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Aging and GABA

Koen Cuypers, Celine Maes, Stephan P. Swinnen
2018 Aging  
Correspondence: Koen Cuypers Email: koen.cuypers@kuleuven.be Keywords: aging, inhibition, gamma-aminobutyric acid (GABA)  ... 
doi:10.18632/aging.101480 pmid:29905530 pmcid:PMC6046222 fatcat:if3zyib2cvci3lmqdimyotoy7m

Double Talk Cancellation In Echo Cancelled Dmt-Systems

Geert Ysebaert, Koen Vanbleu, Gert Cuypers, M. Moonen, Katleen Van Acker
2002 Zenodo  
Koen Vanbleu is a Research Assistant with the F.W.O.  ...  The proposed method allows to use a larger stepsize in the adaptation process resulting in fast tracking and/or convergence * Geert Ysebaert and Gert Cuypers are Research Assistants with the I.W.T.  ... 
doi:10.5281/zenodo.54060 fatcat:plt7lkmdmbgunp2ke4qgl4ox6e

Bit Rate Maximizing Window And Equalizer Design For Dmt-Systems

Geert Ysebaert, Koen Vanbleu, Gert Cuypers, M. Moonen
2004 Zenodo  
Publication in the conference proceedings of EUSIPCO, Viena, Austria, 2004
doi:10.5281/zenodo.38399 fatcat:tlxjj4b6qnhclobjvpkyqbdp64

A Queueing Theoretic Approach to Decoupling Inventory [chapter]

Eline De Cuypere, Koen De Turck, Dieter Fiems
2012 Lecture Notes in Computer Science  
This paper investigates the performance of different hybrid push-pull systems with a decoupling inventory at the semi-finished products and reordering thresholds. Raw materials are 'pushed' into the semifinished product inventory and customers 'pull' products by placing orders. Furthermore, production of semi-finished products starts when the inventory goes below a certain level, referred to as the threshold value and stops when the inventory attains stock capacity. As performance of the
more » ... ing stock is critical to the overall cost and performance of manufacturing systems, this paper introduces a Markovian model for hybrid push-pull systems. In particular, we focus on a queueing model with two buffers, thereby accounting for both the decoupling stock as well as for possible backlog of orders. By means of numerical examples, we assess the impact of different reordering policies, irregular order arrivals, the set-up time distribution and the order processing time distribution on the performance of hybrid push-pull systems.
doi:10.1007/978-3-642-30782-9_11 fatcat:6mycrtqf4fhg3bnrcg2uatfnee

Opinion propagation in bounded medium-sized populations

Eline De Cuypere, Koen De Turck, Sabine Wittevrongel, Dieter Fiems
2016 Performance evaluation (Print)  
We study the dynamics of opinion propagation in a medium-sized population with low population turnover. Opinion spreading is modelled by a Markovian non-standard Susceptible-Infected-Recovered (SIR) epidemic model with stochastic arrivals, departures, infections and recoveries. The system performance is evaluated by two complementary approaches: a numerical but approximate solution approach which relies on Maclaurinseries expansions of the stationary solution of the Markov process and a fluid
more » ... mit approach. Both methods are evaluated numerically. Moreover, convergence to the fluid limit is proved, and explicit expressions for the fixed points of the differential equations are obtained for the case of linearly increasing infection and arrival rates. propagation of opinions on a particular topic: a susceptible or non-opinionated individual has yet to form an opinion on the topic, whereas infected or opinionated individuals do have such an opinion. Susceptible individuals may form an opinion when they encounter infected individuals, like an infection is carried over to a healthy individual upon contact. Finally, individuals loose their interest in the topic after some time and stop spreading their opinion. These individuals have recovered. The SIR epidemic model has been predominantly applied to study disease, see e.g. [19, 20, 21, 23], but there is some prior work in the areas of rumour and opinion propagation as well. Concerning the latter, Zhao extends the SIR model for opinion spreading in social networks by including a hibernator state in which individuals temporary interrupt infecting others [39]. Moreno et. al study SIR like spreading of rumours explicitly accounting for the network structure [31]. Bettencourt et. al [5] draw parallels between epidemics and idea diffusion by applying several epidemiological models to empirical data. Woo et. al [37] show the plausibility to describe the mechanism of violent topic diffusion in web forums by a SIR model while Fan et. al [17] propose an extended SIR model for opinion dynamics in which individuals can have a positive or negative opinion about a topic. Finally, some preliminary results on series expansion techniques (cf. infra) for stochastic SIR models for opinion propagation were presented in [12] . SIR models are not the only models for studying opinion propagation in literature. For example, the threshold model starts from a random directed graph where each node selects a random threshold [25] . Opinion propagation then evolves deterministically: a node becomes active (gets an opinion) if the fraction
doi:10.1016/j.peva.2016.03.001 fatcat:eh3jmh5gkza6vh2rg2d4xo3ia4

