A simple method for the construction of electrode arrays

A simple method is described for the construction of electrode arrays consisting of insulated metal wires (33 μm diameter) spaced at small, equal distances (0.1 mm). No specialized instrumentation and techniques are needed, as only simple mechanical tools are sufficient. The electrode arrays are used for field potential recording from in vitro brain slice preparations

Werking dunne fractie van gescheiden mest lijkt gunstig

Bij Koeien & Kansen-deelnemer Van Wijk in Waardenburg loopt een veldproef naar de stikstofwerking van de dunne fractie van gescheiden mest in gras. Het doel is om te bekijken in hoeverre het gras de stikstof in dunne mestfractie beter benut dan die uit normale drijfmest. Inmiddels zijn twee snedes gras geoogst. De resultaten zien er bemoedigend uit. Bij twee keer een gift van 125 kg stikstof was de droge-stofopbrengst met de dunne fractie 26 % hoger dan die van drijfmest. Voor harde conclusies is het echter nog te vroeg

Development of an electret microphone in silicon

We describe a subminiature electret microphone, which has been realized in silicon using wafer processing techniques. The microphone consists of a rigid backplate fabricated in silicon and a 2.5 μm thick metallized Mylar foil (PETP) acting as the diaphragm. Between the diaphragm and the backplate a 20 μm thick air cavity and a 1.1 μm thick charged SiO2 layer are present. The SiO2 layer is used as the electret and generates an electric field in the air gap. The electret has been changed to 300 V using a corona-charging set-up. The time constant of the charge decay amounts to more than 100 years at ambient laboratory conditions.\ud \ud The microphone cartridge, which measures 3 × 3 × 0.3 mm, shows an open-circuit sensitivity of about 2.5 mV/μbar at 1 kHz

Asymptotically optimal priority policies for indexable and non-indexable restless bandits

We study the asymptotic optimal control of multi-class restless bandits. A restless bandit is a controllable stochastic process whose state evolution depends on whether or not the bandit is made active. Since finding the optimal control is typically intractable, we propose a class of priority policies that are proved to be asymptotically optimal under a global attractor property and a technical condition. We consider both a fixed population of bandits as well as a dynamic population where bandits can depart and arrive. As an example of a dynamic population of bandits, we analyze a multi-class M/M/S+M queue for which we show asymptotic optimality of an index policy.We combine fluid-scaling techniques with linear programming results to prove that when bandits are indexable, Whittle's index policy is included in our class of priority policies. We thereby generalize a result of Weber and Weiss (1990) about asymptotic optimality of Whittle's index policy to settings with (i) several classes of bandits, (ii) arrivals of new bandits, and (iii) multiple actions. Indexability of the bandits is not required for our results to hold. For non-indexable bandits we describe how to select priority policies from the class of asymptotically optimal policies and present numerical evidence that, outside the asymptotic regime, the performance of our proposed priority policies is nearly optimal

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