structuring, we discuss the OTFT performance for different channel lengths from 100 μm down to 2.7 μm. In particular, we show that lithography processing gives rise to increased contact resistances. Apart from that, mobility of C60 as material parameter is only weakly affected which underlines the compatibility of the suggested structuring procedure. The potential of this structuring procedure for future integration of driving transistors in active matrix displays is demonstrated.     

Multitasking on a Single Device: Arousal and the Frequency,Anticipation, and Prediction of Switching Between Media Content on a Computer

This study measured arousal responses to multitasking by recording switches between content on personal computers over a day. Results showed that switches occurred every 19 seconds, more often than has been reported in previous research. Arousal was highest at the point of a switch with declines in skin conductance afterward. Switches were also preceded by a 12‐second period of increasing skin conductance. 2 new methods were used, one an original application that recorded screen shots, and another that measured changes in skin conductance during the day using a wrist sensor. Results are discussed in light of increasing use of single devices displaying multiple types of content, rather than multitasking that occurs when attention is divided between content on multiple devices.     

Addendum to “On the consistency of MPS” [Comput. Phys. Comm. 184 (3) (2013) 732–745]

The analogies between the Moving Particle Semi-implicit method (MPS) and Incompressible Smoothed Particle Hydrodynamics method (ISPH) are established in this note, as an extension of the MPS consistency analysis conducted in Souto-Iglesias et al. (2013).