University of Twente Publications
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University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

2.
Strengthening a comprehensive model for explaining HRD effectiveness - Wognum, A.A.M.; Veldkamp, Bernard P.
This study reports the results of the formative evaluations of two computer-supported tools and the associated strategies for their use. Tools and strategies embedded in web-based courses can increase a supervisor’s involvement in helping employees transfer learning onto the workplace. Issues relating to characteristics of the tools and strategies as well as factors influencing their likelihood of use are identified via summaries of the two evaluation studies.

3.
Tools and strategies for engaging the supervisor in technology-supported work-based learning : evaluation research - Bianco, Manuela; Collis, Betty
This study reports the results of the formative evaluations of two computer-supported tools and the associated strategies for their use. Tools and strategies embedded in web-based courses can increase a supervisor’s involvement in helping employees transfer learning onto the workplace. Issues relating to characteristics of the tools and strategies as well as factors influencing their likelihood of use are identified via summaries of the two evaluation studies.

4.
Learning management systems: one size fits all? - Oliver, Ron; Harper, Ben; Reeves, Tom; Strijker, Allard; Westhuizen, Duan van
Learning management systems such as WebCT and Blackboard are rapidly becoming the principal systems behind institutions' moves to technology-based learning settings. In settings where lecturers have had no or limited exposure to ICT as a teaching tool, LMSs pave the way for quick introduction and eventual adoption of technology-based teaching practices. Many lecturers quickly progress and grow in the field. But there are those who argue that the use of LMS tend to be counter-productive and that in their current forms, they cannot be used effectively as a learning tool. Critics argue that they support only traditional forms of teaching...

6.
Publishing and perishing: The critical importance of educational design research - Reeves, Thomas C.; McKenney, Susan; Herrington, Jan
The outcomes of educational systems continue to lag far behind expectations at all levels, primary, secondary, and tertiary. Meanwhile, the sheer amount of educational research published in refereed journals has expanded enormously. There is an obvious disconnect between the educational research papers published in professional journals or presented at academic conferences and any form of beneficial impact on the students, teachers, and other stakeholders in educational systems. This problem can be traced back to those professors and research supervisors engaged in the preparation of educational researchers who fail to convey to novice researchers important distinctions between the goals and methods...

7.
Publishing and perishing: The critical importance of educational design research - Reeves, Thomas C.; McKenney, Susan; Herrington, Jan
The outcomes of educational systems continue to lag far behind expectations at all levels, primary, secondary, and tertiary. Meanwhile, the sheer amount of educational research published in refereed journals has expanded enormously. There is an obvious disconnect between the educational research papers published in professional journals or presented at academic conferences and any form of beneficial impact on the students, teachers, and other stakeholders in educational systems. This problem can be traced back to those professors and research supervisors engaged in the preparation of educational researchers who fail to convey to novice researchers important distinctions between the goals and methods...

10.
Capturing aerosol droplet nucleation and condensation bursts using PISO and TVD schemes - Frederix, E.M.A.; Kuczaj, A.K.; Nordlund, M.; Geurts, B.J.
A mathematical model for single-species aerosol production and transport is formulated, and solved using an adapted PISO algorithm. The model is applied to a laminar flow diffusion chamber, using a finite volume method on a collocated grid. In tran- sient simulations, a sharp scalar front (e.g., vapor mass fraction), is shown to introduce unphysical oscillation in the solution, when applying a second order linear interpolation in the convective terms. At increased grid resolution, these oscillations are strongly at- tenuated. When applying a TVD scheme (here the MUSCL scheme), a time-accurate monotonicity-preserving solution is obtained. The numerical dissipation introduced by the...

11.
Automated rare event simulation for stochastic petri nets - Reijsbergen, Daniël; Boer, Pieter-Tjerk de; Scheinhardt, Werner
We introduce a method to automatically apply rare event simulation to stochastic Petri nets, which are often used in the stochastic model checking community to model highly reliable systems. Rare event simulation can be much faster than standard simulation by exploiting information about the typical behaviour of the system. Previously, such information came from heuristics, human insight, or analysis on the full state space. We present a formal algorithm that obtains the required information from the (high-level) stochastic Petri net description, without generating the full state space. Essentially, our algorithm reduces the state space of the model to a (much...

12.
In control: methodological and clinical aspects of cerebral autoregulation and haemodynamics - Meel-van den Abeelen, Aisha
Cerebral autoregulation (CA) is a key mechanism to protect the brain against excessive fluctuations in blood pressure (BP) and maintain cerebral blood flow. Analysing the relationship between spontaneous BP and cerebral blood flow velocity (CBFV) using transfer function analysis is a widely used technique to quantify CA in a non-invasive way. The objective of this review was to provide an overview of transfer function techniques used in the assessment of CA.
For this review, 113 publications were included. This literature showed that there is no gold standard for the execution and implementation of the transfer function. There is a high diversity...

