The effect of service time variability on maximum queue lengths in M^X/G/1 queues

We study the impact of service-time distributions on the distribution of the maximum queue length during a busy period for the M^X/G/1 queue. The maximum queue length is an important random variable to understand when designing the buffer size for finite buffer (M/G/1/n) systems. We show the somewhat surprising result that for three variations of the preemptive LCFS discipline, the maximum queue length during a busy period is smaller when service times are more variable (in the convex sense).Comment: 12 page

Dynamic routing policies for multi-skill call centers

We consider the problem of routing calls dynamically in a multiskill call center. Calls from different skill classes are offered to the call center according to a Poisson process. The agents in the center are grouped according to their heterogeneous skill sets that determine the classes of calls they can serve. Each agent group serves calls with independent exponentially distributed service times. We consider two scenarios. The first scenario deals with a call center with no buffers in the system, so that every arriving call either has to be routed immediately or has to be blocked and is lost. The objective in the system is to minimize the average number of blocked calls. The second scenario deals with call centers consisting of only agents that have one skill and fully cross-trained agents, where calls are pooled in common queues. The objective in this system is to minimize the average number of calls in the system. We obtain nearly optimal dynamic routing policies that are scalable with the problem instance and can be computed online. The algorithm is based on one-step policy improvement using the relative value functions of simpler queuing systems. Numerical experiments demonstrate the good performance of the routing policies. Finally, we discuss how the algorithm can be used to handle more general cases with the techniques described in this article. © 2009 Cambridge University Press

Volitional shielding of the self: Effects of action arientation and external demands on implicit self-evaluation

Two studies examined whether volitional resources can shield implicit self-evaluation against the autonomy-undermining influence of external demands. Volitional resources were operationalized as individual differences in action orientation (Kuhl & Beckmann, 1994). Implicit self-evaluation was assessed via an adaptation of the affective priming task (Fazio, 2001). In Study 1, a threatening visualization led participants with low action orientation (or "state-oriented" individuals) to display less autonomous implicit self-evaluations compared to participants with high action orientation. In Study 2, performance-contingent rewards led action-oriented participants to display more autonomous implicit self-evaluations than state-oriented participants. These findings were specific to the autonomy motive. Volitional shielding plays an important role in self-defense processes

Practical Issues in Mobile Education

Practitioners interested in integrating mobile technology effectively into distance learning programs need to consider both the benefits and limitations of such devices. This paper outlines some major limitations of mobile devices and suggests strategies to mitigate them such as chunking information, using appropriate organizational techniques, reducing the number of required actions, and improving ease of use. Properly planned integration of mobile technology also offers some distinct advantages. Learners can benefit from a dynamic and flexible learning environment with anywhere, anytime access to people and information. Practitioners can use these features to help learners enhance their skills in assessing the relevance and appropriateness of information for use in practical settings

Facilitating dental student reflections : using mentor groups to discuss clinical experiences and personal development

Despite the consensus on the importance of reflection for dental professionals, a lack of understanding remains about how students and clinicians should develop their ability to reflect. The aim of this study was to investigate dental students’ and mentors’ perceptions of mentor groups as an instructional method to facilitate students’ reflection in terms of the strategy’s learning potential, role of the mentor, group dynamics, and feasibility. At Ghent University in Belgium, third- and fourth-year dental students were encouraged to reflect on their clinical experiences and personal development in three reflective mentor sessions. No preparation or reports afterwards were required; students needed only to participate in the sessions. Sessions were guided by trained mentors to establish a safe environment, frame clinical discussions, and stimulate reflection. Students’ and mentors’ perceptions of the experience were assessed with a 17-statement questionnaire with response options on a five-point Likert scale (1=totally disagree to 5=totally agree). A total of 50 students and eight mentors completed the questionnaire (response rates 81% and 89%, respectively). Both students and mentors had neutral to positive perceptions concerning the learning potential, role of the mentor, group dynamics, and feasibility. The mean ideal total time for sessions in a year was 99 minutes (third-year students), 111 minutes (fourth-year students), and 147 minutes (mentors). Reported reflective topics related to patient management, frustrations, and practice of dentistry. Overall mean appreciation for the experience ranged from 14.50 to 15.14 on the 20-point scale. These findings about students’ and mentors’ positive perceptions of the experience suggest that mentor groups may be a potentially valuable strategy to promote dental students’ reflection

