14 research outputs found

    Verification of spike separation of synchronous spikes in tetrode recordings by using simultaneous double intracellular recordings

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    Numerous approaches and methods have been introduced to solve the difficult task of sorting extracellular spike waveforms, which is a prerequisite for analyzing the contribution of individual cells to neuronal ensemble codes. However, the performance of many methods dramatically degrades under conditions of highly similar spike waveforms emitted from neighboring cells. An entirely unresolved problem is the separation of temporally overlapping action potentials which are quite numerous and constitute a very important feature of cortical processing. Most established sorting methods classify stable synchronous spikes as separate units and eliminate more variable near synchronous spikes as instable signal. What is missing is a quantitative evaluation of sorting performance by different algorithms for real data containing partially or completely overlapping spikes with reference to ground truth of individual spike timings. We set out to determine the performance of a sorting method based on independent component analysis (ICA) by quantitative analysis of spike times obtained from simultaneous tetrode and double patch clamp recordings in rat cortical slices. To this end, two pyramidal cells were patched and recorded simultaneously together with the extracellular signals of a tetrode placed in their vicinity under IR-DIC microscopic control. Action potentials were induced by current injection into both cells so that variable degrees of temporal overlap were generated. We used an ICA-based method because 1. our tetrode signals were sampled in a real 3D space (the 4 leads being arranged in a tetrahedron) 2. the ICA can fully exploit the spatial information of these tetrode signals. Separation performance on four data sets, each containing more than 3000 spikes of which 44.8%-57.6% (mean 52.6%) of spikes were overlapping, ranged from 87% to 97% (mean 92%). False negatives were on average observed for 0.4% of all events (due to noise in ICA decomposition data, making event detection difficult), false positives on average for 0.8% of identified events. The latter represent spuriously detected events in the ICA decomposition, which may be artifacts or spikes from other nearby cells. In sum, extracellular tetrode recordings of two neighboring cortical neurons can be sorted with a very high degree of confidence. In particular, this holds true for heavily overlapping spikes, producing indiscriminately looking waveform shapes in the extracellular tetrode signal. We conclude that the ICA model fits well on extracellular tetrode recording and enables separation of temporally overlapping action potentials from a limited number of neurons

    Metal Injection Molding (MIM) of NdFeB Magnets

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    Due to the increased and unstable prices for Rare Earth elements there are activities to develop alternative hard magnetic materials. Reducing the amount of material necessary to produce complex sintered NdFeB magnets can also help to reduce some of the supply problem. Metal Injection Molding (MIM) is able to produce near net shape parts and can reduce the amount of finishing to achieve final geometry. Although MIM of NdFeB has been patented and published fairly soon after the development of the NdFeB magnets there has never been an industrial production. This could be due to the fact that MIM was very young at that time and hardly developed. Thus, the feasibility of the process needs to be revaluated. This paper presents results of our work on determining the process parameters influencing the magnetic properties of the sintered magnets as well as the shrinkage during processing. The role of binder and powder loading on the alignment of the particles as well as on the carbon and oxygen contamination was examined

    Pulsed field magnetometer for industrial use

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    An industrial pulsed field magnetometer was developed, focusing on industrial needs. The system is to be used for the complete characterizing of permanent magnets in a production-line situation. The purpose is to create a fast, reliable, and accurate magnetometer for quality control but also, in a later step, as a standard measurement method for magnets

    A pulsed field magnetometer for the qualitiy control of permanent magnets

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    A pulsed field magnetometer (PFM) for industrial applications was developed. The system has a capacitor bank of 5mF for energy storage, which can be charged up to 3000V. The pulse magnet has a bore of 30mm (including the pickup coil), which is subdivided into two coils and produces a maximum field of 5T with pulse frequencies of 17.5 and 25Hz. The magnetisation is measured with a well balanced and temperature stabilised coaxial pickup system. The signal is integrated with a stable analogue integrator with selectable time constants. The signals are connected to a 14bit 5M sample/s two-channel ADC in a computer. For the data handling a C ++ -based computer program was written. The effects of eddy currents on the metallic samples are corrected by using the so-called f/2f method. Here two hysteresis measurements with two different time constants are used to measure the eddy current error. The function and reliability of the system is demonstrated by measuring the hysteresis of standard permanent magnets in the PFM and in a static system
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