13.
Diffusion parameters of flows in stable queueing networks - Nazarathy, Yoni; Scheinhardt, Werner
We consider open multi-class queueing networks with general arrival processes, general processing time sequences and Bernoulli routing. The network is assumed to be operating under an arbitrary work-conserving scheduling policy that makes the system stable. An example is a generalized Jackson network with load less than unity and any work conserving policy. We find a simple diffusion limit for the inter-queue flows with an explicit computable expression for the covariance matrix. Specifically, we present a simple computable expression for the asymptotic variance of arrivals (or departures) of each of the individual queues and each of the flows in the network.

14.
A comparison of random walks in dependent random environments - Scheinhardt, Werner; Kroese, Dirk P.
Although the theoretical behavior of one-dimensional random walks in random environments is well understood, the actual evaluation of various characteristics of such processes has received relatively little attention. This paper develops new methodology for the exact computation of the drift in such models. Focusing on random walks in dependent random environments, including $k$-dependent and moving average environments, we show how the drift can be characterized and found using Perron-Frobenius theory. We compare random walks in various dependent environments and show that their drift behavior can differ signicantly.

15.
Characteristics-based sectional modeling of aerosol nucleation, condensation and transport - Frederix, E.M.A.; Kuczaj, A.K.; Nordlund, M.; Stanic, M.; Geurts, B.J.
Aerosols can be generated by physical processes such as nucleation, conden- sation and coalescence. To predict spatially varying statistical properties of such aerosols, e.g., the size distribution of the droplets, these processes must be captured accurately. We model nucleation using classical nucleation theory, whereas the con- densational growth is captured with a molecular diffusivity model. The droplet size distribution is discretized using a sectional approach, in which droplets are charac- terized in terms of a number of fixed droplet size bins. Often, in such a formula- tion, the numerical time step restrictions arising from condensation and nucleation are more pronounced...

16.
On the energy benefit of compute-and-forward on the hexagonal lattice - Ren, Zhijie; Goseling, Jasper; Weber, Jos; Gastpar, Michael
We study the energy benefit of applying compute-and-forward on a wireless hexagonal lattice network with multiple unicast sessions with a specific session placement. Two compute-and-forward based transmission schemes are proposed, which allow the relays to exploit both the broadcast and superposition nature of the wireless network. The energy consumption of both transmission and reception of the nodes are taken into account. We show that with our schemes, the total energy consumption of the network is significantly reduced compared to traditional routing based transmission schemes. Moreover, our schemes also outperform the plain network coding based transmission scheme in terms of power...

17.
A simple derivation of the waiting time distributions in a non-preemptive M/M/c queue with priorities - Vianen, Lars A. van; Gabor, Adriana F.; Ommeren, Jan-Kees van
In this article we give a new derivation for the waiting time distributions in an M=M=c queue with multiple priorities and a common service rate by using elementary lattice paths counting. An advantage of the approach is that it does not require inversion of the Laplace-Stieltjes transform.

19.
Cryptographically enforced search pattern hiding - Bösch, Christoph Tobias
Searchable encryption is a cryptographic primitive that allows a client to out- source encrypted data to an untrusted storage provider, while still being able to query the data without decrypting. To allow the server to perform the search on the encrypted data, a so-called trapdoor is generated by the client and sent to the server. With help of the trapdoor, the server is able to perform the search, on behalf of the client, on the still encrypted data.
All reasonably efficient searchable encryption schemes have a common prob- lem. They leak the search pattern which reveals whether two searches were performed...

20.
Thermal-wave balancing flow sensor with low-drift power feedback - Dijkstra, M.; Lammerink, T.S.J.; Pjetri, O.; Boer, M.J. de; Berenschot, J.W.; Wiegerink, R.J.; Elwenspoek, M.C.
A control system using a low-drift power-feedback signal was implemented applying thermal waves, giving a sensor output independent of resistance drift and thermo-electric offset voltages on interface wires. Kelvin-contact sensing and power control is used on heater resistors, thereby inhibiting the influence of heater resistance drift. The thermal waves are detected with a sensing resistor using a lock-in amplifier and are mutually cancelled by a thermal-wave balancing controller. Offset due to thermal gradient across the chip and resistor drift are eliminated by the lock-in amplifier and power controller, and therefore do not influence the sensor output signal. A microchannel thermal-wave...