Encoding of information into neural spike trains in an auditory nerve fiber model with electric stimuli in the presence of a pseudospontaneous activity

This paper presents an information-theoretic analysis of neural spike trains in an auditory nerve fiber (ANF) model stimulated extracellularly with Gaussian or sinusoidal waveforms in the presence of a pseudospontaneous activity of spike firings. In the computer simulation, stimulus current waveforms were applied repeatedly to a stimulating electrode located 1 mm above the 26th node of Ranvier, in an ANF axon model having 50 nodes of Ranvier, each consisting of stochastic sodium and potassium channels. From spike firing times recorded at the 36th node of Ranvier, a post-stimulus time histogram (PSTH) was generated, and raster plots were depicted for 30 stimulus presentations, in order to investigate the temporal precision and reliability of the spike firing times. Also, inter spike intervals were generated and then "total" and "noise" entropies were estimated to obtain the mutual information and the information rate of the spike trains. It was shown in the case of Gaussian electric stimuli that the temporal precision of spike firing times and the reliability of spike firings were found to increase as the standard deviation (SD) of the Gaussian electric stimuli increased. It was also shown in the case of sinusoidal electric stimuli where there was a specific amplitude of sinusoidal waveforms, the information rate being maximized. It was implied that setting the parameters of electric stimuli to the specific values which maximize the information rate might contribute to efficiently encoding information into the spike trains in the presence of a pseudospontaneous activity of spike firings.     

A Robust Analog VLSI Reichardt Motion Sensor

Silicon imagers with integrated motion-detection circuitry have been developed and tested for the past 15 years. Many previous circuits estimate motion by identifying and tracking spatial or temporal features. These approaches are prone to failure at low SNR conditions, where feature detection becomes unreliable. An alternate approach to motion detection is an intensity-based spatiotemporal correlation algorithm, such as the one proposed by Hassenstein and Reichardt in 1956 to explain aspects of insect vision. We implemented a Reichardt motion sensor with integrated photodetectors in a standard CMOS process. Our circuit operates at sub-microwatt power levels, the lowest reported for any motion sensor. We measure the effects of device mismatch on these parallel, analog circuits to show they are suitable for constructing 2-D VLSI arrays. Traditional correlation-based sensors suffer from strong contrast dependence. We introduce a circuit architecture that lessens this dependence. We also demonstrate robust performance of our sensor to complex stimuli in the presence of spatial and temporal noise.     

Familiar/unfamiliar face classification from EEG signals by utilizing pairwise distant channels and distinctive time interval

The aim of the study is to classify single trial electroencephalogram and to estimate active regions/locations on skull in unfamiliar/familiar face recognition task. For this purpose, electroencephalographic signals were acquired from ten subjects in different sessions. Sixty-one familiar and fifty-nine unfamiliar face stimuli were shown to the subjects in the experiments. Since channel responses are different for familiar and unfamiliar classes, the channels discriminating the classes were investigated. To do so, three distances and four similarity measures were employed to assess the most distant channel pairs between familiar and unfamiliar classes for a 1-s time duration; 0.6 s from the stimulus to 1.6 s in a channel selection process. It is experimentally observed that this time interval is maintaining the greatest distance between two categories. The electroencephalographic signals were classified using the determined channels and time interval to measure accuracy. The best classification accuracy was 81.30% and was obtained with the Pearson correlation as channel selection method. The most discriminative channel pairs were selected from prefrontal regions.     

