Slow Signal Research Articles

Stability and robustness analysis of cyclic pseudo-downsampled iterative learning control

Cyclic pseudo-downsampled iterative learning control (ILC) has shown advantages to achieve good learning performance for trajectories containing high-frequency components and has been verified on industrial robot application. This scheme is a multirate ILC in nature and downsamples the fast rate signals (with a sampling period T) to slow rate signals (with a sampling period mT) with a ratio m. Then ILC is carried out on the downsampled signals and interpolates its output to a fast rate signal. For the next iteration, ILC scheme downsamples the signals with the same ratio m but at different sampling points with a time shift T. This process is repeated on the iteration axis so that ILC updates the input of all the sampling points once every m cycles. By experiments [Zhang, B., Wang, D., Ye, Y., Zhou, K. and Wang, Y. (2009) ‘Cyclic Pseudo-downsampled Iterative Learning Control for High Performance Tracking’, Control Engineering Practice, 17, 957–965], this scheme has been shown effective and comparisons with other relevant schemes demonstrate its superior performance. In this article, this cyclic pseudo-downsampled ILC scheme is examined analytically and proved mathematically to be stable and robust. Extensions and insights are also established based on the theoretical developments and simulation verification. pseudo-downsampled ILC scheme.

Vision and visual cortical maps in mice with a photoreceptor synaptopathy: Reduced but robust visual capabilities in the absence of synaptic ribbons

How little neurotransmission in the visual system is sufficient to promote decent visual capabilities? This question is of key importance for therapeutic approaches to restore vision in patients who suffer from degenerative retinal diseases. In the retinae of mice, mutant for the presynaptic scaffolding protein Bassoon (Bsn), signal transfer at photoreceptor ribbon synapses is severely disturbed due to impaired ribbon attachment to the active zone. We have used two different behavioural tasks and optical imaging of intrinsic signals to probe vision in young and adult Bsn−/− mice and their wild-type littermates. Here we show that while visual acuity was significantly reduced in mutants compared to controls, vision guided behavioural decisions and optical imaging revealed essentially unperturbed cortical signals and retinotopy in spite of the photoreceptor synaptopathy. In addition, both vision and visual cortical maps were adult-like at 4 weeks of age. These results show that (i) while Bassoon-dependent fast exocytosis is essential for normal vision surprisingly good visual performance can be achieved in the absence of synaptic ribbons, (ii) both the development and maintenance of visual cortical maps is independent of synaptic ribbons and (iii) visual development in the mutants is completed at 4 weeks of age indicating that later developing ectopic synapses do not affect vision. Thus, the central visual system can make use of slow and weak retinal signals to subserve surprisingly robust vision.

Computational Sophistication at a Single GABAergic Connection

Diverse computational roles of GABAergic inhibition are often assumed to reflect heterogeneity in the sources of GABA and in the receptors sensing the neurotransmitter. New data suggest that distinct effects on integration of excitatory inputs by cerebellar granule cells might result from different modes of signaling by individual interneurons.

MIPP Plastic Ball electronics upgrade

An upgrade electronics design for Plastic Ball detector is described. The Plastic Ball detector was a part of several experiments in the past and its back portion (proposed to be used in Main Injector Particle Production (MIPP)) consists of 340 photomultipliers equipped with a sandwich scintillator. The scintillator sandwich has fast and slow signal component with decay times 10 ns and 1 μs, respectively. The upgraded MIPP experiment will collect up to 12,000 events during each 4 s spill and read them out in ∼50 s between spills. The MIPP data acquisition system will employ deadtime-less concept successfully implemented in Muon Electronics of Dzero experiment at Fermilab An 8-channel prototype design of the Plastic Ball Front-End (PBFE) implementing these requirements is discussed. Details of the schematic design, simulation and prototype test results are discussed.

