Long-term characterization of firing dynamics of spontaneous bursts in cultured neural networks

Extracellular action potentials were recorded from developing dissociated rat neocortical networks continuously for up to 49 days in vitro using planar multielectrode arrays. Spontaneous neuronal activity emerged toward the end of the first week in vitro and from then on exhibited periods of elevated firing rates, lasting for a few days up to weeks, which were largely uncorrelated among different recording sites. On a time scale of seconds to minutes, network activity typically displayed an ongoing repetition of distinctive firing patterns, including short episodes of synchronous firing at many sites (network bursts). Network bursts were highly variable in their individual spatio-temporal firing patterns but showed a remarkably stable underlying probabilistic structure (obtained by summing consecutive bursts) on a time scale of hours. On still longer time scales, network bursts evolved gradually, with a significant broadening (to about 2 s) in the third week in vitro, followed by a drastic shortening after about one month in vitro. Bursts at this age were characterized by highly synchronized onsets reaching peak firing levels within less than ca. 60 ms. This pattern persisted for the rest of the culture period. Throughout the recording period, active sites showed highly persistent temporal relationships within network bursts. These longitudinal recordings of network firing have, thus, brought to light a reproducible pattern of complex changes in spontaneous firing dynamics of bursts during the development of isolated cortical neurons into synaptically interconnected networks.     

Extracellular recordings from patterned neuronal networks using planar microelectrode arrays

Neuronal cell networks have been reconstructed on planar microelectrode arrays (MEAs) from dissociated hippocampal pyramidal neurons. Microcontact printing (microCP) and a photoresist-liftoff method were used to selectively localize poly-L-lysine (PLL) on the surface of MEAs. Haptotaxis led to the organization of the neurons into networks localized adjacent to microelectrodes. Various grids of PLL with 2-25-microm-wide lines spaced by 50-200 microm with 15-25-microm nodes at intersection points were used to guide cell body attachment and neurite outgrowth. Bursting activity with spike amplitude attenuation was observed, and multichannel recordings detected instances of coincident firing activity. Finally, we present here an extracellular recording from a approximately 2 microm bundle of guided neurites.     

Analysis of active networks using flow-graph technique

A simplified Coates flow-graph technique, applied to the analysis of an arbitrary active network, is presented. Flow-graph representations of building blocks of active networks are given, which permit construction of the graph from the given network. A flow-graph formula for the sensitivity investigation is also given.     

Investigating the neural correlates of pathological cortical networks in Alzheimer's disease using heterogeneous neuronal models

This paper describes an investigation into the pathophysiological causes of abnormal cortical oscillations in Alzheimer's disease (AD) using two heterogeneous neuronal network models. The effect of excitatory circuit disruption on the beta band power (13-30 Hz) using a conductance-based network model of 200 neurons is assessed. Then, the neural correlates of abnormal cortical oscillations in different frequency bands based on a larger network model of 1000 neurons consisting of different types of cortical neurons are also analyzed. EEG studies in AD patients have shown that beta band power (13-30 Hz) decreased in the early stages of the disease with a parallel increase in theta band power (4-7 Hz). This abnormal change progresses with the later stages of the disease but with decreased power spectra in other fast frequency bands plus an increase in delta band power (1-3 Hz). Our results show that, despite the heterogeneity of the network models, the beta band power is significantly affected by excitatory neural and synaptic loss. Second, the results of modeling a functional impairment in the excitatory circuit shows that beta band power exhibits the most decrease compared with other bands. Previous biological experiments on different types of cultural excitatory neurons show that cortical neuronal death is mediated by dysfunctional ionic behavior that might specifically contribute to the pathogenesis of β-amyloid-peptide-induced neuronal death in AD. Our study also shows that beta band power was the first affected component when the modeled excitatory circuit begins to lose neurons and synapses.     

Analysis of SC networks using continuous-time four-port equivalents

A method of deriving a continuous-time equivalent of an SC network is considered. This method is based on LDI transformation.     

Low voltage firing characteristics of a triggered vacuum gap

The triggered vacuum gap is a normally nonconducting device in which a high-current metal-vapor arc can be established by a suitable pulse of current to a triggering electrode. While this gap is well suited to switching applications at high voltage, it has properties which make it useful at low voltage as well. The operation of the triggered vacuum gap has, therefore, been studied in the range 100 to 1000 volts. It was found that, although the gap could be triggered with currents as low as 0.02 amperes, consistent triggering with firing delays less than a microsecond required trigger pulses of 10 amperes or more. Little or no dependence of firing time on main gap voltage was observed. Below a few hundred volts, however, the probability of establishing a stable main discharge with a short duration trigger pulse falls off rapidly with decreasing gap voltage. The polarity of the main gap voltage and of the trigger pulse strongly influenced the firing characteristics of the gap in the range studied. These effects are discussed in detail.     