The Web of Identity: Selfhood and Belonging in Online Learning Networks

In this paper, the reflexive relationship between social interaction and understanding of self in online learning networks is examined. In keeping with constructionism, we acknowledge the significance of social interaction in learning and identity formation. It is through identification with and differentiation from others that individuals are able to establish their sense of self. Therefore, a sense of self is inherently connected to one's sense of belonging within a community (-ies). Building on the work of Goffman (impressions management) and Foucault (technologies of the self), a model of identity and community formation is introduced: the Web of Identity (WoI). According to the WoI model, community members rely on technical, structural, political, cultural, and idiosyncratic perspectives coupled with performance strategies in a continuous cycle of internalization, understanding, enactment, and revision of their individual identities. We discuss how individuals construct their identities through relational dialogue and interaction in which they express, share, and build upon their histories, practices, and goals. It is an ongoing reciprocal process that constantly changes both personal and collective narratives. The combined perspectives and strategies guide the individual's behaviour, but do not completely restrict it. The individual is free to choose how to perform and may choose performances that support or contravene accepted social practices. Ideally, this process guides the individual towards cognitive resonance, a process in which he/she behaves in accordance with his/her internalized conceptions of society and self. If an individual's actions do not resonate with social expectations, accepted practices, and self, the individual may modulate his/her actions or may cause shifts in accepted practices, expectations, or self identity. Such shifts filter through the WoI performance strategies. The paper concludes with suggestions for further research in identity formation in online learning networks. We recommend study of current social networks and learning management systems to identify existing mechanisms that permit expression of WoI strategies. In addition, we recommend research into how social software systems can be developed or facilitated to encourage strategy use. Since, it is through these performances that the individual enacts his/her identity, we wish to know how, in actual practice, strategy use will affect conceptions of self and community in educational environments

Recruitment characteristics of nerve fascicles stimulated by a multi-groove electrode

The recruitment characteristics of fascicle-selective nerve stimulation by a multigroove electrode have been investigated both theoretically and in acute experiments. A three-dimensional (3-D) volume conductor model of fascicles in a multigroove device and a model of myelinated nerve fiber stimulation were used to calculate threshold stimuli of nerve fibers in these fascicles. After their exposition, fascicles from rat sciatic nerve were positioned in different grooves of appropriate sizes and stimulated separately. The device appeared to be suitable for fascicle-selective stimulation, because both computer simulations and acute animal experiments showed that crosstalk between neighboring fascicles is not a problem, even when monopolar stimulation was used. The threshold stimulus was lower for a small fascicle than for a large one. When the amount of (conducting) medium between contact and perineurium or its conductivity was reduced, threshold stimuli were lower. Moreover, simulations predict that the slopes of recruitment curves are smaller and inverse recruitment order is less pronounced. Simulations also showed that a small contact is preferable to a large one, because a small contact gives a slightly smaller slope of the recruitment curve. Both experimentally and theoretically a significantly smaller slope of recruitment curves was obtained by stimulation with a cathode and an anode at opposite sides of the fascicle, driven by two current sources giving simultaneous pulses with different, but linearly dependent amplitude

Assigning a single server to inhomogeneous queues with switching costs

AbstractIn this paper we study the preemptive assignment of a single server to two queues. Customers arrive at both queues according to Poisson processes, and all service times are exponential, but with rates depending on the queues. The costs to be minimized consist of both holding costs and switching costs. The limiting behavior of the switching curve is studied, resulting in a good threshold policy. Numerical results are included to illustrate the complexity of the optimal policy and to compare the optimal policy with the threshold policy

A Model for Framing Mobile Learning

The Framework for the Rational Analysis of Mobile Education (FRAME) model describes mobile learning as a process resulting from the convergence of mobile technologies, human learning capacities, and social interaction. It addresses contemporary pedagogical issues of information overload, knowledge navigation, and collaboration in learning. This model is useful for guiding the development of future mobile devices, the development of learning materials, and the design of teaching and learning strategies for mobile education.AU Press: http://www.aupress.ca/index.php/books/12015

Sharpening Our Vision, Engaging in Learning, Renewing Our Practice

This article was originally presented at the 1996 B. J. Haan Education Conference at Dordt College