Limb Development Takes a Measured Step Toward Systems Analysis

Growth and patterning of the embryonic vertebrate limb is regulated by feedback loops signaling between the epithelium and mesenchyme of the limb bud. Fibroblast growth factor (FGF) signaling from the epithelium regulates Sonic hedgehog (Shh) expression in the mesenchyme. In turn, SHH activity maintains the expression of Gremlin1, which encodes a bone morphogenetic protein (BMP) antagonist; the interaction between BMP and Gremlin1 regulates Fgf gene expression. A computational model using data from complex genetic analysis and quantitative measurements of gene induction kinetics demonstrates that limb development is robust and thus buffered against certain mutational alterations and epigenetic changes because of these feedback loops.

Mechanisms that limit the light stimulus frequency following through the dl-2-amino-4-phosphonobutyric acid sensitive and insensitive rod Off-pathways

In the retina, rod signal pathways process scotopic visual information. Light decrements are mediated by two distinct groups of rod pathways in the dark-adapted retina that can be differentiated on the basis of their sensitivity to the glutamate agonist dl-2-amino-4-phosphonobutyric acid (APB). We have found that the APB sensitive and insensitive rod Off-pathways signal different light decrement information: the APB sensitive rod Off-pathway conveys slow and low frequency light signals, whereas the APB insensitive rod Off-pathways mediate fast and high frequency light signals [Wang GY (2006) Unique functional properties of the APB sensitive and insensitive rod pathways signaling light decrements in mouse retinal ganglion cells. Vis Neurosci 23:127–135]. However, the mechanisms which limit the frequency following through the APB sensitive and insensitive rod Off-pathways remain unknown. In the current study, whole-cell patch-clamp recordings were made from ganglion cells in dark and light adapted mouse retina to identify the mechanisms that limit the frequency following through the APB sensitive and insensitive rod Off-pathways. The results showed that the sites from AII amacrine cells to Off cone bipolar cells are the major mechanisms that limit the frequency following through the APB sensitive rod Off-pathway. In the APB insensitive rod Off-pathways, rods themselves limited the frequency following through these pathways. Moreover, ganglion cells were able to follow higher frequencies under photopic conditions than under scotopic conditions. The Off responses followed lower frequencies than On responses under photopic conditions. This finding was observed in cells that yielded On or Off responses only as well as in On–Off cells.

Cyclic pseudo-downsampled iterative learning control for high performance tracking

In this paper, a multirate cyclic pseudo-downsampled iterative learning control (ILC) scheme is proposed. The scheme has the ability to produce a good learning transient for trajectories with high frequency components with/without initial state errors. The proposed scheme downsamples the feedback error and input signals every m samples to arrive at slower rate. Then, the downsampled slow rate signals are applied to an ILC algorithm, whose output is then interpolated and applied to an actuator. The main feature of the proposed scheme is that, for two successive iterations, the signal is downsampled with the same m but the downsampling points are time shifted along the time axis. This shifting process makes the ILC scheme cyclic along the iteration axis with a period of m cycles. Experimental results show significant improvement in tracking accuracy. Additional advantages are that the proposed scheme does not need a filter design and also reduces the computation and memory size substantially.

INTRINSIC OPTICAL SIGNAL IMAGING OF RETINAL ACTIVITY IN FROG EYE

Using a near-infrared (NIR) light flood-illumination imager equipped with a high-speed (120 Hz) CCD camera, we demonstrated optical imaging of stimulus-evoked retinal activity in isolated, but intact, frog eye. Both fast and slow transient intrinsic optical signals (IOSs) were observed. Fast optical response occurred immediately after the stimulus onset, could reach peak magnitude within 100 ms, and correlated tightly with ON and OFF edges of the visible light stimulus; while slow optical response lasted a relatively long time (many seconds). High-resolution images revealed both positive (increasing) and negative (decreasing) IOSs, and dynamic optical change at individual CCD pixels could often exceed 10% of the background light intensity. Our experiment on isolated eye suggests that further development of fast, high (sub-cellular) resolution fundus imager will allow robust detection of fast IOSs in vivo, and thus allow noninvasive, three-dimensional evaluation of retinal neural function.

