28,435 research outputs found

    Efficiency of endoneural stimulation with 5- to 24-fold multielectrodes

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    Optimal selective stimulation of nerve with endoneurally (intrafascicularly) inserted multi-microelectrodes means that each electrode activates, with its own threshold stimulation current, as few distinct motoneurons as possible, preferably only one, If the latter is the case, the efficiency of a multi-electrode is 100%. However, neighbouring electrodes may control the same motor fiber(s), as there are generally more fibers than electrodes and because the position of fibers is largely unknown. In that case, efficiency is less than 100%. This paper reports on experiments in rat peroneal nerve with 5- and 24-fold wire multi-microelectrode arrays, The threshold force of the twitch recruitment curve of the corresponding EDL muscle was used to monitor nerve activation, It was found that on average the threshold force efficiency was 0.48=48%, After re-inspection of the data, taking into account that neighbouring electrodes have a higher probability to activate the same motor units, in contrast to distant electrodes, the average efficiency even rises to 81%. For several reasons, threshold forces do not correspond to motor unit forces, implying that the threshold-force-efficiency can not be regarded as motor-unit-efficienc

    Endoneural selective stimulating using wire-microelectrode arrays

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    In acute experiments eight 5- to 24-wire-microelectrode arrays were inserted into the common peroneal nerve of the rat, to investigate whether the electrodes could selectively stimulate motor units of the extensor digitorum longus (EDL) muscle. Twitch-force-recruitment curves were measured from the EDL for each array electrode. The curves were plotted on a double-logarithmic scale and parameterized by the low-force slope (which represents the power p in the power-law relationship of force F versus stimulus current I, or F~Ip) and the threshold current. The slopes and threshold currents measured with array electrodes did not differ significantly from those obtained with randomly inserted single wire-microelectrodes. This indicates that, although involving a more invasive insertion procedure, electrode arrays provide neural contacts with low-force recruitment properties similar to those of single wires. Array results revealed partial blocking of neural conduction, similar to that reported with microneurographic insertion with single needles. The efficiency of the array was defined as the fraction of array electrodes selectively contacting a motor unit and evoking the corresponding threshold force. Efficiency thus expresses the practical value of the used electrode array in terms of the total number of distinct threshold forces that can be stimulated by selecting the appropriate electrodes. The eight arrays were capable of evoking threshold forces selectively with an average efficiency of 0.81 (or 81%

    Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs

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    With the congestion of the sub-6 GHz spectrum, the interest in massive multiple-input multiple-output (MIMO) systems operating on millimeter wave spectrum grows. In order to reduce the power consumption of such massive MIMO systems, hybrid analog/digital transceivers and application of low-resolution digital-to-analog/analog-to-digital converters have been recently proposed. In this work, we investigate the energy efficiency of quantized hybrid transmitters equipped with a fully/partially-connected phase-shifting network composed of active/passive phase-shifters and compare it to that of quantized digital precoders. We introduce a quantized single-user MIMO system model based on an additive quantization noise approximation considering realistic power consumption and loss models to evaluate the spectral and energy efficiencies of the transmit precoding methods. Simulation results show that partially-connected hybrid precoders can be more energy-efficient compared to digital precoders, while fully-connected hybrid precoders exhibit poor energy efficiency in general. Also, the topology of phase-shifting components offers an energy-spectral efficiency trade-off: active phase-shifters provide higher data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin

    An Efficient Representation for Filtrations of Simplicial Complexes

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    A filtration over a simplicial complex KK is an ordering of the simplices of KK such that all prefixes in the ordering are subcomplexes of KK. Filtrations are at the core of Persistent Homology, a major tool in Topological Data Analysis. In order to represent the filtration of a simplicial complex, the entire filtration can be appended to any data structure that explicitly stores all the simplices of the complex such as the Hasse diagram or the recently introduced Simplex Tree [Algorithmica '14]. However, with the popularity of various computational methods that need to handle simplicial complexes, and with the rapidly increasing size of the complexes, the task of finding a compact data structure that can still support efficient queries is of great interest. In this paper, we propose a new data structure called the Critical Simplex Diagram (CSD) which is a variant of the Simplex Array List (SAL) [Algorithmica '17]. Our data structure allows one to store in a compact way the filtration of a simplicial complex, and allows for the efficient implementation of a large range of basic operations. Moreover, we prove that our data structure is essentially optimal with respect to the requisite storage space. Finally, we show that the CSD representation admits fast construction algorithms for Flag complexes and relaxed Delaunay complexes.Comment: A preliminary version appeared in SODA 201

    Dynamic Range Majority Data Structures

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    Given a set PP of coloured points on the real line, we study the problem of answering range α\alpha-majority (or "heavy hitter") queries on PP. More specifically, for a query range QQ, we want to return each colour that is assigned to more than an α\alpha-fraction of the points contained in QQ. We present a new data structure for answering range α\alpha-majority queries on a dynamic set of points, where α(0,1)\alpha \in (0,1). Our data structure uses O(n) space, supports queries in O((lgn)/α)O((\lg n) / \alpha) time, and updates in O((lgn)/α)O((\lg n) / \alpha) amortized time. If the coordinates of the points are integers, then the query time can be improved to O(lgn/(αlglgn)+(lg(1/α))/α))O(\lg n / (\alpha \lg \lg n) + (\lg(1/\alpha))/\alpha)). For constant values of α\alpha, this improved query time matches an existing lower bound, for any data structure with polylogarithmic update time. We also generalize our data structure to handle sets of points in d-dimensions, for d2d \ge 2, as well as dynamic arrays, in which each entry is a colour.Comment: 16 pages, Preliminary version appeared in ISAAC 201

    Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes

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    Monoatomic chains of molybdenum encapsulated in single walled carbon nanotubes of different chiralities are investigated using density functional theory. We determine the optimal size of the carbon nanotube for encapsulating a single atomic wire, as well as the most stable atomic arrangement adopted by the wire. We also study the transport properties in the ballistic regime by computing the transmission coefficients and tracing them back to electronic conduction channels of the wire and the host. We predict that carbon nanotubes of appropriate radii encapsulating a Mo wire have metallic behavior, even if both the nanotube and the wire are insulators. Therefore, encapsulating Mo wires in CNT is a way to create conductive quasi one-dimensional hybrid nanostructures.Comment: 8 pages, 10 figure

    A 3D-printed microfluidic-enabled hollow microneedle architecture for transdermal drug delivery.

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    Embedding microfluidic architectures with microneedles enables fluid management capabilities that present new degrees of freedom for transdermal drug delivery. To this end, fabrication schemes that can simultaneously create and integrate complex millimeter/centimeter-long microfluidic structures and micrometer-scale microneedle features are necessary. Accordingly, three-dimensional (3D) printing techniques are suitable candidates because they allow the rapid realization of customizable yet intricate microfluidic and microneedle features. However, previously reported 3D-printing approaches utilized costly instrumentation that lacked the desired versatility to print both features in a single step and the throughput to render components within distinct length-scales. Here, for the first time in literature, we devise a fabrication scheme to create hollow microneedles interfaced with microfluidic structures in a single step. Our method utilizes stereolithography 3D-printing and pushes its boundaries (achieving print resolutions below the full width half maximum laser spot size resolution) to create complex architectures with lower cost and higher print speed and throughput than previously reported methods. To demonstrate a potential application, a microfluidic-enabled microneedle architecture was printed to render hydrodynamic mixing and transdermal drug delivery within a single device. The presented architectures can be adopted in future biomedical devices to facilitate new modes of operations for transdermal drug delivery applications such as combinational therapy for preclinical testing of biologic treatments
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