GMM执行器电磁仿真与位移输出实验研究

超磁致伸缩执行器(GMA)具有驱动结构简单,响应快,输出力大等特点,在高性能电能-机械能与电能-液压能能量转换领域中具有广泛应用。该文分析了影响GMA位移输出的各个因素,首先介绍了GMA的工作原理及结构,随后对GMA进行电磁场仿真,比较不同线圈长度对GMA内部磁场强度分布的影响。最后搭建实验平台,分析了不同骨架材料、材料的不同处理方式及不同的预压力对GMA输出性能的影响。该文为设计高性能GMA提供参考准则,并总结出不同条件下GMA输出性能的优劣,为提高GMA性能及其结构优化提供可靠方案。     

Interdome interactions in cutaneous Type I receptors

The encoder characteristics of cat, hairy skin, slowly adapting Type I receptors were studied by activating them with 'swept period' grating stimuli. A typical stimulus featured a minimum scan period of 0.3 mm, a maximum scan period of 2.0 mm, and a total of 40 grates. Using these stimuli, single domes could easily encode the temporal frequency (1/period*scan velocity) of a grate, regardless of the scan velocity or direction. Receptors with multiple domes could not encode the temporal frequency of a swept-period stimulus unless the instantaneous grate period matched a receptor's intrinsic ability to encode the stimulus. When this criterion was met, the temporal frequency of the stimulus was encoded in the bursting rate of the receptor's action potential event stream.<>     

Characterization of event related potentials using information theoretic distance measures

Analysis of event-related potentials (ERPs) using signal processing tools has become extremely widespread in recent years. Nonstationary signal processing tools such as wavelets and time-frequency distributions have proven to be especially effective in characterizing the transient phenomena encountered in event-related potentials. In this paper, we focus on the analysis of event-related potentials collected during a psychological experiment where two groups of subjects, spider phobics and snake phobics, are shown the same set of stimulus: A blank stimulus, a neutral stimulus and a spider stimulus. We introduce a new approach, based on time-frequency distributions, for analyzing the ERPs. The difference in brain activity before and after a stimulus is presented is quantified using distance measures as adapted to the time-frequency plane. Three different distance measures, including a new information theoretic distance measure, are applied on the time-frequency plane to discriminate between the responses of the two groups of subjects. The results illustrate the effectiveness of using distance measures combined with time-frequency distributions in differentiating between the two classes of subjects and the different regions of the brain.     

Stimulus artifact cancellation in the serosal recordings of gastric myoelectric activity using wavelet transform

Previous studies have shown that electrical stimulation of the stomach (i.e., gastric pacing) with appropriate parameters is a promising method for treatment of gastroparetic patients. The recording of gastric myoelectric activity (GMA) by serosal electrodes is often used to evaluate the effect of stimulation. However, the major problem with the measurement of GMA during gastric pacing is the stimulus artifacts which are often superimposed on the serosal recording and make analysis difficult. The frequency-domain adaptive filter has been used to reduce the stimulus artifacts but only with limited success. This paper describes a wavelet transform-based method for the reduction of stimulus artifacts in the serosal recordings of GMA. The key of this method lies in the use of the fuzzy set theory to select the stimulus artifact-related modulus maxima in the wavelet domain. Both quantitative and qualitative measures show that significant stimulus artifact cancellation was achieved through a series of computer simulations. Results from both single- and multichannel serosally recorded myoelectric signals during gastric pacing are presented to demonstrate the efficiency of the proposed method for the cancellation of stimulus artifacts.     

An Accurate DNA Sensing and Diagnosis Methodology Using Fabricated Silicon Nanopores

Nanopore-based biomolecular sensing is an emerging nanotechnology which relies on the ability to measure changes in ionic conductance of single nanoscale pores as biomolecular analytes are driven through them, one at a time, by an applied electric field. Nanopores constructed from self-assembled proteins as well as using silicon-based fabrication techniques have been demonstrated to allow sizing and identification of DNA, RNA, proteins, and other biomolecules many times faster than with current technology. Despite the potential of nanopore sensing to produce "next generation" biomolecule analysis devices, its current demonstrations are based on the use of a simple dc stimulus across the nanopore. As a result, the resolution obtained is insufficient for many practical applications. In this paper, we report a novel diagnosis methodology for nanopore sensors based on optimization of a generalized electrical stimulus and a microscopic model of the biomolecule transport process. This methodology is applied to analyze the size distribution of an arbitrary mixture of DNA strands, which is a critical step in DNA sequencing. A transport model for long polymers in nanopores is built and parameterized to reproduce existing experimental data. The electrical stimulus is optimized "on-the-fly" using the model, to obtain a significant increase in the sizing resolution for any given range of DNA sizes and hence a clear identification of all sizes of DNA in the mixture. Hence, it is proposed that nanopore-based DNA sensing can be advanced significantly incurring no (or minimal) hardware overhead, by a combination of optimized stimuli and microscopic transport modeling     