Post-Tetanic Calcium Transients In Adult Skeletal Muscle Fibers Are Frequency-Dependent And Fiber Type Specific

Isolated adult Flexor digitorum brevis fibers from 4-6 weeks-old mice, loaded with Fluo-3 were stimulated with trains of 270, 0.3 ms pulses at different frequencies. We observed a fast calcium tetanus (associated with contraction) and a second, slower signal, similar to those previously described in cultured myotubes. The slow signal (more than the fast one) was inhibited by 25 micro M nifedipine, suggesting a role for DHPR in its onset and by the IP3R inhibitor Xestospongin-C (5 micro M). The amplitude of post-tetanic calcium transients depended on both stimulus train frequency and duration; a bell shaped curve frequency was obtained with a maximum at 10-20 Hz. Likewise, signal amplitude was proportional to stimulus train duration. Fibers isolated from soleus muscle completely lack slow calcium transients. Using immunofluorescence, we have found that all three IP3R isoforms are present in adult muscle at different levels and that IP3R-1 is differentially expressed (with a mosaic pattern) in different types of muscle fibers, being higher in a subset of fast-type fibers. ERK 1/2 phosphorylation of adult muscle fibers after tetanic stimulation appears to relate slow calcium signals to transcription-related events. These results support the idea that different calcium kinetics for the slow signals mediated by IP3R may exist in different types of muscle fibers and participate in the activation of specific transcriptional programs of slow and fast phenotype.FONDAP 15010006, Bicentenario-PSD24, FONDECYT 1080120

ATP Release and P2X/P2Y Receptor Activation Account for Slow Calcium Transients Evoked by Electrical Stimulation in Skeletal Muscle Cells

ATP released to the extracellular medium participates in cell signaling through activation of plasma membrane P2X (ion channels) or P2Y (metabotropic) receptors. Skeletal muscle cells express several P2X and P2Y receptor subtypes and ATP is profusely released during muscle activity. We have previously shown that depolarizing stimuli induce two calcium signals in skeletal myotubes: a fast signal associated with contraction and a slow signal that regulates gene expression. Here we show that extracellular nucleotides released by electrical stimulation are in part responsible for intracellular calcium signals. In rat myotubes, a tetanic stimulus (45 Hz, 400, 1 ms pulses) rapidly increased extracellular levels of ATP, ADP and AMP from 15sec to 3 min, with different half-life times. Exogenous ATP applications induced a dose-dependent increase in intracellular calcium, with an EC50 of 7.8 ± 3.1 μM. Exogenous ADP, UTP and UDP also promote calcium transients. By RT-PCR, we detected mRNA expression for P2X1-7 and P2Y1,2,4,6,11 in these cells. Both fast- and slow-calcium signals evoked by tetanic stimulation were partially inhibited by either 10-100 μM suramin (non selective P2X/P2Y blocker) or 2U/ml apyrase (nucleotidase that metabolizes ATP and ADP to AMP). In hemidiaphragm preparations, we demonstrated that apyrase reduces both twitch- and tetanus-evoked increase in tension. Our results suggest that nucleotides released during skeletal muscle activity act through P2X and P2Y receptors to modulate both calcium homeostasis and muscle physiology.FONDAP 15010006, FONDAP 13980001, Fondecyt 3080016.