Analysis of handover characteristics in shadowed LEO satellite communication networks

In the near future, low earth orbit (LEO) satellite communication networks will partially substitute the fixed terrestrial multimedia networks especially in sparsely populated areas. Unlike fixed terrestrial networks, ongoing calls may be dropped if satellite channels are shadowed. Therefore, in most LEO satellite communication networks more than one satellite needs to be simultaneously visible in order to hand over a call to an unshadowed satellite when the communicating satellite is shadowed. In this paper, handover characteristics for fixed terminals (FTs) in LEO satellite communication networks are analysed. The probability distribution of multiple satellite visibility is analytically obtained and the shadowing process of satelites for FTs are modelled. Using the proposed analysis model, shadowing effects on the traffic performance are evaluated in terms of the number of intersatellite and interbeam handovers during a call. Copyright © 2001 John Wiley & Sons, Ltd.     

基于点火耦合神经网络的多约束QoS路由选择算法

本文针对多约束QoS路由选择问题，将其转化为一个多约束的赋权图最短路问题，并建立点火耦合神经网络，通过在其上所具有的自动波生成和传播特性，并在自动波的传播过程中随时监督约束的满足情况，及时取消不满足约束的自动波，从而最先到达目的节点的自动波所走过的路径即为多约束QoS的最优路径。该算法具有高度的并行性，并总是获得全局最优解，所需的迭代次数相对其他算法而言也是最少的。最后本文给出了实验结果及与其他算法的比较。     

Analysis of trabecular bone structure using Fourier transforms andneural networks

Hip fracture due to osteoporosis (OP) and hip osteoarthritis (OA) are both important causes of locomotor morbidity in the elderly population. In osteoporosis, bone mass gradually decreases until the skeleton is too fragile to support the body and a fracture occurs, typically in the femur, wrist or spine. In osteoarthritis, there is a proliferation of bone, leading to a stiffening of the tissue. Current clinical methods for assessment of bone changes in these disorders largely depend on assessing bone mineral density. However, this does not provide any information about bone structure, which is considered to be an equally important factor in assessing bone quality. This paper presents a novel approach for computer analysis of trabecular (or cancellous) bone structure. The technique uses a Fourier transform to generate a “spectral fingerprint” of an image. Principal components analysis is then applied to identify key features from the Fourier transform and this information is passed to a neural network for classification. Testing this on a series of 100 histological sections of trabecular bone from patients with OP and OA and a normal group correctly classified over 90% of the OP group with an overall accuracy of 77%-84%. Such high success rates on a small group suggest that this may provide a simple, but powerful, method for identifying alterations in bone structure     

CMOS microelectrode array for bidirectional interaction with neuronal networks

A CMOS metal-electrode-based micro system for bidirectional communication (stimulation and recording) with neuronal cells in vitro is presented. The chip overcomes the interconnect challenge that limits today's bidirectional microelectrode arrays. The microsystem has been fabricated in an industrial CMOS technology with several post-CMOS processing steps to realize 128 biocompatible electrodes and to ensure chip stability in physiological saline. The system comprises all necessary control circuitry and on-chip A/D and D/A conversion. A modular design has been implemented, where individual stimulation- and signal-conditioning circuitry units are associated with each electrode. Stimulation signals with a resolution of 8 bits can be sent to any subset of electrodes at a rate of 60 kHz, while all electrodes of the chip are continuously sampled at a rate of 20 kHz. The circuitry at each electrode can be individually reset to its operating point in order to suppress artifacts evoked by the stimulation pulses. Biological measurements from cultured neuronal networks originating from dissociated cortical tissue of fertilized chicken eggs with amplitudes of up to 500 /spl mu/V/sub pp/ are presented.     

Analysis of SC networks using continuous-time equivalent circuits without frequency-dependent elements

Continuous-time equivalent circuits for the analysis of SC networks are derived by using the mixed bilinear and LDI transformation, the developed equivalent circuits contain no frequency-dependent elements.     