任意周期激励函数的模拟电路测试激励优化设计

模拟电路测试中不同的激励源会影响电路的可测性,本文根据任意周期函数可由傅立叶级数展开成一个直流分量和一系列正弦函数叠加的原理,设计一种新的基于任意周期激励函数的模拟电路测试激励优化方法.该方法以任意周期激励函数作为优化对象,以最大特征样本的核类间距离作为优化目标,分析待测电路输入输出信号的幅值、频率和相位关系作为约束条...     

Algorithms for the Clinical Analysis of Nystagmus Eye Movements

Two algorithms used in the clinical analysis of nystagmus are described. Their development was necessitated by the greater complexity of the nystagmus waveforms in response to system identification types of vestibular and optokinetic stimuli as compued to the less complex response to a step input. Practical considerations for clinical application also influenced their development. The first algorithm converts nystagmus data into a regulary sampled estimate of slow phase velocity (SPV), an important feature of the signal. It uses a new set of fast phase detection conditions which allow for automatic processing of reversals in nystagmus direction and for wide variability for clinical data. The second algorithm detects noise induced spikes in this SPV estimate using an adaptive criterion based upon a measure of the overall "noisiness" of the data compared to the stimulus.     

MEG covariance difference analysis: a method to extract targetsource activities by using task and control measurements

A method is proposed for extracting target dipole-source activities from two sets of evoked magnetoencephalographic (MEG) data, one measured using task stimuli and the other using control stimuli. The difference matrix between the two covariance matrices obtained from these two measurements is calculated, and a procedure similar to the MEG-multiple signal classification (MUSIC) algorithm is applied to this difference matrix to extract the target dipole-source configuration. This configuration corresponds to the source-configuration difference between the two measurements. Computer simulation verified the validity of the proposed method. The method was applied to actual evoked-field data obtained from simulated task-and-control experiments. In these measurements, a combination of auditory and somatosensory stimuli was used as the task stimulus and the somatosensory stimulus alone was used as the control stimulus. The proposed covariance difference analysis successfully extracted the target auditory source and eliminated the disturbance from the somatosensory sources     

一种调节飞秒激光脉冲时空重合的新方法

为了实现调节两束飞秒激光脉冲在时间和空间区域上的精确重合,采用利用CCD成像系统调节光束在空间上的重合及利用能量计测量激光脉冲核心能量变化来调节飞秒脉冲间的时间间隔的新方法,取得了核心能量随延迟时间变化的数据,并记录了相应的等离子体荧光图像。结果表明,与传统方法相比,这种方法可以达到飞秒级的时间重合精度。这为确定激光的时空重合提供了一种简便有效的途径,且在激光光束以大角度相交时仍然可以确定最佳重合点。     

SiC(0001)面和(000-1)面CMP抛光对比研究

研究了SiC衬底(0001)面和(000-1)面不同的CMP抛光特性。分别采用pH值为10.38和1.11的改性硅溶胶抛光液对SiC衬底的(0001)Si面和(000-1)C面进行对比抛光实验。使用精密天平测量晶片抛光前后的质量,计算出CMP抛光工艺的材料去除速率。并使用强光灯、微分干涉显微镜和原子力显微镜检测晶片表面质量。发现采用酸性抛光液和碱性抛光液进行抛光,均有VC>VSi;而对于(0001)Si面,有VSi酸>VSi碱;对于(000-1)C面,有VC酸>VC碱。该结论对于探索最佳碳化硅的CMP抛光工艺具有较高价值。     