An analysis of functional connectivity across timescales

Event Abstract Back to Event An analysis of functional connectivity across timescales Methods for estimating functional or effective connectivity between neural signals are becoming increasingly popular. However, different techniques record neural signals at different rates. While spike data is often recorded with a temporal resolution in the sub-millisecond range, other signals like fMRI are typically recorded with much lower temporal resolution. Here examine under what conditions connectivity inferred from slow timescales matches that inferred from fast timescales. Using multi-electrode spike recordings from motor cortex we smooth, down-sample, and estimate the effective connectivity between the underlying signals using pair-wise Granger causality. We find that fast time-scale connectivity is robust to low-pass filtering down to ~1Hz and down-sampling to ~2Hz. Estimates are also fairly robust to fixed-SNR Gaussian noise. These results suggest that there is a large space in which connectivity estimates are relatively independent of temporal filtering and sampling rates. Pooling results from connectivity studies using relatively fast signals, such as intrinsic signal imaging and spike data into joint estimates, thus seems reasonable. It also speaks to the question to how fast imaging data should be acquired to allow for inference of connectivity between individual neurons; such devices should have at least a temporal resolution of about 2Hz. Averaging over populations of neurons may allow for the inference of functional connectivity from very slow signals. This may explain the success of connectivity estimates from fMRI signals using very low temporal resolution. To examine why connectivity should be robust to filtering we fit spike data to two models: an Ising model (maximal entropy, Schneideman et al., 2006) and a generalized linear model (GLM, Pillow et al., 2008). The Ising model assumes that spikes are generated through a Bernoulli process with pair-wise interactions between neurons. The GLM, on the other-hand, assumes that the firing rate of each neuron depends on a history of spikes from the observed neurons. Both models estimate connectivity between neurons, but the GLM takes into account possible delays and variations in the strength of connectivity over fast time-scales. Using these two models we simulate spike data and perform the smoothing, down-sampling analysis above. Connectivity from the Ising model simulations was not robust to smoothing and down-sampling. GLM simulations (200ms history) were slightly more robust but not to the extent of the original data. These results suggest that slow time-scale connectivity, while correlated with fast time-scale connectivity, is not caused by fast time-scale connectivity. One possibility may be that common-input affects connectivity across both fast and slow timescales. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). An analysis of functional connectivity across timescales. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.102 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Feb 2009; Published Online: 02 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Fast and slow light generation using chaotic signals in nonlinear microring resonators for communication security

We propose a new system of signal security using nonlinear micro ring resonators for optical communication system. When a soliton pulse is input into the system, the chaotic signal is generated and multiplexed into the optical link. The chaotic waveform can be canceled using an add/drop device connected into the transmission link. Using the appropriate ring parameters, the original signal can be retrieved. An other application results from the fact that the fast and slow light behaviors can be presented, and can be seen using the add/drop multiplexers. In some cases, we can generate signal to obtain the two identical “signal” and “ghost” signals, which are observed in a different time frame. In this application, communication security can be performed when the required information is multiplexed and performs the link using the chaotic signal, fast and slow light, and signal and ghost signals, where the original signal can be retrieved by the known clients.

Fast optical signal not detected in awake behaving monkeys

While the ability of near-infrared spectroscopy (NIRS) to measure cerebral hemodynamic evoked responses (slow optical signal) is well established, its ability to measure non-invasively the ‘fast optical signal’ is still controversial. Here, we aim to determine the feasibility of performing NIRS measurements of the ‘fast optical signal’ or Event-Related Optical Signals (EROS) under optimal experimental conditions in awake behaving macaque monkeys. These monkeys were implanted with a ‘recording well’ to expose the dura above the primary visual cortex (V1). A custom-made optical probe was inserted and fixed into the well. The close proximity of the probe to the brain maximized the sensitivity to changes in optical properties in the cortex. Motion artifacts were minimized by physical restraint of the head. Full-field contrast-reversing checkerboard stimuli were presented to monkeys trained to perform a visual fixation task. In separate sessions, two NIRS systems (CW4 and ISS FD oximeter), which previously showed the ability to measure the fast signal in human, were used. In some sessions EEG was acquired simultaneously with the optical signal. The increased sensitivity to cortical optical changes with our experimental setup was quantified with 3D Monte Carlo simulations on a segmented MRI monkey head. Averages of thousands of stimuli in the same animal, or grand averages across the two animals and across repeated sessions, did not lead to detection of the fast optical signal using either amplitude or phase of the optical signal. Hemodynamic responses and visual evoked potentials were instead always detected with single trials or averages of a few stimuli. Based on these negative results, despite the optimal experimental conditions, we doubt the usefulness of non-invasive fast optical signal measurements with NIRS.