Analysis of control characteristics using fuel cell plant simulator

To estimate the operational characteristics of duel cell power plants, the authors developed a dynamic simulator and analyzed the operating characteristics. In the simulations, attention is given to the pressure difference between the cathode and anode of the fuel cell and the system base pressure. The former is important for safe operation of the fuel cell and the latter is important for safe operation of the reformer. For load following and shut-down modes of the 1 MW plant studied, calculation results were compared with actual test results and agree fairly well     

Multimedia traffic characteristics in broadband networks

It is pertinent to develop a set of simple parameters that can best characterize the variability and the statistical correlations of the packet arrival process. These parameters are then used by the network to allocate its resources among the different users in order to avoid congestion and maintain a predefined quality of service (QOS) for each user. The traffic characterization and modeling of the real-time bursty traffic, mainly voice and video traffic sources, using statistical methods are described. It is shown that the variability of the variance of the sum of consecutive packet interarrival times leads to significant queuing delays and therefore is a major cause of congestion in broadband networks     

Traffic characteristics of LEOS-based global personalcommunications networks

The authors present important traffic issues in a low earth orbit satellite-based global personal communications network. The article gives an overview of the characteristics of tomorrow's personal communications networks from a subscriber traffic viewpoint. Selection of multiple access scheme as well as traffic modeling in such systems is discussed, and effects of natural, unbalanced global communications traffic on the performance of the system are distinguished     

Image interpolation using neural networks

This work presents an image interpolation method based on a multilayer perceptron. The method is tested in noise-free as well as noisy line doubling and image expansion problems. Two adaptive algorithms are compared. Results show that the proposed method improves image interpolation.     

Design of local networks using USHRs

We consider the problem of designing a local network in a two‐level telecommunication network. Given one or two hub nodes, central offices (COs) and conduits, the problem is to find a set of unidirectional self‐healing rings (USHRs) which covers all COs and satisfies all demands at minimum cost. The solution approach used is the decomposition and column generation. Master problem and subproblem are modeled as integer programming models. After the optimal solution to linear programming relaxation of the master problem is obtained, a branch‐and‐bound algorithm is used to get an integer solution. A set of valid inequalities for a subproblem is given and a branch‐and‐cut algorithm is used to find an optimal solution to the subproblem. Computational results using real data are reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Teleradiology using switched dialup networks

A dialup wide-bandwidth digital teleradiology system is discussed. A laser film digitizer and a gray scale display system are used at Irwin and Munson Army Community Hospitals to digitize radiographic films and display digital images. A laser film printer at the University of Kansas Medical Center generates a film hardcopy of the transmitted digital data, and an interactive gray scale display is used to review the digital image data. The communication system consists of dialup switched multiple 56000 b/s digital channels, transmitting digital image data in parallel. Conventional radiographic films, multiformat camera films, and laser printed films from multimodality imaging systems have been successfully digitized, transmitted, and laser film recorded or gray scale displayed. It was found that the system provided clinically acceptable image quality reproductions     

Allpass networks using Wien's bridge

A general circuit configuration is developed from Wien's bridge which includes two previously described allpass filters. The rate at which the phase changes with frequency may be widely varied. One version has a transfer function whose magnitude is unity for all frequencies and rates of change of phase.     

人工神经网络在金相图像分割中的应用研究

利用多层感知器神经网络和自组织映射神经网络对球墨铸铁、可锻铸铁和灰铸铁的金相图像进行了分割提取.通过对比以上两种方法分割后的图像质量和定量分析样本图像中的石墨结构、珍珠岩/铁氧体结构所占的百分含量后发现,多层感知器网络分割提取的结果与样本实际的结果更加接近,而自组织映射神经网络分割提取的结果则不够理想.据此,可以推断多层感知器网络是实现金属图像分割自动化提取和精确性分析的有效工具.     

The delay characteristics of CSMA/CD networks

A continuous-time Markov chain model of the CSMA/CD (carrier-sense multiple-access with collision detection) protocol is used to find its delay characteristics. For both random-service-order (RSO) and first-come-first-serve (FCFS) CSMA/CD networks, matrix-geometric methods are used to derive and/or compute the throughput-delay and caudal-characteristics curves, the distribution and variance of the delay, and the rate of decay of the tail of the delay distribution. These results can be used to determine the suitability of RSO and FCFS CSMA/CD networks in applications in which they must carry delay-sensitive data. This is illustrated by an example which shows the significant improvement obtained in the delay characteristics of a particular network when FCFS is used instead of RSO