Physical Effects of Mechanical Processes on Bi-2223 Tapes

The effects of intermediate mechanical deformation （IMD） and bending processing on Bi-2223 tapes were studied. Bi-2223 tapes were manufactured by powder-in-tube process with an IMD. Normal rolling （NR）, pressing （P） and sandwich rolling （SR） with different reduction rate were used in the IMD. And there were an optimum reduction rate existing for the three MID techniques, at which critical current reached maximum. Critical current densities Jc of Bi-2223 crystals were measured with an applied magnetic field B respectively parallel to ab face and c axis. Relations of Jc dependences of reduction rate and superconducting materials density D were respectively studied and showed a Gaussian distribution law. Maximum pinning force density Fmax and irreversible magnetic field Birr were introduced to describe the effects of mechanical processing. Analysis of experimental results showed that Jcs Fmax and Birr were linear dependence on D. Obviously, increasing D was a vital way to enhance Jc Bending experiments were performed for SR tapes sheathed by Ag and Ag/Sb and Ag/Mg alloy, respectively. Silver alloy sheathed tapes showed better bending properties than pure silver sheathed one. Therefore, silver alloy sheathed, optimum reduction rate of IMD, and increasing D for Bi-2223 tapes＇ applications were important technical strategies to enhance their mechanical, electrical, and magnetic properties.     

A Universal Coating Strategy for Controllable Functionalized Polymer Surfaces

Development of a universal and stable surface coating, irrespective of surface chemistry or material characteristics, is highly desirable but has proved to be extremely challenging. Conventional coating strategies including the commonly used catechol surface coating are limited to either a certain type of substrates or weak and unreliable surface bonding. Here, a simple, robust, and universal surface coating method capable for attaching any stimuli‐responsive glycidyl methacrylate (GMA)‐based copolymer, consisting of one surface‐adhesive moiety of epoxy groups and one stimuli‐responsive moiety, to any type of hydrophobic and hydrophilic surfaces via a one‐step ring‐opening reaction is proposed and demonstrated. The resultant GMA‐based copolymers are not only strongly adhered on different substrates (e.g., silicon, polypropylene, polyvinyl chloride, indium tin oxide, polyethylene terephthalate, aluminum, glass, polydimethylsiloxane, and even polyvinylidene fluoride with low surface energy), but also are possessed distinct thermal‐, pH‐, and salt‐responsive functions of bacterial killing, bacterial releasing, tunable multicolor fluorescence emission, and heavy metal detection. This coating method is also compatible with the directional quaternization of GMA‐based copolymers for further improving surface adhesion and functionality. This study provides a simple yet universal coating method to solve the long‐standing challenge of robust integration of stimuli‐responsive polymers with strong adhesion between various polymers and substrates.     

Electrical Characteristics of Chronically Implanted Platinum-Irdium Electrodes

The electrical characteristics of platinum 30 percent-iridium microelectrodes implanted in the cruciate gyrus of cats were monitored during pulsing with charge-balanced, symmetric, cathodicfirst, controlled-current pulse pairs. The amplitude of the pulses spanned the range shown in other studies to be effective as neuronal stimuli, but not to induce histologic or physiologic damage in brain tissue adjacent to the microelectrode tips (10-80 ?, A). Two inflections on the cathodic and anodic charging transients induced by the controlled-current pulses were identified as being due to evolution of molecular hydrogen and the adsorption of oxygen, respectively. Despite the pH dependence of the equilibrium potential of these faradaic reactions, the electrode potentials at the inflections were shown to be independent of stimulus current over most of the useful range of stimulus intensities (20-80/?A, 200-800 ?IC/cm2, and 1-4 A/cm2). Hence, these inflections are valid markers of the true electrode potential, independent of accurate computation of access impedance or a stable reference electrode potential. The implications for monitoring the performance of chronically implanted microelectrodes and for the selection of stimulus parameters is discussed.     