Leakage and slow allostery limit performance of single drug-sensing aptazyme molecules based on the hammerhead ribozyme

Engineered "aptazymes" fuse in vitro selected aptamers with ribozymes to create allosteric enzymes as biosensing components and artificial gene regulatory switches through ligand-induced conformational rearrangement and activation. By contrast, activating ligand is employed as an enzymatic cofactor in the only known natural aptazyme, the glmS ribozyme, which is devoid of any detectable conformational rearrangements. To better understand this difference in biosensing strategy, we monitored by single molecule fluorescence resonance energy transfer (FRET) and 2-aminopurine (AP) fluorescence the global conformational dynamics and local base (un)stacking, respectively, of a prototypical drug-sensing aptazyme, built from a theophylline aptamer and the hammerhead ribozyme. Single molecule FRET reveals that a catalytically active state with distal Stems I and III of the hammerhead ribozyme is accessed both in the theophylline-bound and, if less frequently, in the ligand-free state. The resultant residual activity (leakage) in the absence of theophylline contributes to a limited dynamic range of the aptazyme. In addition, site-specific AP labeling shows that rapid local theophylline binding to the aptamer domain leads to only slow allosteric signal transduction into the ribozyme core. Our findings allow us to rationalize the suboptimal biosensing performance of the engineered compared to the natural aptazyme and to suggest improvement strategies. Our single molecule FRET approach also monitors in real time the previously elusive equilibrium docking dynamics of the hammerhead ribozyme between several inactive conformations and the active, long-lived, Y-shaped conformer.

A diamond-based biosensor for the recording of neuronal activity

We have developed a device for recording the extracellular electrical activity of cultured neuronal networks based on a hydrogen terminated (H-terminated) conductive diamond. GT1-7 cells, a neuronal cell line showing spontaneous action potentials firing, could maintain their functional properties for days in culture when plated on the H-terminated diamond surface. The recorded extracellular electrical activity appeared in the form of well-resolved bursts of fast and slow biphasic signals with a mean duration of about 8ms for the fast and 60ms for the slow events. The time courses of these signals were in good agreement with those recorded by means of conventional microelectrode array (MEAs) and with the negative derivative of the action potentials intracellularly recorded with the patch clamp technique from single cells. Thus, although hydrophobic in nature, the conductive H-terminated diamond surface is able to reveal the spontaneous electrical activity of neurons mainly by capacitative coupling to the cell membrane. Having previously shown that the optical properties of H-terminated diamond allow to record cellular activity by means of fluorescent probes (Ariano, P., Baldelli, P., Carbone, E., Giardino, A., Lo Giudice, A., Lovisolo, D., Manfredotti, C., Novara, M., Sternschulte, H., Vittone, E., 2005. Diam. Relat. Mater. 14, 669–674), we now provide evidence for the feasibility of using diamond-based cellular biosensors for multiparametrical recordings of electrical activity from living cells.

EBIC investigations of GaN layers prepared by epitaxial lateral overgrowth

GaN films prepared by lateral overgrowth are investigated by scanning electron microscopy in the electron beam induced current (EBIC) mode. A comparison of experimental and simulated dependences of induced current on beam energy has allowed us to determine not only the diffusion length, but also the donor concentration in different areas of a film. It has been found that the donor distribution is inhomogeneous and this inhomogeneity increases under fast neutron irradiation. This is indicative of the significant influence of structural defects on the rate of radiation defect accumulation. An anomalously slow signal decay outside the Schottky barrier has been found, which can be determined by charged defects formed at the merger boundary.

Direct observation of signal evolution of slow and fast light in media with saturated and reverse saturated absorption

Recently, many researchers had reported their work about sub- and superluminal propagation. And several experiments had demonstrated the signal evolution of slow and fast light. In this letter, the authors described a simple experiment for the tracing of the light signal in saturated absorption (SA) and reverse saturated absorption (RSA) media, firstly. We had, directly, observed the evolution of slow and fast signals with different waveforms that traveled in a ruby crystal and C60. Through tracking the signal when slow light (v g ≪ c) and fast light (v g<0) was observed in a ruby crystal and C60, we concluded that asymmetrical absorption on the periodical signal could account for the generation of slow and fast light in SA and RSA media.