Optimal Inventory Management in a Fluctuating Market [chapter]

Eline De Cuypere, Koen De Turck, Herwig Bruneel, Dieter Fiems
2013 Lecture Notes in Computer Science  
In the highly competitive environment in which companies operate today, it is crucial that the supporting processes such as inventory management are as efficient as possible. In particular, a trade-off between inventory costs and service levels needs to be assessed. In this paper, we determine an optimal batch ordering policy accounting for both demand and market price fluctuations such that the long-term discounted cost is minimised. This means that future costs are multiplied by a constant
more » ... tor smaller than one as we need to take inflation and other factors into account. To this end, the inventory system is modelled as a Markovian queueing system with finite capacity in a random environment. Assuming geometrically distributed lead times, Markovian demand and price fluctuations, the optimal ordering strategy is determined by a Markov decision process (MDP) approach. To illustrate our results, we analyse the ordering policy under several price fluctuation scenarios by some numerical examples.
doi:10.1007/978-3-642-39408-9_12 fatcat:oxr533ctdvax5h4r2pblgs4tvy

A Maclaurin-series expansion approach to multiple paired queues

Eline De Cuypere, Koen De Turck, Dieter Fiems
2014 Operations Research Letters  
Motivated by kitting processes in assembly systems, we consider a Markovian queueing system with K paired finitecapacity buffers. Pairing means that departures from the buffers are synchronised and that service is interrupted if any of the buffers is empty. To cope with the inherent state-space explosion problem, we propose an approximate numerical algorithm which calculates the first L coefficients of the Maclaurin series expansion of the steady-state probability vector in O(KLM ) operations,
more » ... being the size of the state space. * Corresponding author (Dieter.Fiems@UGent.be), Ghent University, Department of Telecommunications and Information Processing St-Pietersnieuwstraat 41, 9000 Gent, Belgium.
doi:10.1016/j.orl.2014.02.003 fatcat:dmgag3nczzaynoemegluf5dhle

Performance Analysis of Hybrid MTS/MTO Systems with Stochastic Demand and Production

Dieter Fiems, Eline De Cuypere, Koen De Turck, Dieter Claeys
2020 Mathematics  
We present a comprehensive numerical approach with reasonably light complexity in terms of implementation and computation for assessing the performance of hybrid make-to-stock (MTS)/make-to-order (MTO) systems. In such hybrid systems, semi-finished products are produced up front and stored in a decoupling inventory. When an order arrives, the products are completed and possibly customised. We study this system in a stochastic setting: demand and production are modelled by random processes. In
more » ... rticular, our model includes two coupled Markovian queues: one queue represents the decoupling inventory and the other the order backlog. These queues are coupled as order processing can only occur when both queues are non-empty. We rely on matrix analytic techniques to study the performance of the MTO/MTS system under non-restrictive stochastic assumptions. In particular, we allow for arrival correlation and non-exponential setup and MTS and MTO processing times, while the hybrid MTS/MTO system is managed by an (s,S)-type threshold policy that governs switching from MTO to MTS and back. By some numerical examples, we assess the impact of inventory control, irregular order arrivals, setup and order processing times on inventory levels and lead times.
doi:10.3390/math8111925 fatcat:q6yp6xtzkbfefgysr3ysrmmtlu

Transcranial magnetic stimulation and magnetic resonance spectroscopy: opportunities for a bimodal approach in human neuroscience