A method for real-time processing to study recovery functions ofevoked potentials

A method for evaluating the recovery function of the evoked potential (EP) in real time is reported. To record the test response of paired stimulation, the responses to alternate presentation of an unpaired stimulus and several kinds of paired stimuli with various interstimulus intervals were averaged, and subtraction was made in real time. The EPs obtained by the proposed method were proved to be accurate even under changing recording conditions. A formula for computing the recovery correlation factor was derived as a measure of the recovery function of the recorded EP, and the recovery curves for three subjects were obtained     

Signal Processing Challenges for Neural Prostheses

Cortically controlled prostheses are able to translate neural activity from the cerebral cortex into control signals for guiding computer cursors or prosthetic limbs. While both noninvasive and invasive electrode techniques can be used to measure neural activity, the latter promises considerably higher levels of performance and therefore functionality to patients. The process of translating analog voltages recorded at the electrode tip into control signals for the prosthesis requires sophisticated signal acquisition and processing techniques. In this article we briefly review the current state-of-the-art in invasive, electrode-based neural prosthetic systems, with particular attention to the advanced signal processing algorithms that enable that performance. Improving prosthetic performance is only part of the challenge, however. A clinically viable prosthetic system will need to be more robust and autonomous and, unlike existing approaches that depend on multiple computers and specialized recording units, must be implemented in a compact, implantable prosthetic processor (IPP). In this article we summarize recent results which indicate that state-of-the-art prosthetic systems can be implemented in an IPP using current semiconductor technology, and the challenges that face signal processing engineers in improving prosthetic performance, autonomy and robustness within the restrictive constraints of the IPP.     

A bipolar load CMOS SRAM cell for embedded applications

This paper presents a new SRAM cell concept which offers cell scaling without requiring complicated, specialized processing technology. The proposed cell utilizes a bipolar transistor in an open-base (base is floating) configuration as a simple means of realizing a high impedance load element. The Bipolar Transistor Load (BTL) is designed such that its open base current (the holding current) is always large enough to compensate for the NMOS pull-down transistor leakage current. The load holding current and the pull-down transistor leakage current are based on the same physical mechanism, namely thermal generation, as a result the load exhibits current tracking properties over varying process and temperature conditions. The cell size is 72 μm² with typical 0.8 μm design rules, which is about a 60% reduction as compared to a standard 6-T full CMOS cell. The operating properties of the BTL cell were studied analytically and characterized experimentally. The BTL SRAM module can be easily integrated as part of any CMOS process with minimal additional processing steps     

A Design-for-Digital-Testability Circuit Structure for Σ- ∆ Modulators

A design-for-digital-testability (DfDT) switched-capacitor circuit structure for testing Sigma-Delta modulators with digital stimuli is presented to reduce the overall testing cost. In the test mode, the DfDT circuits are reconfigured as a one-bit digital-to-charge converter to accept a repetitively applied Sigma-Delta modulated bit-stream as its stimulus. The single-bit characteristic ensures that the generated stimulus is nonlinearity free. In addition, the proposed DfDT structure reuses most of the analog components in the test mode and keeps the same loads for the operational amplifiers as if they were in the normal mode. It thereby achieves many advantages including lower cost, higher fault coverage, higher measurement accuracy, and the capability of performing at-speed tests. A second-order Sigma-Delta modulator was designed and fabricated to demonstrate the effectiveness of the DfDT structure. Our experimental results show that the digital test is able to measure a harmonic distortion lower than -106 dBFS. Meanwhile, the dynamic range measured with the digital stimulus is as high as 84.4 dB at an over-sampling ratio of 128. The proposed DfDT scheme can be easily applied to other types of Sigma-Delta modulators, making them also digitally testable.