Slow Light Beam Splitter

We demonstrate a slow light beam splitter using rapid coherence transport in a wall-coated atomic vapor cell. We show that particles undergoing random and undirected classical motion can mediate coherent interactions between two or more optical modes. Coherence, written into atoms via electromagnetically induced transparency using an input optical signal at one transverse position, spreads out via ballistic atomic motion, is preserved by an antirelaxation wall coating, and is then retrieved in outgoing slow light signals in both the input channel and a spatially-separated second channel. The splitting ratio between the two output channels can be tuned by adjusting the laser power. The slow light beam splitter may improve quantum repeater performance and be useful as an all-optical dynamically reconfigurable router.

Application of seismic interferometry to extract P- and S-wave propagation and observation of shear-wave splitting from noise data at Cold Lake, Alberta, Canada

We extract downward-propagating P- and S-waves from industrial noise generated by human and/or machine activity at the surface propagating down a borehole at Cold Lake, Alberta, Canada, and measure shear-wave splitting from these data. The continuous seismic data are recorded at eight sensors along a downhole well during steam injection into a 420–470-m-deep oil reservoir. We crosscorrelate the waveforms observed at the top sensor and other sensors to extract estimates of the direct P- and S-wave components of the Green’s function that account for wave propagation between sensors. Fast high-frequency and slow low-frequency signals propagating vertically from the surface to the bottom are found for the vertical and horizontal components of the wave motion, which are identified with P- and S-waves, respectively. The fastest S-wave polarized in the east-northeast–west-southwest direction is about 1.9% faster than the slowest S-wave polarized in the northwest-southeast direction. The direction of polarization of the fast S-wave is rotated clockwise by [Formula: see text] from the maximum principal stress axis as estimated from the regional stress field. This study demonstrates the useful application of seismic interferometry to field data to determine structural parameters, which are P- and S-wave velocities and a shear-wave-splitting coefficient, with high accuracy.

STIM1 strengthens clotting

On page 1583, Varga-Szabo et al. show that platelets missing a calcium channel opener build puny, feeble clots that may actually save lives. Figure 1 Vessel-blocking clots (top) are avoided when platelets lack STIM1 (bottom). Platelets require calcium to initiate clotting in response to extracellular cues. When calcium is needed, most cells first deplete their ER stores. This depletion is sensed by an ER protein called STIM1, which sits near enough to the plasma membrane to open up calcium channels on the cell surface. But since platelets have only stunted ER-like tubules, they were thought to rely instead on an activation-induced lipid, which opens surface calcium channels independently of internal stores. Platelets also have plenty of STIM1, however, which Varga-Szabo et al. now show is needed for slow-but-steady clot formation. Activated STIM1-deficient platelets, the authors found, did not accumulate calcium from external sources. Internal calcium stores in the mutant platelets were sufficient for rapid clot formation in response to short-lived ligands such as thrombin. But platelets needed STIM1-induced calcium influx to clot in response to collagen on injured vessels, which triggers a slower signaling pathway. In the absence of STIM1, clots were small and disintegrated easily, particularly under conditions that mimicked blood flow. The defective platelets continually broke away from the clots, suggesting that STIM1 helps make platelets stickier. The results suggest that a quick calcium burst from ER-like tubules might be sufficient to build small clots to patch up a minor tear. The STIM1-driven calcium spike, on the other hand, might be necessary to form larger clots under high shear, as occurs in small or fat-clogged vessels. Mice lacking STIM1 were protected from injury-induced vessel blockage and strokes, as their feeble clots allowed some blood to flow into injured brain tissues. As the clotting problem didn't prolong bleeding, a small, transient clot might be all that's needed to prevent hemorrhage, with the added bonus of avoiding a complete halt in blood flow.