Koen Cuypers, Anouk Marsman
2020 NeuroImage  
Koen Cuypers: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing -original draft, Writing -review & editing, Visualization.  ...  Due to the variability inherent to TMS and in order to obtain a reliable estimate of corticospinal excitability, it is recommended to measure the average MEP over several consecutive trials ( Cuypers  ... 
doi:10.1016/j.neuroimage.2020.117394 pmid:32987106 fatcat:pmsl4gz33jfsdknyfv7seoiqre

Alterations of hand sensorimotor function and cortical motor representations over the adult lifespan

Melina Hehl, Stephan P. Swinnen, Koen Cuypers
2020 Aging  
Using a cross sectional design, we aimed to identify the effect of aging on sensorimotor function and cortical motor representations of two intrinsic hand muscles, as well as the course and timing of those changes. Furthermore, the link between cortical motor representations, sensorimotor function, and intracortical inhibition and facilitation was investigated. Seventy-seven participants over the full adult lifespan were enrolled. For the first dorsal interosseus (FDI) and abductor digiti
more » ... (ADM) muscle, cortical motor representations, GABAA-mediated short-interval intracortical inhibition (SICI), and glutamate-mediated intracortical facilitation (ICF) were assessed using transcranial magnetic stimulation over the dominant primary motor cortex. Additionally, participants' dexterity and force were measured. Linear, polynomial, and piecewise linear regression analyses were conducted to identify the course and timing of age-related differences. Our results demonstrated variation in sensorimotor function over the lifespan, with a marked decline starting around the mid-thirties. Furthermore, an age-related reduction in cortical motor representation volume and maximal MEP of the FDI, but not for ADM, was observed, occurring mainly until the mid-forties. Area of the cortical motor representation did not change with advancing age. Furthermore, cortical motor representations, sensorimotor function, and measures of intracortical inhibition and facilitation were not interrelated.
doi:10.18632/aging.102925 pmid:32160591 pmcid:PMC7093194 fatcat:2wqrvvnncnf5tl5gx3glou6ztm

Age-related GABAergic differences in the primary sensorimotor cortex: a multimodal approach combining PET, MRS and TMS

Koen Cuypers, Melina Hehl, June van Aalst, Sima Chalavi, Mark Mikkelsen, Koen Van Laere, Patrick Dupont, Dante Mantini, Stephan P. Swinnen
2020 NeuroImage  
Healthy aging is associated with mechanistic changes in gamma-aminobutyric acid (GABA), the most abundant inhibitory neurotransmitter in the human brain. While previous work mainly focused on magnetic resonance spectroscopy (MRS)-based GABA+ levels and transcranial magnetic stimulation (TMS)-based GABAA receptor (GABAAR) activity in the primary sensorimotor (SM1) cortex, the aim of the current study was to identify age-related differences in positron emission tomography (PET)-based GABAAR
more » ... bility and its relationship with GABA+ levels (i.e. GABA with the contribution of macromolecules) and GABAAR activity. For this purpose, fifteen young (aged 20-28 years) and fifteen older (aged 65-80 years) participants were recruited. PET and MRS images were acquired using simultaneous time-of-flight PET/MR to evaluate age-related differences in GABAAR availability (distribution volume ratio with pons as reference region) and GABA+ levels. TMS was applied to identify age-related differences in GABAAR activity by measuring short-interval intracortical inhibition (SICI). Whereas GABAAR availability was significantly higher in the SM cortex of older as compared to young adults (18.5%), there were neither age-related differences in GABA+ levels nor SICI. A correlation analysis revealed no significant associations between GABAAR availability, GABAAR activity and GABA+ levels. Although the exact mechanisms need to be further elucidated, it is possible that a higher GABAAR availability in older adults is a compensatory mechanism to ensure optimal inhibitory functionality during the aging process.
doi:10.1016/j.neuroimage.2020.117536 pmid:33186716 pmcid:PMC7894275 fatcat:27ecwqek25f7zaff3mt2fvf3ie

A queueing model of an energy harvesting sensor node with data buffering

Eline De Cuypere, Koen De Turck, Dieter Fiems
2017 Telecommunications Systems  
Battery lifetime is a key impediment to long-lasting low power sensor nodes and networks thereof. Energy harvesting -conversion of ambient energy into electrical energy -has emerged as a viable alternative to battery power. Indeed, the harvested energy mitigates the dependency on battery power and can be used to transmit data. However, unfair data delivery delay and energy expenditure among sensors remain important issues for such networks. We study performance of sensor networks with mobile
more » ... ks: a mobile sink moves towards the transmission range of the different static sensor nodes to collect their data. We propose and analyse a Markovian queueing system to study the impact of uncertainty in energy harvesting, energy expenditure, data acquisition and data transmission. In particular, the energy harvesting sensor node is described by a system with two queues, one queue corresponding to the battery and the other to the data buffer. We illustrate our approach by numerical examples which show that energy harvesting correlation considerably affects performance measures like the mean data delay and the effective data collection rate.
doi:10.1007/s11235-017-0338-8 fatcat:tmtff32qdneyjkxkejxe5q3fwi

Intra-Symbol Windowing for Egress Reduction in DMT Transmitters

Gert Cuypers, Koen Vanbleu, Geert Ysebaert, Marc Moonen
2006 EURASIP Journal on Advances in Signal Processing  
Gert Cuypers et al. 5 We can now distinguish between three cases. (i) A general d (nonsparse).  ...  A Gert Cuypers et al. 3 0 1 0 T L − 1 L t Rectangular window w r (t) Sampled window w r,s (t) Interpolated window w i (t) Next symbol Figure 2 : The first (DC only) symbol as a sampled rectangular window  ... 
doi:10.1155/asp/2006/70387 fatcat:zvjoyzqu6ne2famh7sn2egzfxe

Is Motor Learning Mediated by tDCS Intensity?

Koen Cuypers, Daphnie J. F. Leenus, Femke E. van den Berg, Michael A. Nitsche, Herbert Thijs, Nicole Wenderoth, Raf L. J. Meesen, Guglielmo Foffani
2013 PLoS ONE  
Although tDCS has been shown to improve motor learning, previous studies reported rather small effects. Since physiological effects of tDCS depend on intensity, the present study evaluated this parameter in order to enhance the effect of tDCS on skill acquisition. The effect of different stimulation intensities of anodal tDCS (atDCS) was investigated in a double blind, sham controlled crossover design. In each condition, thirteen healthy subjects were instructed to perform a unimanual motor
more » ... uence) learning task. Our results showed (1) a significant increase in the slope of the learning curve and (2) a significant improvement in motor performance at retention for 1.5 mA atDCS as compared to sham tDCS. No significant differences were reported between 1 mA atDCS and sham tDCS; and between 1.5 mA atDCS and 1 mA atDCS.
doi:10.1371/journal.pone.0067344 pmid:23826272 pmcid:PMC3691194 fatcat:pknxxana3bgullbs6qtahirugi

Age-related differences in corticospinal excitability during a choice reaction time task

Koen Cuypers, Herbert Thijs, Julie Duque, Stephan P. Swinnen, Oron Levin, Raf L. J. Meesen
2012 Age  
Age-related declines in central processing may affect corticospinal (CS) excitability that underlies the emergence of voluntary responses to external stimuli. We used single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex to explore the evolution of CS excitability in 14 young and ten elderly healthy right-handed participants. Motor-evoked potentials (MEPs) were elicited in the right or left first dorsal interosseus (FDI) during the preparatory and premotor periods
more » ... a choice reaction time (CRT) task, which required selection of left or right index finger responses. Both age groups showed significant suppression of CS excitability in the preparatory period. However, suppression was generally less pronounced in older than in young adults. Moreover, our data indicated that a reduced suppression in the right FDI during the preparatory period was associated with longer reaction times (RTs) in older adults only. In the premotor period, both age groups demonstrated comparable facilitation levels towards movement onset. Our findings indicate that increased RTs among older individuals could be directly associated with declines in preparatory processes.
doi:10.1007/s11357-012-9471-1 pmid:23007962 pmcid:PMC3776102 fatcat:4jzg5ixuzbdsvalvuw7tgrlmae
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